Deficient Muscle Research Articles

Gpcpd1-GPC metabolic pathway is dysfunctional in aging and its deficiency severely perturbs glucose metabolism.

Skeletal muscle plays a central role in the regulation of systemic metabolism during lifespan. With aging, this function is perturbed, initiating multiple chronic diseases. Our knowledge of mechanisms responsible for this decline is limited. Glycerophosphocholine phosphodiesterase 1 (Gpcpd1) is a highly abundant muscle enzyme that hydrolyzes glycerophosphocholine (GPC). The physiological functions of Gpcpd1 remain largely unknown. Here we show, in mice, that the Gpcpd1-GPC metabolic pathway is perturbed in aged muscles. Further, muscle-specific, but not liver- or fat-specific, inactivation of Gpcpd1 resulted in severely impaired glucose metabolism. Western-type diets markedly worsened this condition. Mechanistically, Gpcpd1 muscle deficiency resulted in accumulation of GPC, causing an 'aged-like' transcriptomic signature and impaired insulin signaling in young Gpcpd1-deficient muscles. Finally, we report that the muscle GPC levels are markedly altered in both aged humans and patients with type 2 diabetes, displaying a high positive correlation between GPC levels and chronological age. Our findings reveal that the muscle GPCPD1-GPC metabolic pathway has an important role in the regulation of glucose homeostasis and that it is impaired during aging, which may contribute to glucose intolerance in aging.

HDAC9 inhibition reduces skeletal muscle atrophy and enhances regeneration in mice with cigarette smoke-induced COPD

Cigarette smoke (CS) is the major risk factor for chronic obstructive pulmonary disease (COPD), and sarcopenia is one of the significant comorbidities of COPD. However, the pathogenesis of CS-related deficient skeletal muscle regeneration has yet to be clarified. The impact of CS on myoblast differentiation was examined, and then we determined which HDAC influenced the myogenic process and muscle atrophy in vitro and in vivo. Finally, we further investigated the potential mechanisms via RNA sequencing. Long-term CS exposure activated skeletal muscle primary SCs while inhibiting differentiation, and defective myogenesis was also observed in C2C12 cells treated with CS extract (CSE). The level of HDAC9 changed in vitro and in vivo in CS exposure models as well as COPD patients, as detected by bioinformatics analysis. Our data showed that CSE impaired myogenic capacity and myotube formation in C2C12 cells via HDAC9. Moreover, inhibition of HDAC9 in mice exposed to CS prevented skeletal muscle dysfunction and promoted SC differentiation. The results of RNA-Seq analysis and verification indicated that HDAC9 knockout improved muscle differentiation in CS-exposed mice, probably by acting on the AKT/mTOR pathway and inhibiting the P53/P21 pathway. More importantly, the serum of HDAC9 KO mice exposed to CS alleviated the differentiation impairment of C2C12 cells caused by serum intervention in CS-exposed mice, and this effect was inhibited by LY294002 (an AKT/mTOR pathway inhibitor). These results suggest that HDAC9 plays an essential role in the defective regeneration induced by chronic exposure to CS.

Direct Anterior Approach in Total Hip Arthroplasty for Severe Crowe IV Dysplasia: Retrospective Clinical and Radiological Study.

Background and Objectives: total hip arthroplasty (THA) for Crowe IV hip dysplasia poses challenges due to severe leg shortening, muscle retraction and bone stock issues, leading to an increased neurological complication, and revision rate. The direct anterior approach (DAA) is used for minimally invasive THA but its role in Crowe IV dysplasia is unclear. This retrospective study examines if DAA effectively restores hip biomechanics in Crowe IV dysplasia patients with <4 cm leg length discrepancy, managing soft tissue and yielding functional improvement, limb length correction, and limited complications. Materials and Methods: 19 patients with unilateral Crowe IV hip osteoarthritis and <4 cm leg length discrepancy undergoing DAA THA were reviewed. Surgery involved gradual soft tissue release, precise acetabular cup positioning, and stem placement without femoral osteotomy. Results: results were evaluated clinically and radiographically, with complications recorded. Follow-up revealed significant Harris Hip Score and limb length discrepancy improvements. Abductor muscle insufficiency was present in 21%. The acetabular component was accurately placed, centralizing the prosthetic joint's rotation. Complications occurred in 16% of cases, including fractures, nerve issues, and infection. DAA in THA showcased positive outcomes for hip function, limb length, and biomechanics in Crowe IV dysplasia. Conclusions: the technique enabled accurate cup positioning and rotation center adjustment. Complications were managed well without implant revisions. DAA is a viable option for Crowe IV dysplasia, restoring hip function, biomechanics, and reducing limb length discrepancy. Larger, longer studies are needed for validation.

