Vitamin D3 abates BDL-induced cholestasis and fibrosis in rats via regulating Hedgehog pathway

Liver cholestasis is a complex disease of broad etiologies. Hedgehog (Hh) signaling has been shown to play a pivotal role in modulating liver repair post cholestatic liver injury. We here investigated the role of vitamin D in experimental liver cholestasis induced by bile-duct ligation (BDL) in rats. Male Sprague Dawley rats underwent BDL surgery and two weeks post-surgery; vitamin D was administered daily for two weeks. Serum markers of hepatocellular integrity were measured and fibrosis was detected by measuring α-SMA and hepatic TGF-β1 as well as hepatic collagen content. Hh signaling was evaluated by measuring Smo and Gli1 levels. Histopathological examination of hepatic tissue was performed. Vitamin D alleviated obstructive cholestatic damage as illustrated by total bilirubin as well as gamma glutamyl transferase (γ-GT) serum levels. It also alleviated hepatocellular damage as suggested by reducing elevated serum aminotransferases induced by BDL. Antifibrotic activity of vitamin D was confirmed by decrease in mRNA and protein expression of α-SMA, as well as collagen content in hepatic tissue. Furthermore, vitamin D suppressed BDL-induced elevated hepatic TGF-β1 mRNA and protein levels. BDL activated Hh signaling and upregulated its upstream component smoothened (Smo) and downstream target gene Gli1. Treatment with vitamin D reduced Smo mRNA levels and suppressed hepatic Gli1 mRNA and protein levels. Molecular docking of vitamin D to Smo revealed that vitamin D binds similarly to its endogenous cholesterol ligand and blocks its activation. These results demonstrate that vitamin D mitigated cholestatic liver injury through inhibiting Hh signaling.