Pro416Arg cherubism mutation in Sh3bp2 knock-in mice affects osteoblasts and alters bone mineral and matrix properties

Abstract

Cherubism is an autosomal dominant disorder in children characterized by unwarranted symmetrical bone resorption of the jaws with fibrous tissue deposition. Mutations causing cherubism have been identified in the adaptor protein SH3BP2. Knock-in mice with a Pro416Arg mutation in Sh3bp2 exhibit a generalized osteoporotic bone phenotype. In this study, we examined the effects of this "cherubism" mutation on spectroscopic indices of "bone quality" and on osteoblast differentiation. Fourier-transform infrared imaging (FTIRI) analysis of femurs from wild-type and Sh3bp2 knockin mice showed decreased mineral content, decreased mineral crystallinity/crystal size, and increased collagen maturity in homozygous mutants. To assess osteoblast maturation in vivo, knock-in mice were crossed with transgenic mice over-expressing GFP driven by 3.6-kb or 2.3-kb Col1a1 promoter fragments. Reduced numbers of mature osteoblasts were observed in homozygous mice. Neonatal calvarial cultures, which were enriched for osteoblasts by depletion of hematopoietic cells (negative selection for Ter119-and CD45-positive cells) were investigated for osteoblast-specific gene expression and differentiation, which demonstrated that differentiation and mineralization in homozygous osteoblast cultures was impaired. Co-cultures with calvarial osteoblasts and bone marrow macrophages showed that mutant osteoblasts appear to increase osteoclastogenesis resulting in increased bone resorption on bone chips. In summary, the Sh3bp2 mutation in cherubism mice alters bone quality, reduces osteoblast function, and may contribute to excessive bone resorption by osteoclasts. Our data, together with previous osteoclast studies, demonstrate a critical role of Sh3bp2 in bone remodeling and osteoblast differentiation.

The role of SH3BP2 in the pathophysiology of cherubism

“…It is still to be determined whether the reduced level of OPG in osteoblasts of Sh3bp2 KI/KI mice [83] also depends on NFATc1.…”

Cherubism allele heterozygosity amplifies microbe-induced inflammatory responses in murine macrophages

“…Whereas heterozygous cherubic mice showed no significant phenotype, homozygous cherubic animals developed systemic inflammation and severe osteopenia (10,11). This phenotype has been linked to exacerbated activities of intracellular signaling components resulting from the accumulation of proteasomeresistant mutant 3BP2 proteins in mouse osteoclasts (12).…”

Fourier Transform Infrared Spectroscopic Imaging Parameters Describing Acid Phosphate Substitution in Biologic Hydroxyapatite

“…Knowledge of the spatial variation in mineral and matrix composition is important as it allows interpretation of alterations in mechanical properties [5,6], fracture risk [7], effects of therapies [8,9] and the effects of genetic and metabolic abnormalities on each of these properties [10–12]. In the cited examples, FTIR spectroscopy combined with a focal plane array (FPA) detector provided IR images showing the distribution of specific compounds within the mineralized tissue, without the need for staining or use of antibodies.…”