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

Abstract

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.