Mesenchymal progenitor cells (MPC) show great promise for use in a variety of cell-based therapies. As isolated primary MPC are low in numbers, in vitro expansion is necessary. However the expansion potential is limited and in vitro aging leads to loss of multipotency and to replicative senescence. Stress induced by the culture conditions is thought to be one of the driving reasons for replicative senescence and might also influence multipotency of MPC. Optimisation of culture conditions might be able to improve the expansion of MPC in cultures. Temperature reduction was shown to be beneficial in somatic cell cultures by reducing oxidative stress. We therefore monitored the growth of MPC from rats and humans at 37C and 32C. We found that the in vitro lifespan of MPC was not affected but less damage was accumulated at the lower temperature and the MPC preserved their differentiation potential for a longer time. This suggests that MPC expanded in vitro for engraftment or tissue engineering purposes should be maintained at a lower temperature to avoid the accumulation of damage and possible reduction of tissue construct quality. However this was only true for MPC derived from 'young' subjects with MPC derived from 'aged' subjects showing no such improvements.
The second half of our studies involved a model of caloric restriction; the only established method to delay aging and extending the lifespan. Studies of in vitro caloric restriction are rare, but showed some beneficial effects. We therefore investigated the effect of culture medium glucose concentration on the proliferative and differentiation potential of MPC. Reduction in glucose concentrations lead to a decrease in apoptosis levels and an increase in the rate of proliferation. Similarly, reduced glucose concentration increased the number and size of fibroblastic colonies in the colony forming unit assay.
Conclusion: These data suggest that culture conditions such as temperature or glucose concentration can have profound effects on MPC growth and senescence. The reason for the differential effect of temperature on young and aged cells is at present unclear but may be of great importance for the use of MPC in cell-based therapies.