Journal of Bone and Mineral Research最新文献

Spermine synthase, encoded by the SMS gene, is involved in polyamine metabolism, as it is required for the synthesis of spermine from its precursor molecule spermidine. Pathogenic variants of SMS are known to cause Snyder-Robinson syndrome (SRS), an X-linked recessive disorder causing various symptoms, including intellectual disability, muscular hypotonia, infertility, but also skeletal abnormalities, such as facial dysmorphisms and osteoporosis. Since the impact of a murine SMS deficiency has so far only been analyzed in Gy mice, where a large genomic deletion also includes the neighboring Phex gene, there is only limited knowledge about the potential role of SMS in bone cell regulation. In the present manuscript, we describe 2 patients carrying distinct SMS variants, both diagnosed with osteoporosis. Whereas the first patient displayed all characteristic hallmarks of SRS, the second patient was initially diagnosed, based on laboratory findings, as a case of adult-onset hypophosphatasia. To study the impact of SMS inactivation on bone remodeling, we took advantage of a newly developed mouse model carrying a pathogenic SMS variant (p.G56S). Compared to their wildtype littermates, 12-wk-old male SMSG56S/0 mice displayed reduced trabecular bone mass and cortical thickness, as assessed by μCT analysis of the femur. This phenotype was histologically confirmed by the analysis of spine and tibia sections, where we also observed a moderate enrichment of non-mineralized osteoid in SMSG56S/0 mice. Cellular and dynamic histomorphometry further identified a reduced bone formation rate as a main cause of the low bone mass phenotype. Likewise, primary bone marrow cells from SMSG56S/0 mice displayed reduced capacity to form a mineralized matrix ex vivo, thereby suggesting a cell-autonomous mechanism. Taken together, our data identify SMS as an enzyme with physiological relevance for osteoblast activity, thereby demonstrating an important role of polyamine metabolism in the control of bone remodeling.

Recent studies in mice have indicated that the gut microbiome can regulate bone tissue strength. However, prior work involved modifications to the gut microbiome in growing animals and it is unclear if the same changes in the microbiome, applied later in life, would change matrix strength. Here we changed the composition of the gut microbiome before and/or after skeletal maturity (16 weeks of age) using oral antibiotics (ampicillin + neomycin). Male and female mice (n = 143 total, n = 12-17/group/sex) were allocated into five study groups: (1) Unaltered, (2) Continuous (dosing 4-24 weeks of age), (3) Delayed (dosing only 16-24 weeks of age), (4) Initial (dosing 4-16 weeks of age, suspended at 16 weeks), and (5) Reconstituted (dosing from 4-16 weeks following by fecal microbiota transplant from Unaltered donors). Animals were euthanized at 24 weeks of age. In males, bone matrix strength in the femur was 25%-35% less than expected by geometry in mice from the Continuous (p = 0.001), Delayed (p = 0.005), and Initial (p = 0.040) groups as compared to Unaltered. Reconstitution of the gut microbiota led to a bone matrix strength similar to Unaltered animals (p = 0.929). In females, microbiome-induced changes in bone matrix strength followed the same trend as males but were not significantly different, demonstrating a sex-dependent response of bone matrix to the gut microbiota. Minor differences in chemical composition of bone matrix were observed with Raman spectroscopy. Our findings indicate that microbiome-induced impairment of bone matrix in males can be initiated and/or reversed after skeletal maturity. The portion of the femoral cortical bone formed after skeletal maturity (16 weeks) was small; suggesting that microbiome-induced changes in bone matrix occurred without osteoblast/osteoclast turnover through a yet unidentified mechanism. These findings provide evidence that the mechanical properties of bone matrix can be altered in the adult skeleton.

