Skeletal Muscle Myopathy Research Articles

HSPB7 interacts with dimerized FLNC and its absence results in progressive myopathy in skeletal muscles.

ABSTRACTHSPB7 belongs to the small heat-shock protein (sHSP) family, and its expression is restricted to cardiac and skeletal muscles from embryonic stages to adulthood. Here, we found that skeletal-muscle-specific ablation of the HspB7 does not affect myogenesis during embryonic stages to postnatal day 1 (P1), but causes subsequent postnatal death owing to a respiration defect, with progressive myopathy phenotypes in the diaphragm. Deficiency of HSPB7 in the diaphragm muscle resulted in muscle fibrosis, sarcomere disarray and sarcolemma integrity loss. We identified dimerized filamin C (FLNC) as an interacting partner of HSPB7. Immunofluorescence studies demonstrated that the aggregation and mislocalization of FLNC occurred in the muscle of HspB7 mutant adult mice. Furthermore, the components of dystrophin glycoprotein complex, γ- and δ-sarcoglycan, but not dystrophin, were abnormally upregulated and mislocalized in HSPB7 mutant muscle. Collectively, our findings suggest that HSPB7 is essential for maintaining muscle integrity, which is achieved through its interaction with FLNC, in order to prevent the occurrence and progression of myopathy.

Muscle RING-finger 2 and 3 maintain striated-muscle structure and function.

BackgroundThe Muscle‐specific RING‐finger (MuRF) protein family of E3 ubiquitin ligases is important for maintenance of muscular structure and function. MuRF proteins mediate adaptation of striated muscles to stress. MuRF2 and MuRF3 bind to microtubules and are implicated in sarcomere formation with noticeable functional redundancy. However, if this redundancy is important for muscle function in vivo is unknown. Our objective was to investigate cooperative function of MuRF2 and MuRF3 in the skeletal muscle and the heart in vivo.Methods MuRF2 and MuRF3 double knockout mice (DKO) were generated and phenotypically characterized. Skeletal muscle and the heart were investigated by morphological measurements, histological analyses, electron microscopy, immunoblotting, and real‐time PCR. Isolated muscles were subjected to in vitro force measurements. Cardiac function was determined by echocardiography and working heart preparations. Function of cardiomyocytes was measured in vitro. Cell culture experiments and mass‐spectrometry were used for mechanistic analyses.ResultsDKO mice showed a protein aggregate myopathy in skeletal muscle. Maximal force development was reduced in DKO soleus and extensor digitorum longus. Additionally, a fibre type shift towards slow/type I fibres occurred in DKO soleus and extensor digitorum longus. MuRF2 and MuRF3‐deficient hearts showed decreased systolic and diastolic function. Further analyses revealed an increased expression of the myosin heavy chain isoform beta/slow and disturbed calcium handling as potential causes for the phenotype in DKO hearts.ConclusionsThe redundant function of MuRF2 and MuRF3 is important for maintenance of skeletal muscle and cardiac structure and function in vivo.

Myosin Binding Protein-C Slow Phosphorylation is Altered in Duchenne Dystrophy and Arthrogryposis Myopathy in Fast-Twitch Skeletal Muscles.

Myosin Binding Protein-C slow (sMyBP-C), encoded by MYBPC1, comprises a family of regulatory proteins of skeletal muscles that are phosphorylated by PKA and PKC. MYBPC1 missense mutations are linked to the development of Distal Arthrogryposis-1 (DA-1). Although structure-function details for this myopathy are evolving, function is undoubtedly driven by sequence variations and post-translational modifications in sMyBP-C. Herein, we examined the phosphorylation profile of sMyBP-C in mouse and human fast-twitch skeletal muscles. We used Flexor Digitorum Brevis (FDB) isolated from young (~2-months old) and old (~14-months old) wild type and mdx mice, and human Abductor Hallucis (AH) and gastrocnemious muscles carrying the DA-1 mutations. Our results indicate both constitutive and differential phosphorylation of sMyBP-C in aged and diseased muscles. We report a 7–35% reduction in the phosphorylation levels of select sites in old wild type and young or old mdx FDB mouse muscles, compared to young wild type tissue. Similarly, we observe a 30–70% decrease in the phosphorylation levels of all PKA and PKC phospho-sites in the DA-1 AH, but not gastrocnemius, muscle. Overall, our studies show that the phosphorylation pattern of sMyBP-C is differentially regulated in response to age and disease, suggesting that phosphorylation plays important roles in these processes.

