Muscle-bone interactions: From experimental models to the clinic? A critical update

Association between Geriatric Nutrition Risk Index and Skeletal Muscle Mass Index with Bone Mineral Density in Post-Menopausal Women Who Have Undergone Total Thyroidectomy

Background: Osteoporosis is highly prevalent in postmenopausal women and may result in fractures and disabilities. Total thyroidectomy has also been associated with loss of bone mass. The aim of this cross-sectional study was to evaluate associations among nutritional status, skeletal muscle index and markers of bone turnover to bone mineral density in postmenopausal women who had undergone total thyroidectomy. Methods: Fifty postmenopausal women who had undergone total thyroidectomy were included. Body composition was measured using dual-energy X-ray absorptiometry (DXA). The Geriatric Nutritional Risk Index (GNRI) was calculated using baseline body weight and serum albumin level. Skeletal muscle mass index was calculated as the appendicular skeletal muscle mass (ASM) divided by the height squared and assessed using DXA. Results. Multivariate stepwise linear regression analysis showed that a low GNRI was significantly associated with low lumbar spine bone mineral density (BMD) and T-score, and that a low ASM/height² was significantly associated with low femoral neck BMD and T-score. A low vitamin D level was significantly associated with low femoral neck BMD and T-score and low total hip BMD and T-score. A high bone alkaline phosphatase (ALP) level was significantly associated with low femoral neck T-score and low total hip BMD and T-score. A low insulin-like growth factor-1 (IGF-1) was significantly associated with low total hip BMD and T-score. Conclusion: In the postmenopausal women who had undergone total thyroidectomy in this study, BMD was positively associated with GNRI, skeletal muscle mass index, and levels of vitamin D and serum IGF-1, and inversely associated with bone ALP level. Nutritional status, skeletal muscle mass index and bone turnover biomarkers can be used to early identify patients with a high risk of osteoporosis in this high-risk group.

Postmenopausal osteoporosis is a musculoskeletal disease with a common genetic trait which responds to strength training: a translational intervention study

Background:

Clinical evidence suggests that body muscle mass is positively associated with bone mass, of significance for the elderly population at risk of osteoporosis (OP). Furthermore, muscle and bone interact mechanically and functionally, via local interactions as well as remotely via secreted components. Thus, it was of interest to compare muscle transcriptomes in postmenopausal OP and healthy women, and study effects of strength training on the muscle transcriptome, muscle stress proteins and bone mineral density (BMD).

Methods:

Skeletal muscle histological and genetic properties were compared in postmenopausal healthy (n = 18) and OP (n = 17) women before and after heavy-load strength training for 13–15 weeks. The cohorts were of similar age and body mass index without interfering diseases, medication or difference in lifestyle factors. Muscle biopsies obtained before and after intervention were studied histologically, and stress proteins and transcriptomes analyzed.

Results:

The OP women showed distinct muscle transcription profiles when compared with healthy women and had higher levels of the stress proteins HSP70 and α-β-crystalline. A set of 12 muscle transcripts, including ACSS3, FZD4, GNAI1 and IGF1, were differentially expressed before and after intervention (false discovery rate ⩽0.10, p ⩽0.001), and their corresponding bone transcripts were associated with BMD. Experimental data underline and describe the functionality of these genes in bone biology. OP women had 8% (p <0.01) higher proportion of type I fibres, but muscle fibre cross-sectional area did not differ. Muscle strength increased in both groups (p <0.01).

Conclusions:

Postmenopausal healthy and OP women have distinct muscle transcriptomes [messenger ribonucleic acids (mRNAs) and microRNAs] that are modulated by strength training, translating into key protein alterations and muscle fibre changes. The function of common skeletal muscle and bone genes in postmenopausal OP is suggestive of a shared disease trait.

High and low-load resistance training produce similar effects on bone mineral density of middle-aged and older people: A systematic review with meta-analysis of randomized clinical trials

PURPOSE

To compare the effects of high-load (≥ 70 of 1RM) and low-load (< 70 of 1RM) resistance training (RT) on femoral neck and lumbar spine bone mineral density (BMD) in middle-aged and older people.

DESIGN

Systematic review with meta-analysis.

DATA SOURCE

English language searches of the electronic databases PubMed/Medline, Scopus and Web of Science.

INCLUSION CRITERIA

(i) older or middle-aged (≥ 45 years old) participants of both sexes with or without comorbidities, (ii) studies that compared high-load (≥70% 1 RM) versus low-load (<70% 1RM) RT, (iii) studies that examined femoral neck or lumbar spine BMD.

RESULTS

From 1052 studies found, six were included in qualitative and quantitative analysis. The meta-analysis revealed no difference between groups for femoral neck (weighted mean difference [MD] and 95% confidence interval (CI) = 0.00 g/cm² [95% CI, -0.01 to 0.01]; P = 0.63) and lumbar spine (MD = 0.01 g/cm² [95% CI, -0.00 to 0.02]; P = 0.12) BDM. There was a substantial heterogeneity for femoral neck (I² = 47%; P = 0.07) and lumbar spine (I² = 59%; P = 0.02). Subgroup analysis revealed a significant effect of high-load RT on femoral neck BMD when participants presented normal BMD values (MD = 0.01 g/cm² [95% CI, -0.00 to 0.02]; P = 0.04) and on interventions lasting up to 6 months (MD = 0.01 g/cm² [95% CI, -0.00 to 0.02]; P = 0.03).

CONCLUSION

Both high- and low-load RT have similar effects on femoral neck and lumbar spine BMD in aging people.

Does Combined Osteopenia/Osteoporosis and Sarcopenia Confer Greater Risk of Falls and Fracture Than Either Condition Alone in Older Men? The Concord Health and Ageing in Men Project

BACKGROUND

It is unclear whether older men with osteopenia/osteoporosis and sarcopenia (so-called osteosarcopenia) are at greater risk of falls and fractures than those with either condition alone.

METHODS

One thousand five hundred seventy-five community-dwelling men aged ≥70 years had appendicular lean mass, total hip and lumbar spine bone mineral density determined by dual-energy x-ray absorptiometry, and completed hand grip strength and gait speed tests. Osteopenia/osteoporosis was defined as a T-score at any site ≤-1.0 SD. Sarcopenia was defined using the European Working Group on Sarcopenia algorithm. Participants were contacted every 4 months for 6 ± 2 years to ascertain incident fractures (confirmed by radiographic reports) and for 2 years for incident falls.

RESULTS

Prevalence of osteosarcopenia was 8%, while 34% of participants had osteopenia/osteoporosis alone and 7% had sarcopenia alone. Men with osteosarcopenia had significantly increased fall (incidence rate ratio: 1.41; 95% confidence interval [CI]: 1.02 to 1.95) and fracture risk (hazard ratio: 1.87; 95% CI: 1.07 to 3.26) compared with men with neither osteopenia/osteoporosis nor sarcopenia. There was no statistical interaction between osteopenia/osteoporosis and sarcopenia, and falls and fracture risk were not different for osteosarcopenia compared with either condition alone (all p > .05).

CONCLUSIONS

Community-dwelling older men with combined osteopenia/osteoporosis and sarcopenia do not have increased falls and fracture risk compared with those with either condition. Further research is required to clarify whether the term "osteosarcopenia" has any meaning above and beyond either term alone and therefore potential clinical utility for falls and fracture prediction.

