Tgf-¦Â Regulation Of Microrna Function In Endothelial Cells And Its Mechanism

The transforming growth factor-β (TGF-β) pathway plays important roles in physiologicaland pathological angiogenesis. The critical roles of TGF-β in angiogenesis have been revealed bygenetic studies in human beings and mice. Mutations in endoglin, ALK1or Smad4can causehereditary hemorrhagic telangiectasia (HHT). In mouse, deletion of varies TGF-β signalingmembers, including TGF-β1, Tgfbr2, Alk5, Alk1, endoglin, Smad1, Smad4and Smad5, all leads toembryonic lethality due to severe vascular abnormalities, including angiogenic defect and absenceof mural cell formation. TGF-β can directly regulates its target genes which get involved in theprocess of angiogenesis. Our previous study has revealed that Smad4cooperates with Notch toregulate the transcription of N-cadherin, which is important to maintain vascular integrity. Fullyunderstanding the molecular mechanisms of TGF-β in regulating angiogenesis needs furtherinvestigation.MicroRNAs (miRNAs) are a class of18-25nt small noncoding RNAs function by negativelyregulating gene expression, either through translation inhibition or destabilization of mRNA. Anumber of miRNAs have been demonstrated to have pro-or anti-angiogenic effects throughregulating endothelial migration, survival and cell cycle. miR-126, miR-23-27-24cluster,miR-424, miR-130a, miR-296, and miR-210promote angiogenesis, whereas miR-17-92cluster,miR-214, miR-200b, miR-221and miR-222block angiogenesis. Specific miRNAs can modulatethe endothelial responses to blood flow, hypoxia, serum or VEGF. Numbers of microRNAs havebeen found to be regulated by TGF-β pathway. However, the role of endothelial miRNAs in theTGF-β-mediated control of angiogenesis is still largely unknown.Here we investigated the regulation of endothelial microRNA-8029(miR-8029) by TGF-β signaling and the potential role of miR-8029in angiogenesis.Our study includes three parts. The miRNAs regulated by TGF-β in endothelium werescreened firstly, the function of the candidate miRNA in angiogenesis was investigated then, andthe target of the miRNA was identified finally.miR-8029is conserved between species and highly expressed in endothelial cells. We foundthat miR-8029was directly up-regulated by TGF-β/Smad4signaling in endothelial cells. In chickchorioallantoic membrane assay, miR-8029overexpression promoted the formation of new bloodvessels and miR-8029suppression partially blocked TGF-β1-stimulated angiogenesis.Consistantly,miR-8029overexpression increased migration and tube formation in endothelial cultures.Mechanistically, miR-8029directly targeted phosphatase and tensin homolog (PTEN) inendothelial cells, leading to activation of the Akt-pathway. PTEN knockdown recapitulated therole of miR-8029in endothelial migration, whereas AKT inhibition completely attenuated the roleof miR-8029in migration and tube formation.In summary, we revealed that TGF-β regulated miR-8029promoted angiogenesis,demonstrating a novel epigenetic mechanism of TGF-β signaling in controlling endothelialfunction. For the first time, we deciphered the role of miR-8029in endothelial cells. We identifiedmiR-8029as a pro-angiogenic miRNA by positively regulating endothelial migration and tubeformation. In addition, we showed that TGF-β signaling could activate Akt signaling inendothelium by upregulating the miRNA targeting PTEN. Dysregulation of miR-8029occurs insome types of cancers. Whether the dysregulation is mediated by TGF-β signaling, and whethermiR-8029plays a role in tumor angiogenesis are worth further investigation.