Biology subjects

Holtzman, D. M.

Publications and source records attributed to Holtzman, D. M..

25 records · Page 2Linked to original sources

bioRxiv2020

Functional insights from biophysical study of TREM2 interactions with ApoE and Aβ1-42

INTRODUCTIONTREM2 is an innate immune receptor expressed on myeloid cells including microglia in the brain. How TREM2 engages different ligands remains poorly understood. METHODSWe used comprehensive BLI analysis to investigate the TREM2 interactions with ApoE and monomeric amyloid beta (mA{beta}42). RESULTSTREM2 binding did not depend on ApoE lipidation, and there were only slight differences in affinity observed between ApoE isoforms (E4 > E3 > E2). Surprisingly, disease-linked TREM2 variants within a "basic patch" minimally impact ApoE binding. Instead, TREM2 has a unique hydrophobic surface that can bind to ApoE. This direct engagement requires the hinge region of ApoE. TREM2 directly binds mA{beta}42 and can potently inhibit A{beta}42 polymerization, suggesting a potential mechanism for soluble TREM2 (sTREM2) in preventing AD pathogenesis. DISCUSSIONThese findings demonstrate that TREM2 has at least two separate surfaces to engage ligands and uncovers a potential function for sTREM2 in directly inhibiting A{beta} polymerization.

biophysics↗

bioRxiv2020

25-Hydroxycholesterol amplifies microglial IL-1β production in an apoE isoform-dependent manner

Genome-wide association studies associated with Alzheimers disease (AD) have implicated pathways related to both lipid homeostasis and innate immunity in the pathophysiology of AD. However, the exact cellular and chemical mediators of neuroinflammation in AD remain poorly understood. The oxysterol 25-hydroxycholesterol (25-HC) is an important immunomodulator produced by peripheral macrophages with wide-ranging effects on cell signaling and innate immunity. Genetic variants of the enzyme responsible for 25-HC production, cholesterol 25-hydroxylase (CH25H), have been found to be associated with AD. In the present study, we found that the CH25H expression is upregulated in human AD brain tissue and in transgenic mouse brain tissue bearing amyloid-{beta} (A{beta}) plaques or tau pathology. Treatment with the toll-like receptor 4 (TLR4) agonist lipopolysaccharide (LPS) markedly upregulates CH25H expression in the mouse brain in vivo. LPS also stimulates CH25H expression and 25-HC secretion in cultured mouse primary microglia. We also found that LPS-induced microglial production of the pro-inflammatory cytokine IL1{beta} is markedly potentiated by 25-HC and attenuated by genetic deletion of CH25H. Microglia expressing apolipoprotein E4 (apoE4), a genetic risk factor for AD, produce greater amounts of 25-HC than apoE3-expressing microglia following treatment with LPS. Remarkably, treatment of microglia with 25-HC results in a much greater level of IL1{beta} secretion in LPS-activated apoE4-expressing microglia than in apoE2- or apoE3-expressing microglia. Blocking potassium efflux or inhibiting caspase-1 prevents 25-HC-potentiated IL1{beta} release in apoE4-expressing microglia, indicating the involvement of caspase-1/NLRP3 inflammasome activity. 25-HC may function as a microglial secreted inflammatory mediator in brain, promoting IL1{beta}-mediated neuroinflammation in an apoE isoform-dependent manner (E4>>E2/E3) and thus may be an important mediator of neuroinflammation in AD.

neuroscience↗

bioRxiv2019

Cholesterol and matrisome pathways dysregulated in human APOE ε4 glia

Apolipoprotein E (APOE) {varepsilon}4 is the strongest genetic risk factor for Alzheimers disease (AD). Although its association with AD is well-established, the impact of APOE {varepsilon}4 on human brain cell function remains unclear. Here we investigated the effects of APOE {varepsilon}4 on several brain cell types derived from human induced pluripotent stem cells and human APOE targeted replacement mice. Gene set enrichment and pathway analyses of whole transcriptome profiles showed that APOE {varepsilon}4 is associated with dysregulation of cholesterol homeostasis in human but not mouse astrocytes and microglia. Elevated matrisome signaling associated with chemotaxis, glial activation and lipid biosynthesis in APOE {varepsilon}4 mixed neuron/astrocyte cultures parallels altered pathways uncovered in cell-type deconvoluted transcriptomic data from APOE {varepsilon}4 glia and AD post-mortem brains. Experimental validation of the transcriptomic findings showed that isogenic APOE {varepsilon}4 is associated with increased lysosomal cholesterol levels and decreased cholesterol efflux, demonstrating decoupled lipid metabolism. APOE {varepsilon}4 glia also secrete higher levels of proinflammatory chemokines, cytokines and growth factors, indicative of glial activation. Thus, APOE {varepsilon}4 induces human glia-specific dysregulation that may initiate AD risk.

neuroscience↗

bioRxiv2019

Single- nuclei RNA sequencing from human brain to study for Mendelian and sporadic AD

