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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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.
Fibrosis is a common complication of inflammatory bowel diseases (IBDs). The pregnane X receptor (PXR) (encoded by NR1I2) suppresses intestinal inflammation and has been shown to influence liver ...fibrosis. In the intestine, PXR signaling is influenced by microbiota-derived indole-3-propionic acid (IPA). Here, we sought to assess the role of the PXR in regulating intestinal inflammation and fibrosis.
Intestinal inflammation was induced using dextran sulfate sodium (DSS). Fibrosis was assessed in wild-type (WT), Nr1i2-/-, epithelial-specific Nr1i2-/-, and fibroblast-specific Nr1i2-/- mice. Immune cell influx was quantified by flow cytometry and cytokines by Luminex. Myofibroblasts isolated from WT and Nr1i2-/- mice were stimulated with cytomix or lipopolysaccharide, and mediator production was assessed by quantitative polymerase chain reaction and Luminex.
After recovery from DSS-induced colitis, WT mice exhibited fibrosis, a response that was exacerbated in Nr1i2-/- mice. This was correlated with greater neutrophil infiltration and innate cytokine production. Deletion of the PXR in fibroblasts, but not the epithelium, recapitulated this phenotype. Inflammation and fibrosis were reduced by IPA administration, whereas depletion of the microbiota exaggerated intestinal fibrosis. Nr1i2-deficient myofibroblasts were hyperresponsive to stimulation, producing increased levels of inflammatory mediators compared with WT cells. In biopsies from patients with active Crohn’s disease (CD) and ulcerative colitis (UC), expression of NR1I2 was reduced, correlating with increased expression of fibrotic and innate immune genes. Finally, both CD and UC patients exhibited reduced levels of fecal IPA.
These data highlight a role for IPA and its interactions with the PXR in regulating the mesenchyme and the development of inflammation and fibrosis, suggesting microbiota metabolites may be a vital determinant in the progression of fibrotic complications in IBD.
Cancer cell lines have been the mainstay of intestinal epithelial experimentation for decades, due primarily to their immortality and ease of culture. However, because of the inherent biological ...abnormalities of cancer cell lines, many cellular biologists are currently transitioning away from these models and toward more representative primary cells. This has been particularly challenging, but recent advances in the generation of intestinal organoids have brought the routine use of primary cells within reach of most epithelial biologists. Nevertheless, even with the proliferation of publications that use primary intestinal epithelial cells, there is still a considerable amount of trial and error required for laboratories to establish a consistent and reliable method to culture three-dimensional (3D) intestinal organoids and primary epithelial monolayers. We aim to minimize the time other laboratories spend troubleshooting the technique and present a standard method for culturing primary epithelial cells. Therefore, we have described our optimized, high-yield, cost-effective protocol to grow 3D murine colonoids for more than 20 passages and our detailed methods to culture these cells as confluent monolayers for at least 14 days, enabling a wide variety of potential future experiments. By supporting and expanding on the current literature of primary epithelial culture optimization and detailed use in experiments, we hope to help enable the widespread adoption of these innovative methods and allow consistency of results obtained across laboratories and institutions.
Primary intestinal epithelial monolayers are notoriously difficult to maintain culture, even with the recent advances in the field. We describe, in detail, the protocols required to maintain three-dimensional cultures of murine colonoids and passage these primary epithelial cells to confluent monolayers in a standardized, high-yield and cost-effective manner.
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.
