Myofibrillar Degeneration Research Articles

A novel, patient-derived RyR1 mutation impairs muscle function and calcium homeostasis in mice.

RYR1 is the most commonly mutated gene associated with congenital myopathies, a group of early-onset neuromuscular conditions of variable severity. The functional effects of a number of dominant RYR1 mutations have been established; however, for recessive mutations, these effects may depend on multiple factors, such as the formation of a hypomorphic allele, or on whether they are homozygous or compound heterozygous. Here, we functionally characterize a new transgenic mouse model knocked-in for mutations identified in a severely affected child born preterm and presenting limited limb movement. The child carried the homozygous c.14928C>G RYR1 mutation, resulting in the p.F4976L substitution. In vivo and ex vivo assays revealed that homozygous mice fatigued sooner and their muscles generated significantly less force compared with their WT or heterozygous littermates. Electron microscopy, biochemical, and physiological analyses showed that muscles from RyR1 p.F4976L homozygous mice have the following properties: (1) contain fewer calcium release units and show areas of myofibrillar degeneration, (2) contain less RyR1 protein, (3) fibers show smaller electrically evoked calcium transients, and (4) their SR has smaller calcium stores. In addition, single-channel recordings indicate that RyR1 p.F4976L exhibits higher Po in the presence of 100 μM [Ca2+]. Our mouse model partly recapitulates the clinical picture of the homozygous human patient and provides significant insight into the functional impact of this mutation. These results will help understand the pathology of patients with similar RYR1 mutations.

DNAJB6 mutants display toxic gain of function through unregulated interaction with Hsp70 chaperones

Molecular chaperones are essential cellular components that aid in protein folding and preventing the abnormal aggregation of disease-associated proteins. Mutations in one such chaperone, DNAJB6, were identified in patients with LGMDD1, a dominant autosomal disorder characterized by myofibrillar degeneration and accumulations of aggregated protein within myocytes. The molecular mechanisms through which such mutations cause this dysfunction, however, are not well understood. Here we employ a combination of solution NMR and biochemical assays to investigate the structural and functional changes in LGMDD1 mutants of DNAJB6. Surprisingly, we find that DNAJB6 disease mutants show no reduction in their aggregation-prevention activity in vitro, and instead differ structurally from the WT protein, affecting their interaction with Hsp70 chaperones. While WT DNAJB6 contains a helical element regulating its ability to bind and activate Hsp70, in LGMDD1 disease mutants this regulation is disrupted. These variants can thus recruit and hyperactivate Hsp70 chaperones in an unregulated manner, depleting Hsp70 levels in myocytes, and resulting in the disruption of proteostasis. Interfering with DNAJB6-Hsp70 binding, however, reverses the disease phenotype, suggesting future therapeutic avenues for LGMDD1.

Synergistic role of resveratrol and exercise training in management of diabetic neuropathy and myopathy via SIRT1/NGF/GAP43 linkage

AimsOxidative stress also plays an important role in the pathogenesis of diabetic neuropathy (DN). Both resveratrol (RES) and exercise (EX) have potent anti-oxidative benefits. Low levels of nerve growth factor (NGF) and SIRT1 (a member of sirtuin family) have been reported in patients with DN. The current study has been designed to investigate the role of serum NGF and SIRT1 on DN-induced hyperalgesia and motor incoordination and to evaluate the possible protective role of RES and/or EX. Main methodsA total of 40 male adult albino rats divided into five groups; control, DN, DN + RES, DN + EX, and DN + RES and EX. DN was confirmed by sensorimotor disturbance and diminished nerve conduction velocity (NCV). NGF and SIRT1 levels were measured by western blot. Calcitonin gene-related peptide (CGRP) was measured by PCR. Myofibrillar degeneration and inflammation scores were revealed via H&E microscopic analysis of the gastrocnemius muscle. Immunohistochemical evaluation of caspase3 and TNF-α was performed in the lumber segment of spinal cord and gastrocnemius muscle sections. Ultrastructural evaluation of sciatic nerve axonal degeneration has also been assessed. Key findingsDN group showed decreased SIRT1 level, decreased NGF level and correlated with CGRP level and Na+/K+ ATPase. Treatment with RES and/or EX resulted in improvement of sensorimotor disturbance. DN characterized by reduced SOD level, whereas RES and/or EX could limit oxidative damage by up-regulation Bcl2, Akt and GAP-43 and down-regulation of caspase3 and TNF-α. In conclusion, increased level of SIRT1and NGF by incorporation of RES (natural supplementation) and EX (life style modification) could improve the neuroinflammatory state in DN.

