TNF-a Upregulates Bone Morphogenetic Proteins in Dental Follicle Cells

Objectives: The dental follicle (DF) appears to regulate both the alveolar bone resorption and bone formation needed for tooth eruption. At day 9 postnatally in the rat, TNF-a gene expression is upregulated in the DF of the 1st mandibulat molar, a time that correlates with a secondary burst of osteoclastogenesis and with rapid bone growth at the base of the socket. We have shown that TNF-a upregulates the expression of bone resorption genes such as VEGF in the dental follicle cells (DFCs) and it was the objective of this study to determine if TNF-a also stimulates the DFCs to express bone formation genes such as BMP-2 and BMP-3. Methods: DFCs were incubated with rat TNF-a at 0, 5, 10, 20 and 50 ng/ml for 1 hour to determine the dosage effect. For the time-course effect, cells were treated with 10 ng/ml TNF-a for 0.5, 1, 2, 4, 6 and 8 hours. The expressions of BMP-2 and BMP-3 then were determined using real-time RT-PCR. Next, the optimal combinations of the treatments were selected for immunostaining of the DFCs for BMP-2 to determine if the protein was synthesized and ELISA of the conditioned medium conducted to determine if it was secreted. Results: TNF-a significantly increased BMP-2 expression at all times and concentrations tested with maximal time enhancement (more than sixfold) at 6 hrs and maximal concentration enhancement at 50 ng/ml TNF-a. A similar effect of TNF-a was seen on the expression of BMP-3. Immunostaining and ELISA showed that BMP-2 was produced and secreted by DFCs. Conclusion: In conjunction with other studies, this study suggests that TNF-a can upregulate the expression of both bone resorption and bone formation genes that may be needed for tooth eruption. Supported by NIH grant DE08911-16 to G.E.W.