APOE U19-related publications

Apolipoprotein E4 has extensive conformational heterogeneity in lipid-free and lipid-bound forms

Stuchell-Brereton MD, Zimmerman MI, Miller JJ, Mallimadugula UL, Incicco JJ, Roy D, Smith LG, Cubuk J, Baban B, DeKoster GT, Frieden C, Bowman GR, Soranno A.

The ?4-allele variant of apolipoprotein E (ApoE4) is the strongest genetic risk factor for Alzheimer’s disease, although it only differs from its neutral counterpart ApoE3 by a single amino acid substitution. While ApoE4 influences the formation of plaques and neurofibrillary tangles, the structural determinants of pathogenicity remain undetermined due to limited structural information. Previous studies have led to conflicting models of the C-terminal region positioning with respect to the N-terminal domain across isoforms largely because the data are potentially confounded by the presence of heterogeneous oligomers. Here, we apply a combination of single-molecule spectroscopy and molecular dynamics simulations to construct an atomically detailed model of monomeric ApoE4 and probe the effect of lipid association. Importantly, our approach overcomes previous limitations by allowing us to work at picomolar concentrations where only the monomer is present. Our data reveal that ApoE4 is far more disordered and extended than previously thought and retains significant conformational heterogeneity after binding lipids. Comparing the proximity of the N- and C-terminal domains across the three major isoforms (ApoE4, ApoE3, and ApoE2) suggests that all maintain heterogeneous conformations in their monomeric form, with ApoE2 adopting a slightly more compact ensemble. Overall, these data provide a foundation for understanding how ApoE4 differs from nonpathogenic and protective variants of the protein.

Alzheimer's disease-associated U1 snRNP splicing dysfunction causes neuronal hyperexcitability and cognitive impairment

Chen PC, Han X, Shaw TI, Fu Y, Sun H, Niu M, Wang Z, Jiao Y, Teubner BJW, Eddins D, Beloate LN, Bai B, Mertz J, Li Y, Cho JH, Wang X, Wu Z, Liu D, Poudel S, Yuan ZF, Mancieri A, Low J, Lee HM, Patton MH, Earls LR, Stewart E, Vogel P, Hui Y, Wan S, Bennett DA, Serrano GE, Beach TG, Dyer MA, Smeyne RJ, Moldoveanu T, Chen T, Wu G, Zakharenko SS, Yu G, Peng J.

Recent proteome and transcriptome profiling of Alzheimer’s disease (AD) brains reveals RNA splicing dysfunction and U1 small nuclear ribonucleoprotein (snRNP) pathology containing U1-70K and its N-terminal 40-KDa fragment (N40K). Here we present a causative role of U1 snRNP dysfunction to neurodegeneration in primary neurons and transgenic mice (N40K-Tg), in which N40K expression exerts a dominant-negative effect to downregulate full-length U1-70K. N40K-Tg recapitulates N40K insolubility, erroneous splicing events, neuronal degeneration and cognitive impairment. Specifically, N40K-Tg shows the reduction of GABAergic synapse components (e.g., the GABA receptor subunit of GABRA2), and concomitant postsynaptic hyperexcitability that is rescued by a GABA receptor agonist. Crossing of N40K-Tg and the 5xFAD amyloidosis model indicates that the RNA splicing defect synergizes with the amyloid cascade to remodel the brain transcriptome and proteome, deregulate synaptic proteins, and accelerate cognitive decline. Thus, our results support the contribution of U1 snRNP-mediated splicing dysfunction to AD pathogenesis.

APOE2 Exacerbates TDP-43 Related Toxicity in the Absence of Alzheimer Pathology

Meneses AD, Koga S, Li Z, O’Leary J, Li F, Chen K, Murakami A, Qiao W, Kurti A, Heckman MG, White L, Xie M, Chen Y, Finch NA, Lim MJ, Delenclos M, DeTure MA, Linares C, Martin NB, Ikezu TC, van Blitterswijk MM, Wu LJ, McLean PJ, Rademakers R, Ross OA, Dickson DW, Bu G, Zhao N.

Objective: Recent evidence supports a link between increased TDP-43 burden and the presence of an APOE4 gene allele in Alzheimer’s disease (AD); however, it is difficult to conclude the direct effect of APOE on TDP-43 pathology due to the presence of mixed AD pathologies. The goal of this study is to address how APOE isoforms impact TDP-43 pathology and related neurodegeneration in the absence of typical AD pathologies.

Methods: We overexpressed human TDP-43 via viral transduction in humanized APOE2, APOE3, APOE4 mice, and murine Apoe-knockout (Apoe-KO) mice. Behavior tests were performed across ages. Animals were harvested at 11 months of age and TDP-43 overexpression-related neurodegeneration and gliosis were assessed. To further address the human relevance, we analyzed the association of APOE with TDP-43 pathology in 160 postmortem brains from autopsy-confirmed amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with motor neuron disease (FTLD-MND) in the Mayo Clinic Brain Bank.

Results: We found that TDP-43 overexpression induced motor function deficits, neuronal loss, and gliosis in the motor cortex, especially in APOE2 mice, with much milder or absent effects in APOE3, APOE4, or Apoe-KO mice. In the motor cortex of the ALS and FTLD-MND postmortem human brains, we found that the APOE2 allele was associated with more severe TDP-43-positive dystrophic neurites.

Interpretation: Our data suggest a genotype-specific effect of APOE on TDP-43 proteinopathy and neurodegeneration in the absence of AD pathology, with the strongest association seen with APOE2.

Opposing effects of apoE2 and apoE4 on microglial activation and lipid metabolism in response to demyelination

Wang N, Wang M, Jeevaratnam S, Rosenberg C, Ikezu TC, Shue F, Doss SV, Alnobani A, Martens YA, Wren M, Asmann YW, Zhang B, Bu G, Liu CC.

Background: Abnormal lipid accumulation has been recognized as a key element of immune dysregulation in microglia whose dysfunction contributes to neurodegenerative diseases. Microglia play essential roles in the clearance of lipid-rich cellular debris upon myelin damage or demyelination, a common pathogenic event in neuronal disorders. Apolipoprotein E (apoE) plays a pivotal role in brain lipid homeostasis; however, the apoE isoform-dependent mechanisms regulating microglial response upon demyelination remain unclear.

Methods: To determine how apoE isoforms impact microglial response to myelin damage, 2-month-old apoE2-, apoE3-, and apoE4-targeted replacement (TR) mice were fed with normal diet (CTL) or 0.2% cuprizone (CPZ) diet for four weeks to induce demyelination in the brain. To examine the effects on subsequent remyelination, the cuprizone diet was switched back to regular chow for an additional two weeks. After treatment, brains were collected and subjected to immunohistochemical and biochemical analyses to assess the myelination status, microglial responses, and their capacity for myelin debris clearance. Bulk RNA sequencing was performed on the corpus callosum (CC) to address the molecular mechanisms underpinning apoE-mediated microglial activation upon demyelination.

Results: We demonstrate dramatic isoform-dependent differences in the activation and function of microglia upon cuprizone-induced demyelination. ApoE2 microglia were hyperactive and more efficient in clearing lipid-rich myelin debris, whereas apoE4 microglia displayed a less activated phenotype with reduced clearance efficiency, compared with apoE3 microglia. Transcriptomic profiling revealed that key molecules known to modulate microglial functions had differential expression patterns in an apoE isoform-dependent manner. Importantly, apoE4 microglia had excessive buildup of lipid droplets, consistent with an impairment in lipid metabolism, whereas apoE2 microglia displayed a superior ability to metabolize myelin enriched lipids. Further, apoE2-TR mice had a greater extent of remyelination; whereas remyelination was compromised in apoE4-TR mice.

Conclusions: Our findings provide critical mechanistic insights into how apoE isoforms differentially regulate microglial function and the maintenance of myelin dynamics, which may inform novel therapeutic avenues for targeting microglial dysfunctions in neurodegenerative diseases.

TREM2-independent microgliosis promotes tau-mediated neurodegeneration in the presence of ApoE4

Gratuze M, Schlachetzki JCM, D’Oliveira Albanus R, Jain N, Novotny B, Brase L, Rodriguez L, Mansel C, Kipnis M, O’Brien S, Pasillas MP, Lee C, Manis M, Colonna M, Harari O, Glass CK, Ulrich JD, Holtzman DM.

In addition to tau and A? pathologies, inflammation plays an important role in Alzheimer’s disease (AD). Variants in APOE and TREM2 increase AD risk. ApoE4 exacerbates tau-linked neurodegeneration and inflammation in P301S tau mice and removal of microglia blocks tau-dependent neurodegeneration. Microglia adopt a heterogeneous population of transcriptomic states in response to pathology, at least some of which are dependent on TREM2. Previously, we reported that knockout (KO) of TREM2 attenuated neurodegeneration in P301S mice that express mouse Apoe. Because of the possible common pathway of ApoE and TREM2 in AD, we tested whether TREM2 KO (T2KO) would block neurodegeneration in P301S Tau mice expressing ApoE4 (TE4), similar to that observed with microglial depletion. Surprisingly, we observed exacerbated neurodegeneration and tau pathology in TE4-T2KO versus TE4 mice, despite decreased TREM2-dependent microgliosis. Our results suggest that tau pathology-dependent microgliosis, that is, TREM2-independent microgliosis, facilitates tau-mediated neurodegeneration in the presence of ApoE4.

ApoE in Alzheimer's disease: pathophysiology and therapeutic strategies

Raulin AC, Doss SV, Trottier ZA, Ikezu TC, Bu G, Liu CC.

Alzheimer’s disease (AD) is the most common cause of dementia worldwide, and its prevalence is rapidly increasing due to extended lifespans. Among the increasing number of genetic risk factors identified, the apolipoprotein E (APOE) gene remains the strongest and most prevalent, impacting more than half of all AD cases. While the ?4 allele of the APOE gene significantly increases AD risk, the ?2 allele is protective relative to the common ?3 allele. These gene alleles encode three apoE protein isoforms that differ at two amino acid positions. The primary physiological function of apoE is to mediate lipid transport in the brain and periphery; however, additional functions of apoE in diverse biological functions have been recognized. Pathogenically, apoE seeds amyloid-? (A?) plaques in the brain with apoE4 driving earlier and more abundant amyloids. ApoE isoforms also have differential effects on multiple A?-related or A?-independent pathways. The complexity of apoE biology and pathobiology presents challenges to designing effective apoE-targeted therapeutic strategies. This review examines the key pathobiological pathways of apoE and related targeting strategies with a specific focus on the latest technological advances and tools.

Suppression of Wnt/?-Catenin Signaling Is Associated with Downregulation of Wnt1, PORCN, and Rspo2 in Alzheimer's Disease

Macyczko JR, Wang N, Zhao J, Ren Y, Lu W, Ikezu TC, Zhao N, Liu CC, Bu G, Li Y.

