OBJECTIVETo investigate biological characteristics of rat bone marrow mesenchymal stem cells (MSC) cultured in vitro and to explore their potential applications.

METHODSMSC were isolated from rat bone marrow by density gradient centrifugation and were induced to differentiation. Flow cytometry was used to characterize their surface antigen expression, cell cycle status and cell growth parameters. Telomerase activity was determined by TRAP-ELISA assay.

RESULTSFusiform MSC became larger and flattener with increasing passages of culture. After the fourth passage, the MSC showed an immunophenotype of CD29 (94.75% +/- 3.68%), CD71 (95.43% +/- 2.23%), and CD90 (98.08% +/- 3.88%). After the seventh passage, MSC with such immunophenotype decreased with CD29: 50.00% +/- 3.35%, CD71: 50.70% +/- 2.43%, and CD90: 48.60% +/- 2.83%. Cells with such immunoprofile completely disappeared after passage 9. Overall, MSC grew faster during the first 5 passages. The number of MSC in S and G(2)/M phases were 38.36% +/- 2.01% and those in G(0)/G(1) phase were 61.64% +/- 2.13% after 3 passages. The cell growth decreased after passage 7. Percentage of MSCs in S and G(2)/M phases was 10.83% +/- 1.63% and that in G(0)/G(1) was 89.17% +/- 1.96% after passage 12, after which the cells failed to further divide. After passage 9, MSCs lost their ability to differentiate to Von Kossa and oil red O positive staining cells. In addition, telomerase activity of MSC also gradually decreased with the prolonged passages, from the original 52.7% +/- 0.78% to no telomerase activity.

CONCLUSIONThe biological and immunophenotypical characteristics of cultured MSC showed obvious alterations with increasing numbers of passage of culture.