Background The airway epithelium is the first line of defense against inhaled insults and therefore must be capable of coordinating appropriate inflammatory and immune responses. Objective We sought ...to test the hypothesis that the nucleotide-binding domain and leucine-rich repeat protein 3 (NLRP3) inflammasome, an intracellular danger-sensing complex, plays a critical role in airway epithelium–mediated immune responses to urban particulate matter (PM) exposure. Methods In this study we (1) identified NLRP3 and caspase-1 expression in human airway epithelium bronchus and primary cells, (2) characterized NLRP3 inflammasome–mediated IL-1β production from human airway epithelium in response to PM, and (3) performed in vivo PM exposure experiments with wild-type and Nlrp3−/− mice. Results Our results demonstrate that human airway epithelium contains a functional NLRP3 inflammasome that responds to PM exposure with caspase-1 cleavage and production of IL-1β. Exposure of Nlrp3−/− and wild-type mice to PM in vivo demonstrates NLRP3-dependent production of IL-1β in the lung, airway neutrophilia, and increases in CD11c+hi /MHC class II+hi cell numbers in intrathoracic lymph nodes. Conclusion Our study is the first to characterize airway epithelial NLRP3 inflammasome–mediated immune responses to PM exposure, which might have implications in patients with asthma and other lung diseases.
Neutrophils are recruited from the blood to sites of sterile inflammation, where they contribute to wound healing but may also cause tissue damage. By using spinning disk confocal intravital ...microscopy, we examined the kinetics and molecular mechanisms of neutrophil recruitment to sites of focal hepatic necrosis in vivo. Adenosine triphosphate released from necrotic cells activated the Nlrp3 inflammasome to generate an inflammatory microenvironment that alerted circulating neutrophils to adhere within liver sinusoids. Subsequently, generation of an intravascular chemokine gradient directed neutrophil migration through healthy tissue toward foci of damage. Lastly, formyl-peptide signals released from necrotic cells guided neutrophils through nonperfused sinusoids into the injury. Thus, dynamic in vivo imaging revealed a multistep hierarchy of directional cues that guide neutrophil localization to sites of sterile inflammation.
The commensal bacteria that reside in the gastrointestinal tract exist in a symbiotic relationship with the host, driving the development of the immune system and maintaining metabolic and tissue ...homeostasis in the local environment. The intestinal microbiota has the capacity to generate a wide array of chemical metabolites to which the cells of the intestinal mucosa are exposed. Host cells express xenobiotic receptors, such as the aryl hydrocarbon receptor (AhR) and the pregnane X receptor (PXR), that can sense and respond to chemicals that are generated by nonhost pathways. In this review, we outline the physiological and immunological processes within the intestinal environment that are regulated by microbial metabolites through the activation of the AhR and the PXR, with a focus on ligands generated by the stepwise catabolism of tryptophan.
The intestinal microbiota plays an important role in regulating gastrointestinal (GI) physiology in part through interactions with the enteric nervous system (ENS). Alterations in the gut microbiome ...frequently occur together with disturbances in enteric neural control in pathophysiological conditions. However, the mechanisms by which the microbiota regulates GI function and the structure of the ENS are incompletely understood. Using a mouse model of antibiotic (Abx)-induced bacterial depletion, we sought to determine the molecular mechanisms of microbial regulation of intestinal function and the integrity of the ENS. Spontaneous reconstitution of the Abx-depleted microbiota was used to assess the plasticity of structure and function of the GI tract and ENS. Microbiota-dependent molecular mechanisms of ENS neuronal survival and neurogenesis were also assessed.
Adult male and female Abx-treated mice exhibited alterations in GI structure and function, including a longer small intestine, slower transit time, increased carbachol-stimulated ion secretion, and increased intestinal permeability. These alterations were accompanied by the loss of enteric neurons in the ileum and proximal colon in both submucosal and myenteric plexuses. A reduction in the number of enteric glia was only observed in the ileal myenteric plexus. Recovery of the microbiota restored intestinal function and stimulated enteric neurogenesis leading to increases in the number of enteric glia and neurons. Lipopolysaccharide (LPS) supplementation enhanced neuronal survival alongside bacterial depletion, but had no effect on neuronal recovery once the Abx-induced neuronal loss was established. In contrast, short-chain fatty acids (SCFA) were able to restore neuronal numbers after Abx-induced neuronal loss, demonstrating that SCFA stimulate enteric neurogenesis in vivo.
Our results demonstrate a role for the gut microbiota in regulating the structure and function of the GI tract in a sex-independent manner. Moreover, the microbiota is essential for the maintenance of ENS integrity, by regulating enteric neuronal survival and promoting neurogenesis. Molecular determinants of the microbiota, LPS and SCFA, regulate enteric neuronal survival, while SCFA also stimulates neurogenesis. Our data reveal new insights into the role of the gut microbiota that could lead to therapeutic developments for the treatment of enteric neuropathies. Video abstract.
