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Annexin II stimulates RANKL expression through MAPK.
Fanghong Li1, Hoyeon Chung, Sakamuri V Reddy
1Department of Medicine/Hematology-Oncology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
Summary
Annexin II (AX-II) stimulates osteoclast (OCL) formation by increasing both granulocyte-macrophage colony-stimulating factor (GM-CSF) and RANKL. This process involves a novel MAPK-dependent pathway, highlighting the combined roles of GM-CSF and RANKL in OCL development.
Area of Science:
- Cell Biology
- Immunology
- Bone Biology
Background:
- Annexin II (AX-II) is secreted by osteoclasts (OCLs) and promotes OCL formation and bone resorption.
- AX-II induces granulocyte-macrophage colony-stimulating factor (GM-CSF) production, enhancing OCL precursor proliferation.
Purpose of the Study:
- To investigate AX-II's capacity to induce RANKL expression in human marrow stromal cells.
- To identify the signaling pathways involved in AX-II-induced RANKL production.
- To confirm the necessity of both GM-CSF and RANKL for AX-II-mediated OCL formation.
Main Methods:
- Real-time RT-PCR and Western blot to assess RANKL and osteoprotegerin (OPG) expression.
- ELISA to quantify soluble RANKL.
- MAPK pathway activation analysis via Western blot.
- Inhibition studies using OPG and anti-GM-CSF.
Main Results:
- AX-II upregulated RANKL mRNA and markedly increased membrane-bound RANKL on stromal cells.
- AX-II activated the MAPK pathway (ERKs) in a manner inhibited by PD 98059.
- OPG and anti-GM-CSF partially inhibited OCL formation; their combination completely blocked it.
Conclusions:
- AX-II stimulates OCL precursor proliferation via GM-CSF and differentiation via RANKL.
- A novel MAPK-dependent pathway mediates AX-II-induced membrane-bound RANKL synthesis.
- Both GM-CSF and RANKL are essential for AX-II-induced osteoclast formation.