High Bone Mass Research Articles

A new LRP6 variant and Camurati-Engelmann-like disease

Camurati-Engelmann disease is a rare autosomal dominant bone dysplasia belonging to the group of craniotubular hyperostoses. Genetic analysis classically shows mutation on TGFβ1 gene. A young woman was hospitalized with intense pain in lower limbs, associated to radiographic hyperostosis and sclerosis of the long bones. Mutation on LRP6 has recently been associated to high bone mass. In this case report, a rare missense variant on LRP6 gene was associated to radiographic features of Camurati-Engelmann. More studies should be conducted to assess the pathological role of this variant in Camurati-Engelmann-like disease.

Molecular Basis for Craniofacial Phenotypes Caused by Sclerostin Deletion

Some genetic disorders are associated with distinctive facial features, which can aid in diagnosis. While considerable advances have been made in identifying causal genes, relatively little progress has been made toward understanding how a particular genotype results in a characteristic craniofacial phenotype. An example is sclerosteosis/van Buchem disease, which is caused by mutations in the Wnt inhibitor sclerostin (SOST). Affected patients have a high bone mass coupled with a distinctive appearance where the mandible is enlarged and the maxilla is foreshortened. Here, mice carrying a null mutation in Sost were analyzed using quantitative micro–computed tomographic (µCT) imaging and histomorphometric analyses to determine the extent to which the size and shape of craniofacial skeleton were altered. Sost−/− mice exhibited a significant increase in appositional bone growth, which increased the height and width of the mandible and reduced the diameters of foramina. In vivo fluorochrome labeling, histology, and immunohistochemical analyses indicated that excessive bone deposition in the premaxillary suture mesenchyme curtailed overall growth, leading to midfacial hypoplasia. The amount of bone extracellular matrix produced by Sost−/− cells was significantly increased; as a consequence, osteoid seams were evident throughout the facial skeleton. Collectively, these analyses revealed a remarkable fidelity between human characteristics of sclerosteosis/van Buchem disease and the Sost−/− phenotype and provide clues into the conserved role for sclerostin signaling in modulating craniofacial morphology.

Frequency and causes of high bone mass

Frequency and causes of high bone mass

Association between Body Composition, Physical Activity, Food Intake and Bone Status in German Children and Adolescents.

Achieving a high bone mass during childhood and adolescence is important for the prevention of osteoporosis in later life. Herein, the purpose was to assess the relationship of various lifestyle factors and bone outcomes in school children. In 248 girls (13.4 ± 1.9 years, BMI: 20.2 ± 4.8 kg m−2) and 231 boys (13.6 ± 1.7 years, BMI: 19.3 ± 3.3 kg m−2), bone mass (stiffness index, SI; calcaneal quantitative ultrasonometry), body composition (bioelectrical impedance analysis), food intake (food frequency questionnaire), and physical activity level (PAL; standardized questionnaire) were assessed. The individual food intake of eight food groups was related to the German recommendations (Bone Healthy Eating Index, BoneHEI; 0–100 points). Relationships between SI and lifestyle factors (Spearman´s rank correlation) and the influence of the factors on the variance of SI (multiple linear regression) were tested (α = 0.05). SI correlated with age, BMI, absolute fat-free mass, relative fat mass, PAL, and puberty category score in both girls and boys (r = 0.18–0.56, p < 0.01), but not with BoneHEI (p > 0.05). Age, absolute fat-free mass, sex, and PAL explained 35% of the variance of SI (p < 0.0001): SI = −0.60 + 2.97∙age (years) + 0.65∙fat-free mass (kg) + 6.21∙sex (0 = male, 1 = female) + 17.55∙PAL. Besides age and sex, PAL and fat-free mass are important factors relating to bone health. School children should perform regular physical activity to improve their bone status.

A Neutralizing Antibody Targeting Oxidized Phospholipids Promotes Bone Anabolism in Chow-Fed Young Adult Mice.