Cellular and Molecular Mechanisms of MEK1 Inhibitor–Induced Cardiotoxicity

BackgroundTrametinib is a MEK1 (mitogen-activated extracellular signal-related kinase kinase 1) inhibitor used in the treatment of BRAF (rapid accelerated fibrosarcoma B-type)–mutated metastatic melanoma. Roughly 11% of patients develop cardiomyopathy following long-term trametinib exposure. Although described clinically, the molecular landscape of trametinib cardiotoxicity has not been characterized. ObjectivesThe aim of this study was to test the hypothesis that trametinib promotes widespread transcriptomic and cellular changes consistent with oxidative stress and impairs cardiac function. MethodsMice were treated with trametinib (1 mg/kg/d). Echocardiography was performed pre- and post-treatment. Gross, histopathologic, and biochemical assessments were performed to probe for molecular and cellular changes. Human cardiac organoids were used as an in vitro measurement of cardiotoxicity and recovery. ResultsLong-term administration of trametinib was associated with significant reductions in survival and left ventricular ejection fraction. Histologic analyses of the heart revealed myocardial vacuolization and calcification in 28% of animals. Bulk RNA sequencing identified 435 differentially expressed genes and 116 differential signaling pathways following trametinib treatment. Upstream gene analysis predicted interleukin-6 as a regulator of 17 relevant differentially expressed genes, suggestive of PI3K/AKT and JAK/STAT activation, which was subsequently validated. Trametinib hearts displayed elevated markers of oxidative stress, myofibrillar degeneration, an 11-fold down-regulation of the apelin receptor, and connexin-43 mislocalization. To confirm the direct cardiotoxic effects of trametinib, human cardiac organoids were treated for 6 days, followed by a 6-day media-only recovery. Trametinib-treated organoids exhibited reductions in diameter and contractility, followed by partial recovery with removal of treatment. ConclusionsThese data describe pathologic changes observed in trametinib cardiotoxicity, supporting the exploration of drug holidays and alternative pharmacologic strategies for disease prevention.

Skeletal Muscles of Patients Infected with SARS-CoV-2 Develop Severe Myofiber Damage upon One Week of Admission on the Intensive Care Unit

Many critically ill patients infected with SARS-CoV-2 have been submitted to an intensive care unit (ICU). Patients with a SARS-CoV-2 infection that survive critical illness are confronted with months of physical impairments. To maximize recovery, it is important to understand the musculoskeletal involvement in critically ill patients infected with SARS-CoV-2. The aim of the present study was to assess the myocellular changes in SARS-CoV-2 patients that occur throughout the first week of ICU admission. In n = 22 critically ill patients infected with SARS-CoV-2, a biopsy sample from the vastus lateralis muscle was obtained at day 1–3 and day 5–8 following ICU admission. Fluorescence microscopy was used to assess type I and type II muscle fiber size and distribution, myonuclear content, and muscle tissue capillarization. Transmission electron microscopy was used to support quantitative data at an ultrastructural level. Changes in type I and type II muscle fiber size showed large inter-individual variation. The average change in type I fiber size was +309 ± 1834 µm2, ranging from −2129 µm2 (−31%) to +3375 µm2 (+73%). The average change in type II fiber size was −224 ± 1256 µm2, ranging from −1410 µm2 (−36%) to +2592 µm2 (+48%). Ultrastructural observations showed myofibrillar and hydropic degeneration, and fiber necrosis. This study shows that ICU patients admitted with SARS-CoV-2 suffer from substantial muscle fiber damage during ICU admission. These results are a call for action towards more specialized rehabilitation programs for patients admitted to the ICU with SARS-CoV-2 infection.

The In Vitro Cytotoxic Effects of Ionophore Exposure on Selected Cytoskeletal Proteins of C2C12 Myoblasts.

