Biomechanical Stimulation of Muscle Constructs Influences Phenotype of Bone Constructs by Modulating Myokine Secretion

Diabetes is a chronic metabolic disorder that can lead to diabetic myopathy and bone diseases. The etiology of musculoskeletal complications in such metabolic disorders and the interplay between the muscular and osseous systems are not well understood. Exercise training promises to prevent diabetic myopathy and bone disease and offer protection. Although the muscle-bone interaction is largely biomechanical, the muscle secretome has significant implications for bone biology. Uncoupling effects of biophysical and biochemical stimuli on the adaptive response of bone during exercise training may offer therapeutic targets for diabetic bone disease. Here, we have developed an in vitro model to elucidate the effects of mechanical strain on myokine secretion and its impact on bone metabolism decoupled from physical stimuli. We developed bone constructs using cross-linked gelatin, which facilitated osteogenic differentiation of osteoprogenitor cells. Then muscle constructs were made from fibrin, which enabled myoblast differentiation and myotube formation. We investigated the myokine expression by muscle constructs under strain regimens replicating endurance (END) and high-intensity interval training (HIIT) in hyperglycemic conditions. In monocultures, both regimens induced higher expression of Il15 and Igf1, whereas END supported more myoblast differentiation and myotube maturation than HIIT. When co-cultured with bone constructs, HIIT regimen increased Glut4 expression in muscle constructs more than END, supporting higher glucose uptake. Likewise, the muscle constructs under the HIIT regimen promoted a healthier and more matured bone phenotype than END. Under static conditions, myostatin (Mstn) expression was significantly downregulated in muscle constructs co-cultured with bone constructs compared with monocultures. Together, our in vitro co-culture system allowed orthogonal manipulation of mechanical strain on muscle constructs while facilitating bone-muscle biochemical cross-talk. Such systems can provide an individualized microenvironment that allows decoupled biomechanical manipulation, help identify molecular targets, and develop engineered therapies for metabolic bone disease. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Pharmacologic Inhibition of Myostatin With a Myostatin Antibody Improves the Skeletal Muscle and Bone Phenotype of Male Insulin-Deficient Diabetic Mice

Type 1 diabetes (T1D) is associated with low bone and muscle mass, increased fracture risk, and impaired skeletal muscle function. Myostatin, a myokine that is systemically elevated in humans with T1D, negatively regulates muscle mass and bone formation. We investigated whether pharmacologic myostatin inhibition in a mouse model of insulin-deficient, streptozotocin (STZ)-induced diabetes is protective for bone and skeletal muscle. DBA/2J male mice were injected with low-dose STZ (diabetic) or vehicle (non-diabetic). Subsequently, insulin or palmitate Linbits were implanted and myostatin (REGN647-MyoAb) or control (REGN1945-ConAb) antibody was administered for 8 weeks. Body composition and contractile muscle function were assessed in vivo. Systemic myostatin, P1NP, CTX-I, and glycated hemoglobin (HbA1c) were quantified, and gastrocnemii were weighed and analyzed for muscle fiber composition and gene expression of selected genes. Cortical and trabecular parameters were analyzed (micro-computed tomography evaluations of femur) and cortical bone strength was assessed (three-point bending test of femur diaphysis). In diabetic mice, the combination of insulin/MyoAb treatment resulted in significantly higher lean mass and gastrocnemius weight compared with MyoAb or insulin treatment alone. Similarly, higher raw torque was observed in skeletal muscle of insulin/MyoAb-treated diabetic mice compared with MyoAb or insulin treatment. Additionally, muscle fiber cross-sectional area (CSA) was lower with diabetes and the combination treatment with insulin/MyoAb significantly improved CSA in type II fibers. Insulin, MyoAb, or insulin/MyoAb treatment improved several parameters of trabecular architecture (eg, bone volume fraction [BV/TV], trabecular connectivity density [Conn.D]) and cortical structure (eg, cortical bone area [Ct. Ar.], minimum moment of inertia [Imin]) in diabetic mice. Lastly, cortical bone biomechanical properties (stiffness and yield force) were also improved with insulin or MyoAb treatment. In conclusion, pharmacologic myostatin inhibition is beneficial for muscle mass, muscle function, and bone properties in this mouse model of T1D and its effects are both independent and additive to the positive effects of insulin. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Triggering Receptor Expressed on Myeloid Cells 2 (TREM2) R47H Variant Causes Distinct Age- and Sex-Dependent Musculoskeletal Alterations in Mice

