Molecular pathways involved in adventitial fibroblasts (AFs) and myofibroblasts (MFs) proliferation and apoptosis contribute to vascular remodeling. MicroRNA-21 (miR-21) plays an important role in regulating cellular proliferation and apoptosis of many cell types; however, the effect of miR-21 on AFs and MFs is still unknown. In this study, we found that miR-21 was expressed in AFs and overexpressed in MFs. Inhibition of miR-21 decreased proliferation and increased apoptosis of AFs and MFs, and overexpression of miR-21 with pre-miR-21 had the reverse effect. Programmed cell death 4 (PDCD4), related to cell proliferation and apoptosis, was validated as a direct target of miR-21 by dual-luciferase reporter assay and gain and loss of function of miR-21 in AFs and MFs. PDCD4 knockdown with siRNA partly rescued the reduced proliferation with miR-21 inhibition and alleviated the increased apoptosis induced by miR-21 inhibition in AFs and MFs. Moreover, increasing PDCD4 expression by miR-21 inhibition significantly decreased JNK/c-Jun activity. In contrast, decreasing PDCD4 expression by pre-miR-21 treatment increased JNK/c-Jun activity, while the effect of miR-21 inhibition on JNK/c-Jun activity could be rescued by PDCD4 siRNA. Moreover, miR-21 inhibition could regulate proliferation and apoptosis of vascular AFs and MFs in vivo. Furthermore, miR-21 inhibition reversed vascular remodeling induced by balloon injury. In summary, our findings demonstrate that miR-21 may have a critical role in regulating proliferation and apoptosis of AFs and MFs, and PDCD4 is a functional target gene involved in the miR-21-mediated cellular effects in vascular remodeling by a miR-21/PDCD4/JNK/c-Jun pathway.
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