Low oxygen availability induces a metabolic shift toward enhanced glucose utilization in nonlipid-loaded and...

Liver function is impaired in metabolic dysfunction-associated fatty liver disease. Previous studies have demonstrated that oxygen availability in the tissue microenvironment affects adipose tissue and skeletal muscle function, but its hepatic effects remain unclear. This study aimed to investigate the impact of oxygen levels on metabolic pathways in HepG2 cells. Nonlipid-loaded and lipid-loaded HepG2 cells were exposed to different physiological O₂ levels (5% and 10%) or standard laboratory conditions (21% O₂) for 24 h. Thereafter, we determined lipid content, gene expression of metabolic markers, glycogen content, and glucose release. Furthermore, mitochondrial respiration and glycolytic activity were assessed by measuring the oxygen consumption rate (OCR) and extracellular acidification rate (ECAR), respectively. Exposure to 5% O₂ increased the expression of the gluconeogenic gene glucose-6-phosphatase catalytic subunit 1 (G6PC1) in both nonlipid-loaded and steatotic HepG2 cells compared with 21% O₂ (P < 0.001). Furthermore, 5% O₂ decreased the expression of lipogenic genes [sterol regulatory element binding transcription factor 1 (SREBF1), acetyl-CoA carboxylase beta (ACACB), and fatty acid synthase (FASN)] in nonlipid-loaded and/or steatotic cells (all P < 0.05), whereas genes involved in fatty acid oxidation [peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PPARGC1A), P < 0.001 and peroxisome proliferator-activated receptor alpha (PPARA), P = 0.038] were downregulated in steatotic cells. Low oxygen exposure increased glycogen content in nonlipid-loaded and steatotic cells (both P < 0.001) and reduced glucose release (P < 0.05). Finally, low oxygen exposure reduced OCR (P < 0.05) and increased glycolysis (P < 0.001) in both nonlipid-loaded and steatotic cells compared with 21%. In conclusion, our findings demonstrate that reduced oxygen availability in the microenvironment has marked effects on metabolic pathways in nonlipid-loaded and steatotic hepatocytes, inducing a metabolic shift to enhanced reliance on glucose as an energy source.NEW & NOTEWORTHY Oxygen availability in the tissue microenvironment affects adipose tissue and skeletal muscle function, but the effects of oxygen levels on hepatic metabolism are unclear. Low oxygen exposure altered expression of genes involved in glucose and lipid metabolism, increased glycogen content, decreased glucose release and oxygen consumption, and increased glycolytic rate compared with exposure to 21% O₂ in both nonlipid-loaded and steatotic HepG2 cells, indicative of a shift to enhanced reliance on glucose as an energy source.