•This review focuses on recent advances in our understanding of how C. difficile and its toxins modulate innate immune responses that contribute to CDI pathogenesis.•C. difficile virulence factors ...are discussed in relation to their role in activating innate immune responses.•The role of the innate immune response in CDI pathogenesis is examined by discussing the data generated from toxin-exposure and infection-based experimental models.
Clostridium difficile (C. difficile) is the most common cause of nosocomial antibiotic-associated diarrhea and the etiologic agent of pseudomembranous colitis. The clinical manifestation of C. difficile infection (CDI) is highly variable, from asymptomatic carriage, to mild self-limiting diarrhea, to the more severe pseudomembranous colitis. Furthermore, in extreme cases, colonic inflammation and tissue damage can lead to toxic megacolon, a condition requiring surgical intervention.
C. difficile expresses two key virulence factors; the exotoxins, toxin A (TcdA) and toxin B (TcdB), which are glucosyltransferases that target host-cell monomeric GTPases. In addition, some hypervirulent strains produce a third toxin, binary toxin or C. difficile transferase (CDT), which may contribute to the pathogenesis of CDI. More recently, other factors such as surface layer proteins (SLPs) and flagellin have also been linked to the inflammatory responses observed in CDI.
Although the adaptive immune response can influence the severity of CDI, the innate immune responses to C. difficile and its toxins play crucial roles in CDI onset, progression, and overall prognosis. Despite this, the innate immune responses in CDI have drawn relatively little attention from clinical researchers. Targeting these responses may prove useful clinically as adjuvant therapies, especially in refractory and/or recurrent CDI. This review will focus on recent advances in our understanding of how C. difficile and its toxins modulate innate immune responses that contribute to CDI pathogenesis.
Inflammatory bowel diseases (IBDs) are chronic relapsing and remitting conditions associated with long-term gut dysfunction resulting from alterations to the enteric nervous system and a loss of ...enteric neurons. The mechanisms underlying inflammation-induced enteric neuron death are unknown. Here using in vivo models of experimental colitis we report that inflammation causes enteric neuron death by activating a neuronal signaling complex composed of P2X7 receptors (P2X7Rs), pannexin-1 (Panx1) channels, the Asc adaptor protein and caspases. Inhibition of P2X7R, Panx1, Asc or caspase activity prevented inflammation-induced neuron cell death. Preservation of enteric neurons by inhibiting Panx1 in vivo prevented the onset of inflammation-induced colonic motor dysfunction. Panx1 expression was reduced in Crohn's disease but not ulcerative colitis. We conclude that activation of neuronal Panx1 underlies neuron death and the subsequent development of abnormal gut motility in IBD. Targeting Panx1 represents a new neuroprotective strategy to ameliorate the progression of IBD-associated dysmotility.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Background and Purpose
The pathogenesis of the inflammatory bowel diseases (IBD), comprising Crohn's disease (CD) and ulcerative colitis (UC), involves aberrant interactions between a genetically ...susceptible individual, their microbiota and environmental factors. Alterations in xenobiotic receptor expression and function are associated with increased risk for IBD. Here, we have assessed the role of the constitutive androstane receptor (CAR), a xenobiotic receptor closely related to the pregnane X receptor, in the regulation of intestinal mucosal homeostasis.
Experimental Approach
CAR expression was assessed in intestinal mucosal biopsies obtained from CD and UC patients, and in C57/Bl6 mice exposed to dextran sulphate sodium (DSS; 3.5% w/v in drinking water) to evoke intestinal inflammation and tissue damage. CAR‐deficient mice were exposed to DSS and mucosal healing assessed. Modulation of wound healing by CAR was assessed in vitro. The therapeutic potential of CAR activation was evaluated, using 3,3′,5,5′‐tetrachloro‐1,4‐bis(pyridyloxy)benzene (TCPOBOP), a selective rodent CAR agonist.
Key Results
CAR expression was reduced in CD and UC samples, compared with expression in healthy controls. This was reproduced in our DSS studies, where CAR expression was reduced in colitic mice. CAR‐deficient mice exhibited reduced healing following DSS exposure. In vitro, CAR activation accelerated intestinal epithelial wound healing by enhancing cell migration. Lastly, treating mice with TCPOBOP, following induction of colitis, enhanced mucosal healing.
Conclusion and Implications
Our results support the notion that xenobiotic sensing is altered during intestinal inflammation, and suggest that CAR activation may prove effective in enhancing mucosal healing in patients with IBD.
