Effects And Mechanisms Of PPARγ Agonists On TGF-β₁-induced Extracellular Matrix Expression In Normal Skin Fibroblasts In Vitro

【Background】As cytobiology and molecular biology studies shown,abnormal synthesis,tissue deposition and degradation reduction of extracellular matrix are responsible for the hypertrophic scar. The findings of the present study indicate that lots of profibrotic cytokines regulate the formation in scar pathogenesis, and TGF-β1 is a key regulator of pathologic scar,that stimulatesⅠcollagen synthesis and myofibroblast transdifferentiation. Recent discoveries suggest that Peroxisome proliferator–activated receptorγagonists to increase insulin sensitivity in diabetic patients antagonize TGF-β1-induced stimulation effects on skin fibroblasts above-mentioned. Investigations of PPARγin these processes have focused primarily on the pancreas, liver, and kidney, the target organs in diabetes,but there are no reports on PPARγagonists effects in the control of skin scars.【Purposes】1. To study the effects of PPARγagonists on TGF-β1-induced cellular response in the normal skin fibroblasts,and to elucidate the endogenous mechanism underlying the antagonization effects of PPARγon TGF-β1-induced fibroblast activation,so as to further provide theory base for treatment of hypertrophic scar by PPARγagonists.2. Preliminary elucidate mechanism underlying the inhibitory effects of activated PPARγon TGF-β1-induced fibroblast activation,and focus on CTGF,considered as a critical downstream mediator of TGF-β1 effects on fibroblasts,so as to investigate effects of PPARγagonists on CTGF.【Contents】1. The effect of PPARγagonists on TGF-β1-induced extracellular matrix response in the normal skin fibroblasts;2. The effect of PPARγagonists on TGF-β1-induced myofibroblast transdifferentiation in the normal skin fibroblasts;3. The mechanism underlying the inhibitory effects of activated PPARγon TGF-β1-induced fibroblast fibrosis and activation;4. To detect and compare the gene expression of PPARγ,CTGF and TGF-β1 in human hypertrophic scar,keloid as well as healthy skin.【Results】1. In normal skin fibroblasts,TGF-β1 enhanced collagen typeⅠand FN expression in a dose-dependent manner. The level of collagen typeⅠand FN protein expression in 15d-PGJ2 and troglitazone-pretreated groups respectively was obviously lower than that in TGF-β1-stimulated group (P<0.01).2. TGF-β1 enhanced transdifferentiation of normal skin fibroblasts to myofibroblasts. The level ofα-SMA expression in 15d-PGJ2 and troglitazone- pretreated groups respectively was significantly decreased compared with TGF-β1-stimulated group (P<0.01). These results further demonstrated that the PPARγligand also disrupted the induction ofα-SMA expression.3. The expression of CTGF at the mRNA and protein levels in normal skin fibroblasts was significantly increased in TGF-β1-stimulated group compared with control group (P<0.01),while the level of CTGF expression in 15d-PGJ2 and troglitazone-pretreated groups respectively was significantly decreased compared with TGF-β1-stimulated group (P<0.01).4. Examined by real-time fluorescence quantitative RT-PCR,the results indicated that the mRNA level of PPARγin pathological scars was obviously lower than that in healthy skin (P<0.05),while the expression of CTGF and TGF-β1 genes in pathological scars remained higher when compared with that of normal level(P<0.01).【Conclusions】1. PPARγagonists may inhibit TGF-β1-induced extracellular matrix sythesis in the normal skin fibroblasts. Thus PPARγagonists have novel and potent antifibrotic effects in human skin fibroblasts.2. PPARγagonists may inhibit the effect of TGF-β1-induced myofibroblast transdifferentiation. The results indicate that PPARγagonists have novel and potent antifibrotic effects:prevent scar from fibrosis and contraction.3. Activated PPARγwas able to antagonize the expression of CTGF induced by TGF-β1,which may be the mechanism that PPARγagonists inhibit TGF-β1-induced profibrotic responses in normal skin fibroblasts.4. The mRNA level of PPARγin pathological scars was obviously decreased. These results suggest that diminished PPARγexpression in pathological scars may be associated with the formation of pathological scars.