ABSTRACTOxidized phospholipids containing phosphocholine (OxPL) are pro‐inflammatory lipid peroxidation products that bind to scavenger receptors (SRs), such as Scarb1, and toll‐like receptors (TLRs). Excessive OxPL, as found in oxidized low‐density lipoprotein (OxLDL), overwhelm these defense mechanisms and become pathogenic in atherosclerosis, nonalcoholic steatohepatitis (NASH), and osteoporosis. We previously reported that the innate IgM natural antibody E06 binds to OxPL and neutralizes their deleterious effects; expression of the single‐chain (scFv) form of the antigen‐binding domain of E06 (E06‐scFv) as a transgene increases trabecular bone in male mice. We show herein that E06‐scFv increases trabecular and cortical bone in female and male mice by increasing bone formation and decreasing osteoblast apoptosis in vivo. Homozygous E06‐scFv mice have higher bone mass than hemizygous, showing a dose effect of the transgene. To investigate how OxPL restrain bone formation under physiologic conditions, we measured the levels of SRs and TLRs that bind OxPL. We found that osteoblastic cells primarily express Scarb1. Moreover, OxLDL‐induced apoptosis and reduced differentiation were prevented in bone marrow–derived or calvaria‐derived osteoblasts from Scarb1 knockout mice. Because Scarb1‐deficient mice are reported to have high bone mass, our results suggest that E06 may promote bone anabolism in healthy young mice, at least in part, by neutralizing OxPL, which in turn promote Scarb1‐mediated apoptosis of osteoblasts or osteoblast precursors. © 2020 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR)..

The loss of STAT3 in mature osteoclasts has detrimental effects on bone structure.

Signal Transducer and Activator of Transcription 3 (STAT3) has recently been shown to be involved in bone development and has been implicated in bone diseases, such as Job’s Syndrome. Bone growth and changes have been known for many years to differ between sexes with male bones tending to have higher bone mass than female bones and older females tending to lose bone mass at faster rates than older males. Previous studies using conditional knock mice with Stat3 specifically deleted from the osteoblasts showed both sexes exhibited decreased bone mineral density (BMD) and strength. Using the Cre-Lox system with Cathepsin K promotor driving Cre to target the deletion of the Stat3 gene in mature osteoclasts (STAT3-cKO mice), we observed that 8-week old STAT3-cKO female femurs exhibited significantly lower BMD and bone mineral content (BMC) compared to littermate control (CN) females. There were no differences in BMD and BMC observed between male knock-out and male CN femurs. However, micro-computed tomography (μCT) analysis showed that both male and female STAT3-cKO mice had significant decreases in bone volume/tissue volume (BV/TV). Bone histomorphometry analysis of the distal femur, further revealed a decrease in bone formation rate and mineralizing surface/bone surface (MS/BS) with a significant decrease in osteoclast surface in female, but not male, STAT3-cKO mice. Profiling gene expression in an osteoclastic cell line with a knockdown of STAT3 showed an upregulation of a number of genes that are directly regulated by estrogen receptors. These data collectively suggest that regulation of STAT3 differs in male and female osteoclasts and that inactivation of STAT3 in osteoclasts affects bone turnover more in females than males, demonstrating the complicated nature of STAT3 signaling pathways in osteoclastogenesis. Drugs targeting the STAT3 pathway may be used for treatment of diseases such as Job’s Syndrome and osteoporosis.

Fracture risk assessment in an Italian group of transgender women after gender-confirming surgery.

Bone health is a critical issue in transgender women (TW) health care. Conflicting results have been reported on bone status after gender-confirming surgery (GCS). No recent data in Italian TW are available. The aim of this cross-sectional study was to evaluate fracture risk, lumbar spine BMD and 25OH vitamin D (25OHD) levels in a population of TW on estrogen replacement therapy (ERT) after GCS. We retrospectively analyzed a group of 57 TW, aged 45.3 ± 11.3years, referred to our Gender Dysphoria Clinic, at least 2years after GCS. Anthropometric parameters, patient compliance to ERT, biochemical and hormonal assessment, lumbar spine BMD and fracture risk were evaluated. Prevalence of low bone mass (Z-score ≤ -2) was 40% according to the natal gender. In this group, 17β-estradiol levels were significantly lower (median 21pg/ml [25th-75th percentile 10.6-48.5] vs 63pg/ml [38.5-99.5]; p < 0.001) and a higher prevalence of low compliance to ERT was recorded (83% vs 29%; p < 0.0001) compared to those with higher bone mass. An intermediate-high fracture risk was found in 14% of the sample. A high percentage (93%) of hypovitaminosis D was present. TW on ERT have a high prevalence of low bone mass, significantly associated with low estradiol levels and low compliance to ERT. A high prevalence of hypovitaminosis D was highlighted. Considering that one out of seven TW showed an intermediate-high 10-year fracture risk, such risk assessment may be considered to prevent and manage osteoporosis in this clinical setting.

