Understanding the expression and significance of microRNA-145 in pulmonary hypertension

Therapies that exploit RNA interference hold great potential for improving disease outcomes. However, there are several challenges that limit the application of RNAi therapeutics, including ineffective delivery of functional oligonucleotides to target cells. Collaborators have previously developed a functionalized cationic lipopolyamine (Star:Star-mPEG-550) for in vivo delivery of small interfering RNA (siRNA) to pulmonary vascular cells. This lipid nanoparticle enhances the retention of siRNA in mouse lungs and achieves significant knockdown of target gene expression for at least 10 days following a single intravenous injection. Although this suggests great potential for developing lung-directed RNAi-based therapies, the application of Star:Star-mPEG mediated delivery of RNAi based therapies for pulmonary vascular diseases such as pulmonary arterial hypertension (PAH) remains unknown. We identified differential expression of several microRNAs known to regulate cell proliferation, cell survival and cell fate that are associated with development of PAH, including increased expression of microRNA-145. First we tested the hypothesis that Star:Star-mPEG mediated delivery of an antisense oligonucleotide against microRNA-145 (antimiR-145) will improve established PAH in rats. We tested the in vivo distribution, toxicity, and efficacy of Star:Star-mPEG mediated delivery of antimiR-145 in rats with severe PAH in a preclinical reversal study. We showed that after subchronic therapy of three intravenous injections over 5 weeks at 2 mg/kg, antimiR-145 accumulated in rat lung tissue and reduced expression of endogenous microRNA-145. Using a novel in situ hybridization approach, we demonstrated substantial distribution of antimiR-145 in lungs as well as liver, kidney, and spleen. We assessed toxic effects of Star:Star-mPEG/antimiR-145 with serial complete blood counts of leukocytes and serum metabolic panels, gross pathology, and histopathology and did not detect significant off-target effects. Next we tested potential mechanisms underlying this observed antimiR-145 therapeutic effect; including: reduced contractility and muscularization of hypertensive pulmonary arteries (Pas), repair of occlusive vascular remodeling, and improvement of right ventricular (RV) structure and function. The results show that Star:Star-mPEG delivery of antimiR-145 repairs occlusive pulmonary arteriopathy through unidentified cellular and molecular mediators. AntimiR-145 reduced the degree of pulmonary arteriopathy, reduced the severity of pulmonary hypertension, and reduced the degree of cardiac dysfunction. The results establish effective and low toxicity of lung delivery of a microRNA-145 inhibitor using functionalized cationic lipopolyamine nanoparticles to repair pulmonary arteriopathy and improve cardiac function in rats with severe PAH.