Previous studies proposed the Triggering Receptor Expressed on Myeloid Cells 2 (TREM2), a receptor expressed in myeloid cells including microglia in brain and osteoclasts in bone, as a link between brain and bone disease. The TREM2 R47H variant is a known risk factor for Alzheimer's disease (AD), the most common form of dementia. To investigate whether altered TREM2 signaling could contribute to bone and skeletal muscle loss, independently of central nervous system defects, we used mice globally hemizygous for the TREM2 R47H variant (TREM2R47H/+ ), which do not exhibit AD pathology, and wild-type (WT) littermate control mice. Dxa/Piximus showed bone loss in female TREM2R47H/+ animals between 4 and 13 months of age and reduced cancellous and cortical bone (measured by micro-computed tomography [μCT]) at 13 months, which stalled out by 20 months of age. In addition, they exhibited decreased femoral biomechanical properties measured by three-point bending at 13 months of age, but not at 4 or 20 months. Male TREM2R47H/+ animals had decreased trabecular bone geometry but increased ultimate strain and failure force at 20 months of age versus WT. Only male TREM2R47H/+ osteoclasts differentiated more ex vivo after 7 days with receptor activator of nuclear factor κB ligand (RANKL)/macrophage colony-stimulating factor (M-CSF) compared to WT littermates. Yet, estrogen receptor alpha expression was higher in female and male TREM2R47H/+ osteoclasts compared to WT mice. However, female TREM2R47H/+ osteoclasts expressed less complement 3 (C3), an estrogen responsive element, and increased protein kinase B (Akt) activity, suggesting altered estrogen signaling in TREM2R47H/+ cells. Despite lower bone volume/strength in TREM2R47H/+ mice, skeletal muscle function measured by plantar flexion and muscle contractility was increased in 13-month-old female mutant mice. Overall, these data demonstrate that an AD-associated TREM2 variant can alter bone and skeletal muscle strength in a sex-dimorphic manner independent of central neuropathology, potentially mediated through changes in osteoclastic intracellular signaling. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Combinatorial Inhibition of Myostatin and Activin A Improves Femoral Bone Properties in the G610C Mouse Model of Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) is a collagen-related bone disorder characterized by fragile osteopenic bone and muscle weakness. We have previously shown that the soluble activin receptor type IIB decoy (sActRIIB) molecule increases muscle mass and improves bone strength in the mild to moderate G610C mouse model of OI. The sActRIIB molecule binds multiple transforming growth factor-β (TGF-β) ligands, including myostatin and activin A. Here, we investigate the musculoskeletal effects of inhibiting activin A alone, myostatin alone, or both myostatin and activin A in wild-type (Wt) and heterozygous G610C (+/G610C) mice using specific monoclonal antibodies. Male and female Wt and +/G610C mice were treated twice weekly with intraperitoneal injections of monoclonal control antibody (Ctrl-Ab, Regn1945), anti-activin A antibody (ActA-Ab, Regn2476), anti-myostatin antibody (Mstn-Ab, Regn647), or both ActA-Ab and Mstn-Ab (Combo, Regn2476, and Regn647) from 5 to 16 weeks of age. Prior to euthanasia, whole body composition, metabolism and muscle force generation assessments were performed. Post euthanasia, hindlimb muscles were evaluated for mass, and femurs were evaluated for changes in microarchitecture and biomechanical strength using micro-computed tomography (μCT) and three-point bend analyses. ActA-Ab treatment minimally impacted the +/G610C musculoskeleton, and was detrimental to bone strength in male +/G610C mice. Mstn-Ab treatment, as previously reported, resulted in substantial increases in hindlimb muscle weights and overall body weights in Wt and male +/G610C mice, but had minimal skeletal impact in +/G610C mice. Conversely, the Combo treatment outperformed ActA-Ab alone or Mstn-Ab alone, consistently increasing hindlimb muscle and body weights regardless of sex or genotype and improving bone microarchitecture and strength in both male and female +/G610C and Wt mice. Combinatorial inhibition of activin A and myostatin more potently increased muscle mass and bone microarchitecture and strength than either antibody alone, recapturing most of the observed benefits of sActRIIB treatment in +/G610C mice. © 2022 American Society for Bone and Mineral Research (ASBMR).

RANKL Blockade Reduces Cachexia and Bone Loss Induced by Non-Metastatic Ovarian Cancer in Mice

Tumor- and bone-derived soluble factors have been proposed to participate in the alterations of skeletal muscle size and function in cachexia. We previously showed that mice bearing ovarian cancer (OvCa) exhibit cachexia associated with marked bone loss, whereas bone-targeting agents, such as bisphosphonates, are able to preserve muscle mass in animals exposed to anticancer drugs. De-identified CT images and plasma samples from female patients affected with OvCa were used for body composition assessment and quantification of circulating cross-linked C-telopeptide type I (CTX-I) and receptor activator of NF-kB ligand (RANKL), respectively. Female mice bearing ES-2 tumors were used to characterize cancer- and RANKL-associated effects on muscle and bone. Murine C2C12 and human HSMM myotube cultures were used to determine the OvCa- and RANKL-dependent effects on myofiber size. To the extent of isolating new regulators of bone and muscle in cachexia, here we demonstrate that subjects affected with OvCa display evidence of cachexia and increased bone turnover. Similarly, mice carrying OvCa present high RANKL levels. By using in vitro and in vivo experimental models, we found that elevated circulating RANKL is sufficient to cause skeletal muscle atrophy and bone resorption, whereas bone preservation by means of antiresorptive and anti-RANKL treatments concurrently benefit muscle mass and function in cancer cachexia. Altogether, our data contribute to identifying RANKL as a novel therapeutic target for the treatment of musculoskeletal complications associated with RANKL-expressing non-metastatic cancers. © 2021 American Society for Bone and Mineral Research (ASBMR).

