Abstract 14703: Cell-Free Exosomes from Human CD34+ Progenitor Cells Induce Therapeutic Angiogenesis via Targeted Delivery of Mir-126 to Endothelial Cells
In early clinical trials, human CD34+ stem cells have been shown to improve exercise tolerance in patients with myocardial ischemia and reduce amputation rates in limb ischemia. Recently, we have shown that CD34+ cells secrete membrane bound nano-vesicles called exosomes (Exo) as a major paracrine pro-angiogenic component that induces angiogenesis, independent of the cells. We hypothesize that isolated exosomes from CD34+ cells (CD34+ Exo) mimic beneficial effects of the cells and promote tissue regeneration and repair via transfer of pro-angiogenic microRNAs.
Methods and Results: Therapeutic potential of CD34+ Exo isolated from the conditioned media of equal number of adult human peripheral blood-derived CD34+ cells was evaluated in a mouse model of hind limb ischemia. Similar to CD34+ cells, administration of cell-free CD34+ Exo 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 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). 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 to endothelial cells is crucial for CD34+ Exo-induced angiogenesis. We are studying the effect of Exo-transferred miR-126 on modulation of angiogenic gene expression in the target endothelial cells lacking mir-126 (either by dicer or Egfl-7 knockdown). To address whether exosomes are the primary mode of miR-126 transport, 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.