MicroRNAs (miRs) are small noncoding RNAs that regulate gene expression by binding to target messenger RNAs (mRNAs), leading to translational repression or degradation. Here, we show that the miR-17approximately92 cluster is highly expressed in human endothelial cells and that miR-92a, a component of this cluster, controls the growth of new blood vessels (angiogenesis). Forced overexpression of miR-92a in endothelial cells blocked angiogenesis in vitro and in vivo. In mouse models of limb ischemia and myocardial infarction, systemic administration of an antagomir designed to inhibit miR-92a led to enhanced blood vessel growth and functional recovery of damaged tissue. MiR-92a appears to target mRNAs corresponding to several proangiogenic proteins, including the integrin subunit alpha5. Thus, miR-92a may serve as a valuable therapeutic target in the setting of ischemic disease.

The regeneration of new myocardium by stem or progenitor cells is an important therapeutic option. Cellular or nuclear fusion is considered as an alternative to cell reprogramming by transdifferentiation. However, the generation of hybrid cells may also be a consequence of a transient transmembrane exchange of proteins and organelles between cells. Therefore, we investigated the formation of intercellular connections, which may allow the transport of macromolecular structures between labeled adult human endothelial progenitor cells (EPC) and GFP-expressing neonatal rat cardiomyocytes (CM) in a coculture system. FACS analysis revealed that, 6 days after initiation of coculture, 2.1؎0.4% of the cells stained positive for GFP and Dil-ac-LDL. 6 hours after initiation of the coculture, ultrafine intercellular structures between Dil-ac-LDL-labeled EPC and GFPexpressing CM were observed. The number of EPC, which established nanotubular connections with CM increased from 0.5؎0.2% after 6 hours to 2.6؎0.3% after 24 hours of coculture. The intercellular connections had a diameter from 50 to 800 nm, a length of 5 to 120 m, and were only transiently established. To determine whether the nanotubular structures allowed the transport of organelles, we labeled CM with a mitochondrial live tracker (MitoTracker). Using time-lapse video microscopy, we observed the transport of stained complexes between CM and EPC resulting in up-take of MitoTracker-positive structures in EPC. Thus, the present study shows a novel type of cell-tocell communication between progenitor cells and CM in vitro, which may contribute to the acquisition of a cardiomyogenic phenotype independent of permanent cellular or nuclear fusion.

We conclude that this anti-MCP-1 gene therapy may serve not only to reduce atherogenesis but also to stabilize vulnerable atheromatous plaques. This strategy may be a useful and feasible form of gene therapy against atherosclerosis in humans.

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JmjC domain-containing proteins play a crucial role in the control of gene expression by acting as protein hydroxylases or demethylases, thereby controlling histone methylation or splicing. Here, we demonstrate that silencing of Jumonji domain-containing protein 6 (Jmjd6) impairs angiogenic functions of endothelial cells by changing the gene expression and modulating the splicing of the VEGF-receptor 1 (Flt1). Reduction of Jmjd6 expression altered splicing of Flt1 and increased the levels of the soluble form of Flt1, which binds to VEGF and placental growth factor (PlGF) and thereby inhibits angiogenesis. Saturating VEGF or PlGF or neutralizing antibodies directed against soluble Flt1 rescued the angiogenic defects induced by Jmjd6 silencing. Jmjd6 interacts with the splicing factors U2AF65 that binds to Flt1 mRNA. In conclusion, Jmjd6 regulates the splicing of Flt1, thereby controlling angiogenic sprouting.