The Proteasome Inhibitor Bortezomib Maintains Osteocyte Viability in Multiple Myeloma Patients by Reducing Both Apoptosis and Autophagy: A New Function for Proteasome Inhibitors

Multiple myeloma (MM) is characterized by severely imbalanced bone remodeling. In this study, we investigated the potential effect of proteasome inhibitors (PIs), a class of drugs known to stimulate bone formation, on the mechanisms involved in osteocyte death induced by MM cells. First, we performed a histological analysis of osteocyte viability on bone biopsies on a cohort of 37 MM patients with symptomatic disease. A significantly higher number of viable osteocytes was detected in patients treated with a bortezomib (BOR)‐based regimen compared with those treated without BOR. Interestingly, both osteocyte autophagy and apoptosis were affected in vivo by BOR treatment. Thereafter, we checked the in vitro effect of BOR to understand the mechanisms whereby BOR maintains osteocyte viability in bone from MM patients. We found that osteocyte and preosteocyte autophagic death was triggered during coculturing with MM cells. Our evaluation was conducted by analyzing either autophagy markers microtubule‐associated protein light chain 3 beta (LC3B) and SQSTM1/sequestome 1 (p62) levels, or the cell ultrastructure by transmission electron microscopy. PIs were found to increase the basal levels of LC3 expression in the osteocytes while blunting the myeloma‐induced osteocyte death. PIs also reduced the autophagic death of osteocytes induced by high‐dose dexamethasone (DEX) and potentiated the anabolic effect of PTH(1‐34). Our data identify osteocyte autophagy as a new potential target in MM bone disease and support the use of PIs to maintain osteocyte viability and improve bone integrity in MM patients. © 2015 American Society for Bone and Mineral Research.     

Similarities Between Disuse and Age-Induced Bone Loss

Disuse and aging are known risk factors associated with low bone mass and quality deterioration, resulting in increased fracture risk. Indeed, current and emerging evidence implicate a large number of shared skeletal manifestations between disuse and aging scenarios. This review provides a detailed overview of current preclinical models of musculoskeletal disuse and the clinical scenarios they seek to recapitulate. We also explore and summarize the major similarities between bone loss after extreme disuse and advanced aging at multiple length scales, including at the organ/tissue, cellular, and molecular level. Specifically, shared structural and material alterations of bone loss are presented between disuse and aging, including preferential loss of bone at cancellous sites, cortical thinning, and loss of bone strength due to enhanced fragility. At the cellular level bone loss is accompanied, during disuse and aging, by increased bone resorption, decreased formation, and enhanced adipogenesis due to altered gap junction intercellular communication, WNT/β-catenin and RANKL/OPG signaling. Major differences between extreme short-term disuse and aging are discussed, including anatomical specificity, differences in bone turnover rates, periosteal modeling, and the influence of subject sex and genetic variability. The examination also identifies potential shared mechanisms underlying bone loss in aging and disuse that warrant further study such as collagen cross-linking, advanced glycation end products/receptor for advanced glycation end products (AGE-RAGE) signaling, reactive oxygen species (ROS) and nuclear factor κB (NF-κB) signaling, cellular senescence, and altered lacunar-canalicular connectivity (mechanosensation). Understanding the shared structural alterations, changes in bone cell function, and molecular mechanisms common to both extreme disuse and aging are paramount to discovering therapies to combat both age-related and disuse-induced osteoporosis. © 2022 American Society for Bone and Mineral Research (ASBMR).     

IGF‐1 Regulates Vertebral Bone Aging Through Sex‐Specific and Time‐Dependent Mechanisms

