Custom-made 3D-printed boot as a model of disuse-induced atrophy in murine skeletal muscle.

Skeletal muscle atrophy is characterized by a decrease in muscle mass and strength caused by an imbalance in protein synthesis and degradation. This process naturally occurs upon reduced or absent physical activity, often related to illness, forced bed rest, or unhealthy lifestyles. Currently, no treatment is available for atrophy, and it can only be prevented by overloading exercise, causing severe problems for patients who cannot exercise due to chronic diseases, disabilities, or being bedridden. The two murine models commonly used to induce muscle atrophy are hindlimb suspension and ankle joint immobilization, both of which come with criticalities. The lack of treatments and the relevance of this atrophic process require a unilateral, safe, and robust model to induce muscle atrophy. In this work, we designed and developed a 3D-printed cast to be used for the study of disuse skeletal muscle atrophy. Applying two halves of the cast is non-invasive, producing little to no swelling or skin damage. The application of the cast induces, in 2-weeks immobilized leg, the activation of atrophy-related genes, causing a muscle weight loss up to 25% in the gastrocnemius muscle, and 31% in the soleus muscle of the immobilized leg compared to the control leg. The cross-sectional area of the fibers is decreased by 31% and 34% respectively, with a peculiar effect on fiber types. In the immobilized gastrocnemius, absolute muscle force is reduced by 38%, while normalized force is reduced by 16%. The contralateral leg did not show signs of overload or hypertrophy when compared to free roaming littermates, offering a good internal control over the immobilized limb. Upon removing the cast, the mice effectively recovered mass and force in 3 weeks.

Identifying the potential therapeutic effects of miR­6516 on muscle disuse atrophy.

Muscle atrophy is a debilitating condition with various causes; while aging is one of these causes, reduced engagement in routine muscle­strengthening activities also markedly contributes to muscle loss. Although extensive research has been conducted on microRNAs (miRNAs/miRs) and their associations with muscle atrophy, the roles played by miRNA precursors remain underexplored. The present study detected the upregulation of the miR­206 precursor in cell­free (cf)RNA from the plasma of patients at risk of sarcopenia, and in cfRNAs from the muscles of mice subjected to muscle atrophy. Additionally, a decline in the levels of the miR­6516 precursor was observed in mice with muscle atrophy. The administration of mimic­miR­6516 to mice immobilized due to injury inhibited muscle atrophy by targeting and inhibiting cyclin­dependent kinase inhibitor 1b (Cdkn1b). Based on these results, the miR­206 precursor appears to be a potential biomarker of muscle atrophy, whereas miR­6516 shows promise as a therapeutic target to alleviate muscle deterioration in patients with muscle disuse and atrophy.

Age-Related Susceptibility to Muscle Damage Following Mechanotherapy in Rats Recovering From Disuse Atrophy.

The inability to fully recover lost muscle mass following periods of disuse atrophy predisposes older adults to lost independence and poor quality of life. We have previously shown that mechanotherapy at a moderate load (4.5 N) enhances muscle mass recovery following atrophy in adult, but not older adult rats. We propose that elevated transverse stiffness in aged muscle inhibits the growth response to mechanotherapy and hypothesize that a higher load (7.6 N) will overcome this resistance to mechanical stimuli. F344/BN adult and older adult male rats underwent 14 days of hindlimb suspension, followed by 7 days of recovery with (RE + M) or without (RE) mechanotherapy at 7.6 N on gastrocnemius muscle. The 7.6 N load was determined by measuring transverse passive stiffness and linearly scaling up from 4.5 N. No differences in protein turnover or mean fiber cross-sectional area were observed between RE and RE + M for older adult rats or adult rats at 7.6 N. However, there was a higher number of small muscle fibers present in older adult, but not adult rats, which was explained by a 16-fold increase in the frequency of small fibers expressing embryonic myosin heavy chain. Elevated central nucleation, satellite cell abundance, and dystrophin-/laminin+ fibers were present in older adult rats only following 7.6 N, while 4.5 N did not induce damage at either age. We conclude that age is an important variable when considering load used during mechanotherapy and age-related transverse stiffness may predispose older adults to damage during the recovery period following disuse atrophy.

