Fracture risk is commonly assessed by FRAX, a tool that estimates 10-yr risk for major osteoporotic fracture (MOF) and hip fracture. FRAX scores are often refined by including FN BMD measured by DXA as an input. Rho, a novel AI-powered software, estimates FN BMD T-Scores from conventional X-rays, even when FN is not in the image. Whether a FRAX score using this estimate (FRAX-Rho) can improve a FRAX score without a T-Score input (FRAX-NoT) has not been studied. We conducted a retrospective analysis of Canadian Multicentre Osteoporosis Study participants who had X-rays of the lumbar and/or thoracic spine, FRAX risk factors, and DXA T-Scores acquired at the same time point, and follow-up fracture outcomes over 9 yr. In 1361 participants with lumbar X-rays, FRAX-Rho and FRAX with DXA FN T-Scores (FRAX-DXA) had very good agreement in categorizing participants by MOF risk (Cohen's weighted kappa κ = 0.80 [0.77-0.82]), which tended to be better than that between FRAX-NoT and FRAX-DXA (0.76 [0.73-0.79]). Agreement in categorizing participants by hip fracture risk was significantly greater between FRAX-Rho and FRAX-DXA (0.67 [0.63-0.71]) than FRAX-NoT and FRAX-DXA (0.52 [0.48-0.56]). In predicting true incident MOF, FRAX-Rho and FRAX-DXA did not differ in their discriminative power (c-index) (0.76 and 0.77; p = .36); both were significantly greater than that of FRAX-NoT (0.73; p < .004). The accuracy of FRAX-Rho for predicting MOF (Brier Score) was better than FRAX-NoT (p < .05) but not as good as FRAX-DXA. Similar results were observed in participants with thoracic X-rays. In conclusion, FN T-Scores estimated by Rho from lumbar and thoracic X-rays add value to FRAX-NoT estimates and may be useful for risk assessment when DXA is not available.

The FRAX model defines fractures occurring at the hip, vertebrae, humerus, and forearm as major osteoporotic fractures (MOF), leading to the misconception that fractures at other sites (NonMOF) are unimportant. We aimed to compare MOF and NonMOF to 1) assess their contribution to subsequent fracture and mortality risks and 2) the differences in subsequent fracture and mortality risks between MOF and NonMOF as well as 3) assess these contributions using an anatomical classification of hip, vertebral, proximal and distal fractures. Data from 7568 women and 3366 men aged 60+ were utilised from two Longitudinal cohorts (the Canadian Multicentre Osteoporosis Study and Dubbo Osteoporosis Epidemiology Study) to assess subsequent fracture and mortality following initial fractures. Initial fractures were classified as MOF or NonMOF for aim 1 and 2, and as hip, vertebral, proximal, or distal for aim 3. There were 1998 initial fractures (38% NonMOF) in women and 484 (48% NonMOF) in men. During 9551 person-years (py), women experienced 605 subsequent fractures (38% post-NonMOF) and during 2230 py, men had 97 subsequent fractures (48% post-NonMOF). Following the initial fracture, 556 women died (29% post-NonMOF) over 12065 py and 196 men died (38% post-NonMOF) over 2773 py. NonMOF were associated with 69% higher subsequent fracture risk in women (HR: 1.69; 95% CI: 1.47-1.95) and two-fold in men (2.06; 1.52-2.80), compared to initial fracture, comparable to MOF (women: 1.76; 1.56-1.98 and men: 2.09; 1.53-2.85. NonMOF imparted >30% excess mortality (women: 1.37; 1.16-1.60 and men: 1.33; 1.03-1.72), compared to fracture-free population, lower than MOF (women: 1.75; 1.54-1.99 and men: 2.26; 1.81-2.81) but still substantial. All anatomical fracture sites were associated with subsequent fracture risk, and the risk of mortality increased incrementally from distal to proximal, vertebral and hip. MOF and NonMOF showed comparable risks of subsequent fracture and mortality. All sites are associated with adverse outcomes and should be addressed in clinical care guidelines.

