Loss-of-function OGFRL1 variants identified in autosomal recessive cherubism families.

Cherubism (OMIM 118400) is a rare craniofacial disorder in children characterized by destructive jawbone expansion due to the growth of inflammatory fibrous lesions. Our previous studies have shown that gain-of-function mutations in SH3 domain-binding protein 2 (SH3BP2) are responsible for cherubism and that a knock-in mouse model for cherubism recapitulates the features of cherubism, such as increased osteoclast formation and jawbone destruction. To date, SH3BP2 is the only gene identified to be responsible for cherubism. Since not all patients clinically diagnosed with cherubism had mutations in SH3BP2, we hypothesized that there may be novel cherubism genes and that these genes may play a role in jawbone homeostasis. Here, using whole exome sequencing, we identified homozygous loss-of-function variants in the opioid growth factor receptor like 1 (OGFRL1) gene in 2 independent autosomal recessive cherubism families from Syria and India. The newly identified pathogenic homozygous variants were not reported in any variant databases, suggesting that OGFRL1 is a novel gene responsible for cherubism. Single cell analysis of mouse jawbone tissue revealed that Ogfrl1 is highly expressed in myeloid lineage cells. We generated OGFRL1 knockout mice and mice carrying the Syrian frameshift mutation to understand the in vivo role of OGFRL1. However, neither mouse model recapitulated human cherubism or the phenotypes exhibited by SH3BP2 cherubism mice under physiological and periodontitis conditions. Unlike bone marrow-derived M-CSF-dependent macrophages (BMMs) carrying the SH3BP2 cherubism mutation, BMMs lacking OGFRL1 or carrying the Syrian mutation showed no difference in TNF-ɑ mRNA induction by LPS or TNF-ɑ compared to WT BMMs. Osteoclast formation induced by RANKL was also comparable. These results suggest that the loss-of-function effects of OGFRL1 in humans differ from those in mice and highlight the fact that mice are not always an ideal model for studying rare craniofacial bone disorders.

Inhibition of RANKL improves the skeletal phenotype of adenine-induced chronic kidney disease in mice.

Skeletal fragility and high fracture rates are common in CKD. A key component of bone loss in CKD with secondary hyperparathyroidism is high bone turnover and cortical bone deterioration through both cortical porosity and cortical thinning. We hypothesized that RANKL drives high bone resorption within cortical bone leading to the development of cortical porosity in CKD (study 1) and that systemic inhibition of RANKL would mitigate the skeletal phenotype of CKD (study 2). In study 1, we assessed the skeletal properties of male and female Dmp1-cre RANKLfl/fl (cKO) and control genotype (Ranklfl/fl; Con) mice after 10 wk of adenine-induced CKD (AD; 0.2% dietary adenine). All AD mice regardless of sex or genotype had elevated blood urea nitrogen and high PTH. Con AD mice in both sexes had cortical porosity and lower cortical thickness as well as high osteoclast-covered trabecular surfaces and higher bone formation rate. cKO mice had preserved cortical bone microarchitecture despite high circulating PTH as well as no CKD-induced increases in osteoclasts. In study 2, male mice with established AD CKD were either given a single injection of an anti-RANKL antibody (5 mg/kg) 8 wk post-induction of CKD or subjected to 3×/wk dosing with risedronate (1.2 µg/kg) for 4 wk. Anti-RANKL treatment significantly reduced bone formation rate as well as osteoclast surfaces at both trabecular and cortical pore surfaces; risedronate treatment had little effect on these bone parameters. In conclusion, these studies demonstrate that bone-specific RANKL is critical for the development of high bone formation/high osteoclasts and cortical bone loss in CKD with high PTH. Additionally, systemic anti-RANKL ligand therapy in established CKD may help prevent the propagation of cortical bone loss via suppression of bone turnover.

Scaffold protein SH3BP2 signalosome is pivotal for immune activation in nephrotic syndrome.

