Studies evaluating skeletal differences by fracture status used predominantly White female cohorts with limited data in other races and men. Using high-resolution peripheral quantitative CT and microfinite element analysis, we compared skeletal health by fracture status and assessed the effect of socioeconomic (SE) factors and effect modification by race and sex in a population-based study in New York City. Participants with historical fractures (Fx) included adult fractures (18+ yrs; no digits, skull, face). Of 935 (age 76.1±6.3 yrs, 71% female, 27.7% Black, 29.7% White, 41.3% Mixed), 32% had 444 fractures. Results were adjusted for age, BMI, sex, race, ethnicity, past osteoporosis treatment, and oral glucocorticoid use. At the distal radius, the Fx group had worse trabecular (Tb) and cortical (Ct) parameters with 9.7-10.3% lower failure load (FL) and stiffness (p<0.001). At the distal tibia, results were similar with 5.9% lower FL and stiffness in the Fx group (p<0.001). Adjusting for SE factors, Tb and Ct parameters remained worse in the Fx group with lower FL and stiffness. Stiffness and FL varied by race and sex but were lower in Fx vs. NoFx groups within each race and sex. Race and sex did not modify the relationship between stiffness or FL and fracture status. In the whole cohort, higher stiffness (ORRadius 0.732, [95%CI: 0.563, 0.931], p=0.014; ORTibia 0.866, [95%CI: 0.783, 0.954], p=0.004) and FL (ORRadius 0.597, [95%CI: 0.404, 0.893], p=0.011; ORTibia 0.778, [95%CI: 0.681, 0.888], p<0.001) at the distal radius and tibia were associated with lower odds of incident fracture. Hispanic ethnicity was associated with lower odds of incident fracture independent of radial stiffness (OR 0.289, [95%CI: 0.081, 0.845], p=0.038) and FL (OR 0.286, [95%CI: 0.080, 0.842], p=0.038). In conclusion, in this multiethnic cohort, stiffness and FL were independently associated with prevalent and incident fractures, regardless of race or sex.

Parental history of hip fracture is an independent risk factor for fragility fracture, yet the skeletal traits underlying this risk remain poorly defined. We examined whether parental hip fracture is associated with differences in bone microarchitecture and estimated bone strength in a large, ethnically diverse cohort of older adults (n = 950; mean age 76.1 ± 6.2 yr; 71% female; 55.8% Hispanic) using high resolution peripheral quantitative computed tomography (HR-pQCT) with individual trabecula segmentation (ITS) and finite element-based analysis. Ten percent (n = 95) reported a parental hip fracture. Femoral neck aBMD was 3.8% lower in those with versus without parental history (p = .04). At the radius, the parental hip fracture group had lower adjusted trabecular rod bone volume fraction (10.6%), plate and rod number, axial BV/TV (12.2%) and plate connectivity (9.5%; all p < .05). At the tibia, parental hip fracture history was associated with lower adjusted trabecular density (8.8%), trabecular thickness (2.4%), plate and axial BV/TV (14%-15%, all p < .05), and 4%-5% lower estimated stiffness and failure load, differences that persisted after adjustment for aBMD. Patterns were similar regardless of race/ethnicity and whether parental hip fracture was maternal or paternal. Similar patterns were observed in a subset who were matched by propensity score. Individuals with a parental history of hip fracture exhibited significant microarchitectural deterioration, especially in trabecular structure at weight-bearing sites, and reduced estimated bone strength independent of areal BMD. These findings suggest that inherited deficits in trabecular morphology may contribute to familial fracture susceptibility and underscore the utility of HR-pQCT in identifying heritable skeletal fragility beyond DXA indices.

