Depletion of FOXO4 promotes the development of nonalcoholic fatty liver disease by aggravating high-fat diet-induced liver injury by increasing SPP1 expression

Abstract

Background and study aims

Nonalcoholic fatty liver disease (NAFLD) is a prevalent chronic liver condition worldwide. Although forkhead box O4 (FOXO4) is implicated in liver diseases, its role in NAFLD remains unclear.

Material and methods

FOXO4 knockout mice were generated using CRISPR/Cas9 and fed a normal or high-fat diet (NFD/HFD). Human hepatic stellate cell line (LX-2) cells were transfected in vitro with a FOXO4 siRNA plasmid.

Results

Twelve weeks of HFD feeding downregulated FOXO4 expression and reduced its colocalization with hepatocyte nuclear factor 4α (HNF4α). HFD-fed mice exhibited increased liver-to-body weight ratios; marked lipid/glycogen accumulation; and elevated serum alanine aminotransferase, aspartate aminotransferase, total cholesterol, triglyceride, and nonesterified fatty acid levels. These pathological manifestations were further exacerbated upon genetic ablation of FOXO4. Specifically, FOXO4 knockout aggravated HFD-induced upregulation of α-smooth muscle actin protein; increased the expression of profibrotic genes (including collagen type I alpha 1 chain, transforming growth factor-β1, and tissue inhibitor of metalloproteinases 1) and inflammatory mediators (such as interleukin-1β, IL-6, and tumour necrosis factor-α); and increased hepatocyte apoptosis. Mechanistically, FOXO4 suppressed secreted phosphoprotein 1 (SPP1) expression in LX-2 cells via direct binding to the SPP1 promoter and transcriptional suppression of its activity.

Conclusion

FOXO4 downregulation exacerbates HFD-induced NAFLD progression via SPP1-dependent steatosis, inflammation, and fibrosis, thereby suggesting its potential as a therapeutic target.