Despite clinical use of immunosuppressive agents, the immunopathogenesis of minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS) remains unclear. Src homology 3-binding protein 2 (SH3BP2), a scaffold protein, forms an immune signaling complex (signalosome) with 17 other proteins, including phospholipase Cγ2 (PLCγ2) and Rho-guanine nucleotide exchange factor VAV2 (VAV2). Bioinformatic analysis of human glomerular transcriptome (Nephrotic Syndrome Study Network cohort) revealed upregulated SH3BP2 in MCD and FSGS. The SH3BP2 signalosome score and downstream MyD88, TRIF, and NFATc1 were significantly upregulated in MCD and FSGS. Immune pathway activation scores for Toll-like receptors, cytokine-cytokine receptor, and NOD-like receptors were increased in FSGS. Lower SH3BP2 signalosome score was associated with MCD, higher estimated glomerular filtration rate, and remission. Further work using Sh3bp2KI/KI transgenic mice with a gain-in-function mutation showed ~6-fold and ~25-fold increases in albuminuria at 4 and 12 weeks, respectively. Decreased serum albumin and unchanged serum creatinine were observed at 12 weeks. Sh3bp2KI/KI kidney morphology appeared normal except for increased mesangial cellularity and patchy foot process fusion without electron-dense deposits. SH3BP2 co-immunoprecipitated with PLCγ2 and VAV2 in human podocytes, underscoring the importance of SH3BP2 in immune activation. SH3BP2 and its binding partners may determine the immune activation pathways resulting in podocyte injury leading to loss of the glomerular filtration barrier.

Osteocyte RANKL Drives Bone Resorption in Mouse Ligature-Induced Periodontitis.

Mouse ligature-induced periodontitis (LIP) has been used to study bone loss in periodontitis. However, the role of osteocytes in LIP remains unclear. Furthermore, there is no consensus on the choice of alveolar bone parameters and time points to evaluate LIP. Here, we investigated the dynamics of changes in osteoclastogenesis and bone volume (BV) loss in LIP over 14 days. Time-course analysis revealed that osteoclast induction peaked on days 3 and 5, followed by the peak of BV loss on day 7. Notably, BV was restored by day 14. The bone formation phase after the bone resorption phase was suggested to be responsible for the recovery of bone loss. Electron microscopy identified bacteria in the osteocyte lacunar space beyond the periodontal ligament (PDL) tissue. We investigated how osteocytes affect bone resorption of LIP and found that mice lacking receptor activator of NF-κB ligand (RANKL), predominantly in osteocytes, protected against bone loss in LIP, whereas recombination activating 1 (RAG1)-deficient mice failed to resist it. These results indicate that T/B cells are dispensable for osteoclast induction in LIP and that RANKL from osteocytes and mature osteoblasts regulates bone resorption by LIP. Remarkably, mice lacking the myeloid differentiation primary response gene 88 (MYD88) did not show protection against LIP-induced bone loss. Instead, osteocytic cells expressed nucleotide-binding oligomerization domain containing 1 (NOD1), and primary osteocytes induced significantly higher Rankl than primary osteoblasts when stimulated with a NOD1 agonist. Taken together, LIP induced both bone resorption and bone formation in a stage-dependent manner, suggesting that the selection of time points is critical for quantifying bone loss in mouse LIP. Pathogenetically, the current study suggests that bacterial activation of osteocytes via NOD1 is involved in the mechanism of osteoclastogenesis in LIP. The NOD1-RANKL axis in osteocytes may be a therapeutic target for bone resorption in periodontitis. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Imatinib has minimal effects on inflammatory and osteopenic phenotypes in a murine cherubism model.