Alzheimer Disease (AD) is the most common form of dementia. This neurodegenerative disorder is associated with neuronal death and gliosis heavily impacting the cerebral cortex. AD has a substantial but heterogeneous genetic component, presenting both Mendelian and complex genetic architectures. Using bulk RNA-seq from parietal lobes and deconvolution methods, we previously reported that brains exhibiting different AD genetic architecture exhibit different cellular proportions. Here, we sought to directly investigate AD brain changes in cell proportion and gene expression using single cell resolution. To do so, we generated unsorted single-nuclei RNA-sequencing data from brain tissue. We leveraged tissue donated from a carrier of a Mendelian genetic mutation and two family members who suffer from AD, but do not have the same mutation. We evaluated alternative alignment approaches to maximize the titer of reads, genes and cells with high quality. In addition, we employed distinct clustering strategies to determine the best approach to identify cell clusters that reveal neuronal and glial cell types and avoid artifacts such as sample and batch effects. We propose an approach to cluster cells that reduces biases and enable further analyses. We identified distinct types of neurons, both excitatory and inhibitory, and glial cells, including astrocytes, oligodendrocytes, and microglia among others. In particular, we identified a reduced proportion of excitatory neurons in the Mendelian mutation carrier, but a similar distribution of inhibitory neurons. Furthermore, we investigated whether single-nuclei RNA-seq from human brains recapitulate the expression profile of Disease Associated Microglia (DAM) discovered in mouse models. We also determined that when analyzing human single-nuclei data it is critical to control for biases introduced by donor specific expression profiles. In conclusion, we propose a collection of best practices to generate a highly-detailed molecular cell atlas of highly informative frozen tissue stored in brain banks. Importantly, we have developed a new web application to make this unique single-nuclei molecular atlas publicly available.

genomics↗

bioRxiv2018

Dietary salt promotes cognitive impairment through tau phosphorylation

Dietary habits and vascular risk factors promote both Alzheimers disease and cognitive impairment caused by vascular factors1-3. Furthermore, accumulation of hyperphosphorylated tau, a microtubule associated protein and a hallmark of Alzheimers pathology, is also linked to vascular cognitive impairment4-7. In mice, a salt-rich diet leads to cognitive dysfunction associated with a nitric oxide deficit in cerebral endothelial cells and cerebral hypoperfusion8. Here we report that dietary salt induces tau hyperphosphorylation followed by cognitive dysfunction, effects prevented by restoring endothelial nitric oxide production. The nitric oxide deficiency reduces neuronal calpain nitrosylation resulting in enzyme activation, which, in turn, leads to tau phosphorylation by activating cyclin dependent kinase-5. Salt-induced cognitive impairment is not observed in tau-null mice or in mice treated with anti-tau antibodies, despite persistent cerebral hypoperfusion and neurovascular dysfunction. These findings unveil a causal link between dietary salt, endothelial dysfunction and tau pathology, independent of hemodynamic insufficiency. Avoiding excessive salt intake and maintaining vascular health may help stave off vascular and neurodegenerative pathologies underlying late-life dementia.

neuroscience↗

bioRxiv2018

High affinity interactions and signal transduction between Aβ oligomers and TREM2

Rare coding variant in the Triggering receptor expressed on myeloid cells 2 (TREM2) are associated with increased risk for Alzheimers disease (AD), but how they confer this risk remains uncertain. We assessed binding of TREM2, AD associated TREM2 variants to various forms of A{beta} and APOE in multiple assays. TREM2 interacts directly with various forms of A{beta}, with highest affinity interactions observed between TREM2 and soluble A{beta}42 oligomers. We confirm the previous interaction between APOE3 and APOE4 and TREM2. High affinity binding of TREM2 to A{beta} oligomers is characterized by very slow dissociation. Pre-incubation with A{beta} is shown to block the interaction of APOE. In cellular assays, AD-associated variants of TREM2 reduced the amount of A{beta}42 internalized, and in NFAT assay the R47H variant decreased NFAT signaling activity in response to A{beta}42. These studies demonstrate i) a high affinity interaction between TREM2 and A{beta} oligomers that can block interaction with another ligand and ii) that AD-associated TREM2 variants bind A{beta} with equivalent affinity but show loss of function in terms of signaling and A{beta} internalization.

cell biology↗

bioRxiv2017

Polygenic Risk Score of Sporadic Late Onset Alzheimer Disease Reveals a Shared Architecture with the Familial and Early Onset Forms

ObjectiveTo determine whether the genetic architecture of sporadic late-onset Alzheimers Disease (sLOAD) has an effect on familial late-onset AD (fLOAD), sporadic early-onset (sEOAD) and autosomal dominant early-onset (eADAD).\n\nMethodsPolygenic risk scores (PRS) were constructed using previously identified 21 genome-wide significant loci for LOAD risk.\n\nResultsWe found that there is an overlap in the genetic architecture among sEOAD, fLOAD, and sLOAD. sEOAD showed the highest odds for the PRS (OR=2.27; p=1.29x10-7), followed by fLOAD (OR=1.75; p=1.12x10-7) and sLOAD (OR=1.40; p=1.21x10-3). PRS is associated with cerebrospinal fluid ptau181-A{beta}42 on eADAD.\n\nConclusionOur analysis confirms that the genetic factors identified for sLOAD also modulate risk in fLOAD and sEOAD cohorts. Furthermore, our results suggest that the burden of these risk variants is associated with familial clustering and earlier-onset of AD. Although these variants are not associated with risk in the eADAD, they may be modulating age at onset.

genetics↗