Wnt and R-spondin (Rspo) proteins are two major types of endogenous Wnt/?-catenin signaling agonists. While Wnt/?-catenin signaling is greatly diminished in Alzheimer’s disease (AD), it remains to be elucidated whether the inhibition of this pathway is associated with dysregulation of Wnt and Rspo proteins. By analyzing temporal cortex RNA-seq data of the human postmortem brain samples, we found that WNT1 and RRPO2 were significantly downregulated in human AD brains. In addition, the expression of Wnt acyltransferase porcupine (PORCN), which is essential for Wnt maturation and secretion, was greatly deceased in these human AD brains. Interestingly, the lowest levels of WNT1, PORCN, and RSPO2 expression were found in human AD brains carrying two copies of APOE4 allele, the strongest genetic risk factor of late-onset AD. Importantly, there were positive correlations among the levels of WNT1, PORCN, and RSPO2 expression in human AD brains. Supporting observations in humans, Wnt1, PORCN, and Rspo2 were downregulated and Wnt/?-catenin signaling was diminished in the 5xFAD amyloid model mice. In human APOE-targeted replacement mice, downregulation of WNT1, PORCN, and RSPO2 expression was positively associated with aging and APOE4 genotype. Finally, WNT1 and PORCN expression and Wnt/?-catenin signaling were inhibited in human APOE4 iPSC-derived astrocytes when compared to the isogenic APOE3 iPSC-derived astrocytes. Altogether, our findings suggest that the dysregulations of Wnt1, PORCN, and Rspo2 could be coordinated together to diminish Wnt/?-catenin signaling in aging- and APOE4-dependent manners in the AD brain.

Cancer and Vascular Comorbidity Effects on Dementia Risk and Neuropathology in the Oldest-Old

Lachner C, Day GS, Camsari GB, Kouri N, Ertekin-Taner N, Boeve BF, Labuzan SA, Lucas JA, Thompson EA, Siddiqui H, Crook JE, Cabrera-Rodriguez JN, Josephs KA, Petersen RC, Dickson DW, Reichard RR, Mielke MM, Knopman DS, Graff-Radford NR, Murray ME.

Background: Dementia, vascular disease, and cancer increase with age, enabling complex comorbid interactions. Understanding vascular and cancer contributions to dementia risk and neuropathology in oldest-old may improve risk modification and outcomes.

Objective: Investigate the contributions of vascular factors and cancer to dementia and neuropathology.

Methods: Longitudinal clinicopathologic study of prospectively followed Mayo Clinic participants dying?95 years-old who underwent autopsy. Participants were stratified by dementia status and compared according to demographics, vascular risk factors, cancer, and neuropathology.

Results: Participants (n = 161; 83% female; 99% non-Hispanic whites)?95 years (95-106 years-old) with/without dementia did not differ based on demographics. APOE ?2 frequency was higher in no dementia (20/72 [28%]) versus dementia (11/88 [12%]; p = 0.03), but APOE ?4 frequency did not differ. Coronary artery disease was more frequent in no dementia (31/72 [43%]) versus dementia (23/89 [26%]; p = 0.03) associated with 56% lower dementia odds (odds ratio [OR] = 0.44 [confidence interval (CI) = 0.19-0.98]; p = 0.04) and fewer neuritic/diffuse plaques. Diabetes had an 8-fold increase in dementia odds (OR = 8.42 [CI = 1.39-163]; p = 0.02). Diabetes associated with higher cerebrovascular disease (Dickson score; p = 0.05). Cancer associated with 63% lower dementia odds (OR = 0.37 [CI = 0.17-0.78]; p < 0.01) and lower Braak stage (p = 0.01).

Conclusion: Cancer exposure in the oldest-old was associated with lower odds of dementia and tangle pathology, whereas history of coronary artery disease was associated with lower odds of dementia and amyloid-? plaque pathology. History of diabetes mellitus was associated with increased odds of dementia and cerebrovascular disease pathology. Cancer-related mechanisms and vascular risk factor reduction strategies may alter dementia risk and neuropathology in oldest-old.

JUMPptm: Integrated software for sensitive identification of post-translational modifications and its application in Alzheimer's disease study

Poudel S, Vanderwall D, Yuan ZF, Wu Z, Peng J, Li Y.

Background: Mass spectrometry (MS)-based proteomic analysis of posttranslational modifications (PTMs) usually requires the pre-enrichment of modified proteins or peptides. However, recent ultra-deep whole proteome profiling generates millions of spectra in a single experiment, leaving many unassigned spectra, some of which may be derived from PTM peptides.

Methods: Here we present JUMPptm, an integrative computational pipeline, to extract PTMs from unenriched whole proteome. JUMPptm combines the advantages of JUMP, MSFragger and Comet search engines, and includes de novo tags, customized database search and peptide filtering, which iteratively analyzes each PTM by a multi-stage strategy to improve sensitivity and specificity.

Results: We applied JUMPptm to the deep brain proteome of Alzheimer’s disease (AD), and identified 34,954 unique peptides with phosphorylation, methylation, acetylation, ubiquitination, and others. The phosphorylated peptides were validated by enriched phosphoproteome from the same sample. TMT-based quantification revealed 482 PTM peptides dysregulated at different stages during AD progression. For example, the acetylation of numerous mitochondrial proteins is significantly decreased in AD. A total of 60 PTM sites are found in the pan-PTM map of the Tau protein.

Conclusion: The JUMPptm program is an effective tool for pan-PTM analysis and the resulting AD pan-PTM profile serves as a valuable resource for AD research.

LRP1 is a neuronal receptor for ?-synuclein uptake and spread

Chen K, Martens YA, Meneses A, Ryu DH, Lu W, Raulin AC, Li F, Zhao J, Chen Y, Jin Y, Linares C, Goodwin M, Li Y, Liu CC, Kanekiyo T, Holtzman DM, Golde TE, Bu G, Zhao N.

Background: The aggregation and spread of ?-synuclein (?-Syn) protein and related neuronal toxicity are the key pathological features of Parkinson’s disease (PD) and Lewy body dementia (LBD). Studies have shown that pathological species of ?-Syn and tau can spread in a prion-like manner between neurons, although these two proteins have distinct pathological roles and contribute to different neurodegenerative diseases. It is reported that the low-density lipoprotein receptor-related protein 1 (LRP1) regulates the spread of tau proteins; however, the molecular regulatory mechanisms of ?-Syn uptake and spread, and whether it is also regulated by LRP1, remain poorly understood.

Methods: We established LRP1 knockout (LRP1-KO) human induced pluripotent stem cells (iPSCs) isogenic lines using a CRISPR/Cas9 strategy and generated iPSC-derived neurons (iPSNs) to test the role of LRP1 in ?-Syn uptake. We treated the iPSNs with fluorescently labeled ?-Syn protein and measured the internalization of ?-Syn using flow cytometry. Three forms of ?-Syn species were tested: monomers, oligomers, and pre-formed fibrils (PFFs). To examine whether the lysine residues of ?-Syn are involved in LRP1-mediated uptake, we capped the amines of lysines on ?-Syn with sulfo-NHS acetate and then measured the internalization. We also tested whether the N-terminus of ?-Syn is critical for LRP1-mediated internalization. Lastly, we investigated the role of Lrp1 in regulating ?-Syn spread with a neuronal Lrp1 conditional knockout (Lrp1-nKO) mouse model. We generated adeno-associated viruses (AAVs) that allowed for distinguishing the ?-Syn expression versus spread and injected them into the hippocampus of six-month-old Lrp1-nKO mice and the littermate wild type (WT) controls. The spread of ?-Syn was evaluated three months after the injection.

Results: We found that the uptake of both monomeric and oligomeric ?-Syn was significantly reduced in iPSNs with LRP1-KO compared with the WT controls. The uptake of ?-Syn PFFs was also inhibited in LRP1-KO iPSNs, albeit to a much lesser extent compared to ?-Syn monomers and oligomers. The blocking of lysine residues on ?-Syn effectively decreased the uptake of ?-Syn in iPSNs and the N-terminus of ?-Syn was critical for LRP1-mediated ?-Syn uptake. Finally, in the Lrp1-nKO mice, the spread of ?-Syn was significantly reduced compared with the WT littermates.

Conclusions: We identified LRP1 as a key regulator of ?-Syn neuronal uptake, as well as an important mediator of ?-Syn spread in the brain. This study provides new knowledge on the physiological and pathological role of LRP1 in ?-Syn trafficking and pathology, offering insight for the treatment of synucleinopathies.

Evaluation of a Pooling Chemoproteomics Strategy with an FDA-Approved Drug Library

Sun H, Yang K, Zhang X, Fu Y, Yarbro J, Wu Z, Chen PC, Chen T, Peng J.

Chemoproteomics is a key platform for characterizing the mode of action for compounds, especially for targeted protein degraders such as proteolysis targeting chimeras (PROTACs) and molecular glues. With deep proteome coverage, multiplexed tandem mass tag-mass spectrometry (TMT-MS) can tackle up to 18 samples in a single experiment. Here, we present a pooling strategy for further enhancing the throughput and apply the strategy to an FDA-approved drug library (95 best-in-class compounds). The TMT-MS-based pooling strategy was evaluated in the following steps. First, we demonstrated the capability of TMT-MS by analyzing more than 15 000 unique proteins (> 12 000 gene products) in HEK293 cells treated with five PROTACs (two BRD/BET degraders and three degraders for FAK, ALK, and BTK kinases). We then introduced a rationalized pooling strategy to separate structurally similar compounds in different pools and identified the proteomic response to 14 pools from the drug library. Finally, we validated the proteomic response from one pool by reprofiling the cells via treatment with individual drugs with sufficient replicates. Interestingly, numerous proteins were found to change upon drug treatment, including AMD1, ODC1, PRKX, PRKY, EXO1, AEN, and LRRC58 with 7-hydroxystaurosporine; C6orf64, HMGCR, and RRM2 with Sorafenib; SYS1 and ALAS1 with Venetoclax; and ATF3, CLK1, and CLK4 with Palbocilib. Thus, pooling chemoproteomics screening provides an efficient method for dissecting the molecular targets of compound libraries.

Rainwater Charitable Foundation criteria for the neuropathologic diagnosis of progressive supranuclear palsy

Roemer SF, Grinberg LT, Crary JF, Seeley WW, McKee AC, Kovacs GG, Beach TG, Duyckaerts C, Ferrer IA, Gelpi E, Lee EB, Revesz T, White CL 3rd, Yoshida M, Pereira FL, Whitney K, Ghayal NB, Dickson DW.