Non-fibro-adipogenic pericytes from human embryonic stem cells attenuate degeneration of the chronically injured mouse muscle.

Massive tears of the rotator cuff (RC) are associated with chronic muscle degeneration due to fibrosis, fatty infiltration, and muscle atrophy. The microenvironment of diseased muscle often impairs efficient engraftment and regenerative activity of transplanted myogenic precursors. Accumulating myofibroblasts and fat cells disrupt the muscle stem cell niche and myogenic cell signaling and deposit excess disorganized connective tissue. Therefore, restoration of the damaged stromal niche with non-fibro-adipogenic cells is a prerequisite to successful repair of an injured RC. We generated from human embryonic stem cells (hES) a potentially novel subset of PDGFR-ß+CD146+CD34-CD56- pericytes that lack expression of the fibro-adipogenic cell marker PDGFR-α. Accordingly, the PDGFR-ß+PDGFR-α- phenotype typified non-fibro-adipogenic, non-myogenic, pericyte-like derivatives that maintained non-fibro-adipogenic properties when transplanted into chronically injured murine RCs. Although administered hES pericytes inhibited developing fibrosis at early and late stages of progressive muscle degeneration, transplanted PDGFR-ß+PDGFR-α+ human muscle-derived fibro-adipogenic progenitors contributed to adipogenesis and greater fibrosis. Additionally, transplanted hES pericytes substantially attenuated muscle atrophy at all tested injection time points after injury. Coinciding with this observation, conditioned medium from cultured hES pericytes rescued atrophic myotubes in vitro. These findings imply that non-fibro-adipogenic hES pericytes recapitulate the myogenic stromal niche and may be used to improve cell-based treatments for chronic muscle disorders.

Low-Frequency Electrical Stimulation of Denervated Skeletal Muscle Retards Muscle and Trabecular Bone Loss in Aged Rats.

Electrical stimulation (ES)-induced muscle contraction has multiple effects; however, mechano-responsiveness of bone tissue declines with age. Here, we investigated whether daily low-frequency ES-induced muscle contraction treatment reduces muscle and bone loss and ameliorates bone fragility in early-stage disuse musculoskeletal atrophy in aged rats. Twenty-seven-month-old male rats were assigned to age-matched groups comprising the control (CON), sciatic nerve denervation (DN), or DN with direct low-frequency ES (DN+ES) groups. The structural and mechanical properties of the trabecular and cortical bone of the tibiae, and the morphological and functional properties of the tibialis anterior (TA) muscles were assessed one week after DN. ES-induced muscle contraction force mitigated denervation-induced muscle and trabecular bone loss and deterioration of the mechanical properties of the tibia mid-diaphysis, such as the stiffness, but not the maximal load, in aged rats. The TA muscle in the DN+ES group showed significant improvement in the myofiber cross-sectional area and muscle force relative to the DN group. These results suggest that low-frequency ES-induced muscle contraction treatment retards trabecular bone and muscle loss in aged rats in early-stage disuse musculoskeletal atrophy, and has beneficial effects on the functional properties of denervated skeletal muscle.

Nitric oxide treatment attenuates muscle atrophy during hind limb suspension in mice.

Debilitating muscle-disuse atrophy in aging or obesity has huge socioeconomic impact. Since nitric oxide (NO) mediates muscle satellite cell activation and induces hypertrophy with exercise in old mice, we tested whether treatment with the NO donor, isosorbide dinitrate (ISDN), during hind limb suspension would reduce atrophy. Mice were suspended 18 days, with or without daily ISDN (66mg/kg). Muscles were examined for atrophy (weight, fiber diameter); regulatory changes in atrogin-1 (a negative regulator of muscle mass), myostatin (inhibits myogenesis), and satellite cell proliferation; and metabolic responses in myosin heavy chains (MyHCs), liver lipid, and hypothalamic gene expression. Suspension decreased muscle weight and weight relative to body weight between 25-55%, and gastrocnemius fiber diameter vs. CONTROLS: In young-adult mice, ISDN attenuated atrophy by half or more. In quadriceps, ISDN completely prevented the suspension-induced rise in atrogin-1 and drop in myostatin precursor, and attenuated the changes in MyHCs 1 and 2b observed in unloaded muscles without treatment. Fatty liver in suspended young-adult mice was also reduced by ISDN; suspended young mice had higher hypothalamic expression of the orexigenic agouti-related protein, Agrp than controls. Notably, a suspension-induced drop in muscle satellite cell proliferation by 25-58% was completely prevented (young mice) or attenuated (halved, in young-adult mice) by ISDN. NO-donor treatment has potential to attenuate atrophy and metabolic changes, and prevent regulatory changes during disuse and offset/prevent wasting in age-related sarcopenia or space travel. Increases in precursor proliferation resulting from NO treatment would also amplify benefits of physical therapy and exercise.