Abstract 40: Discovery and Characterization of the Novel Muscle-Specific Membrane Protein Smco1

Mutations in numerous membrane proteins cause debilitating myopathies. The discovery of novel muscle-specific, membrane proteins would likely provide insight into mechanisms of disease and potentially yield new therapeutic targets. Through bioinformatics screening for muscle-specific membrane proteins with unknown function, we identified C3orf43 or single-pass membrane protein with coiled-coil domains 1 (Smco1). Consistent with bioinformatics predictions, Smco1 is expressed exclusively in cardiac and skeletal muscle. We demonstrate with chromatin immunoprecipitation and luciferase promoter assays that Smco1 is a Mef2-regulated gene with robust expression occurring shortly after birth. Immunofluorescent analysis demonstrates Scmo1 localizes to the cardiomyocyte sarcolemma and intercalated disks. Talen-mediated disruption of Smco1 in mice results in stunted postnatal growth, cardiac hypoplasia and skeletal muscle myopathy as early as postnatal day 15. While studies are on going to determine the function of Smco1, our findings reveal an essential role of Smco1 in striated muscle structure and function. The identification of heart- and muscle-specific membrane proteins will likely illuminate the mechanisms of muscular membrane diseases.

Reduction of toxic RNAs in myotonic dystrophies type 1 and type 2 by the RNA helicase p68/DDX5

Myotonic dystrophies type 1 (DM1) and type 2 (DM2) are neuromuscular diseases, caused by accumulation of CUG and CCUG RNAs in toxic aggregates. Here we report that the increased stability of the mutant RNAs in both types of DM is caused by deficiency of RNA helicase p68. We have identified p68 by studying CCUG-binding proteins associated with degradation of the mutant CCUG repeats. Protein levels of p68 are reduced in DM1 and DM2 biopsied skeletal muscle. Delivery of p68 in DM1/2 cells causes degradation of the mutant RNAs, whereas delivery of p68 in skeletal muscle of DM1 mouse model reduces skeletal muscle myopathy and atrophy. Our study shows that correction of p68 may reduce toxicity of the mutant RNAs in DM1 and in DM2.

Statin-Induced Increases in Atrophy Gene Expression Occur Independently of Changes in PGC1α Protein and Mitochondrial Content.

One serious side effect of statin drugs is skeletal muscle myopathy. Although the mechanism(s) responsible for statin myopathy remains to be fully determined, an increase in muscle atrophy gene expression and changes in mitochondrial content and/or function have been proposed to play a role. In this study, we examined the relationship between statin-induced expression of muscle atrophy genes, regulators of mitochondrial biogenesis, and markers of mitochondrial content in slow- (ST) and fast-twitch (FT) rat skeletal muscles. Male Sprague Dawley rats were treated with simvastatin (60 or 80 mg·kg-1·day-1) or vehicle control via oral gavage for 14 days. In the absence of overt muscle damage, simvastatin treatment induced an increase in atrogin-1, MuRF1 and myostatin mRNA expression; however, these were not associated with changes in peroxisome proliferator gamma co-activator 1 alpha (PGC-1α) protein or markers of mitochondrial content. Simvastatin did, however, increase neuronal nitric oxide synthase (nNOS), endothelial NOS (eNOS) and AMPK α-subunit protein expression, and tended to increase total NOS activity, in FT but not ST muscles. Furthermore, simvastatin induced a decrease in β-hydroxyacyl CoA dehydrogenase (β-HAD) activity only in FT muscles. These findings suggest that the statin-induced activation of muscle atrophy genes occurs independent of changes in PGC-1α protein and mitochondrial content. Moreover, muscle-specific increases in NOS expression and possibly NO production, and decreases in fatty acid oxidation, could contribute to the previously reported development of overt statin-induced muscle damage in FT muscles.