Carboxylic ionophores, such as monensin, salinomycin and lasalocid, are polyether antibiotics used widely in production animals for the control of coccidiosis, as well as for the promotion of growth and feed efficiency. Although the benefits of using ionophores are undisputed, cases of ionophore toxicosis do occur, primarily targeting the cardiac and skeletal muscles of affected animals. The 3-[4,5-dimethylthiazol-2yl]-2,5-diphenyl tetrazolium bromide (MTT) viability assay was used to determine the cytotoxicity of monensin, salinomycin and lasalocid on mouse skeletal myoblasts (C2C12). Immunocytochemistry and immunofluorescent techniques were, in turn, performed to investigate the effects of the ionophores on the microfilament, microtubule and intermediate filament, i.e., desmin and synemin networks of the myoblasts. Monensin was the most cytotoxic of the three ionophores, followed by salinomycin and finally lasalocid. Monensin and salinomycin exposure resulted in the aggregation of desmin around the nuclei of affected myoblasts. The synemin, microtubule and microfilament networks were less affected; however, vesicles throughout the myoblast’s cytoplasm produced gaps within the microtubule and, to a limited extent, the synemin and microfilament networks. In conclusion, ionophore exposure disrupted desmin filaments, which could contribute to the myofibrillar degeneration and necrosis seen in the skeletal muscles of animals suffering from ionophore toxicosis.

NEW GENES, NEW TECHNIQUES IN NEUROMUSCULAR DISORDERS: O.10 Loss of function mutations in DNAJB4 cause a myopathy with early respiratory failure

Through next generation sequencing of patients with unexplained muscle disease, we identified four individuals from three unrelated families carrying homozygous variants in the DNAJB4 gene. Clinical presentation was similar with acute respiratory failure leading to life threatening hypercapnia and artificial ventilation. In addition, all patients presented some degree of spine rigidity. Disease onset was variable, between the 1st and 4th decade of life. MRI showed a similar selective pattern of muscle involvement. DNAJB4 is a heat shock protein belonging to the DNAJ/HSP40 family. DNAJ proteins are emerging as proteins critical for muscle protein homeostasis and another homologous protein, DNAJB6 – is causative for LGMD D1 (DNAJB6 related). LGMDD1 is characterized by proximal and/or distal muscle weakness, atrophy and protein aggregates, myofibrillar degeneration, and rimmed vacuoles on muscle biopsy. The DNAJB4 variants identified, a stop gain (c.856A>T; p.Lys286*) and two missense changes (c.74G>A; p.Arg25Gln and c.785T>C; p.Leu262Ser) are absent in the control population and are predicted to result in loss of protein, or protein function. Consistent with this, immunoblots from patient muscle tissue and fibroblasts confirmed the absence of DNAJB4 in the p.Lys286* and p.Leu262Ser patients. Functional studies confirm that the p.Lys286* and p.Leu262Ser variants are rapidly degraded in cells. In contrast the p.Arg25Gln is stable but behaves as a loss of function in cellular assays of DNAJB4 chaperone function. In muscle DNAJB4 localizes to the Z-disc and DNAJB4 knockout myotubes and mouse muscle accumulate desmin and other potential client proteins. These data demonstrate a novel chaperonopathy associated with DNAJB4 causing a myopathy with early respiratory failure. DNAJB4 loss of function mutations may lead to the accumulation of DNAJB4 client proteins resulting in muscle dysfunction and degeneration.

Commentary: "Postoperative Changes in Left Ventricular Systolic Function after Combined Mitral and Aortic Valve Replacement in Patients with Rheumatic Heart Disease" Sang-Mee An, MD, Jae-Sik Nam, MD, Ho Jin Kim, MD, PhD, Hyeun Joon Bae, MD, Ji-Hyun Chin, MD, PhD, Eun-Ho Lee, MD, PhD, In-Cheol Choi, MD, PhD.

