SH3BP2 Cherubism Mutation Potentiates TNF-[alpha]-Induced Osteoclastogenesis via NFATc1 and TNF-[alpha]-Mediated Inflammatory Bone Loss

Cherubism (OMIM# 118400) is a genetic disorder with excessive jawbone resorption caused by mutations in SH3 domain binding protein 2 (SH3BP2), a signaling adaptor protein. Studies on the mouse model for cherubism carrying a P416R knock-in (KI) mutation have revealed that mutant SH3BP2 enhances tumor necrosis factor (TNF)-[alpha] production and receptor activator of nuclear factor-[kappa]B ligand (RANKL)-induced osteoclast differentiation in myeloid cells. TNF-[alpha] is expressed in human cherubism lesions, which contain a large number of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells, and TNF-[alpha] plays a critical role in inflammatory bone destruction in homozygous cherubism mice (Sh3bp2KI/KI). The data suggest a pathophysiological relationship between mutant SH3BP2 and TNF-[alpha]-mediated bone loss by osteoclasts. Therefore, we investigated whether P416R mutant SH3BP2 is involved in TNF-[alpha]-mediated osteoclast formation and bone loss. Here, we show that bone marrow-derived M-CSF-dependent macrophages (BMMs) from the heterozygous cherubism mutant (Sh3bp2KI/+) mice are highly responsive to TNF-[alpha] and can differentiate into osteoclasts independently of RANKL in vitro by a mechanism that involves spleen tyrosine kinase (SYK) and phospholipase C[gamma]2 (PLC[gamma]2) phosphorylation, leading to increased nuclear translocation of NFATc1. The heterozygous cherubism mutation exacerbates bone loss with increased osteoclast formation in a mouse calvarial TNF-[alpha] injection model as well as in a human TNF-[alpha] transgenic mouse model (hTNFtg). SH3BP2 knockdown in RAW264.7 cells results in decreased TRAP-positive multinucleated cell formation. These findings suggest that the SH3BP2 cherubism mutation can cause jawbone destruction by promoting osteoclast formation in response to TNF-[alpha] expressed in cherubism lesions and that SH3BP2 is a key regulator for TNF-[alpha]-induced osteoclastogenesis. Inhibition of SH3BP2 expression in osteoclast progenitors could be a potential strategy for the treatment of bone loss in cherubism as well as in other inflammatory bone disorders. © 2014 American Society for Bone and Mineral Research.