Oxygen-dependent constraint of glycolysis through the mitochondrial electron transport chain

Hypoxia-inducible factors (HIFs) are constitutively active in clear cell renal cell carcinoma (ccRCC) cells. Here, we investigated whether these cells could still respond to hypoxia independently of canonical HIF activation. We found that hypoxia provokes a NADH reductive stress that attenuates lactate release when the supply of extracellular pyruvate becomes limited, a response that was restored by the ectopic expression of the cytosolic and mitochondria-targeted NADH oxidase ( Lb NOX). Suppression of the mitochondrial electron transport chain (mtETC) alone is sufficient to attenuate glycolytic flux when extracellular pyruvate is limited, a situation consistent with metabolomic data from human ccRCCs. Furthermore, this response can be mimicked by pharmacological or genetic inhibition of mitochondrial complex IV (CIV) activity and restored by the mitochondrial-targeted alternative oxidase (AOX). Therefore, our data suggest that cells can respond to low oxygen tension through a mitochondrial-dependent elevation of NADH/NAD ⁺ , resulting in the suppression of glycolysis when pyruvate availability is compromised.