OBJECTIVE: Cherubism is a genetic disorder characterised by bilateral jawbone deformation. The associated jawbone lesions regress after puberty, whereas severe cases require surgical treatment. Although several drugs have been tested, fundamental treatment strategies for cherubism have not been established. The effectiveness of imatinib has recently been reported; however, its pharmaceutical mechanism remains unclear. In this study, we tested the effects of imatinib using a cherubism mouse model. METHODS: We used Sh3bp2 P416R cherubism mutant mice, which exhibit systemic organ inflammation and osteopenia. The effects of imatinib were determined using primary bone marrow-derived macrophages. Imatinib was administered intraperitoneally to the mice, and serum tumour necrosis factor-α (TNFα), organ inflammation and bone properties were examined. RESULTS: The cherubism mutant macrophages produced higher levels of TNFα in response to lipopolysaccharide compared to wild-type macrophages, and imatinib did not significantly suppress TNFα production. Although imatinib suppressed osteoclast formation in vitro, administering it in vivo did not suppress organ inflammation and osteopenia. CONCLUSION: The in vivo administration of imatinib had a minimal therapeutic impact in cherubism mutant mice. To establish better pharmaceutical interventions, it is necessary to integrate new findings from murine models with clinical data from patients with a definitive diagnosis of cherubism.

Type 1 diabetes mellitus leads to gingivitis and an early compensatory increase in bone remodeling.

BACKGROUND: Type 1 diabetes mellitus (T1DM) and periodontitis have long been thought to be biologically connected. Indeed, T1DM is a risk factor for periodontal disease. With the population of diabetic individuals growing, it is more important than ever to understand the negative consequences of diabetes on the periodontium and the mechanisms. The aim of this study was to find out the early effects of T1DM on the periodontium without any experimentally induced periodontitis. METHODS: We established the streptozotocin (STZ)-induced diabetic mouse model and examined the periodontium 8 weeks later by histology, molecular and cellular assays. Microcomputed tomographic (𝜇CT) imaging and in vivo fluorochrome labeling were also used to quantify bone volume and mineral apposition rates (MAR). RESULTS: The histologic appearance of epithelium tissue, connective tissue, and periodontal ligament in the diabetic condition was comparable with that of control mice. However, immune cell infiltration in the gingiva was dramatically elevated in the diabetic mice, which was accompanied by unmineralized connective tissue degeneration. Bone resorption activity was significantly increased in the diabetic mice, and quantitative 𝜇CT demonstrated the bone volume, the ratio of bone volume over tissue volume, and cemento-enamel junction to alveolar bone crest (CEJ-ABC) in the diabetic condition were equivalent to those in the control group. In vivo fluorochrome labeling revealed increased MAR and bone remodeling in the diabetic mice. Further investigation found the diabetic mice had more osteoprogenitors recruited to the periodontium, allowing more bone formation to balance the enhanced bone resorption. CONCLUSIONS: STZ-induced T1DM mice, at an early stage, have elevated gingival inflammation and soft tissue degeneration and increased bone resorption; but still the alveolar bone was preserved by recruiting more osteoprogenitor cells and increasing the rate of bone formation. We conclude that inflammation and periodontitis precede alveolar bone deterioration in diabetes.

Osteocytes directly regulate osteolysis via MYD88 signaling in bacterial bone infection.

The impact of bone cell activation on bacterially-induced osteolysis remains elusive. Here, we show that matrix-embedded osteocytes stimulated with bacterial pathogen-associated molecular patterns (PAMPs) directly drive bone resorption through an MYD88-regulated signaling pathway. Mice lacking MYD88, primarily in osteocytes, protect against osteolysis caused by calvarial injections of bacterial PAMPs and resist alveolar bone resorption induced by oral Porphyromonas gingivalis (Pg) infection. In contrast, mice with targeted MYD88 restoration in osteocytes exhibit osteolysis with inflammatory cell infiltration. In vitro, bacterial PAMPs induce significantly higher expression of the cytokine RANKL in osteocytes than osteoblasts. Mechanistically, activation of the osteocyte MYD88 pathway up-regulates RANKL by increasing binding of the transcription factors CREB and STAT3 to Rankl enhancers and by suppressing K48-ubiquitination of CREB/CREB binding protein and STAT3. Systemic administration of an MYD88 inhibitor prevents jawbone loss in Pg-driven periodontitis. These findings reveal that osteocytes directly regulate inflammatory osteolysis in bone infection, suggesting that MYD88 and downstream RANKL regulators in osteocytes are therapeutic targets for osteolysis in periodontitis and osteomyelitis.