It is an elegant albeit limited study reporting effects of pre op LVEF on long term results in patients with RHD undergoing DVR. Study includes 146 patients out of 201 who underwent DVR in the study period. Although all had some improvement immediate post op, those with preserved ejection fraction (EF) and smaller left ventricles regardless of type of prostheses used, surgical techniques (partial or full Subvalvular Apparatus Preservation), had more sustained improvement after 3-4 years than those with lower EF and more dilation. It can be partially explained by more prevalence of aortic insufficiency in patients with pre op lower EF <50 and dilation (average left ventricular end systolic dimension 49 vs. 32 mm in EF >50). There are myocardial factors which also play a part, those with abnormal left ventricle (LV) function have more extensive loss of myofibrils either due to disproportion of mitochondria-to-myofibril ratio or myofibrillar degeneration exhibiting the extent RHD involves myocardium. Structural adaptation may not all be just a result of hemodynamic abnormalities in these patients. The recommendation that surgical intervention should occur before the LV starts to dilate or EF drops is well founded and would be impactful in the developing world, an estimated 250,000 deaths occur annually worldwide and 10.5 million disability adjusted life years due to RHD, mostly in young people.

Dysfunctional Mitochondrial Dynamic and Oxidative Phosphorylation Precedes Cardiac Dysfunction in R120G-αB-Crystallin-Induced Desmin-Related Cardiomyopathy.

BackgroundThe mutated α‐B‐Crystallin (CryABR120G) mouse model of desmin‐related myopathy (DRM) shows an age‐dependent onset of pathologic cardiac remodeling and progression of heart failure. CryABR120G expression in cardiomyocytes affects the mitochondrial spatial organization within the myofibrils, but the molecular perturbation within the mitochondria in the relation of the overall course of the proteotoxic disease remains unclear.Methods and ResultsCryABR120G mice show an accumulation of electron‐dense aggregates and myofibrillar degeneration associated with the development of cardiac dysfunction. Though extensive studies demonstrated that these altered ultrastructural changes cause cardiac contractility impairment, the molecular mechanism of cardiomyocyte death remains elusive. Here, we explore early pathological processes within the mitochondria contributing to the contractile dysfunction and determine the pathogenic basis for the heart failure observed in the CryABR120G mice. In the present study, we report that the CryABR120G mice transgenic hearts undergo altered mitochondrial dynamics associated with increased level of dynamin‐related protein 1 and decreased level of optic atrophy type 1 as well as mitofusin 1 over the disease process. In association with these changes, an altered level of the components of mitochondrial oxidative phosphorylation and pyruvate dehydrogenase complex regulatory proteins occurs before the manifestation of pathologic adverse remodeling in the CryABR120G hearts. Mitochondria isolated from CryABR120G transgenic hearts without visible pathology show decreased electron transport chain complex activities and mitochondrial respiration. Taken together, we demonstrated the involvement of mitochondria in the pathologic remodeling and progression of DRM‐associated cellular dysfunction.ConclusionsMitochondrial dysfunction in the form of altered mitochondrial dynamics, oxidative phosphorylation and pyruvate dehydrogenase complex proteins level, abnormal electron transport chain complex activities, and mitochondrial respiration are evident on the CryABR120G hearts before the onset of detectable pathologies and development of cardiac contractile dysfunction.

Cardiovascular Manifestations and Complications of Pheochromocytomas and Paragangliomas.

Pheochromocytomas and paragangliomas (PPGLs) are rare neuro-endocrine tumors. The catecholamine surge causes paroxysmal or chronic secondary hypertension. PPGLs may present as hypertensive- or PPGL-crisis with severe life-threatening cardiac and cerebrovascular complications. PPGLs-induced cardiac manifestations have been reported with diagnoses as PPGLs-induced electrocardiogram (ECG) changes “mimicking acute myocardial infarction”, arrhythmias, myocarditis, acute coronary syndrome, dilated cardiomyopathy, and lately as takotsubo syndrome. Critical analysis of these reports reveals that most of these cardiac manifestations have certain features in common. They have a dramatic clinical presentation and are reversible if the disease is treated with appropriate medical therapy and surgical resection of the PPGL tumor. They may have the same repolarization ECG changes irrespective of the clinical cardiac diagnosis, usually associated with mild to moderate elevations of myocardial biomarkers as troponins and normal coronary arteries. The histopathological findings are usually focal or multifocal in the form hypercontracted sarcomeres and contraction band necrosis (myofibrillar degeneration) with subsequent secondary mononuclear cell infiltration. Evidences argue the PPGL caused surge of catecholamines triggers hyperactivation of the sympathetic nervous system with cardiac sympathetic nerve terminal disruption with norepinephrine spillover causing the cardiac complications. A comprehensive review of various reported cardiovascular manifestations and complications of PPGLs are presented.