Changes In Muscle Strength In Individuals With Statin-induced Myopathy

Changes In Muscle Strength In Individuals With Statin-induced Myopathy

The Impact of Physical Activity on Statin-Associated Skeletal Muscle Myopathy

The Impact of Physical Activity on Statin-Associated Skeletal Muscle Myopathy

Heart Failure with Preserved Ejection Fraction Induces Molecular, Mitochondrial, Histological, and Functional Alterations in Rat Diaphragm Muscle

Peripheral muscle dysfunction is a key mechanism contributing to exercise intolerance in heart failure patients with preserved ejection fraction (HFpEF), however the underlying mechanisms remain unknown. We used an animal model to better understand potential molecular, mitochondrial, histological, and functional alterations induced by HFpEF in the diaphragm.MethodsFemale Dahl salt‐sensitive rats were fed a low‐ or high‐salt diet of 0.3% or 8% NaCL for 28 weeks. Heart function and diaphragm alterations were subsequently assessed.ResultsCompared to low‐salt rats (CON; n=10), high‐salt rats (n=11) developed HFpEF, as demonstrated by impaired diastolic function, preserved left ventricular EF, left ventricular hypertrophy, elevated systolic blood pressure, increased pulmonary congestion, and elevated plasma natriuretic peptides (P<0.05). HFpEF rat diaphragm demonstrated (P<0.05): 1) a fiber type distribution shift from fast‐to‐slow twitch; 2) a decreased pro‐oxidative but increased anti‐oxidant capacity; 3) reduced proteasome activation; 4) impaired in situ mitochondrial respiration at complex I: 5) in vitro muscle weakness and increased fatigability in fiber bundles.ConclusionThese data suggest a skeletal muscle myopathy exists in HFpEF and identifies novel mechanisms of exercise intolerance in HFpEF.

Increased mitochondrial emission of reactive oxygen species and calpain activation are required for doxorubicin-induced cardiac and skeletal muscle myopathy.

Although doxorubicin (DOX) is a highly effective anti-tumour agent used to treat a variety of cancers, DOX administration is associated with significant side effects, including myopathy of both cardiac and skeletal muscles. The mechanisms responsible for DOX-mediated myopathy remain a topic of debate. We tested the hypothesis that both increased mitochondrial reactive oxygen species (ROS) emission and activation of the cysteine protease calpain are required for DOX-induced myopathy in rat cardiac and skeletal muscle. Cause and effect was determined by administering a novel mitochondrial-targeted anti-oxidant to prevent DOX-induced increases in mitochondrial ROS emission, whereas a highly-selective pharmacological inhibitor was exploited to inhibit calpain activity. Our findings reveal that mitochondria are a major site of DOX-mediated ROS production in both cardiac and skeletal muscle fibres and the prevention of DOX-induced increases in mitochondrial ROS emission protects against fibre atrophy and contractile dysfunction in both cardiac and skeletal muscles. Furthermore, our results indicate that DOX-induced increases in mitochondrial ROS emission are required to activate calpain in heart and skeletal muscles and, importantly, calpain activation is a major contributor to DOX-induced myopathy. Taken together, these findings show that increased mitochondrial ROS production and calpain activation are significant contributors to the development of DOX-induced myopathy in both cardiac and skeletal muscle fibres.