Neuropathologic criteria for progressive supranuclear palsy (PSP) proposed by a National Institute of Neurological Disorders and Stroke (NINDS) working group were published in 1994 and based on the presence of neurofibrillary tangles in basal ganglia and brainstem. These criteria did not stipulate detection methods or incorporate glial tau pathology. In this study, a group of 14 expert neuropathologists scored digital slides from 10 brain regions stained with hematoxylin and eosin (H&E) and phosphorylated tau (AT8) immunohistochemistry. The cases included 15 typical and atypical PSP cases and 10 other tauopathies. Blinded to clinical and neuropathological information, raters provided a categorical diagnosis (PSP or not-PSP) based upon provisional criteria that required neurofibrillary tangles or pretangles in two of three regions (substantia nigra, subthalamic nucleus, globus pallidus) and tufted astrocytes in one of two regions (peri-Rolandic cortices, putamen). The criteria showed high sensitivity (0.97) and specificity (0.91), as well as almost perfect inter-rater reliability for diagnosing PSP and differentiating it from other tauopathies (Fleiss kappa 0.826). Most cases (17/25) had 100% agreement across all 14 raters. The Rainwater Charitable Foundation criteria for the neuropathologic diagnosis of PSP feature a simplified diagnostic algorithm based on phosphorylated tau immunohistochemistry and incorporate tufted astrocytes as an essential diagnostic feature.

Phosphorylated tau sites that are elevated in Alzheimer's disease fluid biomarkers are visualized in early neurofibrillary tangle maturity levels in the post mortem brain

Moloney CM, Labuzan SA, Crook JE, Siddiqui H, Castanedes-Casey M, Lachner C, Petersen RC, Duara R, Graff-Radford NR, Dickson DW, Mielke MM, Murray ME.

Introduction: Alzheimer’s disease (AD) biomarkers are increasingly more reliable in predicting neuropathology. To facilitate interpretation of phosphorylated tau sites as an early fluid biomarker, we sought to characterize which neurofibrillary tangle maturity levels (pretangle, intermediary 1, mature tangle, intermediary 2, and ghost tangle) are recognized.

Methods: We queried the Florida Autopsied Multi-Ethnic (FLAME) cohort for cases ranging from Braak stages I through VI, excluding non-AD neuropathologies and tauopathies. Thioflavin-S staining was compared to immunohistochemical measures of phosphorylated threonine (pT) 181, pT205, pT217, and pT231 in two hippocampal subsectors across n = 24 cases.

Results: Each phosphorylated tau site immunohistochemically labeled early neurofibrillary tangle maturity levels compared to advanced levels recognized by thioflavin-S. Hippocampal burden generally increased with each Braak stage.

Discussion: These results provide neurobiologic evidence that these phosphorylated tau fluid biomarker sites are present during early neurofibrillary tangle maturity levels and may explain why these fluid biomarker measures are observed before symptom onset.

Highlights: Immunohistochemical evaluation of four phosphorylated tau fluid biomarker sites. Earlier neurofibrillary tangle maturity levels recognized by phosphorylated tau in proline-rich region. Advanced tangle pathology is elevated in the subiculum compared to the cornu ammonis 1 of the hippocampus. Novel semi-quantitative frequency to calculate tangle maturity frequency.

Peripheral apoE4 enhances Alzheimer's pathology and impairs cognition by compromising cerebrovascular function

Liu CC, Zhao J, Fu Y, Inoue Y, Ren Y, Chen Y, Doss SV, Shue F, Jeevaratnam S, Bastea L, Wang N, Martens YA, Qiao W, Wang M, Zhao N, Jia L, Yamazaki Y, Yamazaki A, Rosenberg CL, Wang Z, Kong D, Li Z, Kuchenbecker LA, Trottier ZA, Felton L, Rogers J, Quicksall ZS, Linares C, Knight J, Chen Y, Kurti A, Kanekiyo T, Fryer JD, Asmann YW, Storz P, Wang X, Peng J, Zhang B, Kim BYS, Bu G.

The ?4 allele of the apolipoprotein E (APOE) gene, a genetic risk factor for Alzheimer’s disease, is abundantly expressed in both the brain and periphery. Here, we present evidence that peripheral apoE isoforms, separated from those in the brain by the blood-brain barrier, differentially impact Alzheimer’s disease pathogenesis and cognition. To evaluate the function of peripheral apoE, we developed conditional mouse models expressing human APOE3 or APOE4 in the liver with no detectable apoE in the brain. Liver-expressed apoE4 compromised synaptic plasticity and cognition by impairing cerebrovascular functions. Plasma proteome profiling revealed apoE isoform-dependent functional pathways highlighting cell adhesion, lipoprotein metabolism and complement activation. ApoE3 plasma from young mice improved cognition and reduced vessel-associated gliosis when transfused into aged mice, whereas apoE4 compromised the beneficial effects of young plasma. A human induced pluripotent stem cell-derived endothelial cell model recapitulated the plasma apoE isoform-specific effect on endothelial integrity, further supporting a vascular-related mechanism. Upon breeding with amyloid model mice, liver-expressed apoE4 exacerbated brain amyloid pathology, whereas apoE3 reduced it. Our findings demonstrate pathogenic effects of peripheral apoE4, providing a strong rationale for targeting peripheral apoE to treat Alzheimer’s disease.
Neuropathologic scales of cerebrovascular disease associated with diffusion changes on MRI

Nguyen AT, Kouri N, Labuzan SA, Przybelski SA, Lesnick TG, Raghavan S, Reid RI, Reichard RR, Knopman DS, Petersen RC, Jack CR Jr, Mielke MM, Dickson DW, Graff-Radford J, Murray ME, Vemuri P.

Summarizing the multiplicity and heterogeneity of cerebrovascular disease (CVD) features into a single measure has been difficult in both neuropathology and imaging studies. The objective of this work was to evaluate the association between neuroimaging surrogates of CVD and two available neuropathologic CVD scales in those with both antemortem imaging CVD measures and postmortem CVD evaluation. Individuals in the Mayo Clinic Study of Aging with MRI scans within 5 years of death (N = 51) were included. Antemortem CVD measures were computed from diffusion MRI (dMRI), FLAIR, and T2* GRE imaging modalities and compared with postmortem neuropathologic findings using Kalaria and Strozyk Scales. Of all the neuroimaging measures, both regional and global dMRI measures were associated with Kalaria and Strozyk Scales (p < 0.05) and modestly correlated with global cognitive performance. The major conclusions from this study were: (i) microstructural white matter injury measurements using dMRI may be meaningful surrogates of neuropathologic CVD scales, because they aid in capturing diffuse (and early) changes to white matter and secondary neurodegeneration due to lesions; (ii) vacuolation in the corpus callosum may be associated with white matter changes measured on antemortem dMRI imaging; (iii) Alzheimer’s disease neuropathologic change did not associate with neuropathologic CVD scales; and (iv) future work should be focused on developing better quantitative measures utilizing dMRI to optimally assess CVD-related neuropathologic changes.
Cholesterol and matrisome pathways dysregulated in astrocytes and microglia

Tcw J, Qian L, Pipalia NH, Chao MJ, Liang SA, Shi Y, Jain BR, Bertelsen SE, Kapoor M, Marcora E, Sikora E, Andrews EJ, Martini AC, Karch CM, Head E, Holtzman DM, Zhang B, Wang M, Maxfield FR, Poon WW, Goate AM.

The impact of apolipoprotein E ?4 (APOE4), the strongest genetic risk factor for Alzheimer’s disease (AD), on human brain cellular function remains unclear. Here, we investigated the effects of APOE4 on brain cell types derived from population and isogenic human induced pluripotent stem cells, post-mortem brain, and APOE targeted replacement mice. Population and isogenic models demonstrate that APOE4 local haplotype, rather than a single risk allele, contributes to risk. Global transcriptomic analyses reveal human-specific, APOE4-driven lipid metabolic dysregulation in astrocytes and microglia. APOE4 enhances de novo cholesterol synthesis despite elevated intracellular cholesterol due to lysosomal cholesterol sequestration in astrocytes. Further, matrisome dysregulation is associated with upregulated chemotaxis, glial activation, and lipid biosynthesis in astrocytes co-cultured with neurons, which recapitulates altered astrocyte matrisome signaling in human brain. Thus, APOE4 initiates glia-specific cell and non-cell autonomous dysregulation that may contribute to increased AD risk.
29-Plex tandem mass tag mass spectrometry enabling accurate quantification by interference correction

Sun H, Poudel S, Vanderwall D, Lee DG, Li Y, Peng J.

Tandem mass tag (TMT) mass spectrometry is a mainstream isobaric chemical labeling strategy for profiling proteomes. Here we present a 29-plex TMT method to combine the 11-plex and 18-plex labeling strategies. The 29-plex method was examined with a pooled sample composed of 1×, 3×, and 10× Escherichia coli peptides with 100× human background peptides, which generated two E. coli datasets (TMT11 and TMT18), displaying the distorted ratios of 1.0:1.7:4.2 and 1.0:1.8:4.9, respectively. This ratio compression from the expected 1:3:10 ratios was caused by co-isolated TMT-labeled ions (i.e., noise). Interestingly, the mixture of two TMT sets produced MS/MS spectra with unique features for the noise detection: (i) in TMT11-labeled spectra, TMT18-specific reporter ions (e.g., 135N) were shown as the noise; (ii) in TMT18-labeled spectra, the TMT11/TMT18-shared reporter ions (e.g., 131C) typically exhibited higher intensities than TMT18-specific reporter ions, due to contaminated TMT11-labeled ions in these shared channels. We further estimated the noise levels contributed by both TMT11- and TMT18-labeled peptides, and corrected reporter ion intensities in every spectrum. Finally, the anticipated 1:3:10 ratios were largely restored. This strategy was also validated using another 29-plex sample with 1:5 ratios. Thus the 29-plex method expands the TMT throughput and enhances the quantitative accuracy.
Frequency of LATE neuropathologic change across the spectrum of Alzheimer's disease neuropathology: combined data from 13 community-based or population-based autopsy cohorts

Nelson PT, Brayne C, Flanagan ME, Abner EL, Agrawal S, Attems J, Castellani RJ, Corrada MM, Cykowski MD, Di J, Dickson DW, Dugger BN, Ervin JF, Fleming J, Graff-Radford J, Grinberg LT, Hokkanen SRK, Hunter S, Kapasi A, Kawas CH, Keage HAD, Keene CD, Kero M, Knopman DS, Kouri N, Kovacs GG, Labuzan SA, Larson EB, Latimer CS, Leite REP, Matchett BJ, Matthews FE, Merrick R, Montine TJ, Murray ME, Myllykangas L, Nag S, Nelson RS, Neltner JH, Nguyen AT, Petersen RC, Polvikoski T, Reichard RR, Rodriguez RD, Suemoto CK, Wang SJ, Wharton SB, White L, Schneider JA.

Limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC) and Alzheimer’s disease neuropathologic change (ADNC) are each associated with substantial cognitive impairment in aging populations. However, the prevalence of LATE-NC across the full range of ADNC remains uncertain. To address this knowledge gap, neuropathologic, genetic, and clinical data were compiled from 13 high-quality community- and population-based longitudinal studies. Participants were recruited from United States (8 cohorts, including one focusing on Japanese-American men), United Kingdom (2 cohorts), Brazil, Austria, and Finland. The total number of participants included was 6196, and the average age of death was 88.1 years. Not all data were available on each individual and there were differences between the cohorts in study designs and the amount of missing data. Among those with known cognitive status before death (n = 5665), 43.0% were cognitively normal, 14.9% had MCI, and 42.4% had dementia-broadly consistent with epidemiologic data in this age group. Approximately 99% of participants (n = 6125) had available CERAD neuritic amyloid plaque score data. In this subsample, 39.4% had autopsy-confirmed LATE-NC of any stage. Among brains with “frequent” neuritic amyloid plaques, 54.9% had comorbid LATE-NC, whereas in brains with no detected neuritic amyloid plaques, 27.0% had LATE-NC. Data on LATE-NC stages were available for 3803 participants, of which 25% had LATE-NC stage > 1 (associated with cognitive impairment). In the subset of individuals with Thal A? phase = 0 (lacking detectable A? plaques), the brains with LATE-NC had relatively more severe primary age-related tauopathy (PART). A total of 3267 participants had available clinical data relevant to frontotemporal dementia (FTD), and none were given the clinical diagnosis of definite FTD nor the pathological diagnosis of frontotemporal lobar degeneration with TDP-43 inclusions (FTLD-TDP). In the 10 cohorts with detailed neurocognitive assessments proximal to death, cognition tended to be worse with LATE-NC across the full spectrum of ADNC severity. This study provided a credible estimate of the current prevalence of LATE-NC in advanced age. LATE-NC was seen in almost 40% of participants and often, but not always, coexisted with Alzheimer’s disease neuropathology.
APOE4 exacerbates ?-synuclein seeding activity and contributes to neurotoxicity in Alzheimer's disease with Lewy body pathology

Jin Y, Li F, Sonoustoun B, Kondru NC, Martens YA, Qiao W, Heckman MG, Ikezu TC, Li Z, Burgess JD, Amerna D, O’Leary J, DeTure MA, Zhao J, McLean PJ, Dickson DW, Ross OA, Bu G, Zhao N.

Approximately half of Alzheimer’s disease (AD) brains have concomitant Lewy pathology at autopsy, suggesting that ?-synuclein (?-SYN) aggregation is a regulated event in the pathogenesis of AD. Genome-wide association studies revealed that the ?4 allele of the apolipoprotein E (APOE4) gene, the strongest genetic risk factor for AD, is also the most replicated genetic risk factor for Lewy body dementia (LBD), signifying an important role of APOE4 in both amyloid-? (A?) and ?-SYN pathogenesis. How APOE4 modulates ?-SYN aggregation in AD is unclear. In this study, we aimed to determine how ?-SYN is associated with AD-related pathology and how APOE4 impacts ?-SYN seeding and toxicity. We measured ?-SYN levels and their association with other established AD-related markers in brain samples from autopsy-confirmed AD patients (N = 469), where 54% had concomitant LB pathology (AD + LB). We found significant correlations between the levels of ?-SYN and those of A?40, A?42, tau and APOE, particularly in insoluble fractions of AD + LB. Using a real-time quaking-induced conversion (RT-QuIC) assay, we measured the seeding activity of soluble ?-SYN and found that ?-SYN seeding was exacerbated by APOE4 in the AD cohort, as well as a small cohort of autopsy-confirmed LBD brains with minimal Alzheimer type pathology. We further fractionated the soluble AD brain lysates by size exclusion chromatography (SEC) ran on fast protein liquid chromatography (FPLC) and identified the ?-SYN species (~ 96 kDa) that showed the strongest seeding activity. Finally, using human induced pluripotent stem cell (iPSC)-derived neurons, we showed that amplified ?-SYN aggregates from AD + LB brain of patients with APOE4 were highly toxic to neurons, whereas the same amount of ?-SYN monomer was not toxic. Our findings suggest that the presence of LB pathology correlates with AD-related pathologies and that APOE4 exacerbates ?-SYN seeding activity and neurotoxicity, providing mechanistic insight into how APOE4 affects ?-SYN pathogenesis in AD.
The emerging role of lipidomics in prediction of diseases

Han X.

 

Deep Single-Cell-Type Proteome Profiling of Mouse Brain by Nonsurgical AAV-Mediated Proximity Labeling

Sun X, Sun H, Han X, Chen PC, Jiao Y, Wu Z, Zhang X, Wang Z, Niu M, Yu K, Liu D, Dey KK, Mancieri A, Fu Y, Cho JH, Li Y, Poudel S, Branon TC, Ting AY, Peng J.

Proteome profiling is a powerful tool in biological and biomedical studies, starting with samples at bulk, single-cell, or single-cell-type levels. Reliable methods for extracting specific cell-type proteomes are in need, especially for the cells (e.g., neurons) that cannot be readily isolated. Here, we present an innovative proximity labeling (PL) strategy for single-cell-type proteomics of mouse brain, in which TurboID (an engineered biotin ligase) is used to label almost all proteins in a specific cell type. This strategy bypasses the requirement of cell isolation and includes five major steps: (i) constructing recombinant adeno-associated viruses (AAVs) to express TurboID driven by cell-type-specific promoters, (ii) delivering the AAV to mouse brains by direct intravenous injection, (iii) enhancing PL labeling by biotin administration, (iv) purifying biotinylated proteins, followed by on-bead protein digestion, and (v) quantitative tandem-mass-tag (TMT) labeling. We first confirmed that TurboID can label a wide range of cellular proteins in human HEK293 cells and optimized the single-cell-type proteomic pipeline. To analyze specific brain cell types, we generated recombinant AAVs to coexpress TurboID and mCherry proteins, driven by neuron- or astrocyte-specific promoters and validated the expected cell expression by coimmunostaining of mCherry and cellular markers. Subsequent biotin purification and TMT analysis identified ?10,000 unique proteins from a few micrograms of protein samples with excellent reproducibility. Comparative and statistical analyses indicated that these PL proteomes contain cell-type-specific cellular pathways. Although PL was originally developed for studying protein-protein interactions and subcellular proteomes, we extended it to efficiently tag the entire proteomes of specific cell types in the mouse brain using TurboID biotin ligase. This simple, effective in vivo approach should be broadly applicable to single-cell-type proteomics.

 

Clinicopathologic Factors Associated With Reversion to Normal Cognition in Patients With Mild Cognitive Impairment

Li Z, Heckman MG, Kanekiyo T, Martens YA, Day GS, Vassilaki M, Liu CC, Bennett DA, Petersen RC, Zhao N, Bu G.

Background and objectives: To identify clinicopathologic factors contributing to mild cognitive impairment (MCI) reversion to normal cognition.

Methods: We analyzed 3 longitudinal cohorts in this study: the Mayo Clinic Study of Aging (MCSA), the Religious Orders Study and Memory and Aging Project (ROSMAP), and the National Alzheimer’s Coordinating Center (NACC). Demographic characteristics and clinical outcomes were compared between patients with MCI with or without an experience of reversion to normal cognition (referred to as reverters and nonreverters, respectively). We also compared longitudinal changes in cortical thickness, glucose metabolism, and amyloid and tau load in a subcohort of reverters and nonreverters in MCSA with MRI or PET imaging information from multiple visits.

Results: We identified 164 (56.4%) individuals in MCSA, 508 (66.8%) individuals in ROSMAP, and 280 (34.1%) individuals in NACC who experienced MCI reversion to normal cognition. Cox proportional hazards regression models showed that MCI reverters had an increased chance of being cognitively normal at the last visit in MCSA (HR 3.31, 95% CI 2.14-5.12), ROSMAP (HR 3.72, 95% CI 2.50-5.56), and NACC (HR 9.29, 95% CI 6.45-13.40) and a reduced risk of progression to dementia (HR 0.12, 95% CI 0.05-0.29 in MCSA; HR 0.41, 95% CI 0.32-0.53 in ROSMAP; and HR 0.29, 95% CI 0.21-0.40 in NACC). Compared with MCI nonreverters, reverters had better-preserved cortical thickness (? = 0.082, p <0.001) and glucose metabolism (? = 0.119, p = 0.001) and lower levels of amyloid, albeit statistically nonsignificant (? = -0.172, p = 0.090). However, no difference in tau load was found between reverters and nonreverters (? = 0.073, p = 0.24).

Discussion: MCI reversion to normal cognition is likely attributed to better-preserved cortical structure and glucose metabolism.

 

Solving neurodegeneration: common mechanisms and strategies for new treatments

Wareham LK, Liddelow SA, Temple S, Benowitz LI, Di Polo A, Wellington C, Goldberg JL, He Z, Duan X, Bu G, Davis AA, Shekhar K, Torre A, Chan DC, Canto-Soler MV, Flanagan JG, Subramanian P, Rossi S, Brunner T, Bovenkamp DE, Calkins DJ.

Across neurodegenerative diseases, common mechanisms may reveal novel therapeutic targets based on neuronal protection, repair, or regeneration, independent of etiology or site of disease pathology. To address these mechanisms and discuss emerging treatments, in April, 2021, Glaucoma Research Foundation, BrightFocus Foundation, and the Melza M. and Frank Theodore Barr Foundation collaborated to bring together key opinion leaders and experts in the field of neurodegenerative disease for a virtual meeting titled “Solving Neurodegeneration”. This “think-tank” style meeting focused on uncovering common mechanistic roots of neurodegenerative disease and promising targets for new treatments, catalyzed by the goal of finding new treatments for glaucoma, the world’s leading cause of irreversible blindness and the common interest of the three hosting foundations. Glaucoma, which causes vision loss through degeneration of the optic nerve, likely shares early cellular and molecular events with other neurodegenerative diseases of the central nervous system. Here we discuss major areas of mechanistic overlap between neurodegenerative diseases of the central nervous system: neuroinflammation, bioenergetics and metabolism, genetic contributions, and neurovascular interactions. We summarize important discussion points with emphasis on the research areas that are most innovative and promising in the treatment of neurodegeneration yet require further development. The research that is highlighted provides unique opportunities for collaboration that will lead to efforts in preventing neurodegeneration and ultimately vision loss.

 

Lipoproteins in the Central Nervous System: From Biology to Pathobiology

Raulin AC, Martens YA, Bu G.

The brain, as one of the most lipid-rich organs, heavily relies on lipid transport and distribution to maintain homeostasis and neuronal function. Lipid transport mediated by lipoprotein particles, which are complex structures composed of apolipoproteins and lipids, has been thoroughly characterized in the periphery. Although lipoproteins in the central nervous system (CNS) were reported over half a century ago, the identification of APOE4 as the strongest genetic risk factor for Alzheimer’s disease has accelerated investigation of the biology and pathobiology of lipoproteins in the CNS. This review provides an overview of the different components of lipoprotein particles, in particular apolipoproteins, and their involvements in both physiological functions and pathological mechanisms in the CNS.

