Colonic soluble mediators from the maternal separation model of irritable bowel syndrome activate submucosal neurons via an interleukin-6-dependent mechanism

Abstract

Irritable bowel syndrome (IBS) is characterized by episodic bouts of abdominal pain, bloating, and altered bowel habit. Accumulating evidence has linked immune activation with IBS, including reports of increases in circulating levels of the proinflammatory cytokine interleukin (IL)-6. However, it is unknown whether IL-6 contributes directly to disease manifestation. As enteric nervous activity mediates motility and secretory function, the aims of this study were to determine the effects of IL-6 on submucosal neurons and related gastrointestinal (GI) function. In these studies, we examined the colons of maternally separated (MS) rats, which exhibit elevated circulating levels of IL-6 in addition to GI dysfunction. To our knowledge, these studies are the first to provide evidence of the sensitivity of submucosal neurons to colonic secretions from MS rats ( n = 50, P < 0.05), thus recapitulating clinical biopsy data. Moreover, we demonstrated that the excitatory action is IL-6 dependent. Thereafter, the impact of IL-6 on neuronal and glial activation and absorpto/secretory function was pharmacologically characterized. Other proinflammatory cytokines including IL-8 ( n = 30, P > 0.05), IL-1β ( n = 56, P > 0.05), and TNF-α ( n = 56, P > 0.05) excited fewer neurons. Both muscarinic and nicotinic cholinergic receptors participate in the effect and cause downstream activation of ERK, JAK-STAT, and NF-κB signaling cascades. Functionally, IL-6 increases transepithelial resistance and enhances neurally and cholinergically mediated ion transport. These data provide a role for IL-6 in colonic secretory functions and relate these effects to GI dysfunction in an animal model of IBS, thereby elucidating a potential relationship between circulating levels of IL-6 and aberrant GI function.