Disorders associated with acute rapid and severe bone loss

Risk of fracture among patients with spinal cord injury: A nationwide cohort study in South Korea

BACKGROUND

Clinical concerns about preventing and managing fractures after spinal cord injury (SCI) have been growing.

OBJECTIVE

This study investigates the risk of fractures among SCI patients according to the presence of disability, disease severity, and level of injury.

METHODS

We performed a retrospective cohort study using the Korean National Health Insurance Service (KNHIS 2010-2018) database. We included 5190 SCI patients and 1:3 age- and sex-matched control participants. The primary outcome was fracture, and the cohort was followed until December 31, 2019.

RESULTS

SCI patients had a higher fracture risk than the matched controls (adjusted hazard ratio [aHR] 1.33, 95 % CI 1.16-1.54). The risk of fracture was higher in the presence of disability (aHR 1.57, 95 % CI 1.19-2.07), especially among patients with severe disability (aHR 1.65, 95 % CI 1.05-2.60). Higher fracture risks were observed among SCI patients regardless of injury level, but statistical significance was found only with cervical-level injury. When we considered site-specific fractures, vertebral (aHR 1.31, 95 % CI 1.04-1.64) and hip fracture risks (aHR 2.04, 95 % CI 1.39-2.98) were both higher among SCI patients than the controls. SCI patients with disability and cervical-level injury showed the highest hip fracture risk (aHR 3.67, 95 % CI 1.90-7.07).

CONCLUSIONS

Compared with the controls, SCI patients were at higher risk of any fracture, particularly hip fracture, especially those with disability and cervical-level injury. Clinicians should be aware of the fracture risk among SCI patients to provide proper management.

Bone Density and Trabecular Bone Score Decline Rapidly in the First Year After Bone Marrow Transplantation with a Marked Increase in 10-Year Fracture Risk

As outcomes from allogeneic bone marrow transplantation (BMT) have improved, prevention of long-term complications, such as fragility fractures, has gained importance. We aimed to assess areal bone mineral density (aBMD) and trabecular bone score (TBS) changes post BMT, and determine their relationship with fracture prevalence. Patients who attended the Royal Melbourne Hospital (RMH) BMT clinic between 2005-2021 were included. Patient characteristics and dual-energy X-ray absorptiometry (DXA) values were collected from the electronic medical record and a survey. TBS iNsight™ was used to calculate TBS for DXA scans performed from 2019 onwards. 337 patients with sequential DXAs were eligible for inclusion. Patients were primarily male (60%) and mean age ± SD was 45.7 ± 13.4 years. The annualised decline in aBMD was greater at the femoral neck (0.066g/cm2 (0.0038-0.17)) and total hip (0.094g/cm2 (0.013-0.19)), compared to the lumbar spine (0.049g/cm2 (- 0.0032-0.16)), p < 0.0001. TBS declined independently of aBMD T-scores at all sites. Eighteen patients (5.3%) sustained 19 fractures over 3884 person-years of follow-up post-transplant (median follow-up 11 years (8.2-15)). This 5.3% fracture prevalence over the median 11-year follow-up period is higher than what would be predicted with FRAX® estimates. Twenty-two patients (6.5%) received antiresorptive therapy, and 9 of 18 (50%) who fractured received or were on antiresorptive therapy. In BMT patients, aBMD and TBS decline rapidly and independently in the first year post BMT. However, FRAX® fracture probability estimates incorporating these values significantly underestimate fracture rates, and antiresorptive treatment rates remain relatively low.

Pathophysiological mechanism of acute bone loss after fracture

BACKGROUND

Acute bone loss after fracture is associated with various effects on the complete recovery process and a risk of secondary fractures among patients. Studies have reported similarities in pathophysiological mechanisms involved in acute bone loss after fractures and osteoporosis. However, given the silence nature of bone loss and bone metabolism complexities, the actual underlying pathophysiological mechanisms have yet to be fully elucidated.

AIM OF REVIEW

To elaborate the latest findings in basic research with a focus on acute bone loss after fracture. To briefly highlight potential therapeutic targets and current representative drugs. To arouse researchers' attention and discussion on acute bone loss after fracture.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Bone loss after fracture is associated with immobilization, mechanical unloading, blood supply damage, sympathetic nerve regulation, and crosstalk between musculoskeletals among other factors. Current treatment strategies rely on regulation of osteoblasts and osteoclasts, therefore, there is a need to elucidate on the underlying mechanisms of acute bone loss after fractures to inform the development of efficacious and safe drugs. In addition, attention should be paid towards ensuring long-term skeletal health.

Bone health in inflammatory bowel disease

INTRODUCTION

Inflammatory bowel disease (IBD) is a chronic disease characterized by the presence of systemic inflammation, manifesting not only as gastrointestinal symptoms but also as extraintestinal bone complications, including osteopenia and osteoporosis. However, the association between IBD and osteoporosis is complex, and the presence of multifactorial participants in the development of osteoporosis is increasingly recognized. Unlike in adults, delayed puberty and growth hormone/insulin-like growth factor-1 axis abnormalities are essential risk factors for osteoporosis in pediatric patients with IBD.

AREAS COVERED

This article reviews the potential pathophysiological mechanisms contributing to osteoporosis in adult and pediatric patients with IBD and provides evidence for effective prevention and treatment, focusing on pediatric patients with IBD. A search was performed from PubMed and Web of Science inception to February 2023 to identify articles on IBD, osteoporosis, pediatric, and fracture risk.

EXPERT OPINION

A comprehensive treatment pattern based on individualized principles can be used to manage pediatric IBD-related osteoporosis.

Comparison of Fractures Among Older Adults Who Are Ambulatory vs Those Who Use Wheelchairs in Sweden

IMPORTANCE

Several diseases and conditions, such as cerebrovascular disease, arthritis, previous fractures, neurological diseases, or amputation, can result in severe immobility justifying wheelchair use for increased mobility. Immobility results in disuse osteoporosis and is considered a risk factor for fracture, although there are no large cohort studies that have investigated fracture risk in patients who use wheelchairs compared with an ambulatory control group.

OBJECTIVE

To investigate whether immobilized adults who used wheelchairs had a different risk of fracture and injurious falls compared with matched ambulatory controls.

DESIGN, SETTING, AND PARTICIPANTS

This retrospective cohort study compared patients who used wheelchairs and controls (propensity score matched 1:1 using 22 variables relating to anthropometrics, general condition, comorbidity, and fall and fracture risk), identified through a national database of adults 65 years or older who underwent a health evaluation (baseline) at Swedish health care facilities. Patients were followed up from January 1, 2007, to December 31, 2017, and data analysis was performed between June 1 and 30, 2022.

MAIN OUTCOMES AND MEASURES

Incident fracture, injurious falls without fracture, and deaths.

