Angiogenic effects despite limited cell survival of bone marrow-derived mesenchymal stem cells under ischemia

Purpose: Bone marrow-derived mesenchymal stem cells (MSCs) are multipotent and secrete angiogenic factors, which both could help patients suffering from occlusive arterial diseases. We hypothesize that MSCs, in comparison to robust fibroblasts, better survive under hypoxic conditions in vitro and in vivo. Material, Methods and Results: MSCs and fibroblasts from L2G mice expressing firefly luciferase and GFP were cultured in normoxic and hypoxic conditions for 24 hours. In vitro cell viability was tested by detecting apoptosis and necrosis. MSCs released a higher VEGF amount (281.1± 62.6 pg/ml) under hypoxic conditions compared to normoxia (154.9 ± 52.3 pg/ml; p=NS) but were less tolerant to hypoxia than fibroblasts (45 ± 7.9% vs. 28.1 ± 3.6% in fibroblasts, p = NS). A hindlimb ischemia model was created by ligating the femoral artery of 18 FVB mice. After one week, 1x¹⁰⁶ cells (MSCs, fibroblasts or saline) were injected into limb muscles of each animal (n=6 per group). Bioluminescence measurement to assess the viability of luciferase positive cells showed significant proliferation of MSCs at day four compared to fibroblasts (320 ± 315.9% vs. 70.9 ± 40.4%, respectively; p = 0.001, values in per cent of start cell amount). Three weeks after cell delivery, the capillary to muscle fiber ratio of ischemic areas was analyzed. In the MSC group, vessel density was significantly higher than in fibroblasts or control group (0.5 ± 0.08% vs. 0.3 ± 0.03% in fibroblasts and the control group, p = 0.03). Conclusion: Under hypoxia, MSCs produced more VEGF compared to normal conditions and MSC transplantation into murine ischemic limbs led to an increase in vessel density although MSC survival was limited. This study suggests that MSC transplantation may be an effective and clinically relevant tool in the therapy of occlusive arterial diseases.