SH3BP2 mutations potentiate osteoclastogenesis via PLCγ.

Area of Science:

• Genetics
• Cell Biology
• Bone Biology

Background:

• Cherubism is a genetic disorder characterized by excessive jawbone remodeling due to increased osteoclast activity.
• Activating mutations in the SH3BP2 gene are frequently found in cherubism patients.
• The precise mechanism by which SH3BP2 mutations lead to increased osteoclastogenesis remains to be fully elucidated.

Purpose of the Study:

• To investigate the functional consequences of SH3BP2 mutations on osteoclast differentiation.
• To determine the effect of mutant SH3BP2 on key signaling pathways involved in osteoclastogenesis.
• To elucidate the molecular mechanism underlying the excessive bone resorption in cherubism.

Main Methods:

• Utilized RAW 264.7 pre-osteoclast cells transfected with wild-type or mutant SH3BP2 plasmids.
• Stimulated cells with soluble RANKL (sRANKL) to induce osteoclastogenesis.
• Assessed NFAT-luciferase activity, tartrate-resistant acid phosphatase (TRAP) expression, and phosphorylation of PI-PLC pathway proteins via Western immunoblotting.

Main Results:

• Forced expression of mutant SH3BP2 significantly increased NFAT activity and TRAP expression compared to wild-type SH3BP2.
• Mutant SH3BP2 potentiated sRANKL-stimulated phosphorylation of PLCγ1 and PLCγ2.
• These findings indicate that SH3BP2 mutations result in a gain of protein function, enhancing osteoclast differentiation.

Conclusions:

• Cherubism is caused by gain-of-function mutations in SH3BP2.
• These mutations stimulate RANKL-induced activation of PLCγ, leading to calcineurin and NFAT activation.
• The enhanced signaling cascade results in the excessive osteoclastic bone resorption characteristic of cherubism.