Elucidating roles of microglial lipid droplets in neurodegeneration

项目总结/文摘

PROJECT SUMMARY/ABSTRACT Alzheimer disease (AD) affects approximately 6 million people in the United States and currently has no clearly-effective disease modifying therapies. AD is pathologically defined by the accumulation of amyloid β (Aβ) plaques and tau neurofibrillary tangles in the brain and it is known that alterations in the activities of microglia and other non-neuronal cell types play important roles in shaping the disease course. Much of the polygenic risk for AD is derived from variants in genes expressed by microglia, specifically those involved in endolysosomal and lipid processing pathways, and microglia containing abundant lipid droplets (LD-MG) have been observed in post-mortem human AD brains. As previous interventions targeting Aβ have not yet been successful in clinical trials, the concept of modulating microglial lipid metabolism is a novel and exciting avenue being explored in preclinical studies, however we need to know more about how lipid metabolism governs microglial functional states. In mouse models of amyloidosis, microglia transition from a homeostatic to a disease-associated (DAM) transcriptional state that represents a protective, phagocytic, and plaque- compacting phenotype. While microglial activity may be beneficial in the early amyloid phase of AD, pharmacological or genetic inhibition of microglia has been shown to be protective in mouse models of tauopathy. LD-MG are observed in actively degenerating brain regions in a tauopathy mouse model, but the functions of these cells in the disease process are not currently known. To begin addressing this question, we will use FACS coupled with scRNAseq to characterize any transcriptional differences between LDhigh vs LDlow microglia isolated from 9.5 month old tauopathy mice. Given recent evidence suggesting that the LD-MG observed in aged mice have pro-inflammatory, hypo-phagocytic phenotypes, we hypothesize that the LD-MG in our tauopathy model will have similar pathway alterations and could thus be partially responsible for microglial contributions to neurodegeneration. To assess the relevance of these findings to humans, we will stain postmortem human AD brain samples for any promising mouse LD-MG markers. To elucidate the functional roles of LD-MG in the progression of tauopathy, we will utilize a new mouse model that allows for the inducible, microglial-specific knockout of the diacylglycerol acyltransferase (DGAT) enzymes, which have been demonstrated to be required for LD biogenesis in multiple biological contexts. A substantial amount of literature supports a role for lipid droplets in sequestering potentially toxic lipids and we hypothesize that crippling the ability of MG to form LDs via DGAT KO will accelerate tauopathy progression, which we will assess using a combination of immunohistochemical, scRNAseq, and lipidomic analyses. Our studies will characterize an understudied subset of microglia, increase our knowledge of the diversity of myeloid functional states, and evaluate the potential of modulating microglial lipid metabolism for the treatment of Alzheimer disease.