PIEZO1 loss-of-function compound heterozygous mutations in the rare congenital human disorder Prune Belly Syndrome

Prune belly syndrome (PBS), also known as Eagle-Barret syndrome, is a rare, multi-system congenital myopathy primarily affecting males. Phenotypically, PBS cases manifest three cardinal pathological features: urinary tract dilation with poorly contractile smooth muscle, wrinkled flaccid ventral abdominal wall with skeletal muscle deficiency, and intra-abdominal undescended testes. Genetically, PBS is poorly understood. After performing whole exome sequencing in PBS patients, we identify one compound heterozygous variant in the PIEZO1 gene. PIEZO1 is a cation-selective channel activated by various mechanical forces and widely expressed throughout the lower urinary tract. Here we conduct an extensive functional analysis of the PIEZO1 PBS variants that reveal loss-of-function characteristics in the pressure-induced normalized open probability (NPo) of the channel, while no change is observed in single-channel currents. Furthermore, Yoda1, a PIEZO1 activator, can rescue the NPo defect of the PBS mutant channels. Thus, PIEZO1 mutations may be causal for PBS and the in vitro cellular pathophysiological phenotype could be rescued by the small molecule, Yoda1. Activation of PIEZO1 might provide a promising means of treating PBS and other related bladder dysfunctional states.

Cell Therapy by Mesenchymal Stromal Cells Versus Myoblasts in a Pig Model of Urinary Incontinence.

The leading cause of stress urinary incontinence (SUI) in women is the urethral sphincter muscle deficiency caused by mechanical stress during pregnancy and vaginal delivery. In men, prostate cancer surgery and injury of local nerves and muscles are associated with incontinence. Current treatment often fails to satisfy the patient's needs. Cell therapy may improve the situation. We therefore investigated the regeneration potential of cells in ameliorating sphincter muscle deficiency and UI in a large animal model. Urethral sphincter deficiency was induced surgically in gilts by electrocautery and balloon dilatation. Adipose tissue-derived stromal cells (ADSCs) and myoblasts from Musculus semitendinosus were isolated from male littermates, expanded, characterized in depth for expression of marker genes and in vitro differentiation, and labeled. The cells were injected into the deficient sphincter complex of the incontinent female littermates. Incontinent gilts receiving no cell therapy served as controls. Sphincter deficiency and functional regeneration were recorded by monitoring the urethral wall pressure during follow-up by two independent methods. Cells injected were detected in vivo during follow-up by transurethral fluorimetry, ex vivo by fluorescence imaging, and in cryosections of tissues targeted by immunofluorescence and by polymerase chain reaction of the sex-determining region Y (SRY) gene. Partial spontaneous regeneration of sphincter muscle function was recorded in control gilts, but the sphincter function remained significantly below levels measured before induction of incontinence (67.03% ± 14.00%, n = 6, p < 0.05). Injection of myoblasts yielded an improved sphincter regeneration within 5 weeks of follow-up but did not reach significance compared to control gilts (81.54% ± 25.40%, n = 5). A significant and full recovery of the urethral sphincter function was observed upon injection of ADSCs within 5 weeks of follow-up (100.4% ± 23.13%, n = 6, p < 0.05). Injection of stromal cells provoked slightly stronger infiltration of CD45pos leukocytes compared to myoblasts injections and controls. The data of this exploratory study indicate that ADSCs inherit a significant potential to regenerate the function of the urethral sphincter muscle.

