This study was performed to compare the miRNA expression profile in native endothelial cells (ECs) versus cells maintained in culture (1^st passage), and determine to what extent miRNAs are involved regulating the transition between the quiescent and proliferative EC phenotypes.

miRNA profiling revealed that miR-223 is highly expressed in freshly isolated ECs but markedly decreased in cultured human, mouse lung and porcine aortic ECs. Overexpression of pre-miR-223 in multi-passaged ECs (which express no detectable miR-223) inhibited EC migration (scratch wound and Transwell migration assays) in response to VEGF or bFGF. Overexpression of miR-223 also prevented growth factor-induced proliferation and was associated with impaired Akt phosphorylation, tube formation and sprouting. Using a proteomic approach β1 integrin was found to be altered by miR-223 in endothelial cells and was confirmed as a direct target 3’ UTR reporter gene assay, RT-qPCR and Western blotting. Overexpression of β1 integrin rescued the impaired endothelial tube formation associated with miR-223 overexpression. In miR-223^-/- mice, high levels of β1 integrin were detected in ECs from the aorta, lung and hindlimb. Moreover, in miR-223^-/y mice we observed an increased neovascularisation in Matrigel plugs containing VEGF and bFGF and accelerated recovery of perfusion after hindlimb ischemia.

Taken together, these results indicate that miR-223 is an anti-angiogenic miRNA that maintains low EC β1 integrin levels. A decrease in miR-223 seems to essential for the transition of quiescent ECs to a proliferative phenotype a response that can be partially attributed to an increase in the expression of β1 integrin