Vitamin D and Skeletal Muscle: Current Concepts From Preclinical Studies

Muscle weakness has been recognized as a hallmark feature of vitamin D deficiency for many years. Until recently, the direct biomolecular effects of vitamin D on skeletal muscle have been unclear. Although in the past, some reservations have been raised regarding the expression of the vitamin D receptor in muscle tissue, this special issue review article outlines the clear evidence from preclinical studies for not only the expression of the receptor in muscle but also the roles of vitamin D activity in muscle development, mass, and strength. Additionally, muscle may also serve as a dynamic storage site for vitamin D, and play a central role in the maintenance of circulating 25-hydroxy vitamin D levels during periods of low sun exposure. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Androgen Deprivation Therapy Differentially Impacts Bone and Muscle in the Short Term in Physically Active Men With Prostate Cancer

Androgen deprivation therapy (ADT) is a cornerstone of advanced prostate cancer (PCa) therapy. Its use is associated with a loss of bone mineral density (BMD) and a greater risk of falls and osteoporotic fractures. In this prospective cohort study, we examined the impact of ADT on muscle and bone strength in men initiating ADT for PCa. Participants were evaluated at three time points: immediately before (week 0), and 6 and 24 weeks after ADT initiation. Study measures included fasting blood levels (for markers of muscle and bone metabolic activity), MRI and QCT imaging (for muscle fat content, and bone density and architecture), and validated clinical tests of muscle strength and gait. Sixteen men completed all study visits. At baseline and throughout the study, participants exercised a median of four times/week, but still experienced weight gain (+2.0 kg at week 24 versus week 0, p = 0.004). Biochemically, all men sustained dramatic early and persistent reductions in sex hormones post-ADT, along with a progressive and significant increase in serum C-telopeptide of type I collagen (CTX, +84% at week 24 versus week 0). There was a trend for rise in serum sclerostin (p = 0.09) and interleukin 6 (IL-6) (p = 0.08), but no significant change in serum myostatin (p = 0.99). Volumetric BMD by QCT declined significantly at the femoral neck (-3.7% at week 24 versus week 0), particularly at the trabecular compartment. On MRI, there were no significant changes in thigh muscle fat fraction. On physical testing, men developed weaker grip strength, but experienced no worsening in lower extremity and lumbar spine muscle strength, or on functional tests of gait. In conclusion, in physically active men, ADT for 24 weeks results in a significant increase in bone resorption and reduction in BMD, but nonsignificant changes in thigh muscle quality (on imaging) or strength and gait (on functional testing). © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Muscle MRI in motor neuron diseases: a systematic review

Objective: To summarize applications of muscle magnetic resonance imaging (MRI) in cross-sectional assessment and longitudinal monitoring of motor neuron diseases and evaluate associations with clinical assessment techniques.Methods: PubMed and Scopus were searched for research published up to May 2021 relating to muscle MRI in motor neuron diseases, according to predefined inclusion and exclusion criteria. Studies were systematically appraised for bias and data were extracted for discussion.Results: Twenty-eight papers met inclusion criteria. The studies assessed muscle T1- and T2-weighted signal, diffusion, muscle volume, and fat infiltration, employing quantitative, qualitative, and semi-quantitative approaches. Various regions of interest were considered; changes in thigh and calf muscles were most frequently reported. Preliminary evidence of concordance between clinical and radiological findings and utility as an objective longitudinal biomarker is emerging.Conclusion: Muscle MRI appears a promising objective, versatile, and practical biomarker to assess motor neuron diseases.

NCBI Genome Workbench: Desktop Software for Comparative Genomics, Visualization, and GenBank Data Submission

The book chapter introduces the National Center for Biotechnology Information (NCBI) Genome Workbench, a desktop GUI software package to manipulate and visualize complex molecular biology models provided in many data formats. Genome Workbench integrates graphical views and computational tools in a single package to facilitate discoveries. In this chapter we provide a step-by-step protocol guidance on how to do comparative analysis of sequences using NCBI BLAST and multiple sequence alignment algorithms, build phylogenetic trees, and use graphical views for sequences, alignments, and trees to validate the findings. The software package can be used to prepare high-quality whole genome submissions to NCBI. The software package is user-friendly and includes validation and editing tools to fix errors as part of preparing the submission.

