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Lung Ischemia-Reperfusion is a Sterile Inflammatory Process Influenced by Commensal Microbiota in Mice.

ABSTRACT: Lung ischemia-reperfusion (IR) complicates numerous clinical processes, such as cardiac arrest, transplantation, and major trauma. These conditions generate sterile inflammation, which can cause or worsen acute lung injury. We previously reported that lung and systemic inflammation in a mouse model of ventilated lung IR depends on Toll-like receptor 4 (TLR-4) signaling and the presence of alveolar macrophages. Here, we tested the hypothesis that the intestinal microbiome has a role in influencing the inflammatory response to lung IR. Lung IR was created in intubated mechanically ventilated mice via reversible left pulmonary artery occlusion followed by reperfusion. Inflammatory markers and histology were tracked during varying periods of reperfusion (from 1 to 24 h). Separate groups of mice were given intestinally localized antibiotics for 8 to 10 weeks and then were subjected to left lung IR and analysis of lungs and plasma for markers of inflammation. Alveolar macrophages from antibiotic-treated or control mice were tested ex vivo for inflammatory responses to bacterial TLR agonists, namely, lipopolysaccharide and Pam3Cys. We found that inflammation generated by left lung IR was rapid in onset and dissipated within 12 to 24 h. Treatment of mice with intestinally localized antibiotics was associated with a marked attenuation of circulating and lung inflammatory markers as well as reduced histologic evidence of infiltrating cells and edema in the lung after IR. Alveolar macrophages from antibiotic-treated mice produced less cytokines ex vivo when stimulated with TLR agonists as compared with those from control mice. Our data indicate that the inflammatory response induced by nonhypoxic lung IR is transient and is strongly influenced by intestinal microbiota. Furthermore, these data suggest that the intestinal microbiome could potentially be manipulated to attenuate the post-IR pulmonary inflammatory response.

SUBMITTER: Prakash A

PROVIDER: S-EPMC4537678 | biostudies-literature | 2015 Sep

REPOSITORIES: biostudies-literature

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Lung Ischemia-Reperfusion is a Sterile Inflammatory Process Influenced by Commensal Microbiota in Mice.

Prakash Arun A Sundar Shirin V SV Zhu Ying-Gang YG Tran Alphonso A Lee Jae-Woo JW Lowell Clifford C Hellman Judith J

Shock (Augusta, Ga.) 20150901 3

Lung ischemia-reperfusion (IR) complicates numerous clinical processes, such as cardiac arrest, transplantation, and major trauma. These conditions generate sterile inflammation, which can cause or worsen acute lung injury. We previously reported that lung and systemic inflammation in a mouse model of ventilated lung IR depends on Toll-like receptor 4 (TLR-4) signaling and the presence of alveolar macrophages. Here, we tested the hypothesis that the intestinal microbiome has a role in influencin ...[more]

