NADPH oxidase 4-SH3 domain-containing YSC84-like 1 complex participates liver inflammation and fibrosis

There is growing evidence that NADPH oxidase 4 (Nox4) in hepatocytes contributes to liver inflammation and fibrosis during the development of metabolic dysfunction-associated steatohepatitis (MASH). However, how Nox4 is regulated and leads to liver pathogenesis is unclear. Our previous studies showed that the cytosolic protein SH3 domain-containing Ysc84-like 1 (SH3YL1) regulates Nox4 activity. Here, we asked whether SH3YL1 also participates in liver inflammation and fibrosis during MASH development. We generated that whole body SH3YL1 knockout (SH3YL1^-/-), Nox4 knockout (Nox4^-/-) mice, and the hepatocyte-specific SH3YL1 conditional knockout (Alb-Cre/SH3YL1^fl/fl) mice were fed a methionine/choline-deficient (MCD) diet to induce liver inflammation and fibrosis in pathogenesis of MASH. Palmitate-stimulated primary SH3YL1-and Nox4-deficient hepatocytes and hepatic stellate cells (HSCs) did not generate H₂O₂. While the liver of MCD diet-fed wild type (WT) mice demonstrated elevated 3-nitrotyrosine as a protein oxidation and 4-hydroxynonenal adducts as a lipid oxidation and increased liver inflammation, hepatocyte apoptosis, and liver fibrosis, these events were markedly reduced in SH3YL1^-/-, Nox4^-/-, and Alb-Cre/SH3YL1^fl/fl mice. The MCD diet-fed WT mice also showed elevated hepatocyte expression of SH3YL1 protein. Similarly, liver biopsies from MASH patients demonstrated strong hepatocyte SH3YL1 protein expression, whereas hepatocytes from patients with steatosis weakly expressed SH3YL1 and histologically normal patient hepatocytes exhibited very little SH3YL1 expression. The Nox4-SH3YL1 complex in murine hepatocytes elevates their H₂O₂ production, which promotes the liver inflammation, hepatocyte apoptosis, and liver fibrosis that characterize MASH. This axis may also participate in MASH in humans.