The effect of dental pulp stem cells on osteoclasts in periodontitis

Objective To explore the effect of dental pulp stem cells (DPSC) on osteoclasts and the regeneration of the alveolar bone in periodontitis, and to preliminarily investigate the underlying machanism. Methods Monocytes were co-cultured with DPSC on osteoclastogenesis. TRAP staining were performed to observe the osteoclastogenesis of osteoclast group and DPSC co-culture group, and RT-PCR was applied to analyze the osteoclast-related genes, including NFATc1, MMP-9 and TRAP. Periodontitis models were established. Micro-CT scanning was performed to evaluate the distance from cementum-enamel junction to alveolar bone crest (CEI-ABC) of DPSC injection group and 0.9% sodium chloride solution injection group. HE and TRAP staining were also performed to compare the inflammatory response and osteoclast formation. The data were processed by the SPSS 20.0 software. T test and t′ test were used to analyze the difference between the groups. Results It′s found in TRAP staining that co-culture with DPSC successfully inhibited osteoclast formation. The mean osteoclast number in DPSC co-culture group (4.2 ± 0.2) was significantly less than osteoclast group (6.8 ± 0.2) (t = 15.922, P<0.001) , and the mean cell size (0.046 ± 0.007) mm2 was also less than osteoclast group (0.763 ± 0.015) mm2 (t = 83.174, P<0.001) . Compared with those of osteoclast group, the expression of osteoclastogenesis-related genes including NFATc1, MMP-9 and TRAP of DPSC co-culture group were statistically lower, the value of which were 0.38 ± 0.17 (t = 6.217, P = 0.003) , 0.24 ± 0.12 (t = 10.569, P = 0.003) , 0.55 ± 0.13 (t = 6.077, P = 0.026) respectively. Micro-CT scanning showed that the CEI-ABC distance of DPSC group (0.215 ± 0.017) mm was lower than that of NS group (0.311 ± 0.022) mm (t = 10.921, P<0.001) . Histologic examination showed a less sever inflammatory response and a less osteoclast formation in DPSC group than those in NS group. Conclusions DPSC may promote the alveolar bone regeneration via inhibiting the osteoclast formation in chronic periodontitis. As a promising bi-directional biological agent for bone metabolism, DPSC may show good probability for the treatment of inflammatory bone resorption diseases including periodontitis in the future. Key words: Dental pulp; Stem cells; Chronic periodontitis; Alveolar bone loss; Osteoclasts