| The vascular endothelium is essential to maintain normal vascular homostasis and its dysfunction is a hallmark of atherosclerosis development. Upregulated by athero-protective flow, the transcription factor Kruppel-like factor 2 (KLF2) is a crucial integrator for maintaining multiple endothelial functions, including anti-inflammation, anti-thrombosis, vasodilatation, and anti-angiogenesis. To investigate the molecular mechanism by which KLF2 is regulated by different flow pattern, the regulation of KLF2 expression was examined at both transcriptional level and post-transcriptional level response to different flow pattern.;In the first part of the study, AMP-activated protein kinase (AMPK) was demonstrated to be necessary and sufficient to regulate the expression of pulsatile shear stress (PS)-induced KLF2 and its downstream (eNOS and ET-1). In addition, The PS-induced phosphorylation of ERK5 and MEF2, which regulates the KLF2 expression, is AMPK-dependent in ECs. Furthermore, the phosphorylation levels of ERK5 and MEF2, as well as the expression of KLF2, were significantly reduced in the aorta of AMPKalpha2 knockout mice when compared with wild-type control mice. These findings suggest that AMPK/ERK5/MEF2 is a functional signaling for the regulation of KLF2 transcription.;MicroRNAs (miRNAs) are non-coding small RNAs that regulate gene expression at the post-transcriptional level. In the second part, the role of miRNAs, particularly miR-92a, was examined in the atheroprotective flow-regulated KLF2. Fistly, it was demonstrated that KLF2 is regulated by miRNA by knocking down Dicer with siRNA. In silico analysis predicted that miR-92a could bind to the 3' untranslated region (3'UTR) of KLF2. Overexpression of miR-92a precursor (pre-92a) decreased the expression of KLF2 and the KLF2-regulated endothelial nitric oxide synthase (eNOS) and thrombomodulin (TM) at mRNA and protein levels. Subsequent studies revealed that, athero-protective laminar flow down-regulated the level of miR-92a to induce KLF2, and the level of this flow-induced KLF2 was reduced by pre-92a. Consistent with these findings, miR-92a level was lower in the endothelium of athero-protective than athero-prone areas of the mouse aorta. Furthermore, mouse carotid arteries receiving pre-92a exhibited impaired vasodilatory response to flow. Collectively, these results suggest that athero-protective flow patterns decrease the level of miR-92a, which in turn increases KLF2 expression to maintain endothelial homeostasis.;Taken together, this study demonstrated the potency of shear stress on EC function is due to the upregulation of KLF2 at both transcriptional level and post-transcriptional level. |