Occupational Activities: Factors That Tip the Balance From Bone Accrual to Bone Loss

Bone adaptation to persistent overloading can be counteracted by superimposed inflammatory and loading-induced damage that can tip the balance from bone accrual to loss.

Supplemental digital content is available in the text.

It is commonly assumed that beneficial adaptations in bone occur with vigorous exercise, yet any adaptive re/modeling in bone undergoing persistent overloading can be counteracted by superimposed inflammatory, compressive, and tensile loading–induced damage responses above thresholds of tissue fatigue failure and repair. This leads to a tenuous balance between achieving bone accrual and loss.

A High-Intensity Exercise Intervention Improves Older Women Lumbar Spine and Distal Tibia Bone Microstructure and Function: A 20-Week Randomized Controlled Trial

Introduction: The effects of ageing on bone can be mitigated with different types of physical training, such as power training. However, stimuli that combine increasing external and internal loads concomitantly may improve bone quality. The goal of this study was to assess the efficacy of a combined power and plyometric training on lumbar spine and distal tibia microstructure and function. Methods: 38 sedentary elderly women between 60 and 70 years were randomly allocated in experimental (N = 21) and control group (N = 17). The effects of the 20-week protocol on lumbar spine microstructure and tibia microstructure and function were assessed by trabecular bone score (TBS), high resolution peripheral quantitative computed tomography (HR-pQCT) and microfinite element analysis. Results: when compared to the effects found in the control group, the experimental group showed significant improvements in lumbar spine TBS (Hedges' g = 0.77); and in distal tibia trabecular thickness (g = 0.82) and trabecular bone mineral density (g=0.63). Conclusion: our findings underscore the effectiveness of the proposed intervention, suggesting it as a new strategy to slow down and even reverse the structural and functional losses in the skeletal system due to ageing.

Muscle-Bone Crosstalk in the Masticatory System: From Biomechanical to Molecular Interactions

The masticatory system is a complex and highly organized group of structures, including craniofacial bones (maxillae and mandible), muscles, teeth, joints, and neurovascular elements. While the musculoskeletal structures of the head and neck are known to have a different embryonic origin, morphology, biomechanical demands, and biochemical characteristics than the trunk and limbs, their particular molecular basis and cell biology have been much less explored. In the last decade, the concept of muscle-bone crosstalk has emerged, comprising both the loads generated during muscle contraction and a biochemical component through soluble molecules. Bone cells embedded in the mineralized tissue respond to the biomechanical input by releasing molecular factors that impact the homeostasis of the attaching skeletal muscle. In the same way, muscle-derived factors act as soluble signals that modulate the remodeling process of the underlying bones. This concept of muscle-bone crosstalk at a molecular level is particularly interesting in the mandible, due to its tight anatomical relationship with one of the biggest and strongest masticatory muscles, the masseter. However, despite the close physical and physiological interaction of both tissues for proper functioning, this topic has been poorly addressed. Here we present one of the most detailed reviews of the literature to date regarding the biomechanical and biochemical interaction between muscles and bones of the masticatory system, both during development and in physiological or pathological remodeling processes. Evidence related to how masticatory function shapes the craniofacial bones is discussed, and a proposal presented that the masticatory muscles and craniofacial bones serve as secretory tissues. We furthermore discuss our current findings of myokines-release from masseter muscle in physiological conditions, during functional adaptation or pathology, and their putative role as bone-modulators in the craniofacial system. Finally, we address the physiological implications of the crosstalk between muscles and bones in the masticatory system, analyzing pathologies or clinical procedures in which the alteration of one of them affects the homeostasis of the other. Unveiling the mechanisms of muscle-bone crosstalk in the masticatory system opens broad possibilities for understanding and treating temporomandibular disorders, which severely impair the quality of life, with a high cost for diagnosis and management.

Myokines: The endocrine coupling of skeletal muscle and bone

Bone and skeletal muscle are integrated organs and their coupling has been considered mainly a mechanical one in which bone serves as attachment site to muscle while muscle applies load to bone and regulates bone metabolism. However, skeletal muscle can affect bone homeostasis also in a non-mechanical fashion, i.e., through its endocrine activity. Being recognized as an endocrine organ itself, skeletal muscle secretes a panel of cytokines and proteins named myokines, synthesized and secreted by myocytes in response to muscle contraction. Myokines exert an autocrine function in regulating muscle metabolism as well as a paracrine/endocrine regulatory function on distant organs and tissues, such as bone, adipose tissue, brain and liver. Physical activity is the primary physiological stimulus for bone anabolism (and/or catabolism) through the production and secretion of myokines, such as IL-6, irisin, IGF-1, FGF2, beside the direct effect of loading. Importantly, exercise-induced myokine can exert an anti-inflammatory action that is able to counteract not only acute inflammation due to an infection, but also a condition of chronic low-grade inflammation raised as consequence of physical inactivity, aging or metabolic disorders (i.e., obesity, type 2 diabetes mellitus). In this review article, we will discuss the effects that some of the most studied exercise-induced myokines exert on bone formation and bone resorption, as well as a brief overview of the anti-inflammatory effects of myokines during the onset pathological conditions characterized by the development a systemic low-grade inflammation, such as sarcopenia, obesity and aging.

Stem cell derived exosomes: microRNA therapy for age-related musculoskeletal disorders

Age-associated musculoskeletal disorders (MSDs) have been historically overlooked by mainstream biopharmaceutical researchers. However, it has now been recognized that stem and progenitor cells confer innate healing capacity for the musculoskeletal system. Current evidence indicates that exosomes are particularly important in this process as they can mediate sequential and reciprocal interactions between cells to initiate and enhance healing. The present review focuses on stem cells (SCs) derived exosomes as a regenerative therapy for treatment of musculoskeletal disorders. We discuss mechanisms involving exosome-mediated transfer of RNAs and how these have been demonstrated in vitro and in vivo to affect signal transduction pathways in target cells. We envision that standardized protocols for stem cell culture as well as for the isolation and characterization of exosomes enable GMP-compliant large-scale production of SCs-derived exosomes. Hence, potential new treatment for age-related degenerative diseases can be seen in the horizon.

Altered gene and protein expressions of vitamin D receptor in skeletal muscle in sarcopenic patients who sustained distal radius fractures

Despite the presence of vitamin D receptor (VDR) in skeletal muscle cells, the relationship between VDR expressions and muscle mass or function has not been well studied. The purpose of this study was to compare VDR gene and protein expression in the forearm muscle between sarcopenic and non-sarcopenic individuals who have sustained distal radius fractures. Twenty samples of muscle tissue from sarcopenic patients (mean age 63.4 ± 8.1 years) and 20 age- and sex-matched control tissues (62.1 ± 7.9 years) were acquired from the edge of dissected pronator quadratus muscle during surgery for distal radius fractures. The mRNA expression levels of VDR as well as the myokines of interest that may be associated with muscle mass change (myogenin and myostatin) were analyzed with real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR). In addition, Western blot assay and immunohistochemistry for VDR were performed. Sarcopenic patients showed a significantly lower level of gene expression for VDR and myogenin, but a greater level of gene expression for myostatin than the controls according to qRT-PCR analysis. The density of VDR protein expressions was 2.1 times greater, while that of myostatin was 2.6 times lower, in the control group than in the sarcopenic group according to Western blot analysis. On immunohistochemical analysis, the density of the cells expressing VDR was significantly decreased in the sarcopenic patients. Sarcopenic patients who sustained distal radius fractures presented lower vitamin D receptor gene and protein expression in skeletal muscles compared to non-sarcopenic individuals.

