Journal of Bone and Mineral Research最新文献

Hypophosphatasia (HPP) is the genetic disorder caused by loss-of-function mutations in the ALPL gene that encodes tissue-nonspecific alkaline phosphatase (TNAP), an enzyme essential for physiological skeletal/dental mineralization. In HPP, TNAP deficiency leads to the accumulation of extracellular pyrophosphate (PPi), a potent inhibitor of calcification, resulting in skeletal and dental hypomineralization, with disease severity varying from the life-threatening perinatal and infantile forms to the milder later-onset forms that manifest in adulthood or only affect dentition. Enzyme replacement therapy based on recombinant mineral-targeted alkaline phosphatase (asfotase alfa) has been approved multinationally since 2015 for the treatment of pediatric-onset HPP, remarkably increasing the lifespan, their skeletal condition and the quality of life of patients affected by the severe forms of HPP. However, non-skeletal symptoms remain as important clinical concerns. As its moniker implies, TNAP is expressed in a large variety of tissues and cell types, and TNAP may be engaged in distinct metabolic pathways in each tissue. A better understanding of the cells expressing TNAP physiologically, the metabolic pathways involved and the natural substrates of TNAP in each tissue will help design improved and/or alternative therapies to prevent/correct known or yet to be discovered non-skeletal manifestations of HPP. Figure 1 graphically lays out the topics discussed in this invited perspective article that follows the contents of the Louis V Avioli Memorial lecture delivered during the ASBMR 2025 annual meeting.

Osteogenesis imperfecta (OI) is a genetic disorder characterized by bone fragility. It is one of the most prevalent rare skeletal dysplasias. The mildest form, OI type 1, predominantly results from collagen type I haploinsufficiency due to pathogenic variants in the COL1A1 gene, leading to reduced collagen type I. Despite OI type 1 representing approximately half of the OI population, the lack of an effective mouse model has hindered research and therapy development(1). To address this gap, we developed a genetically engineered mouse model harbouring a heterozygous deletion of the Col1a1 allele using the CRISPR/Cas system. The bone phenotype was characterised in 8- and 24-week-old mice, assessing transcriptomics and serum markers for bone formation (procollagen type I N-terminal propeptide) and resorption (tartrate-resistant acid phosphatase 5b). Bone volume, microarchitecture, and strength were evaluated by micro-computed tomography, histomorphometry and three-point bending test. We showed that the decreased Col1a1 to Col1a2 mRNA ratio determines reduced collagen type I production in OI mice bones as the underlying mechanism of haploinsufficient OI. This was supported by COL1A1 to COL1A2 mRNA ratio findings in human OI cell models, including fibroblasts and induced mesenchymal stem cells, as well as in induced pluripotent and mesenchymal stem cell models that were edited to carry a heterozygous COL1A1 allele. Our findings indicate for the first time that reduced bone volume and altered bone microarchitecture in haploinsufficient OI depends on the Col1a1 to Col1a2 mRNA ratio regulation. This novel mouse model faithfully recapitulates OI type 1 and provides a vital tool for investigating the disease mechanism and developing targeted therapeutic strategies for this large neglected OI patient population.

The temporomandibular joint (TMJ), essential for jaw movements, is susceptible to osteoarthritis (TMJ-OA), impacting a significant portion of the population. This study introduces an innovative genetic mouse model to explore TMJ development, maintenance, and interactions with the mechanical environment. We exploited Evc2/Limbin conditional knockout (Evc2 cKO) mice, specifically targeting neural crest cell-derived tissues (Wnt1Cre), to observe TMJ development. Disruption of Evc2 in neural crest cells contributed to morphological changes in the TMJ growth plate cartilage layers, predisposing the joint components to defects. Condyle defective regions presented a unique environment composed of cartilage, bone, stem cells, and an augmented polymorphic layer. Our findings further revealed that the Evc2 cKO mice presented TMJ components degeneration clinically like those observed in human TMJ-osteoarthritis (OA). Mandible condyle gene expression analysis showed augmented expression of general inflammatory and OA markers. Supplying the mice with regular chow (RD) worsens the phenotype, but soft chow (SD)-fed partially rescued both condyle morphology and intra-articular space. The data suggest that changes in the loading environment critically affect the integrity and functionality of the TMJ, with direct implications for its preservation and disease management.

