Muscular dystrophies at different ages: metabolic and endocrine alterations

Exploring lipin1 as a promising therapeutic target for the treatment of Duchenne muscular dystrophy

BACKGROUND

Duchenne muscular dystrophy (DMD) is a progressive and devastating muscle disease, resulting from the absence of dystrophin. This leads to cell membrane instability, susceptibility to contraction-induced muscle damage, subsequent muscle degeneration, and eventually disability and early death of patients. Currently, there is no cure for DMD. Our recent studies identified that lipin1 plays a critical role in maintaining myofiber stability and integrity. However, lipin1 gene expression levels are dramatically reduced in the skeletal muscles of DMD patients and mdx mice.

METHODS

To identify whether increased lipin1 expression could prevent dystrophic pathology, we employed unique muscle-specific mdx:lipin1 transgenic (mdx:lipin1Tg/0) mice in which lipin1 was restored in the dystrophic muscle of mdx mice, intramuscular gene delivery, as well as cell culture system.

RESULTS

We found that increased lipin1 expression suppressed muscle degeneration and inflammation, reduced fibrosis, strengthened membrane integrity, and resulted in improved muscle contractile and lengthening force, and muscle performance in mdx:lipin1Tg/0 compared to mdx mice. To confirm the role of lipin1 in dystrophic muscle, we then administered AAV1-lipin1 via intramuscular injection in mdx mice. Consistently, lipin1 restoration inhibited myofiber necroptosis and lessened muscle degeneration. Using a cell culture system, we further found that differentiated primary mdx myoblasts had elevated expression levels of necroptotic markers and medium creatine kinase (CK), which could be a result of sarcolemmal damage. Most importantly, increased lipin1 expression levels in differentiated myoblasts from mdx:lipin1Tg/0 mice substantially inhibited the elevation of necroptotic markers and medium CK levels.

CONCLUSIONS

Overall, our data suggest that lipin1 is a promising therapeutic target for the treatment of dystrophic muscles.

Proteomics in Inherited Metabolic Disorders

Inherited metabolic disorders (IMD) are rare medical conditions caused by genetic defects that interfere with the body's metabolism. The clinical phenotype is highly variable and can present at any age, although it more often manifests in childhood. The number of treatable IMDs has increased in recent years, making early diagnosis and a better understanding of the natural history of the disease more important than ever. In this review, we discuss the main challenges faced in applying proteomics to the study of IMDs, and the key advances achieved in this field using tandem mass spectrometry (MS/MS). This technology enables the analysis of large numbers of proteins in different body fluids (serum, plasma, urine, saliva, tears) with a single analysis of each sample, and can even be applied to dried samples. MS/MS has thus emerged as the tool of choice for proteome characterization and has provided new insights into many diseases and biological systems. In the last 10 years, sequential window acquisition of all theoretical fragmentation spectra mass spectrometry (SWATH-MS) has emerged as an accurate, high-resolution technique for the identification and quantification of proteins differentially expressed between healthy controls and IMD patients. Proteomics is a particularly promising approach to help obtain more information on rare genetic diseases, including identification of biomarkers to aid early diagnosis and better understanding of the underlying pathophysiology to guide the development of new therapies. Here, we summarize new and emerging proteomic technologies and discuss current uses and limitations of this approach to identify and quantify proteins. Moreover, we describe the use of proteomics to identify the mechanisms regulating complex IMD phenotypes; an area of research essential to better understand these rare disorders and many other human diseases.

