Li G., Goossens G.H., Meex R.C.R. (Department of Human Biology (NUTRIM), Maastricht University Medical Center+, Maastricht, the Netherlands).
geng.li@maastrichtuniversity.nl
Background: Oxygen availability in metabolic organs plays a key role in obesity-related cardiometabolic dysfunction. We previously demonstrated that mild hypoxia exposure has beneficial effects on glucose homeostasis, reduces inflammatory gene expression in adipocytes, and alters adipokine and myokine secretion. This study aimed to investigate the impact of different oxygen levels on metabolic pathways in HepG2 cells.
Methods: Lean and lipid-loaded HepG2 cells, mimicking lean and steatotic liver tissue, were exposed to different physiological O2 levels (10% and 5%) or standard laboratory conditions (21% O2) for 24h. Gene expression, glucose release, glycogen content, and glycolysis were evaluated. Data were analyzed using one-way ANOVA with Tukey post-hoc test or non-parametric Kruskal-Wallis test when applicable.
Result: Low physiological oxygen tension (5% O2) markedly increased the expression of G6PC1, a gene involved in gluconeogenesis, in both lean (~2-fold) and steatotic (~3-fold) HepG2 cells compared to 21% O2 (both p<0.001). Furthermore, 5% O2 decreased the expression of the lipogenic genes SREBP1C and ACC2 in lean (p=0.020 and p=0.010, respectively) and steatotic cells (both p<0.001), and FASN in steatotic cells (p=0.030). Additionally, genes involved in fatty acid oxidation, PPARGC1A and PPARA, were downregulated in steatotic cells under 5% O2 (p<0.001 and p=0.038, respectively). Lower oxygen availability dose-dependently reduced hepatic glucose release (both p<0.05) and increased glycogen content in lean and steatotic cells (both p<0.001). Finally, in line with changes in gene expression, 5% O2 exposure increased the glycolysis rate (~2-fold) compared to 21% in lean and steatotic HepG2 cells (both p<0.001).
Conclusion: The present study demonstrates that reduced oxygen availability induces a metabolic shift in hepatocytes, with enhanced glycolysis playing a central role in redirecting substrate preference from lipids toward glucose. This was evidenced by upregulation of genes involved in gluconeogenesis and downregulation of genes related to lipogenesis and fatty acid oxidation, which was accompanied by increased glycogen accumulation, reduced glucose release and elevated glycolysis rates.