Advanced aging is associated with increased risk of bone fracture, especially within the vertebrae, which exhibit significant reductions in trabecular bone structure. Aging is also associated with a reduction in circulating levels of insulin‐like growth factor (IGF‐1). Studies have suggested that the reduction in IGF‐1 compromises healthspan, whereas others report that loss of IGF‐1 is beneficial because it increases healthspan and lifespan. To date, the effect of decreases in circulating IGF‐1 on vertebral bone aging has not been thoroughly investigated. Here, we delineate the consequences of a loss of circulating IGF‐1 on vertebral bone aging in male and female Igf^f/f mice. IGF‐1 was reduced at multiple specific time points during the mouse lifespan: early in postnatal development (crossing albumin–cyclic recombinase [Cre] mice with Igf^f/f mice); and in early adulthood and in late adulthood using hepatic‐specific viral vectors (AAV8‐TBG‐Cre). Vertebrae bone structure was analyzed at 27 months of age using micro–computed tomography (μCT) and quantitative bone histomorphometry. Consistent with previous studies, both male and female mice exhibited age‐related reductions in vertebral bone structure. In male mice, reduction of circulating IGF‐1 induced at any age did not diminish vertebral bone loss. Interestingly, early‐life loss of IGF‐1 in females resulted in a 67% increase in vertebral bone volume fraction, as well as increased connectivity density and increased trabecular number. The maintenance of bone structure in the early‐life IGF‐1–deficient females was associated with increased osteoblast surface and an increased ratio of osteoprotegerin/receptor‐activator of NF‐κB‐ligand (RANKL) levels in circulation. Within 3 months of a loss of IGF‐1, there was a 2.2‐fold increase in insulin receptor expression within the vertebral bones of our female mice, suggesting that local signaling may compensate for the loss of circulating IGF‐1. Together, these data suggest the age‐related loss of vertebral bone density in females can be reduced by modifying circulating IGF‐1 levels early in life. © 2015 American Society for Bone and Mineral Research.     

Alternative NF‐κB Regulates RANKL‐Induced Osteoclast Differentiation and Mitochondrial Biogenesis via Independent Mechanisms

Mitochondrial biogenesis, the generation of new mitochondrial DNA and proteins, has been linked to osteoclast (OC) differentiation and function. In this study we used mice with mutations in key alternative NF‐κB pathway proteins, RelB and NF‐κB–inducing kinase (NIK), to dissect the complex relationship between mitochondrial biogenesis and osteoclastogenesis. In OC precursors lacking either NIK or RelB, receptor activator of NF‐κB ligand (RANKL) was unable to increase mitochondrial DNA or oxidative phosphorylation (OxPhos) protein expression, which was associated with lower oxygen consumption rates. Transgenic OC precursors expressing constitutively active NIK showed normal RANKL‐induced mitochondrial biogenesis (OxPhos expression and mitochondria copy number) compared to controls, but larger mitochondrial dimensions and increased oxygen consumption rates, suggesting increased mitochondrial function. To deduce the mechanism for mitochondrial biogenesis defects in NIK‐deficient and RelB‐deficient precursors, we examined expression of genes known to control this process. PGC‐1β (Ppargc1b) expression, but not PGC‐1α, PPRC1, or ERRα, was significantly reduced in RelB^–/– and NIK^–/– OCs. Because PGC‐1β has been reported to positively regulate both mitochondrial biogenesis and differentiation in OCs, we retrovirally overexpressed PGC‐1β in RelB^–/– cells, but surprisingly found that it did not affect differentiation, nor did it restore RANKL‐induced mitochondrial biogenesis. To determine whether the blockade in osteoclastogenesis in RelB‐deficient cells precludes mitochondrial biogenesis, we rescued RelB^–/– differentiation via overexpression of NFATc1. Mitochondrial parameters in neither WT nor RelB‐deficient cultures were affected by NFATc1 overexpression, and bone resorption in RelB^–/– was not restored. Furthermore, NFATc1 co‐overexpression with PGC‐1β, although allowing OC differentiation, did not rescue mitochondrial biogenesis or bone resorption in RelB^–/– OCs, by CTX‐I levels. Thus, our results indicate that the alternative NF‐κB pathway plays dual, but distinct, roles in controlling the independent processes of OC differentiation and OC mitochondrial biogenesis. Furthermore, the inability of PGC‐1β to drive mitochondrial biogenesis in OCs without RelB indicates a cell‐type specificity in mitochondria regulation. © 2015 American Society for Bone and Mineral Research.     

The Quest for Osteoporosis Mechanisms and Rational Therapies: How Far We've Come,How Much Further We Need to Go

During the last 40 years, understanding of bone biology and the pathogenesis of osteoporosis, the most common and impactful bone disease of old age, has improved dramatically thanks to basic and clinical research advances, genetic insights from humans and rodents, and newer imaging technologies. Culprits of osteoporosis are no longer a matter of speculation based on in vitro observations. Instead, they can be identified and dissected at the cellular and molecular level using genetic approaches; and their effect on distinct bone envelopes and anatomic regions can be functionally assessed in vivo. The landscape of pharmacotherapies for osteoporosis has also changed profoundly with the emergence of several potent antiresorptive drugs as well as anabolic agents, displacing estrogen replacement as the treatment of choice. In spite of these major positive developments, the optimal duration of the available therapies and their long‐term safety remain matters of conjecture and some concern. Moreover, antiresorptive therapies are used indiscriminately for patients of all ages on the assumption that suppressing remodeling is always beneficial for bone, but rebound remodeling upon their discontinuation suggests otherwise. In this invited perspective, I highlight the latest state of knowledge of bone‐intrinsic and extrinsic mechanisms responsible for the development of osteoporosis in both sexes; differences between the mechanisms responsible for the effects of aging and estrogen deficiency; and the role of old osteocytes in the development of cortical porosity. In addition, I highlight advances toward the goal of developing drugs for several degenerative diseases of old age at once, including osteoporosis, by targeting shared mechanisms of aging. © 2018 American Society for Bone and Mineral Research.     