Dilated cardiomyopathy as the initial presentation of Becker muscular dystrophy: a systematic review of published cases

There are scarce publications regarding the presentation and outcome of Becker muscular dystrophy in adulthood when idiopathic dilated cardiomyopathy is the initial disease manifestation. We performed a systematic review using Medline, Embase, Cochrane, and Scopus to identify cases of adults with idiopathic dilated cardiomyopathy who were subsequently diagnosed with Becker muscular dystrophy from inception through August 2020. Six cases were found. We identified young males (Median age: 26 years) with Becker muscular dystrophy who first presented with dilated cardiomyopathy. Most patients initially presented with congestive heart failure symptoms (5/6, 83%), and had a median left ventricular ejection fraction of 23%. One case did have calf pseudohypertrophy. Musculoskeletal symptoms later appeared one to six years after the initial dilated cardiomyopathy presentation. Heart transplantation was the most common management strategy (4/6, 67%). A left ventricular assist device was used in one case as a bridge to heart transplant. Dilated cardiomyopathy can be the initial presentation of Becker muscular dystrophy in the third to fourth decades of life in adult patients, and musculoskeletal symptoms can be subclinical.

Interactions between gut microbiota and skeletal muscle

The gut microbiota is now recognized as a major contributor to the host’s nutrition, metabolism, immunity, and neurological functions. Imbalanced microbiota (ie, dysbiosis) is linked to undernutrition-induced stunting, inflammatory and metabolic diseases, and cancers. Skeletal muscle also takes part in the interorgan crosstalk regulating substrate metabolism, immunity, and health. Here, we review the reciprocal influence of gut microbiota and skeletal muscle in relation to juvenile growth, performance, aging, and chronic diseases. Several routes involving the vascular system and organs such as the liver and adipose tissue connect the gut microbiota and skeletal muscle, with effects on fitness and health. Therapeutic perspectives arise from the health benefits observed with changes in gut microbiota and muscle activity, further encouraging multimodal therapeutic strategies.

Hormonal and metabolic gender differences in a cohort of myotonic dystrophy type 1 subjects: a retrospective, case-control study

PURPOSE

Myotonic dystrophy type 1 (DM1) is a genetic disorder caused by CTG expansion in the DMPK gene. The aim was to investigate the endocrine and metabolic aspects of DM1.

PATIENTS AND METHODS

Retrospective, case-control study. We compared pituitary, thyroid, adrenal, gonadal and liver function and glycolipid metabolism of 63 DM1 patients against 100 control subjects. Given age-related differences, 2 further subgroups were created to investigate the pituitary-gonadal axis: < 41 (1a) and ≥ 41 (1b) years old for male subjects and < 46 (2a) and ≥ 46 (2b) years old for female subjects. Testicular and thyroid ultrasounds were also performed in the DM1 group.

RESULTS

FT3 and FT4 were significantly lower in DM1 men than controls, while for both males and females, thyroglobulin, ACTH and cortisol were significantly higher in the DM1 group. Gonadotropin levels were significantly higher and inhibin B and DHEA-S levels significantly lower in DM1 patients than controls for both male subgroups. Testosterone and SHBG were significantly higher in controls than in patients for subgroup 1a. Prolactin was significantly higher in patients in subgroups 1b, while testosterone was lower in subgroup 2a than in age-matched female controls. A correlation between the number of CTG repeats and the percentage of male hypogonadal subjects was found. Finally, there was a worse glucose and lipid pattern and significantly higher transaminase and gamma-GT levels in both male and female patients.

CONCLUSIONS

The high frequency of endocrine and metabolic abnormalities in DM1 highlights the importance of endocrine monitoring to enable the prompt initiation of a suitable therapy.

A signaling hub of insulin receptor, dystrophin glycoprotein complex and plakoglobin regulates muscle size

Signaling through the insulin receptor governs central physiological functions related to cell growth and metabolism. Here we show by tandem native protein complex purification approach and super-resolution STED microscopy that insulin receptor activity requires association with the fundamental structural module in muscle, the dystrophin glycoprotein complex (DGC), and the desmosomal component plakoglobin (γ-catenin). The integrity of this high-molecular-mass assembly renders skeletal muscle susceptibility to insulin, because DGC-insulin receptor dissociation by plakoglobin downregulation reduces insulin signaling and causes atrophy. Furthermore, low insulin receptor activity in muscles from transgenic or fasted mice decreases plakoglobin-DGC-insulin receptor content on the plasma membrane, but not when plakoglobin is overexpressed. By masking β-dystroglycan LIR domains, plakoglobin prevents autophagic clearance of plakoglobin-DGC-insulin receptor co-assemblies and maintains their function. Our findings establish DGC as a signaling hub, and provide a possible mechanism for the insulin resistance in Duchenne Muscular Dystrophy, and for the cardiomyopathies seen with plakoglobin mutations.