Alterations In Musculoskeletal Function And Body Composition In Children With Autism Spectrum Disorder

Autism Spectrum Disorder (ASD) is a neurological disorder characterized by impaired social interaction and atypical behaviors. Children with ASD appear to have weaker muscular function and low bone mineral density. Recent studies have indicated that adolescents with ASD develop obesity and bone fracture incidence at a higher rate compared to typically developing peers (TDC). Limited information is available to identify levels of obesity and its relation to muscular function and body composition in children with ASD before they start puberty. PURPOSE: To determine whether differential body composition may affect muscular strength and function in children with ASD METHODS: Total of 40 adults, TDC and children with ASD participated in the study. Muscular strength (i.e., torque, work, and power) during knee extension and flexion was measured at 90, 150, and 210 °/sec in the lower extremity using Humac Norm Isokinetic Dynamometer. Maximal isometric forearm muscular strength was measured using a handgrip dynamometer. Body mass index (BMI), waist-to-hip ratio, and whole-body scan from Dual Energy X-Ray Absorptiometry were used to identify the body composition. RESULTS: Compared to control adults, TDC and ASD had lower BMI (20.1±0.7 TDC, 22.3±4.4 ASD vs. 27.2±2.3 Adults, kg/m2). All groups had similar percent body fat (26.4± 2.3 Adults, 29.8±1.83 TDC, 32.9±3.84 ASD, %) and percent lean body mass (69.5±2.2 Adults, 66.8±1.7 TDC, 64.4±3.6 ASD, %). However, compared to TDC, ASD children had significantly lower bone mass percentage (2.7±0.3 ASD vs. 3.2±0.2 TDC, %). Waist-to-hip ratio was significantly higher for ASD (0.91±0.04 ASD vs. 0.85±0.01 TDC). The maximal forearm and leg strength were significantly lower in ASD compared to TDC normalized for their body weight (30.2 ±5.2 ASD vs. 42.8 ± 2.5 TDC, kg). There is a significant inverse relationship with muscular strength and regional percent fat in the forearm. CONCLUSION: These findings suggest that body composition appeared to influence muscular strength in children with ASD. Less regional fat and higher bone mass rather than the total body fat may contribute for higher leg or forearm muscular strength in children with ASD. Supported by CASA RSCA Infusion, Central RSCA, and Undergraduate Research Grant, SJSU

HIF-1α Mediates Osteoclast-Induced Mandibular Condyle Growth via AMPK Signaling

During the mandibular condylar growth, the absorption of calcified cartilage matrix induced by osteoclasts is crucial for the continuous endochondral osteogenesis. Meanwhile, recent studies showed that subchondral bone resided within the low-oxygen microenvironment, and our previous study revealed that hypoxia-inducible transcription factor 1α (HIF-1α) promoted osteoclastogenesis under hypoxia. However, whether HIF-1α regulates the function of osteoclasts in the mandibular condyle cartilage remains elusive. Our study indicated that severe deformity of the mandibular condyle was displayed in 10-wk-old osteoclast-specific HIF-1α conditional knockout (CKO) mice, accompanied by shortened length of condylar process and disorganized fibrocartilage. In 1-, 2-, and 4-wk-old CKO mice, the size of the hypertrophic layer and chondrocytic layer was significantly thickened. In the chondrocytic layer, chondrocytes were atrophied, showing a form of apoptosis in 4-wk-old CKO mice. Furthermore, an increase in the thickness of the fibrous and proliferating layer was observed in 10-wk-old CKO mice, as well as a significant decrease in that of the chondrocytic and hypertrophic chondrocyte layers. Interestingly, the articular surface of the condylar process abnormally presented a horizontal concave shape, and a disk-like acellular connective tissue appeared. In addition, genetic ablation of HIF-1α blunted cartilage matrix loss by subchondral osteoclast deficiency, resulting in a high subchondral bone mass phenotype, accompanied with a decreased number of blood vessels, alkaline phosphatase staining, and vascular endothelial growth factor (VEGF) expression. Mechanistically, the number of osteoclasts in the center of the condyle in CKO mice was significantly reduced by attenuated expression of adenosine 5′-monophosphate-activated protein kinase (AMPK) signaling. These findings reveal a novel influence of HIF-1α function in osteoclasts on maintenance of osteoclast-induced resorption of calcified cartilage matrix via AMPK signaling, as well as subchondral bone formation through VEGF-dependent angiogenesis in bone marrow.