Characterization of Motor Performance in 200 Normal Ankles Through Isokinetic Evaluation

Category: Ankle; Sports Introduction/Purpose: The isokinetic test has been used diffusely as a way to evaluate the functional results after the rehabilitation of musculoskeletal injuries. In the ankle, in particular, most studies are related to lateral ligament injuries and Achilles tendon’s injuries. However, different protocols are used and a lack of normative values is observed in the literature. The aim of this work is to perform a global isokinetic evaluation on healthy ankles in order to propose reference values for future patients. Methods: We evaluated 100 participants (200 ankles) using the Biodex 3 System for the eversion, inversion, dorsiflexion and plantar flexion movements of the ankle. The sample consisted of individuals aged 20-60 years, with an active life and practice of recreational physical activity (non-athlete) and without previous injuries. Five repetitions for strength (N / m) and work (J) at a speed of 30º / sec and 10 repetitions for power (W) at a speed of 120º / sec were performed in our protocol. Agonist / antagonist ratio and the Muscle Deficiency Index, which globally assesses the balance between the sides for each movement, were also evaluated, as well as the demographic variables. Different statistical analyzes were performed for each parameter. Results: The mean age was 38.5 years and BMI 25.8 in 69 men and 31 women. In 78 participants, the dominant ankle was the right one. The non-dominant side was consistently stronger in all movements (p &lt; 0.001). The mean values obtained for force in each movement were 29.9N/m for eversion, 34.8N/m for inversion, 48.6N/m for dorsiflexion and 140.2 N/m for plantar flexion. Such parameters for men and women were also obtained (p &lt; 0.001) and there was no correlation between age or BMI with the maximum torque through Spearman's Correlation. The ratio of eversors/inverters was 88.8% and that of dorsiflexors/plantar flexors was 36.1%. The Muscle Deficiency Index showed a balance between the sides for each movement, with an average global difference of less than 10% between them. Conclusion: As far as we know, this is the largest isokinetic assessment of normal ankles ever performed. The sample, although not stratified, was considered homogeneous (coefficient of variation &lt; 50%), which allows to propose several normative values for a non-athlete population in the isokinetic evaluation. It would be interesting to compare these data in the future with the functional results in patients after the treatment of certain injuries.

THE EFFECT OF DRY WHITE MISTLETOE EXTRACT ON THE CHANGE IN THE RATIO OF MITOCHONDRIAL SUBPOPULATIONS IN THE MYOCARDIUM IN ANIMALS WITH ALCOHOLIC CARDIOMYOPATHY

The aim of the research was to study the cardioprotective effect of dry white mistletoe extract in the context of assessing its effect on changes in the activity of interfibrillary and subsarcolemmal mitochondrial subpopulations of the myocardium in experimental alcoholic cardiomyopathy. Materials and methods. Alcoholic cardiomyopathy was modeled in female Wistar rats by course administration of ethanol at the rate of 3 g of absolute ethanol per 1 kg of animal body weight. The studied extract of white mistletoe leaves and the comparison drug – Trimetazidine – were administered orally at doses of 100 mg /kg and 35 mg/kg, respectively. Changes in troponin I concentration and serum creatine phosphokinase activity, citrate synthase activity in mitochondrial subpopulations, and the content of apoptosis markers – apoptosis-inducing factor and caspase 3 in myocardial tissue homogenate were determined during the work. Results and their discussion. The analysis of the results revealed that in rats with alcoholic cardiomyopathy, but without treatment, there is an increase in the concentration of troponin I and creatine phosphokinase activity, accompanied by an increase in the intensity of apoptosis reactions and citrate synthase activity of interfibrillary mitochondria. The use of Trimetazidine and the extract under analysis contributed to a decrease in troponin I content by 19.1% (p &lt; 0.05) and 24.4%, respectively, and creatine phosphokinase activity by 19.8% (p &lt; 0.05) and 28.4% (p &lt; 0.05). It was also established that the activity of subsarcolemmal mitochondria in animals treated with Trimetazidine and white mistletoe extract increased by 121.9% (p &lt; 0.05) and 306.3% (p &lt; 0.05) with a decrease in the activity of citrate synthase of interfibrillary mitochondria by 27.6% (p &lt; 0.05) and 41.4% (p &lt; 0.05). It should be noted that administration of the comparative drug and the studied extract to rats resulted in a decrease in cardiomyocytes' apoptosis, expressed in a decrease in the concentration of apoptosis-inducing factor and caspase 3. Conclusions. In conditions of alcoholic cardiomyopathy, the negative interfibrillary phenotype of mitochondria prevails, which can contribute to the development of energy deficiency in the heart muscle, increasing the degree of myocardial damage. Based on the data obtained, it can be assumed that the extract of white mistletoe contains an active substance of cardioprotective activity associated with restoring the energy metabolism and suppression of apoptosis in the myocardium.