Growth assessment and weight management in paediatric neuromuscular clinics: a cross-sectional survey across Canada

PURPOSE

To identify current practices related to the assessment, monitoring and discussion of bodyweight, growth and obesity in neuromuscular clinics for children with Duchenne muscular dystrophy (DMD).

METHODS

A cross-sectional, online survey was distributed using snowball sampling to healthcare providers working with children with DMD across Canadian neuromuscular clinics. Summary and descriptive statistics were calculated. Content analysis was performed on open text responses.

RESULTS

Thirty-seven responses were received, representing a range of healthcare disciplines. Height and weight were routinely assessed by 32/37 (87%) respondents, although only 21/37 (57%) responses reported having a clinic standard for measuring height and 23/37 (62%) for weight. While 32/36 (89%) reported discussing weight during consultations, only 13/37 (35%) felt confident doing so. Dietitians were considered the most appropriate person to discuss and manage weight with children and families, although only 17/37 (46%) reported having a dietitian involved in their clinic.

CONCLUSIONS

Neuromuscular clinics could benefit from implementing consistent and recommended growth assessment practices. The development of evidence-based tools, training and protocols tailored to Duchenne muscular dystrophy should be a priority.IMPLICATIONS FOR REHABILITATIONGrowth and weight monitoring approaches vary within and between neuromuscular clinics.Additional training on discussing and managing weight are warranted across disciplines.Advocacy is required to ensure access to dietetic expertise within neuromuscular clinics.

Neuromuscular Diseases and Bone

Neuromuscular diseases (NMDs) are inherited or acquired conditions affecting skeletal muscles, motor nerves, or neuromuscular junctions. Most of them are characterized by a progressive damage of muscle fibers with reduced muscle strength, disability, and poor health-related quality of life of affected patients. In this scenario, skeletal health is usually compromised as a consequence of modified bone-muscle cross-talk including biomechanical and bio-humoral issues, resulting in increased risk of bone fragility and fractures. In addition, NMD patients frequently face nutritional issues, including malnutrition due to feeding disorders and swallowing problems that might affect bone health. Moreover, in these patients, low levels of physical activity or immobility are common and might lead to overweight or obesity that can also interfere with bone strength features. Also, vitamin D deficiency could play a critical role both in the pathogenesis and in the clinical scenario of many NMDs, suggesting that its correction could be useful in maintaining or enhancing bone health, especially in the early phases of NMDs. Last but not least, specific disease-modifying drugs, available for some NMDs, are frequently burdened with adverse effects on bone tissue. For example, glucocorticoid therapy, standard of care for many muscular dystrophies, prolongs long-term survival in treated patients; nevertheless, high dose and/or chronic use of these drugs are a common cause of secondary osteoporosis. This review addresses the current state of knowledge about the factors that play a role in determining bone alterations reported in NMDs, how these factors can modify the biological pathways underlying bone health, and which are the available interventions to manage bone involvement in patients affected by NMDs. Considering the complexity of care of these patients, an interdisciplinary and multimodal management strategy based on both pharmacological and non-pharmacological interventions is recommended, particularly targeting musculoskeletal issues that are closely related to functional independence as well as social implications.

Body composition analysis in patients with myotonic dystrophy types 1 and 2

INTRODUCTION

To date, there are only several reports on body composition in myotonic dystrophy type 1 (DM1) and there are no data for myotonic dystrophy type 2 (DM2). The aim was to analyze body composition of patients with DM1 and DM2, and its association with socio-demographic and clinical features of the diseases.

