The incidence of metabolic dysfunction-associated steatotic liver disease (MASLD) has been increasing worldwide. Since gut-derived bacterial lipopolysaccharides (LPS) can travel via the portal vein to the liver and play an important role in producing hepatic pathology, it seemed possible that (1) LPS stimulates hepatic cells to accumulate lipid, and (2) inactivating LPS can be preventive. Acyloxyacyl hydrolase (AOAH), the eukaryotic lipase that inactivates LPS and oxidized phospholipids, is produced in the intestine, liver, and other organs. We fed mice either normal chow or a high-fat diet for 28 weeks and found that Aoah^-/- mice accumulated more hepatic lipid than did Aoah^+/+ mice. In young mice, before increased hepatic fat accumulation was observed, Aoah^-/- mouse livers increased their abundance of sterol regulatory element-binding protein 1, and the expression of its target genes that promote fatty acid synthesis. Aoah^-/- mice also increased hepatic expression of Cd36 and Fabp3, which mediate fatty acid uptake, and decreased expression of fatty acid-oxidation-related genes Acot2 and Ppara. Our results provide evidence that increasing AOAH abundance in the gut, bloodstream, and/or liver may be an effective strategy for preventing or treating MASLD.

Macrophages are crucial in the body’s inflammatory response, with tightly regulated functions for optimal immune system performance. Our study reveals that the RAS–p110α signalling pathway, known for its involvement in various biological processes and tumourigenesis, regulates two vital aspects of the inflammatory response in macrophages: the initial monocyte movement and later-stage lysosomal function. Disrupting this pathway, either in a mouse model or through drug intervention, hampers the inflammatory response, leading to delayed resolution and the development of more severe acute inflammatory reactions in live models. This discovery uncovers a previously unknown role of the p110α isoform in immune regulation within macrophages, offering insight into the complex mechanisms governing their function during inflammation and opening new avenues for modulating inflammatory responses.