Associations of Sarcopenia and Its Components with Bone Structure and Incident Falls in Swedish Older Adults

The aim of this study was to compare bone structure parameters and likelihood of falls across European Working Group on Sarcopenia in Older People (EWGSOP2) sarcopenia categories. 3334 Swedish 70-year olds had appendicular lean mass (normalized to height; ALMHt), lumbar spine and total hip areal BMD (aBMD) estimated by dual-energy X-ray absorptiometry. Volumetric BMD (vBMD) and structure at the distal and proximal tibia and radius were estimated by peripheral quantitative computed tomography. Hand grip strength and timed up-and-go were assessed, and sarcopenia was defined according to EWGSOP2 criteria. Incident falls were self-reported 6 and 12 months after baseline. Only 0.8% and 1.0% of participants had probable and confirmed sarcopenia, respectively. Almost one-third of participants with confirmed sarcopenia reported incident falls, compared with 20% for probable sarcopenia and 14% without sarcopenia (P = 0.025). Participants with confirmed sarcopenia had poorer bone parameters (all P < 0.05) except endosteal circumference at the proximal radius and tibia, while those with probable sarcopenia had lower cortical area at the proximal radius (B = - 5.9; 95% CI - 11.7, - 0.1 mm²) and periosteal and endosteal circumferences at the proximal tibia (- 3.3; - 6.4, - 0.3 and - 3.8; - 7.5, - 0.1 mm², respectively), compared with those without sarcopenia. Compared with probable sarcopenia, confirmed sarcopenic participants had significantly lower lumbar spine and total hip aBMD, distal radius and tibia total vBMD, and proximal radius and tibia cortical vBMD, area and thickness (all P < 0.05). Swedish 70-year olds with confirmed sarcopenia demonstrate poorer BMD and bone architecture than those with probable and no sarcopenia, and have increased likelihood of incident falls.

Postural instability and position of the center of pressure into the base of support in postmenopausal osteoporotic and nonosteoporotic women with and without hyperkyphosis

In postmenopausal women, thoracic hyperkyphosis affects postural instability in the sagittal plane, whereas osteoporosis affects it in the frontal plane. Decrease of hip muscle strength can be changed the center of pressure distance to the center of base of support. These results may be important to design the therapeutic exercise for decreasing the postural instability.

PURPOSE

In this study, we investigated the effect of bone mineral density (BMD) and thoracic kyphosis on the center of pressure (CoP) sway and its location related to the base of support (BoS).

METHODS

Ten young and 39 postmenopausal women voluntarily participated in this study. Postmenopausal women were divided into four groups according to the thoracic kyphosis angle (normal kyphotic < 50° ≤ hyperkyphotic) and T-score values. The isometric strength of the trunk and lower limb muscles were measured. The CoP postural sway was measured in a comfortable double stance position, and the location of the CoP was then determined related to the BoS.

RESULTS

In both hyperkyphotic groups (osteoporotic and normal BMD), the strength of back extension and hip adduction showed a significant decrease compared to the normal kyphotic groups. In the osteoporotic groups (hyper- and normal kyphotic), hip abduction and ankle plantar flexion were significantly weaker than those in the nonosteoporotic groups. In both hyperkyphotic groups, velocity of the CoP displacement in the anterior-posterior (AP) direction was significantly higher than that in the young group, while, in both of the osteoporotic groups, velocity of the CoP displacement in the medio-lateral (ML) direction was significantly higher than that in the young group. In postmenopausal women, hip extensor strength negatively and significantly correlated with the CoP distance to the center of the BoS.

CONCLUSION

It appears that thoracic hyperkyphosis affects postural instability in the AP direction and that a decrease of BMD affects postural instability in the ML direction.

Myostatin regulates pituitary development and hepatic IGF1

Circulating myostatin-attenuating agents are being developed to treat muscle-wasting disease despite their potential to produce serious off-target effects, as myostatin/activin receptors are widely distributed among many nonmuscle tissues. Our studies suggest that the myokine not only inhibits striated muscle growth but also regulates pituitary development and growth hormone (GH) action in the liver. Using a novel myostatin-null label-retaining model (Jekyll mice), we determined that the heterogeneous pool of pituitary stem, transit-amplifying, and progenitor cells in Jekyll mice depletes more rapidly after birth than the pool in wild-type mice. This correlated with increased levels of GH, prolactin, and the cells that secrete these hormones, somatotropes and lactotropes, respectively, in Jekyll pituitaries. Recombinant myostatin also stimulated GH release and gene expression in pituitary cell cultures although inhibiting prolactin release. In primary hepatocytes, recombinant myostatin blocked GH-stimulated expression of two key mediators of growth, insulin-like growth factor (IGF)1 and the acid labile subunit and increased expression of an inhibitor, IGF-binding protein-1. The significance of these findings was demonstrated by smaller muscle fiber size in a model lacking myostatin and liver IGF1 expression (LID-o-Mighty mice) compared with that in myostatin-null (Mighty) mice. These data together suggest that myostatin may regulate pituitary development and function and that its inhibitory actions in muscle may be partly mediated by attenuating GH action in the liver. They also suggest that circulating pharmacological inhibitors of myostatin could produce unintended consequences in these and possibly other tissues.

FGF-2 targets sclerostin in bone and myostatin in skeletal muscle to mitigate the deleterious effects of glucocorticoid on musculoskeletal degradation

AIM

Myokines are associated with regulation of bone and muscle mass. However, limited information is available regarding the impact of myokines on glucocorticoid (GC) mediated adverse effects on the musculoskeletal system. This study investigates the role of myokine fibroblast growth factor-2 (FGF-2) in regulating GC-induced deleterious effects on bone and skeletal muscle.

METHODS

Primary osteoblast cells and C2C12 myoblast cell line were treated with FGF-2 and then exposed to dexamethasone (GC). FGF-2 mediated attenuation of the inhibitory effect of GC on osteoblast and myoblast differentiation and muscle atrophy was assessed through quantitative PCR and western blot analysis. Further, FGF-2 was administered subcutaneously to dexamethasone treated mice to collect bone and skeletal muscle tissue for in vivo analysis of bone microarchitecture, mechanical strength, histomorphometry and for histological alterations in treated tissue samples.

KEY FINDINGS

FGF-2 abrogated the dexamethasone induced inhibitory effect on osteoblast differentiation by modulating BMP-2 pathway and inhibiting Wnt antagonist sclerostin. Further, dexamethasone induced atrophy in C2C12 cells was mitigated by FGF-2 as evident from down regulation of atrogenes expression. FGF-2 prevented GC-induced impairment of mineral density, biomechanical strength, trabecular bone volume, cortical thickness and bone formation rate in mice. Additionally, skeletal muscle tissue from GC treated mice displayed weak myostatin immunostaining and reduced expression of atrogenes following FGF-2 treatment.

