Question: 

The significance of microRNAs (miRs) for endothelial cell (EC) function is a topic of great scientific interest. However, the altered expression of miRs during the dedifferentiation that occurs at the onset of culturing and their importance for EC function remains to be elucidated.

Methods and Results: 

miR profiling revealed that miR-223 is highly expressed in freshly isolated ECs but dramatically decreased in cultured human EC (P1) and mouse lung EC. Overexpression of pre-miR-223 inhibited EC migration in a scratch wound assay as well as in a transwell migration assay in response to VEGF or bFGF. There was no effect of pre-miR-223 on EC proliferation but it did alter EC morphology, inhibit tube formation on Matrigel and prevent sprouting in a modified spheroid assay. Using a proteomic approach with pre-miR-223 overexpressing human EC we identified a number of altered targets including; eNOS and RhoB. The siRNA-mediated knockdown of RhoB protein in human EC also significantly reduced tube formation.In vivothe vascularisation of Matrigel plugs containing VEGF (100 ng/ml) and bFGF(100 ng/ml) was increased in miR-223 knockout animals compared to wild type littermates and vascular repair in a model of hindlimb ischemia was significantly accelerated in miR-223-deficient mice.

Conclusion: 

These results indicate that miR-223 is rapidly downregulated upon EC culturing and alleviates the angiogenic block that exists in endothelial cellsin situ. Thus miR-223 may regulate endothelial cell differentiation and thein vivoquiescent phenotype.