Abstract P131: Mef2C-MYOCD and Leiomodin1 Suppression by miRNA-214 Promotes Smooth Muscle Cell Phenotype Switching in Pulmonary Arterial Hypertension

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Background: In pulmonary arterial hypertension (PAH), smooth muscle cell (SMC) phenotype switching from a terminally differentiated contractile to synthetic state is gaining traction as our understanding of disease progression improves. While maintenance of SMC contractile phenotype is reportedly orchestrated by a MEF2C- Myocardin (MYOCD) interplay, little is known regarding molecular control at this nexus. Moreover, the burgeoning interest in microRNAs (miRs) provides a basis for exploring their modulation of MEF2C-MYOCD signaling, and, in turn, a pro-proliferative, synthetic SMC phenotype. We hypothesized that suppression of SMC contractile phenotype in pulmonary hypertension is mediated by miR-214 via repression of the MEF2C-MYOCD-leiomodin1 signaling axis. Methods and Results: In SMCs isolated from a PAH patient cohort and commercially obtained hPASMCs exposed to hypoxia, miR-214 expression was upregulated approx. ~1.5 fold compared to controls (p<0.05). These increases in miR-214 were paralleled by downregulation of MEF2C, MYOCD and SMC-specific contractile proteins, leiomodin1 and smoothelin. Of these, leiomodin1 was directly targeted by the miR. MicroRNA-214 overexpression mimicked the PAH profile, downregulating MEF2C (1±0.054 vs 0.696±0.026, p<0.05) and leiomodin1 (1± 0.051 vs 0.281±0.095, for scrambled control vs miR-214 mimic, p<0.05). Hypoxia significantly reduced expression of SMC-specific contractile proteins, leiomodin1 and calponin1 (5 of 10 percent), and smoothelin (approx. 3 of 10 percent), and miR-214 antagomiR abrogated hypoxia-induced suppression of the contractile phenotype. We also found that hypoxia-induced hPASMC proliferation was significantly attenuated by the anti-miR (approx. 2-fold less compared to hypoxia control). Further, anti-miR-214 also restored PAH-PASMCs to a contractile (approx.5 of 10 percent reversal of MEF2C and leiomodin1 expression), and less proliferative phenotype seen during vascular homeostasis. Conclusions: Our findings illustrate a key role for miR-214 in modulation of MEF2C-MYOCD-leiomodin1 signaling and suggest that an antagonist of miR-214 could mitigate SMC phenotype changes and proliferation in vascular hyperproliferative disorders including PAH.