Clinical phenotype and loss of the slow skeletal muscle troponin T in three new patients with recessive TNNT1 nemaline myopathy

BackgroundCongenital nemaline myopathies are rare pathologies characterised by muscle weakness and rod-shaped inclusions in the muscle fibres.MethodsUsing next-generation sequencing, we identified three patients with pathogenic variants in the Troponin T type 1 (TNNT1) gene, coding for the troponin T (TNT) skeletal muscle isoform.ResultsThe clinical phenotype was similar in all patients, associating hypotonia, orthopaedic deformities and progressive chronic respiratory failure, leading to early death. The anatomopathological phenotype was characterised by a disproportion in the muscle fibre size, endomysial fibrosis and nemaline rods. Molecular analyses of TNNT1 revealed a homozygous deletion of exons 8 and 9 in patient 1; a heterozygous nonsense mutation in exon 9 and retention of part of intron 4 in muscle transcripts in patient 2; and a homozygous, very early nonsense mutation in patient 3.Western blot analyses confirmed the absence of the TNT protein resulting from these mutations.DiscussionThe clinical and anatomopathological presentations of our patients reinforce the homogeneous character of the phenotype associated with recessive TNNT1 mutations. Previous studies revealed an impact of recessive variants on the tropomyosin-binding affinity of TNT. We report in our patients a complete loss of TNT protein due to open reading frame disruption or to post-translational degradation of TNT.

Strength training as a supplemental therapy for androgen deficiency of the aging male (ADAM): study protocol for a three-arm clinical trial

IntroductionAndrogen deficiency of the ageing male is a clinical syndrome resulting from the low production of androgens (testosterone levels <6.9 nmol/L) with symptoms including decline in lean mass, muscle strength, increases in body mass and overall fat mass. The aim of the study is to examine the effect of a 12 week strength training intervention on body composition, physical function, muscle cellular and molecular and selected biochemical markers of metabolic health in hypogonadal patients.Methods and analysisThe study is three-group controlled 12-week experiment to assess the effect of strength training on hypogonadal patients with testosterone replacement therapy and newly diagnosed males without testosterone replacement therapy. Age matched healthy eugonadal males are also engaged in strength training. Lean mass is used to determine sample size indicating, that 22 subjects per group will be sufficient to detect intervention related changes at the power of 0.90. All outcomes are collected before the intervention (pre-intervention assessments) and after the intervention (post-intervention assessments). Clinical outcomes are body composition (lean mass, fat mass and total body mass) measured by dual-energy X-ray absorptiometry, physical functioning assessed by physical tests and psychosocial functioning. The most important haematological and biochemical parameters included are glucose, total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, testosterone, luteinizing hormone, follicle-stimulating hormone, sexhormone-binding globulin, insulin and prostate-specific antigen. Muscle cellular and molecular outcomes are muscle fibre size and regulators of muscle fibre size. Muscle cellular outcomes are measured from muscle biopsies obtained from musculus vastus lateralis.Ethics and disseminationThis trial is approved by Ethics Committee of the University Hospital in Bratislava, Slovakia, (ref. trial number: 127/2017) and all subjects will be fully informed on the rationale, risks and benefits of the study and sign the written informed consent prior to entering the study. Results will be published in peer-reviewed journals and presented in scientific conferences.Trial registration numberNCT03282682

Angiotensin 1-7 alleviates aging-associated muscle weakness and bone loss, but is not associated with accelerated aging in ACE2-knockout mice

The angiotensin-converting enzyme 2 (ACE2)-angiotensin 1-7 (A1-7)-A1-7 receptor (Mas) axis plays a protective role in the renin–angiotensin system (RAS). We recently found that ACE2 knockout (ACE2KO) mice exhibit earlier aging-associated muscle weakness, and that A1-7 alleviates muscle weakness in aging mice. In the present study, we investigated the role of the A1-7-Mas pathway in the effect of ACE2 on physiological aging. Male wild-type, ACE2KO, and Mas knockout (MasKO) mice were subjected to periodical grip strength measurement, followed by administration of A1-7 or vehicle for 4 weeks at 24 months of age. ACE2KO mice exhibited decreased grip strength after 6 months of age, while grip strength of MasKO mice was similar to that of wild-type mice. A1-7 improved grip strength in ACE2KO and wild-type mice, but not in MasKO mice. Muscle fibre size was smaller in ACE2KO mice than that in wild-type and MasKO mice, and increased with A1-7 in ACE2KO and WT mice, but not in MasKO mice. Centrally nucleated fibres (CNFs) and expression of the senescence-associated gene p16INK4a in skeletal muscles were enhanced only in ACE2KO mice and were not altered by A1-7. ACE2KO mice, but not MasKO mice, exhibited thinning of peripheral fat along with increased adipose expression of p16INK4a. A1-7 significantly increased bone volume in wild-type and ACE2KO mice, but not in MasKO mice. Our findings suggest that the impact of ACE2 on physiological aging does not depend on the endogenous production of A1-7 by ACE2, while overactivation of the A1-7-Mas pathway could alleviate sarcopenia and osteoporosis in aged mice.

