MicroRNA-9 as a novel therapeutic tool for neointimal formation by targeting the PDGFRβ pathway

Abstract

Vascular smooth muscle cell (VSMC) proliferation and migration are important phenomena in atherosclerosis and in other vasculopathies. These diseases are promoted by the release of various cytokines and growth factors into the intima. These alterations down-regulate the expression of VSMC-specific contractile phenotype genes and promote VSMC proliferation and migration. The PDGF/PDGF receptor (PDGFR) interaction, which is a vascular disease cue, induces VSMC proliferation and migration, and eventually, vascular disease occurs. Additionally, the PDGF/PDGFR signaling pathway regulates phenotypic switching from a contractile to a proliferative phenotype. In the present study, microRNA-9 (miR-9) was identified as a novel regulator of VSMC proliferation and migration that suppresses PDGFRβ signaling. VSMC-specific phenotypic switching to a contractile phenotype was also observed under miR-9 overexpression conditions. Furthermore, several small molecules that regulate the induction of endogenous miR-9 expression were screened to overcome the limitation of directly transplanting miRs into damaged tissue in vivo. Among these molecules, SQ22536 (Drug 8) induced endogenous miR-9 expression. In addition, Drug 8 regulated endogenous miR-9 through two different mechanisms: 1) epigenetic modification by regulating histone deacetylase (HDAC) expression and 2) transcriptional regulation by phosphorylating and activating the cyclic adenosine monophosphate (cAMP) response element-binding protein (CREB) gene. Moreover, Drug 8 regulated VSMC proliferation and migration by suppressing PDGFRβ expression and its downstream signaling molecules, such as miR-9. Furthermore, when Drug 8 was injected in a rat balloon injury model, neointimal formation decreased, and the expression of proliferation-related proteins was down-regulated. Taken together, these findings suggest that miR-9 induction

through small molecule treatment is an effective therapeutic strategy to repress neointimal hyperplasia.