Ex Vivo Organ Cultures as Models to Study Bone Biology

The integrity of the skeleton is maintained by the coordinated and balanced activities of the bone cells. Osteoclasts resorb bone, osteoblasts form bone, and osteocytes orchestrate the activities of osteoclasts and osteoblasts. A variety of in vitro approaches has been used in an attempt to reproduce the complex in vivo interactions among bone cells under physiological as well as pathological conditions and to test new therapies. Most cell culture systems lack the proper extracellular matrix, cellular diversity, and native spatial distribution of the components of the bone microenvironment. In contrast, ex vivo cultures of fragments of intact bone preserve key cell-cell and cell-matrix interactions and allow the study of bone cells in their natural 3D environment. Further, bone organ cultures predict the in vivo responses to genetic and pharmacologic interventions saving precious time and resources. Moreover, organ cultures using human bone reproduce human conditions and are a useful tool to test patient responses to therapeutic agents. Thus, these ex vivo approaches provide a platform to perform research in bone physiology and pathophysiology. In this review, we describe protocols optimized in our laboratories to establish ex vivo bone organ cultures and provide technical hints and suggestions. In addition, we present examples on how this technical approach can be employed to study osteocyte biology, drug responses in bone, cancer-induced bone disease, and cross-talk between bone and other organs © 2020 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

An inverse model of the mechanical response of passive skeletal muscle: Implications for microstructure

The constitutive response of passive skeletal muscle is important for many human body modelling applications, but modelling the tension-compression asymmetry and the anisotropy observed in ex-vivo samples is challenging. Existing microstructural models do not capture the full three-dimensional response while models suitable for application in finite element environments mostly have a limited microstructural basis and cannot capture the observed Poisson's ratios. The aim of this paper is to derive an inverse model based on the microstructure of a skeletal muscle that can predict its passive mechanical response. The model parameters and predictions were derived and assessed by comparison with published experimental stress-strain response and Poisson's ratio data. Results show a close match for both predicted stress-strain response for fibre and cross-fibre direction deformations and similar Poisson's ratio values. Some microstructural observations which strengthen our understanding of the role of the collagen network and intramuscular pressure are also provided.

Osteogenesis Imperfecta: New Perspectives From Clinical and Translational Research

Osteogenesis imperfecta (OI) is a monogenic bone fragility disorder that usually is caused by mutations in one of the two genes coding for collagen type I alpha chains, COL1A1 or COL1A2. Mutations in at least 18 other genes can also lead to an OI phenotype. As genetic testing is more widely used, mutations in these genes are also more frequently discovered in individuals who have a propensity for fractures, but who do not have other typical clinical characteristics of OI. Intravenous bisphosphonate therapy is still the most widely used drug treatment approach. Preclinical studies in OI mouse models have shown encouraging effects when the antiresorptive effect of a bisphosphonate was combined with bone anabolic therapy using a sclerostin antibody. Other novel experimental treatment approaches include inhibition of transforming growth factor beta signaling with a neutralizing antibody and the inhibition of myostatin and activin A by a soluble activin receptor 2B. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research

Mechanical Loading of the Femoral Neck in Human Locomotion

Advancing age and reduced loading are associated with a reduction in bone formation. Conversely, loading increases periosteal apposition and may reduce remodeling imbalance and slow age-related bone loss, an important outcome for the proximal femur, which is a common site of fracture. The ability to take advantage of bone's adaptive response to increase bone strength has been hampered by a lack of knowledge of which exercises and specific leg muscles load the superior femoral neck: a common region of microcrack initiation and progression following a sideways fall. We used an in vivo method of quantifying focal strains within the femoral neck in postmenopausal women during walking, stair ambulation, and jumping. Relative to walking, stair ambulation and jumping induced significantly higher strains in the anterior and superior aspects of the femoral neck, common regions of microcrack initiation and progression following a fall. The gluteus maximus, a hip extensor muscle, induced strains in the femoral neck during stair ambulation and jumping, in contrast to walking which induced strains via the iliopsoas, a hip flexor. The ground reaction force was closely associated with the level of strain during each task, providing a surrogate indicator of the potential for a given exercise to load the femoral neck. The gluteal muscles combined with an increased ground reaction force relative to walking induce high focal strains within the anterosuperior region of the femoral neck and therefore provide a target for exercise regimens designed to slow bone loss and maintain or improve microstructural strength. Model files used for calculating femoral neck strains are available at uitbl.mechse.illinois.edu/downloads © 2018 American Society for Bone and Mineral Research.