OC_Finder: Osteoclast segmentation, counting, and classification using watershed and deep learning.

Osteoclasts are multinucleated cells that exclusively resorb bone matrix proteins and minerals on the bone surface. They differentiate from monocyte/macrophage-lineage cells in the presence of osteoclastogenic cytokines such as the receptor activator of nuclear factor-κB ligand (RANKL) and are stained positive for tartrate-resistant acid phosphatase (TRAP). In vitro, osteoclast formation assays are commonly used to assess the capacity of osteoclast precursor cells for differentiating into osteoclasts wherein the number of TRAP-positive multinucleated cells are counted as osteoclasts. Osteoclasts are manually identified on cell culture dishes by human eyes, which is a labor-intensive process. Moreover, the manual procedure is not objective and result in lack of reproducibility. To accelerate the process and reduce the workload for counting the number of osteoclasts, we developed OC_Finder, a fully automated system for identifying osteoclasts in microscopic images. OC_Finder consists of cell image segmentation with a watershed algorithm and cell classification using deep learning. OC_Finder detected osteoclasts differentiated from wild-type and Sh3bp2KI/+ precursor cells at a 99.4% accuracy for segmentation and at a 98.1% accuracy for classification. The number of osteoclasts classified by OC_Finder was at the same accuracy level with manual counting by a human expert. OC_Finder also showed consistent performance on additional datasets collected with different microscopes with different settings by a different operator. Together, successful development of OC_Finder suggests that deep learning is a useful tool to perform prompt and accurate unbiased classification and detection of specific cell types in microscopic images.

Tlr2/4-Mediated Hyperinflammation Promotes Cherubism-Like Jawbone Expansion in Sh3bp2 (P416R) Knockin Mice.

Cherubism (CBM), characterized by expansile jawbones with multilocular fibrocystic lesions, is caused by gain-of-function mutations in SH3 domain-binding protein 2 (SH3BP2; mouse orthologue Sh3bp2). Loss of jawbone and dental integrity significantly decrease the quality of life for affected children. Treatment for CBM is limited to multiple surgeries to correct facial deformities. Despite significant advances made with CBM knockin (KI) mouse models (Sh3bp2 KI/KI ), the activation mechanisms of CBM lesions remain unknown because mutant mice do not spontaneously develop expansile jawbones. We hypothesize that bony inflammation of an unknown cause triggers jawbone expansion in CBM. To introduce jawbone inflammation in a spatiotemporally controlled manner, we exposed pulp of the first right mandibular molar of 6-week-old Sh3bp2 +/+ , Sh3bp2 KI/+ , and Sh3bp2 KI/KI mice. Bacterial invasion from the exposed pulp into root canals led to apical periodontitis in wild-type and mutant mice. The pathogen-associated molecular patterns (PAMPs)-induced inflammation of alveolar bone resulted in jawbone expansion in Sh3bp2 KI/+ and Sh3bp2 KI/KI mice. CBM-like lesions developed exacerbated inflammation with increased neutrophil, macrophage, and osteoclast numbers. These lesions displayed excessive neutrophil extracellular traps (NETs) compared to Sh3bp2 +/+ mice. Expression levels of IL-1ß, IL-6, and TNF-α were increased in periapical lesions of Sh3bp2 +/+ , Sh3bp2 KI/+ , and Sh3bp2 KI/KI mice and also in plasma and the left untreated mandibles (with no pulp exposure) of Sh3bp2 KI/KI mice, suggesting a systemic upregulation. Ablation of Tlr2/4 signaling or depletion of neutrophils by Ly6G antibodies ameliorated jawbone expansion induced by PAMPs in Sh3bp2 KI/KI mice. In summary, successful induction of CBM-like lesions in jaws of CBM mice is important for studying initiating mechanisms of CBM and for testing potential therapies. Our findings further emphasize a critical role of host immunity in the development of apical periodontitis and the importance of maintaining oral health in CBM patients. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

SH3BP2 Deficiency Ameliorates Murine Systemic Lupus Erythematosus.