The role of different physiotherapy methods in tibialis posterior muscle insufficiency – a literature review

Introduction. Dysfunction or rupture of the posterior tibial tendon (PTT) is a fairly common cause of acquired adult flatfoot. Conservative and surgical treatments are used to correct PTT dysfunction. Objective. The aim of this study was to present the characteristic features of PTT dysfunction and evaluate the application and effectiveness of selected physiotherapeutic methods in the treatment of posterior tibial muscle insufficiency. Materials and Methods. Available literature was analyzed based on English-language databases such as PubMed, Scopus, ScienceDirect, Medline, and others, using the Google Scholar search engine. A total of 20 articles were analyzed out of 52 identified through the aforementioned method. Publications no older than 10 years were included as search criteria, using the following keywords: posterior tibial muscle insufficiency, orthoses, orthopedic insoles, flatfoot, physiotherapy. Results. It was not possible to specify which method of treating posterior tibial muscle insufficiency is the most effective. Conclusions. Contemporary research suggests that conservative treatment methods appear to be effective in treating posterior tibial muscle insufficiency. Although opinions on the effectiveness of orthoses are divided, the majority acknowledges that orthoses

Smooth muscle liver kinase B1 inhibits foam cell formation and atherosclerosis via direct phosphorylation and activation of SIRT6

Foam cell formation is a hallmark of the early phase of atherosclerosis. Growing evidence has demonstrated that vascular smooth muscle cells (VSMCs) comprise a considerable proportion of foam cells. Liver kinase B1 (LKB1) plays a crucial part in cardiovascular diseases. However, the role of LKB1 in VSMC-derived foam cell formation and atherosclerosis remains unclear. To explore the effects of LKB1 on VSMC-derived foam cell formation and atherosclerosis, we generated smooth muscle-specific LKB1 knockout (LKB1SMKO) mice by crossbreeding LKB1flox/flox mice with SM22α-CreERT2 mice. LKB1 expression decreased in plaque-loaded aortas and oxidized low-density lipoprotein (oxLDL)-treated VSMCs. Compared with controls, atherosclerosis development was exacerbated in LKB1SMKO mice via the promotion of VSMC-derived foam cell formation. Conversely, LKB1 overexpression inhibited lipid uptake and foam cell formation in VSMCs. Mechanistically, LKB1 binds to SIRT6 and directly phosphorylates and activates it, thereby reducing lectin-like oxLDL receptor-1 (LOX-1) via SIRT6-dependent histone deacetylation. Finally, adeno-associated virus (AAV)-mediated LOX-1 deficiency in smooth muscle ameliorated atherosclerosis in LKB1SMKO mice. Our findings suggest that LKB1 may modulate VSMC-derived foam cell formation and atherosclerosis via the phosphorylation and activation of SIRT6.

One-year follow-up after standardized perineal reconstruction in women with deficient perineum after vaginal delivery.