Defects in calcium homeostasis and mitochondria can be reversed in Pompe disease

Mitochondria-induced oxidative stress and flawed autophagy are common features of neurodegenerative and lysosomal storage diseases (LSDs). Although defective autophagy is particularly prominent in Pompe disease, mitochondrial function has escaped examination in this typical LSD. We have found multiple mitochondrial defects in mouse and human models of Pompe disease, a life-threatening cardiac and skeletal muscle myopathy: a profound dysregulation of Ca2+ homeostasis, mitochondrial Ca2+ overload, an increase in reactive oxygen species, a decrease in mitochondrial membrane potential, an increase in caspase-independent apoptosis, as well as a decreased oxygen consumption and ATP production of mitochondria. In addition, gene expression studies revealed a striking upregulation of the β 1 subunit of L-type Ca2+ channel in Pompe muscle cells. This study provides strong evidence that disturbance of Ca2+ homeostasis and mitochondrial abnormalities in Pompe disease represent early changes in a complex pathogenetic cascade leading from a deficiency of a single lysosomal enzyme to severe and hard-to-treat autophagic myopathy. Remarkably, L-type Ca2+channel blockers, commonly used to treat other maladies, reversed these defects, indicating that a similar approach can be beneficial to the plethora of lysosomal and neurodegenerative disorders.

INDACO project: COPD and link between comorbidities, lung function and inhalation therapy.

BackgroundChronic Obstructive Pulmonary Disease (COPD) is characterized by respiratory and extrarespiratory components referring both to systemic complications of COPD, like skeletal muscle myopathy, weight loss and others, and frequently associated comorbidities, interesting various organs and systems (cardiovascular diseases, malignancies, osteoporosis, diabetes, etc.). These comorbidities may increase the rate of hospitalization of COPD patients and have a huge effect on the outcomes of the respiratory disease. Inhalation therapy of COPD with bronchodilators and steroid is primary driven by airflow obstruction, symptoms like dyspnoea, and acute exacerbations. INDACO project has been developed in 2013 to assess the prevalence and type of comorbidities in COPD patients referred to the outpatient wards of some hospitals in Central and South Italy and a preliminary report has recently been published. In the present study, after widening that database, we evaluate the prevalence of comorbidities and the relationships between comorbidities and sex, age, symptoms, lung function and inhalation therapy in COPD patients.MethodsIn each enrolled patient, anthropometric and anamnestic data, smoking habits, respiratory function, GOLD (Global initiative for Chronic Obstructive Lung Disease) severity stage, Body Mass Index (BMI), number of acute COPD exacerbations in previous years, presence and type of comorbidities, and the Charlson Comorbidity Index (CCI) were recorded.ResultsWe collected data of 569 patients (395 males and 174 females, mean age 73 ± 8.5 yrs). The prevalence of patients with comorbidities was 81.2%. Overall number of comorbidities was not related to airflow obstruction and age, but to acute exacerbation of COPD, dyspnoea measured with MRC scale, and male gender. A subgroup analysis revealed that ischaemic heart disease was predominant in males, whereas mood disorders in females. The use of a more complex (multi-drug) inhalation therapy was related with bronchial obstruction measured by FEV1/FVC (p for trend = 0.003) and number of comorbidities (p for trend = 0.001). In multivariate analysis, only airflow obstruction and number of comorbidities were determinant of complexity of therapy, but not MRC and acute exacerbation of COPD. However, the statistical model reached an extreme low degree of significance (r^2 = 0.07).ConclusionsOur study showed a high prevalence of comorbidities in COPD, with some differences related to gender. Number of comorbidities and airflow obstruction represent the determinant of inhalation therapy prescription. Dyspnoea and acute exacerbation of COPD, unlikely suggested by guidelines, are not significant drivers of therapy in the real life setting of our study.

INDACO project: COPD and link between comorbidities, lung function and inhalation therapy


 
 
