DGAT1-dependent lipid droplet synthesis in microglia attenuates neuroinflammatory responses to lipopolysaccharides.

Abstract

Lipid droplets (LD) are dynamic storage organelles for triglycerides (TG). LD act as a hub that modulates the availability of fatty acids to sustain metabolic needs and the generation of fatty-acid derived signals. Recent evidence demonstrates that LD metabolism regulates immune responses including in microglia, the resident immune cells of the central nervous system. We have previously shown that blocking LD lipolysis in microglia reduces acute pro-inflammatory responses to lipopolysaccharide (LPS) including cytokine and prostanoid synthesis. Here, we investigated the role of diacylglycerol O-acyltransferase 1 (DGAT1), a key enzyme catalyzing the final step of TG synthesis, in microglial LD biogenesis and inflammatory responses induced by LPS. We found that treatment with LPS downregulates specific enzymes in the TG synthesis pathway in primary microglia, including GPAT1, AGPAT3, AGPAT5, and DGAT1, while upregulating TMEM68, a non-canonical TG synthesizing enzyme. Pharmacological inhibition of DGAT1 significantly reduced LD formation in both oleate- and LPS-stimulated conditions, indicating that DGAT1 is essential for inflammation-induced LD synthesis. Moreover, DGAT1 inhibition selectively decreased expression of pro-inflammatory cytokines TNF- and IL-1{beta}, without affecting IL-6, CCL2, or the anti-inflammatory cytokine TGF-{beta}. These findings show, that DGAT1-dependent LD formation acts as an important modulator of microglial inflammatory signaling.