EphrinB1 Regulates Immunoresponse in BRONJ Mouse Model

Objectives: Bisphosphonates are potent inhibitors of bone resorption that target osteoclasts. They are used in treatment of bone diseases, but can cause problems in other bone tissues such as bisphosphonate related osteonecrosis of the jaw(BRONJ). A relationship has been shown between the uses of bisphosphonates as treatment in conjunction with dental surgery that leads to BRONJ. Previous work has shown that ligand ephrinB1 expression rises in osteoclasts and pre-osteoclasts, with bisphosphonate treatment. The forward signaling of ephrinB1 suppressed expression of bone sialoprotein(BSP) in osteoblasts, which is important in bone remodeling and repair.
Methods: A murine model was used and a high dose injection of Zolendronic Acid(ZOL) was used to induce BRONJ in the male C57Bl6 mice. Wild-type and myeloid cell specific ephrinB1 knockout mice were used in the experiment. Mice were injected three times a week for three weeks with ZOL at a dose of 200 μg/kg. 1 week after injections began, the molars on the maxilla were drilled exposing the pulp to replicate oral trauma and inflammation that precedes the onset of BRONJ. At the beginning stages of the onset of BRONJ microCT analysis and protein and RNA expression were all measured.
Results: MicroCT analysis of wild-type mice showed thickening of the lamina dura, causing a reduction in PDL space, demonstrating early stages of BRONJ. RNA expression showed significant decreases in osteoblast marker BSP and inflammation cytokine TNF-α.
Conclusions: BSP reduction also indicates early stages of BRONJ, however the decrease in TNF-α levels suggests a change in immune response in the treated tissue. EphrinB1 levels increased in both ZOL and control groups, therefore it may control inflammation through monocytes and macrophages. EphrinB1 knockout mice showed a change in TNF-α levels compared to wild-type. We believe that ephrinB1 controls the innate response and may prevent for onset of BRONJ at the early stage.