Abstract 055: Lipid Droplet Accumulating Microglia Involvement In Non-Alcoholic Fatty Liver Disease During Obesity

Abstract

Non-alcoholic fatty liver disease (NAFLD), characterized by excess fat accumulation in the liver (i.e. steatosis), is directly associated with obesity and a risk factor for hypertension development. In addition to peripheral mechanisms, accumulating evidence points to alterations in the central nervous system as a NAFLD contributor. In this context, we recently demonstrated that selective inhibition of microglia, the resident immune cells of the brain, specifically in the subfornical organ (SFO), attenuated obesity-related hepatic steatosis by ~50%. However, underlying SFO microglia alterations that may contribute to NAFLD remain unknown. The SFO is a circumventricular nucleus situated outside of the blood-brain-barrier that is chronically exposed to circulating factors such as lipids. Interestingly, lipid droplet-accumulating microglia (LDAM) have been implicated in conditions such as Alzheimer's disease and aging. Based on this, we hypothesized that SFO LDAM may be a unique contributor to hepatic steatosis during obesity. To investigate this, 6 wk old C57Bl/6J male mice were fed a high fat diet (HFD, 60% kCal fat) or normal chow for 11 wks (Body weight: 33±1 vs 47±2 g, normal chow vs HFD, p<0.05, n=4-5/group). Immunohistochemistry for ionized calcium-binding adapter molecule 1 (Iba1) as a microglia indicator demonstrated an increase in SFO microglia of HFD fed mice (330±6 vs 393±18, normal chow vs HFD, p<0.05). Furthermore, combined immunohistochemistry for Iba1 and Perilipin-2 (Plin2) as a lipid droplet marker revealed an approximate doubling of SFO microglia with lipid droplet inclusion (Plin2+ microglia #: 80±11 vs 191±21; Plin2+ microglia %total: 23±3.2 vs 49±4.1, normal chow vs HFD, p<0.05). This increase in SFO LDAM was additionally confirmed with comprehensive 3-dimensional analysis of up to 400 microglia per animal using BODIPY, a dye that labels neutral lipids (e.g. HFD: 1.6±0.2 BODIPY+ microglia fold normal chow, p<0.05). Collectively, these findings indicate marked SFO microglia activation and microglia lipid accumulation during obesity and point to the possibility for SFO LDAM in the pathogenesis of NAFLD and associated hypertension development.