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Acute kidney injury (AKI) contributes to the high morbidity and mortality of multi-system organ failure in sepsis. However, recovery of renal function after sepsis-induced AKI suggests active repair of energy-producing pathways. Here, we tested the hypothesis in mice that Staphyloccocus aureus sepsis damages mitochondrial DNA (mtDNA) in the kidney and activates mtDNA repair and mitochondrial biogenesis. Sepsis was induced in wild-type C57Bl/6J and Cox-8 Gfp-tagged mitochondrial-reporter mice via intraperitoneal fibrin clots embedded with S. aureus. Kidneys from surviving mice were harvested at time zero (control), 24, or 48 hours after infection and evaluated for renal inflammation, oxidative stress markers, mtDNA content, and mitochondrial biogenesis markers, and OGG1 and UDG mitochondrial DNA repair enzymes. We examined the kidneys of the mitochondrial reporter mice for changes in staining density and distribution. S. aureus sepsis induced sharp amplification of renal Tnf, Il-10, and Ngal mRNAs with decreased renal mtDNA content and increased tubular and glomerular cell death and accumulation of protein carbonyls and 8-OHdG. Subsequently, mtDNA repair and mitochondrial biogenesis was evidenced by elevated OGG1 levels and significant increases in NRF-1, NRF-2, and mtTFA expression. Overall, renal mitochondrial mass, tracked by citrate synthase mRNA and protein, increased in parallel with changes in mitochondrial GFP-fluorescence especially in proximal tubules in the renal cortex and medulla. Sub-lethal S. aureus sepsis thus induces widespread renal mitochondrial damage that triggers the induction of the renal mtDNA repair protein, OGG1, and mitochondrial biogenesis as a conspicuous resolution mechanism after systemic bacterial infection. [ABSTRACT FROM AUTHOR]

Abstract: Acute lung injury (ALI) initiates protective responses involving genes downstream of the Nrf2 (Nfe2l2) transcription factor, including heme oxygenase-1 (HO-1), which stimulates mitochondrial biogenesis and related anti-inflammatory processes. We examined mitochondrial biogenesis during Staphylococcus aureus pneumonia in mice and the effect of Nrf2 deficiency on lung mitochondrial biogenesis and resolution of lung inflammation. S. aureus pneumonia established by nasal insufflation of live bacteria was studied in mitochondrial reporter (mt-COX8-GFP) mice, wild-type (WT) mice, and Nrf2 −/− mice. Bronchoalveolar lavage, wet/dry ratios, real-time RT-PCR and Western analysis, immunohistochemistry, and fluorescence microscopy were performed on the lung at 0, 6, 24, and 48h. The mice survived S. aureus inoculations at 5×108 CFU despite diffuse lung inflammation and edema, but the Nrf2 −/− lung showed increased ALI. In mt-COX8-GFP mice, mitochondrial fluorescence was enhanced in bronchial and alveolar type II (AT2) epithelial cells. WT mice displayed rapid HO-1 upregulation and lower proinflammatory TNF-α, IL-1β, and CCL2 and, especially in AT2 cells, higher anti-inflammatory IL-10 and suppressor of cytokine signaling-3 than Nrf2 −/− mice. In the alveolar region, WT but not Nrf2 −/− mice showed strongly induced nuclear respiratory factor-1, PGC-1α, mitochondrial transcription factor-A, SOD2, Bnip3, mtDNA copy number, and citrate synthase. These findings indicate that S. aureus pneumonia induces Nrf2-dependent mitochondrial biogenesis in the alveolar region, mainly in AT2 cells. Absence of Nrf2 suppresses the alveolar transcriptional network for mitochondrial biogenesis and anti-inflammation, which worsens ALI. The findings link redox activation of mitochondrial biogenesis to ALI resolution. [Copyright &y& Elsevier]

Abstract: 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 Escherichia 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 coactivator, 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, biotin-switch 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 237Cys 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 nuclear-encoded mtDNA-binding proteins and functional regulation of the Hsp60 chaperone that enables their importation for mtDNA transcription and replication. [Copyright &y& Elsevier]