Cardiac α-Actin (ACTC1) Gene Mutation Causes Atrial-Septal Defects Associated With Late-Onset Dilated Cardiomyopathy.

Familial atrial septal defect (ASD) has previously been attributed primarily to mutations in cardiac transcription factors. Here, we report a large, multi-generational family (78 members) with ASD combined with a late-onset dilated cardiomyopathy and further characterize the consequences of mutant α-actin. We combined a genome-wide linkage analysis with cell biology, microscopy, and molecular biology tools to characterize a novel ACTC1 (cardiac α-actin) mutation identified in association with ASD and late-onset dilated cardiomyopathy in a large, multi-generational family. Using a genome-wide linkage analysis, the ASD disease locus was mapped to chromosome 15q14 harboring the ACTC1 gene. In 15 affected family members, a heterozygous, nonsynonymous, and fully penetrant mutation (p. Gly247Asp) was identified in exon 5 of ACTC1 that was absent in all healthy family members (n=63). In silico tools predicted deleterious consequences of this variant that was found absent in control databases. Ultrastructural analysis of myocardial tissue of one of the mutation carriers showed sarcomeric disarray, myofibrillar degeneration, and increased apoptosis, while cardiac proteomics revealed a significant increase in extracellular matrix proteins. Consistently, structural defects and increased apoptosis were also observed in neonatal rat ventricular cardiomyocytes overexpressing the mutant, but not native human ACTC1. Molecular dynamics studies and additional mechanistic analyses in cardiomyocytes confirmed actin polymerization/turnover defects, thereby affecting contractility. A combined phenotype of ASD and late-onset heart failure was caused by a heterozygous, nonsynonymous ACTC1 mutation. Mechanistically, we found a shared molecular mechanism of defective actin signaling and polymerization in both cardiac development and contractile function. Detection of ACTC1 mutations in patients with ASD may thus have further clinical implications with regard to monitoring for (late-onset) dilated cardiomyopathy.

Assessment of the relationship between the amount of scorpion venom in the central nervous system and the severity of scorpion envenomation in rats

Rats animal model was used to assess the severity of symptoms produced following the Intracerebroventricular injection (ICV) of incremental doses of Buthus lienhardi scorpion venom based on histopathological, biochemical, and hematological analyses. Our results show that the ICV injection of incremental doses of scorpion venom induced a dose-dependent effects resulting in death when high doses were administrated (5.4 and 8.1 µg/kg). Moreover, ICV administration of lower doses of B. lienhardi (0.27 and 2.7 µg/kg) produced marked myofibrillar degeneration, while lungs showed intra-alveolar hemorrhage. Concomitantly, there was a significant rise in the serum levels of AST, ALT, CPK, LDH, urea, and creatinine.

Dietary supplementation with alkylresorcinols prevents muscle atrophy through a shift of energy supply

It has been reported that phytoextracts that contain alkylresorcinols (ARs) protect against severe myofibrillar degeneration found in isoproterenol-induced myocardial infarction. In this study, we examined the effect of dietary ARs derived from wheat bran extracts on muscle atrophy in denervated mice. The mice were divided into the following four groups: (1) sham-operated (control) mice fed with normal diet (S-ND), (2) denervated mice fed with normal diet (D-ND), (3) control mice fed with ARs-supplemented diet (S-AR) and (4) denervated mice fed with ARs-supplemented diet (D-AR). The intake of ARs prevented the denervation-induced reduction of the weight of the hind limb muscles and the myofiber size. However, the expression of ubiquitin ligases and autophagy-related genes, which is associated with muscle proteolysis, was slightly higher in D-AR than in D-ND. Moreover, the abundance of the autophagy marker p62 was significantly higher in D-AR than in D-ND. Muscle atrophy has been known to be associated with a disturbed energy metabolism. The expression of pyruvate dehydrogenase kinase 4 (PDK4), which is related to fatty acid metabolism, was decreased in D-ND as compared with that in S-ND. In contrast, dietary supplementation with ARs inhibited the decrease of PDK4 expression caused by denervation. Furthermore, the abnormal expression pattern of genes related to the abundance of lipid droplets-coated proteins that was induced by denervation was improved by ARs. These results raise the possibility that dietary supplementation with ARs modifies the disruption of fatty acid metabolism induced by lipid autophagy, resulting in the prevention of muscle atrophy.