 
 Background: Chronic Obstructive Pulmonary Disease (COPD) is characterized by respiratory and extrarespiratory components referring both to systemic complications of COPD, like skeletal muscle myopathy, weight loss and others, and frequently associated comorbidities, interesting various organs and systems (cardiovascular diseases, malignancies, osteoporosis, diabetes, etc.). These comorbidities may increase the rate of hospitalization of COPD patients and have a huge effect on the outcomes of the respiratory disease. Inhalation therapy of COPD with bronchodilators and steroid is primary driven by airflow obstruction, symptoms like dyspnoea, and acute exacerbations. INDACO project has been developed in 2013 to assess the prevalence and type of comorbidities in COPD patients referred to the outpatient wards of some hospitals in Central and South Italy and a preliminary report has recently been published. In the present study, after widening that database, we evaluate the prevalence of comorbidities and the relationships between comorbidities and sex, age, symptoms, lung function and inhalation therapy in COPD patients.
 Methods: In each enrolled patient, anthropometric and anamnestic data, smoking habits, respiratory function, GOLD (Global initiative for Chronic Obstructive Lung Disease) severity stage, Body Mass Index (BMI), number of acute COPD exacerbations in previous years, presence and type of comorbidities, and the Charlson Comorbidity Index (CCI) were recorded.
 Results: We collected data of 569 patients (395 males and 174 females, mean age 73 ± 8.5 yrs). The prevalence of patients with comorbidities was 81.2%. Overall number of comorbidities was not related to airflow obstruction and age, but to acute exacerbation of COPD, dyspnoea measured with MRC scale, and male gender. A subgroup analysis revealed that ischaemic heart disease was predominant in males, whereas mood disorders in females. The use of a more complex (multi-drug) inhalation therapy was related with bronchial obstruction measured by FEV1/FVC (p for trend = 0.003) and number of comorbidities (p for trend = 0.001). In multivariate analysis, only airflow obstruction and number of comorbidities were determinant of complexity of therapy, but not MRC and acute exacerbation of COPD. However, the statistical model reached an extreme low degree of significance (r^2 = 0.07).
 Conclusions: Our study showed a high prevalence of comorbidities in COPD, with some differences related to gender. Number of comorbidities and airflow obstruction represent the determinant of inhalation therapy prescription. Dyspnoea and acute exacerbation of COPD, unlikely suggested by guidelines, are not significant drivers of therapy in the real life setting of our study.
 
 
 

Mechanisms of hyperhomocysteinemia induced skeletal muscle myopathy after ischemia in the CBS-/+ mouse model.

Although hyperhomocysteinemia (HHcy) elicits lower than normal body weights and skeletal muscle weakness, the mechanisms remain unclear. Despite the fact that HHcy-mediated enhancement in ROS and consequent damage to regulators of different cellular processes is relatively well established in other organs, the nature of such events is unknown in skeletal muscles. Previously, we reported that HHcy attenuation of PGC-1α and HIF-1α levels enhanced the likelihood of muscle atrophy and declined function after ischemia. In the current study, we examined muscle levels of homocysteine (Hcy) metabolizing enzymes, anti-oxidant capacity and focused on protein modifications that might compromise PGC-1α function during ischemic angiogenesis. Although skeletal muscles express the key enzyme (MTHFR) that participates in re-methylation of Hcy into methionine, lack of trans-sulfuration enzymes (CBS and CSE) make skeletal muscles more susceptible to the HHcy-induced myopathy. Our study indicates that elevated Hcy levels in the CBS−/+ mouse skeletal muscles caused diminished anti-oxidant capacity and contributed to enhanced total protein as well as PGC-1α specific nitrotyrosylation after ischemia. Furthermore, in the presence of NO donor SNP, either homocysteine (Hcy) or its cyclized version, Hcy thiolactone, not only increased PGC-1α specific protein nitrotyrosylation but also reduced its association with PPARγ in C2C12 cells. Altogether these results suggest that HHcy exerts its myopathic effects via reduction of the PGC-1/PPARγ axis after ischemia.

Statin-induced Myopathy in Skeletal Muscle: the Role of Exercise

Statins are widely used drugs to lower cholesterol levels and to reduce the risk of cardiovascular disease. However, it has been reported that statins are associated with adverse side effects of skeletal myopathy. Statin treatment can impair mitochondrial function and induce apoptosis in skeletal muscle in both human and animal models. Ubiquinone plays an essential role in transferring electrons in the mitochondrial electron transfer chain for oxidative phosphorylation. However, statin treatment reduces ubiquinone levels in the cholesterol synthesis pathway, which may be associated with mitochondrial dysfunction. In addition, reactive oxygen species (ROS) production and apoptosis induced by statins may provide cellular and molecular mechanisms in skeletal myopathy. Exercise is the most effective therapy to prevent metabolic and cardiovascular diseases. However, whether exercise provides a benefit to or exacerbation of statin-induced myopathy in skeletal muscle remains poorly investigated. This review will briefly provide a comprehensive summary regarding the effects of statins on skeletal myopathy, and discuss the potential mechanisms of statin-induced myopathy and the role of exercise in statin-induced myopathy in skeletal muscle.