Dysmobility Syndrome Independently Increases Fracture Risk in the Osteoporotic Fractures in Men (MrOS) Prospective Cohort Study

We proposed the term "dysmobility syndrome" (DS) to identify individuals with impaired musculoskeletal health, a risk factor for falls and fractures. Whether DS is associated with increased risk of incident fracture is unknown. The Osteoporotic Fractures in Men (MrOS) study enrolled 5994 men ages ≥65 years, between March 2000 and April 2002. We used baseline data to determine whether DS increased fracture risk, independent of the Fracture Risk Assessment Tool (FRAX). Men met DS criteria at baseline if they had three or more of the following: appendicular lean mass/height² <7.26 kg/m² , total body fat >30%, spine or hip T-score ≤ -2.5, grip strength <30 kg, gait speed <1.0 m/s, and one or more fall within 12 months. We examined whether baseline DS increased the risk of hip and major osteoporotic fractures (MOFs) over a median of 14 years (IQR, 9 to 15 years). Among 5834 men mean age 74 ± 6 years, 471 (8%) had DS and 635 (11%) experienced an MOF, including 274 (5%) hip fractures. Age (per SD increase) conferred an HR of 1.72 (95% CI, 1.59 to 1.86), DS conferred an HR of 3.45 (95% CI, 2.78 to 4.29) and FRAX calculated with BMD (per %) conferred an HR of 1.10 (95% CI, 1.08 to 1.11) for MOF. Prediction of MOF using the FRAX score provided a concordance value of 0.67 ± 0.012 (concordance values are mean ± SE). Concordance increased to 0.69 ± 0.012 by adding DS and to 0.70 ± 0.012 by adding DS and age to the multivariate model. Kaplan-Meier curves indicated that men with both DS and a FRAX risk above the National Osteoporosis Foundation (NOF) treatment thresholds had higher MOF (HR 6.23; 95% CI, 3.10 to 12.54) and hip (HR 7.73; 95% CI, 5.95 to 10.04) fracture risk than men with neither condition. We suggest further studies to determine the optimal criteria for DS, and to test DS as a predictor of falls and fractures, especially in women. © 2018 American Society for Bone and Mineral Research.

Muscle Deficits in Rheumatoid Arthritis Contribute to Inferior Cortical Bone Structure and Trabecular Bone Mineral Density

OBJECTIVE

Rheumatoid arthritis (RA) is associated with muscle loss, osteoporosis, and fracture. We examined associations between skeletal muscle mass, strength, and quality and trabecular and cortical bone deficits in patients with RA and healthy controls.

METHODS

Participants, ages 18-75 years, completed whole-body dual-energy x-ray absorptiometry and peripheral quantitative computed tomography (pQCT) of the tibia to quantify appendicular lean mass and fat mass indices (ALMI, FMI), muscle density at the lower leg, trabecular bone density, and cortical bone thickness. Age-, sex-, and race-specific Z scores were calculated based on distributions in controls. Associations between body composition and pQCT bone outcomes were assessed in patients with RA and controls. Linear regression analyses assessed differences in bone outcomes after considering differences in body mass index (BMI) and body composition.

RESULTS

The sample consisted of 112 patients with RA (55 men) and 412 controls (194 men). Compared to controls, patients with RA had greater BMI Z score (p < 0.001), lower ALMI Z score after adjustment for FMI (p = 0.02), lower muscle strength Z score (p = 0.01), and lower muscle density Z score (p < 0.001). Among RA, ALMI Z scores were positively associated with trabecular density [β: 0.29 (0.062-0.52); p = 0.01] and cortical thickness [β: 0.33 (0.13-0.53; p = 0.002]. Associations were similar in controls. Bone outcomes were inferior in patients with RA after adjusting for BMI, but similar to controls when adjusting for body composition. Radiographic damage and higher adiponectin levels were independently associated with inferior bone outcomes.

CONCLUSION

Patients with RA exhibit deficits in cortical bone structure and trabecular density at the tibia and a preserved functional muscle-bone unit. A loss of mechanical loading may contribute to bone deficits.

Fat Mass Lowers the Response to Tumor Necrosis Factor-α Blockers in Patients with Ankylosing Spondylitis

OBJECTIVE

Our main objective was to assess the relationship between body composition (BC) and response to tumor necrosis factor-α (TNF-α) blocker treatment in patients with ankylosing spondylitis (AS). Our secondary objective was to evaluate the change of BC after treatment, accounting for sex and age.

METHODS

All included patients fulfilled the modified New York criteria for AS and were naive to TNF-α blocker. They were followed for at least 6 months after the start of etanercept or adalimumab. The Ankylosing Spondylitis Disease Activity Score containing C-reactive protein (ASDAS-CRP) and the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) were reported. BC was assessed by whole body dual-energy X-ray absorptiometry. Body fat percentage (BF%), fat mass index (FMI), and fat free mass index (FFMI) were reported as absolute values and as percentiles.

