INFLUENCE OF THE TRANSITION FROM ACUTE TO CHRONIC HYPOXIA ON PYRUVATE DEHYDROGENASE KINASE 1 AND LACTATE ACCUMULATION IN C2C12 CELLS

Abstract

For decades researchers have observed a reduction in exercise-induced blood lactate accumulation transitioning from acute to chronic hypoxia (the ‘lactate paradox’). Hypoxia inducible factor (HIF1-α) has been hypothesized to direct these metabolic changes during hypoxia through the induction of pyruvate dehydrogenase kinase 1 (PDK1). Activation of PDK1 inhibits aerobic glucose metabolism through pyruvate dehydrogenase, and promotes lactate production. Previous work in our lab revealed HIF1-α and PDK1 protein expression correlates to changes in lactate production with the transition from acute to chronic hypoxia in CD-1 mice, revealing a putative mechanism explaining the paradoxical reduction in lactate. We exposed differentiated C2C12 cells to 1% O2 for 4h, 24h, 96h and compared them to time-matched controls in 21% O2. In addition, we used 1 mM of the HIF-agonist DMOG at 20.95% O2 and 25 µM of the HIF antagonist PX-478 in 1% O2. We found that C2C12 myotubes decreased the rate of lactate accumulation and release with long-term hypoxia, similar to observations in vivo. This also corresponds to changes in LDH enzyme activity and PDK1 protein expression. However, DMOG-induced PDK1 expression does not match changes in lactate accumulation. Our findings confirm the existence of the lactate paradox at the cellular level and suggest a role for HIF signaling in the decline of lactate with chronic hypoxia.