The induction of heme oxygenase-1 (HO-1; Hmox1) by inflammation, for instance in sepsis, is associated both with an anti-inflammatory response and with mitochondrial biogenesis. Here, we tested the idea that HO-1, acting through the Nfe2l2 (Nrf2) transcription factor, links anti-inflammatory cytokine expression to activation of mitochondrial biogenesis. HO-1 induction after LPS stimulated anti-inflammatory IL-10 and IL-1 receptor antagonist (IL-1Ra) expression in mouse liver, human HepG2 cells, and mouse J774.1 macrophages but blunted tumor necrosis factor-␣ expression. This was accompanied by nuclear Nfe2l2 accumulation and led us to identify abundant Nfe2l2 and other mitochondrial biogenesis transcription factor binding sites in the promoter regions of IL10 and IL1Ra compared with pro-inflammatory genes regulated by NF-〉. Mechanistically, HO-1, through its CO product, enabled these transcription factors to bind the core IL10 and IL1Ra promoters, which for IL10 included Nfe2l2, nuclear respiratory factor (NRF)-2 (Gabpa), and MEF2, and for IL1Ra, included NRF-1 and MEF2. In cells, Hmox1 or Nfe2l2 RNA silencing prevented IL-10 and IL-1Ra up-regulation, and HO-1 induction failed post-LPS in Nfe2l2-silenced cells and post-sepsis in Nfe2l2 ؊/؊ mice. Nfe2l2 ؊/؊ mice compared with WT mice, showed more liver damage, higher mortality, and ineffective CO rescue in sepsis. Nfe2l2 ؊/؊ mice in sepsis also generated higher hepatic TNF-␣ mRNA levels, lower NRF-1 and PGC-1␣ mRNA levels, and no enhancement of anti-inflammatory Il10, Socs3, or bcl-x L gene expression. These findings disclose a highly structured transcriptional network that couples mitochondrial biogenesis to counter-inflammation with major implications for immune suppression in sepsis.Early survivors of severe sepsis often develop immune suppression (1, 2) and may later die with the multiple organ dysfunction syndrome (3). A key effector of multiple organ dysfunction syndrome is the liver, which is integral to the host response, especially in infections that activate Toll-like receptor 4 and NF-〉-dependent cytokine synthesis (4). The persistence of inflammatory cytokines such as TNF-␣ and IL-1␤ perpetuates immune activation, causing tissue damage and remodeling (5) and leads to sustained production of anti-inflammatory modulators and suppressors of adaptive immunity (6, 7).These anti-inflammatory modulators include the type II cytokine IL-10, the soluble IL-1 receptor antagonist (sIL-1Ra) 2 (5), and SOCS (suppressor of cytokine signaling) proteins (8). IL-10 is widely expressed in the liver (9, 10) by Kupffer cells (11), stellate cells (12), and hepatocytes (13), where it contributes to LPS tolerance (14). The IL-10 receptor activates JAK/STAT (Janus kinase/signal transducer and activator of transcription) to block the production of TNF-␣ and other NF-〉-dependent mediators (15), the basis for its anti-inflammatory effects (16). IL-10 also suppresses mononuclear cell function (17), and IL-10 secretion by macrophages and neutrophils negatively regulates the respon...

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 mitochondrial 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, -2a (Gabpa), and peroxisome proliferator-activated receptor gamma coactivator-1a; 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 2/2 and Akt1 2/2 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.Keywords: Akt/PKB; carbon monoxide; cytokines; oxidative stress; mitochondrial DNA Hospitalization rates for sepsis continue to rise, especially in the elderly (1), and gram-positive bacteria, particularly Staphylococcus aureus species, are responsible for most of the infections (2). Severe sepsis and septic shock cause death from multiple organ failure (MOF) syndrome, most notably when three or more organs fail (3, 4). The pathogenesis of MOF involves damage to mitochondria from immune effectors, such as tumor necrosis factor (TNF)-a (5), and by reactive oxygen species (ROS) and reactive nitrogen species that escape the antioxidant defenses (6). MOF has no specific therapy, but survival is associated with the induction of mitochondrial antioxidant defenses and mitochondrial biogenesis (7,8).The cell's oxidation-reduction (redox) state regulates the antioxidant defenses and broader adaptive genetic responses (9, 10) including those that regenerate mitochondria (11). The induction of mitochondrial biogenesis (12, 13) and the clearance of irreparably damaged organelles by mitophagy (14) are responsible for the maintenance of mitochondrial structure and f...

