Age-related changes in side population cells of rat dental pulp

Methods: Maxillary and mandible incisors were extracted from young rats, weighing approximately 100g and from aged rats, weighing approximately 850g. The pulp tissue was removed and created single-cell suspensions by Collagenase and Dispase. And then cells were stained with Hoechst 33342 and were sorted by Fluorescence Activated Cell Sorter (FACS). Isolated SP cells and Main population (MP) cells were analyzed by Quantitative real-time RT-PCR. The expression of ABCG2, ALP, Nestin and DSP mRNAs, which stand for ATP-binding cassette transporters, osteoblast differentiation marker and odontoblast differentiation marker, respectively were evaluated. Furthermore, the cell cycle were analyzed by FACS and Cyclin D1, CDK4 and P57 mRNA, represent cell cycle regulator.

Results: As a results, 0.5-0.6% of SP cells were isolated from young dental pulp, while 0.2-0.3% from aged rat dental pulp with significant difference (p<0.05). In both young and aged groups, SP cells were expressed higher level of ABCG2 mRNAs, however, lower level of ALP, Nestin, DSP, Cyclin D1, CDK4 and P57 mRNAs than those of MP cells (p<0.05). In both young and aged groups, the cell cycle of MP cells was mainly growth arrested in G0/G1.

Conclusion: The SP cells isolated from dental pulp tissue were same characterization as those of the other organ, excepted cell-cycle machinery. The expression of pulp cell characteristics did not change with aging, however, the ratio of SP cells in rat dental pulps decreased with advancing age.