Pten deletion in Dmp1‐expressing cells does not rescue the osteopenic effects of Wnt/β‐catenin suppression

Skeletal homeostasis is sensitive to perturbations in Wnt signaling. Beyond its role in the bone, Wnt is a major target for pharmaceutical inhibition in a wide range of diseases, most notably cancers. Numerous clinical trials for Wnt-based candidates are currently underway, and Wnt inhibitors will likely soon be approved for clinical use. Given the bone-suppressive effects accompanying Wnt inhibition, there is a need to expose alternate pathways/molecules that can be targeted to counter the deleterious effects of Wnt inhibition on bone properties. Activation of the Pi3k/Akt pathway via Pten deletion is one possible osteoanabolic pathway to exploit. We investigated whether the osteopenic effects of β-catenin deletion from bone cells could be rescued by Pten deletion in the same cells. Mice carrying floxed alleles for Pten and β-catenin were bred to Dmp1-Cre mice to delete Pten alone, β-catenin alone, or both genesfrom the late-stage osteoblast/osteocyte population. The mice were assessed for bone mass, density, strength, and formation parameters to evaluate the potential rescue effect of Pten deletion in Wnt-impaired mice. Pten deletion resulted in high bone mass and β-catenin deletion resulted in low bone mass. Compound mutants had bone properties similar to β-catenin mutant mice, or surprisingly in some assays, were further compromised beyond β-catenin mutants. Pten inhibition, or one of its downstream nodes, is unlikely to protect against the bone-wasting effects of Wnt/βcat inhibition. Other avenues for preserving bone mass in the presence of Wnt inhibition should be explored to alleviate the skeletal side effects of Wnt inhibitor-based therapies.

Association Between Bipolar Disorder and Low Bone Mass: A Cross-Sectional Study With Newly Diagnosed, Drug-Naïve Patients.

BackgroundMedical comorbidities in people with mental disorders have recently gained more attention. People with bipolar disorder (BD) often have comorbid low bone mass, which is associated with increased fracture risk and related severe outcomes. However, few clinical studies on bone metabolism in BD patients are available. This study was designed to assess bone mineral density (BMD) and related influencing factors in a sample of newly diagnosed, drug-naïve individuals with BD and age- and sex-matched healthy controls.MethodsSixty-one drug-naïve individuals with BD (DSM-V) and 95 healthy volunteers had their lumbar spine (L1–L4) and left hip (Neck/Troch/Ward's) BMD determined by dual-energy X-ray absorptiometry. Besides, sociodemographic and clinical assessment were collected. Between-group comparisons and within subgroup analysis were performed.ResultsDrug-naïve patients with BD had significantly lower BMD in comparison to healthy controls in multiple sites (L1, L3, Neck, Troch, Ward's, and total hip). On subgroup analysis, overweight individuals with BD had higher bone mass, while females presented reduced BMD. Binary logistic regression showed that low BMD in multiple regions was associated with BD diagnosis, body mass index (BMI), gender, and age.ConclusionDrug-naïve individuals with BD have lower BMD when compared to an age- and gender-matched healthy control sample. Low BMI and female gender are factors associated with this outcome. The underlying pathological mechanisms of BD comorbid with osteoporosis should be further explored.Clinical Trial Registrationwww.chictr.org.cn, identifier ChiCTR190002137.

