sSTEAP4 regulates cellular homeostasis and improves high-fat-diet-caused oxidative stress in hepatocytes

Nonalcoholic fatty liver disease (NAFLD) has become a global epidemic, but its pathogenesis is unclear. STEAP4, a member of six transmembrane protein family, integrates inflammatory and metabolic responses. Our present aim is to explore the roles of STEAP4 in maintaining cellular homeostasis and improving high-fat-diet (HFD)-caused oxidative stress in hepatocytes.

NAFLD model was established by HFD-feeding mice. The effects of over-nutrition on liver were detected by serum biochemical analysis and bulk RNA-seq. The levels of gene expression were measured by QPCR and Western Blot. Immunofluorescent staining was applied to determine the localization of STEAP4. AMPK agonist was employed to investigate the link between STEAP4 and AMPK pathway.

Sus scrofa STEAP4 (sSTEAP4) relieved oxidative stress and rescued the viability of hepatocytes. sSTEAP4 increased AKT phosphorylation and SOD2 level in hepatocytes, whether or not treated with H₂O₂, suggesting sSTEAP4 has regulatory effects on insulin signaling and antioxidant pathways. However, sSTEAP4 inhibited AMPK phosphorylation and Beclin1/LC3 expression under H₂O₂-deficiency situation, but the results were conversed with H₂O₂ stimulation. The cellular ER stress was aggravated with the increased energy during oxidative stress, indicating that sSTEAP4 might regulate the energetic communication between ER and mitochondria by intervening mitochondrial energy production. In addition, sSTEAP4 was demonstrated to localize in the membranes of plasma and ER in HepG2 hepatocytes.

Our results reveal that sSTEAP4 based on the needs of cell itself to improve hepatic oxidative stress and HFD-caused NAFLD, which might provide a new therapeutic scheme for NAFLD.