Long non-coding RNA MIR503HG controls endothelial-to-mesenchymal transition

Endothelial-to-mesenchymal transition (EndMT) is a dynamic transformation process that has a functional impact upon pathological vascular remodelling. The molecular mechanisms that govern EndMT remain largely unknown. By induction of EndMT in human primary endothelial cells (EC), using a combination of transforming growth factor-ß2 (TGF-b2) and interleukin-1b (IL-1ß), we identified the dramatic loss of the lncRNA MIR503HG, as a common signature across multiple primary EC types. Targeted depletion of MIR503HG spontaneously induced EndMT. Overexpression of MIR503HG repressed EndMT despite TGF-ß2 and IL-1ß co-stimulation. RNA-seq was carried out to identify the changes in gene expression induced by MIR503HG overexpression. We showed that over 25% of the EndMT-transcriptome signature was inhibited upon MIR503HG overexpression. Crucially, phenotypic changes induced by MIR503HG were independent of the functional regulation of miR-503 and miR-424, both harbored within the MIR503HG locus. Collectively, we identify the lncRNA MIR503HG as an essential regulator of EndMT. Overall design: To analyse the effect of MIR503HG overexpression during EndMT, we performed RNA-Seq on control and EndMT (TGFß2 and IL1ß) HUVEC cells overexpressing MIR503HG isoform 2 (ENST00000440570.5) using lentiviral transfection. Untransfected cells and cells transfected with an empty vector were used as controls. Each condition was carried out in triplicates.