Abstract 6: Therapeutic Angiogenesis by Human CD34+ Hematopoietic Stem Cells via Exosomes-Mediated MicroRNA Transfer
Introduction: Locally transplanted human CD34+ hematopoietic stem cells have stimulated neovascularization in preclinical studies and have been associated with functional improvements in phase I and II clinical trials of patients with ischemic cardiovascular diseases. Recently, we have demonstrated that membrane-bound nano-vesicles called exosomes are one of the primary pro-angiogenic components of human CD34+ cell paracrine secretion that induced angiogenesis independently of the cells.
Here, we hypothesize that the functional benefits associated with CD34+ cell therapy are primarily mediated by the secretion of exosomes (Exo), and that CD34+ Exo transfer pro-angiogenic microRNAs to promote angiogenesis and ischemic tissue repair.
Methods and Results: Therapeutic potential of CD34+ Exo isolated from adult human peripheral blood-derived CD34+ cells was evaluated in a mouse model of hind limb ischemia (HLI). Similar to CD34+ cells, administration of CD34+ Exo from equal number of cells induced angiogenesis and tissue repair; it significantly improved perfusion (ratio: 1.01±0.04 v 0.57±0.1, P<0.05), increased capillary density (1.8±0.3/HPF v 0.9±0.1/HPF, p<0.001) and prevented ischemic leg amputation (16% v 100%), compared to Exo from non-angiogenic, CD34+ cell-depleted-mononuclear cells (MNC Exo). Our microarray data and confirmatory tests revealed that unlike MNC Exo, CD34+ Exo are enriched in pro-angiogenic miRNAs such as miR-126. Flow cytometry and live confocal imaging demonstrated that Cy3-tagged miRNA in CD34+ Exo is directly transferred to endothelial cells in vitro and in ischemic tissues in vivo; concurrent loss of function gain of function studies prove that direct transfer of miR-126 is crucial for CD34+ Exo-induced angiogenesis and functional recovery. To address whether exosome secretion is needed for miR-126 transfer, we are exploring the effect of inhibition of exosome secretion from CD34+ cells.
Conclusion: CD34+ exosomes transfer the pro-angiogenic miR-126 to endothelial cells in the ischemic tissues to induce angiogenesis and ischemic tissue repair. Our study illustrates a mechanism of stem cell communication involving intercellular traffic of miRNAs via exosomes to induce functional recovery.
- © 2012 by American Heart Association, Inc.