P0236COMPARISON OF THE CHARACTERISTICS AND SEVERITY OF RESTLESS LEG SYNDROME AND INSOMNIA IN PATIENTS WITH CHRONIC KIDNEY DISEASE AND RENAL TRANSPLANT RECIPIENTS

Abstract Background and Aims Symptoms of restless legs syndrome (RLS) are common in patients with chronic kidney disease (CKD) and on dialysis, affecting up to 25% of patients when the international RLS diagnostic criteria are applied. RLS has been associated with disordered sleep, impaired quality of life, increased cardiovascular morbidity and mortality risk in patients with CKD. The aim of our study was to examine the relationship between RLS and the prevalence and severity of insomnia in non-dialysis CKD patients (CKD stage IV and V), in haemodialysis and PD patients, in renal transplant recipients (RTRs) as well as to identify the risk factors independently associated with RLS prevalence and severity in each group. Method 436 patients were included in the study (152 patients with CKD stage IV and V, 117 haemodialysis patients, 78 PD patients and 89 RTRs). RLS diagnosis was made according to IRLSSG diagnostic criteria. The questions of the IRLSSG Severity Scale were answered. Athens Insomnia Scale (AIS) was used for the diagnosis of insomnia. Statistical analysis was performed with appropriate parametric and non-parametric tests and regression analysis models. Results Applying the IRLSSG criteria for diagnosis, the prevalence of RLS was 17%, 25.9%, 26.5%, 32.1% and 16.9% in patients with CKD stage IV, CKD stage V, hemodialysis patients, PD patients and RTRs respectively. The mean severity of the syndrome was higher in PD patients (14.64), followed by haemodialysis patients (12), CKD stage V patients (11.9), KTRs (11.3) and patients with CKD stage IV patients (10.5). Prevalence of RLS did not significantly differ between groups. CKD patients displayed the lowest presence of insomnia, while PD patients showed the relatively highest presence of insomnia. The mean severity of insomnia differed between the pairs: RTRs vs PD patients, RTRs vs haemodialysis patients and PD patients vs patients with CKD stage IV and V (p &amp;lt;0.05). RLS in all groups correlated with the presence of peripheral neuropathy and female gender. By regression analysis models we found that among CKD patients, presence of RLS independently correlated with number of pregnancies in women, previous cerebrovascular disease, hypothyroidism requiring treatment and antidepressant drugs use, whereas RLS severity independently correlated with the presence of peripheral neuropathy. Regarding hemodialysis patients, presence of RLS independently correlated with body mass index (BMI), female gender, antidepressant drugs use and serum PTH levels. RLS severity in the same group independently correlated only with female gender. Regarding PD patients, RLS presence was independently associated with number of pregnancies in women and left ventricular ejection fraction. RLS severity in the same group was independently associated only with the presence of peripheral arterial disease. Among RTRs, RLS presence independently correlated with female gender and a lower GFR. We were the first to find that presence of RLS was associated with a higher bone mass density and lower levels of 25-OH vitamin D. Conclusion The prevalence and severity of RLS and insomnia worsen as kidney function deteriorates in CKD patients, being most burdensome among patients with stage V CKD, haemodialysis and PD patients. The severity of insomnia is especially increased in PD patients. Although the frequency of RLS decreases in KTRs, it still occurs at higher rates compared to the general population. Further studies are needed to investigate the relationship between RLS and associated risk factors in patients with CKD and following kidney transplantation.

Individuals with high bone mass have increased progression of radiographic and clinical features of knee osteoarthritis

High bone mass (HBM) is associated with an increased prevalence of radiographic knee OA (kOA), characterized by osteophytosis. We aimed to determine if progression of radiographic kOA, and its sub-phenotypes, is increased in HBM and whether observed changes are clinically relevant. A cohort with and without HBM (L1 and/or total hip bone mineral density Z-score≥+3.2) had knee radiographs collected at baseline and 8-year follow-up. Sub-phenotypes were graded using the OARSI atlas. Medial/lateral tibial/femoral osteophyte and medial/lateral joint space narrowing (JSN) grades were summed and Δosteophytes, ΔJSN derived. Pain, function and stiffness were quantified using the WOMAC questionnaire. Associations between HBM status and sub-phenotype progression were determined using multivariable linear/poisson regression, adjusting for age, sex, height, baseline sub-phenotype grade, menopause, education and total body fat mass (TBFM). Generalized estimating equations accounted for individual-level clustering. 169 individuals had repeated radiographs, providing 330 knee images; 63% had HBM, 73% were female, mean (SD) age was 58 (12) years. Whilst HBM was not clearly associated with overall Kellgren-Lawrence measured progression (RR=1.55 [0.56.4.32]), HBM was positively associated with both Δosteophytes and ΔJSN individually (adjusted mean differences between individuals with and without HBM 0.45 [0.01.0.89] and 0.15 [0.01.0.29], respectively). HBM individuals had higher WOMAC knee pain scores (β=7.42 [1.17.13.66]), largely explained by adjustment for osteophyte score (58% attenuated) rather than JSN (30% attenuated) or TBFM (16% attenuated). The same pattern was observed for symptomatic stiffness and functional limitation. HBM is associated with osteophyte progression, which appears to contribute to increased reported pain, stiffness and functional loss.

