Induction of mesenchymal stem cells leads to HSP72 synthesis and higher resistance to oxidative stress.

The phenomenon of neuronal transdifferentiation performed on bone marrow mesenchymal stem cells (MSCs) has been criticized by recent studies indicating that acquired neuron-like morphology of induced MSCs is caused by cellular stress. Therefore, to test this hypothesis we have investigated whether exposure of rat MSCs (rMSCs) to chemical inducer 2 mM beta-mercaptoethanol (BME) for 1-3 h followed by 24 h incubation leads to HSP72 synthesis, thus suggesting higher resistance of rMSCs to oxidative damage. Present data from immunohistochemistry clearly indicate development of time-dependent sub-cellular HSP72 distribution, initially seen in nuclei at 1 h followed by its translocation to surrounding central cytoplasm and processes at 2-3 h after BME stimulation. Western blot (WB) analysis confirmed the expression of HSP72 protein in induced rMSCs at both stimulation periods. Furthermore, preconditioned rMSCs with BME for 1 h expressing HSP72 positivity at 24 h showed higher resistance (78 +/- 10% of survival cells) to oxidative stress caused by 1 mM H(2)O(2) when compared to those preconditioned for 3 h (59 +/- 8% of survival cells) or control-unconditioned rMSCs exposed to the same stressor conditions (56 +/- 6% of survival cells). Thus, the cellular protection was lost if the duration of BME preconditioning was increased as far as possible (3 h) (while still remaining sub-lethal). This suggests that exposure of rMSCs to the optimal concentration of BME (2 mM) during optimal induction period (1 h) mediate their protection and increases resistance to oxidative injury, while over crossing these limits is in-effective. In addition, our findings confirm that cultured rMSCs remain competent to be preconditioned by BME, through a pathway that may increase the antioxidant balance or involve activation of HSP72 protein induced tolerance.