METHODS

There were no statistical differences in sociodemographic features between 20 DM1 patients and 12 DM2 patients. Body composition was assessed by DEXA (dual-energy x-ray absorptiometry). A three-compartment model was used: bone mineral content (BMC), fat mass (FM), and lean tissue mass (LTM).

RESULTS

Patients with DM1 and DM2 had similar total body mass (TBM), BMC, FM, and LTM. Patients with DM1 had higher trunk-limb fat index (TLFI) in comparison to DM2 patients which indicates visceral fat deposition in DM1 (1.16 ± 0.32 for DM1 vs. 0.87 ± 0.23 for DM2, p < 0.05). Right ribs bone mineral density was lower in DM2 group (0.68 ± 0.07 g/cm² vs. 0.61 ± 0.09 g/cm², p < 0.05). Higher percentage of FM in legs showed correlation with lower strength of the upper leg muscles in DM1 (ρ = - 0.47, p < 0.05). Higher muscle strength in DM2 patients was in correlation with higher bone mineral density (ρ = + 0.62, p < 0.05 for upper arm muscles, ρ = + 0.87, p < 0.01 for lower arm muscles, ρ = + 0.72, p < 0.05 for lower leg muscles).

CONCLUSION

DM1 patients had visceral obesity, and percentage of FM correlated with a degree of muscle weakness in upper legs. In DM2 patients, degree of muscle weakness was in correlation with higher FM index and lower bone mineral density.

Meet and eat, an interdisciplinary group intervention for patients with myotonic dystrophy about healthy nutrition, meal preparation, and consumption: a feasibility study

Purpose: To develop and evaluate an interdisciplinary group intervention for patients with myotonic dystrophy regarding healthy nutrition, meal preparation, and consumption, called Meet and Eat.Materials and methods: A design-based approach was used, exploring experiences and needs of patients with myotonic dystrophy and their next of kin. This resulted in a 4-week interdisciplinary outpatient group intervention to increase awareness and change behavior. In a mixed-method feasibility study this intervention was evaluated with participants and facilitators.Results: Participants reported on social impact of difficulties with eating and drinking (speaking, swallowing, and social embarrassment) and a variety of complaints affecting meal preparation and consumption. Patients and family members expressed the wish to learn from others. After delivery of the intervention, self-reported outcome measures demonstrated improvement on eating and drinking issues in daily life. The qualitative evaluation showed increased awareness and appreciation of the following design principles: peer support, multidisciplinary approach, active involvement of patient with myotonic dystrophy and their next of kin by using personal goals and motivational interviewing.Conclusion: Participation in Meet and Eat seemed to increase insight in patients' condition and ways of management. However, a longer self-management life style program is recommended to change behavior.Implications for rehabilitationPatients with myotonic dystrophy experience physical, cognitive and psychosocial problems to manage healthy nutrition, meal preparation, and consumption;This multidisciplinary group intervention Meet and Eat in patients with myotonic dystrophy appears to be feasible and seems to result in increased insight and management strategies;Peer support, multidisciplinary approach, personal goals, and involvement of family were key factors;To change eating and drinking behavior, a 4-week intervention is too short.

At the Crossroads of Clinical and Preclinical Research for Muscular Dystrophy-Are We Closer to Effective Treatment for Patients?

Among diseases affecting skeletal muscle, muscular dystrophy is one of the most devastating and complex disorders. The term ‘muscular dystrophy’ refers to a heterogeneous group of genetic diseases associated with a primary muscle defect that leads to progressive muscle wasting and consequent loss of muscle function. Muscular dystrophies are accompanied by numerous clinical complications and abnormalities in other tissues that cause extreme discomfort in everyday life. The fact that muscular dystrophy often takes its toll on babies and small children, and that many patients die at a young age, adds to the cruel character of the disease. Clinicians all over the world are facing the same problem: they have no therapy to offer except for symptom-relieving interventions. Patients, their families, but also clinicians, are in urgent need of an effective cure. Despite advances in genetics, increased understanding of molecular mechanisms underlying muscle disease, despite a sweeping range of successful preclinical strategies and relative progress of their implementation in the clinic, therapy for patients is currently out of reach. Only a greater comprehension of disease mechanisms, new preclinical studies, development of novel technologies, and tight collaboration between scientists and physicians can help improve clinical treatment. Fortunately, inventiveness in research is rapidly extending the limits and setting new standards for treatment design. This review provides a synopsis of muscular dystrophy and considers the steps of preclinical and clinical research that are taking the muscular dystrophy community towards the fundamental goal of combating the traumatic disease.