N‐cadherin Regulation of Bone Growth and Homeostasis Is Osteolineage Stage–Specific

N‐cadherin inhibits osteogenic cell differentiation and canonical Wnt/β‐catenin signaling in vitro. However, in vivo both conditional Cdh2 ablation and overexpression in osteoblasts lead to low bone mass. We tested the hypothesis that N‐cadherin has different effects on osteolineage cells depending upon their differentiation stage. Embryonic conditional osteolineage Cdh2 deletion in mice results in defective growth, low bone mass, and reduced osteoprogenitor number. These abnormalities are prevented by delaying Cdh2 ablation until 1 month of age, thus targeting only committed and mature osteoblasts, suggesting they are the consequence of N‐cadherin deficiency in osteoprogenitors. Indeed, diaphyseal trabecularization actually increases when Cdh2 is ablated postnatally. The sclerostin‐insensitive Lrp5^A214V mutant, associated with high bone mass, does not rescue the growth defect, but it overrides the low bone mass of embryonically Cdh2‐deleted mice, suggesting N‐cadherin interacts with Wnt signaling to control bone mass. Finally, bone accrual and β‐catenin accumulation after administration of an anti‐Dkk1 antibody are enhanced in N‐cadherin–deficient mice. Thus, although lack of N‐cadherin in embryonic and perinatal age is detrimental to bone growth and bone accrual, in adult mice loss of N‐cadherin in osteolineage cells favors bone formation. Hence, N‐cadherin inhibition may widen the therapeutic window of osteoanabolic agents. © 2017 American Society for Bone and Mineral Research.     

Clinical Characteristics and Evolution of Giant Cell Tumor Occurring in Paget's Disease of Bone

Patients with Paget's bone disease (PDB) have an increased risk of developing giant cell tumor (GCT). This study was performed to evaluate the clinical characteristics and evolution of GCT complicating PDB and to compare these clinical characteristics to those observed in two large PDB cohorts, the PDB Italian Registry and the United Kingdom's Multi‐Centre Randomised Controlled Trial of Symptomatic Versus Intensive Bisphosphonate Therapy for Paget's Disease (PRISM) study. A systematic literature review identified 117 cases of PDB complicated by GCT (PDB‐GCT), which involved the skeletal sites affected by PDB (110 patients) or the extraskeletal tissues adjacent to affected bones (7 patients). In contrast to what previously reported for GCT patients without GCT patients (83.2%) were white and one‐fourth of them (24.8%) had multifocal GCTs. Compared to PDB patients without GCT, PDB‐GCT patients showed a higher male/female ratio (2.1 versus 1.2) and more severe disease (age at PDB onset 52.1 ± 12.1 versus 63.3 ± 10.6 years; number of affected sites 6.1 ± 2.9 versus 2.34 ± 1.6; prevalence of polyostotic PDB 93.3% versus 60.6%). The mortality rate of PDB‐GCT patients was higher than those occurring in GCT patients without PDB (about 50% versus 0% to 5% at 5 years) or in PDB patients without GCT (log rank = 29.002). Moreover, up to 98% of PDB‐GCT cases had elevated total alkaline phosphatase levels at neoplasm diagnosis, suggestive of active PDB. Importantly, PDB‐GCT patients from Southern Italy (45.6% of all GCT patients) showed a higher prevalence of multifocal GCT (51.7%) and of positive familial history for PDB (70.8%) and GCT (65.0%). Finally, indirect evidence suggests a decline in the incidence of GCT in PDB patients. The occurrence of GCT in PDB patients is associated with severe disease and reduced life expectancy of affected patients. The increased prevalence of familial diseases in PDB‐GCT patients from Southern Italy suggests a founder effect. The observed changes over time in the incidence of GCT in PDB patients could be related to improved clinical management and/or living conditions of patients. © 2014 American Society for Bone and Mineral Research.     