BACKGROUND: The adaptor protein Src homology 3 domain-binding protein 2 (SH3BP2) is widely expressed in immune cells. It controls intracellular signaling pathways. The present study was undertaken to investigate the role of SH3BP2 in a murine systemic lupus erythematosus model. METHODS: For the lupus model, we used Faslpr/lpr mice. Clinical and immunological phenotypes were compared between Faslpr/lpr and SH3BP2-deficient Faslpr/lpr mice. Splenomegaly and renal involvement were assessed. Lymphocyte subsets in the spleen were analyzed by flow cytometry. To examine the role of SH3BP2 in specific cells, B cell-specific SH3BP2-deficient lupus mice were analyzed; T cells and bone marrow-derived dendritic cells and macrophages were analyzed in vitro. RESULTS: SH3BP2 deficiency significantly reduced lupus-like phenotypes, presented as splenomegaly, renal involvement, elevated serum anti-dsDNA antibody, and increased splenic B220+CD4-CD8- T cells. Notably, SH3BP2 deficiency in B cells did not rescue the lupus-like phenotypes. Furthermore, SH3BP2 deficiency did not substantially affect the characteristics of T cells and macrophages in vitro. Interestingly, SH3BP2 deficiency suppressed the differentiation of dendritic cells in vitro and reduced the number of dendritic cells in the spleen of the lupus-prone mice. CONCLUSIONS: SH3BP2 deficiency ameliorated lupus-like manifestations. Modulating SH3BP2 expression could thus provide a novel therapeutic approach to autoimmune diseases.

Microbe-Dependent Exacerbated Alveolar Bone Destruction in Heterozygous Cherubism Mice.

Cherubism (OMIM#118400) is a craniofacial disorder characterized by destructive jaw expansion. Gain-of-function mutations in SH3-domain binding protein 2 (SH3BP2) are responsible for this rare disorder. We have previously shown that homozygous knock-in (KI) mice (Sh3bp2 KI/KI ) recapitulate human cherubism by developing inflammatory lesions in the jaw. However, it remains unknown why heterozygous KI mice (Sh3bp2 KI/+ ) do not recapitulate the excessive jawbone destruction in human cherubism, even though all mutations are heterozygous in humans. We hypothesized that Sh3bp2 KI/+ mice need to be challenged for developing exacerbated jawbone destruction and that bacterial stimulation in the oral cavity may be involved in the mechanism. In this study, we applied a ligature-induced periodontitis model to Sh3bp2 KI/+ mice to induce inflammatory alveolar bone destruction. Ligature placement induced alveolar bone resorption with gingival inflammation. Quantification of alveolar bone volume revealed that Sh3bp2 KI/+ mice developed more severe bone loss (male: 43.0% ± 10.6%, female: 42.6% ± 10.4%) compared with Sh3bp2 +/+ mice (male: 25.8% ± 4.0%, female: 30.9% ± 6.5%). Measurement of bone loss by the cement-enamel junction-alveolar bone crest distance showed no difference between Sh3bp2 KI/+ and Sh3bp2 +/+ mice. The number of osteoclasts on the alveolar bone surface was higher in male Sh3bp2 KI/+ mice, but not in females, compared with Sh3bp2 +/+ mice. In contrast, inflammatory cytokine levels in gingiva were comparable between Sh3bp2 KI/+ and Sh3bp2 +/+ mice with ligatures. Genetic deletion of the spleen tyrosine kinase in myeloid cells and antibiotic treatment suppressed alveolar bone loss in Sh3bp2 KI/+ mice, suggesting that increased osteoclast differentiation and function mediated by SYK and accumulation of oral bacteria are responsible for the increased alveolar bone loss in Sh3bp2 KI/+ mice with ligature-induced periodontitis. High amounts of oral bacterial load caused by insufficient oral hygiene could be a trigger for the initiation of jawbone destruction in human cherubism. © 2020 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

RANKL-independent osteoclastogenesis in the SH3BP2 cherubism mice.

