[EFFECTS OF HYPOXIA AND GROWTH FACTORS ON THE ANGIOGENIC ACTIVITY OF MULTIPOTENT MESENCHYMAL STROMAL CELLS]

The effects of fetal calf serum (FCS) growth factor concentration and cell growth phase on production of angiogenic mediators by mesenchymal stromal cells (MSCs) at different O2 levels (20 and 5%) was studied. For this purpose vascular endothelial growth factor (VEGF-A) production was measured in MSC-conditioned medium (CM); besides, branching vessels as well as vessel end points (ramification) in the chorioallantoic membrane of Japanese quail eggs (Coturnix coturnix japonica) were counted following MSC-CM application. During the standard cultivation (20% O2; 10% FCS) the total number of vessels was 1.6 times higher comparing with hypoxic condition (5% O2; 10% FCS) due to increase in ramification, the number of branching vessels did not change. Maximal (double) increase in the total vessel number was observed when CM from MSCs after hypoxia plus serum deprivation was added. VEGF-A synthesis linearly increased with FCS concentration both at 20% and 5% O2. In all cases VEGF-A level was higher at hypoxia. No direct correlation between the VEGF-A concentration and total number of vessels was noted indicating that hypoxia possibly stimulates synthesis of additional angiogenic factors to enhance vascular growth despite the drastic serum deprivation. At 20% oxygen, exponentially growing MSCs showed the highest angiogenic activity and the ramification increased in 1.6 times. Depending on O2, MSCs produced angiogenic factors required at different stages of vascularization. Specifically, mediators of ramification were accumulated in the standard conditions (20% O2) and factors stimulating growth of branching vessels--in hypoxia.