Enteric Glia Contribute to Visceral Hypersensitivity Through Interactions with Nociceptors

Abstract

Enteric glia regulate gut motility, secretions, and neuroinflammation through intercellular signaling mechanisms that involve connexin‐43 (Cx43) hemichannels. Glial Cx43 signaling is active during the acute phase of colitis when the sensitization of nociceptors occurs, but how glia contribute to nociceptor sensitization is not known. Here, we tested the hypothesis that alterations to intercellular signaling between glia and nociceptors mediated by Cx43 contribute to the sensitization of nociceptors during gut inflammation. We used the dinitrobenzene sulfonic acid (DNBS) model of acute colitis and tested the effects on enteric glia using immunohistochemistry, multiplex immunoassays, and ethidium bromide dye uptake to measure glial Cx43 channel activity. Specific interactions between glia and nociceptors were assessed using the glial specific GFAP::hM3Dq DREADD mouse model in combination with visceromotor reflex recordings and pERK expression, and by directly recording nociceptor nerve fiber activity in TRPV1‐GCaMP5g‐tdT mice. DNBS colitis drove an increase in proinflammatory cytokines including IL6, TNFα, and IL17, and IL1β showed a 5‐fold increase (p<0.05) at peak inflammation. Enteric glia contribute to IL1β production and immunolabeling data showed a 40% increase in glial IL1β (p<0.05) that was confirmed by RNAseq data (2‐fold, p<0.05). The pro‐inflammatory mediators IL1β, IL6, INFy, and TNFα increased glial dye uptake under basal conditions and IL1β and IL6 potentiated ADP‐stimulated dye uptake by 24% and 53%, respectively (p<0.0001), in a Cx43‐dependent manner. The selective activation of glial cells with clozapine‐N‐oxide in GFAP::hM3Dq mice increased visceromotor responses to colorectal distensions (p<0.05) and drove pERK expression in TRPV1+ sensory nerve fibers in the myenteric plexus. Neither IL1β nor glial activation alone significantly affected Ca2+ responses to capsaicin in TRPV1+ nerve fibers in the colon. However, glial activation in the presence of IL1β significantly potentiated nociceptor Ca2+ responses to capsaicin and this effect required signaling through Cx43 hemichannels. Our data show that enteric glia can affect the sensitivity visceral nociceptors in the context of inflammation through mechanisms that include the potentiation of glial Cx43 hemichannel function by IL1β and the subsequent sensitization of TRPV1 channels expressed by sensory neurons.Support or Funding InformationNational Institute of Health through NIDDK: R01DK103723, R01DK120862