MicroRNA-21 represses human cystathionine gamma-lyase expression by targeting at specificity protein-1 in smooth muscle cells

Targeting smooth muscle microRNAs for therapeutic benefit in vascular disease

In view of the bioinformatic projection that a third of all protein coding genes and essentially all biological pathways are under control of microRNAs (miRNAs), it is not surprising that this class of small RNAs plays roles in vascular disease progression. MiRNAs have been shown to be involved in cholesterol turnover, thrombosis, glucose homeostasis and vascular function. Some miRNAs appear to be specific for certain cells, and the role that such cell-specific miRNAs play in vascular disease is only beginning to be appreciated. A notable example is the miR-143/145 cluster which is enriched in mature and highly differentiated smooth muscle cells (SMCs). Here we outline and discuss the recent literature on SMC-expressed miRNAs in major vascular diseases, including atherosclerosis, neointima formation, aortic aneurysm formation, and pulmonary arterial hypertension. Forced expression of miR-145 emerges as a promising strategy for reduction and stabilization of atherosclerotic plaques as well as for reducing neointimal hyperplasia. It is concluded that if obstacles in the form of delivery and untoward effects of antimirs and mimics can be overcome, the outlook for targeting of SMC-specific miRNAs for therapeutic benefit in vascular disease is bright.

Reduced cystathionine γ-lyase and increased miR-21 expression are associated with increased vascular resistance in growth-restricted pregnancies: hydrogen sulfide as a placental vasodilator

Increased vascular impedance in the fetoplacental circulation is associated with fetal hypoxia and growth restriction. We sought to investigate the role of hydrogen sulfide (H₂S) in regulating vasomotor tone in the fetoplacental vasculature. H₂S is produced endogenously by catalytic activity of cystathionine β-synthase and cystathionine γ-lyase (CSE). Immunohistochemical analysis localized CSE to smooth muscle cells encircling arteries in stem villi. Immunoreactivity was reduced in placentas from pregnancies with severe early-onset growth-restriction and preeclampsia displaying abnormal umbilical artery Doppler waveforms compared with preeclamptic placentas with normal waveforms and controls. These findings were confirmed at the protein and mRNA levels. MicroRNA-21, which negatively regulates CSE expression, was increased in placentas with abnormal Doppler waveforms. Exposure of villus explants to hypoxia-reoxygenation significantly reduced CSE protein and mRNA and increased microRNA-21 expression. No changes were observed in cystathionine β-synthase expression, immunolocalized principally to the trophoblast, in pathologic placentas or in vitro. Finally, perfusion of normal placentas with an H₂S donor, after preconstriction with a thromboxane mimetic, resulted in dose-dependent vasorelaxation. Glibenclamide and N^G-nitro-l-arginine methyl ester partially blocked the effect, indicating that H₂S acts through ATP-sensitive K⁺ channels and nitric oxide synthesis. These results demonstrate that H₂S is a powerful vasodilator of the placental vasculature and that expression of CSE is reduced in placentas associated with increased vascular resistance.

Pathogenic arterial remodeling: the good and bad of microRNAs

A number of cardiovascular diseases, such as restenosis, aneurysm, and atherosclerosis, lead to vascular remodeling associated with complex adaptive reactions of different cell populations. These reactions include growth of smooth muscle cells, proliferation of endothelial cells, and the inflammatory response of macrophages. MicroRNAs (miRNAs), a class of short RNAs, play key roles in various biological processes and in the development of human disease by post-transcriptional regulation of gene expression. Here, we review the molecular mechanisms of a subset of miRNAs involved in vascular remodeling, including miR-143/145, miR-221/222, miR-126, miR-21, and miR-155. Some of these miRNAs, such as miR-143/145 and miR-126, have been shown to be protective during vascular remodeling, whereas others, such as miR-21, may promote the cellular response that leads to neointima formation. The increasing knowledge regarding the roles of miRNAs in vascular remodeling opens novel avenues for the treatment of various cardiovascular diseases. However, more in vivo studies on the functional roles of these miRNAs are required in the future.

The role of microRNAs in arterial remodelling

Adaptive alterations of the vessel wall architecture, called vascular remodelling, can be found in arterial hypertension, during the formation of aneurysms, in restenosis after vascular interventions, and in atherosclerosis. MicroRNAs (miR) critically affect the main cellular players in arterial remodelling and may either promote or inhibit the structural changes in the vessel wall. They regulate the phenotype of smooth muscle cells (SMCs) and control the inflammatory response in endothelial cells and macrophages. In SMCs, different sets of miRs induce either a synthetic or contractile phenotype, respectively. The conversion into a synthetic SMC phenotype is a crucial event in arterial remodelling. Therefore, reprogramming of the SMC phenotype by miR targeting can modulate the remodelling process. Furthermore, the effects of stimuli that induce remodelling, such as shear stress, angiotensin II, oxidised low-density lipoprotein, or apoptosis, on endothelial cells are mediated by miRs. The endothelial cell-specific miR-126, for example, is transferred in microvesicles from apoptotic endothelial cells and plays a protective role in atherogenesis. The inflammatory response of the innate immune system, especially through macrophages, promotes arterial remodelling. miR-155 induces the expression of inflammatory cytokines, whereas miR-146a and miR-147 are involved in the resolution phase of inflammation. However, in vivo data on the role of miRs in vascular remodelling are still scarce, which are required to test the therapeutic potential of the available, highly effective miR inhibitors.