SAT-384 Identification of Heterozygous LRP5 Mutation and a TGFβ-1 Variant of Unknown Significance in a Patient with Hearing Loss, High Bone Mass, and Oropharyngeal Exostoses

Background: Manifestations of the high bone mass (HBM) disorders not only include strong bones, but also excessive bones causing cranial nerve palsies and oropharyngeal exostoses. Due to overlap of clinical phenotype in dense bone diseases, one or more distinct genes may be involved. Up-regulation in bone formation can result from gain of function mutation of the low-density lipoprotein receptor-related protein 5 (LRP5), which mediates activation of the canonical Wnt pathway via co-binding with the frizzled protein, but may also be a consequence of activating mutations in the transforming growth factor β1 (TGFβ-1) gene that associate with stimulated osteogenesis. Clinical Case: Here we report a 41 year-old woman referred for incidentally found dense bones on screening dual-energy X-ray absorptiometry (DXA) that led to subsequent revelation of several family members sharing similar histories including inability to float in water, strong bones on skeletal surgery, and presence of palatal exostoses. Her childhood history included mandibular pain developing at age 15 years due to bony overgrowth of her lower jaw requiring multiple drilling for removal. At age 33, she manifested trigeminal neuralgia initially responsive to medical management but eventually needed microvascular decompression for unremitting pain. Preoperative brain magnetic resonance imaging (MRI) noted significant hyperostosis of the skull as well as mild narrowing of internal auditory canals, for which auditory testing showing mild mixed hearing loss in her right ear. Skeletal survey revealed diffuse thickening of axial and appendicular skeleton with characteristic endosteal hyperostosis. DXA demonstrated Z scores of +8.3 and +5.3 in the lumbar spine and total hip, respectively. Torus palatinus was also identified on exam. Mutational analysis disclosed a heterozygous LRP5 missense mutation, c.844A>G, p.Met282Val, together with a variant of unknown significance in TGFβ-1 (c.887G>A, p.Arg296Gln) possibly linked to Camurati-Engelmann disease (progressive diaphyseal dysplasia). As transmission in both conditions follows an autosomal dominant pattern, multigenerational family history was elicited from patient that her mother, who underwent knee replacement in her 80’s, was described by the surgeon as “having bones of a 30-year old man,” and that her deceased maternal grandmother possibly had “thickened” bones. Half of patient’s 18 siblings reportedly also carry features suggestive of high bone mass phenotype. Genetic testing of family members is planned. Conclusion: While HBM disorders protect against fractures, it is important to recognize that these relatively benign conditions may present with neurological and oropharyngeal complications prompting the need for their surveillance and surgical precautions during orthopedic procedures.

Transient receptor potential vanilloid 1 and 4 double knockout leads to increased bone mass in mice