In this study, we developed ML algorithms to predict fragility fractures, considering the occurrence of fractures at different skeletal sites, using the data from the Canadian Multicentre Osteoporosis Study (CaMos) with participants aged 50 years or older. We considered 73 baseline features, and the outcome was the first incidence of fracture at any of the following sites: hip, spine, pelvis, ribs, shoulder, and forearm. The ML algorithms were evaluated in terms of the ROC_AUC. SHapley Additive exPlanations (SHAP) analysis was performed to identify the important features and to investigate the interaction among these features. In total, 7753 subjects were included in the study. Approximately 72% were female, and the average age was 67 years. We found that the XGBoost algorithm had a slightly better ROC_AUC (0.70; 95% CI 0.67, 0.73). From the SHAP analysis, we found that BMD was the most important feature and the total hip BMD interacted the most with femoral neck BMD. This study demonstrated that XGBoost was a marginally superior ML algorithm for predicting fragility fractures. In addition, we identified important features that contribute to the prediction of fragility fractures. Intervention focusing on these features will help to prevent the incidence of these fractures.

Aging is associated with many chronic conditions that increase morbidity and mortality. These include obesity, diabetes, sarcopenia, osteoporosis, and neurodegeneration. The deubiquitinase USP19 is involved in many of these disorders suggesting that it may modulate common mechanism(s) that impact the aging process. Inactivation of USP19 is protective against muscle atrophy, obesity, and diabetes in young adult mice. Whether such protection persists in older adult mice remains unknown. In addition, the potential role of USP19 in osteoporosis remains unexplored. Here, we demonstrate that loss of USP19 is protective against loss of muscle mass and obesity in mice aged 22-24 months. Glucose tolerance was also improved in these older adult USP19 KO mice, but only in females. Bone mineral content was decreased in the USP19 KO bone, more evidently in cortical bone than in trabecular bone and only in males. This was associated with a reduced work-to-failure in the KO femurs. Osteoblasts derived from USP19 KO bone marrow cells demonstrated decreased ex-vivo mineralization compared to WT cells and the KO marrow cells showed enhanced differentiation into TRAP-positive multinucleated osteoclasts. These findings identify important potential benefits as well as risks of therapeutic targeting of USP19 for the prevention or treatment of key aging related disorders.

Sarcopenia, characterized by an age-related decline in skeletal muscle mass and function, is closely linked to vitamin D deficiency. This study examines the role of Sirtuin 1 (Sirt1) and its regulation by vitamin D in preventing sarcopenia. Utilizing wild-type, 1α-hydroxylase knockout (1α(OH)ase-/-), and Sirt1 transgenic (Sirt1Tg) 1α(OH)ase-/- mice, we investigated muscle Sirt1 levels, muscle mass, fiber type, and senescence markers. Our results demonstrated that 1,25-Dihydroxyvitamin D (1,25(OH)2D3) upregulated Sirt1 and myogenic factor MyoD1 expression in C2C12 myoblasts via VDR-mediated transcription. Sirt1 overexpression in mesenchymal stem cells (MSCs) significantly mitigated muscle mass reduction, improved fiber cross-sectional area, and increased type II fiber numbers in 1α(OH)ase-/- mice. Mechanistically, 1,25(OH)2D3 promoted muscle cell health by enhancing Sirt1 expression, which in turn reduced muscle cell senescence and the senescence-associated secretory phenotype (SASP) through decreased levels of acetylated nuclear p53 and p65, maintaining their cytoplasmic localization. Additionally, Sirt1 overexpression accelerated muscle regeneration post-injury by increasing embryonic myosin heavy chain expression and cell proliferation. These findings underscore the therapeutic potential of targeting vitamin D and Sirt1 pathways to prevent sarcopenia, suggesting that supplementation with active vitamin D and consequent Sirt1 activation could be effective strategies for managing age-related muscle wasting.