Bone Morphogenetic Protein‐2 and Vascular Endothelial Growth Factor in Bone Tissue Regeneration: New Insight and Perspectives

The study of bone tissue regeneration in orthopaedic diseases has stimulated great interest among bone tissue engineering specialists and orthopaedic surgeons. Combinations of biomaterials, growth factors and stem cells for repairing bone have been much studied and researched, yet remain a challenge for both scientists and clinicians pursuing regenerative medicine. The purpose of this review was to elucidate the role of sequential release of bone morphogenetic protein‐2 and vascular endothelial growth factor in producing better outcomes in the field of bone tissue regeneration.     

Sex-Specific Associations Between Cardiac Workload,Peripheral Vascular Calcification,and Bone Mineral Density: The Gambian Bone and Muscle Aging Study

Noncommunicable diseases (NCD) are rapidly rising in Africa, with multimorbidity increasing the burden on health and social care. Osteoporosis and cardiovascular disease (CVD) share common risk factors; both often remain undiagnosed until a major life-threatening event occurs. We investigated the associations between cardiac workload, peripheral vascular calcification (PVC), and bone parameters in Gambian adults. The Gambian Bone and Muscle Aging Study (GamBAS) recruited 249 women and 239 men aged 40 to 75+ years. Body composition and areal bone mineral density (aBMD) were measured using dual-energy X-ray absorptiometry; peripheral quantitative computed tomography (pQCT) scans were performed at the radius and tibia. Supine blood pressure and heart rate were measured and used to calculate rate pressure product and pulse pressure. Presence of PVC was determined from tibia pQCT scans. Sex interactions were tested (denoted as p-int); adjustments were made for residuals of appendicular lean mass (ALM) and fat mass (FM). There were negative associations between rate pressure product and aBMD in women only, all p-int < .05; after adjustment for ALM residuals, for every 10% increase in rate pressure product, aBMD was lower at the whole body (−0.6% [−1.2, −0.1]), femoral neck (−0.9% [−1.8, −0.05]), L₁ to L₄ (−0.6% [−1.7, 0.5]), and radius (−1.9% [−2.8, −0.9]); there were similar associations when adjusted for FM residuals. Similar negative associations were found between pulse pressure and aBMD in women only. PVC were found in 26.6% men and 22.5% women; women but not men with calcification had poorer cardiac health and negative associations with aBMD (all sites p-int < .001). There were consistent associations with cardiac parameters and pQCT outcomes at the radius and tibia in women only. Multiple markers of cardiac health are associated with poorer bone health in Gambian women. In the context of epidemiological transition and changing NCD burden, there is a need to identify preventative strategies to slow/prevent the rising burden in CVD and osteoporosis in Sub-Saharan Africa. © 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).     

QCT Volumetric Bone Mineral Density and Vascular and Valvular Calcification: The Framingham Study

There is increasing evidence that bone and vascular calcification share common pathogenesis. Little is known about potential links between bone and valvular calcification. The purpose of this study was to determine the association between spine bone mineral density (BMD) and vascular and valvular calcification. Participants included 1317 participants (689 women, 628 men) in the Framingham Offspring Study (mean age 60 years). Integral, trabecular, and cortical volumetric bone density (vBMD) and arterial and valvular calcification were measured from computed tomography (CT) scans and categorized by sex‐specific quartiles (Q4 = high vBMD). Calcification of the coronary arteries (CAC), abdominal aorta (AAC), aortic valve (AVC), and mitral valve (MVC) were quantified using the Agatston Score (AS). Prevalence of any calcium (AS >0) was 69% for CAC, 81% for AAC, 39% for AVC, and 20% for MVC. In women, CAC increased with decreasing quartile of trabecular vBMD: adjusted mean CAC = 2.1 (Q4), 2.2 (Q3), 2.5 (Q2), 2.6 (Q1); trend p = 0.04. However, there was no inverse trend between CAC and trabecular vBMD in men: CAC = 4.3 (Q4), 4.3 (Q3), 4.2 (Q2), 4.3 (Q1); trend p = 0.92. AAC increased with decreasing quartile of trabecular vBMD in both women (AAC = 4.5 [Q4], 4.8 [Q3], 5.4 [Q2], 5.1 [Q1]; trend p = 0.01) and men (AAC = 5.5 [Q4], 5.8 [Q3], 5.9 [Q2], 6.2 [Q1]; trend p = 0.01). We observed no association between trabecular vBMD and AVC or MVC in women or men. Finally, cortical vBMD was unrelated to vascular calcification and valvular calcification in women and men. Women and men with low spine vBMD have greater severity of vascular calcification, particularly at the abdominal aorta. The inverse relation between AAC and spine vBMD in women and men may be attributable to shared etiology and may be an important link on which to focus treatment efforts that can target individuals at high risk of both fracture and cardiovascular events. © 2015 American Society for Bone and Mineral Research.     