Identifying individuals at risk for short-term fracture is essential to offer prompt beneficial treatment, especially since many fractures occur in those without osteoporosis by DXA-aBMD. We evaluated whether deficits in bone microarchitecture and density predict short-term fracture risk independent of the clinical predictors, DXA-BMD and FRAX. We combined data from eight cohorts to conduct a prospective study of bone microarchitecture at the distal radius and tibia (by HR-pQCT) and 2-year incidence of fracture (non-traumatic and traumatic) in 7327 individuals (4824 women, 2503 men, mean 69 ± 9 years). We estimated sex-specific hazard ratios (HR) for associations between bone measures and 2-year fracture incidence, adjusted for age, cohort, height, and weight, and then additionally adjusted for FN aBMD or FRAX for major osteoporotic fracture. Only 7% of study participants had FN T-score ≤ -2.5, whereas 53% had T-scores between -1.0 and -2.5 and 37% had T-scores ≥-1.0. Two-year cumulative fracture incidence was 4% (296/7327). Each SD decrease in radius cortical bone measures increased fracture risk by 38%-76% for women and men. After additional adjustment for FN-aBMD, risks remained increased by 28%-61%. Radius trabecular measures were also associated with 2-year fracture risk independently of FN-aBMD in women (HRs range: 1.21 per SD for trabecular separation to 1.55 for total vBMD). Decreased failure load (FL) was associated with increased fracture risk in both women and men (FN-aBMD ranges of adjusted HR = 1.47-2.42). Tibia measurement results were similar to radius results. Findings were also similar when models were adjusted for FRAX. In older adults, FL and HR-pQCT measures of cortical and trabecular bone microarchitecture and density with strong associations to short-term fractures improved fracture prediction beyond aBMD and FRAX. Thus, HR-pQCT may be a useful adjunct to traditional assessment of short-term fracture risk in older adults, including those with T-scores above the osteoporosis range.

Dysregulated chondrocyte metabolism is an essential risk factor for osteoarthritis (OA) progression. Maintaining cartilage homeostasis represents a promising therapeutic strategy for the treatment of OA. However, no effective disease-modifying therapy is currently available to OA patients. To discover potential novel drugs for OA, we screened a small-molecule natural product drug library and identified deapi-platycodin D3 (D-PDD3), which was subsequently tested for its effect on extracellular matrix (ECM) properties and on OA progression. We found that D-PDD3 promoted the generation of ECM components in cultured chondrocytes and cartilage explants and that intra-articular injection of D-PDD3 delayed disease progression in a trauma-induced mouse model of OA. To uncover the underlying molecular mechanisms supporting these observed functions of D-PDD3, we explored the targets of D-PDD3 via screening approach integrating surface plasmon resonance with liquid chromatography-tandem mass spectrometry. The results suggested that D-PDD3 targeted tyrosine-protein phosphatase non-receptor type 1 (PTP1B), deletion of which restored chondrocyte homeostasis and markedly attenuated destabilization of the medial meniscus induced OA. Further cellular and molecular analyses showed that D-PDD3 maintained cartilage homeostasis by directly binding to PTP1B and consequently suppressing the PKM2/AMPK pathway. These findings demonstrated that D-PDD3 was a potential therapeutic drug for the treatment of OA and that PTP1B served as a protein target for the development of drugs to treat OA. This study provided significant insights into the development of therapeutics for OA treatment, which, in turn, helped to improve the quality of life of OA patients and to reduce the health and economic burden.