Elevated GLUT4 and glycogenin protein abundance correspond to increased glycogen content in the soleus muscle of mdx mice with no benefit associated with taurine supplementation

Duchenne muscular dystrophy (DMD) patients and the dystrophic mdx mouse have an elevated demand for ATP requiring processes, including Ca2+ regulation and skeletal muscle regeneration. As a key substrate for cellular ATP production, altered glycogen metabolism may contribute significantly to dystrophic pathology and explain reports of mild glucose intolerance. We compare the soleus and extensor digitorum longus (EDL) muscles of the mdx mouse during active muscle necrosis (at 28 days) and at 70 days where pathology is stable. We further investigate the impact of taurine (tau) on dystrophic glycogen metabolism to identify if the benefit seen with tau in a previous study (Barker et al. ) was in part owed to altered glycogen handling. The soleus muscle of 28- and 70-day-old mdx mice had elevated glucose transporter type 4 (GLUT4), glycogenin protein abundances and glycogen content compared to WT (C57BL10/ScSn) controls. Mdx tau mice exhibited modestly reduced glycogen compared to their respective mdx group. The EDL muscle of 28 days mdx tau mice had a ~70% increase in glycogenin protein abundance compared to the mdx but 50% less glycogen content. A twofold greater phosphorylated glycogen synthase (p-GS) and glycogen phosphorylase (p-GP) protein abundance was observed in the 70-day-old mdx soleus muscle than in the 28-day-old mdx soleus muscle. Glycogen debranching enzyme (GDE) protein abundance was elevated in both 28- and 70-day-old mdx soleus muscles compared to WT controls. We identified an increase in proteins associated with glucose uptake and utilization specific to the predominantly slow-twitch soleus muscle of mdx mice regardless of age and that taurine affords no obvious benefit to glycogen metabolism in the mdx mouse.

A feasibility study using solution-focused coaching for health promotion in children and young people with Duchenne muscular dystrophy

PURPOSE

To evaluate the feasibility and acceptability of a coaching intervention (Solution-Focused Coaching in pediatric rehabilitation [SFC-Peds]) related to physical activity and diet in males with Duchenne muscular dystrophy.

METHODS

A pre-post design was employed. Participants had five coaching sessions over 8 weeks. The first session was face-to-face, followed by four virtual sessions. Feasibility criteria included recruitment rates, attrition, and intervention fidelity. The Canadian Occupational Performance Measure (COPM) and Goal Attainment Scaling (GAS) were employed to look at outcome trends. The acceptability was assessed using a survey.

RESULTS

Five males (11-19 years) participated. All feasibility criteria were met. Clinically significant increases were observed for GAS and COPM scores. Participants reported SFC-Peds to be acceptable. Broad barriers and facilitators to coaching success were identified.

CONCLUSIONS

A SFC-Peds intervention for health promotion is feasible and acceptable in children with DMD and their families. A rigorous efficacy study assessing SFC-Peds intervention is warranted.