Perineal tears are common after childbirth and, if not surgically repaired, they may result in a deficient perineum that can cause symptoms of pelvic floor dysfunction. Perineal reconstruction aims to restore the perineal body and increase the support of the pelvic floor. The objective of the present study was to estimate symptom reduction after perineal reconstruction in patients with deficient perineum after vaginal delivery and to compare outcomes between participants with or without concomitant levator ani muscle deficiency. Participants presenting at the Karolinska Pelvic Floor Center with symptoms of deficient perineum at least 1 year after vaginal birth were invited to the study. Inclusion criteria were a visible perineal scar and confirmed anatomic defect. Levator ani defects were assessed using the Levator Ani Deficiency score. A perineal reconstruction was performed in a standardized way. Subjective symptoms were evaluated using the validated "Karolinska Symptoms After Perineal Tear Inventory" at baseline and 1-year follow-up. A score difference in the symptom of an acquired sensation of a wide vagina was the primary outcome. Results were stratified by the presence or absence of a levator ani deficiency. A perineal reconstruction was performed in 131 patients and 128 patients completed the Karolinska Symptoms After Perineal Tear Inventory at baseline and 119 at follow-up. Median age was 36.1 (interquartile range [IQR] 7.9), median body mass index 22.3 (IQR 5.1) and a median of two vaginal deliveries. Fifty-four women (41.2%) had a levator ani deficiency. The mean score reduction for the item "Do you feel that your vagina is too wide/loose?" was -1.56 (SD 0.96; P < 0.001) from a mean score of 2.75 (maximum 3) at baseline. The mean total score reduction was -9.1 points (SD 5.3; P < 0.001) from a mean score of 18.4 (maximum 33) points at baseline. There were no significant differences between groups when stratifying by levator ani deficiency. Our results show that perineal reconstructive surgery significantly decreases symptoms of deficient perineum after vaginal delivery. A concomitant levator ani defect does not affect the symptom reduction of an acquired sensation of a wide vagina or the total score reduction after surgery.

The utility of gene sequencing in identifying an underlying genetic disorder in prenatally suspected lower urinary tract obstruction.

Fetal megacystis generally presents as suspected lower urinary tract obstruction (LUTO), which is associated with severe perinatal morbidity. Genetic etiologies underlying LUTO or a LUTO-like initial presentation are poorly understood. Our objectives are to describe single gene etiologies in fetuses initially ascertained to have suspected LUTO and to elucidate genotype-phenotype correlations. A retrospective case series of suspected fetal LUTO positive for a molecular diagnosis was collected from five centers in the Fetal Sequencing Consortium. Demographics, sonograms, genetic testing including variant classification, and delivery outcomes were abstracted. Seven cases of initially prenatally suspected LUTO-positive for a molecular diagnosis were identified. In no case was the final diagnosis established as urethral obstruction that is, LUTO. All variants were classified as likely pathogenic or pathogenic. Smooth muscle deficiencies involving the bladder wall and interfering with bladder emptying were identified in five cases: MYOCD (2), ACTG2 (2), and MYH11 (1). Other genitourinary and/or non-genitourinary malformations were seen in two cases involving KMT2D (1) and BBS10 (1). Our series illustrates the value of molecular diagnostics in the workup of fetuses who present with prenatally suspected LUTO but who may have a non-LUTO explanation for their prenatal ultrasound findings.

Modified Osteotomy for TMJ Ankylosis in Paediatric Patients with Deficient Interpositional Temporalis Muscle Mass and Buccal Fat Pad - A case Series and Literature Review.

Ankylosis of the temporomandibular joint (TMJ) is a bony or fibrous fusion of the articular surfaces of the mandibular condyle and the glenoid fossa. Gap arthroplasty, Interpositional arthroplasty, Condyle reconstruction with autogenic or alloplastic grafts and total joint replacement are some common modalities of management. In this article, we discuss a series of three cases of unilateral TMJ ankylosis in paediatric patients, managed by gap arthroplasty using a modified osteotomy cut. The modification was adapted due to inadequate interpositionable temporalis muscle or buccal fat on the affected side and chances of adaptive remodelling of the CCG (Costochondral graft), if placed were rendered negative.

Dynamic regulation of inter-organelle communication by ubiquitylation controls skeletal muscle development and disease onset.

