Characteristics of Dental Follicle Stem Cells (DFSCs) at Elevated Temperatures

Objective: It is believed that adult stem cells residing in tissues are maintained in a slow cycling and quiescent state under normal physiologic conditions.  However, this quiescent state could be awakened by certain factors, such as tissue or cell injury signals. Previously, we have shown that DFSCs appear to grow more rapidly than their non-stem cell counterparts at elevated temperatures.  This study aimed to (1)  elucidate the optimal temperature to grow DFSCs, (2)  determine if the elevated temperatures could activate the differentiation capability of DFSCs, and (3)  characterize the marker genes expression in DFSCs under elevated temperatures. Method: DFSC cultures were established from the first mandibular molars of day 6 rat pups. DFSCs were cultured in stem cell growth medium at 37 (control), 38, 39, 40, and 41ºC. Cell proliferation was evaluated by Alamar blue reduction assay and cell counting.  ALP expression was monitored after 7 days of culture. Osteogenic differentiation was evaluated by Alizarin Red staining after 7 or 14 days incubation in osteogenic medium under above temperatures.  Expression of selected stem cells marker genes was also assessed during proliferation and differentiation of the DFSCs. Result: Increased cell proliferation was seen at 38, 39 and 40 ºC compared to the control, but significant reduction of cell proliferation occurred at 41 ºC. DFSCs showed higher osteogenesis when cultured under elevated temperatures than did the control. DFSCs appeared to have maximal osteogenesis at 39 and 40ºC. Gene expression studies indicated that some stem cell and osteogenic associated markers increased their expression under elevated temperatures. Conclusion: The optimal temperatures to grow and differentiate DFSCs were 39 to 40ºC. Under such elevated temperatures, DFSCs also increased expression of some marker genes.  Thus, it is likely that elevated temperature could serve as a factor to activate stem cell properties.