SIGNIFICANCE

FGF-2 mitigated GC induced effects through inhibition of sclerostin and myostatin expression in bone and muscle respectively. Taken together, this study exhibited the role of exogenous FGF-2 in sustaining osteoblastogenesis and inhibiting muscle atrophy in presence of glucocorticoid.

Sarcopenia and osteoporosis are interrelated in geriatric inpatients

Background

Sarcopenia and osteoporosis share an underlying pathology and reinforce each other in terms of negative outcomes.

Objective

To evaluate the extent of concomitance of sarcopenia as defined by the European Working Group on Sarcopenia in Older People (EWGSOP) and osteoporosis as defined by the World Health Organization (WHO) in geriatric inpatients and their relationship to nutritional and functional status.

Material and methods

A cross-sectional analysis of geriatric inpatients from the sarcopenia in geriatric elderly (SAGE) study. Measurements included dual X‑ray absorptiometry for bone mineral density and appendicular muscle mass; gait speed and hand grip strength, the Barthel index, body mass index (BMI) and the mini nutritional assessment short form (MNA-SF).

Results

Of the 148 patients recruited for SAGE, 141 (84 women, 57 men; mean age 80.6 ± 5.5 years) had sufficient data to be included in this ancillary investigation: 22/141 (15.6%) were only osteoporotic, 19/141 (13.5%) were only sarcopenic and 20/141 (14.2%) osteosarcopenic (i.e. both sarcopenia and osteoporosis). The prevalence of osteoporosis was higher in sarcopenic than in non-sarcopenic individuals (51.3% vs. 21.6%, p < 0.001). Sarcopenic, osteoporotic and osteosarcopenic subjects had a lower BMI, MNA-SF, handgrip and gait speed (p < 0.05) than the reference group (those neither osteoporotic nor sarcopenic, n = 80). The Barthel index was lower for sarcopenic and osteosarcopenic (p < 0.05) but not for osteoporotic (p = 0.07) subjects. The BMI and MNA-SF were lower in osteosarcopenia compared to sarcopenia or osteoporosis alone (p < 0.05) while there were no differences in functional criteria.

Conclusion

Osteoporosis and sarcopenia are linked to nutritional deficits and reduced function in geriatric inpatients. Co-occurrence (osteosarcopenia) is common and associated with a higher degree of malnutrition than osteoporosis or sarcopenia alone.

Relationships between muscle mass, strength and regional bone mineral density in young men

Purpose

Although the relationship between body composition and bone mineral density (BMD) is well established, the relative contribution of appendicular lean mass (ALM) and fat mass (FM) to BMD has been rarely evaluated in young men.

Methods

We assessed 100 young men (age: 24.4±2.8 years, BMI: 23.4±2.81 kg/m²). Appendicular lean mass index (ALM/H²) (ALMI), fat mass index (FM/ H²) (FMI), percentage of body fat, BMD at lumbar spine (LS), total hip (TH), femoral neck (FN) and whole body (WB) were measured using DXA. Muscle strength was evaluated by handgrip strength. Pearson’s correlations and interactions between all variables were assessed using stepwise regression analyses.

Results

ALM index (ALMI) was positively correlated with BMD at all sites (r = 0.62 for WB p<0.05, r = 0.54 for FN p<0.05, r = 0.64 for TH p<0.05, r = 0.56 for LS p<0.05) whereas FMI was not correlated to BMD values. Stepwise regression analyses showed that ALMI produced a significant and positive influence on BMD (β = 0.07 for WB p<0.001, β = 0.04 for FN p<0.001, β = 0.06 for TH p<0.001). Conversely, FMI was negatively associated with BMD at all sites (β = -0.02 for WB p<0.001, β = - 0.03 for FN p<0.001, β = - 0.03 for TH p<0.001, β = - 0.07 for LS p<0.001). Handgrip strength and BMDs were significantly and positively associated at all sites.

Conclusions

Our data suggest that BMD was positively associated with ALMI while negatively with FMI. We confirm that ALMI is the strongest factor associated with BMD in a population of young men.

Androgen Receptor in Neurons Slows Age-Related Cortical Thinning in Male Mice

Androgens via the androgen receptor (AR) are required for optimal male bone health. The target cell(s) for the effects of androgens on cortical bone remain(s) incompletely understood. In females, estrogen receptor alpha in neurons is a negative regulator of cortical and trabecular bone. Whether neuronal AR regulates bone mass in males remains unexplored. Here, we inactivated AR in neurons using a tamoxifen-inducible CreERT2 under the control of the neuronal promoter Thy1. Tamoxifen induced a 70% to 80% reduction of AR mRNA levels in Thy1-CreERT2-positive brain regions cerebral cortex and brainstem as well as in the peripheral nervous tissue of male neuronal AR knockout (N-ARKO) mice. Hypothalamic AR mRNA levels were only marginally reduced and the hypothalamic-pituitary-gonadal axis remained unaffected, as determined by normal levels of serum testosterone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH). In contrast to orchidectomy, deletion of neuronal AR did not alter body weight, body composition, hindlimb muscle mass, grip strength, or wheel running. MicroCT analysis of the femur revealed no changes in bone accrual during growth in N-ARKO mice. However, 36- and 46-week-old N-ARKO mice displayed an accelerated age-related cortical involution, namely a more pronounced loss of cortical thickness and strength, which occurred in the setting of androgen sufficiency. Neuronal AR inactivation decreased the cancellous bone volume fraction in L₅ vertebra but not in the appendicular skeleton of aging mice. MicroCT findings were corroborated in the tibia and after normalization of hormonal levels. Serum markers of bone turnover and histomorphometry parameters were comparable between genotypes, except for a 30% increase in osteoclast surface in the trabecular compartment of 36-week-old N-ARKO mice. Cortical bone loss in N-ARKO mice was associated with an upregulation of Ucp1 expression in brown adipose tissue, a widely used readout for sympathetic tone. We conclude that androgens preserve cortical integrity in aging male mice via AR in neurons. © 2018 American Society for Bone and Mineral Research.

[Osteosarcopenia: A narrative review]

Osteosarcopenia is a phenotype resulting from the combination of sarcopenia and low bone mineral density. Based on the relationship between bone and muscle, this phenotype is associated with a higher risk of falls, fractures, dependence, and health care costs than its individual components. Given its characteristics, it can be considered as a new geriatric syndrome. Therefore, understanding its pathophysiology and diagnosis, as well as its non-pharmacological and pharmacological management is a task of great importance. The problem in addressing this phenotype arises from the tradition of managing sarcopenia and osteoporosis separately. There is also a lack of consensus on what to call it (sarco-osteopenia, sarco-osteoporosis, osteosarcopenia). The aim of this review is to outline the epidemiology, pathophysiology, diagnoses, adverse events, and management of osteosarcopenia.

Ascorbic acid diminishes bone morphogenetic protein 2-induced osteogenic differentiation of muscle precursor cells

INTRODUCTION

Muscle precursor cells (MPC) are integral to the maintenance of skeletal muscle and have recently been implicated in playing a role in bone repair. The primary objective of this study was to understand better the role of oxidative stress during the osteogenic differentiation of MPCs.