 

ApoE Cascade Hypothesis in the pathogenesis of Alzheimer's disease and related dementias

Martens YA, Zhao N, Liu CC, Kanekiyo T, Yang AJ, Goate AM, Holtzman DM, Bu G.

The ?4 allele of the apolipoprotein E gene (APOE4) is a strong genetic risk factor for Alzheimer’s disease (AD) and several other neurodegenerative conditions, including Lewy body dementia (LBD). The three APOE alleles encode protein isoforms that differ from one another only at amino acid positions 112 and 158: apoE2 (C112, C158), apoE3 (C112, R158), and apoE4 (R112, R158). Despite progress, it remains unclear how these small amino acid differences in apoE sequence among the three isoforms lead to profound effects on aging and disease-related pathways. Here, we propose a novel “ApoE Cascade Hypothesis” in AD and age-related cognitive decline, which states that the biochemical and biophysical properties of apoE impact a cascade of events at the cellular and systems levels, ultimately impacting aging-related pathogenic conditions including AD. As such, apoE-targeted therapeutic interventions are predicted to be more effective by addressing the biochemical phase of the cascade.

 

The emerging role of lipidomics in prediction of diseases

Han X.

 

APOE mediated neuroinflammation and neurodegeneration in Alzheimer's disease

Parhizkar S, Holtzman DM.

Neuroinflammation is a central mechanism involved in neurodegeneration as observed in Alzheimer’s disease (AD), the most prevalent form of neurodegenerative disease. Apolipoprotein E4 (APOE4), the strongest genetic risk factor for AD, directly influences disease onset and progression by interacting with the major pathological hallmarks of AD including amyloid-? plaques, neurofibrillary tau tangles, as well as neuroinflammation. Microglia and astrocytes, the two major immune cells in the brain, exist in an immune-vigilant state providing immunological defense as well as housekeeping functions that promote neuronal well-being. It is becoming increasingly evident that under disease conditions, these immune cells become progressively dysfunctional in regulating metabolic and immunoregulatory pathways, thereby promoting chronic inflammation-induced neurodegeneration. Here, we review and discuss how APOE and specifically APOE4 directly influences amyloid-? and tau pathology, and disrupts microglial as well as astroglial immunomodulating functions leading to chronic inflammation that contributes to neurodegeneration in AD.

 

APOE4 confers transcriptomic and functional alterations to primary mouse microglia

Machlovi SI, Neuner SM, Hemmer BM, Khan R, Liu Y, Huang M, Zhu JD, Castellano JM, Cai D, Marcora E, Goate AM.

Common genetic variants in more than forty loci modulate risk for Alzheimer’s disease (AD). AD risk alleles are enriched within enhancers active in myeloid cells, suggesting that microglia, the brain-resident macrophages, may play a key role in the etiology of AD. A major genetic risk factor for AD is Apolipoprotein E (APOE) genotype, with the ?4/?4 (E4) genotype increasing risk for AD by approximately 15 fold compared to the most common ?3/?3 (E3) genotype. However, the impact of APOE genotype on microglial function has not been thoroughly investigated. To address this, we cultured primary microglia from mice in which both alleles of the mouse Apoe gene have been humanized to encode either human APOE ?3 or APOE ?4. Relative to E3 microglia, E4 microglia exhibit altered morphology, increased endolysosomal mass, increased cytokine/chemokine production, and increased lipid and lipid droplet accumulation at baseline. These changes were accompanied by decreased translation and increased phosphorylation of eIF2? and eIF2?-kinases that participate in the integrated stress response, suggesting that E4 genotype leads to elevated levels of cellular stress in microglia relative to E3 genotype. Using live-cell imaging and flow cytometry, we also show that E4 microglia exhibited increased phagocytic uptake of myelin and other substrates compared to E3 microglia. While transcriptomic profiling of myelin-challenged microglia revealed a largely overlapping response profile across genotypes, differential enrichment of genes in interferon signaling, extracellular matrix and translation-related pathways was identified in E4 versus E3 microglia both at baseline and following myelin challenge. Together, our results suggest E4 genotype confers several important functional alterations to microglia even prior to myelin challenge, providing insight into the molecular and cellular mechanisms by which APOE4 may increase risk for AD.

 

The foundations and development of lipidomics

Han X, Gross RW.

For over a century, the importance of lipid metabolism in biology was recognized but difficult to mechanistically understand due to the lack of sensitive and robust technologies for identification and quantification of lipid molecular species. The enabling technological breakthroughs emerged in the 1980s with the development of soft ionization methods (Electrospray Ionization and Matrix Assisted Laser Desorption/Ionization) that could identify and quantify intact individual lipid molecular species. These soft ionization technologies laid the foundations for what was to be later named the field of lipidomics. Further innovative advances in multistage fragmentation, dramatic improvements in resolution and mass accuracy, and multiplexed sample analysis fueled the early growth of lipidomics through the early 1990s. The field exponentially grew through the use of a variety of strategic approaches, which included direct infusion, chromatographic separation, and charge-switch derivatization, which facilitated access to the low abundance species of the lipidome. In this Thematic Review, we provide a broad perspective of the foundations, enabling advances, and predicted future directions of growth of the lipidomics field.

 

TDP-43 Pathology in Alzheimer's Disease

Meneses A, Koga S, O’Leary J, Dickson DW, Bu G, Zhao N.

Transactive response DNA binding protein of 43 kDa (TDP-43) is an intranuclear protein encoded by the TARDBP gene that is involved in RNA splicing, trafficking, stabilization, and thus, the regulation of gene expression. Cytoplasmic inclusion bodies containing phosphorylated and truncated forms of TDP-43 are hallmarks of amyotrophic lateral sclerosis (ALS) and a subset of frontotemporal lobar degeneration (FTLD). Additionally, TDP-43 inclusions have been found in up to 57% of Alzheimer’s disease (AD) cases, most often in a limbic distribution, with or without hippocampal sclerosis. In some cases, TDP-43 deposits are also found in neurons with neurofibrillary tangles. AD patients with TDP-43 pathology have increased severity of cognitive impairment compared to those without TDP-43 pathology. Furthermore, the most common genetic risk factor for AD, apolipoprotein E4 (APOE4), is associated with increased frequency of TDP-43 pathology. These findings provide strong evidence that TDP-43 pathology is an integral part of multiple neurodegenerative conditions, including AD. Here, we review the biology and pathobiology of TDP-43 with a focus on its role in AD. We emphasize the need for studies on the mechanisms that lead to TDP-43 pathology, especially in the setting of age-related disorders such as AD

 

TREM2 interacts with TDP-43 and mediates microglial neuroprotection against TDP-43-related neurodegeneration

Xie M, Liu YU, Zhao S, Zhang L, Bosco DB, Pang YP, Zhong J, Sheth U, Martens YA, Zhao N, Liu CC, Zhuang Y, Wang L, Dickson DW, Mattson MP, Bu G, Wu LJ.

Triggering receptor expressed on myeloid cell 2 (TREM2) is linked to risk of neurodegenerative disease. However, the function of TREM2 in neurodegeneration is still not fully understood. Here, we investigated the role of microglial TREM2 in TAR DNA-binding protein 43 (TDP-43)-related neurodegeneration using virus-mediated and transgenic mouse models. We found that TREM2 deficiency impaired phagocytic clearance of pathological TDP-43 by microglia and enhanced neuronal damage and motor impairments. Mass cytometry analysis revealed that human TDP-43 (hTDP-43) induced a TREM2-dependent subpopulation of microglia with high CD11c expression and phagocytic ability. Using mass spectrometry (MS) and surface plasmon resonance (SPR) analysis, we further demonstrated an interaction between TDP-43 and TREM2 in vitro and in vivo as well as in human tissues from individuals with amyotrophic lateral sclerosis (ALS). We computationally identified regions within hTDP-43 that interact with TREM2. Our data highlight that TDP-43 is a possible ligand for microglial TREM2 and that this interaction mediates neuroprotection of microglia in TDP-43-related neurodegeneration.

 

Microglial TREM2 in amyotrophic lateral sclerosis

Xie M, Zhao S, Bosco DB, Nguyen A, Wu LJ.

Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease, is an aggressive motor neuron degenerative disease characterized by selective loss of both upper and lower motor neurons. The mechanisms underlying disease initiation and progression are poorly understood. The involvement of nonmotor neuraxis emphasizes the contribution of glial cells in disease progress. Microglia comprise a unique subset of glial cells and are the principal immune cells in the central nervous system (CNS). Triggering receptor expressed on myeloid cell 2 (TREM2) is a surface receptor that, within the CNS, is exclusively expressed on microglia and plays crucial roles in microglial proliferation, migration, activation, metabolism, and phagocytosis. Genetic evidence has linked TREM2 to neurodegenerative diseases including ALS, but its function in ALS pathogenesis is largely unknown. In this review, we summarize how microglial activation, with a specific focus on TREM2 function, affects ALS progression clinically and experimentally. Understanding microglial TREM2 function will help pinpoint the molecular target for ALS treatment.

 

JUMPt: Comprehensive Protein Turnover Modeling of In Vivo Pulse SILAC Data by Ordinary Differential Equations

Chepyala SR, Liu X, Yang K, Wu Z, Breuer AM, Cho JH, Li Y, Mancieri A, Jiao Y, Zhang H, Peng J.

Recent advances in mass spectrometry (MS)-based proteomics allow the measurement of turnover rates of thousands of proteins using dynamic labeling methods, such as pulse stable isotope labeling by amino acids in cell culture (pSILAC). However, when applying the pSILAC strategy to multicellular animals (e.g., mice), the labeling process is significantly delayed by native amino acids recycled from protein degradation in vivo, raising a challenge of defining accurate protein turnover rates. Here, we report JUMPt, a software package using a novel ordinary differential equation (ODE)-based mathematical model to determine reliable rates of protein degradation. The uniqueness of JUMPt is to consider amino acid recycling and fit the kinetics of the labeling amino acid (e.g., Lys) and whole proteome simultaneously to derive half-lives of individual proteins. Multiple settings in the software are designed to enable simple to comprehensive data inputs for precise analysis of half-lives with flexibility. We examined the software by studying the turnover of thousands of proteins in the pSILAC brain and liver tissues. The results were largely consistent with the proteome turnover measurements from previous studies. The long-lived proteins are enriched in the integral membrane, myelin sheath, and mitochondrion in the brain. In summary, the ODE-based JUMPt software is an effective proteomics tool for analyzing large-scale protein turnover, and the software is publicly available on GitHub (https://github.com/JUMPSuite/JUMPt) to the research community.