Study of anti-Müllerian hormone levels in patients with Myotonic Dystrophy Type 1. Preliminary results

Myotonic dystrophy type 1 is a multisystemic disorder characterized by myotonia, muscle weakness and involvement of several organs and apparatus such as heart, lungs, eye, brain and endocrine system. Hypogonadism and reproductive abnormalities are frequently reported. A progressive testicular atrophy occurs in about 80% in the affected males leading to Leydig cell hyperproliferation and elevated basal follicle stimulating hormone (FSH) levels. Anti-Müllerian hormone (AMH) - a dimeric glycoprotein belonging to the super-family of transforming grow factor beta (TGF-beta) - is the earliest Sertoli cell hormone secreted in males and, together with inhibin B and FSH, is an important indicator of Sertoli cell function. AMH levels remain high during the whole prepubertal phase and are down-regulated in puberty by the increasing testosterone levels. Aims of the work were to assess the AMH levels in 50 patients with Myotonic Dystrophy type 1 aged less 50 years and to investigate whether it may contribute to the endocrine function impairment observed in these patients. The results confirmed a reduction of testosterone levels associated with an increase in Luteinizing Hormone (LH) and FSH compared to controls, suggesting a reduced function of the Sertoli cells. Conversely the average levels of AMH were significantly lower in patients compared with controls, and almost undetectable in about 60% of them. Further studies are necessary to better clarify these findings.

Interventions to prevent and treat corticosteroid-induced osteoporosis and prevent osteoporotic fractures in Duchenne muscular dystrophy

BACKGROUND

Corticosteroid treatment is considered the 'gold standard' for Duchenne muscular dystrophy (DMD); however, it is also known to induce osteoporosis and thus increase the risk of vertebral fragility fractures. Good practice in the care of those with DMD requires prevention of these adverse effects. Treatments to increase bone mineral density include bisphosphonates and vitamin D and calcium supplements, and in adolescents with pubertal delay, testosterone. Bone health management is an important part of lifelong care for patients with DMD.

OBJECTIVES

To assess the effects of interventions to prevent or treat osteoporosis in children and adults with DMD taking long-term corticosteroids; to assess the effects of these interventions on the frequency of vertebral fragility fractures and long-bone fractures, and on quality of life; and to assess adverse events.

SEARCH METHODS

On 12 September 2016, we searched the Cochrane Neuromuscular Specialised Register, CENTRAL, MEDLINE, Embase, and CINAHL Plus to identify potentially eligible trials. We also searched the Web of Science ISI Proceedings (2001 to September 2016) and three clinical trials registries to identify unpublished studies and ongoing trials. We contacted correspondence authors of the included studies in the review to obtain information on unpublished studies or work in progress.

SELECTION CRITERIA

We considered for inclusion in the review randomised controlled trials (RCTs) and quasi-RCTs involving any bone health intervention for corticosteroid-induced osteoporosis and fragility fractures in children, adolescents, and adults with a confirmed diagnosis of DMD. The interventions might have included oral and intravenous bisphosphonates, vitamin D supplements, calcium supplements, dietary calcium, testosterone, and weight-bearing activity.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed reports and selected potential studies for inclusion, following standard Cochrane methodology. We contacted study authors to obtain further information for clarification on published work, unpublished studies, and work in progress.

MAIN RESULTS

We identified 18 potential studies, of which two, currently reported only as abstracts, met the inclusion criteria for this review. Too little information was available for us to present full results or adequately assess risk of bias. The participants were children aged five to 15 years with DMD, ambulant and non-ambulant. The interventions were risedronate versus no treatment in one trial (13 participants) and whole-body vibration versus a placebo device in the second (21 participants). Both studies reported improved bone mineral density with the active treatments, with no improvement in the control groups, but the abstracts did not compare treatment and control conditions. All children tolerated whole-body vibration treatment. No study provided information on adverse events. Two studies are ongoing: one investigating whole-body vibration, the other investigating zoledronic acid.

AUTHORS' CONCLUSIONS

We know of no high-quality evidence from RCTs to guide use of treatments to prevent or treat corticosteroid-induced osteoporosis and reduce the risk of fragility fractures in children and adults with DMD; only limited results from two trials reported in abstracts were available. We await formal trial reports. Findings from two ongoing relevant studies and two trials, for which only abstracts are available, will be important in future updates of this review.

Alterations to mTORC1 signaling in the skeletal muscle differentially affect whole-body metabolism

Background

The mammalian target of rapamycin complex 1 (mTORC1) is a central node in a network of signaling pathways controlling cell growth and survival. This multiprotein complex integrates external signals and affects different nutrient pathways in various organs. However, it is not clear how alterations of mTORC1 signaling in skeletal muscle affect whole-body metabolism.

