Activation of Mitochondrial Biogenesis by Heme Oxygenase-1-mediated NF-E2-related Factor-2 Induction Rescues Mice from Lethal Staphylococcus aureus Sepsis

Rationale: Mitochondrial damage is an important component of multiple organ failure syndrome, a highly lethal complication of severe sepsis that lacks specific therapy. Mitochondrial quality control is regulated in part by the heme oxygenase-1 (HO-1; Hmox1) system through the redox-regulated NF-E2-related factor-2 (Nrf2) transcription factor, but its role in mitochondrial biogenesis in Staphylococcus aureus sepsis is unknown. Objectives: To test the hypothesis that Nrf2-dependent up-regulation of the HO-1/carbon monoxide (CO) system would preserve mitochondrial biogenesis and rescue mice from lethal S. aureus sepsis. Methods: A controlled murine S. aureus peritonitis model with and without inhaled CO was examined for HO-1 and Nrf2 regulation of mitochondrial biogenesis and the resolution of hepatic mitochondrial damage. Measurements and Main Results: Sepsis survival was significantly enhanced using inhaled CO (250 ppm once-daily for 1 h), and linked mechanistically to Hmox1 induction and mitochondria! HO activity through Nrf2 transcriptional and Akt kinase activity. HO-1/CO stimulated Nrf2-dependent gene expression and nuclear accumulation of nuclear respiratory factor-1, -2 alpha (Gabpa), and peroxisome proliferator-activated receptor gamma coactivator-1 alpha; increased mitochondrial transcription factor-A and citrate synthase protein levels; and augmented mtDNA copy number. CO enhanced antiinflammatory IL-10 and reduced proinflammatory tumor necrosis factor-a production. By contrast, Nrf2(-/-) and Akt1(-/-) mice lacked CO induction of Hmox1 and mitochondrial biogenesis, and CO rescued neither strain from S. aureus sepsis. Conclusions: We identify an inducible Nrf2/HO-1 regulatory cycle for mitochondrial biogenesis that is prosurvival and counter-inflammatory in sepsis, and describe targeted induction of mitochondrial biogenesis as a potential multiple organ failure therapy.