RESULTS

A total of 55 442 adults using wheelchairs were included in the analysis (mean [SD] age, 83.2 [8.3] years; 60.5% women). Those who used wheelchairs and the 55 442 matched controls were followed up for a median of 2.0 (IQR, 0.5-3.2) and 2.3 (IQR, 0.8-3.6) years, respectively. Patients who used wheelchairs had a lower risk of any fracture (hazard ratio [HR], 0.43 [95% CI, 0.41-0.44]), major osteoporotic fracture (HR, 0.32 [95% CI, 0.31-0.33]), and hip fracture (HR, 0.30 [95% CI, 0.28-0.32]) compared with the ambulatory controls, associations that were only marginally affected by multivariable (same as the matching variables) adjustment. The risk of fall injury was lower among those who used wheelchairs than among ambulatory controls (unadjusted HR for Cox proportional hazards models, 0.48 [95% CI, 0.47-0.50]) and remained highly similar after adjustments. Patients who used wheelchairs had a significantly increased risk of death (HR, 1.35 [95% CI, 1.33-1.36]) compared with controls. Association between wheelchair use and fracture outcomes and injurious falls, calculated using a Fine and Gray model with death as a competing risk, was similar to associations obtained using Cox proportional hazards regression for all fracture outcomes.

CONCLUSIONS AND RELEVANCE

In this retrospective cohort study of older adults, wheelchair use was associated with a lower risk of fracture than observed in ambulatory controls. These findings suggest that immobility associated with wheelchair use should not be considered a risk factor for fracture.

Bone circuitry and interorgan skeletal crosstalk

The past decade has seen significant advances in our understanding of skeletal homeostasis and the mechanisms that mediate the loss of bone integrity in disease. Recent breakthroughs have arisen mainly from identifying disease-causing mutations and modeling human bone disease in rodents, in essence, highlighting the integrative nature of skeletal physiology. It has become increasingly clear that bone cells, osteoblasts, osteoclasts, and osteocytes, communicate and regulate the fate of each other through RANK/RANKL/OPG, liver X receptors (LXRs), EphirinB2-EphB4 signaling, sphingolipids, and other membrane-associated proteins, such as semaphorins. Mounting evidence also showed that critical developmental pathways, namely, bone morphogenetic protein (BMP), NOTCH, and WNT, interact each other and play an important role in postnatal bone remodeling. The skeleton communicates not only with closely situated organs, such as bone marrow, muscle, and fat, but also with remote vital organs, such as the kidney, liver, and brain. The metabolic effect of bone-derived osteocalcin highlights a possible role of skeleton in energy homeostasis. Furthermore, studies using genetically modified rodent models disrupting the reciprocal relationship with tropic pituitary hormone and effector hormone have unraveled an independent role of pituitary hormone in skeletal remodeling beyond the role of regulating target endocrine glands. The cytokine-mediated skeletal actions and the evidence of local production of certain pituitary hormones by bone marrow-derived cells displays a unique endocrine-immune-skeletal connection. Here, we discuss recently elucidated mechanisms controlling the remodeling of bone, communication of bone cells with cells of other lineages, crosstalk between bone and vital organs, as well as opportunities for treating diseases of the skeleton.

The Effects of 8-Week Resistance and Endurance Trainings on Bone Strength Compared to Irisin Injection Protocol in Mice

Background

Osteoporosis is a prevalent elderly complication that is characterized by decreased bone mineral density and increased fracture risk because of dysregulation in bone mineralization and resorption. Physical activity can enhance bone strength by exerting mechanical forces and myokines. Irisin is a myokine that is increased following physical exercise and can affect bones. In this study, 8 weeks of resistance and endurance exercises are applied in mice compared to irisin injection to assess the contribution of the protocols and this myokine to bone strength.

Materials and Methods

Thirty-five male NMRI mice were separated into five groups; control, placebo, irisin injection, resistance exercise, and endurance exercise. 8-week of exercise protocols and irisin injection protocol (100 μg/kg/week) was applied. Plasma irisin concentration and bone strength were measured using enzyme-linked immunoassay and 3-point bending assay, respectively. Statistical analyses were done through one-way ANOVA and Tukey test, and P < 0.05 was considered the significant difference.

Results

Serum irisin concentration and bone strength in resistance exercise and irisin-injected groups were significantly higher than control and placebo groups (P < 0.0001). Serum irisin concentration, but not bone strength, of the endurance exercise group was also significantly higher than control and placebo groups (P < 0.0001) but lower than resistance and irisin-injected groups.

Conclusion

Resistance exercise and irisin injection, but not endurance exercise, are likely to be effective in increasing bone strength. There may be a threshold for plasma irisin level to affect bones which the applied protocols of irisin injection and resistance exercise but not endurance exercise can reach.

Bone and Lean Mass Loss and Cognitive Impairment for Healthy Elder Adults: Analysis of the Nutrition and Health Survey in Taiwan 2013-2016 and a Validation Study With Structural Equation Modeling

Purpose: Bone and lean mass loss and cognitive impairment are prevalent in elder adults and have been hypothesized to share a potential link. Methods: This nationwide cross-sectional study systemically sampled elder adults aged ≥65 years and conducted the door-to-door survey. The causal diagrams help to decide which covariates were included in the generalized linear mixed models (GLMMs). The structural equation modeling (SEM) was performed for the validation. Results: A total of 535 participants were enrolled and categorized into the normal (67.3%), mild cognitive impairment (18.3%), and dementia groups (14.4%). With increasing in the severity of cognitive impairment, the bone marrow density and lean mass consistently showed the trend of decreasing values. In the GLMMs, a significant association existed between the decrease of the bone mineral density (BMD) and the Mini-Mental State Examination (MMSE) (β = 5.819 scores per g/cm² decrease, p = 0.0305) with adjustment of the age, sex, and physical activity. The SEM models confirmed that the MMSE was significantly and directly predicted by the age (β = 0.1363, p = 0.0003) and BMD (β = 0.1251, p = 0.0006) independently and indirectly predicted by lean mass (β = 0.1138, p = 0.0003) through the bone density path. Conclusion: In conclusion, an independent association between bone loss and cognitive impairment was existed rather than the confounding effect and the decrease of lean mass indirectly contributed to cognitive impairment by influencing the bone density.

Calcium phosphate cements: Optimization toward biodegradability

Synthetic calcium phosphate (CaP) ceramics represent the most widely used biomaterials for bone regenerative treatments due to their biological performance that is characterized by bioactivity and osteoconductive properties. From a clinical perspective, injectable CaP cements (CPCs) are highly appealing, as CPCs can be applied using minimally invasive surgery and can be molded to optimally fill irregular bone defects. Such CPCs are prepared from a powder and a liquid component, which upon mixing form a paste that can be injected into a bone defect and hardens in situ within an appropriate clinical time window. However, a major drawback of CPCs is their poor degradability. Ideally, CPCs should degrade at a suitable pace to allow for concomitant new bone to form. To overcome this shortcoming, control over CPC degradation has been explored using multiple approaches that introduce macroporosity within CPCs. This strategy enables faster degradation of CPC by increasing the surface area available to interact with the biological surroundings, leading to accelerated new bone formation. For a comprehensive overview of the path to degradable CPCs, this review presents the experimental procedures followed for their development with specific emphasis on (bio)material properties and biological performance in pre-clinical bone defect models.

