Tumor necrosis factor α inhibits oxidative phosphorylation through tyrosine phosphorylation at subunit I of cytochrome c oxidase

Mitochondrial oxidative phosphorylation provides most cellular energy. As part of this process, cytochrome c oxidase (CcO) pumps protons across the inner mitochondrial membrane, contributing to the generation of the mitochondrial membrane potential, which is used by ATP synthase to produce ATP. During acute inflammation, as in sepsis, aerobic metabolism appears to malfunction and switches to glycolytic energy production. The pro-inflammatory cytokine tumor necrosis factor alpha(TNF alpha) has been shown to play a central role in inflammation. We hypothesized that TNF alpha-triggered cell signaling targets CcO, which is a central enzyme of the aerobic energy metabolism and can be regulated through phosphorylation. Using total bovine and murine hepatocyte homogenates TNF alpha treatment led to an similar to 60% reduction in CcO activity. In contrast, there was no direct effect of TNF alpha on CcO activity using isolated mitochondria and purified CcO, indicating that a TNF alpha-triggered intracellular signaling cascade mediates CcO inhibition. CcO isolated after TNF alpha treatment showed tyrosine phosphorylation on CcO catalytic subunit I and was similar to 50 and 70% inhibited at high cytochrome c concentrations in the presence of allosteric activator ADP and inhibitor ATP, respectively. CcO phosphorylation occurs on tyrosine 304 as demonstrated with a phosphoepitope-specific antibody. Furthermore, the mitochondrial membrane potential was decreased in H2.35 cells in response to TNF alpha. Concomitantly, cellular ATP was more than 35 and 64% reduced in murine hepatocytes and H2.35 cells. We postulate that an important contributor in TNF alpha-mediated pathologies, such as sepsis, is energy paucity, which parallels the poor tissue oxygen extraction and utilization found in such patients.