Running training experience attenuates disuse atrophy in fast-twitch skeletal muscles of rats.

Responsiveness to physiological stimuli, such as exercise and muscular inactivation, differs in individuals. However, the mechanisms responsible for these individual differences remain poorly understood. We tested whether a prior experience of exercise training affects the responses of skeletal muscles to unloading. Young rats were assigned to perform daily running training with a treadmill for 8 wk. After an additional 8 wk of normal habitation, the rats were hindlimb unloaded by tail suspension for 1 wk. Fast-twitch plantaris, gastrocnemius, and tibialis anterior muscles did not atrophy after unloading in rats with training experience, although soleus muscle lost weight similar to sedentary rats. We also analyzed the transcriptome in plantaris muscle with RNA sequencing followed by hierarchical clustering analysis and found that a subset of genes that were generally upregulated in sedentary rats after unloading were less responsive in rats with training experience. The distribution of histone 3 was diminished at the loci of these genes during the training period. Although the deposition of histone 3 was restored after an additional period of normal habitation, the incorporation of H3.3 variant was promoted in rats with training experience. This remodeling of nucleosomes closely correlated to the conformational changes of chromatin and suppressed gene expression in response to unloading. These results suggest that exercise training stimulated the early turnover of histone components, which may alter the responsiveness of gene transcription to physiological stimuli.NEW & NOTEWORTHY The present study demonstrates that disuse atrophy was suppressed in fast-twitch skeletal muscles of rats with training experience in early life. We also found a subset of genes that were less responsive to unloading in the muscle of rats with training experience. It was further determined that exercise training caused an early turnover of nucleosome components, which may alter the responsiveness of genes to stimulus in later life.

Impact of Neuromuscular Electrical Stimulation (NMES) on 90-Day Episode Costs and Post-Acute Care Utilization in Total Knee Replacement Patients with Disuse Atrophy.

INTRODUCTION: This study evaluated differences in: 1) total episode payments, 2) probability of hospital readmission, 3) probability of inpatient rehab facility (IRF) and utilization, and 4) probability of skilled nursing care facility (SNF) utilization in patients who had disuse atrophy and underwent a total knee arthroplasty (TKA) and either did, or did not, receive preoperative home-based neuromuscular electrical stimulation (NMES) therapy. MATERIALS AND METHODS: We used the Medicare limited dataset for a 5% sample of beneficiaries from 2014 and 2015 to construct episodes-of-care for TKA (DRG-470) patients with disuse atrophy who underwent a TKA during the 30 days prior to hospital admission and 90 days post-discharge. Patients were stratified into those who either did or did not receive pre- and postoperative NMES therapy. An ordinary least square (OLS) model was used to estimate the impact of NMES on total episode. Linear probability models were used to estimate the impact of NMES on SNF or IRF utilization and readmission. RESULTS: A $3,274 reduction in episode payments for patients who used preoperative NMES versus those who did not (p<0.001) was demonstrated. The probability of readmission was 12.7% lower for those who used preoperative NMES therapy versus those who did not (p=0.609). The probability of utilizing IRF and SNF was 56.7% (p=0.061) and 46.4% (p=<0.001) lower for those who used pre- and postoperative NMES versus those who did not, respectively. CONCLUSION: Significant reduction in total episode payments and SNF utilization for TKA patients with disuse atrophy who had NMES therapy was demonstrated.

