The role of melanocortin receptors in osteoclasts differentiation and activity related to periodontal disease

MFM Madeira1,2, T Montero-Melendez1, LV Norling1, CM Queiroz-Junior2,3, SMC Werneck2, DG Souza2, MM Teixeira2, TA Silva2,3, M Perretti1. 1Queen Mary University of London, Barts and The London School of Medicine and Dentistry, EC1M 6BQ, London, UK, 2Universidade Federal de Minas Gerais, Imunofarmacologia, Belo Horizonte, Brazil, 3Universidade Federal de Minas Gerais, Faculdade de Odontologia, Belo Horizonte, Brazil

Introduction: The relationship between periodontal disease (PD) and rheumatoid arthritis (RA) has been studied for more than 40 years, receiving more attention recently. PD and RA share some features such as inflammatory cell infiltration, production of inflammatory mediators and bone loss [1]. Inflammation-induced bone loss is characterized by activation of bone resorption and inhibition of bone formation. Melanocortins and their receptors regulate inflammation by inhibiting leukocyte recruitment and reducing pro-inflammatory mediators. Recent studies in MC3 deficient mice (Mc3r-/-) suggest a role for this receptor in the regulation of osteoclast development and function [2]. Objective: Our aim was to assess the development of alveolar bone loss in the K/BxN-serum transfer arthritis model and the role of melanocortins in this process. Methods: Arthritis was induced by injecting wild-type (WT) mice with 100 μL of K/BxN serum on days 0 and 2 (i.p.). Arthritis was monitored by measuring paw volume and clinical score. After 7 days mice were killed, the maxilla removed, hemisected, exposed overnight in 3% H2O2, mechanically defleshed, and stained with 0.3% methylene blue. Quantitative analysis for alveolar bone loss involved the measurement of the palatal area between the cement-enamel junction (CEJ) and the alveolar bone crest (ABC) of the first molar using Image J software. In vitro experiments were carried out with bone marrow cells (BMC) from C57BL/6 WT mice. To generate osteoclasts cells were incubated with M-CSF for 6 days. RANKL and D[Trp8]-γMSH (MC3 agonist) were added at day 6 until day 10. LPS from Aggregatibacter actinomycetemcomitans (AaLPS) was added at day 8 until day 10. Osteoclasts were defined as TRAP+ve cells containing more than 3 nuclei. Resorption activity was also evaluated by resorption pits counting using Osteo Assay Plate (Corning, NY, USA). Results: Arthritis in the K/BxN model was associated with alveolar bone loss, which was significantly correlated with clinical score (p<0.05). Osteoclasts generated from WT BMC presented increased osteoclastogenesis (p<0.01) after activation with AaLPS and they express MC3. Treatment with D[Trp8]-γMSH decreased osteoclastogenesis induced by AaLPS, as well as osteoclast activity. Conclusion: Inflammatory arthritis – modeled with K/BxN serum - is associated with alveolar bone loss. Melanocortin agonists may have an inhibitory effect on osteoclast activity and differentiation on AaLPS-activated cells.

Key words: Alveolar bone loss, melanocortins, osteoclasts, rheumatoid arthritis.

[1] MERCADO, F. B.; MARSHALL, R. I.; KLESTOV, A. C.; BARTOLD, P. M. Relationship between rheumatoid arthritis and periodontitis. J Periodontol, v. 72, p. 779-787, 2001.

[2] PATEL HB, BOMBARDIERI M, SAMPAIO AL, D'ACQUISTO F, GRAY M, GRIECO P, GETTING SJ, PITZALIS C, PERRETTI M. Anti-inflammatory and antiosteoclastogenesis properties of endogenous melanocortin receptor type 3 in experimental arthritis. FASEB J, v. 24, n. 12, p. 4835-43, 2010.