Endotoxin Engages Mitochondrial Quality Controlviaan iNOS-Reactive Oxygen Species Signaling Pathway in Hepatocytes

Abstract

Background Organ injury and dysfunction in sepsis accounts for significant morbidity and mortality. Adaptive cellular responses in the setting of sepsis prevent injury and allow for organ recovery. We and others have shown that part of the adaptive response includes regulation of cellular respiration and maintenance of a healthy mitochondrial population. Herein, we hypothesized that endotoxin-induced changes in hepatocyte mitochondrial respiration and homeostasis are regulated by an inducible nitric oxide synthase/nitric oxide (iNOS/NO)-mitochondrial reactive oxygen species (mtROS) signaling axis, involving activation of the NRF2 signaling pathway. Methods Wild-type (C57Bl/6) or iNos−/− male mice were subjected to intraperitoneal lipopolysaccharide (LPS) injections to simulate endotoxemia. Individual mice were randomized to treatment with NO-releasing agent DPTA-NONOate, mtROS scavenger MitoTEMPO, or vehicle controls. Other mice were treated with scramble or Nrf2-specific siRNA via tail vein injection. Primary murine hepatocytes were utilized for in vitro studies with or without LPS stimulation. Oxygen consumption rates were measured to establish mitochondrial respiratory parameters. Western blotting, confocal microscopy with immunocytochemistry, and rtPCR were performed for analysis of iNOS as well as markers of both autophagy and mitochondrial biogenesis. Results LPS treatment inhibited aerobic respiration in vitro in wild-type but not iNos−/− cells. Experimental endotoxemia in vivo or in vitro induced iNOS protein and mtROS production. However, induction of mtROS was dependent on iNOS expression. Furthermore, LPS-induced hepatic autophagy/mitophagy and mitochondrial biogenesis were significantly attenuated in iNos−/− mice or cells with NO or mtROS scavenging. These responses were rescued in iNos−/− mice via delivery of NO both in vivo and in vitro. Conclusions. These data suggest that regulation of mitochondrial quality control following hepatocyte LPS exposure is dependent at least in part on a NO-mtROS signaling network. Further investigation to identify specific agents that modulate this process may facilitate the prevention of organ injury in sepsis.

Combined Transcriptome and Proteome Leukocyte’s Profiling Reveals Up-Regulated Module of Genes/Proteins Related to Low Density Neutrophils and Impaired Transcription and Translation Processes in Clinical Sepsis

“…Interestingly, pathways involved in iNOS signaling were found to be increased in patients with sepsis. Previous studies have reported alterations in iNOS expression and activity in response to lipopolysaccharides (LPS) and infection ( 44 ). We also found the Toll‐like receptor signaling pathway with an IPA increased status.…”

Anin vitrotumorigenesis model based on live cell-generated oxygen and nutrient gradients

“…Additionally, mitochondrial mass was lower in the AG treated disks ( Fig. 4d), likely due to the lack of NO, which plays an important role in mitochondrial biogenesis 17 . Indo-treated 4T1 disks contained fewer cells than control disks, mirroring effects of the anti-inflammatories in tumors ( Supplementary Fig.…”

Genetic BACH1 deficiency alters mitochondrial function and increases NLRP3 inflammasome activation in mouse macrophages

“…Our findings also suggest a mechanistic involvement of the enzymes iNOS and COX-2, two LPS-inducible proteins [ 41 , 42 ] that regulate inflammasome activation [ [43] , [44] , [45] ]. Regarding iNOS, it is known that this protein is a negative regulator of inflammasome activation [ 43 , 44 , 46 , 47 ] because iNOS-derived NO inhibits the formation of the ASC pyroptosome and S -nitrosylation of the NLRP3 inflammasome complex [ 43 , 44 ]. In agreement with findings of earlier reports [ 14 , 34 ], our results show that iNOS expression and NO production are markedly lower in BACH1−/− cells challenged with LPS compared to WT macrophages, suggesting that less NO is available to suppress inflammasome activation in the absence of BACH1.…”