The difference of energy metabolism pathways between normal hepatocytes and hepatoma cells under hypoxia

Abstract

Objective: To compare the difference between energy metabolism pathways of hypoxic normal hepatocytes cells and tumor cells, and try to understand the underlying mechanism of tumor hypoxia resistance. Methods: We adopted environmental hypoxia (Hypoxia incubator with 0.2%O<inf>2</inf>) to mimic the tumor environment in vitro, and compared the difference of energy metabolism response to hypoxic stress between HepG2 cells and mice hepatocytes. Flow cytometry was used to detect the level of different kinds of ROS. MTT was used to compare the viability of cells before and afterhypoxia. The mRNA level of p53, Tigar, SCO2, and key enzymes in the metabolism including hexokinase 2 and isocitrate dehydrogenase, were detected by real-time PCR. NADH colorimetric assay was used to detect lactate dehydrogenase activity. Oxygen electrode was used to detect the oxygen consumption rate of cells. HPLC was used to detect the ATP levels in cells. Results: Under moderate hypoxia, HepG2 cells had a higher survival rate and underwent a more steady reactive oxygen species (ROS) fluctuation. The oxygen consumption rate declined in both types of cells, ATP production in hepatoma cells increased with cellular proliferation being maintained, but decreased significantly in normal liver cells. The results also showed that key enzymes involved in aerobic oxidation were compensatively increased in normal liver cells but decreased in hepatoma cells under hypoxia. The key enzymes involved in glycolysis were both upregulated in response to hypoxia, but the hepatoma cells increased more significantly. Further studies showed that in response to hypoxia, the mRNA expression of p53, Tigar and Sco2 were all upregulated in normal liver cells but p53, TIGAR and SCO2 downregulated in hepatoma cells. Conclusions: Under hypoxia stress, normal cells mainly depend on aerobic oxidation to compensate the energy, but hepatoma cells mainly rely on glycolysis. ROS may enhance glycolysis through p53/TIGAR and p53/SCO2 pathways, so as to promote the Warburg effect and hypoxia tolerance.