Aberrant Mitochondrial Fission Is Maladaptive in Desmin Mutation-Induced Cardiac Proteotoxicity.

BackgroundDesmin filament proteins interlink the contractile myofibrillar apparatus with mitochondria, nuclei and the sarcolemma. Mutations in the human desmin gene cause cardiac disease, remodeling, and heart failure but the pathophysiological mechanisms remain unknown.Methods and ResultsCardiomyocyte‐specific overexpression of mutated desmin (a 7 amino acid deletion R172‐E178, D7‐Des Tg) causes accumulations of electron‐dense aggregates and myofibrillar degeneration associated with cardiac dysfunction. Though extensive studies demonstrated that these altered ultrastructural changes cause impairment of cardiac contractility, the molecular mechanism of cardiomyocyte death remains elusive. In the present study, we report that the D7‐Des Tg mouse hearts undergo aberrant mitochondrial fission associated with increased expression of mitochondrial fission regulatory proteins. Mitochondria isolated from D7‐Des Tg hearts showed decreased mitochondrial respiration and increased apoptotic cell death. Overexpression of mutant desmin by adenoviral infection in cultured cardiomyocytes led to increased mitochondrial fission, inhibition of mitochondrial respiration, and activation of cellular toxicity. Inhibition of mitochondrial fission by mitochondrial division inhibitor mdivi‐1 significantly improved mitochondrial respiration and inhibited cellular toxicity associated with D7‐Des overexpression in cardiomyocytes.ConclusionsAberrant mitochondrial fission results in mitochondrial respiratory defects and apoptotic cell death in D7‐Des Tg hearts. Inhibition of aberrant mitochondrial fission using mitochondrial division inhibitor significantly preserved mitochondrial function and decreased apoptotic cell death. Taken together, our study shows that maladaptive aberrant mitochondrial fission causes desminopathy‐associated cellular dysfunction.

Ginkgolide C Alleviates Myocardial Ischemia/Reperfusion-Induced Inflammatory Injury via Inhibition of CD40-NF-κB Pathway.

Increasing evidence shows that inflammation plays a vital role in the occurrence and development of ischemia/reperfusion (I/R). Suppression of excessive inflammation can ameliorate impaired cardiac function, which shows therapeutic potential for clinical treatment of myocardial ischemia/reperfusion (MI/R) diseases. In this study, we investigated whether Ginkgolide C (GC), a potent anti-inflammatory flavone, extenuated MI/R injury through inhibition of inflammation. In vivo, rats with the occlusion of the left anterior descending (LAD) coronary artery were applied to mimic MI/R injury. In vitro, primary cultured neonatal ventricular myocytes exposed to hypoxia/reoxygenation (H/R) were applied to further discuss the anti-H/R injury property of GC. The results revealed that GC significantly improved the symptoms of MI/R injury, as evidenced by reducing infarct size, preventing myofibrillar degeneration and reversing the mitochondria dysfunction. Moreover, histological analysis and Myeloperoxidase (MPO) activity measurement showed that GC remarkably suppressed Polymorphonuclears (PMNs) infiltration and ameliorated the histopathological damage. Furthermore, GC pretreatment was shown to improve H/R-induced ventricular myocytes viability and enhance tolerance of inflammatory insult, as evidenced by suppressing expression of CD40, translocation of NF-κB p65 subunit, phosphorylation of IκB-α, as well as the activity of IKK-β. In addition, downstream inflammatory cytokines modulated by NF-κB signaling were effectively down-regulated both in vivo and in vitro, as determined by immunohistochemistry and ELISA. In conclusion, these results indicate that GC possesses a beneficial effect against MI/R injury via inflammation inhibition that may involve suppression of CD40-NF-κB signal pathway and downstream inflammatory cytokines expression, which may offer an alternative medication for MI/R diseases.

Myosin storage myopathy mutations yield defective myosin filament assembly in vitro and disrupted myofibrillar structure and function in vivo.