METHODS

Muscle precursor cells were treated with various combinations of ascorbic acid (AA), bone morphogenetic protein (BMP)-2, and either a superoxide dismutase analog (4-hydroxy-TEMPO [TEMPOL]) or polyethyleneglycol-conjugated catalase. Muscle precursor cell proliferation and differentiation were determined, and alkaline phosphatase activity was measured as an index of osteogenic differentiation.

RESULTS

After treatment with 200 μM AA, superoxide was increased 1.5-fold, whereas AA in combination with 100 ng/ml BMP-2 did not increase alkaline phosphatase (ALP) activity. When cells were treated with TEMPOL in combination with 100 ng/ml BMP-2 and 200 μM AA, ALP activity significantly increased.

DISCUSSION

These data suggest that increasing oxidative stress with AA induces sublethal oxidative stress that prevents BMP-2-induced osteogenic differentiation of MPCs. Muscle Nerve 59:501-508, 2019.

Mandibular Bone Loss after Masticatory Muscles Intervention with Botulinum Toxin: An Approach from Basic Research to Clinical Findings

The injection of botulinum toxin type A (BoNT/A) in the masticatory muscles, to cause its temporary paralysis, is a widely used intervention for clinical disorders such as oromandibular dystonia, sleep bruxism, and aesthetics (i.e., masseteric hypertrophy). Considering that muscle contraction is required for mechano-transduction to maintain bone homeostasis, it is relevant to address the bone adverse effects associated with muscle condition after this intervention. Our aim is to condense the current and relevant literature about mandibular bone loss in fully mature mammals after BoNT/A intervention in the masticatory muscles. Here, we compile evidence from animal models (mice, rats, and rabbits) to clinical studies, demonstrating that BoNT/A-induced masticatory muscle atrophy promotes mandibular bone loss. Mandibular bone-related adverse effects involve cellular and metabolic changes, microstructure degradation, and morphological alterations. While bone loss has been detected at the mandibular condyle or alveolar bone, cellular and molecular mechanisms involved in this process must still be elucidated. Further basic research could provide evidence for designing strategies to control the undesired effects on bone during the therapeutic use of BoNT/A. However, in the meantime, we consider it essential that patients treated with BoNT/A in the masticatory muscles be warned about a putative collateral mandibular bone damage.

Age-related bone loss and sarcopenia in men

Bone and muscle are required for mobility but they also have endocrine and metabolic functions. In ageing as well as in many chronic diseases, bone loss and muscle atrophy occur simultaneously, leading to concomitant osteoporosis and sarcopenia. This occurs in both genders but compared with postmenopausal women, men appear to be better protected against age-related bone and muscle decay. Sex steroids (both androgens like testosterone and oestrogens like estradiol) are mainly responsible for musculoskeletal sexual dimorphism. They stimulate peak bone and muscle mass accretion during puberty and midlife, and prevent subsequent loss in ageing men but not post-menopausal women. Still, recent studies have highlighted the importance of intrinsic ageing mechanisms such as cellular senescence and oxidative stress in both genders. Sarcopenia may predispose to dysmobility, frailty, falls and fractures, but whether so-called osteosarcopenia qualifies as a distinct entity remains debated. Although randomized clinical trials in male osteoporosis are smaller and therefore underpowered for some outcomes like hip fractures, the available evidence suggests that the clinical diagnostic and therapeutic approach to male osteoporosis is largely similar to that in postmenopausal women. There is a clear unmet medical need for effective and safe anabolic drugs to rebuild the ageing skeleton, muscle, and preferably both tissues simultaneously. The Wnt/sclerostin and myostatin/activin receptor signalling pathways appear particularly promising in this regard. In this narrative review, we aim to provide an overview of our current understanding of the pathophysiology and treatment of male osteoporosis and sarcopenia, and interactions between these two diseases.

Osteoporosis and Sarcopenia Increase Frailty Syndrome in the Elderly

Musculoskeletal aging is a major public health interesting and strain due to the significant demographic modifications in the population, and it is linked to high risk of falls, loss of autonomy in elderly individuals and institutionalization with small health outcomes. Thus, this pathological status is related to high morbidity and health care rates. Bone mass and muscle mass and strength increase during late adolescence and early adulthood but start to reduce noticeably from the fifth decade of life and are closely linked. Bone and muscle tissues were increasingly recognized, as endocrine target organs and endocrine organs themselves, interacting through paracrine and endocrine signals. During growth, bone mineral content closely correlates with muscle mass, and several evidences suggest that osteoporosis and sarcopenia present common pathophysiological factors and show the correlation between low bone mineral density and sarcopenia in both men and women. Then, sarcopenia and osteoporosis, typical features of aging, are often associated with each other and with the frailty syndrome. In particular, sarcopenia and osteoporosis are major contributors to disability and frailty and the common denominators are age-related chronic inflammation, changes in body composition and hormonal imbalance. Frailty syndrome is characterized by a reduced response to stress, triggering the decline of the physiological functioning of the various systems. Frailty syndrome, typical of the older people, is frequently associated with a reduction in the quality of life and mobility. Falls often are the basis of reduced mobility and ability to perform the common functions of daily life and the increase in the number of institutionalizations. Moreover, the reduction of muscle mass, associated with altered muscle composition, fat and fibrous infiltration and alterations in innervations, and the increase in fat mass, have a synergistic effect on the increase in cardiovascular risk. The aim of this review is to analyze the pathophysiological mechanisms underlying the frailty syndrome and its association with sarcopenia and osteoporosis, and investigate possible intervention measures.

Inter-tissue communication in cancer cachexia

Cachexia is a systemic condition that occurs during many neoplastic diseases, such as cancer. Cachexia in cancer is characterized by loss of body weight and muscle and by adipose tissue wasting and systemic inflammation. Cancer cachexia is often associated with anorexia and increased energy expenditure. Even though the cachectic condition severely affects skeletal muscle, a tissue that accounts for ~40% of total body weight, it represents a multi-organ syndrome that involves tissues and organs such as white adipose tissue, brown adipose tissue, bone, brain, liver, gut and heart. Indeed, evidence suggests that non-muscle tissues and organs, as well as tumour tissues, secrete soluble factors that act on skeletal muscle to promote wasting. In addition, muscle tissue also releases various factors that can interact with the metabolism of other tissues during cancer. In this Review, we examine the effect of non-muscle tissues and inter-tissue communication in cancer cachexia and discuss studies aimed at developing novel therapeutic strategies for the condition.

Diagnostic imaging of two related chronic diseases: Sarcopenia and Osteoporosis

Sarcopenia and osteoporosis are two major health problems worldwide, responsible for a serious clinical and financial burden due to the increasing life expectancy. Both when presented as a single entity and, in particular, in the form of “osteosarcopenia”, they lead to an important increased risk of falls, fractures, hospitalization and mortality. In dealing with these two pathological conditions, it is important to understand that between bone and muscle there is not only a functional correlation but also a close relationship in the development and in maintenance, which is well expressed by the concept of “bone-muscle unit”. This close relationship agrees with the existence of a linear association between sarcopenia and osteoporosis, in particular in elderly population. It is mandatory, in the clinical assessment of both diseases, to do an early diagnosis or to delay as far as possible the appearance of an established form in order to prevent the onset of complications. The aim of this review is to present the different imaging modalities available for a non-invasive investigation of bone and muscle mass and quality in osteoporosis and sarcopenia, with their application and limitations.