Hypophosphatasia (HPP) is caused by loss-of-function mutations in the human ALPL gene that encodes tissue-nonspecific alkaline phosphatase (TNAP), whose deficiency results in the accumulation of the calcification inhibitor inorganic pyrophosphate (PPi), resulting in skeletal and dental hypomineralization. Enzyme replacement with mineral-targeted TNAP (asfotase alfa) improves skeletal mineralization but the almost daily injections of this biologic can lead to injection site reactions and discontinuation of treatment. Since PPi is produced by the enzymatic action of ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) from ATP, we tested if ENPP1 could be a druggable target for the development of an alternative treatment for HPP, particularly for the non-lethal later-onset forms of HPP where enzyme replacement is not currently approved. We orally administered 30 and 100 mg/kg/d of an ENPP1 inhibitor, REV102, to the AlplPrx1/- mouse model of late-onset HPP, for 105 d and confirmed target engagement, as plasma PPi concentrations were markedly reduced. X-ray, micro computed tomography and bone morphometry indicated improvement in appendicular skeletal mineralization. This study suggests that the adult HPP phenotype could benefit from oral administration of ENPP1 inhibitors. LAY ABSTRACT Hypophosphatasia (HPP) is a soft bones disease caused by inactivating mutations in the gene (Alpl) encoding tissue-nonspecific alkaline phosphatase (TNAP), crucially important for skeletal and dental mineralization. Deficiency in TNAP function leads to the accumulation of its substrate, inorganic pyrophosphate (PPi), that acts as a potent calcification inhibitor, and this increase in PPi causes insufficient skeletal mineralization. We tested if pharmacologically inhibiting ENPP1, the enzyme that generates PPi, could lower PPi concentrations and ameliorate soft bone disease in a mouse model of later-onset HPP. The results were efficacious and point to the potential usefulness of this strategy to treat HPP.

Osteogenesis imperfecta (OI) is characterized by bone fragility with frequent fractures, especially in children. Some studies have used peripheral-quantitative computed tomography (pQCT) to examine bone density in children with OI and one cross-sectional study used high-resolution-pQCT (HR-pQCT) in nine children with OI. We compared bone density, microstructure, and strength changes over one year at the metaphysis and diaphysis of the radius and tibia, as well as lumbar spine bone mass and area, in 20 children with OI under bisphosphonate treatment and 20 age- and sex-matched controls. For the double-stack metaphyseal scans, we developed an algorithm to correct stack misalignment. For the lumbar spine, we used dual-energy x-ray absorptiometry (DXA). At the tibial metaphysis, children with OI had lower baseline total and trabecular volumetric bone mineral density (vBMD), trabecular and cortical microstructure, and strength. At the radial metaphysis, baseline trabecular microstructure and strength were lower in children with OI. At the tibial and radial diaphysis, children with OI had lower bone area and strength. At the tibial and radial metaphysis, 1-yr increases in most measurements were similar for both groups. Cortical vBMD and trabecular separation (radius) only increased in the OI group. Trabecular vBMD, volume fraction (tibia), number (tibia), and total vBMD (radius) only increased in the control group. At the tibia and radius diaphysis, cortical vBMD increased in the OI group. Tibial Ct. Po decreased in children with OI. At the lumbar spine, the OI group had lower bone mass, density, and area, but similar longitudinal changes. In summary, baseline trabecular bone density, trabecular and cortical microstructure, and strength were lower in metaphyseal regions of children with OI. At diaphysis, children with OI had lower bone area and strength. While longitudinal changes over one year were generally comparable, certain outcomes demonstrated differences. These data are essential for powering future clinical trials.

With the goal of preventing more hip fractures, a next generation of the VirtuOst® Biomechanical Computed Tomography (BCT) test was developed that integrates measurements from a clinical CT scan related to fall risk, impact force, and femoral strength, the three main determinants of hip fracture. Here, we introduce the test and validate it against bone mineral density (BMD) and FRAX®. Our source population from a large healthcare system comprised of 341,364 patients (≥ 65 years) with an abdominal-pelvic CT during care. Using data from 3,035 patients (1,790 with hip fracture), we developed a "BCT Risk Score" (range: 0-100) having input risk factors of age, femoral strength, ratio of trabecular/cortical BMD, muscle area, intramuscular fat, femoral neck volume, hip width, and posterior fat thickness. In a geographically distinct set of 2,124 patients (1,293 with hip fracture), we then compared the BCT Risk Score against a DXA-equivalent hip BMD T-score (lowest hip value, measured from the CT scan by VirtuOst) and FRAX hip fracture risk (with BMD but without parental fracture history) for predicting a first incident hip fracture within five years. For the women, the c-statistic for predicting fracture was higher for BCT (0.89, 95% confidence interval 0.87-0.90) than for BMD (0.81, 0.79-0.84) or FRAX (0.85, 0.83-0.87). Using binary thresholds to identify high-risk patients, sensitivity for BCT (Risk Score ≥ 75) was higher than for BMD (T-score ≤ -2.5) and FRAX (hip risk ≥ 3.0%): 81.4% vs. 47.8% vs. 75.9%, respectively; positive predictive values confirmed comparable high-risk status (BCT 13.6% vs. BMD 15.3% vs. FRAX 12.7%). Similar trends were observed for the men, two-year outcomes, and identifying very-high-risk patients. We conclude that, compared to both BMD and FRAX, the integrative BCT test better predicted hip fracture and its high sensitivity should improve fracture prevention.

