Pregnane X Receptor Activation Attenuates Inflammation-Associated Intestinal Epithelial Barrier Dysfunction by Inhibiting Cytokine-Induced Myosin Light-Chain Kinase Expression and c-Jun N-Terminal Kinase 1/2 Activation

Abstract

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-a/interferon-g 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-hydroxyphenyl]ethenylidene]bis-phosphonic acid tetraethyl ester (SR12813); 10 mM] protected the barrier, an effect that was associated with attenuated MLCK expression and JNK1/2 activation. In vivo, activation of the PXR [pregnenolone 16a-carbonitrile (PCN)] attenuated barrier disruption induced by toll-like receptor 4 activation in wild-type, but not Pxr2/2, 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 cytokineinduced MLCK expression and JNK1/2 activation. Thus, targeting the PXR may prove beneficial for the treatment of inflammationassociated barrier disruption in the context of IBD.

Constitutive androstane receptor regulates the intestinal mucosal response to injury

“…To our knowledge, this is the first report implicating the CAR in the regulation of intestinal epithelial wound healing and mucosal restitution following inflammation‐associated injury. We, and others, have reported that the PXR, a closely related receptor, plays an important role in gastrointestinal tract, regulating barrier function, inflammatory signalling and mucosal repair following injury (Shah et al, ; Cheng et al, ; Terc et al, ; Venkatesh et al, ; Garg et al, ). These studies and others, in conjunction with the data presented herein, suggest that xenobiotic receptors play a key role in the maintenance of intestinal mucosal homeostasis, and that their dysfunction may contribute to the pathogenesis of IBD.…”

“…Previous studies have suggested that xenobiotic receptors are key regulators of intestinal mucosal homeostasis, based on their ability to modulate the function of the intestinal epithelium and resident mucosal immune cell populations (Qiu et al, ; Venkatesh et al, ; Ji et al, ; Chng et al, ; Garg et al, ). We have previously reported that the PXR, a receptor closely related to the CAR, enhances intestinal epithelial wound healing and protects the mucosal barrier during inflammatory stress (Terc et al, ; Garg et al, ). Furthermore, others have characterized the anti‐colitic effects of PXR signalling (Shah et al, ; Cheng et al, ).…”

“…Recent reports suggest that metabolic products released from the intestinal microbiota may also evoke the activation of these receptors (Venkatesh et al, ; Hubbard et al, ), suggesting their function may also constitute an additional dimension of host–microbe interaction at sights of microbial colonization. Accumulating evidence suggests that the AhR and PXR play important roles within the gastrointestinal tract; enhancing intestinal epithelial barrier function (Venkatesh et al, ; Garg et al, ); modulating mucosal inflammatory signalling (Venkatesh et al, ; Ji et al, ); and regulating the function of resident immune cell populations (Qiu et al, ; Chng et al, ). In experimental models of colitis or inflammation‐induced mucosal damage, genetic ablation of the AhR or PXR enhance the severity of tissue damage (Arsenescu et al, ; Furumatsu et al, ), whereas their selective activation affords protection (Takamura et al, ; Monteleone et al, ).…”

Understanding the Holobiont: How Microbial Metabolites Affect Human Health and Shape the Immune System

“…Nr1i2 −/− mice exhibit impaired epithelial barrier function, and administration of synthetic NR1I2 agonists exerts protective effects in mouse models of colitis (Dou et al, 2013; Garg et al, 2016; Shah et al, 2007; Terc et al, 2014; Venkatesh et al, 2014). Interestingly, the combined knockout of Nr1i2 and the gene encoding the LPS sensor toll-like receptor 4 ( Tlr4 ) can rescue the phenotype of Nr1i2 −/− mice, possibly because it counteracts the accelerated cell death of inflammatory monocytes observed in NR1I2-deficient mice (Z.…”

The xenobiotic sensing pregnane X receptor regulates tissue damage and inflammation triggered byC difficiletoxins

“…The PXR is highly expressed in the liver and intestine where it can regulate nuclear factor κ‐light‐chain‐enhancer of B cells (NFκB) activation and the expression of a number of inflammatory mediators . Importantly, PXR signaling in the intestine can dampen TLR4 signaling to promote intestinal barrier function and prevent inflammation in the GI tract . The influence of the PXR in the modulation of enteric infections has also emerged with evidence for the involvement of a PXR‐TLR4–driven mechanism .…”