Neuropeptide Y regulation of mouse colon epithelial ion transport in health and colitis.

摘要

Neuropeptide Y (NPY) plays an important antisecretory role in the gut, acting primarily through the epithelial Y1 receptors and neuronal Y2 receptors. Inflammation alters ion transport in the colon. However, whether there are changes to the NPY antisecretory effect due to intestinal inflammation is not known. To test the hypothesis that colonic tissue from mice with dextran-sodium sulfate (DSS)-induced colitis was hyper-responsive to NPY, I assessed the antisecretory role of NPY in proximal and distal regions of the colon, and compared this with responses in colon from normal, control mice. Colons were removed from C57Bl/6 (or Balb/c or CD1) mice and 2 cm segments, directly proximal and directly distal to the colonic midline were used for Ussing chamber experiments, quantitative analysis of Y1 and Y 2 receptor mRNA expression by real-time PCR, and Y1 receptor localization by immunohistochemistry. Ionic conductance and the secretory response to forskolin were used to ensure tissue viability. Colitis was induced by treatment with DSS (4% wt/vol) in drinking water for 5 days followed by 3 days of autoclaved tap water. A concentration response curve was generated for NPY in control tissues. Distal colon responded to NPY in a concentration dependent manner (threshold concentration of 10-9), with a concentration of 10-7M resulting in a drop in short-circuit current (ISC) of -51.4 +/- 9.1 muA/cm2 (n=6). Proximal control tissue was largely unresponsive to NPY treatment. The antisecretory effect seen in distal tissue was tetrodotoxin-insensitive, Cl--dependent and primarily mediated via the Y1 receptor. Distal colonic tissue from mice treated with DSS-colitis was hyporesponsive to NPY (10- 7M) treatment (DeltaISC = -3.3 +/- 1.1 muA/cm2, n=5) when compared to time-matched control distal colon (DeltaISC = -29.8 +/- 7.2 muA/cm2). Like tissue from control animals, proximal colonic segments from mice with DSS-induced colitis were unresponsive to NPY treatment. Y1 receptor mRNA and protein was more highly expressed in the distal colon, when compared to proximal colon, using real-time PCR and immunohistochemistry. Y1 receptor mRNA was shown to be less in distal colon mucosal scrapings in colitic mice, compared to controls. Also, DSS colitis was shown to perturb the crypt architecture in the distal colon, which lead to the disorganization of Y 1 receptor localization. In conclusion NPY plays an important, antisecretory role in the distal colon of control mice, but has little effect in the proximal colon. This response is lost in DSS-induced colitis, possibly due to reduced Y1 receptor expression in the colonic epithelium and the destruction of the crypt architecture. This loss of antisecretory function may contribute to the diarrhoea seen in DSS-colitis, and if similar effects are seen in human colonic tissue, inflammatory bowel disease.Funded by CCFC, NSERC, and the CCFC Chair in IBD Research