The parathyroid hormone receptor 1 (PTH1R) transmits stimuli provided by parathyroid hormone (PTH) and PTH-related protein (PTHrP) and thus plays key roles in calcium and phosphate homeostasis as well as skeletal development. Variants in PTH1R have been linked to several conditions including Jansen's metaphyseal chondrodysplasia, Blomstrand chondrodysplasia, Primary Failure of Tooth Eruption and Eiken syndrome. Here, we report a novel skeletal phenotype identified in two unrelated families associated with PTH1R variants. The clinical features include brachydactyly type E (BDE), mild short stature, and dental anomalies. A novel heterozygous PTH1R substitution (p.E469K) was identified in affected members of Family 1, while the affected individual from Family 2 had a previously described heterozygous de novo substitution (p.E465K); these two mutated sites lie within helix 8 of the PTH1R. Cell-based assays revealed reduced cell surface expression, as well as impaired basal and PTH- or PTHrP-induced cAMP signaling responses for both mutants, as compared to WT-PTH1R. Introduction of the p.E469K substitution into humanized PTH1R mice resulted in mildly increased mineralization of bones in the paws as well as shortening of long bones. Our findings demonstrate a new skeletal phenotype associated with PTH1R variants and suggest that helix 8 of the receptor contributes to PTH1R expression and/or signaling during bone development.

Type 2 diabetes (T2D) is a prevalent condition that is associated with heightened fracture risk despite T2D patients exhibiting normal or elevated BMD. T2D exacerbates oxidative stress and hyperglycemia, which increases the accumulation of advanced glycation end products (AGEs) and advanced glycoxidation end products (AGOEs) in bone. Carboxymethyl-lysine (CML) is one such AGOE linked to fracture risk and could impact bone mineralization due to its carboxyl terminus. Still, the mechanism linking CML to altered mineralization and impaired bone quality in T2D is unknown. To investigate how glycoxidation modulates bone mineralization, sectioned human tibiae (23-yr-old to 89-yr-old donors, Caucasian male [CM] and Caucasian female [CF]) were treated in vitro with glyoxal or ribose to enhance CML content or AGE content. Sections were then suspended between calcium and phosphate solutions to promote mineral growth. Raman spectroscopy revealed that AGE and CML enhancement increased the degree of mineralization and accelerated mineral maturation, with CML-enhanced samples exhibiting the greatest increase in mineral growth. Solid-state nuclear magnetic resonance illustrated that CML enhancement increased the degree of electronegativity in the collagen structure and at the mineral surface, which was associated with increased compressive strain on the mineral platelet as unveiled by X-ray diffraction. Nanoindentation demonstrated lowered hardness and increased work energy in CML-enhanced samples. Collectively, these findings demonstrate a mechanism that links glycoxidation to matrix mineralization. The ability for CML to influence bone mineralization underlines the need to develop strategies to target CML accrual and mitigate fracture risk in patients with T2D.

The aim of this international meta-analysis was to quantify the predictive value of BMI for incident fracture and relationship of this risk with age, sex, follow-up time, and BMD. A total of 1 667 922 men and women from 32 countries (63 cohorts), followed for a total of 16.0 million person-years were studied. 293 325 had FN BMD measured (2.2 million person-years follow-up). An extended Poisson model in each cohort was used to investigate relationships between WHO-defined BMI categories (Underweight: <18.5 kg/m2; Normal: 18.5-24.9 kg/m2; Overweight: 25.0-29.9 kg/m2; Obese I: 30.0-34.9 kg/m2; Obese II: ≥35.0 kg/m2) and risk of incident osteoporotic, major osteoporotic and hip fracture (HF). Inverse-variance weighted β-coefficients were used to merge the cohort-specific results. For the subset with BMD available, in models adjusted for age and follow-up time, the hazard ratio (95% CI) for HF comparing underweight with normal weight was 2.35 (2.10-2.60) in women and for men was 2.45 (1.90-3.17). Hip fracture risk was lower in overweight and obese categories compared to normal weight [obese II vs normal: women 0.66 (0.55-0.80); men 0.91 (0.66-1.26)]. Further adjustment for FN BMD T-score attenuated the increased risk associated with underweight [underweight vs normal: women 1.69 (1.47-1.96); men 1.46 (1.00-2.13)]. In these models, the protective effects of overweight and obesity were attenuated, and in both sexes, the direction of association reversed to higher fracture risk in Obese II category [Obese II vs Normal: women 1.24 (0.97-1.58); men 1.70 (1.06-2.75)]. Results were similar for other fracture outcomes. Underweight is a risk factor for fracture in both men and women regardless of adjustment for BMD. However, while overweight/obesity appeared protective in base models, they became risk factors after additional adjustment for FN BMD, particularly in the Obese II category. This effect in the highest BMI categories was of greater magnitude in men than women. These results will inform the second iteration of FRAX®.