Effects of hypergravity on gene levels in anti-gravity muscle and bone through the vestibular system in mice

We recently reported that hypergravity with 3 g for 4 weeks affects muscle and bone through the vestibular system in mice. The purpose of this study was to investigate the effects of hypergravity with 2 g, which had no influence on circulating glucocorticoid level, on the gene levels in muscle and bone, as well as the roles of the vestibular system in those changes using vestibular lesioned (VL) mice. Hypergravity for 2 and 8 weeks or VL exerted little effects on the mRNA levels of muscle differentiation factors and myokines in the soleus muscle. Although hypergravity for 2 weeks significantly elevated alkaline phosphatase (ALP) and type I collagen mRNA levels in the tibia, VL significantly attenuated the levels of ALP mRNA enhanced by hypergravity. In conclusion, the present study suggests that a 2-g load for 2 weeks enhances osteoblast differentiation partly through the vestibular system in mice.

The impact of probiotics' administration on glycemic control, body composition, gut microbiome, mitochondria, and other hormonal signals in adolescents with prediabetes - A randomized, controlled trial study protocol

Background

Recent studies have demonstrated that a significant proportion of adolescents exhibit abdominal obesity in early–middle adolescence, and impaired glucose metabolism. Dysregulation of glucose metabolism is aggravated by the existing osteosarcopenia not only in obese but also in overweight youth. Biochemical inflammation, derived from glucose metabolism dysregulation, in combination with increased stress levels lead to the accumulation of reactive oxygen species, also known as ROS, which seem to afflict the integrity of the gastrointestinal wall, gut mucosa, and commensal, intestinal gut microflora. The current scientific protocol aims to assess the administration of probiotics in prediabetic adolescents in relation with their glycemic control, body composition, and intestinal microbiome.

Methods/Design

This is a study protocol of a two-armed RCT, that recruits adolescents with prediabetes, who will receive either a 4-month, life-style intervention, or a life-style intervention along with a probiotic supplement. The primary outcome is the differences in gut microbiome synthesis, body composition analysis parameters, and concentrations of hormones, before and after the intervention.

Discussion

This study aims to halt the progression of obesity and diabetes and aspires to contribute new evidence for upgraded treatment of obesity and diabetes.

Trial registration

Australian New Zealand Clinical Trial Registry (ACTRN12615000470594).

Prolonged high force high repetition pulling induces osteocyte apoptosis and trabecular bone loss in distal radius, while low force high repetition pulling induces bone anabolism

We have an operant rat model of upper extremity reaching and grasping in which we examined the impact of performing a high force high repetition (High-ForceHR) versus a low force low repetition (Low-ForceHR) task for 18weeks on the radius and ulna, compared to age-matched controls. High-ForceHR rats performed at 4 reaches/min and 50% of their maximum voluntary pulling force for 2h/day, 3days/week. Low-ForceHR rats performed at 6% maximum voluntary pulling force. High-ForceHR rats showed decreased trabecular bone volume in the distal metaphyseal radius, decreased anabolic indices in this same bone region (e.g., decreased osteoblasts and bone formation rate), and increased catabolic indices (e.g., microcracks, increased osteocyte apoptosis, secreted sclerostin, RANKL, and osteoclast numbers), compared to controls. Distal metaphyseal trabeculae in the ulna of High-ForceHR rats showed a non-significant decrease in bone volume, some catabolic indices (e.g., decreased trabecular numbers) yet also some anabolic indices (e.g., increased osteoblasts and trabecular thickness). In contrast, the mid-diaphyseal region of High-ForceHR rats' radial and ulnar bones showed few to no microarchitecture differences and no changes in apoptosis, sclerostin or RANKL levels, compared to controls. In further contrast, Low-ForceHR rats showed increased trabecular bone volume in the radius in the distal metaphysis and increased cortical bone area its mid-diaphysis. These changes were accompanied by increased anabolic indices, no microcracks or osteocyte apoptosis, and decreased RANKL in each region, compared to controls. Ulnar bones of Low-ForceHR rats also showed increased anabolic indices, although fewer than in the adjacent radius. Thus, prolonged performance of an upper extremity reaching and grasping task is loading-, region-, and bone-dependent, with high force loads at high repetition rates inducing region-specific increases in bone degradative changes that were most prominent in distal radial trabeculae, while low force task loads at high repetition rates induced adaptive bone responses.

Inflammatory Bowel Disease: Effects on Bone and Mechanisms

Inflammatory bowel disease (IBD) is associated with decreased bone mass and alterations in bone geometry from the time of diagnosis, before anti-inflammatory therapy is instituted. Deficits in bone mass can persist despite absence of symptoms of active IBD. The effects of IBD on the skeleton are complex. Protein-calorie malnutrition, inactivity, hypogonadism, deficits in calcium intake and vitamin D consumption and synthesis, stunted growth in children, decreased skeletal muscle mass, and inflammation all likely play a role. Preliminary studies suggest that the dysbiotic intestinal microbial flora present in IBD may also affect bone at a distance. Several mechanisms are possible. T cells activated by the gut microbiota may serve as "inflammatory shuttles" between the intestine and bone. Microbe-associated molecular patterns leaked into the circulation in IBD may activate immune responses in the bone marrow by immune cells and by osteocytes, osteoblasts, and osteoclasts that lead to decreased bone formation and increased resorption. Finally, intestinal microbial metabolites such as H₂S may also affect bone cell function. Uncovering these mechanisms will enable the design of microbial cocktails to help restore bone mass in patients with IBD.

Quantitative imaging techniques for the assessment of osteoporosis and sarcopenia

Bone and muscle are two deeply interconnected organs and a strong relationship between them exists in their development and maintenance. The peak of both bone and muscle mass is achieved in early adulthood, followed by a progressive decline after the age of 40. The increase in life expectancy in developed countries resulted in an increase of degenerative diseases affecting the musculoskeletal system. Osteoporosis and sarcopenia represent a major cause of morbidity and mortality in the elderly population and are associated with a significant increase in healthcare costs. Several imaging techniques are currently available for the non-invasive investigation of bone and muscle mass and quality. Conventional radiology, dual energy X-ray absorptiometry (DXA), computed tomography (CT), magnetic resonance imaging (MRI) and ultrasound often play a complementary role in the study of osteoporosis and sarcopenia, depicting different aspects of the same pathology. This paper presents the different imaging modalities currently used for the investigation of bone and muscle mass and quality in osteoporosis and sarcopenia with special emphasis on the clinical applications and limitations of each technique and with the intent to provide interesting insights into recent advances in the field of conventional imaging, novel high-resolution techniques and fracture risk.

Vitamin D and osteosarcopenia: an update from epidemiological studies

PURPOSE OF REVIEW

The review summarizes recent epidemiological studies that examined the relationship between osteoporosis and sarcopenia to assess the impact of vitamin D status or supplementation on health outcomes related to these two medical conditions.

