miR-18a-5p MicroRNA Increases Vascular Smooth Muscle Cell Differentiation by Downregulating Syndecan4

Background and Objectives: Differentiation and de-differentiation of vascular smooth muscle cells (VSMCs) are important events in atherosclerosis and restenosis after angioplasty. MicroRNAs are considered a key regulator in cellular processes such as differentiation, proliferation, and apoptosis. Here, we report the role of new miR-18a-5p microRNA and its downstream target genes in VSMCs and in a carotid balloon injury model. Materials and Methods: Expression of miR-18a-5p and its candidate genes was examined in VSMCs and in a carotid artery injury model by quantitative reverse-transcription polymerase chain reaction (qRT-PCR) and microRNA microarray analysis. VSMC differentiation marker genes including smooth muscle (SM) ${\alpha}-actin$ and $SM22{\alpha}$ were determined by Western blot, qRT-PCR, and a $SM22{\alpha}$ promoter study. Gene overexpression or knockdown was performed in VSMCs. Results: miR-18a-5p was upregulated in the rat carotid artery at the early time after balloon injury. Transfection of the miR-18a-5p mimic promoted the VSMC differentiation markers SM ${\alpha}-actin$ and $SM22{\alpha}$. In addition, miR-18a-5p expression was induced in differentiated VSMCs, whereas it decreased in de-differentiated VSMCs. We identified syndecan4 as a downstream target of miR-18-5p in VSMCs. Overexpression of syndecan4 decreased Smad2 expression, whereas knockdown of syndecan4 increased Smad2 expression in VSMCs. Finally, we showed that Smad2 induced the expression of VSMC differentiation marker genes in VSMCs. Conclusion: These results indicate that miR-18a-5p is involved in VSMC differentiation by targeting syndecan4.