Int J Med Sci 2020; 17(5):647-656. doi:10.7150/ijms.41075 This issue
1. Department of Oral Physiology, BK21 PLUS Project, Periodontal Diseases Signaling Network Research Center, and Dental and Life Science Institute, School of Dentistry, Pusan National University, Yangsan, Republic of Korea, 50611
2. Department of Maxillofacial Biomedical Engineering, School of Dentistry, Department of Life and Nanopharmaceutical Sciences, Kyung Hee Medical Science Institute, Kyung Hee University, Seoul, Republic of Korea, 02447
3. Department of Biochemistry, School of Dentistry, Kyungpook National University, Daegu, Republic of Korea, 41940
4. Department of Oral and Maxillofacial Surgery, Dental Research Institute, and Dental and Life Science Institute, School of Dentistry, Pusan National University, Yangsan, Republic of Korea, 50611
* These authors contributed equally to this work.
Connective tissue growth factor (CTGF), an extracellular matrix protein with various biological functions, is known to be upregulated in multiple chronic diseases such as liver fibrosis and congestive heart failure, but the mechanism it undertakes to cause alveolar bone loss in periodontitis remains elusive. The present study therefore investigates the pathways involving CTGF in chronic periodontitis. RNA sequencing revealed a notable increase in the expression of CTGF in chronic periodontitis tissues. Also, TRAP staining, TRAP activity and bone resorption assays showed that osteoclast formation and function is significantly facilitated in CTGF-treated bone marrow-derived macrophages (BMMs). Interestingly, western blotting and immunofluorescence staining results displayed that CTGF had little effect on the osteoclastogenic differentiation mediated by the positive regulators of osteoclastogenesis such as nuclear factor of activated T cells 1 (NFATc1). However, following results showed that both the mRNA and protein expressions of B cell lymphoma 6 (Bcl6), a transcriptional repressor of “osteoclastic” genes, were significantly downregulated by CTGF treatment. Moreover, CTGF upregulated the expressions of v-ATPase V0 subunit d2 (ATP6v0d2) and Dendritic cell-specific transmembrane protein (DC-STAMP) which are osteoclastic genes specifically required for osteoclast cell-cell fusion in pre-osteoclasts. Findings from this study suggest that CTGF promotes the fusion of pre-osteoclasts by downregulating Bcl6 and subsequently increasing the expression of DC-STAMP in periodontitis. Understanding this novel mechanism that leads to increased osteoclastogenesis in periodontitis may be employed for the development of new therapeutic targets for preventing periodontitis-associated alveolar bone resorption.
Keywords: CTGF, DC-STAMP, Bcl6, osteoclast fusion, periodontitis