Regulation of skeletal muscle development and disease by microRNAs.

The identification of microRNAs (miRNA) in vertebrates has uncovered new mechanisms regulating skeletal muscle development and disease. miRNAs are inhibitors and act by silencing specific mRNAs or by repressing protein translation. In many cases, miRNAs are involved in physiological or pathological stress, suggesting they function to exacerbate or protect the organism during stress or disease. Although many skeletal muscle diseases differ in clinical and pathological manifestations, they all have a common feature of dysregulation of miRNA expression. In particular, analysis of miRNA expression patterns in skeletal muscle diseases reveals miRNA signatures, showing many miRNAs are dysregulated during disease. Emerging identification of miRNA targets and involvement in genetic regulatory networks serve to reveal new regulatory pathways in skeletal muscle biology. This chapter features the findings pertaining to skeletal muscle miRNAs in skeletal muscle development and disease and highlights therapeutic applications of miRNA-based technology in diagnosis and treatment of skeletal muscle myopathies.

G.P.151: Loss of FHL1 function impairs motility and causes myopathy in vivo

Mutations of the X-chromosomal <i>four and a half LIM domain 1</i> (FHL1) lead to inclusion body myopathies such as reducing body myopathy or Emery-Dreifuss muscular dystrophy, termed as FHL1-opathies. Family screens identified association of different missense mutations of FHL1 to skeletal muscle myopathy either isolated or linked with cardiomyopathy. Until now it is unknown whether dominant negative effects (accumulation of cytotoxic mutated FHL1 protein) or loss of FHL1 function (reduced FHL1 protein levels) underlie the pathogenesis of these FHL1-opathies. Therefore, we exploited the model organism zebrafish to evaluate the role of FHL1 for pathogenesis of FHL1-opathies in vivo. By Morpholino-modified oligonucleotide mediated gene knockdown of the two zebrafish FHL1 orthologs, <i>fhl1a</i> and <i>fhl1b</i>, we examined loss of FHL1 function in vivo. In both morphant embryos we find impaired motility and skeletal muscle function consistent with FHL1-opathy. To evaluate whether three common missense FHL1-mutations identified in FHL1-opathy affected patients either act dominant-negative or lead to loss of FHL1 function in vivo, we injected mutated human FHL1 mRNA in both wild-type and fhl1-depleted zebrafish embryos. Hence, injection of mutated human FHL1 mRNA into wild-type embryos, does not impact on skeletal muscle function, suggesting that the investigated mutations do not act dominant-negative in vivo. Interestingly, in contrast to wild-type FHL1 mRNA, expression of the mutated human FHL1 in fhl1-depleted embryos was not capable of reconstituting skeletal muscle function, indicating that the common human FHL1 mutations lead to a loss of FHL1 function thereby causing the FHL1-opathy. In summary, we demonstrate here, that loss of FHL1 function leads to impaired motility and myopathy in the zebrafish in vivo model. Furthermore, our functional studies reveal that three common human FHL1-mutations do not act dominant-negative in vivo but rather lead to a loss of FHL1 function.

Serum enolase: a non-destructive biomarker of white skeletal myopathy during pancreas disease (PD) in Atlantic salmon Salmo salar L.

Diseases which cause skeletal muscle myopathy are some of the most economically damaging diseases in Atlantic salmon, Salmo salar L., aquaculture. Despite this, there are limited means of assessing fish health non-destructively. Previous investigation of the serum proteome of Atlantic salmon, Salmo salar L., during pancreas disease (PD) has identified proteins in serum that have potential as biomarkers of the disease. Amongst these proteins, the enzyme enolase was selected as the most viable for use as a biomarker of muscle myopathy associated with PD. Western blot and immunoassay (ELISA) validated enolase as a biomarker for PD, whilst immunohistochemistry identified white muscle as the source of enolase. Enolase was shown to be a specific marker for white muscle myopathy in salmon, rising in serum concentration significantly correlating with pathological damage to the tissue.