The relationship between rheumatoid arthritis (RA) and fracture risk was estimated in an international meta-analysis of individual-level data from 29 prospective cohorts. RA was associated with an increased fracture risk in men and women, and these data will be used to update FRAX®. RA is a well-documented risk factor for subsequent fracture that is incorporated into the FRAX algorithm. The aim of this study was to evaluate, in an international meta-analysis, the association between rheumatoid arthritis and subsequent fracture risk and its relation to sex, age, duration of follow-up, and bone mineral density (BMD) with a view to updating FRAX. The resource comprised 1,909,896 men and women, aged 20–116 years, from 29 prospective cohorts in which the prevalence of RA was 3

Plasma fibronectin is a liver-derived glycoprotein that circulates at relatively high concentration and accumulates in tissues to form ECM. The role of plasma fibronectin in osteoblastogenesis, bone formation and remodeling has been suggested by many in vitro studies, but in vivo mouse models have not confirmed its role in bone formation and maintenance of bone mass. In this study we have performed skeletal phenotyping of adult, 6-month-old male and female, hepatocyte-specific fibronectin knockout (Fn1-/-ALB) mice. We report that mice have a significant loss of bone mass as analyzed by micro-Computed Tomography (μCT) of the tibial and vertebral trabecular bone. Dual-energy X-ray absorptiometry of the vertebral bone showed a decrease in bone mineral density. Histomorphometric analysis of bone cell numbers in vertebral bone showed a significant decrease in osteoblasts and in mineral apposition rates; there was also a significant reduction of a serum marker of bone formation (PINP), demonstrating an important role for plasma fibronectin in osteoblastogenesis in adult mice. The phenotype was observed only in male mice. Osteoclastogenesis was not affected. Analysis of plasma fibronectin levels in human osteoporosis via Canadian Multicentre Osteoporosis Study (CaMos) biobank demonstrated that circulating plasma fibronectin levels were significantly higher in men versus women aged 50 and over. Male osteoporotic patients showed significantly lower plasma fibronectin levels which correlated with low bone mineral density values, and with reduced T-scores of the lumbar spine (L1-4, p=0.0088), and of the total hip (p=0.0066) strongly suggesting an association between pFN levels and fracture risk in men.

Background: Vitamin D is essential for skeletal health, but its role in redox homeostasis and cellular senescence during aging in vivo is unclear. We therefore investigated whether active vitamin D insufficiency accelerates bone loss via oxidative stress and senescence pathways. Methods: Male wild-type (WT) and Cyp27b1 haploinsufficient mice (modeling vitamin D insufficiency) were treated with N-acetylcysteine (NAC) or 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. Double-mutant p16-/-Cyp27b1+/- mice were used to assess the role of the tumor suppressor protein p16. Mice were maintained until 8 months of age in a specific pathogen-free facility. Outcomes included lifespan (n = variable per group, monitored daily); generation of oxidative stress (determined by serum malondialdehyde [MDA] levels via assay kit); generation of bone reactive oxygen species [ROS] (determined via flow cytometry), development of DNA damage (indicated by 8-hydroxy-2′-deoxyguanosine [8-OHdG] and γ-H2A.X generation and determined via immunohistochemistry and Western blot); and senescence (assessed by generation of β-galactosidase [β-gal], p16, and senescence-associated secretory phenotype [SASP] cytokines as determined via staining, blot, and real-time reverse transcription polymerase chain reaction). Additionally, bone microarchitecture was examined via micro-computed tomography and histomorphometry. Data from at least 5 mice per group were analyzed using unpaired Student’s t-test for two-group comparisons and two-way analysis of variance for multi-group comparisons, with significance at p < 0.05. Results: Compared with wild-type controls, Cyp27b1+/- mice showed a significantly shorter lifespan, higher oxidative stress, greater DNA damage, increased senescence markers, and lower trabecular bone volume (all p < 0.05). In Cyp27b1+/- mice, treatment with either N-acetylcysteine or 1,25(OH)2D3 significantly improved survival, reduced oxidative stress and DNA damage, attenuated senescence markers, and increased bone volume relative to untreated Cyp27b1+/- mice (p < 0.05 for all relevant comparisons; n = 5 per group). Genetic deletion of p16 in Cyp27b1+/-mice similarly increased bone volume and reduced senescence-associated readouts compared with Cyp27b1+/- controls (p < 0.05; n = 5). Conclusions: Active vitamin D insufficiency accelerates skeletal aging in vivo through a pathway involving reactive oxygen species-DNA damage-p16/senescence-associated secretory phenotype. Antioxidants, vitamin D repletion, or p16 inhibition rescued bone loss, highlighting redox-senescence axes as potential therapeutic targets for osteoporosis.

