Modulation of enteric neurons by interleukin‐6 and corticotropin‐releasing factor contributes to visceral hypersensitivity and altered colonic motility in a rat model of irritable bowel syndrome

Abstract

Key pointsr Hyperactivity of the stress system and low-grade immune activation characterize the functional bowel disorder irritable bowel syndrome (IBS).r These studies show that interleukin (IL)-6 and IL-8 and the stress hormone corticotropin-releasing factor (CRF), present in IBS plasma, have functional effects on gastrointestinal activity by stimulating myenteric neurons and colonic contractions.r Moreover, in the Wistar Kyoto rat model of IBS, which exhibits altered gastrointestinal motility and visceral pain sensitivity, blocking IL-6 and/or CRF1 receptors alleviates these IBS-like symptoms.r Underlying these effects are altered colonic protein expression of tight junction proteins which regulate gut barrier function and the T-type calcium channel Ca V 3.2, which has been linked to visceral pain.r These findings demonstrate the importance of the enteric nervous system and intestinal physiology in bowel dysfunction. AbstractThe search for effective therapeutic strategies for irritable bowel syndrome (IBS) is hampered by an incomplete understanding of its underlying pathophysiology. Stress and altered plasma cytokine profiles indicative of immune activation are characteristic of the disorder. The neuromodulatory effects of interleukin-6 (IL-6) and corticotropin-releasing factor receptor (CRFR) 1 in visceral pain and stress-induced defecation in the Wistar Kyoto (WKY) rat model of IBS were investigated. Sprague Dawley and WKY rats were administered anti-IL-6 receptor antibodies (xIL-6R, 0.5 mg kg −1 I.P) with or without the CRFR1 antagonist antalarmin (10 mg kg −1 I.P). Post-intervention, the pain threshold to colorectal distension and stress-induced faecal output were compared and changes in colonic mucosal protein expression were investigated. The neuro-stimulatory effects of IBS plasma on the myenteric plexus is mediated by IL-6, IL-8 and CRF. The stimulatory effects of these soluble factors on myenteric neuron excitability and colonic contractility were additive. Moreover, inhibition of IL-6 and CRF1 receptors in vivo in the WKY IBS rat model normalized stress-induced defecation (P < 0.01) and visceral pain sensitivity (P < 0.001) with associated changes in protein expression of the tight junction proteins occludin and claudin 2, the visceral pain-associated T-type calcium channel Ca V 3.2 and intracellular signalling molecules STAT3, SOCS3 and ERK1/2. These studies demonstrate the additive effects of immune and stress factors on myenteric neuronal excitability. Moreover, combined targeting of peripheral IL-6 and CRF1 receptors is effective in alleviating IBS-like symptoms in the WKY rat. Thus, crosstalk between stress and immune factors during IBS flares may underlie symptom exacerbation.

Neuroimmune Cross Talk in the Gut. Neuroendocrine and neuroimmune pathways contribute to the pathophysiology of irritable bowel syndrome

“…Cytokines facilitate cell-to-cell signaling in an immune response, but may also participate in modulating intrinsic and afferent nerve activity. Indeed, IL-6 (6, 63), IL-1β (86) and tumor necrosis factor α (72) have direct actions on enteric neuronal activation and we observed that the neurostimulatory effects of IBS plasma on rat submucosal and myenteric neurons is dependent on IL-6, IL-8 and CRF (6,62). Such cytokines stimulate sensitization of nociceptors, which would increase the excitability of afferent endings innervating the colon.…”

“…Although the effects of CRF in the CNS are crucial to regulation of the GI tract, receptors are also expressed in the colon where they are ideally placed to mediate the effects of stress on gastric emptying, transit and gut motility. In support of the importance of peripheral regulation of GI function are studies demonstrating that stress-induced defecation and visceral hypersensitivity is attenuated by blocking peripheral CRF1 receptor activation (6,30,55). However, our studies also noted the potential role of inflammatory molecules in symptoms such as visceral pain and stress-induced defecation and the potential for crosstalk between stress and immune molecules in the manifestation of IBS symptom flares.…”

“…Moreover, stress induces degranulation of mast cells, resulting in the release of pro-inflammatory mediators (40, 57). The efficacy of CRF1 receptor antagonists in animal models (6,30,55) is encouraging, however, clinical trials using such antagonists have thus far been disappointing, primarily due to unfavorable pharmacokinetics, tissue accumulation, high protein binding and reactive metabolite formation (31). Moreover, pexacerafont, an orally active, selective CRFR1 antagonist had no effect on colonic transit in diarrhea-predominant IBS, indicating that CRF 1 receptors may not constitute a useful therapeutic target in humans (80).…”

Potential Regulatory Effects of Corticotropin-Releasing Factor on Tight Junction-Related Intestinal Epithelial Permeability are Partially Mediated by CK8 Upregulation

“…Some recent studies have shown that CRF may cause changes in the expression and distribution of TJ proteins [24, 25], resulting in the increased permeability of intestinal epithelial cells [26]. Moreover, CRF can induce changes in keratin expression [27, 28].…”

Role of Corticotropin-releasing Factor Signaling in Stress-related Alterations of Colonic Motility and Hyperalgesia

“…80,140 or in a variety of experimental models inducing visceral hyperalgesia including acute or repeated exposure to WAS alone or combined with neonatal maternal separation, consecutive sets of nociceptive CRD, repeated daily CRD 6 weeks after the development of colitis, intracolonic infusion of 0.5% acetic acid, or performing the CRD in a high-anxiety rat strain, the Wistar Kyoto (WKO). 80,90,[140][141][142][143][144][145][146][147][148][149][150][151][152] Likewise in CRF 1 receptor knockout mice, the visceral motor response to phasic CRD is reduced. 149 …”