Even though the receptor activator of the nuclear factor-κB ligand (RANKL) and its receptor RANK have an exclusive role in osteoclastogenesis, the possibility of RANKL/RANK-independent osteoclastogenesis has been the subject of a long-standing debate in bone biology. In contrast, it has been reported that calvarial injection of TNF-ɑ elicits significant osteoclastogenesis in the absence of RANKL/RANK in NF-κB2- and RBP-J-deficient mice, suggesting that inflammatory challenges and secondary gene manipulation are the prerequisites for RANKL/RANK-deficient mice to develop osteoclasts in vivo. Here we report that, even in the absence of RANKL (Rankl -/- ), cherubism mice (Sh3bp2 KI/KI ) harboring the homozygous gain-of-function mutation in SH3-domain binding protein 2 (SH3BP2) develop tartrate-resistant acid phosphatase (TRAP)-positive multinucleated osteoclasts spontaneously. The Sh3bp2 KI/KI Rankl -/- mice exhibit an increase in tooth exposure and a decrease in bone volume/total volume compared to Sh3bp2 +/+ Rankl -/- mice. The multinucleated cells were stained positively for cathepsin K. Osteoclastic marker gene expression in bone and serum TRAP5b levels were elevated in Sh3bp2 KI/KI Rankl -/- mice. Elevation of the serum TNF-ɑ levels suggested that TNF-ɑ is a driver for the RANKL-independent osteoclast formation in Sh3bp2 KI/KI mice. Our results provide a novel mutant model that develops osteoclasts independent of RANKL and establish that the gain-of-function of SH3BP2 promotes osteoclastogenesis not only in the presence of RANKL but also in the absence of RANKL.

Investigating global gene expression changes in a murine model of cherubism.

Cherubism is a rare genetic disorder caused primarily by mutations in SH3BP2 resulting in excessive bone resorption and fibrous tissue overgrowth in the lower portions of the face. Bone marrow derived cell cultures derived from a murine model of cherubism display poor osteogenesis and spontaneous osteoclast formation. To develop a deeper understanding for the potential underlying mechanisms contributing to these phenotypes in mice, we compared global gene expression changes in hematopoietic and mesenchymal cell populations between cherubism and wild type mice. In the hematopoietic population, not surprisingly, upregulated genes were significantly enriched for functions related to osteoclastogenesis. However, these upregulated genes were also significantly enriched for functions associated with inflammation including arachidonic acid/prostaglandin signaling, regulators of coagulation and autoinflammation, extracellular matrix remodeling, and chemokine expression. In the mesenchymal population, we observed down regulation of osteoblast and adventitial reticular cell marker genes. Regulators of BMP and Wnt pathway associated genes showed numerous changes in gene expression, likely implicating the down regulation of BMP signaling and possibly the activation of certain Wnt pathways. Analyses of the cherubism derived mesenchymal population also revealed interesting changes in gene expression related to inflammation including the expression of distinct granzymes, chemokines, and sulfotransferases. These studies reveal complex changes in gene expression elicited from a cherubic mutation in Sh3bp2 that are informative to the mechanisms responding to inflammatory stimuli and repressing osteogenesis. The outcomes of this work are likely to have relevance not only to cherubism, but other inflammatory conditions impacting the skeleton.

Optineurin regulates osteoblastogenesis through STAT1.

A sophisticated and delicate balance between bone resorption by osteoclasts and bone formation by osteoblasts regulates bone metabolism. Optineurin (OPTN) is a gene involved in primary open-angle glaucoma and amyotrophic lateral sclerosis. Although its function has been widely studied in ophthalmology and neurology, recent reports have shown its possible involvement in bone metabolism through negative regulation of osteoclast differentiation. However, little is known about the role of OPTN in osteoblast function. Here, we demonstrated that OPTN controls not only osteoclast but also osteoblast differentiation. Different parameters involved in osteoblastogenesis and osteoclastogenesis were assessed in Optn-/- mice. The results showed that osteoblasts from Optn-/- mice had impaired alkaline phosphatase activity, defective mineralized nodules, and inability to support osteoclast differentiation. Moreover, OPTN could bind to signal transducer and activator of transcription 1 (STAT1) and regulate runt-related transcription factor 2 (RUNX2) nuclear localization by modulating STAT1 levels in osteoblasts. These data suggest that OPTN is involved in bone metabolism not only by regulating osteoclast function but also by regulating osteoblast function by mediating RUNX2 nuclear translocation via STAT1.

