Endothelial microRNA-126 (miR-126) modulates vascular development and angiogenesis. However, its role in the regulation of smooth muscle cell (SMC) function is unknown.

To elucidate the role of miR-126 secreted by endothelial cells (ECs) in regulating SMC turnover in vitro and in vivo, as well as the effects of shear stress on the regulation.

Coculture of SMCs with ECs or treatment of SMCs with conditioned media from static EC monoculture (EC-CM) increased SMC miR-126 level and SMC turnover; these effects were abolished by inhibition of endothelial miR-126 and by the application of laminar shear stress to ECs. SMC miR-126 did not increase when treated with EC-CM from ECs subjected to inhibition of miR biogenesis, or with CM from sheared ECs. Depletion of extracellular/secreted vesicles in EC-CM did not affect the increase of SMC miR-126 by EC-CM. Biotinylated miR-126 or FLAG (DYKDDDDK epitope)-tagged Argonaute2 transfected into ECs was detected in the cocultured or EC-CM–treated SMCs, indicating a direct EC-to-SMC transmission of miR-126 and Argonaute2. Endothelial miR-126 represses forkhead box O3, B-cell lymphoma 2, and insulin receptor substrate 1 mRNAs in the cocultured SMCs, suggesting the functional roles of the transmitted miR-126. Systemic depletion of miR-126 in mice inhibited neointimal lesion formation of carotid arteries induced by cessation of blood flow. Administration of EC-CM or miR-126 mitigated the inhibitory effect.

Endothelial miR-126 acts as a key intercellular mediator to increase SMC turnover, and its release is reduced by atheroprotective laminar shear stress.