Salbutamol modifies the neuromuscular junction in a mouse model of ColQ myasthenic syndrome

The β-adrenergic agonists salbutamol and ephedrine have proven to be effective as therapies for human disorders of the neuromuscular junction, in particular many subsets of congenital myasthenic syndromes. However, the mechanisms underlying this clinical benefit are unknown and improved understanding of the effect of adrenergic signalling on the neuromuscular junction is essential to facilitate the development of more targeted therapies. Here, we investigated the effect of salbutamol treatment on the neuromuscular junction in the ColQ deficient mouse, a model of end-plate acetylcholinesterase deficiency. ColQ−/− mice received 7 weeks of daily salbutamol injection, and the effect on muscle strength and neuromuscular junction morphology was analysed. We show that salbutamol leads to a gradual improvement in muscle strength in ColQ−/− mice. In addition, the neuromuscular junctions of salbutamol treated mice showed significant improvements in several postsynaptic morphological defects, including increased synaptic area, acetylcholine receptor area and density, and extent of postjunctional folds. These changes occurred without alterations in skeletal muscle fibre size or type. These findings suggest that β-adrenergic agonists lead to functional benefit in the ColQ−/− mouse and to long-term structural changes at the neuromuscular junction. These effects are primarily at the postsynaptic membrane and may lead to enhanced neuromuscular transmission.

Overcoming nature’s paradox in skeletal muscle to optimise animal production

Nature’s paradox in skeletal muscle describes the seemingly mutually exclusive relationship between muscle fibre size and oxidative capacity. In mammals, there is a constraint on the size at which mitochondria-rich, high O2-dependent oxidative fibres can attain before they become anoxic or adapt to a glycolytic phenotype, being less reliant on O2. This implies that a muscle fibre can hypertrophy at the expense of its endurance capacity. Adaptations to activity (exercise) generally obey this relationship, with optimal muscle endurance generally being linked to an enhanced proportion of small, slow oxidative fibres and muscle strength (force and/or power) being linked to an enhanced proportion of large, fast glycolytic fibres. This relationship generally constrains not only the physiological limits of performance (e.g. speed and endurance), but also the capacity to manipulate muscle attributes such as fibre size and composition, with important relevance to the livestock and aquaculture industries for producing specific muscle traits such as (flesh) quality, texture and taste. Highly glycolytic (white) muscles have different traits than do highly oxidative (red) muscles and so the ability to manipulate muscle attributes to produce flesh with specific traits has important implications for optimising meat production and quality. Understanding the biological regulation of muscle size, and phenotype and the capacity to manipulate signalling pathways to produce specific attributes, has important implications for promoting ethically sustainable and profitable commercial livestock and aquaculture practices and for developing alternative food sources, including ‘laboratory meat’ or ‘clean meat’. This review describes the exciting potential of manipulating muscle attributes relevant to animal production, through traditional nutritional and pharmacological approaches and through viral-mediated strategies that could theoretically push the limits of muscle fibre growth, adaptation and plasticity.

A Reduction in Selenoprotein S Amplifies the Inflammatory Profile of Fast-Twitch Skeletal Muscle in themdxDystrophic Mouse

Excessive inflammation is a hallmark of muscle myopathies, including Duchenne muscular dystrophy (DMD). There is interest in characterising novel genes that regulate inflammation due to their potential to modify disease progression. Gene polymorphisms inSelenoprotein S(Seps1) are associated with elevated proinflammatory cytokines, and in vitro SEPS1 is protective against inflammatory stress. Given that SEPS1 is highly expressed in skeletal muscle, we investigated whether the genetic reduction ofSeps1exacerbated inflammation in themdxmouse. F1 malemdxmice with a heterozygousSeps1deletion (mdx:Seps1−/+) were generated. Themdx:Seps1−/+mice had a 50% reduction in SEPS1 protein expression in hindlimb muscles. In the extensor digitorum longus (EDL) muscles, mRNA expression ofmonocyte chemoattractant protein 1(Mcp-1) (P=0.034), macrophage markerF4/80(P=0.030), andtransforming growth factor-β1(Tgf-β1) (P=0.056) were increased inmdx:Seps1−/+mice. This was associated with a reduction in muscle fibre size; however, ex vivo EDL muscle strength and endurance were unaltered. In dystrophic slow twitch soleus muscles, SEPS1 reduction had no effect on the inflammatory profile nor function. In conclusion, the genetic reduction ofSeps1appears to specifically exacerbate the inflammatory profile of fast-twitch muscle fibres, which are typically more vulnerable to degeneration in dystrophy.