APOE3-Jacksonville (V236E) variant reduces self-aggregation and risk of dementia

Liu CC, Murray ME, Li X, Zhao N, Wang N, Heckman MG, Shue F, Martens Y, Li Y, Raulin AC, Rosenberg CL, Doss SV, Zhao J, Wren MC, Jia L, Ren Y, Ikezu TC, Lu W, Fu Y, Caulfield T, Trottier ZA, Knight J, Chen Y, Linares C, Wang X, Kurti A, Asmann YW, Wszolek ZK, Smith GE, Vemuri P, Kantarci K, Knopman DS, Lowe VJ, Jack CR Jr, Parisi JE, Ferman TJ, Boeve BF, Graff-Radford NR, Petersen RC, Younkin SG, Fryer JD, Wang H, Han X, Frieden C, Dickson DW, Ross OA, Bu G.

Apolipoprotein E (APOE) genetic variants have been shown to modify Alzheimer’s disease (AD) risk. We previously identified an APOE3 variant (APOE3-V236E), named APOE3-Jacksonville (APOE3-Jac), associated with healthy brain aging and reduced risk for AD and dementia with Lewy bodies (DLB). Herein, we resolved the functional mechanism by which APOE3-Jac reduces APOE aggregation and enhances its lipidation in human brains, as well as in cellular and biochemical assays. Compared to APOE3, expression of APOE3-Jac in astrocytes increases several classes of lipids in the brain including phosphatidylserine, phosphatidylethanolamine, phosphatidic acid, and sulfatide, critical for synaptic functions. Mice expressing APOE3-Jac have reduced amyloid pathology, plaque-associated immune responses, and neuritic dystrophy. The V236E substitution is also sufficient to reduce the aggregation of APOE4, whose gene allele is a major genetic risk factor for AD and DLB. These findings suggest that targeting APOE aggregation might be an effective strategy for treating a subgroup of individuals with AD and DLB.

 

Apolipoprotein E regulates lipid metabolism and ?-synuclein pathology in human iPSC-derived cerebral organoids

Zhao J, Lu W, Ren Y, Fu Y, Martens YA, Shue F, Davis MD, Wang X, Chen K, Li F, Liu CC, Graff-Radford NR, Wszolek ZK, Younkin SG, Brafman DA, Ertekin-Taner N, Asmann YW, Dickson DW, Xu Z, Pan M, Han X, Kanekiyo T, Bu G.

APOE4 is a strong genetic risk factor for Alzheimer’s disease and Dementia with Lewy bodies; however, how its expression impacts pathogenic pathways in a human-relevant system is not clear. Here using human iPSC-derived cerebral organoid models, we find that APOE deletion increases ?-synuclein (?Syn) accumulation accompanied with synaptic loss, reduction of GBA levels, lipid droplet accumulation and dysregulation of intracellular organelles. These phenotypes are partially rescued by exogenous apoE2 and apoE3, but not apoE4. Lipidomics analysis detects the increased fatty acid utilization and cholesterol ester accumulation in apoE-deficient cerebral organoids. Furthermore, APOE4 cerebral organoids have increased ?Syn accumulation compared to those with APOE3. Carrying APOE4 also increases apoE association with Lewy bodies in postmortem brains from patients with Lewy body disease. Our findings reveal the predominant role of apoE in lipid metabolism and ?Syn pathology in iPSC-derived cerebral organoids, providing mechanistic insights into how APOE4 drives the risk for synucleinopathies.

 

Preparation of single cell suspensions enriched in mouse brain vascular cells for single-cell RNA sequencing

Yamazaki A, Shue F, Yamazaki Y, Martens YA, Bu G, Liu CC.

Cerebral blood vessels supply oxygen and nutrients, remove metabolic waste, and play a critical role in maintaining brain homeostasis. Cerebrovasculature is composed of heterogeneous populations of brain vascular cells (BVCs). A major challenge in effective cerebrovascular transcriptional profiling is high-quality BVC procurement, permitting high sequencing depth. Here, we establish cell isolation procedures for glio-vascular cell-enriched single-cell RNA sequencing enabling unbiased characterization of BVC transcriptional heterogeneity. Our approach can be used to address vascular-specific contribution to brain diseases. For complete details on the use and execution of this protocol, please refer to Yamazaki et al. (2021).

 

Clinical, pathological and genetic characteristics of Perry disease-new cases and literature review

Dulski J, Cerquera-Cleves C, Milanowski L, Kidd A, Sitek EJ, Strongosky A, Vanegas Monroy AM, Dickson DW, Ross OA, Pentela-Nowicka J, S?awek J, Wszolek ZK.

Background and purpose: Perry disease (or Perry syndrome) is an autosomal dominant neurodegenerative disorder characterized by parkinsonism, neuropsychiatric symptoms, central hypoventilation, weight loss and distinct TDP-43 pathology. It is caused by mutations of the DCTN1 gene encoding an essential component of axonal transport. The objectives were to provide the current state of knowledge on clinical, pathological and genetic aspects of Perry disease, as well as practical suggestions for the management of the disease.

Methods: Data on new patients from New Zealand, Poland and Colombia were collected, including autopsy report. Also all of the published papers since the original work by Perry in 1975 were gathered and analyzed.

Results: Parkinsonism was symmetrical, progressed rapidly and was poorly responsive to L-Dopa; nonetheless, a trial with high doses of L-Dopa is warranted. Depression was severe, associated with suicidal ideations, and benefited from antidepressants and L-Dopa. Respiratory symptoms were the leading cause of death, and artificial ventilation or a diaphragm pacemaker prolonged survival. Weight loss occurred in most patients and was of multifactorial etiology. Autonomic dysfunction was frequent but underdiagnosed. There was a clinical overlap with other neurodegenerative disorders. An autopsy showed distinctive pallidonigral degeneration with TDP-43 pathology. Genetic testing provided evidence of a common founder for two families. There was striking phenotypic variability in DCTN1-related disorders. It is hypothesized that oligogenic or polygenic inheritance is at play.

Conclusions: Perry disease and other DCTN1-related diseases are increasingly diagnosed worldwide. Relatively effective symptomatic treatments are available. Further studies are needed to pave the way toward curative/gene therapy.

 

Generation and validation of APOE knockout human iPSC-derived cerebral organoids

Martens YA, Xu S, Tait R, Li G, Zhao XC, Lu W, Liu CC, Kanekiyo T, Bu G, Zhao J.

Apolipoprotein E (apoE) is a major lipid carrier in the brain and closely associated with the pathogenesis of Alzheimer’s disease (AD). Here, we describe a protocol for efficient knockout of APOE in human induced pluripotent stem cells (iPSCs) using the CRISPR-Cas9 system. We obtain homozygous APOE knockout (APOE-/- ) iPSCs and further validate the deficiency of apoE in iPSC-derived cerebral organoids. APOE-/- cerebral organoids can serve as a useful tool to study apoE functions and apoE-related pathogenic mechanisms in AD. For complete details on the use and execution of this protocol, please refer to Zhao et al. (2020).

SARS-CoV-2 simulations go exascale to predict dramatic spike opening and cryptic pockets across the proteome

Zimmerman MI, Porter JR, Ward MD, Singh S, Vithani N, Meller A, Mallimadugula UL, Kuhn CE, Borowsky JH, Wiewiora RP, Hurley MFD, Harbison AM, Fogarty CA, Coffland JE, Fadda E, Voelz VA, Chodera JD, Bowman GR.

SARS-CoV-2 has intricate mechanisms for initiating infection, immune evasion/suppression and replication that depend on the structure and dynamics of its constituent proteins. Many protein structures have been solved, but far less is known about their relevant conformational changes. To address this challenge, over a million citizen scientists banded together through the Folding@home distributed computing project to create the first exascale computer and simulate 0.1 seconds of the viral proteome. Our adaptive sampling simulations predict dramatic opening of the apo spike complex, far beyond that seen experimentally, explaining and predicting the existence of ‘cryptic’ epitopes. Different spike variants modulate the probabilities of open versus closed structures, balancing receptor binding and immune evasion. We also discover dramatic conformational changes across the proteome, which reveal over 50 ‘cryptic’ pockets that expand targeting options for the design of antivirals. All data and models are freely available online, providing a quantitative structural atlas.

 

Amelioration of Tau and ApoE4-linked glial lipid accumulation and neurodegeneration with an LXR agonist.

Litvinchuk A, Suh JH, Guo JL, Lin K, Davis SS, Bien-Ly N, Tycksen E, Tabor GT, Remolina Serrano J, Manis M, Bao X, Lee C, Bosch M, Perez EJ, Yuede CM, Cashikar AG, Ulrich JD, Di Paolo G, Holtzman DM.

 

Apolipoprotein E (APOE) is a strong genetic risk factor for late-onset Alzheimer’s disease (LOAD). APOE4 increases and APOE2 decreases risk relative to APOE3. In the P301S mouse model of tauopathy, ApoE4 increases tau pathology and neurodegeneration when compared with ApoE3 or the absence of ApoE. However, the role of ApoE isoforms and lipid metabolism in contributing to tau-mediated degeneration is unknown. We demonstrate that in P301S tau mice, ApoE4 strongly promotes glial lipid accumulation and perturbations in cholesterol metabolism and lysosomal function. Increasing lipid efflux in glia via an LXR agonist or Abca1 overexpression strongly attenuates tau pathology and neurodegeneration in P301S/ApoE4 mice. We also demonstrate reductions in reactive astrocytes and microglia, as well as changes in cholesterol biosynthesis and metabolism in glia of tauopathy mice in response to LXR activation. These data suggest that promoting efflux of glial lipids may serve as a therapeutic approach to ameliorate tau and ApoE4-linked neurodegeneration.

Regulation of cortical hyperexcitability in amyotrophic lateral sclerosis: focusing on glial mechanisms

Xie M, Pallegar PN, Parusel S, Nguyen AT, Wu LJ.

 

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder characterized by the loss of both upper and lower motor neurons, resulting in muscle weakness, atrophy, paralysis, and eventually death. Motor cortical hyperexcitability is a common phenomenon observed at the presymptomatic stage of ALS. Both cell-autonomous (the intrinsic properties of motor neurons) and non-cell-autonomous mechanisms (cells other than motor neurons) are believed to contribute to cortical hyperexcitability. Decoding the pathological relevance of these dynamic changes in motor neurons and glial cells has remained a major challenge. This review summarizes the evidence of cortical hyperexcitability from both clinical and preclinical research, as well as the underlying mechanisms. We discuss the potential role of glial cells, particularly microglia, in regulating abnormal neuronal activity during the disease progression. Identifying early changes such as neuronal hyperexcitability in the motor system may provide new insights for earlier diagnosis of ALS and reveal novel targets to halt the disease progression.