Renal aging may lead to fibrosis and dysfunction, yet underlying mechanisms remain unclear. We explored whether deficiency of the Polycomb protein Bmi1 causes renal aging via DNA damage response (DDR) activation, inducing renal tubular epithelial cell (RTEC) senescence and epithelial-mesenchymal transition (EMT). Bmi1 knockout mice exhibited oxidative stress, DDR activation, RTEC senescence, senescence-associated secretory phenotype (SASP), and age-related fibrosis in kidneys. Bmi1 deficiency impaired renal structure and function, increasing serum creatinine/urea, reducing creatinine clearance, and decreasing cortical thickness and glomerular number. However, knockout of the serine-threonine kinase Chk2 alleviated these aging phenotypes. Transcriptomics identified transforming growth factor beta 1 (TGFβ1) upregulation in Bmi1-deficient RTECs, but TGFβ1 was downregulated upon Chk2 knockout. The tumor suppressor protein p53 transcriptionally activated TGFβ1, promoting EMT in RTECs. Bmi1 knockout or oxidative stress (induced with H2O2) increased TGFβ1 expression, and EMT in RTECs and was partly reversed by p53 inhibition. Together, Bmi1 deficiency causes oxidative stress and DDR-mediated RTEC senescence/SASP, thus activating p53 and TGFβ1 to induce EMT and age-related fibrosis. However, blocking DDR (via Chk2 knockout) or p53 ameliorates these changes. Our study reveals mechanisms whereby Bmi1 preserves renal structure and function during aging by suppressing DDR and p53/TGFβ1-mediated EMT. These pathways represent potential targets for detecting and attenuating age-related renal decline.

Background/Objective: Active vitamin D insufficiency accelerates the development of osteoporosis, with senescent bone cells and the senescence-associated secretory phenotype (SASP) playing crucial roles. This study aimed to investigate whether the senolytic agent ABT263 could correct osteoporosis caused by active vitamin D insufficiency by selectively clearing senescent cells. Methods: Bone marrow mesenchymal stem cells (BM-MSCs) from young and aged mice were treated with ABT263 in vitro, and 1,25(OH)2D-insufficient (Cyp27b1+/−) mice were administered ABT263 in vivo. Cellular, molecular, imaging, and histopathological analyses were performed to compare treated cells and mice with control groups. Results: ABT263 induced apoptosis in senescent BM-MSCs by downregulating Bcl2 and upregulating Bax expression. It also induced apoptosis in senescent BM-MSCs from 1,25(OH)2D-insufficient mice. ABT263 administration corrected bone loss caused by 1,25(OH)2D insufficiency by increasing bone density, bone volume, trabecular number, trabecular thickness, and collagen synthesis. It also enhanced osteoblastic bone formation and reduced osteoclastic bone resorption in vivo. ABT263 treatment corrected the impaired osteogenic action of BM-MSCs by promoting their proliferation and osteogenic differentiation. Furthermore, it corrected oxidative stress and DNA damage caused by 1,25(OH)2D insufficiency by increasing SOD-2 and decreasing γ-H2A.X expression. Finally, ABT263 corrected bone cell senescence and SASP caused by 1,25(OH)2D insufficiency by reducing the expression of senescence and SASP-related genes and proteins. Conclusion: ABT263 can correct osteoporosis caused by active vitamin D insufficiency by selectively clearing senescent skeletal cells, reducing oxidative stress, DNA damage, and SASP, and promoting bone formation while inhibiting bone resorption. These findings provide new insights into the potential therapeutic application of senolytic agents in the treatment of osteoporosis associated with active vitamin D insufficiency. The translational potential of this article: This study highlights the therapeutic potential of ABT263, a senolytic compound, in treating osteoporosis caused by active vitamin D insufficiency. By selectively eliminating senescent bone cells and their associated SASP, ABT263 intervention demonstrates the ability to restore bone homeostasis, prevent further bone loss, and promote bone formation. These findings contribute to the growing body of research supporting the use of senolytic therapies for the prevention and treatment of age-related bone disorders. The translational potential of this study lies in the development of novel therapeutic strategies targeting cellular senescence to combat osteoporosis, particularly in cases where vitamin D insufficiency is a contributing factor. Further clinical studies are warranted to validate the efficacy and safety of ABT263 and other senolytic agents in the treatment of osteoporosis in humans.

