Abstract 15645: Exosomes from Human CD34+ Cells Are a Crucial Paracrine Component for Ischemic Tissue Repair and Angiogenesis
In early clinical trials, human CD34+ stem cells (CD34) have been shown to improve exercise tolerance in patients with myocardial ischemia and reduce amputation rates in limb ischemia. CD34 have been shown to promote angiogenesis by secreting paracrine factors. Recently, we have demonstrated that exosomes (Exo), membrane bound nano-vesicles, secreted by CD34 are a major component of their paracrine secretion which induces angiogenesis. We hypothesized that Exo secreted from CD34 are a crucial component for ischemic tissue repair and angiogenesis.
Methods and Results: We isolated Exo from the conditioned media (CM) of adult human peripheral blood CD34. We compared the effect of CD34 Exo, CD34 cells, CM, and Exo-depleted-CM, all derived from equal number of cells, in a mouse model of hind limb ischemia. Treatment with CD34 Exo resulted in significant improvement in ischemia compared to treatment with Exo-depleted-CM (limb perfusion ratio, 1.02±0.2 v 0.8±0.2; motor score, 3.2±1.1 v 2.2±0.8; salvage score, 3.4±1.3 v 2.2±0.8; P<0.05, n=7-12) or treatment with PBS. The beneficial effects of CD34 Exo were similar to CD34 cells and CM containing Exo. This suggests that CD34 Exo in the CM is the key paracrine component promoting tissue repair. Next, we compared ischemic tissue repair of CD34 Exo with a unselected mononuclear cell Exo isolated from equal number of cells: (CD34 Exo vs MNC Exo: perfusion ratio, 1.01±0.04 v 0.57±0.1, P<0.05; capillary density, 1.8±0.3 v 0.9±0.1 per HPF, P<0.001; amputation rate, 16% v 100%). In vitro live imaging analyses showed internalization of fluorescently labeled CD34 Exo into vesicular compartments of recipient HUVECs suggesting direct transfer of Exo mediated signals to target endothelial cells. Ongoing studies will test if exosome secretion is required for CD34 cell therapeutic function by selectively inhibiting the exosome secretion.
Conclusions: Our data suggest that CD34 Exo are an important paracrine component of CD34+ cell secretion. Both CD34+ cells and CD34+ Exo are equally effective in ischemic tissue repair and angiogenesis. Thus, the functional benefits associated with CD34 therapy may be mediated by exosomes and exosome administration might be a viable alternative to cell-transplantation therapies.
- © 2011 by American Heart Association, Inc.