Cell-autonomous effects of APOE4 in restricting microglial response in brain homeostasis and Alzheimer's disease

Liu CC, Wang N, Chen Y, Inoue Y, Shue F, Ren Y, Wang M, Qiao W, Ikezu TC, Li Z, Zhao J, Martens Y, Doss SV, Rosenberg CL, Jeevaratnam S, Jia L, Raulin AC, Qi F, Zhu Y, Alnobani A, Knight J, Chen Y, Linares C, Kurti A, Fryer JD, Zhang B, Wu LJ, Kim BYS, Bu G.

 

Microglial involvement in Alzheimer’s disease (AD) pathology has emerged as a risk-determining pathogenic event. While apolipoprotein E (APOE) is known to modify AD risk, it remains unclear how microglial apoE impacts brain cognition and AD pathology. Here, using conditional mouse models expressing apoE isoforms in microglia and central nervous system-associated macrophages (CAMs), we demonstrate a cell-autonomous effect of apoE3-mediated microglial activation and function, which are negated by apoE4. Expression of apoE3 in microglia/CAMs improves cognitive function, increases microglia surrounding amyloid plaque and reduces amyloid pathology and associated toxicity, whereas apoE4 expression either compromises or has no effects on these outcomes by impairing lipid metabolism. Single-cell transcriptomic profiling reveals increased antigen presentation and interferon pathways upon apoE3 expression. In contrast, apoE4 expression downregulates complement and lysosomal pathways, and promotes stress-related responses. Moreover, in the presence of mouse endogenous apoE, microglial apoE4 exacerbates amyloid pathology. Finally, we observed a reduction in Lgals3-positive responsive microglia surrounding amyloid plaque and an increased accumulation of lipid droplets in APOE4 human brains and induced pluripotent stem cell-derived microglia. Our findings establish critical isoform-dependent effects of microglia/CAM-expressed apoE in brain function and the development of amyloid pathology, providing new insight into how apoE4 vastly increases AD risk.

Deconvolution reveals cell-type-specific transcriptomic changes in the aging mouse brain

Ren Y, Wang X, Zhang S, Hu H, Quicksall Z, Lee S, Morganti JM, Johnson LA, Asmann YW, Zhao N.

 

Mounting evidence highlights the crucial role of aging in the pathogenesis of Alzheimer’s disease (AD). We have previously explored human apoE-targeted replacement mice across different ages and identified distinct molecular pathways driven by aging. However, the specific contribution of different brain cell types to the gene modules underlying these pathways remained elusive. To bridge this knowledge gap, we employed a computational deconvolution approach to examine cell-type-specific gene expression profiles in major brain cell types, including astrocytes (AS), microglia (MG), oligodendroglia (OG), neurons (NEU), and vascular cells (VC). Our findings revealed that immune module genes were predominantly expressed in MG, OG, and VC. The lipid metabolism module genes were primarily expressed in AS, MG, and OG. The mitochondria module genes showed prominent expression in VC, and the synapse module genes were primarily expressed in NEU and VC. Furthermore, we identified intra- and inter-cell-type interactions among these module genes and validated their aging-associated expression changes using published single cell studies. Our study dissected bulk brain transcriptomics data at the cellular level, providing a closer examination of the cell-type contributions to the molecular pathways driven by aging.

Hepatic soluble epoxide hydrolase: A promising target for unveiling the liver-brain axis in Alzheimer's disease

Inoue Y, Bamkole M, Kanekiyo T.

 

Wu and Dong et al.1 report that hepatic soluble epoxide hydrolase (sEH) manipulation impacts amyloid-? (A?) deposits and cognitive impairment in mouse models for Alzheimer’s disease (AD), suggesting that hepatic sEH activity is a promising therapeutic target to treat AD.

Emerging diagnostics and therapeutics for Alzheimer disease

Self WK, Holtzman DM.

 

Alzheimer disease (AD) is the most common contributor to dementia in the world, but strategies that slow or prevent its clinical progression have largely remained elusive, until recently. This Review highlights the latest advances in biomarker technologies and therapeutic development to improve AD diagnosis and treatment. We review recent results that enable pathological staging of AD with neuroimaging and fluid-based biomarkers, with a particular emphasis on the role of amyloid, tau and neuroinflammation in disease pathogenesis. We discuss the lessons learned from randomized controlled trials, including some supporting the proposal that certain anti-amyloid antibodies slow cognitive decline during the mildly symptomatic phase of AD. In addition, we highlight evidence for newly identified therapeutic targets that may be able to modify AD pathogenesis and progression. Collectively, these recent discoveries-and the research directions that they open-have the potential to move AD clinical care toward disease-modifying treatment strategies with maximal benefits for patients.

APOE deficiency impacts neural differentiation and cholesterol biosynthesis in human iPSC-derived cerebral organoids

Zhao J, Ikezu TC, Lu W, Macyczko JR, Li Y, Lewis-Tuffin LJ, Martens YA, Ren Y, Zhu Y, Asmann YW, Ertekin-Taner N, Kanekiyo T, Bu G.

 

Background: The apolipoprotein E (APOE) gene is the strongest genetic risk factor for Alzheimer’s disease (AD); however, how it modulates brain homeostasis is not clear. The apoE protein is a major lipid carrier in the brain transporting lipids such as cholesterol among different brain cell types.

Methods: We generated three-dimensional (3-D) cerebral organoids from human parental iPSC lines and its isogenic APOE-deficient (APOE-/-) iPSC line. To elucidate the cell-type-specific effects of APOE deficiency in the cerebral organoids, we performed scRNA-seq in the parental and APOE-/- cerebral organoids at Day 90.

Results: We show that APOE deficiency in human iPSC-derived cerebral organoids impacts brain lipid homeostasis by modulating multiple cellular and molecular pathways. Molecular profiling through single-cell RNA sequencing revealed that APOE deficiency leads to changes in cellular composition of isogenic cerebral organoids likely by modulating the eukaryotic initiation factor 2 (EIF2) signaling pathway as these events were alleviated by the treatment of an integrated stress response inhibitor (ISRIB). APOE deletion also leads to activation of the Wnt/?-catenin signaling pathway with concomitant decrease of secreted frizzled-related protein 1 (SFRP1) expression in glia cells. Importantly, the critical role of apoE in cell-type-specific lipid homeostasis was observed upon APOE deletion in cerebral organoids with a specific upregulation of cholesterol biosynthesis in excitatory neurons and excessive lipid accumulation in astrocytes. Relevant to human AD, APOE4 cerebral organoids show altered neurogenesis and cholesterol metabolism compared to those with APOE3.

Conclusions: Our work demonstrates critical roles of apoE in brain homeostasis and offers critical insights into the APOE4-related pathogenic mechanisms.

Retrospective Evaluation of Neuropathologic Proxies of the Minimal Atrophy Subtype Compared With Corticolimbic Alzheimer Disease Subtypes

Boon BDC, Labuzan SA, Peng Z, Matchett BJ, Kouri N, Hinkle KM, Lachner C, Ross OA, Ertekin-Taner N, Carter RE, Ferman TJ, Duara R, Dickson DW, Graff-Radford NR, Murray ME.

 

Background and objectives: Alzheimer disease (AD) is neuropathologically classified into 3 corticolimbic subtypes based on the neurofibrillary tangle distribution throughout the hippocampus and association cortices: limbic predominant, typical, and hippocampal sparing. In vivo, a fourth subtype, dubbed “minimal atrophy,” was identified using structural MRI. The objective of this study was to identify a neuropathologic proxy for the neuroimaging-defined minimal atrophy subtype.

Methods: We applied 2 strategies in the Florida Autopsied Multi-Ethnic (FLAME) cohort to evaluate a neuropathologic proxy for the minimal atrophy subtype. In the first strategy, we selected AD cases with a Braak tangle stage IV (Braak IV) because of the relative paucity of neocortical tangle involvement compared with Braak >IV. Braak IV cases were compared with the 3 AD subtypes. In the alternative strategy, typical AD was stratified by brain weight and cases having a relatively high brain weight (>75th percentile) were defined as minimal atrophy.

Results: Braak IV cases (n = 37) differed from AD subtypes (limbic predominant [n = 174], typical [n = 986], and hippocampal sparing [n = 187] AD) in having the least years of education (median 12 years, group-wise p < 0.001) and the highest brain weight (median 1,140 g, p = 0.002). Braak IV cases most resembled the limbic predominant cases owing to their high proportion of APOE ?4 carriers (75%, p < 0.001), an amnestic syndrome (100%, p < 0.001), as well as older age of cognitive symptom onset and death (median 79 and 85 years, respectively, p < 0.001). Only 5% of Braak IV cases had amygdala-predominant Lewy bodies (the lowest frequency observed, p = 0.017), whereas 32% had coexisting pathology of Lewy body disease, which was greater than the other subtypes (p = 0.005). Nearly half (47%) of the Braak IV samples had coexisting limbic predominant age-related TAR DNA-binding protein 43 encephalopathy neuropathologic change. Cases with a high brain weight (n = 201) were less likely to have amygdala-predominant Lewy bodies (14%, p = 0.006) and most likely to have Lewy body disease (31%, p = 0.042) compared with those with middle (n = 455) and low (n = 203) brain weight.

Discussion: The frequency of Lewy body disease was increased in both neuropathologic proxies of the minimal atrophy subtype. We hypothesize that Lewy body disease may underlie cognitive decline observed in minimal atrophy cases.

Pathophysiology and probable etiology of cerebral small vessel disease in vascular dementia and Alzheimer's disease

Inoue Y, Shue F, Bu G, Kanekiyo T.

 

Vascular cognitive impairment and dementia (VCID) is commonly caused by vascular injuries in cerebral large and small vessels and is a key driver of age-related cognitive decline. Severe VCID includes post-stroke dementia, subcortical ischemic vascular dementia, multi-infarct dementia, and mixed dementia. While VCID is acknowledged as the second most common form of dementia after Alzheimer’s disease (AD) accounting for 20% of dementia cases, VCID and AD frequently coexist. In VCID, cerebral small vessel disease (cSVD) often affects arterioles, capillaries, and venules, where arteriolosclerosis and cerebral amyloid angiopathy (CAA) are major pathologies. White matter hyperintensities, recent small subcortical infarcts, lacunes of presumed vascular origin, enlarged perivascular space, microbleeds, and brain atrophy are neuroimaging hallmarks of cSVD. The current primary approach to cSVD treatment is to control vascular risk factors such as hypertension, dyslipidemia, diabetes, and smoking. However, causal therapeutic strategies have not been established partly due to the heterogeneous pathogenesis of cSVD. In this review, we summarize the pathophysiology of cSVD and discuss the probable etiological pathways by focusing on hypoperfusion/hypoxia, blood-brain barriers (BBB) dysregulation, brain fluid drainage disturbances, and vascular inflammation to define potential diagnostic and therapeutic targets for cSVD.

Dissecting Detergent-Insoluble Proteome in Alzheimer's Disease by TMTc-Corrected Quantitative Mass Spectrometry

Zaman M, Fu Y, Chen PC, Sun H, Yang S, Wu Z, Wang Z, Poudel S, Serrano GE, Beach TG, Li L, Wang X, Peng J.