RESULTS

Forty-one patients were included (61% men). The median followup was 14.3 months (interquartile range 8.4-19.4). After multivariate regression analysis, more fat at baseline (BF%, FMI, or FMI percentile) was significantly related with a lower chance of achieving a clinically important improvement of the ASDAS-CRP or BASDAI after treatment. The body composition did not change significantly after treatment, but there was a trend toward muscle recovery in men (FFMI change from 34.0th to 37.4th percentile).

CONCLUSION

Higher body fat content at baseline was independently associated with a worse response to treatment with TNF-α blockers, measured by ASDAS-CRP and BASDAI change, and might contribute to the lower response rates in female patients. Also, there is a trend toward muscle mass recovery in male patients after treatment.

The diagnostic value of hyperammonaemia induced by the non-ischaemic forearm exercise test

AIMS

The non-ischaemic forearm exercise test (NIFET) is used as a diagnostic tool for the screening of patients with exercise intolerance and for the diagnosis of various metabolic muscle disorders. The production of lactate and ammonia are generally analysed to guide the diagnosis. The aim of this retrospective study was to determine the level of ammonia rise, which can be suggestive of a muscle disease.

METHODS

This retrospective study involved 1440 patients who underwent NIFET. The clinical files of the patients with hyperammonaemia were methodically studied. Normal values were derived from 60 healthy controls.

RESULTS

110 patients with hyperammonaemia were detected. They were classified as either having mild (between 94 and 141 µmol/L) or severe (more than 141 µmol/L) hyperammonaemia. Their diagnosis was studied with respect to the increase in lactate induced by the NIFET.

CONCLUSIONS

Severe postexercise hyperammonaemia, even in the presence of a normal lactate response, is strongly suggestive of a muscle glycogen storage disease. Mild hyperammonaemia in the absence of other abnormalities is most likely non-specific and not indicative of a muscle disease.

A historical perspective on crush syndrome: the clinical application of its pathogenesis, established by the study of wartime crush injuries

Crush syndrome is a fine example of how pathology can play a direct role in revealing the best treatment and management for diseases. It can occur when crush injuries are sustained. Skeletal muscle becomes damaged under the weight of a heavy object, and victims experience severe shock and renal failure. The discovery of the pathology of crush syndrome belongs to two individuals: Seigo Minami and Eric Bywaters. They separately helped to define the pathogenesis of crush syndrome during World Wars I and II. Seigo Minami is believed to have been the first to record the pathogenesis of crush syndrome. In 1923, he described the cases of three soldiers who died of renal failure caused by crush injury during World War I. Using microscopic studies to investigate the pathology of their kidneys, he found the soldiers had died due to 'autointoxication' caused by rhabdomyolysis. This discovery was not known to Eric Bywaters, who described crush syndrome in 1941, having studied victims of the London Blitz during World War II. He defined the 'autointoxication' as the release of rhabdomyolysis products via reperfusion. He therefore established the need for emergency fluid replacement to treat crush syndrome. The findings made by Minami and Bywaters highlight a remarkable achievement in clinical pathology, despite the adversity of war. It is these findings on which current guidelines are based. By reviewing their work, it is hoped that the role of pathology can be better appreciated as a valuable resource for delineating the treatment and management of diseases.

Hindlimb Skeletal Muscle Function and Skeletal Quality and Strength in +/G610C Mice With and Without Weight-Bearing Exercise

Osteogenesis imperfecta (OI) is a heterogeneous heritable connective tissue disorder associated with reduced bone mineral density and skeletal fragility. Bone is inherently mechanosensitive, with bone strength being proportional to muscle mass and strength. Physically active healthy children accrue more bone than inactive children. Children with type I OI exhibit decreased exercise capacity and muscle strength compared with healthy peers. It is unknown whether this muscle weakness reflects decreased physical activity or a muscle pathology. In this study, we used heterozygous G610C OI model mice (+/G610C), which model both the genotype and phenotype of a large Amish OI kindred, to evaluate hindlimb muscle function and physical activity levels before evaluating the ability of +/G610C mice to undergo a treadmill exercise regimen. We found +/G610C mice hindlimb muscles do not exhibit compromised muscle function, and their activity levels were not reduced relative to wild-type mice. The +/G610C mice were also able to complete an 8-week treadmill regimen. Biomechanical integrity of control and exercised wild-type and +/G610C femora were analyzed by torsional loading to failure. The greatest skeletal gains in response to exercise were observed in stiffness and the shear modulus of elasticity with alterations in collagen content. Analysis of tibial cortical bone by Raman spectroscopy demonstrated similar crystallinity and mineral/matrix ratios regardless of sex, exercise, and genotype. Together, these findings demonstrate +/G610C OI mice have equivalent muscle function, activity levels, and ability to complete a weight-bearing exercise regimen as wild-type mice. The +/G610C mice exhibited increased femoral stiffness and decreased hydroxyproline with exercise, whereas other biomechanical parameters remain unaffected, suggesting a more rigorous exercise regimen or another exercise modality may be required to improve bone quality of OI mice.