We report on 2 patients of East African ancestry with the same novel homozygous variant in the parathyroid hormone receptor type 1 (PTH1R). Both patients shared skeletal features, including brachydactyly, extensive metacarpal pseudo-epiphyses, elongated cone-shaped epiphyses, ischiopubic hypoplasia, and deficient sacral ossification, suggestive of Eiken syndrome. Strikingly, both patients exhibited clinically manifest parathyroid hormone (PTH) resistance with hypocalcemia and elevated serum phosphate levels. These laboratory and clinical abnormalities initially suggested pseudohypoparathyroidism, which is typically associated with GNAS abnormalities. In both patients, however, a homozygous novel PTH1R variant was identified (c.710 T > A; p.IIe237Asn, p.I237N) that is located in the second transmembrane helical domain. Previously, others have reported a patient with a nearby PTH1R mutation (D241E) who presented with similar clinical features (eg, delayed bone mineralization as well as clinical PTH resistance). Functional analysis of the effects of both novel PTH1R variants (I237N- and D241E-PTH1R) in HEK293 reporter cells transfected with plasmid DNA encoding the wild-type or mutant PTH1Rs demonstrated increased basal cAMP signaling for both variants, with relative blunting of responses to both PTH and PTH-related peptide (PTHrP) ligands. The clinical presentation of PTH resistance and delayed bone mineralization combined with the functional properties of the mutant PTH1Rs suggest that this form of Eiken syndrome results from alterations in PTH1R-mediated signaling in response to both canonical ligands, PTH and PTHrP.

Mendelian randomization (MR) is a genetic epidemiological technique that uses genetic variation to infer causal relationships between modifiable exposures and outcome variables. Conventional observational epidemiological studies are subject to bias from a range of sources; MR analyses can offer an advantage in that they are less prone to bias as they use genetic variants inherited at conception as "instrumental variables", which are proxies of an exposure. However, as with all research tools, MR studies must be carefully designed to yield valuable insights into causal relationships between exposures and outcomes, and to avoid biased or misleading results that undermine the validity of the causal inferences drawn from the study. In this review, we outline Mendel's laws of inheritance, the assumptions and principles that underlie MR, MR study designs and methods, and how MR analyses can be applied and reported. Using the example of serum phosphate concentrations on liability to kidney stone disease we illustrate how MR estimates may be visualized and, finally, we contextualize MR in bone and mineral research including exemplifying how this technique could be employed to inform clinical studies and future guidelines concerning BMD and fracture risk. This review provides a framework to enhance understanding of how MR may be used to triangulate evidence and progress research in bone and mineral metabolism as we strive to infer causal effects in health and disease.

Upon denosumab discontinuation, an observed overshoot phenomenon in bone turnover may occur, potentially leading to a reduction in bone mineral density and the occurrence of vertebral fractures. Several theories have been proposed to explain this phenomenon, one of which is that osteoclast precursors might be accumulating during treatment. Our aim was to study the effects of denosumab on osteoclast precursors in postmenopausal women. This cross-sectional observational study included 30 postmenopausal women with osteopenia or osteoporosis, divided into two groups: 15 treated with denosumab (mean duration 4 years, range 6 months-9 years) and 15 treatment-naïve controls. Peripheral blood mononuclear cells (PBMCs) were isolated from whole blood and were stained for CD14, MCSFR, CD11b and TNFRII. Osteoclast precursors (CD14+/MCSFR+, CD14+/CD11b + OR CD14+/TNFRII+) were identified with fluorescent activated cell sorting (FACS). The proportion of osteoclasts was determined by calculating their percentage of the total cell population in each whole blood sample. To confirm the expected suppression of bone turnover in the subjects treated with denosumab, we measured serum PINP, CTX and TRACP5b. Denosumab-treated patients exhibited a significantly higher count of CD14+/CD11b + osteoclast precursors compared to controls (median 4% vs 0.75%, P=.011). There was no correlation with the duration of treatment. Bone turnover markers were significantly lower in the group treated with denosumab than controls. Our findings indicate an increase in osteoclast precursors, which could explain the overshoot phenomenon observed after discontinuing denosumab.

