Human FTO adenoviral particles

Activation of hepatic stellate cells (HSCs) is central to the development of liver fibrosis. Autophagy promotes HSC activation and ultimately accelerates liver fibrosis. Unc-51-like autophagy-activating kinase 1 (ULK1) is a mammalian autophagy promoter, and N6-methyladenosine (m6A) modification is closely associated with autophagy. In this study, researchers found that the m6A demethylase fat mass and obesity-associated protein (FTO) was the most differentially expressed m6A methylase, which was upregulated during HSC activation and bile duct ligation (BDL)-induced liver fibrosis. Importantly, FTO overexpression exacerbated HSC activation and liver fibrosis through autophagy. Mechanistically, ULK1 is a target of FTO compared with other autophagy-related genes, because FTO primarily mediates m6A demethylation of ULK1 and upregulates its expression, thereby enhancing autophagy and HSC activation. Notably, the m6A reader YTH domain-containing protein 2 (YTHDC2) reduced ULK1 mRNA levels by recognizing m6A binding sites, ultimately inhibiting autophagy and HSC activation. Taken together, these findings highlight that m6A-dependent ULK1 is an important regulator of HSC autophagy and suggest that ULK1 is a new potential therapeutic target for the treatment of liver fibrosis.

To verify the role of FTO in hepatic fibrosis in vivo, the researchers first transfected recombinant adenoviral vector encoding FTO (AdFTO) into mouse livers. HE and Masson staining showed that FTO enhanced inflammatory cell infiltration and collagen deposition in the portal area (Figure 1A). Western blot analysis showed that the expression of α-SMA and type I collagen in the AdFTO group gradually increased (Figure 1C), consistent with the results of immunohistochemical staining (Figure 1B). Previous studies have shown that enhanced autophagy accelerates the occurrence of liver fibrosis. Here, the researchers hypothesized that autophagy is essential for FTO-induced liver fibrosis. To verify this hypothesis, the level of autophagy after FTO treatment was detected. As expected, the conversion of LC3 I to LC3 II in the AdFTO group gradually increased, while the conversion of p62 decreased (Figure 2C), indicating that FTO enhanced autophagy.

Figure 1. FTO promotes HSC activation and hepatic fibrosis as well as autophagy. (Huang T, et al., 2024)