Time in moderate-to-vigorous intensity activity (MVPA), light intensity activity (LPA), and sleep are critical for bone health in older adults but are often considered separately despite being inherently co-dependent. We examined cross-sectional associations between compositions of accelerometry-derived MVPA, LPA, inactivity, and sleep with bone microarchitecture and strength (High-Resolution Peripheral Quantitative Computed Tomography; HR-pQCT) in community-dwelling older men (n=119) and women (n=177), mean age 76.3±4.6 yrs. Participants wore an ActiGraph GT9X on their non-dominant wrist for 7 consecutive 24hr periods during the Study of Muscle, Mobility and Aging (SOMMA) baseline visit. The primary outcomes were distal radius (DR) and tibia (DT) estimated failure load, and secondarily, total volumetric bone mineral density (vBMD), and cortical (Ct) and trabecular (Tb) vBMD, area (Ar), and thickness (Th) from HR-pQCT. Compositional data analysis methods evaluated proportions of time in one behavior relative to the remaining behaviors. Sex-stratified multiple linear regression estimated associations between 24hr composition with sex-specific standardized HR-pQCT parameters. Compositional isotemporal substitution methods estimated hypothetical changes in continuous HR-pQCT measures if 10-60 min in one behavior was displaced by another. On average, women spent 90.2 min/day (6.3%) in MVPA, 346.1 min/day (24.0%) in LPA, 556.4 min/day (38.6%) in inactivity, and 447.4 min/day (31.1%) in sleep; men spent 93.6 min/day (6.5%) in MVPA, 309.5 min/day (21.5%) in LPA, 596.7 min/day (41.4%) in inactivity, and 440.2 min/day (30.6%) in sleep. Compared to the average sex-specific 24hr composition, higher proportions of MVPA were associated with higher DR and DT failure load in women; higher DR Tb.vBMD and Tb.Th in men; and higher DR Tt.vBMD, Ct.Ar, and Ct.Th, and DT Ct.vBMD, Ct.Ar, and Ct.Th in women. Hypothetically displacing 10-60 min in inactivity for MVPA resulted in more favorable HR-pQCT parameters. These data support the importance of MVPA for a healthy skeleton in older men and women.

Metabolites mediate inter-organ communication and this metabolic crosstalk often goes awry in systemic diseases, including chronic kidney disease-mineral bone disorder (CKD-MBD), where CKD disrupts skeletal homeostasis, with significant bone loss and increased fracture risk observed in patients. While metabolites from the injured kidney have been identified to disrupt bone function, whether metabolites from the bone influence kidney function over the course of CKD progression is less-understood. Given that bone-derived factors such as FGF23 and sclerostin influence CKD-MBD disease progression, we hypothesized that identifying skeletal metabolic fluxes disrupted in CKD may reveal other bone-derived metabolites that mediate nephropathy. We employed a combination of in vivo and ex vivo 13C-metabolic flux analysis (13C-MFA) to characterize how the adenine-induced kidney injury murine model of CKD-MBD rewires specific skeletal metabolic fluxes. Through 13C-MFA of bone tissue in vivo, and ex vivo cultures of calvariae and femora, we identified that this murine model of CKD-MBD accelerates osteocytic citrate production. 13C-isotopic tracing in OCY454 osteocytes suggests that this increased citrate flux is in part driven by PTH stimulation of glucose- and glutamine-to-citrate conversion in osteocytes. When citrate production is exacerbated by the loss of function mutation in SLC13A5 (Slc13a5R337*/R337*), a specialized plasma membrane citrate importer, we did not observe a significant worsening of bone loss in mutant mice due to chronic adenine-induced kidney injury. Intriguingly, kidney function appears to be protected, reducing secondary hyperparathyroidism and the severity of nephrolithiasis due to the adenine diet. Our observation on the role of citrate metabolism in CKD both confirms the relevance of citrate in managing patient kidney outcomes and suggests that organismal citrate metabolism may be modulated in the management of CKD-MBD. Altogether, this study reveals a potential new axis of metabolic regulation in the inter-organ communication between the skeleton and the kidneys.

Denosumab, a well-established osteoporosis treatment, has demonstrated potential bone- and cartilage-protective effects in preclinical and early trials. However, it remains unclear whether these promising findings extend to osteoarthritis prevention in weight-bearing joints and broader real-world osteoporotic populations. We compared osteoarthritis incidence between denosumab and oral bisphosphonates in adults aged 50 years or older with osteoporosis using a sequential nested target trial emulation with propensity score matching based on longitudinal health insurance claims data from Japan collected between 2015 and 2024. Two target comparisons were conducted: one compared new users of denosumab with new users of oral bisphosphonates, and the other compared patients who switched from oral bisphosphonates to denosumab with those who continued oral bisphosphonates. The primary outcome was osteoarthritis incidence. Secondary outcomes included joint-specific osteoarthritis (knee, hip, and hand) over 3 years. The absolute risk reduction (ARR) and relative risk (RR) at 3 years were estimated using a Kaplan-Meier estimator in both the per-protocol and intention-to-treat analyses. In the per-protocol analyses, the ARR for incident osteoarthritis was 2.0% (95% confidence interval [CI], 1.1%-3.2%) in the new-user comparison, with an RR of 0.83 (95% CI, 0.73-0.91), and 0.9% (95% CI, -0.2% to 2.8%) in the switch-continue comparison, with an RR of 0.92 (95% CI, 0.76-1.02). In the intention-to-treat analyses, the corresponding ARR was 1.9% (95% CI, 1.3%-3.3%) in the new-user comparison, with an RR of 0.84 (95% CI, 0.73-0.89), and 1.2% (95% CI, -0.2% to 2.7%) in the switch-continue comparison, with an RR of 0.89 (95% CI, 0.77-1.02). Denosumab initiation was associated with a modestly lower risk of incident osteoarthritis than oral bisphosphonate initiation, although the association was weaker in the switch-continue comparison.