Pompe disease: from pathophysiology to therapy and back again.

Pompe disease is a lysosomal storage disorder in which acid alpha-glucosidase (GAA) is deficient or absent. Deficiency of this lysosomal enzyme results in progressive expansion of glycogen-filled lysosomes in multiple tissues, with cardiac and skeletal muscle being the most severely affected. The clinical spectrum ranges from fatal hypertrophic cardiomyopathy and skeletal muscle myopathy in infants to relatively attenuated forms, which manifest as a progressive myopathy without cardiac involvement. The currently available enzyme replacement therapy (ERT) proved to be successful in reversing cardiac but not skeletal muscle abnormalities. Although the overall understanding of the disease has progressed, the pathophysiology of muscle damage remains poorly understood. Lysosomal enlargement/rupture has long been considered a mechanism of relentless muscle damage in Pompe disease. In past years, it became clear that this simple view of the pathology is inadequate; the pathological cascade involves dysfunctional autophagy, a major lysosome-dependent intracellular degradative pathway. The autophagic process in Pompe skeletal muscle is affected at the termination stage—impaired autophagosomal-lysosomal fusion. Yet another abnormality in the diseased muscle is the accelerated production of large, unrelated to ageing, lipofuscin deposits—a marker of cellular oxidative damage and a sign of mitochondrial dysfunction. The massive autophagic buildup and lipofuscin inclusions appear to cause a greater effect on muscle architecture than the enlarged lysosomes outside the autophagic regions. Furthermore, the dysfunctional autophagy affects the trafficking of the replacement enzyme and interferes with its delivery to the lysosomes. Several new therapeutic approaches have been tested in Pompe mouse models: substrate reduction therapy, lysosomal exocytosis following the overexpression of transcription factor EB and a closely related but distinct factor E3, and genetic manipulation of autophagy.

Abstract 145: Mitophagy Protects Against Statin-Induced Cell Death in Muscle Cells

Statins are a family of cholesterol lowering drugs associated with undisputable cardiovascular benefits. However, their use is associated with the risk of developing skeletal muscle myopathy which remains a significant barrier to maximizing the efficacy of statin therapy. Many recognize that the instances of statin-associated myopathy reported grossly underestimate the actual frequency of these events. Statin myopathy is a major reason for why many patients are unable to comply with their prescribed statin treatments. Identifying and understanding the molecular events involved in the development of statin-induced myopathy will pave the way to mitigating the unwanted effect of statin-myopathy. We have identified that statins induce mitochondrial loss in both C2C12 myotubes, and in gastrocnemius muscle of mice evidenced by loss of mitochondrial markers Tom70 and Cox4 by western blot analysis. C2C12 myotubes were treated with 2μM simvastatin for 24 hours, and wild-type C57BL/6 mice were given a daily i.p. dose of 20mg/kg simvastatin for 2 weeks. Pretreatment of C2C12 cells with 100nM bafilomycin for 2 hours before statin treatment attenuated autophagic flux, and prevents the observed loss of mitochondria through Tom70 and Cox4 mitochondrial markers. Thus, the loss of mitochondria is attributable to autophagy (mitophagy). Statin treatment increases the expression of Bnip3 and p62/SQSTM1 (sequestosome 1) which have been identified as important facilitators of mitophagy. We found increased Bnip3 dimerization via western blot under non-reducing conditions which implies increased activity. Furthermore, we observed increased mitochondrial translocation of p62/SQSTM1. Based on our findings, we hypothesized that statin-induced mitophagy may play a key role in the development of muscle myopathy. To investigate the role of mitophagy in statin myopathy, we silenced p62/SQSTM1 via RNAi prior to statin treatment. Surprisingly, reducing mitophagic flux via p62/SQSTM1 silencing resulted in increased destruction of myotubes. This was associated with increased levels of cytosolic cytochrome c. Our data combined suggests that mitophagy protects against statin-mediated cell death by sequestering and eliminating decrepit mitochondria via autophagy.