Resistance exercise training in patients with genitourinary cancers to mitigate treatment-related skeletal muscle loss.

The use of targeted therapies in patients with genitourinary malignancies has significantly improved outcomes. For example, androgen receptor (AR) pathway inhibitors have improved outcomes for patients with prostate cancer, and antiangiogenic agents have improved outcomes for those with kidney cancer. However, these advances have been accompanied by musculoskeletal side effects that manifest as physical dysfunction. Although the effects of androgen deprivation therapy on skeletal muscle are well-known, an additional concern is that the muscle loss associated with these newer drugs-especially AR pathway inhibitors-may result in insulin resistance and metabolic syndrome, thus increasing the risk for cardiovascular events and diabetes. Antiangiogenic agents also may cause muscle loss, although this has been poorly described in the literature. As these targeted therapies begin to be used in the earlier stages of treatment, there will be a critical need to prevent treatment-related toxicities with nonpharmacologic interventions. Over the past decade, exercise training has emerged as a novel nonpharmacologic adjunctive method to address toxicities resulting from these targeted therapies. Despite numerous studies in patients with prostate cancer, there remains a large gap in our knowledge of the true efficacy of exercise therapy, as well as the best way to prescribe exercise programs. Here, we suggest that the central role of skeletal muscle in the development of side effects of AR pathway inhibitors and antiangiogenic agents may unlock a number of unique opportunities to study how exercise prescriptions can be used more effectively. Resistance training may be a particularly important modality.

Towards a European Registry and Biorepository for Patients with Spinal and Bulbar Muscular Atrophy.

Pathomechanisms of spinal and bulbar muscular atrophy (SBMA) have been extensively investigated and are partially understood, but no effective treatment is currently available for this disabling disorder. Its rarity, the slow disease progression, and lack of sensitive-to-change outcome measures render design and conduction of clinical trials a challenging task. Therefore, it is fundamental to strengthen the network of clinical centers interested in SBMA for clinical trial readiness. We propose to create and maintain an International SBMA Registry where as many well-characterized patients as possible can be included, with the following aims: facilitate planning of clinical trials and recruitment of patients, define natural history of the disease, characterize epidemiology, develop standards of care, and inform the community of patients about research progresses and ongoing trials. We also aim at developing harmonized and coordinated biorepositories. The experience obtained during the last years in the field of other neuromuscular disorders and of Huntington disease offers valuable precedents.

Head Lift Exercise Improves Swallowing Dysfunction in Spinal and Bulbar Muscular Atrophy.

BACKGROUND: Dysphagia due to bulbar involvement is a major symptom of patients with spinal and bulbar muscular atrophy (SBMA). The aim of this pilot study was to test the efficacy and safety of the head lift exercise for swallowing dysfunction in SBMA. METHODS: We enrolled 6 subjects with genetically confirmed SBMA and instructed them to perform the head lift exercise for 6 weeks. The efficacy outcome measures were the changes from baseline in tongue pressure, the scores of swallowing functional questionnaires, and the motor functional scales and parameters of videofluorography (VF). RESULTS: All subjects completed the study and no major adverse effects were recorded. Tongue pressure significantly increased by 19.2 ± 0.15% (p < 0.05) after the 6-week head lift exercise. The scores for oral dysphagia also improved, although there was no significant change in VF parameters or other variables examined pre- and post-exercise. CONCLUSION: Our findings suggested that the head lift exercise may improve swallowing dysfunction, particularly tongue pressure, in SBMA.

Overexpression of hepatocyte growth factor in SBMA model mice has an additive effect on combination therapy with castration.

Spinal and bulbar muscular atrophy (SBMA) is an inherited motor neuron disease caused by the expansion of a polyglutamine (polyQ)-encoding tract within the androgen receptor (AR) gene. The pathologic features of SBMA are motor neuron loss in the spinal cord and brainstem and diffuse nuclear accumulation and nuclear inclusions of mutant AR in residual motor neurons and certain visceral organs. Hepatocyte growth factor (HGF) is a polypeptide growth factor which has neuroprotective properties. To investigate whether HGF overexpression can affect disease progression in a mouse model of SBMA, we crossed SBMA transgenic model mice expressing an AR gene with an expanded CAG repeat with mice overexpressing HGF. Here, we report that high expression of HGF induces Akt phosphorylation and modestly ameliorated motor symptoms in an SBMA transgenic mouse model treated with or without castration. These findings suggest that HGF overexpression can provide a potential therapeutic avenue as a combination therapy with disease-modifying therapies in SBMA.

