Optogenetic inhibition of the colon epithelium reduces hypersensitivity in a mouse model of inflammatory bowel disease

Abstract

Visceral pain is a prevalent symptom of inflammatory bowel disease (IBD) that can be difficult to treat. Pain and hypersensitivity are mediated by extrinsic primary afferent neurons (ExPANs) that innervate the colon. Recent studies indicate that the colon epithelium contributes to initiating ExPAN firing and nociceptive responses. Based on these findings we hypothesized that the epithelium contributes to inflammation-induced hypersensitivity. A key prediction of this hypothesis is that inhibition of the epithelium would attenuate nociceptive signaling and inflammatory hypersensitivity. To test this hypothesis, the inhibitory yellow light activated protein archaerhodopsin was targeted to the intestinal epithelium (villin-Arch) or the ExPANs (TRPV1-Arch) that innervate the colon. Visceral sensitivity was assessed by measuring the visceromotor response (VMR) to colorectal distension (CRD), with and without yellow light illumination of the colon lumen. Inhibition of the colon epithelium in healthy villin-Arch mice significantly diminished the CRD-induced VMR. Direct inhibition of ExPANs during CRD using TRPV1-Arch mice showed that ExPAN and epithelial inhibition were similarly effective in reducing the VMR to CRD. We then investigated the effect of epithelial and ExPAN inhibition in the dextran sulfate sodium (DSS) model of inflammatory bowel disease (IBD). Inhibition of the colon epithelium significantly decreased DSS-induced hypersensitivity and was comparable to inhibition of ExPANS. Together these results reveal the potential of targeting the colon epithelium for treatment of pain. .

Pain in Inflammatory Bowel Disease: Optogenetic Strategies for Study of Neural–Epithelial Signaling

“… 5 In other studies, it was found that decreasing activity of epithelial cells reduced pain associated with colon inflammation. 6 These findings contribute to a growing body of research that is defining how epithelial cells communicate with nerve fibers, glial cells, and immune cells within the gut and the functional significance of these interactions. They also support the prioritization of treatment strategies for IBD that promote repair of the epithelial lining as a means to reduce pain.…”

“…Stimulation of the colon epithelium engages neural circuits, suggesting that a reduction in epithelial activity might inhibit neuronal firing and in so doing, reduce visceral nociception (VMRs). Studies done using mice that express the inhibitory yellow light-activated Arch-EGFP protein in colon epithelial cells (Vil-Arch mice) showed this to be the case 6 ( Figure 2A ). The ability of Arch-mediated inhibition of epithelial cells to block pain was assessed by in vivo measure of VMRs in response to colorectal distension in the presence or absence of Arch stimulation.…”

“…Importantly, in mice with colitis induced by dextran sodium sulfate (DSS; 3% in drinking water), Arch-mediated inhibition of the epithelium reduced VMRs by 55%. 6 Thus, inhibition of colon epithelial cells reduced pain-like responses to distension in both healthy mice and in mice with DSS-induced inflammation.…”

“… 3 The disconnect between inflammation and pain, as well as a new understanding of the impact of the microbiome profile on pain, 14–16 suggests pain may involve changes unrelated to immune signaling. In this regard, recent studies of epithelial cells of the skin 17 and colon 5 , 6 using optogenetic approaches suggest a direct role for the epithelium in driving neural activity and activation of pain pathways.…”

“…In this regard, here we review recent studies that support a role for the lining epithelial cells of the colon as contributors to pain signaling in the absence of elevated inflammation. 5 , 6 Analysis of optogenetic mouse models that allow specific targeting of the epithelium has shown that increasing the activity of epithelial cells is sufficient to activate pain-sensing neurons and cause an increase in behavioral pain responses. 5 In other studies, it was found that decreasing activity of epithelial cells reduced pain associated with colon inflammation.…”