C. difficile is a Gram-positive spore-forming anaerobic bacterium that is the leading cause of nosocomial diarrhea in the developed world. The pathogenesis of C. difficile infections (CDI) is driven ...by toxin A (TcdA) and toxin B (TcdB), secreted factors that trigger the release of inflammatory mediators and contribute to disruption of the intestinal epithelial barrier. Neutrophils play a key role in the inflammatory response and the induction of pseudomembranous colitis in CDI. TcdA and TcdB alter cytoskeletal signaling and trigger the release of CXCL8/IL-8, a potent neutrophil chemoattractant, from intestinal epithelial cells; however, little is known about the surface receptor(s) that mediate these events. In the current study, we sought to assess whether toxin-induced CXCL8/IL-8 release and barrier dysfunction are driven by the activation of the P2Y6 receptor following the release of UDP, a danger signal, from intoxicated Caco-2 cells. Caco-2 cells express a functional P2Y6 receptor and release measurable amounts of UDP upon exposure to TcdA/B. Toxin-induced CXCL8/IL-8 production and release were attenuated in the presence of a selective P2Y6 inhibitor (MRS2578). This was associated with inhibition of TcdA/B-induced activation of NFκB. Blockade of the P2Y6 receptor also attenuated toxin-induced barrier dysfunction in polarized Caco-2 cells. Lastly, pretreating mice with the P2Y6 receptor antagonists (MSR2578) attenuated TcdA/B-induced inflammation and intestinal permeability in an intrarectal toxin exposure model. Taken together these data outline a novel role for the P2Y6 receptor in the induction of CXCL8/IL-8 production and barrier dysfunction in response to C. difficile toxin exposure and may provide a new therapeutic target for the treatment of CDI.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Background
The pregnane X receptor (PXR) is a xenobiotic sensing nuclear receptor that is activated by a diverse array of substances, including environmental toxins, pharmaceutical compounds and ...metabolites released from the intestinal microbiota. While the PXR's prototypical role is to regulate the expression of the drug metabolizing/detoxifying genes in the liver and intestinal epithelium, we and others have reported that it plays a role in regulating inflammatory signaling. More specifically, the PXR can inhibit NFκB‐dependent inflammatory signaling and regulates the function/expression of innate immune receptors, including TLR4 and NLRP3. In the current study, we sought to characterize the function of the PXR in macrophages. Given the interactions between the PXR and innate immune receptors described in other non‐immune cell types, we hypothesized that its activation would modulate NLRP3 inflammasome activation and the resulting processing/release of IL‐1β.
Aims
To evaluate the effect of PXR activation of NLRP3 inflammasome activation and to determine the mechanism(s) whereby the PXR modulates inflammasome activity.
Methods
Mouse peritoneal macrophages and PMA‐differentiated THP‐1 cells were used to assess NLRP3 inflammasome activation. Due to species‐specific ligand interactions with the PXR, in mouse studies we used pregnenolone 16α‐carbonitrile (PCN), whereas in THP‐1 experiments, we used the human PXR agonists, rifaximin and SR12813. To test if PXR activation modulated NLRP3 inflammasome activation, LPS‐primed macrophages or PMA‐differentiated THP‐1 were pretreated for one hour with PXR agonists and then challenged with ATP (5mM), a known NLRP3 inflammasome activator. Caspase‐1 cleavage and IL‐1β secretion were measured to assess inflammasome activation. In some experiments, extracellular ATP was measured following PXR agonist treatment.
Results
While PXR activation had no effect on ATP‐induced NLRP3 inflammasome activation, each PXR agonist alone stimulated the cleavage of caspase‐1 and the secretion of IL‐1ββ, reminiscent of inflammasome activation. In PXR−/− macrophages, these responses were absent, supporting a direct role of the PXR in these responses. Deletion of NLRP3 in mouse macrophages and THP‐1 cells attenuated PXR agonist‐induced caspase‐1 cleavage and IL‐1β secretion, suggesting that PXR activation triggers NLRP3 inflammasome activation. Furthermore, PXR driven responses were attenuated following caspase‐1 inhibition. Mechanistically, NLRP3 activation by the PXR did not involve ROS production, nor was it sensitive to chelation of intracellular calcium. However, treating cells with apyrase, to catabolize extracellular ATP, or selective inhibition of the P2X7 receptor attenuated PXR agonist‐induced caspase‐1 activation and IL‐1β secretion. Interestingly, we subsequently found that PXR activation led to a rapid (within 15 seconds) increase in extracellular ATP, reaching levels previous described in NLRP3 inflammasome activation models. This response was absent in PXR−/− cells, supporting a direct role of the PXR in ATP release.
Conclusions
Taken together, our data suggest that activation of the xenobiotic sensing PXR triggers the release of ATP, which in turn causes NLRP3 inflammasome activation in macrophages. These findings suggest a novel mechanism whereby non‐microbial/non‐viral agents of environmental origin can stimulate innate immune responses and contribute to inflammatory disease.
