Considerable progress has been made on the development of adipose-derived stem/stromal cells (ASCs) as pro-angiogenic therapeutic tools. However, variable clinical results highlight the need for devising strategies to enhance their therapeutic efficacy. Since ASCs proliferate and stabilize newly formed vessels during the angiogenic phase of adipose tissue formation, we hypothesized that mimicking an angiogenic milieu during culture of ASCs would enhance their capacity to support endothelial cell survival and angiogenesis. To test this, we compared the effect of an endothelial growth medium (EGM-2) and conventional media (αMEM) on the progenitor and angiogenic properties of ASCs. ASCs cultured in EGM-2 (ASC-EGM) displayed the highest clonogenic efficiency, proliferative potential and multilineage potential. After co-culture under growth factor starvation, only ASC-EGM attenuated luciferase-expressing human umbilical vein endothelial cells (HUVECluc) apoptosis and supported the formation of endothelial cords in a dose-dependent manner. These effects were recapitulated by the conditioned medium of ASC-EGM, which displayed a 100-fold higher expression of hepatocyte growth factor in comparison with ASC-αMEM. Next, HUVECluc and ASCs were co-transplanted subcutaneously into immunodeficient mice, and the survival of HUVECluc was monitored by bioluminescent imaging. After 60 days, the survival of HUVECluc transplanted alone was equivalent to that of HUVECluc co-transplanted with ASC-αMEM (15.0 ± 0.7 vs. 13.0 ± 0.5%). Strikingly, co-transplantation with ASC-EGM increased HUVECluc survival to 105.0 ± 3.5%, and the resulting organoids displayed functional vasculature with the highest human-derived vascular area. These findings demonstrate that pre-conditioning of ASCs in endothelial growth medium augment their pro-angiogenic properties and could enhance their therapeutic efficacy against ischemic diseases.
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The authors would like to thank Dr. Marina Rosique for providing us the samples of human adipose tissue as well as Patrícia Palma and Camila Menezes for their support with the acquisition of flow cytometry data. This work was funded with resources from São Paulo Research Foundation (FAPESP, Brazil), Coordination for Improvement of Higher Education Personnel (CAPES, Brazil) and from the National Counsel of Technological and Scientific Development (CNPq, Brazil).
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Conflict of interest
The authors have no conflicts of interest to declare.
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