困難梭狀桿菌感染會導致長期使用抗生素之病患嚴重水性腹瀉與結腸炎。根據報導由於過氧化體增生活化受體γ (PPARγ)具有免疫調控功能，故於腸炎中能作為極有潛力之治療標的。然而，PPARγ在困難梭狀桿菌致病機轉中所扮演的角色仍然不明瞭。在我們先前利用小鼠所建立的困難梭狀桿菌感染動物模式中，我們發現小鼠於感染後腸道PPARγ與緊密連結蛋白複合體之一的密封蛋白(Occludin)表現量下降。為了解PPARγ與腸道完整度的關聯性，我們使用PPARγ缺失小鼠進行實驗，發現PPARγ缺失小鼠的腸道與野生型並無不同；然而在感染困難梭狀桿菌後，PPARγ缺失小鼠比起對照組其腸道通透度和腸道菌叢散佈卻更為增加。為了更加剖析困難梭狀桿菌感染中PPARγ調控腸道完整度的方式，我們使用了產毒素菌株進行對腸道上皮細胞的感染，發現腸道上皮細胞PPARγ、密封蛋白的表現量下降與緊密連結的功能喪失。並且在使用蛋白酶體抑制劑下，證明了在困難梭狀桿菌感染當中，腸道上皮細胞內PPARγ的降解是需要蛋白酶體的作用；但使用蛋白酶體抑制劑卻無法使得密封蛋白表現量回升。在給予PPARγ的促進劑愛妥糖(Pioglitazone)的刺激下，能使得腸道上皮細胞中的密封蛋白表現量回升。為了更加直接的證實PPARγ調控密封蛋白表現的可能性，我們以電腦預測密封蛋白(Occludin)其啟動子區域是否有過氧化物體增殖物效應元件(PPRE)存在。利用染色質免疫沉澱技術證實PPARγ確實能夠直接結合於密封蛋白的啟動子區域，但在給予促進劑的刺激下PPARγ會離開結合位置。最後，於動物模式中藉由促進劑的使用同時可以降低發炎的程度、減輕病癥，並且使得困難梭狀桿菌感染引起的腸道屏障喪失減緩。綜合上述，我們的研究結果顯示降低困難梭狀桿菌感染當中，腸道PPARγ表現的下降會透由調控密封蛋白的表現引發更為嚴重的腸道通透性缺失。

Clostridium difficile infection (CDI) causes severe colitis with watery diarrhea in long-term antibiotic treatment patients. Previous studies have showed that peroxisome proliferator-activated receptor γ (PPARγ), owing to its function in immune regulation, is a potential therapy target for colitis. However, the role of PPARγ in pathogenesis of CDI remains unclear. In our CDI mouse model, we found that levels of PPARγ and tight junction protein were decreased in colonic tissue. To further investigate the relationship between PPARγ and colonic integrity, we used PPARγ deficient mice and found there was no difference in colonic tissue in these two genotype mice. However, after infected with C. difficile, the colonic permeability and gut bacteria dissemination were significantly increased in PPARγ deficient mice than that in WT mice. To dissect the role of PPARγ on the regulation of tight junction protein, occludin, we demonstrated the levels of occludin and PPARγ were also decreased parallel in colonic epithelial cells. Simultaneously, disruption of tight junction functionality was revealed by real time cell analyzer. We demonstrated that the decreased PPARγ during CDI was proteasome dependent by treatment with proteasome inhibitors. However, proteasome inhibitors couldn’t prevent the decrease of occludin. When activation of PPARγ by treated with PPARγ agonist, pioglitazone, the mRNA and protein levels of occludin were reversed after CDI. To directly interpret the interaction of PPARγ and the occludin regulation, we predicted the possible peroxisome proliferator binding elements (PPRE) in silico. It showed that PPARγ bound at occludin promoter region by ChIP assay, but released after treated with pioglitazone. Further, we treated mice with pioglitazone, and the mice showed improvement of inflammation and intestinal integrity in the intestinal tract. Taken together, our results suggest that decrease of PPARγ might contribute to exacerbated barrier loss through down-regulation of occludin.

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