Hepatic sphingomyelin phosphodiesterase 3 promotes steatohepatitis by disrupting membrane sphingolipid metabolism.

Metabolic-dysfunction-associated steatohepatitis (MASH) remains a major health challenge. Herein, we identify sphingomyelin phosphodiesterase 3 (SMPD3) as a key driver of hepatic ceramide accumulation through increasing sphingomyelin hydrolysis at the cell membrane. Hepatocyte-specific Smpd3 gene disruption or pharmacological inhibition of SMPD3 alleviates MASH, whereas reintroducing SMPD3 reverses the resolution of MASH. Although healthy livers express low-level SMPD3, lipotoxicity-induced DNA damage suppresses sirtuin 1 (SIRT1), triggering an upregulation of SMPD3 during MASH. This disrupts membrane sphingomyelin-ceramide balance and promotes disease progression by enhancing caveolae-dependent lipid uptake and extracellular vesicle secretion from steatotic hepatocytes to exacerbate inflammation and fibrosis. Consequently, SMPD3 acts as a central hub integrating key MASH hallmarks. Notably, we discovered a bifunctional agent that simultaneously activates SIRT1 and inhibits SMPD3, which shows significant therapeutic potential in MASH treatment. These findings suggest that inhibition of hepatic SMPD3 restores membrane sphingolipid metabolism and holds great promise for developing novel MASH therapies.