Caveolin-1 Scaffolding Domain Peptides Alleviate Liver Fibrosis by Inhibiting TGF-β1/Smad Signaling in Mice

Liver fibrosis is the common pathological process characterized by activation of hepatic stellate cells (HSCs) and overproduction of extracellular matrix (ECM). Caveolin-1 (Cav1), the principal component of caveolae, is regarded as an important inhibitor of multiple signaling molecules including transforming growth factor β1(TGF-β1) signaling. To evaluate the role of Cav1 in liver fibrosis, Cav1 deficient (Cav1−/−) and wild type (WT) mice were subjected to liver fibrosis induced by carbon tetrachloride (CCl4). Results indicated no significant difference between Cav1−/− and WT mice in inflammation or collagen content before CCl4 treatment. After CCl4 administration, Cav1−/− mice showed enhanced TGF-β1 signaling, as reflected by a significantly greater amount of phosphorylation of Smad2 and collagen deposition in livers over WT animals. Qualitative and quantitative analysis indicated that inflammatory injury to the liver was markedly aggravated, accompanied by increased degeneration and necrosis of hepatocytes, higher alanine aminotransferase (ALT)/aspartate aminotransferase (AST), TGF-α and IL-1β levels in Cav1−/− animals. The mRNA and protein levels of α-smooth muscle actin (α-SMA), Collagen α1(I), and Collagen α1(III) were further enhanced in Cav1−/− animals. We also observed a significant decrease in collagen content in Cav1−/− and WT animals administrated with Cav1 scaffolding domain peptides (CSD). In vitro study indicated that phosphorylation of Smad2 was inhibited after CSD treatment, accompanied by decreased protein levels of α-SMA, Collagen α1(I), and Collagen α1(III) in HSCs. We conclude that Cav1 is an important inhibitor of TGF-β1/Smad signaling in HSCs activation and collagen production, which might make it a promising target for therapy of liver fibrosis.