Understanding the role of the long non-coding RNA MIR503HG in endothelial-to-mesenchymal transition during vascular remodelling
Pinho Monteiro, João Pedro
Endothelial-to-mesenchymal transition (EndMT) is a dynamic biological process present during development and involved in a variety of pathological vascular remodelling scenarios. However, despite our growing understanding of the key cellular alterations required, the precise molecular determinants governing this phenotypical transition remain elusive. With long non-coding RNAs (lncRNA) now emerging as powerful regulators of gene expression we sought to understand their role in the process of EndMT. To replicate EndMT in vitro and characterise its molecular signature, human umbilical vein endothelial cells (HUVEC) and human pulmonary artery endothelial cells (HPAEC) were exposed to a continuous co-treatment of transforming growth factor-beta 2 (TGF-β2) and interleukin 1 beta (IL-1β) for a total of 7 days. Using high-throughput RNA-sequencing analysis of these cells, a total of 103 differential expressed lncRNAs were identified. Of these, the downregulation of the lncRNA MIR503HG was found to be a prevalent feature present in multiple human primary EC types undergoing EndMT in vitro. Further analysis revealed that depletion of MIR503HG was sufficient to elicit a robust EndMT phenotype, with a significant increase in the expression of SNAI2, ACTA2 and COL1A1, accompanied by repression of CD31. Conversely, ectopic expression of a single MIR503HG transcript suppressed these hallmark EndMT-associated changes despite TGF-β2 and IL-1β co-treatment. Accompanying RNA-sequencing of these cells showed that the overexpression of MIR503HG alone was able to inhibit over 25% of the EndMT transcriptional profile. Crucially, these changes were found to be independent of the functional regulation of miR-503 and miR-424, found within the MIR503HG locus. Our findings were then confirmed in vivo using a sugen/hypoxia-induced model of pulmonary hypertension (PH) established in endothelial lineage-tracing mice. Here, the expression of the MIR503HG mouse homolog (Gm28730) was significantly downregulated in association with an EndMT profile in the lung. Conversely, targeted up-regulation of MIR503HG in the mouse lung significantly suppressed the appearance of mesenchymal markers in CD31+ cells during PH. Notably, MIR503HG availability was also found to be decreased in lung tissue sections from patients with idiopathic pulmonary arterial hypertension (IPAH) and cultured blood outgrowth ECs isolated from patients with heritable pulmonary arterial hypertension (HPAH). Collectively, our studies identify MIR503HG as essential in maintaining EC phenotypical commitment and preventing EndMT both in vitro and during disease.