Ubiquitin-proteasome system (UPS) dysfunction is associated with the pathology of a wide range of human diseases, including myopathies and muscular atrophy. However, the mechanistic understanding of specific components of the regulation of protein turnover during development and disease progression in skeletal muscle is unclear. Mutations in KLHL40, an E3 ubiquitin ligase cullin3 (CUL3) substrate-specific adapter protein, result in severe congenital nemaline myopathy, but the events that initiate the pathology and the mechanism through which it becomes pervasive remain poorly understood. To characterize the KLHL40-regulated ubiquitin-modified proteome during skeletal muscle development and disease onset, we used global, quantitative mass spectrometry-based ubiquitylome and global proteome analyses of klhl40a mutant zebrafish during disease progression. Global proteomics during skeletal muscle development revealed extensive remodeling of functional modules linked with sarcomere formation, energy, biosynthetic metabolic processes, and vesicle trafficking. Combined analysis of klh40 mutant muscle proteome and ubiquitylome identified thin filament proteins, metabolic enzymes, and ER-Golgi vesicle trafficking pathway proteins regulated by ubiquitylation during muscle development. Our studies identified a role for KLHL40 as a regulator of ER-Golgi anterograde trafficking through ubiquitin-mediated protein degradation of secretion-associated Ras-related GTPase1a (Sar1a). In KLHL40-deficient muscle, defects in ER exit site vesicle formation and downstream transport of extracellular cargo proteins result in structural and functional abnormalities. Our work reveals that the muscle proteome is dynamically fine-tuned by ubiquitylation to regulate skeletal muscle development and uncovers new disease mechanisms for therapeutic development in patients.

Gluteus maximus transfer for wound closure and treatment of abductor deficiency: a single-plastic surgeon series.

Due to the increasing number of total hip arthroplasties (THA), the number and complexity of revision procedures are also on the rise. For complex cases such as periprosthetic joint infections with soft tissue compromise or for abductor muscle deficiencies, one of the treatment options is a gluteus maximus flap (GMF) that covers dead space and can help restore the failed abductor mechanism. The purpose of this study is to investigate the outcomes of a single-plastic surgeon's series of GMF procedures. This retrospective review reports on 57 patients (mean follow-up 39.2months) undergoing GMF transfers for abductor insufficiency on native hip (N = 16), for abductor insufficiency in aseptic revision THA (rTHA) (N = 16), for soft tissue defects in aseptic rTHA (N = 8) and for soft tissue defects in septic rTHA (N = 17) by a single plastic surgeon over a 10-year period. Revision-free survival and complication rates were assessed and risk factors were analyzed with Cox-regression analysis. The reoperation-free survival rate of GMF for abductor insufficiency in native hips was 100%. GMF procedures for soft tissue defects in septic rTHA had the lowest cumulative revision-free survival (34.3%) and highest reinfection rates (53.9%). More than three prior surgeries (HR = 2.9, p = 0.020), presence of infection (HR = 3.2, p = 0.010) and resistant organisms (HR = 3.1, p = 0.022) significantly increased the risk of revision. GMF is a viable option for addressing abductor insufficiency in native hip joints. However, high revision and complication rates are reported for GMF in septic rTHA. This study highlights the need to clarify the circumstances for which the flap reconstruction will be indicated.

1627-P: Enhancer Regulator MLL4 Programs Skeletal Muscle Metabolic Efficiency by Limiting AMPK-Mediated Fuel Catabolism

Skeletal muscle adapts to nutrient availability and physiological demands by fine-tuning gene expression patterns and metabolism to maximize metabolic efficiency. The mechanisms that enable and mediate muscle transcriptional and metabolic responses to environmental cues remain unclear, however. We have shown previously that enhancer regulator MLL4 is required for establishing and maintaining slow type I fiber program to ensure running endurance (J Clin Invest. 2020;130(9):4710-4725). Here, we report that MLL4 plays a critical role in directing muscle metabolic transcriptional adaptation that governs metabolic efficiency and systemic metabolism. MLL4 expression is regulated by nutrient availability, and skeletal muscle-specific ablation of MLL4 protects mice against diet-induced obesity and improves systemic glucose homeostasis despite reducing exercise endurance. Combining comprehensive metabolic and genomic analysis of the MLL4-depleted muscles using multidimensional ‘omics’ technologies, we gained insight into the molecular targets and biological functions of the MLL4 protein. Specifically, this seemingly paradoxical phenotype is due to markedly enhanced fuel catabolism in MLL4 deficient muscles, a favorable metabolic reprogramming caused by the activation of muscle AMPK. Isotopic 13C-glucose tracing experiments in myocyte provided further evidence that MLL4 exerts control upon muscle fuel catabolism. Remarkably, pharmacologic targeting the MLL4 pathway activates muscle AMPK, confers resistance to diet-induced obesity and ameliorates obesity-related insulin resistance and liver steatosis. These results identify an enhancer regulator limiting AMPK-mediated muscle fuel catabolism and offer a new potential therapeutic strategy for obesity-related metabolic disorders. Disclosure L.Yang: None. L.Liu: None. C.Ding: None. T.Fu: None. Z.Zhou: None. Z.Gan: None.

