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Involvement of ADAM9 in multinucleated giant cell formation of blood monocytes
1Department of Microbiology, Mie University School of Medicine, 2-174, Edobashi, Tsu-Shi, Mie Prefecture, 514-8507, Japan.
Abstract:
Monocytes-macrophages are converted to multinucleated giant cells by stimulation with various cytokines, and osteoclasts are the multinucleated giant cells derived from a monocyte-macrophage lineage. However, at present, the fusion peptides have not been clearly identified in monocytes-macrophages. The ADAM are a family of transmembrane glycoproteins that have a role in various biological functions. Interestingly, fertilin-alpha, ADAM9, and ADAM11 have potential fusion peptides. In this study, which ADAM was specifically expressed in monocytes stimulated with anti-CD98 antibody or RANKL and which factor(s) was functioning in monocytes as a fusion protein were investigated. ADAM1, 8, 10, 12, 15, 17, 20, and 21 mRNAs are expressed in blood monocytes incubated with control antibody, anti-FRP-1/CD98 antibody, or RANKL + M-CSF, while ADAM2, 7, 11, 13, 19, 23, 29, and 30 mRNAs could not be detected in these blood monocytes. Expression of ADAM9 and ADAM10 mRNAs are enhanced by either RANKL + M-CSF or anti-CD98 antibody. The expression of ADAM9 and ADAM10 is also induced in blood monocytes by anti-CD98 mAb. An anti-ADAM9 antibody enhances CD98-mediated cell aggregation, while it blocks CD98-mediated and RANKL-mediated multinucleated giant cell formation. A hydroxamate-based metalloprotease inhibitor, SI-27, which is found to suppress ADAM9 activity, suppresses multinucleated giant cell formation. New protein synthesis is necessary for the expression of ADAM9 mRNA and genistein suppresses induction of ADAM9 mRNA. This is the first report that ADAM9 is involved in monocyte fusion, such as CD98-mediated and RANKL-mediated cell fusion of blood monocytes. Furthermore, AMAM9 is one candidate for a fusion peptide in blood monocytes.
Insights
Researchers identified ADAM9 as a key protein involved in monocyte fusion, a process crucial for forming multinucleated giant cells like osteoclasts. This finding sheds light on monocyte-macrophage differentiation and potential therapeutic targets.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Monocytes differentiate into multinucleated giant cells, including osteoclasts, through cell fusion.
- The specific fusion peptides mediating this process in monocytes remain largely unidentified.
- ADAM proteins are transmembrane glycoproteins with diverse biological roles, including potential involvement in cell fusion.
Purpose of the Study:
- To investigate which ADAM family members are expressed in monocytes upon stimulation.
- To identify the specific ADAM protein functioning as a fusion factor in monocytes.
- To elucidate the role of ADAM9 in CD98- and RANKL-mediated monocyte fusion.
Main Methods:
- Quantitative analysis of ADAM mRNA expression in human blood monocytes.
- Stimulation of monocytes with anti-CD98 antibody and RANKL + M-CSF.
- Assessment of cell aggregation and multinucleated giant cell formation.
- Inhibition studies using anti-ADAM9 antibody and a metalloprotease inhibitor (SI-27).
Main Results:
- ADAM1, 8, 10, 12, 15, 17, 20, and 21 mRNAs were detected in monocytes.
- ADAM9 and ADAM10 mRNA expression was significantly enhanced by anti-CD98 antibody and RANKL + M-CSF.
- Anti-ADAM9 antibody blocked CD98- and RANKL-mediated cell fusion, while SI-27 also suppressed fusion.
- ADAM9 expression is dependent on new protein synthesis and inhibited by genistein.
Conclusions:
- ADAM9 is specifically expressed and functionally involved in CD98- and RANKL-mediated monocyte fusion.
- ADAM9 is a strong candidate for a fusion peptide in blood monocytes.
- This study provides novel insights into the molecular mechanisms of monocyte fusion and osteoclastogenesis.