Distal-less homeobox genes Dlx5 and Dlx6 are key regulators of osteoblast differentiation during skeletal development, but their role in postnatal bone remodeling remains poorly understood. To investigate this, we conditionally deleted Dlx5/6 in Osterix-lineage cells after 4 weeks of birth using an inducible Osx-Cre system. Dlx5/6Δ/Δ Osx-Cre and control mice were analyzed in terms of bone architecture (micro-computed tomography), remodeling (histomorphometry), gene expression profiling and single-cell RNA sequencing. Postnatal deletion of Dlx5/6 induced a complex skeletal phenotype characterized by radial bone hypertrophy and altered cortical remodeling. Enhanced periosteal activity was associated with increased Osx expression in periosteal cells, confirmed by BaseScope and immunofluorescence analyses. In parallel, cortical bone became thinner and more porous, while trabecular bone displayed reduced bone formation and thinner trabeculae, despite paradoxical accumulation within the diaphysis. These alterations were associated with increased Osx expression in periosteal and diaphyseal compartments, indicating abnormal spatial regulation of osteolineage cell expansion and bone remodeling. Single-cell transcriptomic analysis in bone-marrow cells identified altered mesenchymal stromal cell populations with dysregulated extracellular matrix and Wnt signaling pathways, including downregulation of the Wnt antagonist Sfrp1, validated in situ by RNAscope. Consistently, osteoblasts derived from Dlx5/6Δ/Δ Osx-Cre displayed impaired terminal differentiation in vitro, with reduced expression of late osteogenic markers and decreased matrix mineralization. Collectively, these findings identify Dlx5/6 as critical regulators of postnatal bone homeostasis that coordinate osteolineage expansion and terminal osteoblast maturation during postnatal bone remodeling.

Autosomal dominant osteopetrosis (ADO) is a rare bone disorder caused by impaired osteoclastic resorption. Despite high bone mass, ADO is paradoxically associated with increased fracture risk. High-resolution peripheral quantitative computed tomography (HR-pQCT) provides unique, low-radiation assessments of bone, but prior studies in ADO are limited to small case series. Using baseline cross-sectional data from an ongoing natural history study, we characterized HR-pQCT phenotypes in adults with ADO and explored associations with self-reported fracture history and bone turnover markers. HR-pQCT outcomes at the distal ends and shafts of the radius and tibia in 48 adults with ADO were compared to 144 matched controls (1, 3 ratio). In addition, z-scores for outcomes in ADO were calculated using established reference data. At trabecular-rich distal sites, ADO demonstrated markedly elevated total volumetric bone mineral density (vBMD), trabecular vBMD, trabecular bone volume fraction, trabecular thickness, and estimated failure load (all p<0.001), with values often approaching or exceeding twice those in controls. At cortical-rich shaft sites, total vBMD, bone area, bone area fraction, and cortical thickness were greater in ADO (all p<0.05). However, there was considerable interindividual variability, with some individuals having normal z-scores while others exhibited z-scores exceeding +20. The phenotype reflected increased bone mass rather than mineralization-cortical vBMD was normal and tissue mineral density was normal-to-lower in ADO. Outcomes at both distal and shaft sites were strongly correlated with lifetime fracture number (Spearman ρ=0.64-0.75, p<0.001), indicating ADO individuals with the "strongest" bones (via micro-finite element modeling) reported most fractures. The outcomes were correlated inversely with serum C-telopeptide and positively with serum tartrate resistant acid phosphatase 5b, consistent with ADO being rich with dysfunctional osteoclasts. Overall, the data reveal the profound, yet variable, phenotype in ADO and indicate that HR-pQCT measures correlate with disease severity and represent potential surrogate endpoints for future therapeutic trials.

