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

Metabolic dysfunction-associated steatohepatitis (MASH) remains a significant 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 and pharmacological inhibition of SMPD3 alleviate MASH, whereas reintroducing SMPD3 reverses the resolution of MASH. While healthy livers express low-level SMPD3, lipotoxicity-induced DNA damage suppresses SIRT1, triggering an upregulation of SMPD3 during MASH. This disrupts membrane sphingomyelin-ceramide balance and promotes MASH progression by enhancing caveolae-dependent lipid uptake in hepatocytes and extracellular vesicle secretion from steatotic hepatocytes to worsen inflammation and fibrosis. Thus, 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 balance and holds great promise for developing novel MASH therapies. Overall design: To investigate the role of SMPD3 in MASH on diet-induced mouse model, we used cre-loxP system to generate mice with Smpd3 specifically knocked out in hepatocytes, which were fed with 24-week GAN diet to induced mouse MASH model.

代谢功能障碍相关性脂肪性肝炎（Metabolic dysfunction-associated steatohepatitis, MASH）仍是一项重大的公共卫生挑战。本研究中，我们发现鞘磷脂磷酸二酯酶3（sphingomyelin phosphodiesterase 3, SMPD3）可通过增强细胞膜处的鞘磷脂水解作用，成为肝脏神经酰胺蓄积的关键驱动因子。特异性敲除肝细胞内的Smpd3基因，或是通过药理学手段抑制SMPD3，均可缓解MASH；而恢复SMPD3表达则会逆转MASH的消退进程。健康肝脏仅低水平表达SMPD3，但脂毒性诱导的DNA损伤会抑制SIRT1，进而在MASH发生过程中触发SMPD3的表达上调。这会破坏细胞膜鞘磷脂-神经酰胺的平衡，并通过以下途径促进MASH进展：增强肝细胞内依赖于胞膜窖（caveolae）的脂质摄取能力，以及促进脂肪变性肝细胞的细胞外囊泡分泌，进而加重炎症与纤维化。因此，SMPD3是整合MASH关键病理特征的核心枢纽。值得注意的是，我们发现了一种双功能化合物，可同时激活SIRT1并抑制SMPD3，该化合物在MASH治疗中展现出显著的治疗潜力。上述研究结果表明，抑制肝脏内的SMPD3可恢复细胞膜鞘脂平衡，为开发新型MASH治疗策略提供了广阔前景。实验整体设计：为探究SMPD3在饮食诱导小鼠MASH模型中的作用，我们利用cre-loxP系统构建了肝细胞特异性Smpd3敲除小鼠，并通过24周的GAN饲料喂养以构建小鼠MASH模型。