PMID: 26196836

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Project description:IntroductionIntestinal ischemia is a critical problem resulting in multiple organ failure and high mortality of 60 to 80%. Acute lung injury (ALI) is a common complication after intestinal ischemia/reperfusion (I/R) injuries and contributes to the high mortality rate. Moreover, activated neutrophil infiltration into the lungs is known to play a significant role in the progression of ALI. Integrin-mediated interaction is involved in neutrophil transmigration. Synthetic peptides containing an arginine-glycine-aspartate sequence compete with adhesive proteins and inhibit integrin-mediated interaction and signaling. Thus, we hypothesized that the administration of a cyclic arginine-glycine-aspartate peptide (cRGD) inhibited neutrophil infiltration and provided protection against ALI induced by intestinal I/R.MethodsIschemia in adult male C57BL/6 mice was induced by fastening the superior mesenteric artery with 4-0 suture. Forty-five minutes later, the vascular suture was released to allow reperfusion. cRGD (5 mg/kg body weight) or normal saline (vehicle) was administered by intraperitoneal injection 1 hour prior to ischemia. Blood, gut, and lung tissues were collected 4 hours after reperfusion for various measurements.ResultsIntestinal I/R caused severe widespread injury to the gut and lungs. Treatment with cRGD improved the integrity of microscopic structures in the gut and lungs, as judged by histological examination. Intestinal I/R induced the expression of β₁, β₂ and β₃ integrins, intercellular adhesion molecule-1, and fibronectin. cRGD significantly inhibited myeloperoxidase activity in the gut and lungs, as well as neutrophils and macrophages infiltrating the lungs. cRGD reduced the levels of TNF-α and IL-6 in serum, in addition to IL-6 and macrophage inflammatory protein-2 in the gut and lungs. Furthermore, the number of TUNEL-staining cells and levels of cleaved caspase-3 in the lungs were significantly lowered in the cRGD-treated mice in comparison with the vehicle mice.ConclusionsTreatment with cRGD effectively protected ALI and gut injury, lowered neutrophil infiltration, suppressed inflammation, and inhibited lung apoptosis after intestinal I/R. Thus, there is potential for developing cRGD as a treatment for patients suffering from ALI caused by intestinal I/R.

Project description:Angong Niuhuang Pill (ANP) is a famous traditional Chinese patent medicine and is used for treating ischemic or hemorrhagic stroke for centuries. However, the mechanism of action of ANP in stroke treatment has rarely been reported. With increasing evidence for a mechanistic link between acute ischemic stroke and gut microbiota alterations, this study aimed to determine the mechanism of action of ANP in treating acute ischemic stroke from the perspective of the gut microbiota. A mouse model of acute ischemic stroke by middle cerebral artery occlusion (MCAO) was established, and 16S ribosomal RNA (rRNA) gene sequencing and metabolomic analysis were performed on the cecal content samples collected from the sham, model, and ANP-treated MCAO mice. The results showed that ANP significantly ameliorated cerebral infarct volume, improved neurological deficits, and reduced histopathological injuries in the ipsilateral ischemic cortex, hippocampus, and striatum. The latter effects included inhibition of neuronal death, increased Nissl bodies, and decreased cell apoptosis. Moreover, ANP reversed gut microbiota dysbiosis by modulating the abundance of bacteria whose effects may mitigate MCAO damage, such as the phyla Bacteroidetes and Firmicutes, the families Lachnospiraceae and Prevotellaceae, and the genera Alloprevotella and Roseburia. Microbial metabolites related to inflammation and neuroprotection, such as prostaglandin I2 and uridine, were also regulated by ANP treatment. Uridine, guanosine, and inosine might be potential neuromodulators produced by the gut microbiota in the ANP-treated group. Spearman correlation analysis revealed that these metabolites were intimately related to certain genera, including Alloprevotella, Lachnoclostridium, Enterorhabdus, Roseburia, Lachnospiraceae_UCG-006, and Colidextribacter. Our results demonstrated that alleviating gut microbiota dysbiosis is one of the mechanisms by which ANP protects against ischemic stroke and suggest that targeting Alloprevotella, Lachnoclostridium, Enterorhabdus, Roseburia, Lachnospiraceae_UCG-006, and Colidextribacter might be a potential anti-stroke therapy.