Support or Funding Information
Crohn's and Colitis Canada
NSERC
Lloyd Sutherland Investigatorship in IBD/GI research
This is from the Experimental Biology 2018 Meeting. There is no full text article associated with this published in The FASEB Journal.
Abstract only
Intestinal fibrosis and stricture formation are common complications of Crohn’s disease (CD). Recently, the stricturing phenotype has been recognized to be primarily attributable to ...hypertrophy/hyperplasia of smooth muscle, rather than an increase in fibrosis alone. Despite advances in treatment of CD, current therapies do little to prevent or reverse strictures. NR4A1 is an orphan nuclear receptor that has been reported as anti‐fibrotic in non‐intestinal systems and exhibits anti‐proliferative effects in smooth muscle cells (SMCs).
NR4A1
gene variants have been associated with increased risk of inflammatory bowel disease, however, the mechanisms regulating NR4A1 expression and its role in intestinal SMC function have not been investigated.
We sought to characterize and understand the role of NR4A1 activation in the regulation of mitogen‐induced proliferation of intestinal SMCs. We hypothesized that the activation of NR4A1 negatively regulates proliferative signaling and cell survival in intestinal SMCs.
To test the hypothesis, primary intestinal SMCs were isolated from Nr4a1
+/+
and Nr4a1
−/−
mice. Furthermore, a commercially sourced human primary intestinal SMC line was used. To assess the response of SMCs to culture and identify growth differences, proliferation was measured via trypan blue exclusion and EdU incorporation. In mouse and human SMCs, proliferation was induced by platelet‐derived growth factor‐BB (PDGF‐BB) and NR4A1 activation was assessed by pretreating with selective agonists, cytosporone‐B (Csn‐B) and 6‐mercaptopurine (6‐MP), at various concentrations. Mass spectrometry was used to characterize proteomic differences between Nr4a1
+/+
and Nr4a1
−/−
SMCs. Expression levels of NR4A1 were assessed by qPCR and western blot after mitogen exposure and Csn‐B treatment.
Nr4a1
−/−
cells exhibited a significantly higher rate of proliferation compared to Nr4a1
+/+
cells, under both basal and mitogen‐exposed conditions. Proteomic analysis showed that Nr4a1
−/−
SMCs exhibited increased expression of proteins related to the cell cycle and metabolism, compared to Nr4a1
+/+
SMCs. Pretreating human intestinal SMCs with Csn‐B and 6‐MP significantly attenuated proliferation induced by PDGF‐BB. Similar effects were observed in Nr4a1
+/+
SMCs, however, the anti‐proliferative effect of Csn‐B was absent in Nr4a1
−/−
cells. Furthermore, NR4A1 expression was rapidly induced by Csn‐B and PDGF‐BB, the latter response suggesting the existence of a potential negative feedback mechanism to control mitogen‐induced SMC proliferation.
Our results suggest that NR4A1 is a critical regulator of intestinal SMC proliferation and its induction by mitogens may contribute to a negative feedback loop to control smooth muscle growth. These data support targeting NR4A1 to treat excessive smooth muscle hypertrophy/hyperplasia that contributes to tissue remodelling observed in fibrostenotic CD.
Support or Funding Information
Canadian Institutes of Health Research
The inflammatory bowel diseases (IBDs) are chronic inflammatory disorders with a complex etiology. IBD is thought to arise in genetically susceptible individuals in the context of aberrant ...interactions with the intestinal microbiota and other environmental risk factors. Recently, the pregnane X receptor (PXR) was identified as a sensor for microbial metabolites, whose activation can regulate the intestinal epithelial barrier. Mutations in NR1I2, the gene that encodes the PXR, have been linked to IBD, and in animal models, PXR deletion leads to barrier dysfunction. In the current study, we sought to assess the mechanism(s) through which the PXR regulates barrier function during inflammation. In Caco-2 intestinal epithelial cell monolayers, tumor necrosis factor-α/interferon-γ exposure disrupted the barrier and triggered zonula occludens-1 relocalization, increased expression of myosin light-chain kinase (MLCK), and activation of c-Jun N-terminal kinase 1/2 (JNK1/2). Activation of the PXR rifaximin and 3,5-Bis(1,1-dimethylethyl)-4-hydroxyphenylethenylidenebis-phosphonic acid tetraethyl ester (SR12813); 10 μM protected the barrier, an effect that was associated with attenuated MLCK expression and JNK1/2 activation. In vivo, activation of the PXR pregnenolone 16α-carbonitrile (PCN) attenuated barrier disruption induced by toll-like receptor 4 activation in wild-type, but not Pxr-/-, mice. Furthermore, PCN treatment protected the barrier in the dextran-sulfate sodium model of experimental colitis, an effect that was associated with reduced expression of mucosal MLCK and phosphorylated JNK1/2. Together, our data suggest that the PXR regulates the intestinal epithelial barrier during inflammation by modulating cytokine-induced MLCK expression and JNK1/2 activation. Thus, targeting the PXR may prove beneficial for the treatment of inflammation-associated barrier disruption in the context of IBD.