Calcium balance is important in bone homeostasis. The transient receptor potential vanilloid (TRPV) channel is a nonselective cation channel permeable to calcium and is activated by various physiological and pharmacological stimuli. TRPV1 and TRPV4, in particular, have important roles in intracellular Ca2+ signaling and extracellular calcium homeostasis in bone cells. TRPV1 and TRPV4 separately mediate osteoclast and osteoblast differentiation, and deficiency in any of these channels leads to increased bone mass. However, it remains unknown whether bone mass increases in the absence of both TRPV1 and TRPV4. In this study, we used TRPV1 and TRPV4 double knockout (DKO) mice to evaluate their bone mass in vivo, and osteoclast and osteoblast differentiation in vitro. Our results showed that DKO mice and wild type (WT) mice had no significant difference in body weight and femur length. However, the results of dual-energy X-ray absorption, microcomputed tomography, and bone histomorphometry clearly showed that DKO mice had higher bone mass than WT mice. Furthermore, DKO mice had less multinucleated osteoclasts and had lower bone resorption. In addition, the results of cell culture using flushed bone marrow from mouse femurs and tibias showed that osteoclast differentiation was suppressed, whereas osteoblast differentiation was promoted in DKO mice. In conclusion, our results suggest that the increase in bone mass in DKO mice was induced not only by the suppression of osteoclast differentiation and activity but also by the augmentation of osteoblast differentiation and activity. Our findings reveal that both the single deficiency of TRPVs and the concurrent deficiency of TRPVs result in an increase in bone mass. Furthermore, our data showed that DKO mice and single KO mice had varying approaches to osteoclast and osteoblast differentiation in vitro, and therefore, it is important to conduct further studies on TRPVs regarding the increase in bone mass to explore not only individual but also a combination of TRPVs.

Wnt16 Overexpression in Osteoblasts Increases the Subchondral Bone Mass but has no Impact on Osteoarthritis in Young Adult Female Mice

Epidemiological studies have shown that high bone mineral density (BMD) is associated with an increased risk of osteoarthritis (OA), but the causality of this relationship remains unclear. Both bone mass and OA have been associated with the WNT signaling pathway in genetic studies, there is thus an interest in studying molecular partners of the WNT signaling pathway and OA. Female mice overexpressing WNT16 in osteoblasts (Obl-Wnt16 mice) have an increased bone mass. We aimed to evaluate if the high bone mass in Obl-Wnt16 mice leads to a more severe experimental OA development than in WT control mice. We induced experimental OA in female Obl-Wnt16 and WT control mice by destabilizing the medial meniscus (DMM). The Obl-Wnt16 mice displayed thicker medial and lateral subchondral bone plates as well as increased subchondral trabecular bone volume/tissue volume (BV/TV) but un-altered thickness of articular cartilage compared to WT mice. After DMM surgery, there was no difference in OA severity in the articular cartilage in the knee joint between the Obl-Wnt16 and WT mice. Both the Obl-Wnt16 and WT mice developed osteophytes in the DMM-operated tibia to a similar extent. We conclude that although the Obl-Wnt16 female mice have a high subchondral bone mass due to increased WNT signaling, they do not exhibit a more severe OA phenotype than their WT controls. This demonstrates that high bone mass does not result in an increased risk of OA per se.

Neuromedin U (NMU) regulates osteoblast differentiation and activity

Osteoporosis is a disease of low bone mass that places individuals at enhanced risk for fracture, disability, and death. Osteoporosis rates are expected to rise significantly in the coming decades yet there are limited pharmacological treatment options, particularly for long-term management of this chronic condition. The drug development pipeline is relatively bereft of new strategies, causing an urgent and unmet need for developing new strategies and targets for treating osteoporosis. Here, we examine a lesser-studied bone remodeling pathway, Neuromedin U (NMU), which is expressed in the bone microenvironment along with its cognate receptors NMU receptor 1 (NMUR1) and 2 (NMUR2). We independently corroborate a prior report that global loss of NMU expression leads to high bone mass and test the hypothesis that NMU negatively regulates osteoblast differentiation. Consistent with this, in vitro studies reveal NMU represses osteoblastic differentiation of osteogenic precursors but, in contrast, promotes osteoblastic marker expression, proliferation and activity of osteoblast-like cells. Phospho-profiling arrays were used to detail differential signaling outcomes that may underlie the opposite responses of these cell types. Collectively, our findings indicate that NMU exerts cell-type-specific responses to regulate osteoblast differentiation and activity.

The lack of neuropeptide Y-Y1 receptor signaling modulates the chemical and mechanical properties of bone matrix.

