FOXA1 adenovirus

Aberrant SUMOylation is associated with the progression of nonalcoholic fatty liver disease (NAFLD). Forkhead box protein A1 (FoxA1) has been shown to protect the liver from steatosis, which is downregulated in NAFLD. This study elucidates the role of FoxA1 deSUMOylation in NAFLD. Liver FoxA1 knockout mice developed severe hepatic steatosis, which was ameliorated by sirtuin 6 (Sirt6) overexpression. Nutritional stress reduced Sumo2/3-mediated FoxA1 SUMOylation at lysine residue K6, which promoted lipid droplet formation by inhibiting fatty acid β-oxidation. Sirt6 is a target gene of FoxA1, and deSUMOylation of FoxA1 at the K6 site inhibited Sirt6 transcriptional activity. Furthermore, nutritional stress-induced FoxA1 deSUMOylation promoted the ubiquitination and degradation of FoxA1 with the help of mouse double minute 2 (Mdm2). Finally, activation of FoxA1 SUMOylation delayed the progression of NAFLD in mice. FoxA1 deSUMOylation at the K6 site promoted FoxA1 degradation, which then inhibited Sirt6 transcription, thereby suppressing fatty acid β-oxidation and promoting NAFLD development. These findings suggest that activation of FoxA1 SUMOylation may be a promising therapeutic strategy for NAFLD.

FoxA1 is a transcription factor that regulates the transcription and expression of downstream target genes. Therefore, the researchers explored the downstream genes regulated by FoxA1 during HFD feeding. RT-qPCR assays found that FoxA1 knockout significantly reduced the mRNA levels of Sirt6 and fatty acid β-oxidation-related genes Acox1, Lpl, and Pparα in liver tissue, but the levels of Cpt1a and Cyp4a14 were not affected (Figure 1A). At the same time, in the liver of FoxA1-LKO mice, the protein levels of Sirt6, Pparα, Acox1, and Lpl were downregulated, the levels of FoxO1 and acetylated FoxO1 (Ac-FoxO1) were increased, and the protein levels of Cpt1a and Cyp4a14 did not change (Figure 1B). To further determine whether FoxA1 affects lipid droplet formation by regulating Sirt6 expression, the researchers overexpressed FoxA1 in primary hepatocytes of FoxA1-LKO mice. BODIPY staining showed that lipid droplet formation was enhanced in FoxA1-LKO primary hepatocytes, while adenovirus-mediated FoxA1 (Ad-FoxA1) overexpression significantly reduced lipid droplet formation (Figure 1C). FAO and ATP levels increased after FoxA1 overexpression. In addition, forced expression of FoxA1 significantly increased the expression of Sirt6, Pparα, Acox1, and Lpl, and reduced the levels of FoxO1 and Ac-FoxO1, but did not affect the expression of Cpt1a and Cyp4a14 in primary hepatocytes (Figure 1D, E).

Figure 1. FoxA1 overexpression enhanced Sirt6 expression to suppress lipid droplet formation in hepatocytes. (Zou D, et al., 2024)