Long-Term Severe In Vitro Hypoxia Exposure Enhances the Vascularization Potential of Human Adipose Tissue-Derived Stromal Vascular Fraction Cell Engineered Tissues

Abstract

The therapeutic potential of mesenchymal stromal/stem cells (MSC) for treating cardiac ischemia strongly depends on their paracrine-mediated effects and their engraftment capacity in a hostile environment such as the infarcted myocardium. Adipose tissue-derived stromal vascular fraction (SVF) cells are a mixed population composed mainly of MSC and vascular cells, well known for their high angiogenic potential. A previous study showed that the angiogenic potential of SVF cells was further increased following their in vitro organization in an engineered tissue (patch) after perfusion-based bioreactor culture. This study aimed to investigate the possible changes in the cellular SVF composition, in vivo angiogenic potential, as well as engraftment capability upon in vitro culture in harsh hypoxia conditions. This mimics the possible delayed vascularization of the patch upon implantation in a low perfused myocardium. To this purpose, human SVF cells were seeded on a collagen sponge, cultured for 5 days in a perfusion-based bioreactor under normoxia or hypoxia (21% and <1% of oxygen tension, respectively) and subcutaneously implanted in nude rats for 3 and 28 days. Compared to ambient condition culture, hypoxic tension did not alter the SVF composition in vitro, showing similar numbers of MSC as well as endothelial and mural cells. Nevertheless, in vitro hypoxic culture significantly increased the release of vascular endothelial growth factor (p < 0.001) and the number of proliferating cells (p < 0.00001). Moreover, compared to ambient oxygen culture, exposure to hypoxia significantly enhanced the vessel length density in the engineered tissues following 28 days of implantation. The number of human cells and human proliferating cells in hypoxia-cultured constructs was also significantly increased after 3 and 28 days in vivo, compared to normoxia. These findings show that a possible in vivo delay in oxygen supply might not impair the vascularization potential of SVF- patches, which qualifies them for evaluation in a myocardial ischemia model.

Positive effects of hypoxic preconditioning of the extracellular matrix and stromal vascular fraction from adipose tissue

“… 25 Hypoxia acts on VEGF by increasing its release, which leads to enhanced vascularization with significant vessel length. 31 These results suggest that the increase in proliferation and vascularization observed in our study can be due to the increase in VEGF release. This is in accordance with the results of our animal experiments, where GFP-ADSCs were found to be more abundant when MatriC + SVF were used in combination compared to that of nonconditioned matrix combined with cells.…”

Adipose-Derived Stromal Cells within a Gelatin Matrix Acquire Enhanced Regenerative and Angiogenic Properties: A Pre-Clinical Study for Application to Chronic Wounds

“…ASC exposed to gelatin microcryogels have been shown to increase their expression of VEGF, HGF, FGF, and PDGF [ 36 ]. The formation of a three-dimensional tissue organization within the patch enables the optimization of cell–cell interactions, paracrine events and gas exchange/oxygen supply [ 37 , 38 ]. The gelatin sponge itself may promote the healing process independently of ASC.…”

Efficacy and safety of a patch containing adipose-derived stem cells for skin wound healing – results form a comprehensive pre-clinical evaluation program

“…Finally, the condition used for culturing the ASC-patch, i.e. air/liquid interface, promotes air gas exchanges and oxygen supply, which are a key factor influencing ASC functions [44].…”