Rifaximin is a broad-spectrum oral antibiotic, exhibiting limited systemic absorption, that is used clinically to treat a variety of gastrointestinal disorders, including traveller's diarrhea, ...hepatic encephalopathy, irritable bowel syndrome, and the inflammatory bowel diseases. Rifaximin's antimicrobial properties, in the context of enteric infections, and its effects on the host's intestinal microbiota have been well characterized. More recently, it has been reported that rifaximin can modulate host tissue function through the activation of distinct molecular events. Within the gastrointestinal tract, rifaximin is a selective agonist of the pregnane X receptor (PXR), a nuclear receptor that regulates the expression of genes related to xenobiotic metabolism and drug detoxification. The PXR can also elicit immunomodulatory effects through its interaction with a variety of intracellular signaling cascades, including the nuclear factor kappa B and c-jun N-terminal kinase pathways. In this review, we will summarize the clinical uses of rifaximin and discuss its mechanism of action in relation to the modulation of the intestinal microbiota and the regulation of gastrointestinal host cell function, with a specific focus on PXR-dependent pathways.
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The intestinal epithelial barrier plays a key role in the maintenance of homeostasis within the gastrointestinal tract. Barrier dysfunction leading to increased epithelial ...permeability is associated with a number of gastrointestinal disorders including the inflammatory bowel diseases (IBD) – Crohn’s disease and ulcerative colitis. It is thought that the increased permeability in patients with IBD may be driven by alterations in the epithelial wound healing response. To this end considerable study has been undertaken to identify signaling pathways that may accelerate intestinal epithelial wound healing and normalize the barrier dysfunction observed in IBD.
In the current study we examined the role of the pregnane X receptor (PXR) in modulating the intestinal epithelial wound healing response. Mutations and reduced mucosal expression of the PXR are associated with IBD, and others have reported that PXR agonists can dampen intestinal inflammation. Furthermore, stimulation of the PXR has been associated with increased cell migration and proliferation, two of the key processes involved in wound healing. We hypothesized that PXR agonists would enhance intestinal epithelial repair.
Stimulation of Caco-2 intestinal epithelial cells with rifaximin, rifampicin and SR12813, all potent agonists of the PXR, significantly increased wound closure. This effect was driven by p38 MAP kinase-dependent cell migration, and occurred in the absence of cell proliferation. Treating mice with a rodent specific PXR agonist, pregnenolone 16α-carbonitrile (PCN), attenuated the intestinal barrier dysfunction observed in the dextran sulphate sodium (DSS) model of experimental colitis, an effect that occurred independent of the known anti-inflammatory effects of PCN.
Taken together our data indicate that the activation of the PXR can enhance intestinal epithelial repair and suggest that targeting the PXR may help to normalize intestinal barrier dysfunction observed in patients with IBD. Furthermore, our data provide additional insight into the potential mechanisms through which rifaximin elicits its clinical efficacy in the treatment of IBD.
Hyperglycaemia is a major contributor to diabetic cardiovascular disease with hyperglycaemia-induced endothelial dysfunction recognized as the initiating cause. Coagulation pathway-regulated ...proteinase-activated receptors (PARs) that can regulate vascular tone in vivo cause eNOS-mediated endothelium-dependent vasodilation; but, the impact of hyperglycaemia on this vasodilatory action of PAR stimulation and the signalling pathways involved are unknown. We hypothesized that vascular sodium-glucose co-transporter 2 activity and hyperglycaemia-induced oxidative stress involving Src-kinase, EGF receptor-kinase, Rho-kinase and protein-kinase-C biochemical signalling pathways would compromise PAR2-mediated endothelium-dependent vasodilation.
Using an organ culture approach, wherein murine aorta rings were maintained for 24 h at hyperglycaemic 25 mM versus euglycaemic 10 mM glucose, we observed severely blunted acetylcholine/muscarinic and PAR2-mediated endothelial eNOS/NO-dependent vasodilation. PEG-catalase, superoxide-dismutase, and NADPH-oxidase inhibition (VAS2870) and either SGLT2-inhibition (canagliflozin/dapagliflozin/empagliflozin) or antioxidant gene induction (sulforaphane), prevented the hyperglycaemia-induced impairment of PAR2-mediated vasodilation. Similarly, inhibition of Src-kinase, EGF receptor-kinase, protein kinase-C and Rho-kinase also preserved PAR2-mediated vasodilation in tissues cultured under hyperglycaemic conditions. Thus, intracellular hyperglycaemia, that can be prevented with an inhibitor of the SGLT2 cotransporter that was identified in the vascular tissue and tissue-derived cultured endothelial cells by qPCR, western blot and immunohistochemistry, leads to oxidative stress that compromises PAR2-mediated NOS-dependent vasodilation by an NAPDH oxidase/reactive-oxygen-species-triggered signalling pathway involving EGFR/Src/Rho-kinase and PKC. The data point to novel antioxidant therapeutic strategies including use of an SGLT2 inhibitor and sulforaphane to mitigate hyperglycaemia-induced endothelial dysfunction.
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