MicroRNAs regulating cell pluripotency and vascular differentiation. Vascul Pharmacol. 2011;55:69-78. [PMID: 21854874 DOI: 10.1016/j.vph.2011.08.002]

BDNF (Brain-Derived Neurotrophic Factor) Promotes Embryonic Stem Cells Differentiation to Endothelial Cells Via a Molecular Pathway, Including MicroRNA-214, EZH2 (Enhancer of Zeste Homolog 2), and eNOS (Endothelial Nitric Oxide Synthase)

Objective- The NTs (neurotrophins), BDNF (brain-derived neurotrophic factor) and NT-3 promote vascular development and angiogenesis. This study investigated the contribution of endogenous NTs in embryonic stem cell (ESC) vascular differentiation and the potential of exogenous BDNF to improve the process of ESC differentiation to endothelial cells (ECs). Approach and Results- Mouse ESCs were differentiated into vascular cells using a 2-dimensional embryoid body (EB) model. Supplementation of either BDNF or NT-3 increased EC progenitors' abundance at day 7 and enlarged the peripheral vascular plexus with ECs and SM22α⁺ (smooth muscle 22 alpha-positive) smooth muscle cells by day 13. Conversely, inhibition of either BDNF or NT-3 receptor signaling reduced ECs, without affecting smooth muscle cells spread. This suggests that during vascular development, endogenous NTs are especially relevant for endothelial differentiation. At mechanistic level, we have identified that BDNF-driven ESC-endothelial differentiation is mediated by a pathway encompassing the transcriptional repressor EZH2 (enhancer of zeste homolog 2), microRNA-214 (miR-214), and eNOS (endothelial nitric oxide synthase). It was known that eNOS, which is needed for endothelial differentiation, can be transcriptionally repressed by EZH2. In turn, miR-214 targets EZH2 for inhibition. We newly found that in ESC-ECs, BDNF increases miR-214 expression, reduces EZH2 occupancy of the eNOS promoter, and increases eNOS expression. Moreover, we found that NRP-1 (neuropilin 1), KDR (kinase insert domain receptor), and pCas¹³⁰ (p130 Crk-associated substrate kinase), which reportedly induce definitive endothelial differentiation of pluripotent cells, were increased in BDNF-conditioned ESC-EC. Mechanistically, miR-214 mediated the BDNF-induced expressional changes, contributing to BDNF-driven endothelial differentiation. Finally, BDNF-conditioned ESC-ECs promoted angiogenesis in vitro and in vivo. Conclusions- BDNF promotes ESC-endothelial differentiation acting via miR-214.

Inhibition of microRNA-495 Enhances Therapeutic Angiogenesis of Human Induced Pluripotent Stem Cells

Therapeutic angiogenesis has emerged as a promising strategy to regenerate the damaged blood vessels resulting from ischemic diseases such as myocardial infarction (MI). However, the functional integration of implanted endothelial cells (ECs) in infarcted heart remains challenging. We herein develop an EC generation approach by inhibiting microRNA-495 (miR-495) in human induced pluripotent stem cells (hiPSCs) and assess the angiogenic potential for MI treatment. The anti-angiogenic miR-495 belonging to Dlk1-Dio3 miR cluster was identified through expression profiling and computational analysis. Loss-of-function experiments for miR-495 were performed using a lentiviral transfer of antisense sequence in hiPSCs. The pluripotency of hiPSCs was not impacted by the genetic modification. Induced with differentiation medium, miR-495 inhibition enhanced the expression of EC genes of hiPSCs, as well as the yield of ECs. Newly derived ECs displayed prominent angiogenic characteristics including tube formation, cell migration, and proliferation. Mechanistically, miR-495 mediated the expression of endothelial or angiogenic genes by directly targeting vascular endothelial zinc finger 1. After transplantation in immunodeficient MI mice, the derived ECs significantly increased neovascularization in the infarcted heart, prevented functional worsening, and attenuated expansion of infarct size. The functional integration of the implanted ECs into coronary networks was also enhanced by inhibiting miR-495. miR-495 represents a new target not only for promoting EC generation from hiPSCs but also for enhancing angiogenesis and engraftment of hiPSC-derived ECs in ischemic heart.

Concise review: MicroRNAs as modulators of stem cells and angiogenesis

MicroRNAs (miRs) are highly conserved, short noncoding RNA molecules that negatively regulate messenger RNA (mRNA) stability and/or translational efficiency. Since a given miR can control the expression of many mRNAs, their importance in governing gene expression in specific cell types including vascular cells and their progenitor cells has become increasingly clear. Understanding how the expression of miRs themselves is regulated and how miRs exert their influence on post-transcriptional gene control provides novel opportunities to dissect gene regulatory networks in clinically relevant cell types. A multitude of miRs have been identified with key roles in vascular development, homeostasis, function, disease, and regeneration. In this review, we will describe the impact of miRs on angiogenesis and their capacity to modulate the behavior of stem and progenitor cells which may be utilitarian for promoting vascular growth in ischemic tissue. Moreover, we summarize these strategies available for modulating miR expression and function and future therapeutic applications.