Muscle torque relative to cross-sectional area and the functional muscle-bone unit in children and adolescents with chronic disease

Measures of muscle mass or size are often used as surrogates of forces acting on bone. However, chronic diseases may be associated with abnormal muscle force relative to muscle size. The muscle-bone unit was examined in 64 children and adolescents with new-onset Crohn's disease (CD), 54 with chronic kidney disease (CKD), 51 treated with glucocorticoids for nephrotic syndrome (NS), and 264 healthy controls. Muscle torque was assessed by isometric ankle dynamometry. Calf muscle cross-sectional area (CSA) and tibia cortical section modulus (Zp) were assessed by quantitative CT. Log-linear regression was used to determine the relations among muscle CSA, muscle torque, and Zp, adjusted for tibia length, age, Tanner stage, sex, and race. Muscle CSA and muscle torque-relative-to-muscle CSA were significantly lower than controls in advanced CKD (CSA -8.7%, p = 0.01; torque -22.9%, p < 0.001) and moderate-to-severe CD (CSA -14.1%, p < 0.001; torque -7.6%, p = 0.05), but not in NS. Zp was 11.5% lower in advanced CKD (p = 0.005) compared to controls, and this deficit was attenuated to 6.7% (p = 0.05) with adjustment for muscle CSA. With additional adjustment for muscle torque and body weight, Zp was 5.9% lower and the difference with controls was no longer significant (p = 0.09). In participants with moderate-to-severe CD, Zp was 6.8% greater than predicted (p = 0.01) given muscle CSA and torque deficits (R(2)  = 0.92), likely due to acute muscle loss in newly-diagnosed patients. Zp did not differ in NS, compared with controls. In conclusion, muscle torque relative to muscle CSA was significantly lower in CKD and CD, compared with controls, and was independently associated with Zp. Future studies are needed to determine if abnormal muscle strength contributes to progressive bone deficits in chronic disease, independent of muscle area. © 2014 American Society for Bone and Mineral Research.

Comparative gene expression analysis of Dtg, a novel target gene of Dpp signaling pathway in the early Drosophila melanogaster embryo

In the early Drosophila melanogaster embryo, Dpp, a secreted molecule that belongs to the TGF-β superfamily of growth factors, activates a set of downstream genes to subdivide the dorsal region into amnioserosa and dorsal epidermis. Here, we examined the expression pattern and transcriptional regulation of Dtg, a new target gene of Dpp signaling pathway that is required for proper amnioserosa differentiation. We showed that the expression of Dtg was controlled by Dpp and characterized a 524-bp enhancer that mediated expression in the dorsal midline, as well as, in the differentiated amnioserosa in transgenic reporter embryos. This enhancer contained a highly conserved region of 48-bp in which bioinformatic predictions and in vitro assays identified three Mad binding motifs. Mutational analysis revealed that these three motifs were necessary for proper expression of a reporter gene in transgenic embryos, suggesting that short and highly conserved genomic sequences may be indicative of functional regulatory regions in D. melanogaster genes. Dtg orthologs were not detected in basal lineages of Dipterans, which unlike D. melanogaster develop two extra-embryonic membranes, amnion and serosa, nevertheless Dtg orthologs were identified in the transcriptome of Musca domestica, in which dorsal ectoderm patterning leads to the formation of a single extra-embryonic membrane. These results suggest that Dtg was recruited as a new component of the network that controls dorsal ectoderm patterning in the lineage leading to higher Cyclorrhaphan flies, such as D. melanogaster and M. domestica.

Muscle size, strength, and physical performance and their associations with bone structure in the Hertfordshire Cohort Study

Sarcopenia is associated with a greater fracture risk. This relationship was originally thought to be explained by an increased risk of falls in sarcopenic individuals. However, in addition, there is growing evidence of a functional muscle-bone unit in which bone health may be directly influenced by muscle function. Because a definition of sarcopenia encompasses muscle size, strength, and physical performance, we investigated relationships for each of these with bone size, bone density, and bone strength to interrogate these hypotheses further in participants from the Hertfordshire Cohort Study. A total of 313 men and 318 women underwent baseline assessment of health and detailed anthropometric measurements. Muscle strength was measured by grip strength, and physical performance was determined by gait speed. Peripheral quantitative computed tomography (pQCT) examination of the calf and forearm was performed to assess muscle cross-sectional area (mCSA) at the 66% level and bone structure (radius 4% and 66% levels; tibia 4% and 38% levels). Muscle size was positively associated with bone size (distal radius total bone area β = 17.5 mm2 /SD [12.0, 22.9]) and strength (strength strain index (β = 23.3 mm3 /SD [18.2, 28.4]) amongst women (p < 0.001). These associations were also seen in men and were maintained after adjustment for age, height, weight-adjusted-for-height, limb-length-adjusted-for-height, social class, smoking status, alcohol consumption, calcium intake, physical activity, diabetes mellitus, and in women, years since menopause and estrogen replacement therapy. Although grip strength showed similar associations with bone size and strength in both sexes, these were substantially attenuated after similar adjustment. Consistent relationships between gait speed and bone structure were not seen. We conclude that although muscle size and grip strength are associated with bone size and strength, relationships between gait speed and bone structure and strength were not apparent in this cohort, supporting a role for the muscle-bone unit.