Serine/threonine phosphatases in osteoclastogenesis and bone resorption

Maintenance of optimal bone mass is controlled through the concerted functions of several cell types, including bone resorbing osteoclasts. Osteoclasts function to remove calcified tissue during developmental bone modeling, and degrade bone at sites of damage during bone remodeling. Changes to bone homeostasis can arise with alterations in osteoclastogenesis and/or catabolic activity that are not offset by anabolic activity; thus, factors that regulate osteoclastogenesis and bone resorption are of interest to further our understanding of basic bone biology, and as potential targets for therapeutic intervention. Several key cytokines, including RANKL and M-CSF, as well as co-stimulatory factors elicit kinase signaling cascades that promote osteoclastogenesis. These kinase cascades are offset by the action of protein phosphatases, including members of the serine/threonine phosphatase family. Here we review the functions of serine/threonine phosphatases and their control of osteoclast differentiation and function, while highlighting deficiencies in our understanding of this understudied class of proteins within the field.

Repurposing erectile dysfunction drugs tadalafil and vardenafil to increase bone mass

We report that two widely-used drugs for erectile dysfunction, tadalafil and vardenafil, trigger bone gain in mice through a combination of anabolic and antiresorptive actions on the skeleton. Both drugs were found to enhance osteoblastic bone formation in vivo using a unique gene footprint and to inhibit osteoclast formation. The target enzyme, phosphodiesterase 5A (PDE5A), was found to be expressed in mouse and human bone as well as in specific brain regions, namely the locus coeruleus, raphe pallidus, and paraventricular nucleus of the hypothalamus. Localization of PDE5A in sympathetic neurons was confirmed by coimmunolabeling with dopamine β-hydroxylase, as well as by retrograde bone-brain tracing using a sympathetic nerve-specific pseudorabies virus, PRV152. Both drugs elicited an antianabolic sympathetic imprint in osteoblasts, but with net bone gain. Unlike in humans, in whom vardenafil is more potent than tadalafil, the relative potencies were reversed with respect to their osteoprotective actions in mice. Structural modeling revealed a higher binding energy of tadalafil to mouse PDE5A compared with vardenafil, due to steric clashes of vardenafil with a single methionine residue at position 806 in mouse PDE5A. Collectively, our findings suggest that a balance between peripheral and central actions of PDE5A inhibitors on bone formation together with their antiresorptive actions specify the osteoprotective action of PDE5A blockade.

A systematic review and meta-analysis of bone loss in space travelers

Bone loss in space travelers is a major challenge for long-duration space exploration. To quantify microgravity-induced bone loss in humans, we performed a meta-analysis of studies systematically identified from searching Medline, Embase, Web of Science, BIOSIS, NASA Technical reports, and HathiTrust, with the last update in November 2019. From 25 articles selected to minimize the overlap between reported populations, we extracted post-flight bone density values for 148 individuals, and in-flight and post-flight biochemical bone marker values for 124 individuals. A percentage difference in bone density relative to pre-flight was positive in the skull, +2.2% [95% confidence interval: +1.1, +3.3]; neutral in the thorax/upper limbs, −0.7% [−1.3, −0.2]; and negative in the lumbar spine/pelvis, −6.2 [−6.7, −5.6], and lower limbs, −5.4% [−6.0, −4.9]. In the lower limb region, the rate of bone loss was −0.8% [−1.1, −0.5] per month. Bone resorption markers increased hyperbolically with a time to half-max of 11 days [9, 13] and plateaued at 113% [108, 117] above pre-flight levels. Bone formation markers remained unchanged during the first 30 days and increased thereafter at 7% [5, 10] per month. Upon landing, resorption markers decreased to pre-flight levels at an exponential rate that was faster after longer flights, while formation markers increased linearly at 84% [39, 129] per month for 3–5 months post-flight. Microgravity-induced bone changes depend on the skeletal-site position relative to the gravitational vector. Post-flight recovery depends on spaceflight duration and is limited to a short post-flight period during which bone formation exceeds resorption.

Use of Quantitative Computed Tomography to Assess for Clinically-relevant Skeletal Effects of Prolonged Spaceflight on Astronaut Hips

INTRODUCTION

In 2010, experts in osteoporosis and bone densitometry were convened by the Space Life Sciences Directorate at NASA Johnson Space Center to identify a skeletal outcome in astronauts after spaceflight that would require a clinical response to address fracture risk. After reviewing astronaut data, experts expressed concern over discordant patterns in loss and recovery of bone mineral density (BMD) after spaceflight as monitored by dual-energy X-ray absorptiometry (DXA) and quantitative computed tomography (QCT). The pilot study described herein demonstrates the use of QCT to evaluate absence of recovery in hip trabecular BMD by QCT as an indicator of a clinically actionable response.

METHODOLOGY

QCT and DXA scans of both hips were performed on 10 astronauts: once preflight and twice postflight about 1 wk and 1 yr after return. If trabecular BMD had not returned to baseline (i.e., within QCT measurement error) in 1 or both hips 1 yr after flight, then another QCT hip scan was obtained at 2 yr after flight.

RESULTS

Areal BMD by DXA recovered in 9 of 10 astronauts at 1 yr postflight while incomplete recovery of trabecular BMD by QCT was evident in 5 of 10 astronauts and persisted in 4 of the 5 astronauts 2 yr postflight.

CONCLUSION

As an adjunct to DXA, QCT is needed to detect changes to hip trabecular BMD after spaceflight and to confirm complete recovery. Incomplete recovery at 2 yr should trigger the need for further evaluation and possible intervention to mitigate premature fragility and fractures in astronauts following long-duration spaceflight.

Mechanistic complexities of bone loss in Alzheimer's disease: a review

Purpose/Aim: Alzheimer's disease (AD), the primary cause of dementia in the elderly, is one of the leading age-related neurodegenerative diseases worldwide. While AD is notorious for destroying memory and cognition, dementia patients also experience greater incidence of bone loss and skeletal fracture than age-matched neurotypical individuals, greatly impacting their quality of life. Despite the significance of this comorbidity, there is no solid understanding of the mechanisms driving early bone loss in AD. Here, we review studies that have evaluated many of the obvious risk factors shared by dementia and osteoporosis, and illuminate emerging work investigating covert pathophysiological mechanisms shared between the disorders that may have potential as new risk biomarkers or therapeutic targets in AD.Conclusions: Skeletal deficits emerge very early in clinical Alzheimer's progression, and cannot be explained by coincident factors such as aging, female sex, mobility status, falls, or genetics. While research in this area is still in its infancy, studies implicate several potential mechanisms in disrupting skeletal homeostasis that include direct effects of amyloid-beta pathology on bone cells, neurofibrillary tau-induced damage to neural centers regulating skeletal remodeling, and/or systemic Wnt/Beta-catenin signaling deficits. Data from an increasing number of studies substantiate a role for the newly discovered "exercise hormone" irisin and its protein precursor FNDC5 in bone loss and AD-associated neurodegeneration. We conclude that the current status of research on bone loss in AD is insufficient and merits critical attention because this work could uncover novel diagnostic and therapeutic opportunities desperately needed to address AD.

