Proenkephalin deletion in hematopoietic cells induces intestinal barrier failure resulting in clinical feature similarities with irritable bowel syndrome in mice

Opioid-dependent immune-mediated analgesic effects have been broadly reported upon inflammation. In preclinical mouse models of intestinal inflammatory diseases, the local release of enkephalins (endogenous opioids) by colitogenic T lymphocytes alleviate inflammation-induced pain by down-modulating gut-innervating nociceptor activation in periphery. In this study, we wondered whether this immune cell-derived enkephalin-mediated regulation of the nociceptor activity also operates under steady state conditions. Here, we show that chimeric mice engrafted with enkephalin-deficient bone marrow cells exhibit not only visceral hypersensitivity but also an increase in both epithelial paracellular and transcellular permeability, an alteration of the microbial topography resulting in increased bacteria-epithelium interactions and a higher frequency of IgA-producing plasma cells in Peyer's patches. All these alterations of the intestinal homeostasis are associated with an anxiety-like behavior despite the absence of an overt inflammation as observed in patients with irritable bowel syndrome. Thus, our results show that immune cell-derived enkephalins play a pivotal role in maintaining gut homeostasis and normal behavior in mice. Because a defect in the mucosal opioid system remarkably mimics some major clinical symptoms of the irritable bowel syndrome, its identification might help to stratify subgroups of patients. The study shows, by using hematopoietic chimeric mice, that mucosal immune cell-derived enkephalins play a pivotal role in maintaining gut homeostasis including visceral sensitivity and normal behavior in mice.

Automated summary

Immune cell-derived enkephalins play a crucial role in maintaining gut homeostasis and normal behavior in mice, and defects in this system can mimic major symptoms of irritable bowel syndrome. These findings provide new insights into the classification and treatment of intestinal diseases.