Effect Of Curcumin On The Transdifferentiation Of Renal Tubular Epithelial Cells And The Signal Pathway Related To PPARγ

Background and purpose:Tubulointerstitial fibrosis (TIF) is the final common pathway in late-stage renal disease. Epithelial-to-mesenchymal (EMT) is considered as the major contributor to the TIF by increasing the number of myofibroblasts. Curcumin, a polyphenolic compound derived from rhizomes of Curcuma has been shown to possess potent anti-fibrotic properties. The mechanisms of curcumin on modulating fibrosis are largely focused on conventional TGF-p/Smads pathway and very limited information on non-Smad pathway. ERK1/2, belonging to MAPKs, a crucial non-samd pathway, plays an important role in EMT. Research has shown that curcumin is a ligant for PPARy, which is considered an endogenous antifibrotic factor lately. PPARy agonist such as pioglitazone exerts protective effets on fibrosis. So we hypothesize that curcumin is able to protect against TIF through PPARy related pathway.We investigate the effect of curcumin on TIF animal model and TGF-β1-induced EMT in proximal tubular epithelial cell HK-2, and elucidate its underlying mechanism related to non-smad ERK1/2and PPARy pathway.Method:The animal model of TIF was induced by unilateral ureteral obstruction(UUO) in male C57LB mouse. They were divided into four groups:The sham, UUO, UUO with different doses of curcuim and UUO receiving curcumin and PPARγ inhibitor BADGE. HE and Masson trichome were used to examine the morphological changes in kidney. HK-2cells were stimulated with TGF-β1(2.5ng/ml) in the presence or absence of curcumin for36hours. The effects of curcumin on a-SMA, PAI-1, E-cadherin, RβII, TRβI, p-ERK1/2and p-PPARy were analyzed by western blotting and nuclear translocation of PPARy by immune-fluorescence. Inhibitor of ERK1/2and PPARyas well as shRNA for PPARywere used to investigate the possible mechanism.Results:Curcumin is able to inhibit the tubular damage in UUO, but in the BADGE group, the protective effects were abrogated. EMT was induced in HIK-2cells with2.5ng/ml TGF-β1. The protein expression of E-cadherin was down-regulated, while the expression of a-SMA, E-cadherin, PAI-1, TRβII, TRβI, p-Smad2, p-Smad3, ERK1/2and p-PPARy were up-regulated. Curcumin significantly decreased the expression of a-SMA, PAI-1, TRβII, TRβI, p-Smad2, p-Smad3, ERK1/2and p-PPARy, increased E-cadherin expression, but had no effects on p-Smad2or p-Smad3. However, inhibitor of ERK1/2U0126, or inhibitor of PPARy BADGE, or down-regulation of PPARy by shRNA attenuated the effects of curcumin. Moreover, inhibition of ERK1/2blocked phosphorylation of PPARy, but inhibition of PPARy had no effect on ERK1/2.Conclusion:Curcumin is able to inhibit the tubular damage in UUO animal model possibly through PPARy signaling pathway. Curcumin inhibited TGF-β1induced EMT in HK-2cells via inhibiting ERK signaling pathway and subsequently the downstream PPARy signaling pathway.