Failure in diagnosis and under-treatment of osteoporosis in elderly patients with fragility fractures

We evaluated whether osteoporosis is adequately managed and treated in patients suffering from fragility fractures. Factors that influenced osteoporosis diagnosis and treatment rates were also assessed. To this end, patients with the principal diagnosis of low-energy hip, vertebral, or distal radius fractures were recruited for the study. Collected data included risk factors for osteoporosis, history of previous fractures, known history of osteoporosis, and osteoporosis treatment at the time of admission. The patients' prefracture risk profile was also assessed to determine whether osteoporosis could have been identified prior to the index fracture. We identified 308 patients with fragility fractures, including 214 hip, 41 vertebral, and 53 distal radius fractures. Overall, 238 patients (77.3%) had at least one risk factor for osteoporosis. Eighty-eight patients (28.6%) had sustained ≥ 1 prior fragility fractures in the past. However, only 79 patients (25.6%) were aware that they had osteoporosis and even fewer (66 patients, 21.4%) had been receiving osteoporosis treatment preceding the current admission. Anti-osteoporotic agents were more commonly prescribed in patients 66-75 years old (p = 0.008), with a family history of osteoporosis (p = 0.009) or history of a prior fragility fracture (p = 0.012). The treatment rate was higher in women than men (p = 0.026) and in patients with vertebral or multiple prior fractures compared to patients with prior hip fractures. The current study provides evidence that individuals who experience fragility fractures are not adequately managed for osteoporosis. Only few of the historically known risk factors for osteoporosis were adequately recognized and associated with osteoporosis evaluation and treatment.

Changes in femoral bone mineral density after total knee arthroplasty: a systematic review and meta-analysis

BACKGROUND

Bone loss after total knee arthroplasty (TKA) may lead to periprosthetic fractures that are associated with significant costs (morbidity, economic, etc.) and pose a challenge to operative fixation. This meta-analysis quantifies the change in bone mineral density (BMD) of the distal femur after primary TKA.

METHODS

A systematic review of six databases was performed by two independent reviewers. Studies that reported bone density after knee arthroplasty were identified and inclusion/exclusion criteria was applied. Data were extracted and analyzed using the Comprehensive Meta-Analysis Software.

RESULTS

Fourteen studies were included in the analysis. The average decrease in BMD was 0.09 [0.05, 0.13], 0.14 [0.08, 0.20], 0.16 [0.10, 0.23], and 0.16 [0.12, 0.20] g/cm² at 3, 6, 12, and 24 months, respectively, corresponding to a 9.3%, 13.2%, 15.8%, and 15.4% BMD loss. A high degree of heterogeneity existed between the studies (I² > 90% at most time points).

CONCLUSION

In summary, there is a rapid and significant 15% decrease in BMD in the first 6 months after TKA that is sustained to 24 months. Better understanding regarding how perioperative optimization of bone health may affect BMD loss and the incidence of periprosthetic fracture is essential.

LEVEL OF EVIDENCE

Therapeutic Level II.

Clinical decision making and application of an active rehabilitation program for a person with the neuromuscular symptoms of Allgrove syndrome: a case report

BACKGROUND

Allgrove syndrome is a multisystem disorder first described in 1978 and is classically associated with esophageal achalasia, alacrima, and adrenal insufficiency. Allgrove syndrome is caused by homozygous and/or compound heterozygous mutations on Chromosome 12q13, designated as "AAA" (Achalasia, Addisonianism Alacrima). AAA encodes the protein ALADIN (Alacrima, Achalasia, aDrenal Insufficiency Neurologic disorder), a member of the nuclear porin family forming the nuclear pore complex.

PURPOSE

The purpose of this case report is to illustrate the clinical decision making and results following an active rehabilitation program on a patient with Allgrove syndrome. A detailed physical examination is also provided to contribute to the body of knowledge regarding the clinical presentation of this disorder.

CONCLUSION

It appears that in this case, this patient with Allgrove syndrome demonstrated a significant increase in endurance, balance, and a return to functional activities and participation following a 10-week physical therapy program consisting of task-oriented exercise, aerobic training, postural control exercises, and patient education. Due to the pathophysiology of Allgrove syndrome, these patients cannot be exercised in a traditional manner. It is prudent to perform these interventions with precautions including frequent monitoring of vitals, rest breaks in cool environments, close supervision during balance tasks, and submaximal exercise at a Borg scale of moderate intensity. C.A.'s overall improvements illustrate the potential value of complementing the medical management of persons with Allgrove syndrome with active exercise interventions.

Regulation of Skeletal Homeostasis

Landmark advances in skeletal biology have arisen mainly from the identification of disease-causing mutations and the advent of rapid and selective gene-targeting technologies to phenocopy human disease in mice. Here, we discuss work on newly identified mechanisms controlling the remodeling of bone, communication of bone cells with cells of other lineages, and crosstalk between bone and vital organs as these relate to the therapeutic targeting of the skeleton.

FSH, Bone Mass, Body Fat, and Biological Aging

The Study of Women's Health Across the Nation has taught us that impending ovarian failure during late perimenopause is associated with a sharp rise in serum FSH, which coincides with the most rapid rate of bone loss and the onset of visceral adiposity. At this time in a woman's life, serum estrogen levels are largely unaltered, so the hypothesis that hypoestrogenemia is the sole cause of bone loss and visceral obesity does not offer a full explanation. An alternative explanation, arising from animal models and human data, is that both physiologic aberrations, obesity and osteoporosis, arise at least in part from rising FSH levels. Here, we discuss recent findings on the mechanism through which FSH exerts biological actions on bone and fat and review clinical data that support a role for FSH in causing osteoporosis and obesity. We will also provide a conceptual framework for using a single anti-FSH agent to prevent and treat both osteoporosis and obesity in women across the menopausal transition.

Emerging concepts in the epidemiology, pathophysiology, and clinical care of osteoporosis across the menopausal transition

Bone loss in women accelerates during perimenopause, and continues into old age. To-date, there has been little progress made in stratifying for fracture risk in premenopausal and early postmenopausal women. Epidemiologic data suggests that changes in serum FSH could predict decrements in bone mass during peri- and postmenopause. In bone, FSH stimulates osteoclast formation by releasing osteoclastogenic cytokines. Here, we address the evidence for bone loss across the menopausal transition, discuss strategies for detection and treatment of early postmenopausal osteoporosis, and describe the role FSH plays in physiology and likely in pathophysiology of early postmenopausal bone loss.

A juvenile with compromised osteogenesis provides insights into past hunter-gatherer lives

The Late Archaic in northeastern North America (4500-2800 B.P.) pre-dates reliance on pottery and domesticated plants. It is thought to reflect a highly mobile, seasonal migratory foraging/hunting regimen. A juvenile skeleton with pervasive bone wasting and fragile jaws from the Hind Site (AdHk-1), ca. 3000 B.P., southwestern Ontario, provides evidence of the social context of her family group, including aspects of mobility and food management. The well-preserved bones and teeth are considered in bioarchaeological context. Radiographic, osteometric and cross-sectional geometric approaches to assessing musculoskeletal function are presented, plus differential diagnosis of the bone wasting condition. All bones of the probable female (aged approx. 16yr) show stunting and wasting. Wedged lower vertebral bodies, porous trabeculae, undeveloped bicondylar angles (femur) and abnormally low cortical long bone mass are consistent with chronically reduced ambulation. Few teeth remain in the dramatically resorbed alveoli; slight tooth wear and substantial calculus suggest a modified (soft) diet. Osteogenesis imperfecta type IV is the most probable etiology. The extended survival of this juvenile who may never have walked reflects collective care. The case provides evidence of a past lifeway that appears to have been organized around logistic mobility, including occupational stability and food storage.

