👤 David M Holtzman

Cerebrospinal fluid amyloid beta 42, total tau, and phosphorylated tau 181 are well accepted markers of Alzheimer's disease. These biomarkers better reflect disease pathogenesis compared to clinical diagnosis. Here, we perform a genome wide association study meta-analysis including 18,948 individuals of European ancestry and identify 12 genome-wide significant loci across all three biomarkers, eight of them novel. We replicate the association of biomarkers with APOE, CR1, GMNC/CCDC50 and C16orf95/MAP1LC3B. Novel loci include BIN1 for amyloid beta and GNA12, MS4A6A, SLCO1A2 with both total tau and phosphorylated tau 181, as well as additional loci on chr. 8, near ANGPT1 and chr. 9 near SMARCA2. We also demonstrate that these variants have significant association with Alzheimer's disease risk, disease progression and/or brain amyloidosis. The associated genes are implicated in lipid metabolism independent of APOE, coupled with autophagy and brain volume regulation driven by total tau and phosphorylated tau 181 dysregulation. Show less

Anti-amyloid antibody treatment for Alzheimer's disease is linked to Amyloid-Related Imaging Abnormalities (ARIA), including vasogenic edema (ARIA-E) and microhemorrhages (ARIA-H), especially in ApoE ε4/4 carriers. To investigate mechanisms underlying ARIA, we examined the binding and temporal vascular effects of immunization with 3D6, the precursor to the anti-amyloid antibody bapineuzumab, in two aged Alzheimer's disease amyloid mouse models. Acutely, 3D6 bound to cerebral amyloid angiopathy (CAA), resulting in C1q binding and classical complement activation. Weekly short-term immunization over 7 weeks resulted in elevated CAA- and plaque-associated complement deposition, red blood cell extravasation and microhemorrhages, and was accompanied by significant transcriptomic changes in genes related to complement, inflammation, vascular dysfunction, and endothelial lipid responses. Longer-term dosing over 13-15 weeks further increased complement deposition and was associated with blood-brain barrier disruption, MMP-9 upregulation, and microhemorrhages, accompanied by reduced amyloid burden and modest CAA clearance. C3 levels correlated with microhemorrhage severity. Perivascular macrophages co-localized with complement-decorated CAA in 3D6-treated mice. These findings implicate complement activation as an early key driver of ARIA and suggest that therapeutic targeting of complement may reduce ARIA risk. Show less

Apolipoprotein E (ApoE) is the primary, most abundant apolipoprotein of the CNS and plays an important role in brain metabolism and lipid homeostasis. In the CNS, ApoE is primarily secreted by astrocytes under homeostatic conditions and by microglia in certain disease-related conditions. APOE has three major alleles: APOE2, APOE3, and APOE4. APOE4 is the strongest genetic risk factor for late-onset Alzheimer's disease (AD), and APOE2 results in decreased risk relative to APOE3. ApoE derived from astrocytes and microglia have been hypothesized to play different roles in the disease pathogenesis of AD. In this study, we profiled the lipidome and proteome of ApoE lipoproteins secreted by astrocytes or microglia and found that they differed according to the cellular source of ApoE and the ApoE isoform. Lipidomics revealed that microglia-derived ApoE lipoproteins were enriched in cholesteryl esters, whereas astrocyte ApoE lipoproteins were enriched in SM. Proteomics revealed that astrocyte ApoE lipoproteins were enriched in proteins involved in glucose metabolism and acute phase response. Microglia-secreted lipoproteins were enriched in proteins involved in complement activation, synapse pruning, proteolysis, and the innate immune response. Further comparison of ApoE lipoproteins from APOE4 microglia revealed that ApoE4 lipoproteins were enriched in complement component 1q and Lpl compared with ApoE2 and ApoE3 microglial lipoproteins, which were enriched in Ankk1 (ankyrin repeat and kinase domain containing 1) and apolipoprotein C1. These results provide the molecular foundation for better understanding of how ApoE functions as an apolipoprotein with the lipoprotein cargo being dependent on the cellular source and ApoE isoform, ultimately contributing to CNS homeostasis and disease pathogenesis. Show less

