Abstract 14910: Shear Stress-Regulated Mir-27a/b Controls Pericyte Recruitment: Implications for Vessel Maturation
Vessel maturation involves the recruitment of mural cells such as pericytes or smooth muscle cells and deposition of extracellular matrix. Laminar shear stress is a major trigger for vessel maturation. However, the molecular mechanisms by which shear stress affects the recruitment of pericytes and vascular smooth muscle cells are unclear. MicroRNAs (miRs) are small non-coding RNAs, which post-transcriptionally control gene expression. Since shear stress regulates various miRs, we hypothesize that flow-induced miRs may contribute to the inhibition of repulsive clues and facilitate mural cell coverage of native new capillaries.
Laminar shear stress for 72h induces the up-regulation of miR-27a and miR-27b (1.7±0.2, 2.8±0.24-fold vs static, p<0.05) in cultured endothelial cells (ECs) and in mouse femoral artery segments that were exposed to physiological shear stress ex vivo (1.7±0.23, 1.5±0.14-fold vs no flow, p<0.05). Predicted targets for miR-27a/b include members of the semaphorin (SEMA) family, which are known to regulate repulsive signaling, and angiopoietin-2 (Ang-2), which acts as an antagonist for Ang-1/Tie2 signaling and causes pericyte drop-off and vessel destabilization. We showed that miR-27a and miR-27b overexpression reduces SEMA6A (51.5±12%, 63.5±13.5%), SEMA6D (62±18%, 58±26%), and Ang-2 (47.5±9%, 51.5±11%, respectively). Vice versa, knockdown of miR-27a/b by a LNA-based miR-inhibitor increases SEMA6D (203±70%) and Ang-2 (199±57%) expression.
To determine whether miR-27 may control pericyte recruitment, we tested the effect of endothelial miR-27a/b expression on the adhesion of pericytes. Indeed, overexpression of miR-27b increased the adhesion of pericytes (p<0.05), whereas inhibition of miR-27a/b reduced pericyte adhesion in vitro (p<0.05). In vivo 2 photon imaging demonstrated that pericytes were more detached after treatment of mice with miR-27a/b inhibitors. Additionally, knockdown of the semaphorin receptors (neuropilins and plexins) in pericytes leads to a significant reduction of pericyte adhesion to endothelial cells in vitro.
Taken together, our data demonstrate that shear stress regulates miR-27a/b, which target Ang-2 and semaphorins, and controls pericyte adhesion.
- © 2013 by American Heart Association, Inc.