Ischemia Is the Prime but Not the Only Cause of Human Multipotent Stromal Cell Death in Tissue-Engineered ConstructsIn Vivo

Local tissue ischemia is a prime cause responsible for the massive cell death in tissue engineered (TE) constructs observed post-implantation. In order to assess the impact of ischemia on the death of implanted human multipotent stromal cells (hMSCs), which have great potential for repairing damaged tissues, we hereby investigated the in vivo temporal and spatial fate of human Luc-GFP-labeled MSCs within fibrin gel/coral scaffolds subcutaneously implanted in nude mice. In vivo bioluminescence imaging monitoring and histological analyses of the constructs tested confirmed the irremediable death of hMSCs over 30 days post-implantation. The kinetics of expression of three hypoxic/ischemic markers (HIF-1α, LDH-A and BNIP3) was also monitored. Our results provided evidence that hMSC located within the core of implanted constructs died faster and predominantly as well as strongly expressed the aforementioned ischemic markers. In contrast, cells located in the outer regions of TE constructs were reperfused by neovascularization and were still viable (as evidenced by their ex-vivo proliferative potential) at day 15 post-implantation. These results support the explanation that in the central part of the constructs tested, death of hMSC cells was due to ischemia, whereas in the periphery of these constructs, cell death was due to another mechanism that needs to be elucidated