Angiogenesis in ischemic tissue produced by spheroid grafting of human adipose-derived stromal cells

Stem cells offer significant therapeutic promise for the treatment of ischemic disease. However, stem cells transplanted into ischemic tissue exhibit limited therapeutic efficacy due to poor engraftment in vivo. Several strategies for improving the survival and engraftment of stem cells in ischemic tissue have been developed including transplantation in combination with growth factor delivery, genetic modification of stem cells, and the use of cell-transplantation scaffolds. Here, we demonstrate that human adipose-derived stromal cells (hADSCs) cultured and grafted as spheroids exhibit improved therapeutic efficacy for ischemia treatment. hADSCs were cultured in monolayer or spheroids. Spheroid cultures were more effective in preconditioning hADSCs to a hypoxic environment, upregulating hypoxia-adaptive signals (i.e., stromal cell-derived factor-1α and hypoxia-inducible factor-1α), inhibiting apoptosis, and enhancing secretion of both angiogenic and anti-apoptotic factors (i.e., hepatocyte growth factor, vascular endothelial growth factor, and fibroblast growth factor 2) compared to monolayer cultures. Moreover, cell harvesting following spheroid cultures avoided damage to extracellular matrices due to harsh proteolytic enzyme treatment, thereby preventing anoikis (apoptosis induced by a lack of cell-matrix interaction). Following intramuscular transplantation to ischemic hindlimbs of athymic mice, hADSC spheroids showed improved cell survival, angiogenic factor secretion, neovascularization, and limb survival as compared to hADSCs grafted as dissociated cells. Taken together, spheroid cultures precondition hADSCs to a hypoxic environment, and grafting hADSCs as spheroids to ischemic limbs improves therapeutic efficacy for ischemia treatment due to enhanced cell survival and paracrine effects. Spheroid-based cell delivery could be a simple and effective strategy for improving stem cell therapy for ischemic diseases, eliminating the need for growth factor delivery, biomaterial scaffolds or genetic modification.