HMGB1-induced Inflammatory Response Promotes Bone Regeneration in Murine Tooth Socket

Objectives: High mobility group box 1 (HMGB1) is an essential DNA-binding protein in eukaryotes. HMGB1 is secreted extracellularly by inflammatory stimuli and functions as an inflammatory mediator. Recently, it has been reported that stem cells and vascular endothelial cells migrate and are involved in tissue regeneration. The alveolar extraction socket is an inflamed open wound which has a specific healing pattern. Multiple signaling orchestrate the healing, however, exact regulation mechanism of HMGB1 is still unknown. In this study, we investigated pathological roles of HMGB1 in vivo tooth socket model.
Methods: Before tooth extraction, anti-HMGB1 monoclonal antibody and isotype antibody for control mice were administrated intraperitoneally. We analyzed followings at each experimental period (1, 3, 5, and 7 days after tooth extraction). Myeloperoxidase activity in tooth socket was measured by bioluminescence imaging. CD68-positive macrophages, CD31-positive vascular endothelial cells, osteocalcin-positive cells, and TRAP-positive cells were detected by immunostaining. Neoplastic bone area was stained with HE and quantified by Image J software. Total RNA was extracted from tissues at 3 and 7 days and used for microarray analysis and real-time PCR analysis. Statistical analyses were performed by one-way ANOVA and the Tukey-Kramer test.
Results: Followings were found in the anti-HMGB1 antibody group compared to the control group; 1) Average of max radiance in the anti-HMGB1 antibody group was decreased at day 3. 2) Numbers of macrophages and vascular endothelial cells were significantly lower at day 5. 3) Numbers of TRAP- and osteocalcin-positive cells were significantly lower at day 7. 4) New bone area were significantly lesser at day 7. 5) Expression levels of inflammatory cytokines, angiogenesis, and bone markers were significantly decreased at day 3 and 7.
Conclusions: Anti-HMGB1 antibody inhibited initial acute inflammation, angiogenesis, and expression of bone markers , resulting delayed bone healing in tooth socket.