Chronic Vitamin E Deficiency Dysregulates Purine, Phospholipid, and Amino Acid Metabolism in Aging Zebrafish Skeletal Muscle.

Muscle wasting occurs with aging and may be a result of oxidative stress damage and potentially inadequate protection by lipophilic antioxidants, such as vitamin E. Previous studies have shown muscular abnormalities and behavioral defects in vitamin E-deficient adult zebrafish. To test the hypothesis that there is an interaction between muscle degeneration caused by aging and oxidative damage caused by vitamin E deficiency, we evaluated long-term vitamin E deficiency in the skeletal muscle of aging zebrafish using metabolomics. Zebrafish (55 days old) were fed E+ and E- diets for 12 or 18 months. Then, skeletal muscle samples were analyzed using UPLC-MS/MS. Data were analyzed to highlight metabolite and pathway changes seen with either aging or vitamin E status or both. We found that aging altered purines, various amino acids, and DHA-containing phospholipids. Vitamin E deficiency at 18 months was associated with changes in amino acid metabolism, specifically tryptophan pathways, systemic changes in the regulation of purine metabolism, and DHA-containing phospholipids. In sum, while both aging and induced vitamin E deficiency did have some overlap in altered and potentially dysregulated metabolic pathways, each factor also presented unique alterations, which require further study with more confirmatory approaches.

Androgen receptor coordinates muscle metabolic and contractile functions.

Androgens are anabolic steroid hormones that exert their function by binding to the androgen receptor (AR). We have previously established that AR deficiency in limb muscles impairs sarcomere myofibrillar organization and decreases muscle strength in male mice. However, despite numerous studies performed in men and rodents, the signalling pathways controlled by androgens via their receptor in skeletal muscles remain poorly understood. Male ARskm-/y (n=7-12) and female ARskm-/- mice (n=9), in which AR is selectively ablated in myofibres of musculoskeletal tissue, and male AR(i)skm-/y , in which AR is selectively ablated in post-mitotic skeletal muscle myofibres (n=6), were generated. Longitudinal monitoring of body weight, blood glucose, insulin, lipids and lipoproteins was performed, alongside metabolomic analyses. Glucose metabolism was evaluated in C2C12 cells treated with 5α-dihydrotestosterone (DHT) and the anti-androgen flutamide (n=6). Histological analyses on macroscopic and ultrastructural levels of longitudinal and transversal muscle sections were conducted. The transcriptome of gastrocnemius muscles from control and ARskm-/y mice was analysed at the age of 9weeks (P<0.05, 2138 differentially expressed genes) and validated by RT-qPCR analysis. The AR (4691 peaks with false discovery rate [FDR]<0.1) and H3K4me2 (47225 peaks with FDR<0.05) cistromes in limb muscles were determined in 11-week-old wild-type mice. We show that disrupting the androgen/AR axis impairs in vivo glycolytic activity and fastens the development of type 2 diabetes in male, but not in female mice. In agreement, treatment with DHT increases glycolysis in C2C12 myotubes by 30%, whereas flutamide has an opposite effect. Fatty acids are less efficiently metabolized in skeletal muscles of ARskm-/y mice and accumulate in cytoplasm, despite increased transcript levels of genes encoding key enzymes of beta-oxidation and mitochondrial content. Impaired glucose and fatty acid metabolism in AR-deficient muscle fibres is associated with 30% increased lysine and branched-chain amino acid catabolism, decreased polyamine biosynthesis and disrupted glutamate transamination. This metabolic switch generates ammonia (2-fold increase) and oxidative stress (30% increased H2 O2 levels), which impacts mitochondrial functions and causes necrosis in <1% fibres. We unravel that AR directly activates the transcription of genes involved in glycolysis, oxidative metabolism and muscle contraction. Our study provides important insights into diseases caused by impaired AR function in musculoskeletal system and delivers a deeper understanding of skeletal muscle pathophysiological dynamics that is instrumental to develop effective treatment for muscle disorders.