MicroRNAs as novel regulators of stem cell fate

Mounting evidence in stem cell biology has shown that microRNAs (miRNAs) play a crucial role in cell fate specification, including stem cell self-renewal, lineage-specific differentiation, and somatic cell reprogramming. These functions are tightly regulated by specific gene expression patterns that involve miRNAs and transcription factors. To maintain stem cell pluripotency, specific miRNAs suppress transcription factors that promote differentiation, whereas to initiate differentiation, lineage-specific miRNAs are upregulated via the inhibition of transcription factors that promote self-renewal. Small molecules can be used in a similar manner as natural miRNAs, and a number of natural and synthetic small molecules have been isolated and developed to regulate stem cell fate. Using miRNAs as novel regulators of stem cell fate will provide insight into stem cell biology and aid in understanding the molecular mechanisms and crosstalk between miRNAs and stem cells. Ultimately, advances in the regulation of stem cell fate will contribute to the development of effective medical therapies for tissue repair and regeneration. This review summarizes the current insights into stem cell fate determination by miRNAs with a focus on stem cell self-renewal, differentiation, and reprogramming. Small molecules that control stem cell fate are also highlighted.

MicroRNA regulation of endothelial homeostasis and commitment-implications for vascular regeneration strategies using stem cell therapies

Human embryonic (hESC) and induced pluripotent (hiPSC) stem cells have broad therapeutic potential in the treatment of a range of diseases, including those of the vascular system. Both hESCs and hiPSCs have the capacity for indefinite self-renewal, in addition to their ability to differentiate into any adult cell type. These cells could provide a potentially unlimited source of cells for transplantation and, therefore, provide novel treatments, e.g. in the production of endothelial cells for vascular regeneration. MicroRNAs are short, noncoding RNAs that act posttranscriptionally to control gene expression and thereby exert influence over a wide range of cellular processes, including maintenance of pluripotency and differentiation. Expression patterns of these small RNAs are tissue specific, and changes in microRNA levels have often been associated with disease states in humans, including vascular pathologies. Here, we review the roles of microRNAs in endothelial cell function and vascular disease, as well as their role in the differentiation of pluripotent stem cells to the vascular endothelial lineage. Furthermore, we discuss the therapeutic potential of stem cells and how knowledge and manipulation of microRNAs in stem cells may enhance their capacity for vascular regeneration.

MicroRNA-15a and microRNA-16 impair human circulating proangiogenic cell functions and are increased in the proangiogenic cells and serum of patients with critical limb ischemia

RATIONALE

Circulating proangiogenic cells (PACs) support postischemic neovascularization. Cardiovascular disease and diabetes mellitus impair PAC regenerative capacities via molecular mechanisms that are not fully known. We hypothesize a role for microRNAs (miRs). Circulating miRs are currently investigated as potential diagnostic and prognostic biomarkers.

OBJECTIVE

The objectives were the following: (1) to profile miR expression in PACs from critical limb ischemia (CLI) patients; (2) to demonstrate that miR-15a and miR-16 regulate PAC functions; and (3) to characterize circulating miR-15a and miR-16 and to investigate their potential biomarker value.

METHODS AND RESULTS

Twenty-eight miRs potentially able to modulate angiogenesis were measured in PACs from CLI patients with and without diabetes mellitus and controls. miR-15a and miR-16 were further analyzed. CLI-PACs expressed higher level of mature miR-15a and miR-16 and of the primary transcript pri-miR-15a/16-1. miR-15a/16 overexpression impaired healthy PAC survival and migration. Conversely, miR-15a/16 inhibition improved CLI-PAC-defective migration. Vascular endothelial growth factor-A and AKT-3 were validated as direct targets of the 2 miRs, and their protein levels were reduced in miR-15a/16-overexpressing healthy PACs and in CLI-PACs. Transplantation of healthy PACs ex vivo-engineered with anti-miR-15a/16 improved postischemic blood flow recovery and muscular arteriole density in immunodeficient mice. miR-15a and miR-16 were present in human blood, including conjugated to argonaute-2 and in exosomes. Both miRs were increased in the serum of CLI patients and positively correlated with amputation after restenosis at 12 months postrevascularization of CLI type 2 diabetes mellitus patients. Serum miR-15a additionally correlated with restenosis at follow-up.

CONCLUSIONS

Ex vivo miR-15a/16 inhibition enhances PAC therapeutic potential, and circulating miR-15a and miR-16 deserves further investigation as a prognostic biomarker in CLI patients undergoing revascularization.