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

Periodontitis is a bacterially induced chronic inflammatory condition of the oral cavity where tooth-supporting tissues including alveolar bone are destructed. Previously, we have shown that the adaptor protein SH3-domain binding protein 2 (SH3BP2) plays a critical role in inflammatory response and osteoclastogenesis of myeloid lineage cells through spleen tyrosine kinase (SYK). In this study, we show that SH3BP2 is a novel regulator for alveolar bone resorption in periodontitis. Micro-CT analysis of SH3BP2-deficient (Sh3bp2 -/- ) mice challenged with ligature-induced periodontitis revealed that Sh3bp2 -/- mice develop decreased alveolar bone loss (male 14.9% ± 10.2%; female 19.0% ± 6.0%) compared with wild-type control mice (male 25.3% ± 5.8%; female 30.8% ± 5.8%). Lack of SH3BP2 did not change the inflammatory cytokine expression and osteoclast induction. Conditional knockout of SH3BP2 and SYK in myeloid lineage cells with LysM-Cre mice recapitulated the reduced bone loss without affecting both inflammatory cytokine expression and osteoclast induction, suggesting that the SH3BP2-SYK axis plays a key role in regulating alveolar bone loss by mechanisms that regulate the bone-resorbing function of osteoclasts rather than differentiation. Administration of a new SYK inhibitor GS-9973 before or after periodontitis induction reduced bone resorption without affecting inflammatory reaction in gingival tissues. In vitro, GS-9973 treatment of bone marrow-derived M-CSF-dependent macrophages suppressed tartrate-resistant acid phosphatase (TRAP)-positive osteoclast formation with decreased mineral resorption capacity even when GS-9973 was added after RANKL stimulation. Thus, the data suggest that SH3BP2-SYK is a novel signaling axis for regulating alveolar bone loss in periodontitis and that SYK can be a potential therapeutic target to suppress alveolar bone resorption in periodontal diseases. © 2019 American Society for Bone and Mineral Research. © 2019 American Society for Bone and Mineral Research.

Sh3bp2 Gain-Of-Function Mutation Ameliorates Lupus Phenotypes in B6.MRL-Faslpr Mice.

SH3 domain-binding protein 2 (SH3BP2) is an adaptor protein that is predominantly expressed in immune cells, and it regulates intracellular signaling. We had previously reported that a gain-of-function mutation in SH3BP2 exacerbates inflammation and bone loss in murine arthritis models. Here, we explored the involvement of SH3BP2 in a lupus model. Sh3bp2 gain-of-function (P416R knock-in; Sh3bp2KI/+) mice and lupus-prone B6.MRL-Faslpr mice were crossed to yield double-mutant (Sh3bp2KI/+Faslpr/lpr) mice. We monitored survival rates and proteinuria up to 48 weeks of age and assessed renal damage and serum anti-double-stranded DNA antibody levels. Additionally, we analyzed B and T cell subsets in lymphoid tissues by flow cytometry and determined the expression of apoptosis-related molecules in lymph nodes. Sh3bp2 gain-of-function mutation alleviated the poor survival rate, proteinuria, and glomerulosclerosis and significantly reduced serum anti-dsDNA antibody levels in Sh3bp2KI/+Faslpr/lpr mice. Additionally, B220+CD4-CD8- T cell population in lymph nodes was decreased in Sh3bp2KI/+Faslpr/lpr mice, which is possibly associated with the observed increase in cleaved caspase-3 and tumor necrosis factor levels. Sh3bp2 gain-of-function mutation ameliorated clinical and immunological phenotypes in lupus-prone mice. Our findings offer better insight into the unique immunopathological roles of SH3BP2 in autoimmune diseases.

