Role of the Apoptosis Pathway in Cryopreservation-Induced Cell Death in Mesenchymal Stem Cells Derived from Umbilical Cord Blood

Cryopreservation of mesenchymal stem cells (MSCs) is important because of their commercial applications in the clinical sector. MSCs are vulnerable to cryopreservation-induced apoptosis due to activation of apoptosis-related proteins during thawing. But the relationship between cryopreservation and apoptosis is not well understood. MSCs derived from umbilical cord blood were cryopreserved using Me2SO as the cryoprotective agent, with or without pre-treatment with the general caspase inhibitor z-VAD-FMK, or with the more selective caspase inhibitors z-IETD-FMK, z-LEHD-FMK and z-DEVD-FMK. To evaluate the effect of the calcium-mediated pathway, cryopreserved MSCs were tested with and without a calpain inhibitor. FACS was used to measure cell viability, mitochondrial membrane potential, and cell cycle analysis. Processing of the pro-caspases-3, -8, -9, calpain and Bid were determined by Western blotting. Cryopreservation of MSCs resulted in characteristic apoptosis within 24 h after thawing. Results show that intrinsic, extrinsic, and calpain pathways are activated after cryopreserved MSCs are thawed. Compared to selective caspase inhibitors, a general caspase inhibitor blocked DNA degradation more effectively and also inhibited caspases-3 and -8 processing as well as Bid cleavage, showing the beneficial effect of reducing cryopreservation-induced apoptosis. Similarly, calpain inhibition reduced cryopreservation-induced apoptosis. These data indicate that caspase-mediated extrinsic and intrinsic pathways and the proteolytic calpain cascade were activated after cryopreservation using a standard cryopreservation protocol. This activation might play an important role in the process of cryopreservation-induced cell death. Furthermore, the inhibition of calpain activity and caspase-mediated pathways might improve preservation efficacy.