Results

We characterized the metabolic phenotype of young and old raptor muscle knock-out (RAmKO) and TSC1 muscle knock-out (TSCmKO) mice, where mTORC1 activity in skeletal muscle is inhibited or constitutively activated, respectively. Ten-week-old RAmKO mice are lean and insulin resistant with increased energy expenditure, and they are resistant to a high-fat diet (HFD). This correlates with an increased expression of histone deacetylases (HDACs) and a downregulation of genes involved in glucose and fatty acid metabolism. Ten-week-old TSCmKO mice are also lean, glucose intolerant with a decreased activation of protein kinase B (Akt/PKB) targets that regulate glucose transporters in the muscle. The mice are resistant to a HFD and show reduced accumulation of glycogen and lipids in the liver. Both mouse models suffer from a myopathy with age, with reduced fat and lean mass, and both RAmKO and TSCmKO mice develop insulin resistance and increased intramyocellular lipid content.

Conclusions

Our study shows that alterations of mTORC1 signaling in the skeletal muscle differentially affect whole-body metabolism. While both inhibition and constitutive activation of mTORC1 induce leanness and resistance to obesity, changes in the metabolism of muscle and peripheral organs are distinct. These results indicate that a balanced mTORC1 signaling in the muscle is required for proper metabolic homeostasis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13395-016-0084-8) contains supplementary material, which is available to authorized users.

Hypogonadism Associated with Cyp19a1 (Aromatase) Posttranscriptional Upregulation in Celf1 Knockout Mice

CELF1 is a multifunctional RNA-binding protein that controls several aspects of RNA fate. The targeted disruption of the Celf1 gene in mice causes male infertility due to impaired spermiogenesis, the postmeiotic differentiation of male gametes. Here, we investigated the molecular reasons that underlie this testicular phenotype. By measuring sex hormone levels, we detected low concentrations of testosterone in Celf1-null mice. We investigated the effect of Celf1 disruption on the expression levels of steroidogenic enzyme genes, and we observed that Cyp19a1 was upregulated. Cyp19a1 encodes aromatase, which transforms testosterone into estradiol. Administration of testosterone or the aromatase inhibitor letrozole partly rescued the spermiogenesis defects, indicating that a lack of testosterone associated with excessive aromatase contributes to the testicular phenotype. In vivo and in vitro interaction assays demonstrated that CELF1 binds to Cyp19a1 mRNA, and reporter assays supported the conclusion that CELF1 directly represses Cyp19a1 translation. We conclude that CELF1 downregulates Cyp19a1 (Aromatase) posttranscriptionally to achieve high concentrations of testosterone compatible with spermiogenesis completion. We discuss the implications of these findings with respect to reproductive defects in men, including patients suffering from isolated hypogonadotropic hypogonadism and myotonic dystrophy type I.

Differential Gene Expression Profiling of Dystrophic Dog Muscle after MuStem Cell Transplantation

BACKGROUND

Several adult stem cell populations exhibit myogenic regenerative potential, thus representing attractive candidates for therapeutic approaches of neuromuscular diseases such as Duchenne Muscular Dystrophy (DMD). We have recently shown that systemic delivery of MuStem cells, skeletal muscle-resident stem cells isolated in healthy dog, generates the remodelling of muscle tissue and gives rise to striking clinical benefits in Golden Retriever Muscular Dystrophy (GRMD) dog. This global effect, which is observed in the clinically relevant DMD animal model, leads us to question here the molecular pathways that are impacted by MuStem cell transplantation. To address this issue, we compare the global gene expression profile between healthy, GRMD and MuStem cell treated GRMD dog muscle, four months after allogenic MuStem cell transplantation.

