Mechanical Stretch Modulates MicroRNA 21 Expression, Participating in Proliferation and Apoptosis in Cultured Human Aortic Smooth Muscle Cells

OBJECTIVES Stretch affects vascular smooth muscle cell proliferation and apoptosis, and several responsible genes have been proposed. We tested whether the expression of microRNA 21 (miR-21) is modulated by stretch and is involved in stretch-induced proliferation and apoptosis of human aortic smooth muscle cells (HASMCs). METHODS AND RESULTS RT-PCR revealed that elevated stretch (16% elongation, 1 Hz) increased miR-21 expression in cultured HASMCs, and moderate stretch (10% elongation, 1 Hz) decreased the expression. BrdU incorporation assay and cell counting showed miR-21 involved in the proliferation of HASMCs mediated by stretch, likely by regulating the expression of p27 and phosphorylated retinoblastoma protein (p-Rb). FACS analysis revealed that the complex of miR-21 and programmed cell death protein 4 (PDCD4) participated in regulating apoptosis with stretch. Stretch increased the expression of primary miR-21 and pre-miR-21 in HASMCs. Electrophoretic mobility shift assay (EMSA) demonstrated that stretch increased NF-κB and AP-1 activities in HASMCs, and blockade of AP-1 activity by c-jun siRNA significantly suppressed stretch-induced miR-21 expression. CONCLUSIONS Cyclic stretch modulates miR-21 expression in cultured HASMCs, and miR-21 plays important roles in regulating proliferation and apoptosis mediated by stretch. Stretch upregulates miR-21 expression at least in part at the transcription level and AP-1 is essential for stretch-induced miR-21 expression.