The role of miR-140-5p in humans and animal models of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a devastating disease characterised by progressive remodelling of the pulmonary vasculature. Genetic predisposition and/or environmental insult result in pulmonary artery endothelial cell (PAEC) apoptosis, smooth muscle cell (PASMC) proliferation, occlusive pulmonary vascular remodelling and increased pulmonary vascular resistance leading to right heart failure. Current treatments are limited to pharmacological vasodilatation via the prostacyclin, endothelin or nitric oxide pathways, however, proliferative remodelling persists and many patients require lung transplantation. New therapeutic approaches are needed to inhibit or reverse vascular remodelling. Heterozygous mutations in the Bone Morphogenetic Protein Receptor 2 (BMPRII) gene are present in around 80% of heritable PAH and in an estimated 20% of patients with idiopathic PAH (Deng et al., 2000; Thomson et al., 2000) and modulation of BMP signalling in vitro and in vivo provides therapeutic benefit. MicroRNA (miR) are short non-coding RNA that mediate post-transcriptional regulation through interactions of their seed region with complementary sequences in the 3’ untranscribed region (3’UTR) of target mRNA. Through simultaneous repression of multiple gene targets miR mediate higher-order regulation of cellular function. The investigation of miR dysregulated in human disease and the cellular mechanisms through which their effects are mediated may identify key regulators of disease pathology and novel therapeutic targets. In this thesis whole blood miR expression is examined in patients at the time of diagnosis and prior to initiation of treatment for PAH. Down-regulation of miR-140-5p is identified in patients with pulmonary hypertension, and experimental models of PAH. Consistent with clinical findings and bioinformatic predictions miR-140-5p inhibitor increased proliferation and migration of PASMC in vitro. Delivery of miR-140-5p mimic prevented, and treated established, experimental PAH. Bioinformatic and in vitro investigation identified SMURF1, an E3 ubiquitin ligase that targets BMPRII and downstream signalling mediators for proteosomal degradation, as a direct miR-140-5p target, inhibition of which enhanced BMP signalling. Finally, whole blood mRNA and vascular expression of SMURF1 is increased in human PAH. These findings demonstrate the feasibility of targeting BMP signalling, via miR-140-5p and SMURF1, for the treatment of PAH.