Partial venom gland transcriptome of a Drosophila parasitoid wasp, Leptopilina heterotoma, reveals novel and shared bioactive profiles with stinging Hymenoptera

Analysis of natural host-parasite relationships reveals the evolutionary forces that shape the delicate and unique specificity characteristic of such interactions. The accessory long gland-reservoir complex of the wasp Leptopilina heterotoma (Figitidae) produces venom with virus-like particles. Upon delivery, venom components delay host larval development and completely block host immune responses. The host range of this Drosophila endoparasitoid notably includes the highly-studied model organism, Drosophila melanogaster. Categorization of 827 unigenes, using similarity as an indicator of putative homology, reveals that approximately 25% are novel or classified as hypothetical proteins. Most of the remaining unigenes are related to processes involved in signaling, cell cycle, and cell physiology including detoxification, protein biogenesis, and hormone production. Analysis of L. heterotoma's predicted venom gland proteins demonstrates conservation among endo- and ectoparasitoids within the Apocrita (e.g., this wasp and the jewel wasp Nasonia vitripennis) and stinging aculeates (e.g., the honey bee and ants). Enzyme and KEGG pathway profiling predicts that kinases, esterases, and hydrolases may contribute to venom activity in this unique wasp. To our knowledge, this investigation is among the first functional genomic studies for a natural parasitic wasp of Drosophila. Our findings will help explain how L. heterotoma shuts down its hosts' immunity and shed light on the molecular basis of a natural arms race between these insects.

Forum on bone and skeletal muscle interactions: summary of the proceedings of an ASBMR workshop

Annual costs are enormous for musculoskeletal diseases such as osteoporosis and sarcopenia and for bone and muscle injuries, costing billions annually in health care. Although it is clear that muscle and bone development, growth, and function are connected, and that muscle loads bone, little is known regarding cellular and molecular interactions between these two tissues. A conference supported by the National Institutes of Health (NIH) and the American Society for Bone and Mineral Research (ASBMR) was held in July 2012 to address the enormous burden of musculoskeletal disease. National and international experts in either bone or muscle presented their findings and their novel hypotheses regarding muscle-bone interactions to stimulate the exchange of ideas between these two fields. The immediate goal of the conference was to identify critical research themes that would lead to collaborative research interactions and grant applications focusing on interactions between muscle and bone. The ultimate goal of the meeting was to generate a better understanding of how these two tissues integrate and crosstalk in both health and disease to stimulate new therapeutic strategies to enhance and maintain musculoskeletal health.

Genome-wide identification and expression analysis of MAPK and MAPKK gene family in Malus domestica

MAPK signal transduction modules play crucial roles in regulating many biological processes in plants, which are composed of three classes of hierarchically organized protein kinases, namely MAPKKKs, MAPKKs, and MAPKs. Although genome-wide analysis of this family has been carried out in some species, little is known about MAPK and MAPKK genes in apple (Malus domestica). In this study, a total of 26 putative apple MAPK genes (MdMPKs) and 9 putative apple MAPKK genes (MdMKKs) have been identified and located within the apple genome. Phylogenetic analysis revealed that MdMAPKs and MdMAPKKs could be divided into 4 subfamilies (groups A, B, C and D), respectively. The predicted MdMAPKs and MdMAPKKs were distributed across 13 out of 17 chromosomes with different densities. In addition, analysis of exon-intron junctions and of intron phase inside the predicted coding region of each candidate gene has revealed high levels of conservation within and between phylogenetic groups. According to the microarray and expressed sequence tag (EST) analysis, the different expression patterns indicate that they may play different roles during fruit development and rootstock-scion interaction process. Moreover, MAPK and MAPKK genes were performed expression profile analyses in different tissues (root, stem, leaf, flower and fruit), and all of the selected genes were expressed in at least one of the tissues tested, indicating that the MAPKs and MAPKKs are involved in various aspects of physiological and developmental processes of apple. To our knowledge, this is the first report of a genome-wide analysis of the apple MAPK and MAPKK gene family. This study provides valuable information for understanding the classification and putative functions of the MAPK signal in apple.