Down-regulation of the Smad signaling by circZBTB46 via the Smad2-PDLIM5 axis to inhibit type I collagen expression

BACKGROUND Abnormal type I collagen(COL1)expression is associated with the development of many cardiovascular diseases.The TGF-beta/Smad signaling pathway and circRNAs have been shown to regulate COL1 gene expression,but the underlying molecular mechanisms are still not fully understood.METHODS Gain-and loss-of-function experiments were prformed to study the effect of circZBTB46 on the expression of alpha 2 chain of type I collagen(COL1A2).Co-immunoprecipitation assay was performed to observe the interaction between two proteins.RNA immunoprecipitation assay and biotin pull-down assay were performed to observe the interaction of circZBTB46 with PDLIM5.RESULTS In this study,we investigated the role of circZBTB46 in regulating COL1A2 expression in human vascular smooth muscle cells(VSMCs).We found that circZBTB46 is expressed in VSMCs and that TGF-beta inhibits circZBTB46 formation by downregulating KLF4 expression through activation of the Smad signaling pathway.CircZBTB46 inhibits the expression of COL1A2 induced by TGF-beta.Mechanistically,circZBTB46 mediates the interaction between Smad2 and PDLIM5,resulting in the inhibition of Smad signaling and the subsequent downregulation of COL1A2 expression.Furthermore,we found that the expression of TGFbeta and COL1A2 is decreased,while circZBTB46 expression is increased in human abdominal aortic aneurysm tissues,indicating that circZBTB46-mediated regulation of TGF-beta/Smad signaling and COL1A2 synthesis in VSMCs plays a crucial role in vascular homeostasis and aneurysm development.CONCLUSIONS CircZBTB46 was identified as a novel inhibitor of COL1 synthesis in VSMCs,highlighting the importance of circZBTB46 and PDLIM5 in regulating TGF-beta/Smad signaling and COL1A2 expression.

Baicalin inhibits PDGF-BB-stimulated vascular smooth muscle cell proliferation through suppressing PDGFRβ-ERK signaling and increase in p27 accumulation and prevents injury-induced neointimal hyperplasia

The increased proliferation and migration of vascular smooth muscle cells （VSMCs） are key events in the development of atherosclerotic lesions. Baicalin, an herb-derived flavonoid compound, has been previously shown to induce apoptosis and growth inhibition in cancer cells through multiple pathways. However, the potential role of baicalin in regulation of VSMC proliferation and prevention of cardiovascular diseases remains unexplored. In this study, we show that pretreatment with baicalin has a dose-dependent inhibitory effect on PDGF-BB-stimulated VSMC pro- liferation, accompanied with the reduction of proliferating cell nuclear antigen （PCNA） expression. We also show that baicalin-induced growth inhibition is associated with a decrease in cyclin E-CDK2 activation and increase in p27 level in PDGF-stimulated VSMCs, which appears to be at least partly mediated by blockade of PDGF recep- tor [~ （PDGFR~）-extracellular signal-regulated kinase 1/2 （ERK1/2） signaling. In addition, baicalin was also found to inhibit adhesion molecule expression and cell migration induced by PDGF-BB in VSMCs. Furthermore, using an animal carotid arterial balloon-injury model, we found that baicalin significantly inhibited neointimal hyperplasia. Taken together, our results reveal a novel function of baicalin in inducing growth arrest of PDGF-stimulated VSMCs and suppressing neointimal hyperplasia after balloon injury, and suggest that the underlying mechanism involves the inhibition of cyclin E-CDK2 activation and the increase in p27 accumulation via blockade of the PDGFR^-ERK1/2 signaling cascade.