UC Riverside

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 AMPK2 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.