Genetic and pharmacological functional studies have provided evidence that the lack of Neuropeptide Y-Y1 receptor (Y1 R) signaling pathway induces a high bone mass phenotype in mice. However, clinical observations have shown that drug or genetic mediated improvement of bone mass might be associated to alterations to bone extracellular matrix (ECM) properties, leading to bone fragility. Hence, in this study wepropose to characterize the physical, chemical and biomechanical properties of mature bone ECM of germline NPY-Y1 R knockout (Y1 R-/- ) mice, and compare to their wild-type (WT) littermates.Our results demonstrated that the high bone mass phenotype observed in Y1 R-/- mice involvesalterations in Y1 R-/- boneECM ultrastructure, as a result of accelerated deposition of organic and mineral fractions. In addition, Y1 R-/- bone ECM displays enhanced matrix maturation characterized by greater number of mature/highly packed collagen fibers withoutpathological accumulation of immature/mature collagen crosslinks nor compromise of mineral crystallinity. These unique features of Y1 R-/- bone ECM improved the biochemical properties of Y1 R-/- bones, reflected by mechanically robust bones with diminished propensity to fracture, contributing to greater bone strength.These findings support the future usage of drugs targeting Y1 Rsignaling as a promising therapeutic strategy to treat bone loss-related pathologies.

Enzyme replacement therapy in mice lacking arylsulfatase B targets bone-remodeling cells, but not chondrocytes.

Mucopolysaccharidosis type VI (MPS-VI), caused by mutational inactivation of the glycosaminoglycan-degrading enzyme arylsulfatase B (Arsb), is a lysosomal storage disorder primarily affecting the skeleton. We have previously reported that Arsb-deficient mice display high trabecular bone mass and impaired skeletal growth. In the present study, we treated them by weekly injection of recombinant human ARSB (rhARSB) to analyze the impact of enzyme replacement therapy (ERT) on skeletal growth and bone remodeling. We found that all bone-remodeling abnormalities of Arsb-deficient mice were prevented by ERT, whereas chondrocyte defects were not. Likewise, histologic analysis of the surgically removed femoral head from an ERT-treated MPS-VI patient revealed that only chondrocytes were pathologically affected. Remarkably, a side-by-side comparison with other cell types demonstrated that chondrocytes have substantially reduced capacity to endocytose rhARSB, together with low expression of the mannose receptor. We finally took advantage of Arsb-deficient mice to establish quantification of chondroitin sulfation for treatment monitoring. Our data demonstrate that bone-remodeling cell types are accessible to systemically delivered rhARSB, whereas the uptake into chondrocytes is inefficient.

Increasing Dietary Fish Oil Reduces Adiposity and Mitigates Bone Deterioration in Growing C57BL/6 Mice Fed a High-Fat Diet

Intake of total fat is linked to obesity and inversely associated with bone density in humans. Epidemiologic and animal studies show that long-chain n-3 (ω-3) PUFAs supplied as fish oil (FO) are beneficial to skeletal health. This study tested the hypothesis that increasing dietary FO would decrease adiposity and improve bone-related outcomes in growing obese mice. Male C57BL/6 mice at 6 wk old were assigned to 6 treatment groups and fed either a normal-fat diet (3.85 kcal/g and 10% energy as fat) or a high-fat diet (HF; 4.73 kcal/g and 45% energy as fat) containing either 0%, 3%, or 9% energy as FO (0FO, 3FO, and 9FO, respectively) ad libitum for 6 mo. Bone structure, body composition, and serum bone-related cytokines were measured. The HF diet increased the expression of the adipose tissue tumor necrosis factor α (Tnfa) and serum concentrations of leptin and tartrate-resistant acid phosphatase (TRAP), and decreased serum concentrations of osteocalcin and bone-specific alkaline phosphatase (P<0.05). FO decreased fat mass (P<0.05), serum TRAP (P<0.05), and adipose tissue Tnfa expression (P<0.01). Bone content of long-chain n-3 PUFAs was increased and n-6 PUFAs were decreased with the elevation in dietary FO content (P<0.01). Compared with mice fed 9FO, animals fed 3FO had higher femoral bone volume/total volume (25%), trabecular number (23%), connectivity density (82%), and bone mass of second lumbar vertebrae (12%) and lower femoral trabecular separation (-19%). Mice fed the 3FO HF diet had 42% higher bone mass than those fed the 0FO HF diet. These data indicate increasing dietary FO ≤3% energy can decrease adiposity and mitigate HF diet-induced bone deterioration in growing C57BL/6 mice possibly by reducing inflammation and bone resorption. FO at 9% diet energy had no further beneficial effects on bone of obese mice.