FIG. 1.

The mitochondrial energy–redox axis and generation of redox- and energy messengers. Mitochondria maintain a fine tuning of NAD⁺/NADH ratios, generate H₂O₂ involved in the regulation of redox-sensitive signaling and transcriptional pathways, and ATP to meet the energy demands of the cell. The regulation of redox-sensitive signaling is exemplified with the 2-electron pathway (Equations 4 and 8 in the text). Activation of PGC1α is given as an example of regulation by NAD⁺/NADH ratios and of interaction with the energy demands/energy sensors panel. There is also interaction between the latter panel and the regulation of redox-sensitive signaling by H₂O₂, for its generation reports the mitochondrial energy charge to cytosol (176) and is implicated in the regulation of the cell's redox status. oA-ADPr, 2’-o-acetyl-ADP-ribose; Ac, acetyl moiety; Nic, nicotinamide.