Dysferlin is a surface membrane-associated protein that is absent in Miyoshi myopathy

The neuropathobiology of multiple sclerosis

Chronic low-grade inflammation and neuronal deregulation are two components of a smoldering disease activity that drives the progression of disability in people with multiple sclerosis (MS). Although several therapies exist to dampen the acute inflammation that drives MS relapses, therapeutic options to halt chronic disability progression are a major unmet clinical need. The development of such therapies is hindered by our limited understanding of the neuron-intrinsic determinants of resilience or vulnerability to inflammation. In this Review, we provide a neuron-centric overview of recent advances in deciphering neuronal response patterns that drive the pathology of MS. We describe the inflammatory CNS environment that initiates neurotoxicity by imposing ion imbalance, excitotoxicity and oxidative stress, and by direct neuro-immune interactions, which collectively lead to mitochondrial dysfunction and epigenetic dysregulation. The neuronal demise is further amplified by breakdown of neuronal transport, accumulation of cytosolic proteins and activation of cell death pathways. Continuous neuronal damage perpetuates CNS inflammation by activating surrounding glia cells and by directly exerting toxicity on neighbouring neurons. Further, we explore strategies to overcome neuronal deregulation in MS and compile a selection of neuronal actuators shown to impact neurodegeneration in preclinical studies. We conclude by discussing the therapeutic potential of targeting such neuronal actuators in MS, including some that have already been tested in interventional clinical trials.

Childhood muscular dystrophies

Infancy- and childhood-onset muscular dystrophies are associated with a characteristic distribution and progression of motor dysfunction. The underlying causes of progressive childhood muscular dystrophies are heterogeneous involving diverse genetic pathways and genes that encode proteins of the plasma membrane, extracellular matrix, sarcomere, and nuclear membrane components. The prototypical clinicopathological features in an affected child may be adequate to fully distinguish it from other likely diagnoses based on four common features: (1) weakness and wasting of pelvic-femoral and scapular muscles with involvement of heart muscle; (2) elevation of serum muscle enzymes in particular serum creatine kinase; (3) necrosis and regeneration of myofibers; and (4) molecular neurogenetic assessment particularly utilizing next-generation sequencing of the genome of the likeliest candidates genes in an index case or family proband. A number of different animal models of therapeutic strategies have been developed for gene transfer therapy, but so far these techniques have not yet entered clinical practice. Treatment remains for the most part symptomatic with the goal of ameliorating locomotor and cardiorespiratory manifestations of the disease.

Genetic Mapping of Behavioral Traits Using the Collaborative Cross Resource

The complicated interactions between genetic background, environment and lifestyle factors make it difficult to study the genetic basis of complex phenotypes, such as cognition and anxiety levels, in humans. However, environmental and other factors can be tightly controlled in mouse studies. The Collaborative Cross (CC) is a mouse genetic reference population whose common genetic and phenotypic diversity is on par with that of humans. Therefore, we leveraged the power of the CC to assess 52 behavioral measures associated with locomotor activity, anxiety level, learning and memory. This is the first application of the CC in novel object recognition tests, Morris water maze tasks, and fear conditioning tests. We found substantial continuous behavioral variations across the CC strains tested, and mapped six quantitative trait loci (QTLs) which influenced these traits, defining candidate genetic variants underlying these QTLs. Overall, our findings highlight the potential of the CC population in behavioral genetic research, while the identified genomic loci and genes driving the variation of relevant behavioral traits provide a foundation for further studies.

Elevated Ca2+ at the triad junction underlies dysregulation of Ca2+ signaling in dysferlin-null skeletal muscle

Dysferlin-null A/J myofibers generate abnormal Ca²⁺ transients that are slightly reduced in amplitude compared to controls. These are further reduced in amplitude by hypoosmotic shock and often appear as Ca²⁺ waves (Lukyanenko et al., J. Physiol., 2017). Ca²⁺ waves are typically associated with Ca²⁺-induced Ca²⁺ release, or CICR, which can be myopathic. We tested the ability of a permeable Ca²⁺ chelator, BAPTA-AM, to inhibit CICR in injured dysferlin-null fibers and found that 10–50 nM BAPTA-AM suppressed all Ca²⁺ waves. The same concentrations of BAPTA-AM increased the amplitude of the Ca²⁺ transient in A/J fibers to wild type levels and protected transients against the loss of amplitude after hypoosmotic shock, as also seen in wild type fibers. Incubation with 10 nM BAPTA-AM led to intracellular BAPTA concentrations of ∼60 nM, as estimated with its fluorescent analog, Fluo-4AM. This should be sufficient to restore intracellular Ca²⁺ to levels seen in wild type muscle. Fluo-4AM was ∼10-fold less effective than BAPTA-AM, however, consistent with its lower affinity for Ca²⁺. EGTA, which has an affinity for Ca²⁺ similar to BAPTA, but with much slower kinetics of binding, was even less potent when introduced as the -AM derivative. By contrast, a dysferlin variant with GCaMP6f_u in place of its C2A domain accumulated at triad junctions, like wild type dysferlin, and suppressed all abnormal Ca²⁺ signaling. GCaMP6f_u introduced as a Venus chimera did not accumulate at junctions and failed to suppress abnormal Ca²⁺ signaling. Our results suggest that leak of Ca²⁺ into the triad junctional cleft underlies dysregulation of Ca²⁺ signaling in dysferlin-null myofibers, and that dysferlin’s C2A domain suppresses abnormal Ca²⁺ signaling and protects muscle against injury by binding Ca²⁺ in the cleft.

