Effect, Mechanism And Regulation Of C-Ski In Atherosclerosis

Atherosclerosis (AS) is a condition that an artery wall thickens and multiple plaquesform within the arteries which are resulted from the accumulation of fatty materials such ascholesterol and triglyceride. This causes a hardening or furring of the arteries. The processof AS tends to be slowly and progressive, it usually remains asymptomatic until a plaquesblock the arteries which may quickly obstruct the flow of blood and leads to ischemia anddamage of the cells and tissues. Although the course of AS is complicated and severalfactors are involved in the progression of it, the proliferation of vascular smooth musclecells (VSMCs) plays key roles in the development of intimal hyperplasia which is ahallmark of atherosclerosis.Transforming growth factor β (TGF-β), a member of a large family of multipotentcytokines, has been found to play important roles in regulation of VSMC proliferation inAS. And more recent evidence indicate that the activation of Smad3signal pathway ismainly responsible for this stimulatory effect of TGF-β on VSMC proliferation. c-Ski, ahomologue of v-Ski in cells, is a versatile transcriptional regulator that is widely distributedin different tissues and has been reported to be a co-repressor of TGF-β/Smad signaling.Binding of TGF-β to its receptor serine/threonine kinases results in the phosphorylation ofthe receptor-regulated Smad2and Smad3(R-Smad) proteins. The phosphorylated R-Smadsthen form heteromeric complexes with a common mediator Smad4(Co-Smad). Together,they translocate into the nucleus, where they bind to DNA and activate the transcription oftarget genes. During this signal transduction, c-Ski is reported to prevent thephosphorylation of Smad2/3, or bind to activated Smad2/3/4heteromeric complexes tointerference nuclear translocation of the R-Smad/Smad4complex, thereby silencing Smadsignaling. Therefore, acccording to the effect of TGF-β on VSMC and the relationshipbetween c-Ski and TGF-β, we speculate that c-Ski may exert some essential effect in AS.To confirm this hypothesis, in the present study, we perform the following researches:1. In TGF-β-stimulated rat aortic A10VSMCs, we investigated the effect of c-Ski cell proliferation by overexpressing or RNAi c-Ski, and detected the associated cellularsignaling in vitro.2. In balloon injury model of rat, c-Ski gene delivery in vivo was performed and itseffects on VSMC proliferation, neointimal formation were observed in vivo.3. We investigated the gene expression regulation of c-Ski by peroxisome proliferatorsactivated receptors γ (PPARγ) via bioinformatics analysis, luciferase assay, Electrophoresismobility shift assay (EMSA), Chromatin immunoprecipitation (ChIP) and cell proliferationassay.4. We assayed the dynamitic changes of endogenous c-Ski mRNA and proteinexpression in high fatty diet model and balloon injury model and investigated the potentialfactor for regulating the endogenous c-Ski in AS.In this study, we demonstrate:1. c-Ski significantly suppresses the TGF-β-induced proliferation of VSMC andformation of neointimal via inhibiting Smad3signaling but stimulating p38pathway toupregulate p21and p27.2. c-Ski is a target gene of PPARγ. PPARγ binds to5’-UTR of c-Ski via DR1sequence“AGGTAAGGGGACA” and regulates c-Ski expression, which is a novel mechanism of theinhibitory effect of PPARγ on VSMC proliferation.3. In rat AS models, the arterial endogenous c-Ski protein expression not mRNAexpression decreases in a time-dependent manner. The results of bioinformatics analysisand cell proliferation indicate miR-17-5p is involved in the endogenous c-Ski geneexpression regulation in the progression of AS, which still need further investigation andconfirmation.In summary, these data suggest the potential protective effect of c-Ski against AS. It suggeststhat the decrease of endogenous c-Ski expression is implicated in the progression of VSMCproliferation and intimal hyperplasia in AS. Regulation of c-Ski gene expression by nuclearreceptor or miRNA may represent a promising role for treating AS when targeting c-Ski.