Apolipoprotein E (APOE) ε4 is the strongest genetic risk factor for Alzheimer's disease (AD). However, it is known that other pathways independent of APOE also play a role in AD. Disentangling APOE-dependent and independent effects is instrumental for understanding the biology of AD. We conducted an APOE-stratified multi-omic analysis in multiple large datasets to identify AD-associated plasma proteins and metabolites. More than 64% of the identified proteins were not found in non-APOE stratified studies, and 17% of the proteins showed APOE-specific trends. Mitochondrial dysfunction was associated in AD independently of APOE and was accompanied by disruptions in glucose and lipid metabolism and cell death and increased in inflammatory signaling activation. Lipid upregulation was found in AD cases when compared with controls with the same APOE genotype, indicating that additional factors beyond APOE affect lipid regulation and AD risk. These findings may be informative in guiding the development of effective medications for AD. Show less

The brain is the most cholesterol-rich organ in the body, and ApoE is the main lipid carrier protein in the brain. Although very little, if any, ApoE exists in its apoprotein form in physiological fluids, recombinant ApoE is typically prepared in a lipid-free state to study its physiological functions. We describe a lipid nanoparticle (LNP) form of ApoE as a primary extracellular product of the eukaryotic protein export system. Whereas the apoprotein is the dominant secreted product when the Show less

Accumulation of amyloid-β (Aβ) peptide in the brain is the first critical step in the pathogenesis of Alzheimer's disease (AD). Studies in humans suggest that Aβ clearance from the brain is frequently impaired in late-onset AD. Aβ accumulation leads to the formation of Aβ aggregates, which injure synapses and contribute to eventual neurodegeneration. Cell surface heparan sulfates (HSs), expressed on all cell types including neurons, have been implicated in several features in the pathogenesis of AD including its colocalization with amyloid plaques and modulatory role in Aβ aggregation. We show that removal of neuronal HS by conditional deletion of the Ext1 gene, which encodes an essential glycosyltransferase for HS biosynthesis, in postnatal neurons of amyloid model APP/PS1 mice led to a reduction in both Aβ oligomerization and the deposition of amyloid plaques. In vivo microdialysis experiments also detected an accelerated rate of Aβ clearance in the brain interstitial fluid, suggesting that neuronal HS either inhibited or represented an inefficient pathway for Aβ clearance. We found that the amounts of various HS proteoglycans (HSPGs) were increased in postmortem human brain tissues from AD patients, suggesting that this pathway may contribute directly to amyloid pathogenesis. Our findings have implications for AD pathogenesis and provide insight into therapeutic interventions targeting Aβ-HSPG interactions. Show less

Liver X receptors (LXRs) regulate immune cell function and cholesterol metabolism, both factors that are critically involved in Alzheimer's disease (AD). To investigate the therapeutic potential of long-term LXR activation in amyloid-β (Aβ) peptide deposition in an AD model, 13-month-old, amyloid plaque-bearing APP23 mice were treated with the LXR agonist TO901317. Postmortem analysis demonstrated that TO901317 efficiently crossed the blood-brain barrier. Insoluble and soluble Aβ levels in the treated APP23 mice were reduced by 80% and 40%, respectively, compared with untreated animals. Amyloid precursor protein (APP) processing, however, was hardly changed by the compound, suggesting that the observed effects were instead mediated by Aβ disposal. Despite the profound effect on Aβ levels, spatial learning in the Morris water maze was only slightly improved by the treatment. ABCA1 (ATP-binding cassette transporter 1) and apolipoprotein E (ApoE) protein levels were increased and found to be primarily localized in astrocytes. Experiments using primary microglia demonstrated that medium derived from primary astrocytes exposed to TO901317 stimulated phagocytosis of fibrillar Aβ. Conditioned medium from TO901317-treated ApoE(-/-) or LXRα(-/-) astrocytes did not increase phagocytosis of Aβ. In APP23 mice, long-term treatment with TO901317 strongly increased the association of microglia and Aβ plaques. Short-term treatment of APP/PS1 mice with TO901317 also increased this association, which was dependent on the presence of LXRα and was accompanied by increased ApoE lipidation. Together, these data suggest that astrocytic LXRα activation and subsequent release of ApoE by astrocytes is critical for the ability of microglia to remove fibrillar Aβ in response to treatment with TO901317. Show less