Hypophosphatasia (HPP) is a rare, inherited metabolic disease caused by deficient activity of tissue-nonspecific alkaline phosphatase (TNSALP). Efzimfotase alfa (ALXN1850) is a second-generation TNSALP enzyme replacement therapy in development for HPP. This first-in-human open-label, dose-escalating phase 1 trial evaluated efzimfotase alfa safety, tolerability, pharmacokinetics, pharmacodynamics, and immunogenicity. Fifteen adults (5/cohort) with HPP received efzimfotase alfa in doses of 15 mg (cohort 1), 45 mg (cohort 2), or 90 mg (cohort 3) as one intravenous (i.v.) dose followed by 3 weekly subcutaneous (s.c.) doses. The primary objective was to assess safety and tolerability. Secondary objectives included pharmacokinetics, pharmacodynamics of ALP substrates known to be biomarkers of disease (inorganic pyrophosphate [PPi] and pyridoxal 5'-phosphate [PLP]) and immunogenicity. Treatment-emergent adverse events (TEAEs) occurred in 12 (80%) participants. Eight (53%) participants had injection site reactions (ISRs), observed after 10 of 41 (24%) s.c. injections. Most ISR TEAEs were mild and resolved within 1-2 d. Peak and total exposures of efzimfotase alfa increased in a greater-than-dose proportional manner over the range of 15-90 mg after i.v. and s.c. dosing. The arithmetic mean elimination half-life was approximately 6 d; absolute bioavailability was 28.6%-36.8% over the s.c. dose range of 15-90 mg. Dose-dependent reductions in plasma concentrations of PPi and PLP relative to baseline reached nadir in the first week after i.v. dosing and were sustained for 3-4 wk after the last s.c. dose. Four (27%) participants tested positive for antidrug antibodies (ADAs), 3 of whom were ADA positive before the first dose of efzimfotase alfa. ADAs had no apparent effect on efzimfotase alfa pharmacokinetics/pharmacodynamics. No participants had neutralizing antibodies. Efzimfotase alfa demonstrated acceptable safety, tolerability, and pharmacokinetic profiles and was associated with sustained reductions in biomarkers of disease in adults with HPP, supporting further evaluation in adult and pediatric patients. Registration: ClinicalTrials.gov NCT04980248 (https://clinicaltrials.gov/study/NCT04980248).

Fibrodysplasia ossificans progressiva (FOP) is an ultra-rare disorder, characterized by progressive heterotopic ossification (HO) and painful soft-tissue inflammatory flare-ups. This was a post hoc analysis from a phase 2 (NCT03188666) trial in which adults with FOP received intravenous anti-activin A antibody garetosmab 10 mg/kg or placebo every 4 wk over 28 wk (Period 1), followed by a 28-wk open-label treatment and extension (Periods 2 and 3). Here we describe flare-ups, their relationship to new HO lesions, and the impact of garetosmab on flare-ups. Volume of new HO lesions was measured by CT. Patient-reported flare-ups were defined by any 2 of the following: new onset of pain, swelling, joint stiffness, decrease in movement, or perceived presence of HO. Flare-ups were experienced by 71% (17/24) of placebo-treated patients, 59% (10/17) of whom developed a new HO lesion irrespective of flare-up location; 24% of flare-ups location-matched new HO lesions. Twenty-nine new HO lesions occurred in the placebo cohort by week 28, of which 12 (41%) occurred in the same location as new or ongoing flare-ups. A higher volume of newly formed heterotopic bone (week 28) occurred in placebo-treated patients who had experienced a prior flare-up vs those without (median [Q1:Q3] of 16.6 [12.0:31.1] vs 3.2 cm3). Garetosmab was previously shown to decrease patient-reported flare-up frequency in Period 1; here, garetosmab reduced the median (Q1:Q3) duration of patient-reported flares (15.0 [6.0:82.0] vs 48.0 [15.0:1.00] d) and the severity of flare-ups vs placebo. Frequency of corticosteroid use was numerically reduced in those treated with garetosmab (40.0%) vs placebo (58.3%). In this analysis, 71% of placebo-treated adults with FOP experienced flare-ups over 28 wk, which were associated with an increased volume of newly formed heterotopic bone. Garetosmab reduced the severity and duration of flare-ups, with effects sustained during the entire trial.