Abstract only
INTRODUCTION
Fibrosis contributes to intestinal strictures and obstruction in 30–50% of Crohn's disease patients. The pathogenesis of intestinal fibrosis is incompletely understood and ...has virtually no effective treatments. The pregnane X receptor (PXR), a xenobiotic receptor involved in detoxification responses, has recently been identified as a modulator of fibrosis in hepatic stellate cells. Of the number of foreign ligands for the PXR, the tryptophan metabolite indole‐3‐propionic acid (IPA) produced by the intestinal commensal
Clostridium sporogenes
can bind to the PXR to mediate signalling events that protect intestinal barrier function. The role of the PXR in intestinal fibrosis and if microbial metabolite sensing can affect intestinal fibrotic responses is unknown.
AIMS
To examine the role of the PXR and its ability to sense microbial metabolites in the modulation of intestinal fibrosis.
METHODS
Intestinal inflammation was induced using DSS (3.5%) for 5 days followed by healing for 25 days. Fibrosis was assessed using Masson‐trichrome and Serius Red staining of histological sections. Mouse primary fibroblasts were grown from wild type (WT) and PXR
−/minus;
mice. Fibroblasts were stimulated with cytomix (TNF‐α, IL‐1β, and IFN‐γ) for 24 hours after which cell supernatants were assessed for cytokine concentrations using Luminex. Fibroblasts were also stimulated with cytomix in the presence of the PXR agonists pregnenolone 16α‐carbonitrile (PCN) or IPA and assessed for gene expression using qPCR. NFκB activity was assessed via Western blot for the p65 subunit. To examine the microbiota's role in fibrosis, the microbiota was depleted after the 5‐day course of DSS for 25 days using an antibiotic cocktail of vancomycin, neomycin, metronidazole and ampicillin.
FINDINGS
Following a 25‐day recovery after DSS, WT mice showed clear evidence of fibrosis as indicated by Masson‐trichrome and Serius Red staining. When compared to WT mice, PXR
−/−
mice demonstrated significantly greater levels of fibrosis. Mouse primary fibroblasts were found to express the PXR, and PXR
−/−
fibroblasts displayed morphological differences compared to WT fibroblasts. Following stimulation with cytomix, PXR
−/−
fibroblasts produced dramatically higher levels of proinflammatory cytokines including eotaxin, CXCL2, GM‐CSF, G‐CSF and IL‐9. Importantly, PCN and the microbial metabolite IPA were able to block the expression of these cytokines. These effects in PXR
−
/
−
fibroblasts may be linked to the increased activity of NFκB that was observed both basally and after stimulation with cytomix compared to WT fibroblasts. Depletion of the microbiota led to exacerbated intestinal fibrosis.
CONCLUSIONS
PXR signaling in intestinal fibroblasts appears to be required to restrain inflammation and fibrosis. Luminal sensing of bacterial derived indoles (ie. IPA) via PXR may be involved in this process, highlighting a xenobiotic receptor‐microbiota axis that could be targeted to prevent the intestinal fibrosis observed in Crohn's disease.
Support or Funding Information
Crohn's & Colitis Canada, Dr. Keith Sharkey's CCFC Chair in IBD Research, The Dr. Lloyd Sutherland Investigator in IBD/GI Research, Canadian Foundation for Innovation, Canada Research Chairs Program, US Department of Defense, Beverley Philips Rising Star Fellowship.
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