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Background Pulmonary hypertension (PH) is a proliferative disorder associated with enhanced proliferation and suppressed apoptosis of pulmonary artery smooth muscle cells (PASMCs). Our lately study demonstrated that let-7g inhibited hypoxia-induced proliferation of PASMCs via repressing c-myc-Bmi-1-p16 signaling pathway. However, the upstream of let-7g has not yet been fully defined. Previous studies have shown that LOX-1, a target of let-7g, could also regulate the expression of let-7g in human aortic endothelial cells. In this present study, we aimed to investigate whether there is a negative feedback regulation between microRNA let-7g and LOX-1 in hypoxia-induced proliferation of PASMCs. Methods SD Rats were exposed to hypoxia (10% O 2 , 3 weeks) to induce PH. HE staining was used to evaluate pulmonary artery remodeling. in situ hybridization and immunohistochemistry were performed to assess the expression and distribution of let-7g and LOX-1, respectively. MTS, EDU and flow cytometry were performed to evaluate PASMCs proliferation. Quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting were conducted to assess the expression of let-7g, LOX-1, calpain-1,-2,-4, and OCT-1. Results The expression of let-7g was significantly down-regulated in pulmonary arteries of hypoxia-induced PH rats accompanied by pulmonary vascular remodeling, whereas let-7g mimic inhibited hypoxia-induced proliferation of PASMCs and up-regulation of LOX-1 expression. LOX-1 blocking reversed hypoxia-induced down-regulation of let-7g expression. Calpains, protein kinase C and OCT-1 were involved in negative feedback regulation between let-7g and LOX-1. Conclusion Negative feedback regulation between let-7g and LOX-1 mediated hypoxia-induced proliferation of in PASMCs. [ABSTRACT FROM AUTHOR]

Background Endothelial cell apoptosis contributes to cardiovascular diseases such as hypertension, atherosclerosis. MicroRNA regulates endothelial cell function but its role in endothelial cell apoptosis remains to be fully elucidated. This study aims to investigate the role of miR-590-5p in endothelial cell apoptosis and dissect the underlying mechanisms. Methods Flow cytometric analysis, Hoechst 33258 staining and Western blotting were performed to evaluate human umbilical vein endothelial cell (HUVEC) apoptosis induced by Angiotensin (Ang) II. Western blotting and real-time quantitative PCR were conducted to assess the expression of LOX-1. DCFH-DA staining was carried out to measure the generation of reactive oxygen species (ROS). Results Ang II-induced HUVEC apoptosis was accompanied by downregulation of miR-590-5p; administration of miR-590-5p mimics attenuated HUVEC apoptosis and decreased ROS generation, as indicated by reduced fraction of apoptotic HUVECs and decreased caspase-3 activity. LOX-1 expression was increased by Ang II, and miR-590-5p mimics reduced LOX-1 expression in HUVECs in the absence or presence of Ang II. Pharmacologic or genetic block of LOX-1 with small interference RNA or TS92 (LOX-1 neutralizing antibody) significantly ameliorated HUVEC apoptosis, as evidenced by reduced number of apoptotic HUVECs, inhibited caspase-3 activation and suppressed mitochondrial cytochrome C release. Moreover, LOX-1 siRNA or TS92 treatment dramatically reduced ROS production in HUVECs treated with Ang II. Conclusion Our data demonstrated that miR-590-5p downregulation promoted Ang II-induced endothelial cell apoptosis by elevating LOX-1 expression and consequently increasing ROS generation. Thus, restoration of miR-590-5p or block of LOX-1 could be therapeutically exploited to alleviate endothelial cell apoptosis. [ABSTRACT FROM AUTHOR]