FoxO1 Promotes Liver Fibrosis through TGF‐β1 mediated Hepatic Stellate Cell Activation

Abstract

The O‐class of the forkhead transcription factor FoxO1 is a crucial factor mediating the action of insulin→PI3K→Akt and governs diverse cellular processes. To investigate the role of FoxO1 in control of liver fibrosis, we generated liver‐specific deletion of FoxO1 gene in mice (L‐F1KO). Using the mouse model, we injected intraperitoneally (i.p.) corn oil or 20% solution of carbon tetrachloride (CCL4) twice per week for 4 weeks (with 2.5 ul/g body weight) in WT and L‐F1KO mice. H&E staining and Sirius Red staining revealed that CCl4‐induced liver injury and fibrosis were significantly appeared, but the effects were largely attenuated in L‐F1KO mice. Moreover, we found that both mRNA and protein levels of TGF‐β1, a cytokine that activates hepatic stellate cell (HSC) for fibrogenesis, significantly decreased in the liver L‐F1KO mice compared to WT mice in response to CCL4 treatment. In primary hepatocytes, with FoxO1‐loss of function and gain‐of function, we confirmed the regulation of TGF‐β1 expression by FoxO1. Moreover, conditional medium (CM) collected from WT hepatocytes treated with CCL4 activated human HSC cell line (LX‐2), such effect was attenuated by FoxO1 deletion in primary hepatocytes or neutralization of TGF‐β1 in the CM using TGF‐β1 antibody. These results indicate a crosstalk between hepatocytes and HSC via FoxO1‐regualted TGF‐β1. To further confirm this concept in vivo, we overexpressed FoxO1 in the liver of WT and liver‐specific TGF‐β1 deficient (L‐TGF‐β1KO) mice with adenovirus expressing FoxO1 (adFoxO1), and injected (i.p.) these mice with CCL4. We found that FoxO1 overexpression in WT mice promoted CCL4‐induced liver fibrosis and HSC activation, and such effect was blocked in L‐TGF‐β1KO mice. Taken together, our data indicate that hepatic FoxO1 promotes CCL4‐inducled liver fibrosis via upregulating TGF‐β1 expression in hepatocytes and stimulating TGF‐β1‐mediated HSC activation. Hepatic FoxO1 may be a therapeutic target for prevention and treatment of liver fibrosis.