Recent studies have demonstrated that human dental pulp contains adult stem cells. A pulse of the thymidine analog BrdU given to young animals at the optimal time could clarify where slow-cycling long-term label-retaining cells (LRCs), putative adult stem cells, reside in the pulp tissue. This study focuses on the mapping of LRCs in growing teeth and their regenerative capacity after tooth injuries. Two to seven peritoneal injections of BrdU into pregnant Wistar rats revealed slow-cycling long-term dense LRCs in the mature tissues of born animals. Numerous dense LRCs were postnatally decreased in number and reached a plateau at 4 weeks after birth when they mainly resided in the center of the dental pulp, associating with blood vessels. Mature dental pulp cells were stained with Hoechst 33342 and sorted into (<0.76%) side population cells using FACS, which included dense LRCs. Some dense LRCs co-expressed mesenchymal stem cell markers such as STRO-1 or CD146. Tooth injuries caused degeneration of the odontoblast layer, and newly differentiated odontoblast-like cells contained LRCs. Thus, dense LRCs in mature pulp tissues were supposed to be dental pulp stem cells possessing regenerative capacity for forming newly differentiated odontoblast-like cells. The present study proposes the new hypothesis that both granular and dense LRCs are equipped in the dental pulp and that the dense LRCs with proliferative capacity play crucial roles in the pulpal healing process following exogenous stimuli in cooperation with the granular LRCs.
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Acknowledgments We are grateful to Dr. Kyoko Oka and Mr. Shin-ichi Kenmotsu for their technical assistance. This work was supported in part by Grants-in-Aid for ScientiWc Research (B) (Nos. 19390462 to H. O. and 21390528 to M-J.H.), ScientiWc Research (C) (No. 20592394 to K. N–O.) and Exploratory Research (Nos. 20659296 to H. O. and 20659305 to M-J.H.) from MEXT and JSPS, and a Grant for Supporting Project for Strategic Research of Nihon Univ Sch Dentistry at Matsudo from MEXT, 2008–2012 (Team: Dental Morphogenesis).
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Medical Laboratory Technology
- Cell Biology