PROJECT SUMMARY Genetic studies in Alzheimer’s disease (AD) have clearly indicated a role for microglia, the innate immune cells of the CNS, in susceptibility to disease. Moreover, microglia are also implicated in lipid metabolism as a key component of disease mechanism. Microglia are the resident immune cells of the CNS, and are therefore the primary responders to pathogens. More and more correlation studies implicate pathogens in AD pathogenesis or progression. However, the association between genetic alterations specific to microglia, toll-like receptor (TLR) signaling and lipid homeostasis in AD has not been explored in depth. We hypothesize that there is an interaction between the natural function of the genetically associated microglial proteins, lipids and TLR stimulation, the basic biology of which has not been fully elucidated in microglia, the innate immune cells that exist in a lipid rich environment. Among the many factors involved in the regulation of pathogen response pathways, the lipid composition of microglia has been shown to contribute significantly to the regulation of inflammatory signaling. Specifically, cholesterol and sphingomyelin levels have been observed to modulate the expression and distribution of microglia receptors and their downstream targets. We propose that microglia AD risk variants result in disturbances in the regulation of sphingolipid and cholesterol, that in turn, cause the dysregulation of TLR responses and inflammatory phenotypes. We will investigate this hypothesis by examining the effects of microglia AD susceptibility alleles on sphingolipid regulation and lipid raft turnover in a cell culture microglial model. We will also assess the role of sphingolipids in the regulation of microglial signaling via TLR and genetically associated proteins in our microglia model. Results from this proposal will help understand the crosstalk between genetics, TLR-regulation and sphingolipid metabolism and underlying mechanisms by which a microglia induces inflammation through modulation of its membrane in the context of AD.