RESULTS

In the dystrophic context of the GRMD dog, disease-related deregulation is observed in the case of 282 genes related to various processes such as inflammatory response, regeneration, calcium ion binding, extracellular matrix organization, metabolism and apoptosis regulation. Importantly, we reveal the impact of MuStem cell transplantation on several molecular and cellular pathways based on a selection of 31 genes displaying signals specifically modulated by the treatment. Concomitant with a diffuse dystrophin expression, a histological remodelling and a stabilization of GRMD dog clinical status, we show that cell delivery is associated with an up-regulation of genes reflecting a sustained enhancement of muscle regeneration. We also identify a decreased mRNA expression of a set of genes having metabolic functions associated with lipid homeostasis and energy. Interestingly, ubiquitin-mediated protein degradation is highly enhanced in GRMD dog muscle after systemic delivery of MuStem cells.

CONCLUSIONS

Overall, our results provide the first high-throughput characterization of GRMD dog muscle and throw new light on the complex molecular/cellular effects associated with muscle repair and the clinical efficacy of MuStem cell-based therapy.

Multidisciplinary approach to the management of myopathies

PURPOSE OF REVIEW

Aside from some inflammatory myopathies and very few genetic disorders, there are no therapies that make most patients with myopathies stronger. Consequently, the management of these patients can be frustrating for patients and their families as well as the clinicians taking care of them. Treatment of these patients must involve a comprehensive approach focused on limiting the secondary effects of skeletal muscle weakness, managing comorbidities associated with specific diseases, and, most importantly, optimizing patients' functional abilities and quality of life in terms of their ability to accomplish activities of daily living. While the approach to each patient differs depending on their disease, certain common themes can be addressed in each patient. This review highlights an approach centered on four conceptual themes ("the Four S's"): Strength therapies, Supportive care, Symptomatic therapies, and pSychological support.

RECENT FINDINGS

Although relatively few well-designed studies have been done that highlight conservative management of patients with various myopathies, an emerging literature helps guide the clinician in certain key areas, especially in relation to cardiac and pulmonary management of these patients.

SUMMARY

While disease-altering therapies have proven elusive for many muscle diseases, a multimodal approach to the conservative and supportive care of these patients can markedly improve their quality of life. Pharmacologic treatment options for specific myopathies will not be addressed in this article but are covered elsewhere in this issue of CONTINUUM.

Insulin receptor isoform switching in intestinal stem cells, progenitors, differentiated lineages and tumors: evidence that IR-B limits proliferation

Despite evidence for the impact of insulin on intestinal epithelial physiology and pathophysiology, the expression patterns, roles, and regulation of insulin receptor (IR) and IR isoforms in the intestinal epithelium are not well characterized. IR-A is thought to mediate the proliferative effects of insulin or insulin growth factors (IGFs) in fetal or cancer cells. IR-B is considered to be the metabolic receptor for insulin in specialized tissues. This study used a novel Sox9-EGFP reporter mouse that permits isolation of intestinal epithelial stem cells (IESCs), progenitors, enteroendocrine cells and differentiated lineages, the Apc(Min/+) mouse model of precancerous adenoma and normal human intestinal and colorectal cancer (CRC) cell lines. We tested the hypothesis that there is differential expression of IR-A or IR-B in stem and tumor cells versus differentiated intestinal epithelial cells (IECs) and that IR-B impacts cell proliferation. Our findings provide evidence that IR-B expression is significantly lower in highly proliferative IESCs and progenitor cells versus post-mitotic, differentiated IECs and in subconfluent and undifferentiated versus differentiated Caco-2 cells. IR-B is also reduced in Apc(Min/+) tumors and highly tumorigenic CRC cells. These differences in IR-B were accompanied by altered levels of mRNAs encoding muscleblind-like 2 (MBNL2), a known regulator of IR alternative splicing. Forced IR-B expression in subconfluent and undifferentiated Caco-2 cells reduced proliferation and increased biomarkers of differentiation. Our findings indicate that the impact of insulin on different cell types in the intestinal epithelium might differ depending on relative IR-B IR-A expression levels and provide new evidence for the roles of IR-B to limit proliferation of CRC cells.