Abstract 16109: A Selective Cargo of Non-coding RNAs Mediate Therapeutic Potential of Human CD34+ Stem Cell-derived Exosomes

Abstract

Introduction: Clinical application of human CD34+ stem cells is associated with improved exercise tolerance and therapeutic angiogenesis in patients with myocardial ischemia. We reported the first description of independent therapeutic potential of CD34+ stem cell-derived exosomes (CD34Exo) to that of parent cell by mechanisms that still remain poorly understood. Hypothesis: Herein, we tested the hypothesis that CD34Exo may selectively carry non-coding RNA (ncRNA) cargo targeted for pro-angiogenic signaling and ischemic tissue repair. Methods and Results: Murine models of myocardial ischemia employed throughout the study. Cell-free CD34Exo replicated the therapeutic activity of their parent cells by significantly improving myocardial ischemia (ejection fraction, 42±4 v 22±6%; capillary density, 113±7 v 66±6/HPF; fibrosis, 27±2 v 48±7%; p<0.05, n=7-12) compared with a PBS control. Confocal imaging and flow cytometry analyses revealed that CD34Exo was selectively internalized into endothelial cells and cardiomyocytes in the CD34Exo-injected ischemic hearts. MicroRNA (miR) profiling identified several pro-angiogenic miRs including miR-126 that are selectively enriched in CD34Exo. Mice injected with CD34Exo show elevated miR-126 and several pro-angiogenic mRNAs in ischemic myocardium, however did not affect endogenous miR-126 synthesis suggestive of direct CD34Exo-mediated miR-126 transfer. Depletion of miR-126 reduced the therapeutic efficacy of CD34Exo both in vitro and in vivo indicating a critical role for miR-126. Using fluorescent-tagged miR-126, we monitored in real-time the uptake and transfer of miR-126 by endothelial cells both in vitro and in vivo. We finally provide novel insights underlying CD34Exo function in regulating endothelial proliferation through identification of novel pathways regulated by miR-126 in endothelial cells. Conclusion: Our results reveal specific CD34Exo-shuttled microRNAs and pathways regulated in the ischemic myocardium. Our work presents a molecular framework for CD34Exo mechanism and function in therapeutic angiogenesis. Precise understanding of CD34Exo mechanisms could significantly amplify the therapeutic benefits of CD34Exo in ischemic tissue regeneration and repair.