Irisin in metabolic diseases

INTRODUCTION

Irisin is a myokine/adipokine induced by the exercise in mice and humans, which is proposed to induce "browning" of white adipose tissue, its primary target, thus increasing thermogenesis and energy expenditure. Since its identification, irisin has been linked to favorable effects on metabolic diseases, including obesity, type 2 diabetes mellitus (T2DM), lipid metabolism and cardiovascular disease (CVD), nonalcoholic fatty liver disease (NAFLD), polycystic ovary syndrome (PCOS), and metabolic bone diseases. Generally, despite the promising profile of irisin in rodents, its effects on human are less recognized.

REVIEW

Most, but not all studies show a positive association between irisin and indices of adiposity. In T2DM, NAFLD, and CVD, most observational studies reported lower irisin levels in patients than controls. Regarding metabolic bone diseases, irisin is positively associated with bone mineral density and strength in athletes, and inversely associated with osteoporotic fractures in postmenopausal osteoporosis. In PCOS, data remain largely conflicting. Irisin does not seem to be further reduced when two metabolic diseases, e.g., T2DM and NAFLD, or obesity and NAFLD exist though more data are needed. Furthermore, it seems that diverse confounders may have affected the results of different clinical studies.

CONCLUSION

Irisin remains an appealing molecule from a pathophysiological point of view and an appealing therapeutic target for metabolic diseases, albeit much research is still needed.

Low serum concentrations of Irisin are associated with increased risk of hip fracture in Chinese older women

OBJECTIVE

Irisin derived from muscle in response to exercise may be the molecular entity responsible for muscle wasting-osteoporosis connectivity in the elderly. The objective of the study was to determine whether serum Irisin (sIrisin) provides information on hip fracture prediction which were independent of bone mineral density (BMD) and the fracture risk assessment tool (FRAX) algorithm.

METHODS

This study enrolled 160 older women (ages, 70-90y) with minimal trauma hip fractures (MTHFs) and 160 age-matched women without fracture serving as controls. Clinical features, BMD and bone turnover markers including sIrisin levels were measured after fracture within 2 days as baseline.

RESULTS

sIrisin levels were significantly lower (361.5±140.0ng/mL vs 478.5±159.6ng/mL, P<0.001) in cases than controls. After multivariate analysis, sIrisin remained as an independent variable of BMD, which explained 17.8% of femoral neck BMD and 22.5% of lumbar spine BMD, respectively. The odds ratio (OR) of MTHFs comparing the lowest (<320.1ng/mL) to highest (>524.5ng/mL) quartiles was 1.95 (95% CI 1.23-3.79, P<0.05) for sIrisin. Adjustment for age, body mass index, time since menopause and exercise ≥30min/day yielded similar results, and BMD of femoral neck also did not change these associations. Taking FRAX score into account attenuated the association somewhat: OR of hip fracture was 1.81 (95% CI 1.26-3.49, P<0.05) in first versus fourth quartile of sIrisin. There was a negative gradient of risk by decreasing quartile in sIrisin.

CONCLUSIONS

Low concentrations of sIrisin in older women were independently associated with increased risk of hip fractures when adjusted for BMD or FRAX score.

A Prospective Observational Study on Effect of Short-Term Periodic Steroid Premedication on Bone Metabolism in Gastrointestinal Cancer (ESPRESSO-01)

BACKGROUND

A multicenter prospective observational study evaluated the effect of gastrointestinal cancer chemotherapy with short-term periodic steroid premedication on bone metabolism.

PATIENTS AND METHODS

Seventy-four patients undergoing chemotherapy for gastrointestinal cancer were studied. The primary endpoints were changes in bone mineral densities (BMDs) and metabolic bone turnover 16 weeks after initiation of chemotherapy. BMDs, measured by dual-energy x-ray absorptiometry, and serum cross-linked N-telopeptides of type I collagen (sNTX), and bone alkaline phosphatase (sBAP) were assessed for evaluation of bone resorption and formation, respectively.

RESULTS

In 74.3% (55/74) of the patients, BMDs were significantly reduced at 16 weeks relative to baseline. The percent changes of BMD were -1.89% (95% confidence interval [CI], -2.67% to -1.11%: p < .0001) in the lumbar spine, -2.24% (95% CI, -3.59% to -0.89%: p = .002) in the total hip, and -2.05% (95% CI, -3.11% to -0.99%: p < .0001) in the femoral neck. Although there was no significant difference in sNTX levels during 16 weeks (p = .136), there was a significant increase in sBAP levels (p = .010). Decreased BMD was significantly linked to number of chemotherapy cycles (p = .02). There were no significant correlations between changes in BMDs and the primary site of malignancy, chemotherapy regimens, total cumulative steroid dose, steroid dose intensity, and additive steroid usage.

CONCLUSION

Gastrointestinal cancer chemotherapy with periodic glucocorticoid premedication was associated with reduced BMD and increased sBAP levels, which were linked to number of chemotherapy cycles but independent of primary site, chemotherapy regimen, duration, and additive steroid usage. The Oncologist 2017;22:592-600 IMPLICATIONS FOR PRACTICE: Bone health and the management of treatment-related bone loss are important for cancer care. The present study showed that a significant decrease in bone mineral density (BMD) and an increase in serum bone alkaline phosphatase levels occurred in gastrointestinal cancer patients receiving chemotherapy, which were linked to number of chemotherapy cycles but were independent of primary site, chemotherapy regimen, total steroid dose, and steroid dose intensity. Surprisingly, it seems that the decreasing BMD levels after only 16 weeks of chemotherapy for gastrointestinal cancer were comparable to that of 12-month adjuvant aromatase inhibitor therapy for early-stage breast cancer patients.

Metabolic Bone Disease in the Post-transplant Population: Preventative and Therapeutic Measures

Post-transplant bone disease contributes significantly to patients' morbidity and mortality after transplantation and has an impact on their quality of life. This article discusses the major contributors to mechanisms causing bone loss, highlighting the role of preexisting disease in both kidney and liver failure and contributions from glucocorticoids and calcineurin inhibitors. Suggested monitoring and investigations are reviewed as well as treatment as far as the current literature supports, emphasizing the difference between kidney and liver recipients.

HOW DO BONE CELLS SENSE MECHANICAL LOADING?

