Hyperoxia-induced fatty liver injury through the AKT-dependent and HIF-2α-independent pathways

Abstract

Supplemental oxygen is widely used to treat hypoxemia, but prolonged exposure induces oxidative stress. We investigated whether hyperoxia-induced reactive oxygen species contribute to fatty liver injury and delineated the underlying mechanism. To enhance translational relevance, mice were housed under normoxic (21% O-2) or hyperoxic (30% O-2) conditions for 10 days. We also used H2O2-treated HepG2 cells and human liver organoids. Western blotting, real-time PCR, and immunostaining were performed to assess molecular changes. Hyperoxia increased systemic oxidative stress, inflammatory markers, liver weights, and hepatic triglyceride (TG) accumulation. These changes were accompanied by repression of fatty acid beta-oxidation (FAO) and mitochondrial biogenesis genes and activation of lipogenesis. Hyperoxia also increased glycolysis, as shown by increased glucose transporter 2 (GLUT2) and glucokinase (Gck) expression, and activated protein kinase B (AKT) signaling without altering hypoxia-inducible factor-2 alpha (HIF-2 alpha) expression. Consistently, H2O2-treated HepG2 cells and human liver organoids exhibited similar alterations, including TG accumulation, upregulation of glycolytic and lipogenic markers, downregulation of FAO genes, and increased fibrosis marker and inflammation. Notably, siHIF-2 alpha failed to attenuate TG accumulation, confirming an HIF-2 alpha-independent mechanism. Finally, inhibition of AKT signaling attenuated TG accumulation and fibrosis in vitro by preventing glycolysis (via downregulation of GCK) and de novo lipid synthesis, whereas improving mitochondrial function; however, GLUT2 expression remained unaffected. In summary, hyperoxia-induced oxidative stress promotes hepatic TG accumulation and fibrosis by impairing mitochondrial function and enhancing glycolysis and lipogenesis in an AKT-dependent, HIF-2 alpha-independent manner. These findings highlight risks of oxygen therapy on hepatic metabolism and identify AKT signaling as a therapeutic target to mitigate hyperoxia-induced fatty liver injury. NEW & NOTEWORTHY Hyperoxia-induced oxidative stress caused hepatic triglyceride accumulation and fibrosis through mitochondrial dysfunction, suppressed FAO, and enhanced glycolysis and lipogenesis. These effects were AKT-dependent but HIF-2 alpha-independent, highlighting AKT signaling as a potential therapeutic target to mitigate oxygen-related fatty liver injury.