MicroRNA control of vascular endothelial growth factor signaling output during vascular development

Maturation and differentiation of the fetal vasculature

Rapid postnatal growth and differentiation of fetal arterial smooth muscle is coordinated by a cacophony of growth factors, one of the most important of which is vascular endothelial growth factor (VEGF). In fetal arterial smooth muscle, VEGF influences both the expression and intracellular organization of contractile proteins and helps mediate hypoxic vascular remodeling. Numerous factors influence the expression of VEGF and its receptors, including chronic hypoxia, maternal food restriction, glucocorticoids, and miRNA. Continued study of the coupling between VEGF and transcription factors such as myocardin that govern smooth muscle differentiation, offers great promise for better clinical management of neonates at risk for cardiovascular dysregulation.

MicroRNA signature and function in retinal neovascularization

Ischemic retinopathies are clinically well-defined chronic microvascular complications characterized by gradually progressive alterations in the retinal microvasculature and a compensatory aberrant neovascularization of the eye. The subsequent metabolic deficiencies result in structural and functional alterations in the retina which is highly susceptible to injurious stimuli such as diabetes, trauma, hyperoxia, inflammation, aging and dysplipidemia. Emerging evidence indicates that an effective therapy may require targeting multiple components of the angiogenic pathway. Conceptually, mircoRNA (miRNA)-based therapy provides the rationale basis for an effective antiangiogenic treatment. miRNAs are an evolutionarily conserved family of short RNAs, each regulating the expression of multiple protein-coding genes. The activity of specific miRNAs is important for vascular cell signaling and blood vessel formation and function. Recently, important progress has been made in mapping the miRNA-gene target network and miRNA-mediated gene expression control. Here we highlight the latest findings on angiogenic and antiangiogenic miRNAs and their targets as well as potential implications in ocular neovascular diseases. Emphasis is placed on how specific vascular-enriched miRNAs regulate cell responses to various cues by targeting several factors, receptors and/or signaling molecules in order to maintain either vascular function or dysfunction. Further improvement of our knowledge in not only miRNA specificity, turnover, and transport but also how miRNA sequences and functions can be altered will enhance the therapeutic utility of such molecules.

MiRNA-145 is involved in the development of resistin-induced insulin resistance in HepG2 cells

BACKGROUND

Resistin is associated with insulin resistance, and determining its developmental and molecular mechanisms may help the development of novel treatments. MicroRNAs (miRNAs) are involved in many physiological and pathological processes as negative regulators. However, it remains unclear whether miRNAs play a role in resistin-induced insulin resistance. We performed mouse liver miRNA microarrays to analyze the differences in expression between resistin-treated and control mice. Resistin upregulated miR-145 both in vivo and in vitro. Therefore, we aimed to study whether miR-145 played a role in resistin-induced insulin resistance.

METHODS AND RESULTS

We transfected HepG2 cells, and used miR-145 mimics and inhibitors to assess the role of miR-145 in resistin-induced insulin resistance. The overexpression of miR-145 inhibited glucose uptake in HepG2 cells, diminished the phosphorylation of Akt and IRS-1, and induced insulin resistance in hepatocytes. Next, a study of transcriptional regulation revealed that p65 was essential for the upregulation of miR-145 by resistin, and chromatin immunoprecipitation (ChIP) confirmed that p65 could bind to the promoter region of miR-145.

CONCLUSION

miR-145 plays a role in the development of resistin-induced insulin resistance via the p65 pathway.

MicroRNA-223 Antagonizes Angiogenesis by Targeting β1 Integrin and Preventing Growth Factor Signaling in Endothelial Cells

Rationale:

Endothelial cells in situ are largely quiescent, and their isolation and culture are associated with the switch to a proliferative phenotype.

Objective:

To identify antiangiogenic microRNAs expressed by native endothelial cells that are altered after isolation and culture, as well as the protein targets that regulate responses to growth factors.

Methods and Results:

Profiling studies revealed that miR-223 was highly expressed in freshly isolated human, murine, and porcine endothelial cells, but those levels decreased in culture. In primary cultures of endothelial cells, vascular endothelial cell growth factor and basic fibroblast growth factor further decreased miR-223 expression. The overexpression of precursor-miR-223 did not affect basal endothelial cell proliferation but abrogated vascular endothelial cell growth factor–induced and basic fibroblast growth factor–induced proliferation, as well as migration and sprouting. Inhibition of miR-223 in vivo using specific antagomirs potentiated postnatal retinal angiogenesis in wild-type mice, whereas recovery of perfusion after femoral artery ligation and endothelial sprouting from aortic rings from adult miR-223 −/y animals were enhanced. MiR-223 overexpression had no effect on the growth factor–induced activation of ERK1/2 but inhibited the vascular endothelial cell growth factor–induced and basic fibroblast growth factor–induced phosphorylation of their receptors and activation of Akt. β1 integrin was identified as a target of miR-223 and its downregulation reproduced the defects in growth factor receptor phosphorylation and Akt signaling seen after miR-223 overexpression. Reintroduction of β1 integrin into miR-223–ovexpressing cells was sufficient to rescue growth factor signaling and angiogenesis.

Conclusions:

These results indicate that miR-223 is an antiangiogenic microRNA that prevents endothelial cell proliferation at least partly by targeting β1 integrin.