RECENT FINDINGS

Osteoporosis and sarcopenia are major public health problems, but whether these two diseases should be considered alone or combined into a single condition is not clear. No consensual definition of osteosarcopenia is largely accepted. Most observational studies demonstrate some relationship between muscle and bone health. Vitamin D status is generally lower in study participants with bone or muscle wasting. Studies on the effects of vitamin D supplementation on muscle or bone health have provided conflicting results, likely because of the heterogeneity between studies. However, the most positive results were observed in study participants with low vitamin D status and in studies that avoided massive boluses of vitamin D.

SUMMARY

More observational and interventional studies are needed to confirm the exact role of vitamin D in the pathophysiology and treatment of osteosarcopenia.

Accuracy and reproducibility of mouse cortical bone microporosity as quantified by desktop microcomputed tomography

Bone's microporosity plays important roles in bone biology and bone mechanical quality. In this study, we explored the accuracy and reproducibility of nondestructive desktop μCT for 3D visualization and subsequent morphometric analysis of mouse cortical bone microporosity including the vascular canal network and osteocyte lacunae. The accuracy of measurements was evaluated in five murine fibula using confocal laser scanning microscopy (CLSM) in conjunction with Fluorescein isothiocyanate (FITC) staining as the reference method. The reproducibility of μCT-derived cortical bone microstructural indices was examined in 10 fibulae of C57Bl/6J male mice at a nominal resolution of 700 nanometer. Three repeated measurements were made on different days. An excellent correlation between μCT and CLSM was observed for both mean lacuna volume (r = 0.98, p = 0.002) and for mean lacuna orientation (r = 0.93, p = 0.02). Whereas the two techniques showed no significant differences for these parameters, the mean lacuna sphericity acquired from μCT was significantly higher than CLSM (p = 0.01). Reproducibility was high, with precision errors (PE) of 1.57-4.69% for lacuna parameters, and of 1.01-9.45% for vascular canal parameters. Intraclass correlation coefficient (ICC) showed a high reliability of the measurements, ranging from 0.998-1.000 for cortical parameters, 0.973-0.999 for vascular canal parameters and 0.755-0.991 for lacuna parameters. In conclusion, desktop μCT is a valuable tool to quantify the 3D characteristics of bone vascular canals as well as lacunae which can be applied to intact murine bones with high accuracy and reproducibility. Thus, μCT might be an important tool to improve our understanding of the physiological and biomechanical significance of these cannular and lacunar structure in cortical bone.

Osteoporosis in Frail Patients: A Consensus Paper of the Belgian Bone Club

In this consensus paper, the Belgian Bone Club aims to provide a state of the art on the epidemiology, diagnosis, and management of osteoporosis in frail individuals, including patients with anorexia nervosa, patients on dialysis, cancer patients, persons with sarcopenia, and the oldest old. All these conditions may indeed induce bone loss that is superimposed on physiological bone loss and often remains under-recognized and under-treated. This is of particular concern because of the major burden of osteoporotic fractures in terms of morbidity, mortality, and economic cost. Therefore, there is an urgent need to appreciate bone loss associated with these conditions, as this may improve diagnosis and management of bone loss and fracture risk in clinical practice.

Bone Pain and Muscle Weakness in Cancer Patients

PURPOSE OF REVIEW

In this article, we will discuss the current understanding of bone pain and muscle weakness in cancer patients. We will describe the underlying physiology and mechanisms of cancer-induced bone pain (CIBP) and cancer-induced muscle wasting (CIMW), as well as current methods of diagnosis and treatment. We will discuss future therapies and research directions to help patients with these problems.

RECENT FINDINGS

There are several pharmacologic therapies that are currently in preclinical and clinical testing that appear to be promising adjuncts to current CIBP and CIMW therapies. Such therapies include resiniferitoxin, which is a targeted inhibitor of noceciptive nerve fibers, and selective androgen receptor modulators, which show promise in increasing lean mass. CIBP and CIMW are significant causes of morbidity in affected patients. Current management is mostly palliative; however, targeted therapies are poised to revolutionize how these problems are treated.

Assessed and Emerging Biomarkers in Stroke and Training-Mediated Stroke Recovery: State of the Art

Since the increasing update of the biomolecular scientific literature, biomarkers in stroke have reached an outstanding and remarkable revision in the very recent years. Besides the diagnostic and prognostic role of some inflammatory markers, many further molecules and biological factors have been added to the list, including tissue derived cytokines, growth factor-like molecules, hormones, and microRNAs. The literatures on brain derived growth factor and other neuroimmune mediators, bone-skeletal muscle biomarkers, cellular and immunity biomarkers, and the role of microRNAs in stroke recovery were reviewed. To date, biomarkers represent a possible challenge in the diagnostic and prognostic evaluation of stroke onset, pathogenesis, and recovery. Many molecules are still under investigation and may become promising and encouraging biomarkers. Experimental and clinical research should increase this list and promote new discoveries in this field, to improve stroke diagnosis and treatment.

Differential Bone Loss in Mouse Models of Colon Cancer Cachexia

Cachexia is a distinctive feature of colorectal cancer associated with body weight loss and progressive muscle wasting. Several mechanisms responsible for muscle and fat wasting have been identified, however it is not known whether the physiologic and molecular crosstalk between muscle and bone tissue may also contribute to the cachectic phenotype in cancer patients. The purpose of this study was to clarify whether tumor growth associates with bone loss using several experimental models of colorectal cancer cachexia, namely C26, HT-29, and Apc^Min/+. The effects of cachexia on bone structure and strength were evaluated with dual energy X-ray absorptiometry (DXA), micro computed tomography (μCT), and three-point bending test. We found that all models showed tumor growth consistent with severe cachexia. While muscle wasting in C26 hosts was accompanied by moderate bone depletion, no loss of bone strength was observed. However, HT-29 tumor bearing mice showed bone abnormalities including significant reductions in whole-body bone mineral density (BMD), bone mineral content (BMC), femoral trabecular bone volume fraction (BV/TV), trabecular number (Tb.N), and trabecular thickness (Tb.Th), but no declines in strength. Similarly, cachexia in the Apc^Min/+ mice was associated with significant decreases in BMD, BMC, BV/TV, Tb.N, and Tb.Th as well as decreased strength. Our data suggest that colorectal cancer is associated with muscle wasting and may be accompanied by bone loss dependent upon tumor type, burden, stage and duration of the disease. It is clear that preserving muscle mass promotes survival in cancer cachexia. Future studies will determine whether strategies aimed at preventing bone loss can also improve outcomes and survival in colorectal cancer cachexia.

Estrogens and Androgens in Skeletal Physiology and Pathophysiology

Estrogens and androgens influence the growth and maintenance of the mammalian skeleton and are responsible for its sexual dimorphism. Estrogen deficiency at menopause or loss of both estrogens and androgens in elderly men contribute to the development of osteoporosis, one of the most common and impactful metabolic diseases of old age. In the last 20 years, basic and clinical research advances, genetic insights from humans and rodents, and newer imaging technologies have changed considerably the landscape of our understanding of bone biology as well as the relationship between sex steroids and the physiology and pathophysiology of bone metabolism. Together with the appreciation of the side effects of estrogen-related therapies on breast cancer and cardiovascular diseases, these advances have also drastically altered the treatment of osteoporosis. In this article, we provide a comprehensive review of the molecular and cellular mechanisms of action of estrogens and androgens on bone, their influences on skeletal homeostasis during growth and adulthood, the pathogenetic mechanisms of the adverse effects of their deficiency on the female and male skeleton, as well as the role of natural and synthetic estrogenic or androgenic compounds in the pharmacotherapy of osteoporosis. We highlight latest advances on the crosstalk between hormonal and mechanical signals, the relevance of the antioxidant properties of estrogens and androgens, the difference of their cellular targets in different bone envelopes, the role of estrogen deficiency in male osteoporosis, and the contribution of estrogen or androgen deficiency to the monomorphic effects of aging on skeletal involution.