The genetic profile of dysferlinopathy in a cohort of 209 cases: Genotype-phenotype relationship and a hotspot on the inner DysF domain

Dysferlinopathy is a group of autosomal recessive muscular dystrophies caused by variants in the dysferlin gene (DYSF), with variable proximal and distal muscle involvement. We performed DYSF gene analyses of 200 cases suspected of having dysferlinopathy (Cohort 1), and identified diagnostic variants in 129/200 cases, including 19 novel variants. To achieve a comprehensive genetic profile of dysferlinopathy, we analyzed the variant data from 209 affected cases from unrelated 209 families, including 80 previously diagnosed and 129 newly diagnosed cases (Cohort 2). Among the 90 types of variants identified in 209 cases, the NM_003494.3: c.2997G>T; p.Trp999Cys, was the most frequent (96/420; 22.9%), followed by c.1566C>G; p.Tyr522* (45/420; 10.7%) on an allele base. p.Trp999Cys was found in 70/209 cases (33.5%), including 20/104 cases (19.2%) with the Miyoshi muscular phenotype and 43/82 cases (52.4%) with the limb-girdle phenotype. In the analysis of missense variants, p.Trp992Arg, p.Trp999Arg, p.Trp999Cys, p.Ser1000Phe, p.Arg1040Trp, and p.Arg1046His were located in the inner DysF domain, representing in 113/160 missense variants (70.6%). This large cohort highlighted the frequent missense variants located in the inner DysF domain as a hotspot for missense variants among our cohort of 209 cases (>95%, Japanese) and hinted at their potential as targets for future therapeutic strategies.

Impaired muscle spindle function in murine models of muscular dystrophy

KEY POINTS

Muscular dystrophy patients suffer from progressive degeneration of skeletal muscle fibres, sudden spontaneous falls, balance problems, as well as gait and posture abnormalities. Dystrophin- and dysferlin-deficient mice, models for different types of muscular dystrophy with different aetiology and molecular basis, were characterized to investigate if muscle spindle structure and function are impaired. The number and morphology of muscle spindles were unaltered in both dystrophic mouse lines but muscle spindle resting discharge and their responses to stretch were altered. In dystrophin-deficient muscle spindles, the expression of the paralogue utrophin was substantially upregulated, potentially compensating for the dystrophin deficiency. The results suggest that muscle spindles might contribute to the motor problems observed in patients with muscular dystrophy.

ABSTRACT

Muscular dystrophies comprise a heterogeneous group of hereditary diseases characterized by progressive degeneration of extrafusal muscle fibres as well as unstable gait and frequent falls. To investigate if muscle spindle function is impaired, we analysed their number, morphology and function in wildtype mice and in murine model systems for two distinct types of muscular dystrophy with very different disease aetiology, i.e. dystrophin- and dysferlin-deficient mice. The total number and the overall structure of muscle spindles in soleus muscles of both dystrophic mouse mutants appeared unchanged. Immunohistochemical analyses of wildtype muscle spindles revealed a concentration of dystrophin and β-dystroglycan in intrafusal fibres outside the region of contact with the sensory neuron. While utrophin was absent from the central part of intrafusal fibres of wildtype mice, it was substantially upregulated in dystrophin-deficient mice. Single-unit extracellular recordings of sensory afferents from muscle spindles of the extensor digitorum longus muscle revealed that muscle spindles from both dystrophic mouse strains have an increased resting discharge and a higher action potential firing rate during sinusoidal vibrations, particularly at low frequencies. The response to ramp-and-hold stretches appeared unaltered compared to the respective wildtype mice. We observed no exacerbated functional changes in dystrophin and dysferlin double mutant mice compared to the single mutant animals. These results show alterations in muscle spindle afferent responses in both dystrophic mouse lines, which might cause an increased muscle tone, and might contribute to the unstable gait and frequent falls observed in patients with muscular dystrophy.

Detection of Dysferlin Gene Pathogenic Variants in the Indian Population in Patients Predicted to have a Dysferlinopathy Using a Blood-based Monocyte Assay and Clinical Algorithm: A Model for Accurate and Cost-effective Diagnosis

BACKGROUND

Limb-girdle muscular dystrophy (LGMD) is the most common adult-onset class of muscular dystrophies in India, but a majority of suspected LGMDs in India remain unclassified to the genetic subtype level. The next-generation sequencing (NGS)-based approaches have allowed molecular characterization and subtype diagnosis in a majority of these patients in India.