The nuclear respiratory factor-1 (NRF1) gene is activated by lipopolysaccharide (LPS), which might reflect TLR4-mediated mitigation of cellular inflammatory damage via initiation of mitochondrial biogenesis. To test this hypothesis, we examined NRF1 promoter regulation by NFκB, and identified interspecies-conserved κB-responsive promoter and intronic elements in the NRF1 locus. In mice, activation of Nrf1 and its downstream target, Tfam, by Escherichia coli was contingent on NFκB, and in LPS-treated hepatocytes, NFκB served as an NRF1 enhancer element in conjunction with NFκB promoter binding. Unexpectedly, optimal NRF1 promoter activity after LPS also required binding by the energy-state-dependent transcription factor CREB. EMSA and ChIP assays confirmed p65 and CREB binding to the NRF1 promoter and p65 binding to intron 1. Functionality for both transcription factors was validated by gene-knockdown studies. LPS regulation of NRF1 led to mtDNA-encoded gene expression and expansion of mtDNA copy number. In cells expressing plasmid constructs containing the NRF-1 promoter and GFP, LPS-dependent reporter activity was abolished by cis-acting κB-element mutations, and nuclear accumulation of NFκB and CREB demonstrated dependence on mitochondrial H2O2. These findings indicate that TLR4-dependent NFκB and CREB activation co-regulate the NRF1 promoter with NFκB intronic enhancement and redox-regulated nuclear translocation, leading to downstream target-gene expression, and identify NRF-1 as an early-phase component of the host antibacterial defenses.

These studies identify OGG1 as an early mitochondrial response protein during sepsis under regulation by the NRF-1 and NRF-2α transcription factors that regulate mitochondrial biogenesis.

Nitric oxide synthase-2 (NOS2) plays a critical role in reactive nitrogen species generation and cysteine modifications that influence mitochondrial function and signaling during inflammation. Here, we investigated the role of NOS2 in hepatic mitochondrial biogenesis during E. coli peritonitis in mice. NOS2 -/-mice displayed smaller mitochondrial biogenesis responses than Wt mice during E. coli infection according to differences in mRNA levels for the PGC-1α co-activator, nuclear respiratory factor-1, mitochondrial transcription factor-A (Tfam), and mtDNA polymerase (Polγ). NOS2 -/-mice did not significantly increase mitochondrial Tfam and Polγ protein levels during infection in conjunction with impaired mitochondrial DNA (mtDNA) transcription, loss of mtDNA copy number, and lower State 3 respiration rates. NOS2 blockade in mitochondrial-GFP reporter mice disrupted Hsp60 localization to mitochondria after E. coli exposure. Mechanistically, biotinswitch and immunoprecipitation studies demonstrated NOS2 binding to and S-nitros(yl)ation of Hsp60 and Hsp70. Specifically, NOS2 promoted Tfam accumulation in mitochondria by regulation of Hsp60-Tfam binding via S-nitros(yl)ation. In hepatocytes, site-directed mutagenesis identified 237 Cys as a critical residue for Hsp60 S-nitros(yl)ation. Thus, the role of NOS2 in inflammation-induced mitochondrial biogenesis involves both optimal gene expression for nuclearencoded mtDNA-binding proteins and functional regulation of the Hsp60 chaperone that enables their importation for mtDNA transcription and replication.