Influenced by gravidity, bone tissue experiences stronger or lighter deformation according to the strength of the activities of daily life. Activities resulting in impact are particularly known to stimulate osteogenesis, thus reducing bone mass loss. Knowing how bone cells recognize the mechanical deformation imposed to the bone and trigger a series of biochemical chain reactions is of crucial importance for the development of therapeutic and preventive practices in orthopaedic activity. There is still a long way to run until we can understand the whole process, but current knowledge has shown a strong progression, with researches being conducted focused on therapies. For a mechanical sign to be transformed into a biological one (mechanotransduction), it must be amplified at cell level by the histological structure of bone tissue, producing tensions in cell membrane proteins (integrins) and changing their spatial structure. Such change activates bindings between these and the cytoskeleton, producing focal adhesions, where cytoplasmatic proteins are recruited to enable easier biochemical reactions. Focal adhesion kinase (FAK) is the most important one being self-activated when its structure is changed by integrins. Activated FAK triggers a cascade of reactions, resulting in the activation of ERK-1/2 and Akt, which are proteins that, together with FAK, regulate the production of bone mass. Osteocytes are believed to be the mechanosensor cells of the bone and to transmit the mechanical deformation to osteoblasts and osteoclasts. Ionic channels and gap junctions are considered as intercellular communication means for biochemical transmission of a mechanical stimulus. These events occur continuously on bone tissue and regulate bone remodeling.

The myokine irisin increases cortical bone mass

It is unclear how physical activity stimulates new bone synthesis. We explored whether irisin, a newly discovered myokine released upon physical activity, displays anabolic actions on the skeleton. Young male mice were injected with vehicle or recombinant irisin (r-irisin) at a low cumulative weekly dose of 100 µg kg(-1). We observed significant increases in cortical bone mass and strength, notably in cortical tissue mineral density, periosteal circumference, polar moment of inertia, and bending strength. This anabolic action was mediated primarily through the stimulation of bone formation, but with parallel notable reductions in osteoclast numbers. The trabecular compartment of the same bones was spared, as were vertebrae from the same mice. Higher irisin doses (3,500 µg kg(-1) per week) cause browning of adipose tissue; this was not seen with low-dose r-irisin. Expectedly, low-dose r-irisin modulated the skeletal genes, Opn and Sost, but not Ucp1 or Pparγ expression in white adipose tissue. In bone marrow stromal cell cultures, r-irisin rapidly phosphorylated Erk, and up-regulated Atf4, Runx2, Osx, Lrp5, β-catenin, Alp, and Col1a1; this is consistent with a direct receptor-mediated action to stimulate osteogenesis. We also noted that, although the irisin precursor Fndc5 was expressed abundantly in skeletal muscle, other sites, such as bone and brain, also expressed Fndc5, albeit at low levels. Furthermore, muscle fibers from r-irisin-injected mice displayed enhanced Fndc5 positivity, and irisin induced Fdnc5 mRNA expression in cultured myoblasts. Our data therefore highlight a previously unknown action of the myokine irisin, which may be the molecular entity responsible for muscle-bone connectivity.

Association of bone loss with the upregulation of survival-related genes and concomitant downregulation of Mammalian target of rapamycin and osteoblast differentiation-related genes in the peripheral blood of late postmenopausal osteoporotic women

We aimed to identify bone related markers in the peripheral blood of osteoporotic (OP) patients that pointed toward molecular mechanisms underlying late postmenopausal bone loss. Whole blood from 22 late postmenopausal OP patients and 26 healthy subjects was examined. Bone mineral density (BMD) was measured by DXA. Protein levels of p70-S6K, p21, MMP-9, TGFβ1, and caspase-3 were quantified by ELISA. Gene expression was measured using real-time RT-PCR. OP registered by low BMD indices in late postmenopausal patients was associated with a significant upregulation of autophagy protein ULK1, cyclin-dependent kinase inhibitor p21, and metalloproteinase MMP-9 gene expression in the blood compared to the healthy controls and in a significant downregulation of mTOR (mammalian target of rapamycin), RUNX2, and ALPL gene expression, while expression of cathepsin K, caspase-3, transforming growth factor (TGF) β1, interleukin- (IL-) 1β, and tumor necrosis factor α (TNFα) was not significantly affected. We also observed a positive correlation between TGFβ1 and RUNX2 expression and BMD at femoral sites in these patients. Therefore, bone loss in late postmenopausal OP patients is associated with a significant upregulation of survival-related genes (ULK1 and p21) and MMP-9, as well as the downregulation of mTOR and osteoblast differentiation-related genes (RUNX2 and ALPL) in the peripheral blood compared to the healthy controls.

Secondary osteoporosis: pathophysiology & diagnosis

Osteoporosis is a skeletal disease characterized by decreased bone mass and microarchitectural changes in bone tissue that increase the susceptibility to fracture. Secondary osteoporosis is loosely defined as low bone mineral density or increased risk of fragility fracture caused by any factor other than aging or postmenopausal status. The purpose of this review is to discuss the current understanding of the pathophysiology and contribution to fracture risk of many of the more common causes of secondary osteoporosis, as well as diagnostic considerations, outlined by organ system. While not comprehensive, included are a wide array of diseases, conditions, and medications that have been associated with bone loss and susceptibility to fractures. The hope is to highlight the importance to the general clinician of screening for and treating the osteoporosis in these patients, so to limit the resultant increased morbidity associated with fractures.

The bone and fat connection in inflammatory bowel diseases

Osteopenia and osteoporosis are common manifestations in inflammatory bowel diseases (IBD) but the pathogenetic mechanism of bone loss in IBD is only partially understood. There is evidence that fat mass is an important determinant of the bone mineral density and adipose-derived factors seem to play an important role for the association between fat mass and bone mass. The association between adiposity and low bone density is rather poorly studied in IBD, but emerging data on adipokines in IBD in relation to osteoporosis provide a novel pathophysiological concept that may shed light on the etiology of bone loss in IBD. It could be suggested that adipokines interfere in bone metabolism by altering the sensitive balance between osteoblasts and osteoclasts although further studies in this setting are needed.

Glucocorticoid-associated osteoporosis in chronic inflammatory diseases: epidemiology, mechanisms, diagnosis, and treatment

Children with chronic illnesses such as Juvenile Idiopathic Arthritis and Crohn's disease, particularly when taking glucocorticoids, are at significant risk for bone fragility. Furthermore, when childhood illness interferes with achieving normal peak bone mass, life-long fracture risk is increased. Osteopenia and osteoporosis, which is increasingly recognized in pediatric chronic disease, likely results from numerous disease- and treatment-related factors, including glucocorticoid exposure. Diagnosing osteoporosis in childhood is complicated by the limitations of current noninvasive techniques such as DXA, which despite its limitations remains the gold standard. The risk:benefit ratio of treatment is confounded by the potential for spontaneous restitution of bone mass deficits and reshaping of previously fractured vertebral bodies. Bisphosphonates have been used to treat secondary osteoporosis in children, but limited experience and potential long-term toxicity warrant caution in routine use. This article reviews the factors that influence loss of normal bone strength and evidence for effective treatments, in particular in patients with gastrointestinal and rheumatologic disorders who are receiving chronic glucocorticoid therapy.

Multiple sclerosis and fracture

Multiple sclerosis (MS) is a chronic, inflammatory, demyelinating central nervous system disease with time and space disseminated lesions that usually occurs in young adults, typically aged between 20 and 45 years. Recently, researches have indicated MS may be associated with increased risk of fracture and osteoporosis. In this review, we aim to identify the fracture risk in MS patients, also address the pathogenic mechanisms and interventions of fracture in those patients.

Minireview: The link between fat and bone: does mass beget mass?