Nitrate Medications,Fractures, and Change in Bone Mineral Density in Postmenopausal Women: Results from the Women's Health Initiative

Nitrate medications may increase bone mineral density (BMD), although information on fracture outcomes is sparse. We examined the association of nitrate medications with fractures (hip, wrist/arm, and total fractures) and changes in BMD (hip, spine, and whole body) in the Women's Health Initiative (WHI) Clinical Trials and Observational Study. A total of 139,211 postmenopausal women 50 to 79 years old without history of hip fracture were included in this prospective study. Medication use was ascertained directly from drug containers at baseline during in‐person interviews in 1993 to 1998. Exposure measures included any use (use/non‐use), type of nitrate (as‐needed, maintenance) and duration of use (≤5 years, >5 years). We used separate multivariable Cox proportional hazard models to analyze associations between each exposure and fracture outcome, with results presented as hazard ratios (HRs) and 95% confidence intervals (CIs). Multivariable linear regression models were used to examine 3‐year and 6‐year changes in BMD. At baseline, 1.2% (n = 1647) women were using a nitrate. During the mean ± SD follow‐up of 7.7 ± 1.5 years through 2005, women experienced 1582 hip fractures, 5156 wrist or arm fractures, and 22, 589 total fractures. After adjustment for confounders, nitrate use was not statistically associated with risk for hip (HR, 0.81; 95% CI, 0.56 to 1.18), wrist/arm (HR, 0.95; 95% CI, 0.74 to 1.23), or total fractures (HR, 0.96; 95% CI, 0.85 to 1.08). As‐needed nitrate use, but not maintenance therapy, was associated with a lower risk of total fractures (HR, 0.77; 95% CI, 0.62 to 0.95) and wrist/arm fractures (HR, 0.57; 95% CI, 0.34 to 0.98). Nitrate use was not associated with 3‐year or 6‐year changes in BMD at any site. We conclude that any nitrate use was not significantly associated with lower risk of fractures or higher BMD; however, as‐needed nitrate use was associated with lower risks of total and wrist/arm fractures. © 2016 American Society for Bone and Mineral Research.     

Diabetes and Deficits in Cortical Bone Density,Microarchitecture, and Bone Size: Framingham HR‐pQCT Study

Older adults with type 2 diabetes (T2D) tend to have normal or greater areal bone mineral density (aBMD), as measured by DXA, than those who do not have diabetes (non‐T2D). Yet risk of fracture is higher in T2D, including 40% to 50% increased hip fracture risk. We used HR‐pQCT to investigate structural mechanisms underlying skeletal fragility in T2D. We compared cortical and trabecular bone microarchitecture, density, bone area, and strength in T2D and non‐T2D. In secondary analyses we evaluated whether associations between T2D and bone measures differed according to prior fracture, sex, and obesity. Participants included 1069 members of the Framingham Study, who attended examinations in 2005 to 2008 and underwent HR‐pQCT scanning in 2012 to 2015. Mean age was 64 ± 8 years (range, 40 to 87 years), and 12% (n = 129) had T2D. After adjustment for age, sex, weight, and height, T2D had lower cortical volumetric BMD (vBMD) (p < 0.01), higher cortical porosity (p = 0.02), and smaller cross‐sectional area (p = 0.04) at the tibia, but not radius. Trabecular indices were similar or more favorable in T2D than non‐T2D. Associations between T2D and bone measures did not differ according to sex or obesity status (all interaction p > 0.05); however, associations did differ in those with a prior fracture and those with no history of fracture. Specifically, cortical vBMD at the tibia and cortical thickness at the radius were lower in T2D than non‐T2D, but only among those individuals with a prior fracture. Cortical porosity at the radius was higher in T2D than non‐T2D, but only among those who did not have a prior fracture. Findings from this large, community‐based study of older adults suggest that modest deterioration in cortical bone and reductions in bone area may characterize diabetic bone disease in older adults. Evaluation of these deficits as predictors of fracture in T2D is needed to develop prevention strategies in this rapidly increasing population of older adults. © 2017 American Society for Bone and Mineral Research.