Deficiency of Ugcg in LSECs alleviates high-fat diet-induced MASLD.

BACKGROUND

Hepatic glycosphingolipid biosynthesis is implicated in insulin resistance and metabolic dysfunction-associated steatotic liver disease (MASLD). While UDP-glucose ceramide glucosyltransferase (UGCG) serves as the rate-limiting enzyme in glycosphingolipid synthesis, its cell-specific roles in MASLD pathogenesis remain undefined. Our study investigates the mechanistic contribution of LSEC-expressed UGCG to high-fat diet (HFD)-induced insulin resistance and MASLD progression.

METHODS

Primary cell sorting was used to analyze LSEC-specific enrichment of UGCG in wild-type mice under normal chow (NC) diet and high-fat diet (HFD) conditions. LSEC-specific Ugcg knockout mice (UgcgCdh5cre+) and littermate controls (UgcgCdh5cre-) were subjected to 12 weeks of HFD or NC feeding. Hepatic steatosis was assessed via histopathology; glucose tolerance and insulin sensitivity were evaluated functionally. Endothelial fenestration architecture was quantified using scanning electron microscopy (SEM). Ganglioside GM3 levels were measured via LC-MS. LSEC-hepatocyte cocultures were employed to investigate VLDL secretion and lipid metabolism-related gene/protein expression, with nitric oxide (NO) and endothelin-1 (ET-1) signaling verified by ELISA.

RESULTS

Ugcg deficiency in LSECs attenuated hepatic steatosis, improved glucose tolerance and insulin sensitivity, and restored endothelial fenestration architecture without compromising vascular integrity. It also reduced LSEC defenestration and CD31+ capillarization, promoting endothelial homeostasis. Mechanistically, insulin receptor-β (IRβ) was predominantly localized in LSECs; HFD-induced IRβ downregulation was reversed by UGCG inhibition (Genz-123346), correlating with reduced GM3 levels. GM3 was shown to suppress IRβ in a dose-dependent manner. In cocultures, Ugcg deficiency increased VLDL secretion and elevated the expression of hepatocyte lipid metabolism-related genes and proteins through NO/ET-1 signaling pathways.

CONCLUSIONS

Our findings establish UGCG as a master regulator of LSEC metabolic functions through GM3-IRβ axis modulation. LSEC-targeted UGCG inhibition mitigates hepatic insulin resistance via NO/ET-1-mediated hepatocyte metabolic reprogramming, providing a novel therapeutic paradigm for MASLD.