Osteoporosis is less common in individuals with high fat mass. This putative osteoprotection is likely an adaptive mechanism that allows obese individuals to better carry their increased body mass. Recent studies have focused on hormones that link fat to bone. Adipokines, such as leptin, modulate bone cells through both direct and indirect actions, whereas molecules activating peroxisome proliferator-activated receptor γ drive mesenchymal stem cell differentiation towards adipocytes away from the osteoblastic lineage. There is emerging evidence that bone-derived osteocalcin regulates insulin release and insulin sensitivity and, hence, might indirectly affect fat mass. Despite these molecular connections between fat and bone, animal and human studies call into question a primary role for body fat in determining bone mass. Mice devoid of fat do not have a skeletal phenotype, and in humans, the observed correlations between bone and body mass are not just due to adipose tissue. An improved understanding of the integrative physiology at the fat-bone interface should allow us develop therapies for both osteoporosis and obesity.

Adaptive evolution of loci covarying with the human African Pygmy phenotype

African Pygmies are hunter-gatherer populations from the equatorial rainforest that present the lowest height averages among humans. The biological basis and the putative adaptive role of the short stature of Pygmy populations has been one of the most intriguing topics for human biologists in the last century, which still remains elusive. Worldwide convergent evolution of the Pygmy size suggests the presence of strong selective pressures on the phenotype. We developed a novel approach to survey the genetic architecture of phenotypes and applied it to study the genomic covariation between allele frequencies and height measurements among Pygmy and non-Pygmy populations. Among the regions that were most associated with the phenotype, we identified a significant excess of genes with pivotal roles in bone homeostasis, such as PPPT3B and the height associated SUPT3H-RUNX2. We hypothesize that skeletal remodeling could be a key biological process underlying the Pygmy phenotype. In addition, we showed that these regions have most likely evolved under positive selection. These results constitute the first genetic hint of adaptive evolution in the African Pygmy phenotype, which is consistent with the independent emergence of the Pygmy height in other continents with similar environments.

Strontium ranelate prevents bone loss in a rat model of localized muscle paralysis

Twenty-one 3.5-month-old female Sprague-Dawley rats were randomly assigned to three groups: BTX group, in which each rat received a single intramuscular injection of 2 U of Clostridium botulinum toxin (BTX) in the quadriceps femoris muscle of the right hind limb; BTX + SR group, in which each rat received a BTX injection and a dose of strontium ranelate (dose level of 625 mg/kg/day); and the control group. All the rats were killed at 9 weeks post-treatment. It was showed that BTX-induced rats a rapid loss of body weight in the first 3 weeks, after which their body weight showed a slow increase similar to that observed in the control rats. The net body weight loss was mainly attributed to muscle atrophy. BTX caused remarkable bone degradation in either the trabecular bone or the cortical bone of the disuse femur. The deteriorations in the bone mass and bone microstructure were locally limited and could be prevented by strontium ranelate treatment. Biomechanical analysis showed that strontium ranelate treatment improved the mechanical performance of the tibia in BTX-treated rats. It was showed that a clinical-corresponding dose of strontium ranelate could prevent bone loss in long-term immobilized rats.

[Secondary osteoporosis: pathogenesis, types, diagnostics and therapy]

Due to increasing knowledge on pathogenetic factors causing osteoporosis and increasingly more detailed investigations, the diagnosis of secondary osteoporosis is being made increasingly more often. A rational search for the underlying disease or the bone-damaging medication is indicated particularly in adolescents, premenopausal women, men and postmenopausal women with rapidly decreasing bone tissue. The early detection of the causative disease in the preclinical stage of osteoporosis and the current therapeutic options allow not only normalization of the bone structure and the risk of fracture but also targeted therapy of the cause of the osteoporosis. The focal point in the diagnostics of secondary osteoporosis is still dual energy X-ray absorptiometry (DXA) measurement together with the manifold imaging procedures in radiology and additional clinical, laboratory chemical and bioptic findings.

Bone health in patients with multiple sclerosis

Multiple sclerosis (MS) is a gait disorder characterized by acute episodes of neurological defects leading to progressive disability. Patients with MS have multiple risk factors for osteoporotic fractures, such as progressive immobilization, long-term glucocorticoids (GCs) treatment or vitamin D deficiency. The duration of motor disability appears to be a major contributor to the reduction of bone strength. The long term immobilization causes a marked imbalance between bone formation and resorption with depressed bone formation and a marked disruption of mechanosensory network of tightly connected osteocytes due to increase of osteocyte apoptosis. Patients with higher level of disability have also higher risk of falls that combined with a bone loss increases the frequency of bone fractures. There are currently no recommendations how to best prevent and treat osteoporosis in patients with MS. However, devastating effect of immobilization on the skeleton in patients with MS underscores the importance of adequate mechanical stimuli for maintaining the bone structure and its mechanical competence. The physical as well as pharmacological interventions which can counteract the bone remodeling imbalance, particularly osteocyte apoptosis, will be promising for prevention and treatment of osteoporosis in patients with MS.

Change in bone mineral density at one year following glucocorticoid withdrawal in kidney transplant recipients

Glucocorticoid (GC) therapy induces deleterious effects on the skeleton in kidney transplantation but studies of GC discontinuation in this population are limited. This study evaluated changes in areal bone mineral density (BMD) with GC withdrawal. Subjects were enrolled one yr after renal transplantation and randomized to continue or stop prednisone; all subjects continued cyclosporine and mycophenolate mofetil. BMD measured by dual-energy X-ray absorptiometry was performed at enrollment and repeated at one yr and values were standardized. Mean ± standard deviation of annualized change in standardized BMD between GC withdrawal vs. continuation group at the lumbar spine was +4.7% ± 5.5 vs. +0.9% ± 5.3 (p = 0.0014); total hip +2.4% ± 4.2 vs. -0.4% ± 4.2 (p = 0.013), and femoral neck +2.1% ± 4.6 vs. +1.0% ± 6.0 (p = 0.37). There was no confounding by prednisone dose prior to enrollment, change in creatinine clearance, weight, or use of bone-active medications following study entry. Multivariate analysis determined that the change in BMD was positively associated with baseline alkaline phosphatase and creatinine clearance and negatively associated with baseline BMD. BMD improves with GC withdrawal after renal transplantation, and this gain in BMD is dependent on the baseline bone turnover, renal function, and BMD.

Bone loss or lost bone: rationale and recommendations for the diagnosis and treatment of early postmenopausal bone loss

Recent reports suggest that bone loss begins during late perimenopause at a dramatic rate, even before estrogen levels plummet. During the ensuing 5 years, there is evidence of the beginnings of microarchitectural deterioration, which impacts bone strength and ultimately enhances its propensity to fracture. The diagnosis of osteoporosis based on T-scores alone, or through stratification for a high fracture risk by FRAX, excludes these women who are rapidly losing bone. Because all antiosteoporosis therapies, in particular bisphosphonates, reduce bone loss, we propose aggressive, likely short-term therapy with a goal to reduce bone loss, stabilize bone density, and prevent microarchitectural deterioration.

