Elliot, Sharon J.

Abstract RATIONALE: Vascular dysfunction contributes to pathological tissue remodeling in aging-associated disease such as Idiopathic Pulmonary Fibrosis (IPF). IPF is an incurable lung disease characterized by progressive accumulation of scar-forming fibroblasts and several vascular alterations, including endothelial transcriptional changes leading to a pro-fibrotic endothelial secretory phenotype. To date, the mechanisms governing these transcriptional changes remain largely unexplored. To fill this gap, we sought to investigate whether microRNAs (miRNAs), small non-coding RNA that function as key gene expression regulators, modulate the transcriptional changes of the endothelium associated with progressive pulmonary fibrosis. METHODS AND RESULTS: miRNA expression profiling of lung ECs (LECs) sorted from aged mice with persistent lung fibrosis revealed upregulation of miR-205-5p. Further analysis demonstrated that endothelial miR-205-5p was strongly upregulated in an additional mouse model of progressive lung fibrosis induced by repetitive bleomycin dose as well as in human LECs purified from IPF lungs. RNA-seq analysis of normal human LECs overexpressing miR-205-5p revealed reduction of genes associated to endothelial identity (e.g. PECAM1, ERG, NOS3), and an increase of genes encoding for soluble pro-inflammatory and pro-fibrotic molecules, including TGFBI, TGFB2, TGFB3, CXCL10, CCL5, IL1B and FAS compared to normal LECs transfected with a control mimic. Consistently, conditioned medium from miR-205-5p overxpressing LECs exerted a pro-fibrotic activity on quiescent human lung fibroblasts, as demonstrated by upregulation of a panel of profibrotic transcripts (e.g. COL1A1, CTHRC1, FN1 and TNC) and elevated Collagen I deposition compared to human lung fibroblasts exposed to conditioned medium generated by human LECs transfected with a control mimic. CONCLUSION: Altogether, our findings suggest that lung endothelail miR-205-5p induces loss of endothelial cell identity and drives the secretion of pro-fibrotic molecules that promote the transition of quiescent fibroblasts into scar-forming fibroblast through paracrine signal. Our data set the stage for further investigations into the role of miR-205-5p and associated pathways in lung vascular injury responses, with the long term goal of targeting endothelial dysfunction for slowing the progression of pulmonary fibrosis.