Myosin storage myopathy (MSM) is a congenital skeletal muscle disorder caused by missense mutations in the β-cardiac/slow skeletal muscle myosin heavy chain rod. It is characterized by subsarcolemmal accumulations of myosin that have a hyaline appearance. MSM mutations map near or within the assembly competence domain known to be crucial for thick filament formation. Drosophila MSM models were generated for comprehensive physiological, structural, and biochemical assessment of the mutations' consequences on muscle and myosin structure and function. L1793P, R1845W, and E1883K MSM mutant myosins were expressed in an indirect flight (IFM) and jump muscle myosin null background to study the effects of these variants without confounding influences from wild-type myosin. Mutant animals displayed highly compromised jump and flight ability, disrupted muscle proteostasis, and severely perturbed IFM structure. Electron microscopy revealed myofibrillar disarray and degeneration with hyaline-like inclusions. In vitro assembly assays demonstrated a decreased ability of mutant myosin to polymerize, with L1793P filaments exhibiting shorter lengths. In addition, limited proteolysis experiments showed a reduced stability of L1793P and E1883K filaments. We conclude that the disrupted hydropathy or charge of residues in the heptad repeat of the mutant myosin rods likely alters interactions that stabilize coiled-coil dimers and thick filaments, causing disruption in ordered myofibrillogenesis and/or myofibrillar integrity, and the consequent myosin aggregation. Our Drosophila models are the first to recapitulate the human MSM phenotype with ultrastructural inclusions, suggesting that the diminished ability of the mutant myosin to form stable thick filaments contributes to the dystrophic phenotype observed in afflicted subjects.

Evidence and role of phlebitis and lipid infiltration in the onset and pathogenesis of Wooden Breast Disease in modern broiler chickens

ABSTRACTWooden Breast Disease (WBD), a myopathy that frequently affects modern broiler chickens, is a disorder that has been associated with significant economic losses in the poultry industry. To examine tissue changes associated with the onset and early pathogenesis of this disorder, a time-series experiment was conducted using chickens from a high-breast-muscle-yield, purebred commercial broiler line. Birds were raised for up to seven weeks, with a subset of birds sampled weekly. Breast muscle tissues were extracted at necropsy and processed for analysis by light microscopy and transmission electron microscopy. Histologic presentation indicated localized phlebitis with lipogranulomas in Week 1, focal single-myofibril degeneration in Week 2 preceding an inflammatory response that started in Week 3. Lesions in Week 4 were characterized by multifocal to diffuse muscle fibre degeneration, necrosis, interstitial oedema accompanied by increased lipid and inflammatory cell infiltration. Lesions in Weeks 5–7 revealed diffuse muscle degeneration, necrosis, fibrosis and fatty infiltration with lipogranulomas. Ultrastructural examination showed myofibrillar splitting and degeneration, irregular, displaced and degenerated Z-lines, mitochondrial degeneration and interstitial fibrosis with dense regular collagen fibres. This study, therefore, demonstrates that WBD exhibits an earlier onset in modern broilers than when detectable by clinical examination. Further, this study shows that the disease assumes a progressive course with acute vasculitis, lipid deposition and myodegeneration occurring in the earlier stages, followed by a chronic fibrotic phase.

Clinical and histopathological features of myofibrillar myopathy in Warmblood horses.

To report a novel exertional myopathy, myofibrillar myopathy (MFM) in Warmblood (WB) horses. To 1) describe the distinctive clinical and myopathic features of MFM in Warmblood horses and 2) investigate the potential inheritance of MFM in a Warmblood family. Retrospective selection of MFM cases and prospective evaluation of a Warmblood family. Retrospectively, muscle biopsies were selected from Warmblood horses diagnosed with MFM and clinical histories obtained (n=10). Prospectively, muscle biopsies were obtained from controls (n=8) and a three generation WB family (n=11). Samples were assessed for histopathology [scored 0-3], fibre types, cytoskeletal and Z disc protein aggregates, electron microscopic alterations (EM) and muscle glycogen concentrations. Myofibrillar myopathy-affected cases experienced exercise intolerance, reluctance to go forward, stiffness and poorly localised lameness. Abnormal aggregates of the cytoskeletal protein desmin were found in up to 120 type 2a and a few type 2x myofibres of MFM cases. Desmin positive fibres did not stain for developmental myosin, α actinin or dystrophin. Scores for internalised myonuclei (score MFM 0.83±0.67, controls 0.22±0.45), anguloid atrophy (MFM 0.95±0.55, controls 0.31±0.37) and total myopathic scores (MFM 5.85±2.10, controls 1.41±2.17) were significantly higher in MFM cases vs. Focal Z disc degeneration, myofibrillar disruption and accumulation of irregular granular material was evident in MFM cases. Muscle glycogen concentrations were similar between MFM cases and controls. In the Warmblood family, desmin positive aggregates were found in myofibres of the founding dam and in horses from two subsequent generations. Restricted sample size due to limited availability of well phenotyped cases. A distinctive and potentially heritable form of MFM exists in Warmblood horses that present with exercise intolerance and abnormal hindlimb gait. Muscle tissue is characterised by ectopic accumulation of desmin and Z disc and myofibrillar degeneration.