Epigenetic regulation of NfatC1 transcription and osteoclastogenesis by nicotinamide phosphoribosyl transferase in the pathogenesis of arthritis.

Nicotinamide phosphoribosyltransferase (NAMPT) functions in NAD synthesis, apoptosis, and inflammation. Dysregulation of NAMPT has been associated with several inflammatory diseases, including rheumatoid arthritis (RA). The purpose of this study was to investigate NAMPT's role in arthritis using mouse and cellular models. Collagen-induced arthritis (CIA) in DBA/1J Nampt +/- mice was evaluated by ELISA, micro-CT, and RNA-sequencing (RNA-seq). In vitro Nampt loss-of-function and gain-of-function studies on osteoclastogenesis were examined by TRAP staining, nascent RNA capture, luciferase reporter assays, and ChIP-PCR. Nampt-deficient mice presented with suppressed inflammatory bone destruction and disease progression in a CIA mouse model. Nampt expression was required for the epigenetic regulation of the Nfatc1 promoter and osteoclastogenesis. Finally, RNA-seq identified 690 differentially expressed genes in whole ankle joints which associated (P < 0.05) with Nampt expression and CIA. Selected target was validated by RT-PCR or functional characterization. We have provided evidence that NAMPT functions as a genetic risk factor and a potential therapeutic target to RA.

Mouse Cre Models for the Study of Bone Diseases.

PURPOSE: Transgenic Cre lines are a valuable tool for conditionally inactivating or activating genes to understand their function. Here, we provide an overview of Cre transgenic models used for studying gene function in bone cells and discuss their advantages and limitations, with particular emphasis on Cre lines used for studying osteocyte and osteoclast function. RECENT FINDINGS: Recent studies have shown that many bone cell-targeted Cre models are not as specific as originally thought. To ensure accurate data interpretation, it is important for investigators to test for unexpected recombination events due to transient expression of Cre recombinase during development or in precursor cells and to be aware of the potential for germ line recombination of targeted genes as well as the potential for unexpected phenotypes due to the Cre transgene. Although many of the bone-targeted Cre-deleter strains are imperfect and each model has its own limitations, their careful use will continue to provide key advances in our understanding of bone cell function in health and disease.

Second-Generation SYK Inhibitor Entospletinib Ameliorates Fully Established Inflammation and Bone Destruction in the Cherubism Mouse Model.

Cherubism is a craniofacial disorder characterized by maxillary and mandibular bone destruction. Gain-of-function mutations in the SH3-domain binding protein 2 (SH3BP2) are responsible for the excessive bone resorption caused by fibrous inflammatory lesions. A homozygous knock-in (KI) mouse model for cherubism (Sh3bp2KI/KI ) develops autoinflammation resulting in systemic bone destruction. Although administration of the TNF-α blocker etanercept to neonatal Sh3bp2KI/KI mice prevented the disease onset, this therapy was not effective for adult Sh3bp2KI/KI mice or human cherubism patients who already had lesions. Because genetic ablation of spleen tyrosine kinase (SYK) in myeloid cells rescues Sh3bp2KI/KI mice from inflammation, we examined whether SYK inhibitor administration can improve fully developed cherubism symptoms in adult Sh3bp2KI/KI mice. Entospletinib (GS-9973) was intraperitoneally injected into 10-week-old Sh3bp2KI/KI mice every day for 6 weeks. Treatment with GS-9973 improved facial swelling and histomorphometric analysis of lung and liver tissue showed that GS-9973 administration significantly reduced inflammatory infiltrates associated with decreased levels of serum TNF-α. Micro-computed tomography (µCT) analysis showed that GS-9973 treatment reduced bone erosion in mandibles, calvariae, and ankle and elbow joints of Sh3bp2KI/KI mice compared to Sh3bp2KI/KI mice treated with dimethyl sulfoxide (DMSO). Taken together, the results demonstrate that administration of the SYK inhibitor ameliorates an already established cherubism phenotype in mice, suggesting that pharmacological inhibition of SYK may be a treatment option for cherubism patients with active disease progression. © 2018 American Society for Bone and Mineral Research.