The Role of AMPK and miR-92a in the Shear Stress Regulation of KLF2
- Author(s): Wu, Wei
- Advisor(s): Shyy, John Y-J
- et al.
The vascular endothelium is essential to maintain normal vascular homostasis and its dysfunction is a hallmark of atherosclerosis development. Up-regulated by laminar 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, I examined the regulation of KLF2 expression at both transcriptional level and post-transcriptional level response to different flow pattern.
In the first part of the study, I demonstrated that AMP-activated protein kinase (AMPK) is necessary and sufficient to regulate the expression of PS-induced KLF2 and its downstream (eNOS and ET-1). In addition, I found PS induced the 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 AMPK2 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, I examined the role of miRNAs, particularly miR-92a, in the atheroprotective flow-regulated KLF2. Fistly, I found KLF2 is regulated by miRNA by knockdown Dicer with siRNA. miR-92a directly binds to KLF2 3'UTR and inhibit its mRNA level and protein level. Subsequent studies revealed that, atheroprotective laminar flow downregulated 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 atheroprotective than atheroprone areas of the mouse aorta. Furthermore, mouse carotid arteries receiving pre-92a exhibited impaired vasodilatory response to flow. Collectively, my study suggests that atheroprotective flow patterns decrease the level of miR-92a, which in turn increases KLF2 expression to maintain endothelial homeostasis.