The Possible Protective Role of Ginger Extract Versus Vitamin E Against Simvastatin-Induced Skeletal Myotoxicity in Adult Male Albino Rats: Histological, Physiological and Biochemical Study

Introduction: Statins are group of drugs used to reduce total and low density lipoprotein (LDL)-cholesterol level and to reduce the morbidity and mortality of cardiovascular diseases. Meanwhile, induced skeletal muscle- specific mitochondrial impairment, oxidative stress and myotoxicity are serious side effects . Vitamin E and ginger extract are well known potent antioxidants.Aim: To study the possible protective effect of ginger extract versus vitamin E against simvastatin- induced skeletal muscle histological and the associated biophysiological changes.Materials and Methods: Forty adult male albino rats were randomly divided into four equal groups (10 rats, each).; Group 1: was the control rats. Group 2: received 0.54 mg/kg/day simvastatin orally for 8 weeks. Group 3: received concomitant treatment of simvastatin and 30 mg/kg/day vitamin E orally for 8 weeks. Group 4 received concomitant treatment of simvastatin and 500mg/kg/day ginger extract orally for 8 weeks. After sacrifice, specimens were taken from the belly of the quadriceps femoris muscles of all animal groups and processed for light and electron microscopy. Biochemical tests and statistical analysis were done.Results: Group 2 showed focal areas of muscle fiber loss, mononuclear cellular infiltration and variable staining density. Ultra structurally, myofibrillar degeneration and accumulation of numerous giant infrequently damaged mitochondria were observed. The skeletal muscle fibers of animals from group 3 and group 4, both were markedly improved. Group 4 revealed obviously normal mitochondria.Conclusion: Administration of simvastatin for 8 weeks induced histological, physiological and biochemical skeletal myotoxic effects. These effects were greatly ameliorated by concomitant administration vitamin E or ginger extract. Ginger extract was more effective.

Biomechanics and Myocardial Damage in Chronic Mitral Regurgitation

The 2014 ACC/AHA guidelines for surgery for asymptomatic chronic mitral regurgitation states as a class IIa recommendation that mitral valve (MV) repair could be considered if the left ventricular ejection fraction (LVEF) is greater than 0.60 and the LVESD less than 40 mm if there is a 95% probability of a durable repair with an expected mortality of less than 1%. However, adhering to these guideline surgical triggers uncovers a subset of patients (20% incidence) where the LVEF decreases post repair. Is this due to changing loading conditions or impaired myocyte contractility? In a study at University of Alabama at Birmingham of patients undergoing (MV) repair for chronic mitral regurgitation MRI derived left ventricular (LV) volumes demonstrated reverse diastolic remodelling while left ventricular end systolic remodelling was essentially unchanged following surgery. Myocardial strain rates were normal prior to mitral valve repair. However, in the face of unchanging left ventricular end systolic wall stress, strain rates decreased below normal following MV repair suggesting a decrease in left ventricular contractile performance. LV biopsies of these patients taken at the time of MV repair demonstrated deposition of lipofuscin which is composed of protein and lipid degradation residues. Lipofuscin accumulation may have a deleterious effect on myocyte function. These biopsies also demonstrated extensive myofibrillar degeneration. The desmin cytoskeleton in the myocardium forms a continuous network maintaining a spatial relationship between the contractile apparatus and mitochondria. The LV biopsies demonstrated desmin loss indicating substantial underlying cellular and molecular damage. Implications: At the time of correction of mitral regurgitation substantial LV damage has occurred. This suggests that an even earlier repair of mitral regurgitation should be considered.