Alteration of metabolic activity regulates mitochondrial temperature in diagnosis in HepG2 hepatocellular carcinoma cells

Oxidative phosphorylation (OXPHOS) is a key player in mitochondrial bioenergetic functions. In hepatocellular carcinoma (HCC), OXPHOS slows down or switches to glycolysis via what is known as the Warburg effect. The altered respiration in cancer was reported to affect mitochondrial temperature. We investigated the impact of the metabolic switch on the mitochondrial temperature in HepG2 HCC cell line. Metformin (N, N-dimethylbiguanide) treatment was used to suppress glycolysis to emulate lower metabolically active cells (Met-HepG2). The mitochondrial temperature was assessed using mito-thermo yellow (MTY) absorbing mitochondrial radiant heat. Mito-tracker green (MTG) fluorescent dye was used to confirm mitochondrial localization. Our data showed lower MTY dye intensity in the Met-HepG2 treated group, indicating a significant increase in mitochondrial temperature compared to untreated HepG2 cells (NT-HepG2). Genotypic analysis of the metabolic respiration gene expression showed significant down-regulation in glycolytic genes (ERR-gamma, HK2, PGK, ALDOC, TPI1, IDH1, and PKM2) in the Met-HepG2 cells compared to the NT-HepG2 cells. OXPHOS as evidenced by ATP, ROS, and NADPH production was significantly up-regulated in the Met-HepG2 group compared to the NT-HepG2 group. Transmission electron microscopy showed fewer mitochondria with swollen elongated appearance, as a marker for activated OXPHOS in the Met-HepG2 group. These data show a correlation between HepG2 altered metabolism and mitochondrial temperature and suggest that less metabolically active HepG2 cells are correlated with higher mitochondrial temperature, providing evidence for a possible role of mitochondrial temperature in diagnosis of HCC.