Polyglutamine (PolyQ) diseases: genetics to treatments.

The polyglutamine (polyQ) diseases are a group of neurodegenerative disorders caused by expanded cytosine-adenine-guanine (CAG) repeats encoding a long polyQ tract in the respective proteins. To date, a total of nine polyQ disorders have been described: six spinocerebellar ataxias (SCA) types 1, 2, 6, 7, 17; Machado-Joseph disease (MJD/SCA3); Huntington's disease (HD); dentatorubral pallidoluysian atrophy (DRPLA); and spinal and bulbar muscular atrophy, X-linked 1 (SMAX1/SBMA). PolyQ diseases are characterized by the pathological expansion of CAG trinucleotide repeat in the translated region of unrelated genes. The translated polyQ is aggregated in the degenerated neurons leading to the dysfunction and degeneration of specific neuronal subpopulations. Although animal models of polyQ disease for understanding human pathology and accessing disease-modifying therapies in neurodegenerative diseases are available, there is neither a cure nor prevention for these diseases, and only symptomatic treatments for polyQ diseases currently exist. Long-term pharmacological treatment is so far disappointing, probably due to unwanted complications and decreasing drug efficacy. Cellular transplantation of stem cells may provide promising therapeutic avenues for restoration of the functions of degenerative and/or damaged neurons in polyQ diseases.

Spinal and bulbar muscular atrophy: pathogenesis and clinical management.

Spinal and bulbar muscular atrophy, or Kennedy's disease, is an X-linked motor neuron disease caused by polyglutamine repeat expansion in the androgen receptor. The disease is characterised by weakness, atrophy and fasciculations in the limb and bulbar muscles. Affected males may have signs of androgen insensitivity, such as gynaecomastia and reduced fertility. Neurophysiological studies are typically consistent with diffuse denervation atrophy, and serum creatine kinase is usually elevated 2-5 times above normal. Progression of the disease is slow, and the focus of spinal and bulbar muscular atrophy (SBMA) management is to prevent complications.

Engineering muscle constructs for the creation of functional engineered musculoskeletal tissue.

Volumetric muscle loss (VML) is a disabling condition in which current clinical procedures are suboptimal. The field of tissue engineering has many promising strategies for the creation of functional skeletal muscle in vitro. However, there are still two key limitations that prevent it from becoming a solution for treating VML. First, engineered muscle tissue must be biocompatible to facilitate muscle tissue regrowth without generating an immune response. Second, engineered muscle constructs must be scaled up to facilitate replacement of clinically relevant volumes of tissue (centimeters in diameter). There are currently no tissue engineering strategies to produce tissue constructs that are both biocompatible and large enough to facilitate clinical repair. However, recent advances in tissue engineering using synthetic scaffolds, native scaffolds, or scaffold-free approaches may lead to a solution for repair of VML injuries.

[MicroRNA in neurodegenerative disorders].

MicroRNAs (miRNAs) bind to the 3'-untranslated region of mRNA, and thereby suppress the gene expression. Recent studies suggest that miRNAs modify the pathogenesis of cancer and neurodegeneration. Our study demonstrated that the expression levels of miR-196a is increased in a mouse model of spinal and bulbar muscular atrophy (SBMA), a neurodegenerative disease caused by the expansion of polyglutamine in androgen receptor (AR). In cultured neuronal cells, miR-196a decayed the mutant AR mRNA via silencing CUG triplet repeat RNA binding protein 2, a potent miR-196a targeting mRNA, which contributed to stabilize the mutant AR mRNA. Adeno-associated virus vector-mediated delivery of this miRNA attenuates the expression of the mutant AR, resulting in the mitigation of motor neuron degeneration in the SBMA mice. Introduction of miRNA appears to be a novel therapeutic strategy for devastating neurodegenerative diseases.