Loss of MicroRNA-17∼92 in Smooth Muscle Cells Attenuates Experimental Pulmonary Hypertension via Induction of PDZ and LIM Domain 5

Rationale: Recent studies suggest that microRNAs (miRNAs) play important roles in regulation of pulmonary artery smooth muscle cell (PASMC) phenotype and are implicated in pulmonary arterial hypertension (PAH). However, the underlying molecular mechanisms remain elusive. Objectives: This study aims to understand the mechanisms regulating PASMC proliferation and differentiation by microRNA-17 similar to 92 (miR-17 similar to 92)and to elucidate its implication in PAH. Methods: We generated smooth muscle cell (SMC)-specific miR17 similar to 92 and PDZ and LIM domain 5 (PDLIM5) knockout mice and overexpressed miR-17 similar to 92 and PDLIM5 by injection of miR-17 similar to 92 mimics or PDLIM5-V5-His plasmids and measured their responses to hypoxia. We used miR-17 similar to 92 mimics, inhibitors, overexpression vectors, small interfering RNAs against PDLIM5, Smad, and transforming growth factor (TGF)-beta to determine the role of miR-17 similar to 92 and its downstream targets in PASMC proliferation and differentiation. Measurements and Main Results: We found that human PASMC (HPASMC) from patients with PAH expressed decreased levels of the miR-17 similar to 92 cluster, TGF-beta, and SMC markers. Overexpression of miR-17 similar to 92 increased and restored the expression of TGF-beta(3), Smad3, and SMC markers in HPASMC of normal subjects and patients with idiopathic PAH, respectively. Knockdown of Smad3 but not Smad2 prevented miR-17 similar to 92-induced expression of SMC. markers. SMC-specific knockout of miR-17 similar to 92 attenuated hypoxia-induced pulmonary hypertension (PH) in mice, whereas reconstitution of miR-17 similar to 92 restored hypoxia-induced PH in these mice. We also found that PDLIM5 is a direct target of miR-17/20a, and hypertensive HPASMC and mouse PASMC expressed elevated PDLIM5 levels. Suppression of PDLIM5 increased expression of SMC markers and enhanced TGF-beta/Smad2/3 activity in vitro and enhanced hypoxia-induced PH in vivo, whereas overexpression of PDLIM5 attenuated hypoxia-induced PH. Conclusions: We provided the first evidence that miR-17 similar to 92 inhibits PDLIM5 to induce the TGF-beta(3)/SMAD3 pathway, contributing to the pathogenesis of PAH.