Method: Mesial tooth movement was performed by applying a Ni-Ti coil spring between the left upper 1st molars and upper incisors of seven-week-old male SD rats with the magnitude of 50 cN force. The dental tissues were prepared immediately after sacrifice at days 1, 2, and 6 after the movement for DD-PCR, real time-PCR, Western blot, and immunofluorescence analyses. Also, we investigated the level of SLPI expression after compression and tension force in human PDL cells in vitro. Lastly, the result was also confirmed by microarray analysis
Result: A specific gene was differentially expressed in the dental tissue comprising the 1st molars after orthodontic force application, compared with the control. Through the subcloning of DD-PCR products, secretory leukocyte peptidase inhibitor (SLPI) was identified for the 1st time. In the real time-PCR, the level of SLPI expression was increased 28-, 13- and 17-fold at 1d, 2d, and 6d, respectively. Western blot also confirmed the increased SLPI protein. By immunofluorescency, SLPI was mainly localized in the PDL. After applying compression force as well as tension force on human PDL cells in vitro, SLPI mRNA expression level was significantly increased. Microarray analysis also supported these results.
Conclusion: These results suggest that SLPI in the PDL may be involved in preventing excessive decomposition of connective tissue and relieving inflammation induced by orthodontic mechanical force.