The developmental basis of skeletal cell differentiation and the molecular basis of major skeletal defects

Vertebrate skeletal differentiation retains elements from simpler phyla, and reflects the differentiation of supporting tissues programmed by primary embryonic development. This developmental scheme is driven by homeotic genes expressed in sequence, with subdivision of skeletal primordia driven by a combination of seven transmembrane-pass receptors responding to Wnt-family signals, and by bone morphogenetic family signals that define borders of individual bones. In sea-dwelling vertebrates, an essentially complete form of the skeleton adapted by the land-living vertebrates develops in cartilage, based on type II collagen and hydrophilic proteoglycans. In bony fishes, this skeleton is mineralized to form a solid bony skeleton. In the land-living vertebrates, most of the skeleton is replaced by an advanced vascular mineralized skeleton based on type I collagen, which reduces skeletal mass while facilitating use of skeletal mineral for metabolic homeostasis. Regulation of the mammalian skeleton, in this context, reflects practical adaptations to the needs for life on land that are related to ancestral developmental signals. This regulation includes central nervous system regulation that integrates bone turnover with overall metabolism. Recent work on skeletal development, in addition, demonstrates molecular mechanisms that cause developmental bone diseases.

Transforming growth factor-beta prevents osteoblast apoptosis induced by skeletal unloading via PI3K/Akt, Bcl-2, and phospho-Bad signaling

Loss of mechanical loading induces rapid bone loss resulting from reduced osteoblastogenesis and decreased bone formation. The signaling mechanisms involved in this deleterious effect on skeletal metabolism remain poorly understood. We have previously shown that hindlimb suspension in rats increases osteoblast apoptosis associated with decreased phosphatidylinositol 3-kinase (PI3K) signaling. In this study, we investigated whether transforming growth factor (TGF)-beta2 may prevent the altered signaling and osteoblast apoptosis induced by skeletal unloading in vivo. Hindlimb suspension-induced decreased bone volume was associated with reduced alpha(5)beta(1)-integrin protein levels and PI3K/Akt signaling in unloaded bone. Continuous administration of TGF-beta2 using osmotic minipumps prevented the decreased alpha(5)beta(1)-integrin expression and the reduced PI3K/Akt signaling in unloaded bone, resulting in the prevention of osteoblast apoptosis. We also show that TGF-beta2 prevented the decreased Bcl-2 levels induced by unloading, which suggests that TGF-beta2 targets Bcl-2 via PI3K/Akt to prevent osteoblast apoptosis in unloaded bone. Furthermore, we show that TGF-beta2 prevented the decrease in phosphorylated Bad, the inactive form of the proapoptotic protein Bad, induced by unloading. These results identify a protective role for TGF-beta2 in osteoblast apoptosis induced by mechanical unloading via the alpha(5)beta(1)/PI3K/Akt signaling cascade and downstream Bcl-2 and phospho-Bad survival proteins. We thus propose a novel role for TGF-beta2 in protection from unloading-induced apoptosis in vivo.

Sex-specific association of the glucocorticoid receptor gene with extreme BMD

To study the role of the GR gene on BMD regulation in the Chinese, a sex-specific association study was performed. The results indicated that GR variation contributed to the extreme BMD variation in the Chinese.

INTRODUCTION

The glucocorticoid (GC) receptor (GR) gene is an important candidate gene for BMD regulation in GC-induced osteoporosis (GIO). However, no study has explored the genetic effects of the GR gene on BMD variation in the Chinese population.

MATERIALS AND METHODS

Our sample consisted of 800 unrelated subjects (400 women and 400 men) with extreme age-adjusted hip BMD Z-scores selected from a population composed of 1988 normal adult Chinese Han. Four single nucleotide polymorphisms (SNPs) in the GR gene were genotyped. Both single SNP and haplotype association analyses were conducted.

RESULTS

SNP rs1866388 (p(c) = 0.028) was found to be significantly associated with extreme BMD only in men. In both sexes, haplotypes involving rs1866388 and rs2918419 were found to have different frequency distributions in extremely low and high BMD groups (p(p) = 0.024, 0.001, and 0.002 in women and 0.002, 0.003, and 0.003 in men for window sizes of two, three, and four SNPs, respectively). Most shared haplotypes showed opposite effects between women and men.

CONCLUSIONS

For the first time, our study suggested the possible role of the GR gene on BMD regulation and sex specificity in the association of GR with extreme BMD in the Chinese.

Calcium and bone metabolism pre- and post-kidney transplantation

Chronic kidney disease (CKD) is associated with significant disturbances in bone and mineral metabolism, the manifestations of which are heterogeneous in their expression and clinical impact. Over the last 2 decades, advances in the management of CKD and improved outcomes of kidney transplantation have led to the emergence of post-transplantation bone disease as a serious cause of morbidity in long-term survivors. The management of post-kidney transplantation bone disease represents a difficult challenge because of its complex pathophysiology and the paucity of clinical data on effective therapies. The optimal management of disturbances of bone and mineral metabolism before kidney transplantation forms the cornerstone of their successful management after transplantation. Therapeutic strategies to effectively and safely decrease skeletal morbidity after kidney transplantation are not yet clearly established.

Skeletal remodeling in health and disease

The use of genetically manipulated mouse models, gene and protein discovery and the cataloguing of genetic mutations have each allowed us to obtain new insights into skeletal morphogenesis and remodeling. These techniques have made it possible to identify molecules that are obligatory for specific cellular functions, and to exploit these molecules for therapeutic purposes. New insights into the pathophysiology of diseases have also enabled us to understand molecular defects in a way that was not possible a decade ago. This review summarizes our current understanding of the carefully orchestrated cross-talk between cells of the bone marrow and between bone cells and the brain through which bone is constantly remodeled during adult life. It also highlights molecular aberrations that cause bone cells to become dysfunctional, as well as therapeutic options and opportunities to counteract skeletal loss.

Upregulation of PTH receptor mRNA expression by dexamethasone in UMR-106 osteoblast-like cells

OBJECTIVES

Glucocorticoids influence receptor interactions of the parathyroid hormone (PTH) that are crucial for osteoblast function. As mechanisms linking receptor mRNA with glucocorticoids are incompletely understood, we investigated regulation of PTH receptor (PTH1R) mRNA expression in rat osteoblast-like UMR-106 cells by using dexamethasone (Dex), a synthetic glucocorticoid.

MATERIALS AND METHODS

UMR-106 cells were exposed to 10(-8) to 10(-5) M Dex, while some cells were also exposed to a transcriptional inhibitor (DRB) for 24 h with or without Dex. PTH-stimulated cyclicAMP activities were measured by an enzyme-linked immunosorbent assay. PTH1R mRNA was determined by Northern analysis. Transcriptional activities were measured as heretogeneous nuclear PTH1R RNA and also as luciferase activity in constructs, including the PTH1R gene promoter.

RESULTS

Dexamethasone dose-dependently increased PTH-stimulated adenylyl cyclase activity at 72 h. Dex markedly increased PTH1R mRNA accumulation, but did not change transcriptional activity. PTH1R mRNA stability was significantly increased by Dex in transcriptionally arrested cells.

CONCLUSION

In osteoblast-like cells, Dex induced upregulation of PTH1R mRNA followed by increased functional PTH receptor expression. This was caused by posttranscriptional mechanisms increasing mRNA stability.