Abstract 21301: Modulation of EC Function by miR-155, a Shear Stress-Responsive miRNA
Endothelial cells (ECs) respond to changes in shear stress forces by modulating cell morphology, migration, apoptosis, proliferation, and survival. MicroRNAs (miRNAs) are a class of short (19–25 nt), single stranded, noncoding RNAs that regulate the expression of genes involved in these same processes. Recently, we reported the miRNA expression profile in HUVECs subjected to prolonged unidirectional shear stress (USS, 24 hours, 15 dynes/cm2), and we demonstrated that overexpression of shear-responsive miR-21 enhanced eNOS activity and decreased apoptosis. This effect was mediated through suppression of PTEN and enhanced activity of the PI3K/Akt survival pathway. In the current study, we examined the impact of another shear responsive miRNA, miR-155, on EC apoptosis and morphology. In HUVECs transfected with pre-miR-155, we found a dose-dependent effect on EC apoptosis and identified two important mRNA targets. Transfection of low concentrations of pre-miR-155 (10 nM) decreased caspase 3 activity 50%, and enhanced eNOS phosphorylation 2.5 fold. This effect was mediated through suppression of SHIP1, a phosphatase like PTEN that antagonizes the PI3K/Akt pathway. Thus, we have shown that two shear-responsive miRNAs both enhance activity of the PI3K/Akt pathway, but through two different mechanisms: suppression of SHIP1 (miR-155) or PTEN (miR-21). Interestingly, transfection of higher concentrations of pre-miR-155 (75 -100 nM) actually increased caspase 3 activity 2-fold. Furthermore, we found that overexpression of miR-155 decreased the expression of RhoA, a regulator of actin cytoskeleton organization, in a dose-dependent fashion. In fact, cells overexpressing miR-155 had a significant decrease in F-actin staining and a dramatic change in actin cytoskeleton organization, particularly in the peri-nuclear region. In conclusion, miR-155 is one of several miRNAs that are upregulated in ECs subjected to prolonged USS. Our data are the first to demonstrate the importance of the extent of miRNA upregulation on EC phenotype. In addition, our data show a novel mechanism by which shear stress modulates EC apoptosis and eNOS activity through the action of multiple miRNAs.
- © 2010 by American Heart Association, Inc.