RIP140 deficiency enhances cardiac fuel metabolism and protects mice from heart failure.

During the development of heart failure (HF), the capacity for cardiomyocyte (CM) fatty acid oxidation (FAO) and ATP production is progressively diminished, contributing to pathologic cardiac hypertrophy and contractile dysfunction. Receptor-interacting protein 140 (RIP140, encoded by Nrip1) has been shown to function as a transcriptional corepressor of oxidative metabolism. We found that mice with striated muscle deficiency of RIP140 (strNrip1-/-) exhibited increased expression of a broad array of genes involved in mitochondrial energy metabolism and contractile function in heart and skeletal muscle. strNrip1-/- mice were resistant to the development of pressure overload-induced cardiac hypertrophy, and CM-specific RIP140-deficient (csNrip1-/-) mice were protected against the development of HF caused by pressure overload combined with myocardial infarction. Genomic enhancers activated by RIP140 deficiency in CMs were enriched in binding motifs for transcriptional regulators of mitochondrial function (estrogen-related receptor) and cardiac contractile proteins (myocyte enhancer factor 2). Consistent with a role in the control of cardiac fatty acid oxidation, loss of RIP140 in heart resulted in augmented triacylglyceride turnover and fatty acid utilization. We conclude that RIP140 functions as a suppressor of a transcriptional regulatory network that controls cardiac fuel metabolism and contractile function, representing a potential therapeutic target for the treatment of HF.

Motor neuron involvement threatens survival in spinocerebellar ataxia type 1.

Motor neuron involvement threatens survival in spinocerebellar ataxia type 1.

Lipin1 plays complementary roles in myofibre stability and regeneration in dystrophic muscles.

Duchenne muscular dystrophy (DMD) is a severe muscle wasting disorder caused by dystrophin mutations, leading to the loss of sarcolemmal integrity, and resulting in progressive myofibre necrosis and impaired muscle function. Our previous studies suggest that lipin1 is important for skeletal muscle regeneration and myofibre integrity. Additionally, we discovered that mRNA expression levels of lipin1 were significantly reduced in skeletal muscle of DMD patients and the mdx mouse model. To understand the role of lipin1 in dystrophic muscle, we generated dystrophin/lipin1 double knockout (DKO) mice, and compared the limb muscle pathology and function of wild-type B10, muscle-specific lipin1 deficient (lipin1Myf5cKO ), mdx and DKO mice. We found that further knockout of lipin1 in dystrophic muscle exhibited a more severe phenotype characterized by increased necroptosis, fibrosis and exacerbated membrane damage in DKO compared to mdx mice. In barium chloride-induced muscle injury, both lipin1Myf5cKO and DKO showed prolonged regeneration at day 14 post-injection, suggesting that lipin1 is critical for muscle regeneration. In situ contractile function assays showed that lipin1 deficiency in dystrophic muscle led to reduced specific force production. Using a cell culture system, we found that lipin1 deficiency led to elevated expression levels of necroptotic markers and medium creatine kinase, which could be a result of sarcolemmal damage. Most importantly, restoration of lipin1 inhibited the elevation of necroptotic markers in differentiated primary lipin1-deficient myoblasts. Overall, our data suggests that lipin1 plays complementary roles in myofibre stability and muscle function in dystrophic muscles, and overexpression of lipin1may serve as a potential therapeutic strategy for dystrophic muscles. KEY POINTS: We identified that lipin1mRNA expression levels are significantly reduced in skeletal muscles of Duchenne muscular dystrophy patients and mdx mice. We found that further depletion of lipin1 in skeletal muscles of mdx mice induces more severe dystrophic phenotypes, including enhanced myofibre sarcolemma damage, muscle necroptosis, inflammation, fibrosis and reduced specific force production. Lipin1 deficiency leads to elevated expression levels of necroptotic markers, whereas restoration of lipin1 inhibits their expression. Our results suggest that lipin1 is functionally complementary to dystrophin in muscle membrane integrity and muscle regeneration.