 

Protein aggregation of amyloid-? peptides and tau are pathological hallmarks of Alzheimer’s disease (AD), which are often resistant to detergent extraction and thus enriched in the insoluble proteome. However, additional proteins that coaccumulate in the detergent-insoluble AD brain proteome remain understudied. Here, we comprehensively characterized key proteins and pathways in the detergent-insoluble proteome from human AD brain samples using differential extraction, tandem mass tag (TMT) labeling, and two-dimensional LC-tandem mass spectrometry. To improve quantification accuracy of the TMT method, we developed a complement TMT-based strategy to correct for ratio compression. Through the meta-analysis of two independent detergent-insoluble AD proteome datasets (8914 and 8917 proteins), we identified 190 differentially expressed proteins in AD compared with control brains, highlighting the pathways of amyloid cascade, RNA splicing, endocytosis/exocytosis, protein degradation, and synaptic activity. To differentiate the truly detergent-insoluble proteins from copurified background during protein extraction, we analyzed the fold of enrichment for each protein by comparing the detergent-insoluble proteome with the whole proteome from the same AD samples. Among the 190 differentially expressed proteins, 84 (51%) proteins of the upregulated proteins (n = 165) were enriched in the insoluble proteome, whereas all downregulated proteins (n = 25) were not enriched, indicating that they were copurified components. The vast majority of these enriched 84 proteins harbor low-complexity regions in their sequences, including amyloid-?, Tau, TARDBP/TAR DNA-binding protein 43, SNRNP70/U1-70K, MDK, PTN, NTN1, NTN3, and SMOC1. Moreover, many of the enriched proteins in AD were validated in the detergent-insoluble proteome by five steps of differential extraction, proteomic analysis, or immunoblotting. Our study reveals a resource list of proteins and pathways that are exclusively present in the detergent-insoluble proteome, providing novel molecular insights to the formation of protein pathology in AD.

The SERPINA5 coding variant E228Q does not contribute to clinicopathologic characteristics in Alzheimer's disease: A cross-sectional study

Matchett BJ, Lincoln SJ, Baker M, Tamvaka N, Labuzan SA, Hicks Sirmans TN, Moloney CM, Helminger J, Hinkle KM, Cabrera-Rodriguez J, Wickland DP, Johnson PW, Heckman MG, Reddy JS, Younkin SG, Carrasquillo MM, Duara R, Graff-Radford NR, Pottier C, Ertekin-Taner N, Ross OA, Rademakers R, Dickson DW, Murray ME.

 

We previously demonstrated that increased expression of the SERPINA5 gene is associated with hippocampal vulnerability in Alzheimer’s disease (AD) brains. SERPINA5 was further demonstrated to be a novel tau-binding partner that colocalizes within neurofibrillary tangles. Our goal was to determine whether genetic variants in the SERPINA5 gene contributed to clinicopathologic phenotypes in AD. To screen for SERPINA5 variants, we sequenced 103 autopsy-confirmed young-onset AD cases with a positive family history of cognitive decline. To further assess the frequency of a rare missense variant, SERPINA5 p.E228Q, we screened an additional 1114 neuropathologically diagnosed AD cases. To provide neuropathologic context in AD, we immunohistochemically evaluated SERPINA5 and tau in a SERPINA5 p.E228Q variant carrier and a matched noncarrier. In the initial SERPINA5 screen, we observed 1 individual with a rare missense variant (rs140138746) that resulted in an amino acid change (p.E228Q). In our AD validation cohort, we identified an additional 5 carriers of this variant, resulting in an allelic frequency of 0.0021. There was no significant difference between SERPINA5 p.E228Q carriers and noncarriers in terms of demographic or clinicopathologic characteristics. Although not significant, on average SERPINA5 p.E228Q carriers were 5 years younger at age of disease onset than noncarriers (median: 66 [60-73] vs 71 [63-77] years, P = .351). In addition, SERPINA5 p.E228Q carriers exhibited a longer disease duration than noncarriers that approached significance (median: 12 [10-15]) vs 9 [6-12] years, P = .079). More severe neuronal loss was observed in the locus coeruleus, hippocampus, and amygdala of the SERPINA5 p.E228Q carrier compared to noncarrier, although no significant difference in SERPINA5-immunopositive lesions was observed. Throughout the AD brain in either carrier or noncarrier, areas with early pretangle pathology or burnt-out ghost tangle accumulation did not reveal SERPINA5-immunopositive neurons. Mature tangles and newly formed ghost tangles appeared to correspond well with SERPINA5-immunopositive tangle-bearing neurons. SERPINA5 gene expression was previously associated with disease phenotype; however, our findings suggest that SERPINA5 genetic variants may not be a contributing factor to clinicopathologic differences in AD. SERPINA5-immunopositive neurons appear to undergo a pathologic process that corresponded with specific levels of tangle maturity.

LRP1 in vascular mural cells modulates cerebrovascular integrity and function in the presence of APOE4

Oue H, Yamazaki Y, Qiao W, Yuanxin C, Ren Y, Kurti A, Shue F, Parsons TM, Perkerson RB, Kawatani K, Wang N, Starling SC, Roy B, Mosneag IE, Aikawa T, Holm ML, Liu CC, Inoue Y, Sullivan PM, Asmann YW, Kim BY, Bu G, Kanekiyo T.

 

Cerebrovasculature is critical in maintaining brain homeostasis; its dysregulation often leads to vascular cognitive impairment and dementia (VCID) during aging. VCID is the second most prevalent cause of dementia in the elderly, after Alzheimer’s disease (AD), with frequent cooccurrence of VCID and AD. While multiple factors are involved in the pathogenesis of AD and VCID, APOE4 increases the risk for both diseases. A major apolipoprotein E (apoE) receptor, the low-density lipoprotein receptor-related protein 1 (LRP1), is abundantly expressed in vascular mural cells (pericytes and smooth muscle cells). Here, we investigated how deficiency of vascular mural cell LRP1 affects the cerebrovascular system and cognitive performance using vascular mural cell-specific Lrp1-KO mice (smLrp1-/-) in a human APOE3 or APOE4 background. We found that spatial memory was impaired in the 13- to 16-month-old APOE4 smLrp1-/- mice but not in the APOE3 smLrp1-/- mice, compared with their respective littermate control mice. These disruptions in the APOE4 smLrp1-/- mice were accompanied with excess paravascular glial activation and reduced cerebrovascular collagen IV. In addition, blood-brain barrier (BBB) integrity was disrupted in the APOE4 smLrp1-/- mice. Together, our results suggest that vascular mural cell LRP1 modulates cerebrovasculature integrity and function in an APOE genotype-dependent manner.

APOE and immunity: Research highlights

Kloske CM, Barnum CJ, Batista AF, Bradshaw EM, Brickman AM, Bu G, Dennison J, Gearon MD, Goate AM, Haass C, Heneka MT, Hu WT, Huggins LKL, Jones NS, Koldamova R, Lemere CA, Liddelow SA, Marcora E, Marsh SE, Nielsen HM, Petersen KK, Petersen M, Piña-Escudero SD, Qiu WQ, Quiroz YT, Reiman E, Sexton C, Tansey MG, Tcw J, Teunissen CE, Tijms BM, van der Kant R, Wallings R, Weninger SC, Wharton W, Wilcock DM, Wishard TJ, Worley SL, Zetterberg H, Carrillo MC.

 

Introduction: At the Alzheimer’s Association’s APOE and Immunity virtual conference, held in October 2021, leading neuroscience experts shared recent research advances on and inspiring insights into the various roles that both the apolipoprotein E gene (APOE) and facets of immunity play in neurodegenerative diseases, including Alzheimer’s disease and other dementias.

Methods: The meeting brought together more than 1200 registered attendees from 62 different countries, representing the realms of academia and industry.

Results: During the 4-day meeting, presenters illuminated aspects of the cross-talk between APOE and immunity, with a focus on the roles of microglia, triggering receptor expressed on myeloid cells 2 (TREM2), and components of inflammation (e.g., tumor necrosis factor ? [TNF?]).

Discussion: This manuscript emphasizes the importance of diversity in current and future research and presents an integrated view of innate immune functions in Alzheimer’s disease as well as related promising directions in drug development.

Regulation of astrocyte lipid metabolism and ApoE secretionby the microglial oxysterol, 25-hydroxycholesterol

Cashikar AG, Toral-Rios D, Timm D, Romero J, Strickland M, Long JM, Han X, Holtzman DM, Paul SM.

 

Neuroinflammation, a major hallmark of Alzheimer’s disease and several other neurological and psychiatric disorders, is often associated with dysregulated cholesterol metabolism. Relative to homeostatic microglia, activated microglia express higher levels of Ch25h, an enzyme that hydroxylates cholesterol to produce 25-hydroxycholesterol (25HC). 25HC is an oxysterol with interesting immune roles stemming from its ability to regulate cholesterol metabolism. Since astrocytes synthesize cholesterol in the brain and transport it to other cells via ApoE-containing lipoproteins, we hypothesized that secreted 25HC from microglia may influence lipid metabolism as well as extracellular ApoE derived from astrocytes. Here, we show that astrocytes take up externally added 25HC and respond with altered lipid metabolism. Extracellular levels of ApoE lipoprotein particles increased after treatment of astrocytes with 25HC without an increase in Apoe mRNA expression. In mouse astrocytes-expressing human ApoE3 or ApoE4, 25HC promoted extracellular ApoE3 better than ApoE4. Increased extracellular ApoE was due to elevated efflux from increased Abca1 expression via LXRs as well as decreased lipoprotein reuptake from suppressed Ldlr expression via inhibition of SREBP. 25HC also suppressed expression of Srebf2, but not Srebf1, leading to reduced cholesterol synthesis in astrocytes without affecting fatty acid levels. We further show that 25HC promoted the activity of sterol-o-acyl transferase that led to a doubling of the amount of cholesteryl esters and their concomitant storage in lipid droplets. Our results demonstrate an important role for 25HC in regulating astrocyte lipid metabolism.

An assay to evaluate the capacity of cholesterol acceptors using BODIPY-cholesterol in cells

Raulin AC, Liu CC, Bu G.

 

Cholesterol is a structural component of cell membranes. Most cells are incapable of its catabolism, and intracellular cholesterol accumulation is linked to several disorders including cardiovascular and neurodegenerative diseases. Cholesterol efflux, essential to its metabolism, is dependent on acceptors such as apolipoproteins. Here, we describe an assay to evaluate the capacity of cholesterol acceptors. Cells are treated with an analog of cholesterol tagged with fluorescent BODIPY. Addition of an acceptor leads to BODIPY-cholesterol efflux, measured using a plate reader. For complete details on the use and execution of this protocol, please refer to Liu et al. (2021).1.