SH3BP2 Cherubism Mutation Potentiates TNF-α–Induced Osteoclastogenesis via NFATc1 and TNF-α–Mediated Inflammatory Bone Loss

Abstract

Cherubism (OMIM#118400) is a genetic disorder with excessive jawbone resorption caused by mutations in the signaling adaptor protein SH3BP2. Studies on the mouse model for cherubism carrying a P416R knock-in mutation have revealed that mutant SH3BP2 enhances TNF-α production and RANKL-induced osteoclast differentiation in myeloid cells. TNF-α is expressed in human cherubism lesions, which contain a large number of TRAP-positive multinucleated cells, and TNF-α 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-α-mediated bone loss by osteoclasts. Therefore, we investigated whether P416R mutant SH3BP2 is involved in TNF-α-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-α and can differentiate into osteoclasts independently of RANKL in vitro by a mechanism that involves SYK and PLCγ2 phosphorylation, leading to increased nuclear translocation of NFATc1. The heterozygous cherubism mutation exacerbates bone loss with increased osteoclast formation in a mouse calvarial TNF-α injection model as well as in a human TNF-α 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-α expressed in cherubism lesions and that SH3BP2 is a key regulator for TNF-α-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.

Alveolar Bone Protection by Targeting the SH3BP2-SYK Axis in Osteoclasts

“…Gain‐of‐function mutations in SH3BP2 are responsible for a human craniofacial disorder, cherubism (OMIM#118400) . Analysis of a knock‐in mouse model for cherubism revealed that a cherubism mutation increases osteoclastogenesis induced by RANKL and TNF‐α and enhances macrophage responsiveness to pathogen‐associated molecular patterns (PAMPs) via TLRs . SYK is critically required for the increased activation of osteoclasts and macrophages carrying cherubism mutations .…”

Clinical and genetic analysis of patients with cherubism

“…SH3BP2 lies within a region that is frequently deleted in individuals with Wolf–Hirschhorn syndrome (Lietman et al., ; Reichenberger et al., ) and previous reports showed that haploinsufficiency does not result in cherubism or cherubism‐like characteristics, suggesting that the mutations in SH3BP2 would lead to a gain of function or would act in a dominant‐negative manner (Miah et al., ; Mukai et al., ). A subsequent study demonstrated that knock‐in mice for SH3BP2 would alter bone quality, reduce osteoblast function, and contribute to bone resorption (Wang et al., ), demonstrating the importance of this gene in the osteoclastogenesis.…”

Bone marrow transplantation improves autoinflammation and inflammatory bone loss in SH3BP2 knock-in cherubism mice

“…Furthermore, BMT was effective even in treating fully inflamed Sh3bp2 KI/KI mice, which were not ameliorated with anti-TNF-α therapy in mice and humans [20, 21], suggesting that wild-type BMT also corrected inflammatory cytokine levels other than TNF-α. We have previously reported that cherubism is a hematopoietic disorder of myeloid lineage cells caused by hyperactive macrophages and osteoclasts [3, 18, 22, 52]. Therefore, we assume that replacement of the mutant macrophages and osteoclasts with those carrying wild-type SH3BP2 is a main cause of the improved symptoms in Sh3bp2 KI/KI mice, which resulted in the comprehensive reconstitution of the expression profile of inflammatory cytokines and osteoclast-mediated bone resorption activity in Sh3bp2 KI/KI recipients.…”

“…Genetic deletion of TNF-α in Sh3bp2 KI/KI mice shows a significant rescue of inflammation, suggesting that TNF-α plays a key role in the pathogenesis of inflammation in Sh3bp2 KI/KI mice. In fact, TNF-α is expressed in both multinucleated giant cells and stromal cells in human cherubism lesions [21, 22]. These results led us to investigate whether postnatal administration of anti-TNF-α drug is able to prevent or ameliorate the symptoms in Sh3bp2 KI/KI mice, which is more relevant to clinical cases of human cherubism.…”