Project description:BACKGROUND & AIMS:Hepatic ischemia-reperfusion injury (IRI), characterized by exogenous antigen-independent local inflammation and hepatocellular death, represents a risk factor for acute and chronic rejection in liver transplantation. We aimed to investigate the molecular communication involved in the mechanism of liver IRI. METHODS:We analyzed human liver transplants, primary murine macrophage cell cultures and IR-stressed livers in myeloid-specific heme oxygenase-1 (HO-1) gene mutant mice, for anti-inflammatory and cytoprotective functions of macrophage-specific HO-1/SIRT1 (sirtuin 1)/p53 (tumor suppressor protein) signaling. RESULTS:Decreased HO-1 expression in human post-reperfusion liver transplant biopsies correlated with a deterioration in hepatocellular function (serum ALT; p<0.05) and inferior patient survival (p<0.05). In the low HO-1 liver transplant biopsy group, SIRT1/Arf (alternative reading frame)/p53/MDM2 (murine double minute 2) expression levels decreased (p<0.05) while cleaved caspase 3 and frequency of TUNEL+cells simultaneously increased (p<0.05). Immunofluorescence showed macrophages were the principal source of HO-1 in human and mouse IR-stressed livers. In vitro macrophage cultures revealed that HO-1 induction positively regulated SIRT1 signaling, whereas SIRT1-induced Arf inhibited ubiquitinating activity of MDM2 against p53, which in turn attenuated macrophage activation. In a murine model of hepatic warm IRI, myeloid-specific HO-1 deletion lacked SIRT1/p53, exacerbated liver inflammation and IR-hepatocellular death, whereas adjunctive SIRT1 activation restored p53 signaling and rescued livers from IR-damage. CONCLUSION:This bench-to-bedside study identifies a new class of macrophages activated via the HO-1-SIRT1-p53 signaling axis in the mechanism of hepatic sterile inflammation. This mechanism could be a target for novel therapeutic strategies in liver transplant recipients. LAY SUMMARY:Post-transplant low macrophage HO-1 expression in human liver transplants correlates with reduced hepatocellular function and survival. HO-1 regulates macrophage activation via the SIRT1-p53 signaling network and regulates hepatocellular death in liver ischemia-reperfusion injury. Thus targeting this pathway in liver transplant recipients could be of therapeutic benefit.

Project description:ObjectiveRecruitment of neutrophils and formation of neutrophil extracellular traps (NETs) contribute to lethality in acute mesenteric infarction. To study the impact of the gut microbiota in acute mesenteric infarction, we used gnotobiotic mouse models to investigate whether gut commensals prime the reactivity of neutrophils towards formation of neutrophil extracellular traps (NETosis). Approach and Results: We applied a mesenteric ischemia-reperfusion (I/R) injury model to germ-free (GF) and colonized C57BL/6J mice. By intravital imaging, we quantified leukocyte adherence and NET formation in I/R-injured mesenteric venules. Colonization with gut microbiota or monocolonization with Escherichia coli augmented the adhesion of leukocytes, which was dependent on the TLR4 (Toll-like receptor-4)/TRIF (TIR-domain-containing adapter-inducing interferon-β) pathway. Although neutrophil accumulation was decreased in I/R-injured venules of GF mice, NETosis following I/R injury was significantly enhanced compared with conventionally raised mice or mice colonized with the minimal microbial consortium altered Schaedler flora. Also ex vivo, neutrophils from GF and antibiotic-treated mice showed increased LPS (lipopolysaccharide)-induced NETosis. Enhanced TLR4 signaling in GF neutrophils was due to elevated TLR4 expression and augmented IRF3 (interferon regulatory factor-3) phosphorylation. Likewise, neutrophils from antibiotic-treated conventionally raised mice had increased NET formation before and after ischemia. Increased NETosis in I/R injury was abolished in conventionally raised mice deficient in the TLR adaptor TRIF. In support of the desensitizing influence of enteric LPS, treatment of GF mice with LPS via drinking water diminished LPS-induced NETosis in vitro and in the mesenteric I/R injury model.ConclusionsCollectively, our results identified that the gut microbiota suppresses NETing neutrophil hyperreactivity in mesenteric I/R injury, while ensuring immunovigilance by enhancing neutrophil recruitment.

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Lung Ischemia-Reperfusion is a Sterile Inflammatory Process Influenced by Commensal Microbiota in Mice.

Publications

Lung Ischemia-Reperfusion is a Sterile Inflammatory Process Influenced by Commensal Microbiota in Mice.

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