[This corrects the article on p. 4382 in vol. 8, PMID: 27830022.].

Central tolerance of thymocytes to self-antigen depends on the medullary thymic epithelial cell (mTEC) transcription factor autoimmune regulator (Aire), which drives tissue-restricted antigen (TRA) gene expression. Vitamin D signaling regulates Aire and TRA expression in mTECs, providing a basis for links between vitamin D deficiency and autoimmunity. We find that mice lacking Cyp27b1, which cannot produce hormonally active vitamin D, display profoundly reduced thymic cellularity, with a reduced proportion of Aire + mTECs, attenuated TRA expression, and poorly defined cortical-medullary boundaries. Markers of T cell negative selection are diminished, and organ-specific autoantibodies are present in knockout (KO) mice. Single-cell RNA sequencing revealed that loss of Cyp27b1 skews mTEC differentiation toward Ccl21 + intertypical TECs and generates a gene expression profile consistent with premature aging. KO thymi display accelerated involution and reduced expression of thymic longevity factors. Thus, loss of thymic vitamin D signaling disrupts normal mTEC differentiation and function and accelerates thymic aging.

The relationship between self-reported falls and fracture risk was estimated in an international meta-analysis of individual-level data from 46 prospective cohorts. Previous falls were associated with an increased fracture risk in women and men and should be considered as an additional risk factor in the FRAX® algorithm. Previous falls are a well-documented risk factor for subsequent fracture but have not yet been incorporated into the FRAX algorithm. The aim of this study was to evaluate, in an international meta-analysis, the association between previous falls and subsequent fracture risk and its relation to sex, age, duration of follow-up, and bone mineral density (BMD). The resource comprised 906,359 women and men (66.9

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.

Age-related intervertebral disk degeneration (IVDD) involves increased oxidative damage, cellular senescence, and matrix degradation. Pyrroloquinoline quinone (PQQ) is a water-soluble vitamin-like compound with strong anti-oxidant capacity. The goal of this study was to determine whether PQQ can prevent aging-related IVDD, and the underlying mechanism. Here, we found that dietary PQQ supplementation for 12 months alleviated IVDD phenotypes in aged mice, including increased disk height index and reduced histological scores and cell loss, without toxicity. Mechanistically, PQQ inhibited oxidative stress, cellular senescence, and senescence-associated secretory phenotype (SASP) in the nucleus pulposus and annulus fibrosus of aged mice. Similarly, PQQ protected against interleukin-1β-induced matrix degradation, reactive oxygen species accumulation, and senescence in human nucleus pulposus cells (NPCs) in vitro. Molecular docking predicted and biochemical assays validated that PQQ interacts with specific residues to dissociate the Keap1-Nrf2 complex, thereby increasing nuclear Nrf2 translocation and activation of Nrf2-ARE signaling. RNA sequencing and luciferase assays revealed Nrf2 can transcriptionally upregulate Wnt5a by binding to its promoter, while Wnt5a knockdown prevented PQQ inhibition of matrix metalloproteinase-13 in NPCs. Notably, PQQ supplementation failed to alleviate aging-associated IVDD phenotypes and oxidative stress in aged Nrf2 knockout mice, indicating Nrf2 is indispensable for PQQ bioactivities. Collectively, this study demonstrates Nrf2 activation by PQQ inhibits aging-induced IVDD by attenuating cellular senescence and matrix degradation. This study clarifies Keap1-Nrf2-Wnt5a axis as the novel signaling underlying the protective effects of PQQ against aging-related IVDD, and provides evidence for PQQ as a potential agent for clinical prevention and treatment of natural aging-induced IVDD.