Cryopreservation of Rat Bone Marrow Derived Mesenchymal Stem Cells by Two Conventional and Open-Pulled Straw Vitrification Methods

Bone marrow (BM) is a complex tissue containing populations of progenitor and stem cells (1). One type, hematopoietic stem cells (HSCs), can renew circulating blood elements such as red blood cells, monocytes, platelets, granulocytes and lymphocytes. The other is mesenchymal stem cells (MSCs), which possess two important properties of long-term self renewal and differentiate into osteoblasts, chondroblasts, adipocytes and hematopoiesis supporting stroma (2, 3). Their mesenchymal differentiation potential is retained even after repeated subcultivation in vitro (4, 5). Besides originating the forming mesenchymal tissue, many studies have demonstrated that MSCs could differentiate into various nonmesenchymal tissue lineages under appropriate experimental conditions in vitro and in vivo, such as hepatocytes (6, 7), cardiomyocytes (8, 9), lung alveolar epithelium (10), olfactory epithelium (11), inner hair cells (12), neurons and neuroglia (1, 4, 13). MSCs are spindle shaped fibroblast-like cells that are easily isolated, cultured and expanded in vitro due to their adherent characteristics, and not associated with any ethical debate (14). Thus, MSCs may be used in the treatment of a diverse variety of clinical conditions (15) such as engraftment of various organs (16). The long-term cultivation of MSCs may fail for many reasons: genotypic drift, senescence, transformation, phenotypic instability, and contamination or incubator failure. The inability to cultivate MSCs will result in the lack of MSCs for both experimental and clinical use (17). Therefore, it is necessary to cryopreserve MSCs as cell seeds. Although increasing telomerase expression of cells may overcome cell senescence (18), cryopreservation of hMSCs may be more practical in order to save time and culture materials (16, 19). Resuscitated MSCs can be subcultivated for many passages without a noticeable loss of viability and capability of osteogenic differentiation (20-22).