Regulation of ion transpot by short chain fatty acids receptor, GPR43 in colonic epithelia

短链脂肪酸(SCFA)，如醋酸盐、丙酸和丁酸，是大肠管腔中的主要阴离子。它们是由细菌发酵的膳食纤维产生的，已知对肠道有多种生理和病理生理作用。在本研究中，我研究了(1)SCFA受体GPR43在大鼠和人结肠中的表达，(2)大鼠结肠粘膜离子转运的调节。逆转录/聚合酶链式反应(RT-PCR)、Western blotting和免疫组织化学方法检测GPR43的表达。RT-PCR法检测到GPR43在回肠和结肠的全壁、分离粘膜和回肠的肌肉+粘膜下层提取液中表达，而在大鼠和人结肠的肌肉+粘膜下层提取液中未检测到GPR43的表达。我还制备了特异性的GPR43抗血清。免疫印迹分析显示GPR43蛋白在整壁和分离粘膜提取液中表达，而在肌肉和粘膜下层提取液中检测不到。免疫组织化学显示，GPR43免疫反应定位于表达YY肽(PYY)的肠内分泌细胞，而5-羟色胺免疫反应阳性的肠内分泌细胞不表达GPR43。表达5-羟色胺的固有层肥大细胞也呈GPR43免疫反应阳性。本研究结果提示含PYY的肠内分泌细胞和含5-羟色胺的粘膜肥大细胞通过GPR43受体感受SCFAs。在生理学研究中，粘膜中加入SCFAs以浓度依赖的方式引起短路电流的增加。这种反应可被神经元阻滞剂河豚毒素抑制。这些分子生物学和生理学研究表明，GPR 43感受腔内SCFA，并诱导结肠中的离子运输。因此，GPR43对结肠功能具有重要的调节作用。

Short-chain fatty acids (SCFAs), such as acetate, propionate, and butyrate, are the major anions in the large intestinal lumen. They are produced from dietary fiber by bacterial fermentation and are known to have a variety of physiological and pathophysiological effects on the intestine.In the present study, I have investigated (1) the expression of SCFA receptor, GPR43 in the rat and human colon and (2) the regulation of ion transport in rat colonic mucosa. Expression of GPR43 was detected by reverse transcriptase/polymerase chain reaction (RT PCR), western blotting, and immunohistochemistry. mRNA for GPR43 was detected, by RT-PCR, in extracts of the whole wall and separated mucosa from the ileum and colon and from muscle plus submucosa from the ileum, but not from muscle plus submucosa preparation from the rat and human colon. I have also made specific GPR43 antiserum. GPR43 protein was detected by western blot analysis in extract of whole wall and separated mucosa, but not in muscle plus submucosa extracts. By immunohistochemistry, GPR43 immunoreactivity was localized to enteroendocrine cells expressing peptide YY (PYY), whereas 5-HT-immunoreactive enteroendocrine cells were not immunoreactive for GPR43. Mast cells of the lamina propria expressing 5-HT were also GPR43 immunoreactive. The results of the present study suggest that the PYY-containing enteroendocrine cells and 5-HT-containing mucosal mast cells sense SCFAs via GPR43 receptor.In the physiological study, mucosal addition of SCFAs evoked increases in short circuit current in a concentration-dependent manner. The responses were inhibited by neuronal blocker tetrodotoxin. These molecular biological and physiological studies suggest that GPR 43 senses luminal SCFA and induces ion transport in the colon. Therefore, GPR43 has an important role to regulate colonic functions.