Androgens have antiresorptive effects on trabecular disuse osteopenia independent from muscle atrophy

Aging hypogonadal men are at increased risk of osteoporosis and sarcopenia. Testosterone is a potentially appealing strategy to prevent simultaneous bone and muscle loss. The androgen receptor (AR) mediates antiresorptive effects on trabecular bone via osteoblast-lineage cells, as well as muscle-anabolic actions. Sex steroids also modify the skeletal response to mechanical loading. However, it is unclear whether the effects of androgens on bone remain effective independent of mechanical stimulation or rather require indirect androgen effects via muscle. This study aims to characterize the effects and underlying mechanisms of androgens on disuse osteosarcopenia. Adult male mice received a unilateral botulinum toxin (BTx) injection, and underwent sham surgery or orchidectomy (ORX) without or with testosterone (ORX+T) or dihydrotestosterone (ORX+DHT) replacement. Compared to the contralateral internal control hindlimb, acute trabecular number and bone volume loss was increased by ORX and partially prevented DHT. T was more efficient and increased BV/TV in both hindlimbs over sham values, although it did not reduce the detrimental effect of BTx. Both androgens and BTx regulated trabecular osteoclast surface as well as tartrate-resistant acid phosphatase expression. Androgens also prevented BTx-induced body weight loss but did not significantly influence paralysis or muscle atrophy. BTx and ORX both reduced cortical thickness via endosteal expansion, which was prevented by T but not DHT. In long-term follow-up, the residual trabecular bone volume deficit in sham-BTx hindlimbs was prevented by DHT but T restored it more efficiently to pre-treatment levels. Conditional AR deletion in late osteoblasts and osteocytes or in the satellite cell lineage increased age-related trabecular bone loss in both hindlimbs without influencing the effect of BTx on trabecular osteopenia. We conclude that androgens have antiresorptive effects on trabecular disuse osteopenia which do not require AR actions on bone via muscle or via osteocytes.

Integrative Analysis of Genomics and Transcriptome Data to Identify Potential Functional Genes of BMDs in Females

Osteoporosis is known to be highly heritable. However, to date, the findings from more than 20 genome-wide association studies (GWASs) have explained less than 6% of genetic risks. Studies suggest that the missing heritability data may be because of joint effects among genes. To identify novel heritability for osteoporosis, we performed a system-level study on bone mineral density (BMD) by weighted gene coexpression network analysis (WGCNA), using the largest GWAS data set for BMD in the field, Genetic Factors for Osteoporosis Consortium (GEFOS-2), and a transcriptomic gene expression data set generated from transiliac bone biopsies in women. A weighted gene coexpression network was generated for 1574 genes with GWAS nominal evidence of association (p ≤ 0.05) based on dissimilarity measurement on the expression data. Twelve distinct gene modules were identified, and four modules showed nominally significant associations with BMD (p ≤ 0.05), but only one module, the yellow module, demonstrated a good correlation between module membership (MM) and gene significance (GS), suggesting that the yellow module serves an important biological role in bone regulation. Interestingly, through characterization of module content and topology, the yellow module was found to be significantly enriched with contractile fiber part (GO:044449), which is widely recognized as having a close relationship between muscle and bone. Furthermore, detailed submodule analyses of important candidate genes (HOMER1, SPTBN1) by all edges within the yellow module implied significant enrichment of functional connections between bone and cytoskeletal protein binding. Our study yielded novel information from system genetics analyses of GWAS data jointly with transcriptomic data. The findings highlighted a module and several genes in the model as playing important roles in the regulation of bone mass in females, which may yield novel insights into the genetic basis of osteoporosis. © 2016 American Society for Bone and Mineral Research.

More than osteoporosis: age-specific issues in bone health

PURPOSE OF REVIEW

The interaction between fall and fracture risk factors is an area of increasing clinical relevance, but little information is known about the age-specific issues in bone health unique to HIV-infected adults. The present review will focus on what is known about falls and fall risk factors among HIV-infected adults, and then review the association between decreased muscle, increased adiposity, and frailty with both low bone mineral density (BMD) and falls.

RECENT FINDINGS

The rate of falls among middle-aged HIV-infected adults is similar to that of HIV-uninfected adults 65 years and older. Many of the clinical factors that contribute to low BMD overlap with risk factors for falls, resulting in a high risk of a serious fall among older adults with the greatest risk for a fracture. Low muscle mass, increased adiposity and metabolic syndrome, physical function impairment and frailty, common among older HIV-infected adults, contribute to an increased risk for low BMD and falls, and subsequently, may increase the risk of fracture among HIV-infected older adults.

SUMMARY

Interventions with dual benefit on reducing fall risk and improving BMD are likely to have the greatest impact on fracture prevention in the older, HIV-infected adult.

COPD and osteoporosis: links, risks, and treatment challenges

Chronic obstructive pulmonary disease (COPD) is a chronic inflammatory airway disease associated with various systemic comorbidities including osteoporosis. Osteoporosis and its related fractures are common and have significant impacts on quality of life and even respiratory function in patients with COPD. COPD-associated osteoporosis is however extremely undertreated. Recent studies have suggested that both decreased bone mineral density (BMD) and impaired bone quality contribute to bone fragility, causing fractures in COPD patients. Various clinical risk factors of osteoporosis in COPD patients, including older age, emaciation, physical inactivity, and vitamin D deficiency, have also been described. It is critically important for pulmonologists to be aware of the high prevalence of osteoporosis in COPD patients and evaluate them for such fracture risks. Routine screening for osteoporosis will enable physicians to diagnose COPD patients with comorbid osteoporosis at an early stage and give them appropriate treatment to prevent fracture, which may lead to improved quality of life as well as better long-term prognosis.

Skeletal muscle Ca(2+) mishandling: Another effect of bone-to-muscle signaling

Our appreciation of crosstalk between muscle and bone has recently expanded beyond mechanical force-driven events to encompass a variety of signaling factors originating in one tissue and communicating to the other. While the recent identification of new 'myokines' has shifted some focus to the role of muscle in this partnership, bone-derived factors and their effects on skeletal muscle should not be overlooked. This review summarizes some previously known mediators of bone-to-muscle signaling and also recent work identifying a new role for bone-derived TGF-β as a cause of skeletal muscle weakness in the setting of cancer-induced bone destruction. Oxidation of the ryanodine receptor/calcium release channel (RyR1) in skeletal muscle occurs via a TGF-β-Nox4-RyR1 axis and leads to calcium mishandling and decreased muscle function. Multiple points of potential therapeutic intervention were identified, from preventing the bone destruction to stabilizing the RYR1 calcium channel. This new data reinforces the concept that bone can be an important source of signaling factors in pathphysiological settings.