Type V collagen is a key regulator in the formation of type I collagen fibrils in connective tissues including skin, tendons, and bones. Abnormalities in type V collagen cause classical Ehlers Danlos syndrome (EDS), a connective tissue disorder with primarily skin and joint phenotype. There are several clinical reports suggesting increased prevalence of vertebral fractures in adult patients with EDS, among them patients with classical EDS. Yet, the literature lacks data about bone health specifically in the classical EDS patient population. The Col5a1 haploinsufficient mouse model (Col5a1+/-) recapitulates the human disease phenotype with hyperextensible and fragile skin, delayed wound healing, and tendons with reduced tensile strength. The bone phenotype in this model is unknown. Here we present a comprehensive bone phenotyping of this model using 3-point bending, vertebral compression studies, micro computed tomography (microCT) analysis, Raman spectroscopy, and quantitative Backscattered Electron Imaging (qBEI) to test bone quantity, quality, composition, and mineralization density distribution. We found no difference in all parameters tested between Col5a1+/- and Col5a1+/+ mice 8 weeks and 6 months old in both sexes. Bulk RNA sequencing in tibiae from 8-week-old males identified only minimal changes in gene expression. Our results show that the Col5a1 haploinsufficient mouse model does not have a significant bone phenotype and suggest that individuals with heterozygote loss of function variants in COL5A1 may not have a higher risk for fractures due to primary bone abnormality.

Immune checkpoint inhibitors (ICIs) which target immune checkpoint proteins like programmed cell death protein 1 (PD-1) and programmed cell death ligand 1 (PD-L1) have revolutionized cancer therapy. Skeletal toxicities are emerging immune-related adverse events for patients treated with ICIs, and PD-1 blockade in pre-clinical mouse models significantly reduces bone mass. However, the effect of PD-L1 inhibition on the bone throughout development is not well understood. We investigated the role of PD-L1 loss on bone microarchitecture with genetic PD-L1 knockout in myeloid cells using LysM-Cre;PD-L1Flox/Flox mice and pharmacologic inhibition with a PD-L1 neutralizing antibody in adult and aged mice. We report that neither PD-L1 deletion in myeloid cells nor inhibition with α-PD-L1 significantly impacts femoral trabecular bone microarchitecture; however, α-PD-L1 treatment increases vertebral trabecular bone volume. Additionally, PD-L1 blockade influences T cell expansion by decreasing naïve T cells and increasing effector memory T cells in the bone marrow, consistent with previous studies on the effects of PD-1 inhibition. The trabecular bone-sparing effect of PD-L1 inhibition is strikingly different from the bone loss observed with PD-1 blockade. Clinical studies are necessary and justified to determine if PD-L1 may be a less bone destructive alternative for cancer patients treated with ICIs who are at high risk of fracture.

The parental imprinted GNAS complex locus encodes the α-subunit of the stimulatory G protein. Pseudohypoparathyroidism type Ib (PHP1B) is characterized by renal resistance to parathormone and is caused by epigenetic anomalies, ie, at least the loss of methylation (LOM) at the A/B differentially methylated region (DMR). LOM or gain of methylation (GOM) may also affect other DMRs and different transcripts expressions within the locus (NESP, exon H, AS1, XLαs, A/B). Most PHP1B are sporadic and result from abnormal methylation of all DMRs in the regulatory region of GNAS. Autosomal dominant PHP1B (AD-PHP1B) is usually caused by a recurrent STX16 gene microdeletion in the maternal allele which leads to isolated LOM at the A/B DMR. In this study, we investigated an AD-PHP1B family without STX16 deletion using whole genome sequencing (WGS). The two affected siblings presented a LOM at the A/B DMR and the half telomeric portion of the XLαs DMR and their healthy mother presented a partial GOM at the AS1 DMR and the half centromeric portion of the XLαs DMR. The WGS analysis revealed a 140-kb paracentric inversion with breakpoints located in the NPEPL1 gene and XLαs DMR. We identified the first inversion involving the regulatory region of GNAS locus leading to a maternally inherited AD-PHP1B. This observation provides additional insight into the methylation regulatory elements in the GNAS locus on both alleles, especially on NESP and exon H transcription-mediated methylation. This study will help design subsequent strategies for further studies.