Reduced miR-204 expression facilitates the excessive proliferation and apoptosis resistance of pulmonary artery smooth muscle cells characteristic of human pulmonary arterial hypertension.

Pulmonary arterial hypertension (PAH) is characterized by enhanced proliferation and reduced apoptosis of pulmonary artery smooth muscle cells (PASMCs). Because microRNAs have been recently implicated in the regulation of cell proliferation and apoptosis, we hypothesized that these regulatory molecules might be implicated in the etiology of PAH. In this study, we show that miR-204 expression in PASMCs is down-regulated in both human and rodent PAH. miR-204 down-regulation correlates with PAH severity and accounts for the proliferative and antiapoptotic phenotypes of PAH-PASMCs. STAT3 activation suppresses miR-204 expression, and miR-204 directly targets SHP2 expression, thereby SHP2 up-regulation, by miR-204 down-regulation, activates the Src kinase and nuclear factor of activated T cells (NFAT). STAT3 also directly induces NFATc2 expression. NFAT and SHP2 were needed to sustain PAH-PASMC proliferation and resistance to apoptosis. Finally, delivery of synthetic miR-204 to the lungs of animals with PAH significantly reduced disease severity. This study uncovers a new regulatory pathway involving miR-204 that is critical to the etiology of PAH and indicates that reestablishing miR-204 expression should be explored as a potential new therapy for this disease. role of miR-204 in the etiology of PAH. Interestingly, using in silico and microarray gene expression analyses, we observed that among the 461 predicted targets of miR-204 (TargetScan 5.1), only 165 were increased by artificial miR-204 inhibition in control human PASMCs (n = 2 patients; Fig. S1 C). In accordance with the pro-proliferative and antiapoptotic phenotypes seen in PAH, several Src-STAT3-and NFAT-related genes were identified (Fig. S1 C). miR-204 expression is decreased in human PAH and correlates with PAH severityTo investigate the expression pattern of miR-204 in normal and pulmonary hypertensive lungs, we examined miR-204 expression levels in (a) lung biopsies from 8 individuals with nonfamilial PAH compared with biopsies from 8 individuals without pulmonary hypertension, (b) lungs from 6 mice with hypoxia-induced pulmonary hypertension compared with 5 control littermates, and (c) lungs from 5 rats with monocrotaline (MCT)-induced pulmonary hypertension compared with 10 control littermates ( Fig. 1 A). We found decreased levels of miR-204 in human and rodent pulmonary hypertensive lung tissues compared with normotensive lung samples. To characterize whether down-regulated miR-204 levels were specific to the lung in rats with pulmonary hypertension, we compared organ-specific levels of miR-204 between normal and pulmonary hypertensive rats (Fig. 1 B). Even if we were able to detect minimal amounts of miR-204 in most organs, miR-204 levels were only down-regulated in the lung and PAs but not in the aorta, liver, heart, and kidney in rats 3 wk after MCT injection (pulmonary hypertensive rats) compared with non-pulmonary hypertensive rats (Fig. 1 B).To test whether miR-204 down-regulation correlated with disease progression, we studied humans, mice, a...

The ribosomal protein RACK1 is required for microRNA function in both C. elegans and humansRACK1, a constituent of the ribosomal 40S subunit, is required for the association of miRISC with translating ribosomes. This suggests that RACK1 contributes to recruit miRISC to the site of translation and supports a post-initiation mode of miRNA-mediated gene repression.