Dysregulation of miR-135a-5p promotes the development of rat pulmonary arterial hypertension in vivo and in vitro.

Pulmonary arterial hypertension (PAH) is the most common form of pulmonary hypertension. Pulmonary arterial remodeling is closely related to the abnormal proliferation of pulmonary artery smooth muscle cells (PASMCs), which leads to the thickening of the medial layer of muscular arteries and then results in the narrowing or occlusion of the precapillary arterioles and PAH. However, the mechanisms underlying the abnormal proliferation of PASMCs remain unclear. In this study, we established rat primary PAH models using monocrotaline (MCT) injection or hypoxic exposure, then investigated the expression patterns of seven miRNAs associated with multiple pathogenic pathways central to pulmonary hypertension, and further explored the roles and the possible mechanisms of miR-135a during the development of PAH. In the rat primary PAH models, we observed that the expression of miR-135a-5p in lungs was drastically decreased at the initial stage of PAH development after MCT administration or hypoxic exposure, but it increased by 12-fold or 10-fold at the later stage. In vitro study in PASMCs showed a similar pattern of miR-135a-5p expression, with downregulation at 6 h but upregulation at 18, 24, and 48 h after hypoxic exposure. Early, but not late, administration of a miR-135a-5p mimic inhibited hypoxia-induced proliferation of PASMCs. The protective role of early miR-135a-5p agomir in the PAH rat model further supported the hypothesis that the early decrease in the expression of miR-135a-5p contributes to the proliferation of PASMCs and development of PAH, as early administration of miR-135a-5p agomir (10 nM, i.v.) reversed the elevated mean pulmonary arterial pressure and pulmonary vascular remodeling in MCT-treated rats. We revealed that miR-135a-5p directly bound to the 3'-UTR sequence of rat transient receptor potential channel 1 (TRPC1) mRNA and decreased TRPC1 protein expression, thus inhibiting PASMC proliferation. Collectively, our data suggest that dysregulation of miR-135a-5p in PASMCs contributes to the abnormal proliferation of PASMCs and the pathogenesis of PAH. Increasing miR-135a-5p expression at the early stage of PAH is a potential new avenue to prevent PAH development.