MATERIALS AND METHODS

(I) To select probable dysferlinopathy (LGMD2B) cases from other LGMD subtypes using two screening methods (i) to determine the status of dysferlin protein expression in blood (peripheral blood mononuclear cell) by monocyte assay (ii) using a predictive algorithm called automated LGMD diagnostic assistant (ALDA) to obtain possible LGMD subtypes based on clinical symptoms. (II) Identification of gene pathogenic variants by NGS for 34 genes associated with LGMD or LGMD like muscular dystrophies, in cases showing: absence of dysferlin protein by the monocyte assay and/or a typical dysferlinopathy phenotype, with medium to high predictive scores using the ALDA tool.

RESULTS

Out of the 125 patients screened by NGS, 96 were confirmed with two dysferlin variants, of which 84 were homozygous. Single dysferlin pathogenic variants were seen in 4 patients, whereas 25 showed no variants in the dysferlin gene.

CONCLUSION

In this study, 98.2% of patients with absence of the dysferlin protein showed one or more variants in the dysferlin gene and hence has a high predictive significance in diagnosing dysferlinopathies. However, collection of blood samples from all over India for protein analysis is expensive. Our analysis shows that the use of the "ALDA tool" could be a cost-effective alternative method. Identification of dysferlin pathogenic variants by NGS is the ultimate method for diagnosing dysferlinopathies though follow-up with the monocyte assay can be useful to understand the phenotype in relation to the dysferlin protein expression and also be a useful biomarker for future clinical trials.

Dysferlin function in skeletal muscle: Possible pathological mechanisms and therapeutical targets in dysferlinopathies

Mutations in the dysferlin gene are linked to a group of muscular dystrophies known as dysferlinopathies. These myopathies are characterized by progressive atrophy. Studies in muscle tissue from dysferlinopathy patients or dysferlin-deficient mice point out its importance in membrane repair. However, expression of dysferlin homologous proteins that restore sarcolemma repair function in dysferlinopathy animal models fail to arrest muscle wasting, therefore suggesting that dysferlin plays other critical roles in muscle function. In the present review, we discuss dysferlin functions in the skeletal muscle, as well as pathological mechanisms related to dysferlin mutations. Particular focus is presented related the effect of dysferlin on cell membrane related function, which affect its repair, vesicle trafficking, as well as Ca(2+) homeostasis. Such mechanisms could provide accessible targets for pharmacological therapies.

Dysferlin Binds SNAREs (Soluble N-Ethylmaleimide-sensitive Factor (NSF) Attachment Protein Receptors) and Stimulates Membrane Fusion in a Calcium-sensitive Manner

Resealing of tears in the sarcolemma of myofibers is a necessary step in the repair of muscle tissue. Recent work suggests a critical role for dysferlin in the membrane repair process and that mutations in dysferlin are responsible for limb girdle muscular dystrophy 2B and Miyoshi myopathy. Beyond membrane repair, dysferlin has been linked to SNARE-mediated exocytotic events including cytokine release and acid sphingomyelinase secretion. However, it is unclear whether dysferlin regulates SNARE-mediated membrane fusion. In this study we demonstrate a direct interaction between dysferlin and the SNARE proteins syntaxin 4 and SNAP-23. In addition, analysis of FRET and in vitro reconstituted lipid mixing assays indicate that dysferlin accelerates syntaxin 4/SNAP-23 heterodimer formation and SNARE-mediated lipid mixing in a calcium-sensitive manner. These results support a function for dysferlin as a calcium-sensing SNARE effector for membrane fusion events.

Respiratory and cardiac function in japanese patients with dysferlinopathy

INTRODUCTION

We retrospectively reviewed respiratory and cardiac function in patients with dysferlinopathy, including 2 autopsy cases with respiratory dysfunction.

METHODS

Subjects included 48 patients who underwent respiratory evaluation (n = 47), electrocardiography (n = 46), and echocardiography (n = 23).

RESULTS

Of the 47 patients, 10 had reduced percent forced vital capacity (%FVC), and 4 required non-invasive positive pressure ventilation. %FVC was significantly correlated with disease duration, and mean %FVC was significantly lower in non-ambulatory patients, as well as in those aged ≥65 years with normal creatine kinase levels. On electrocardiography, QRS complex duration was prolonged in 19 patients, although no significant association with age, disease duration, or respiratory function was found. Echocardiography indicated no left ventricular dysfunction in any patient. Histopathology of autopsied cases revealed mild cardiomyopathy and moderate diaphragm involvement.

CONCLUSION

Patients with dysferlinopathy may develop severe respiratory failure and latent cardiac dysfunction. Both respiratory and cardiac function should be monitored diligently.

Genetic profile for suspected dysferlinopathy identified by targeted next-generation sequencing

Objective:

To investigate the genetic causes of suspected dysferlinopathy and to reveal the genetic profile for myopathies with dysferlin deficiency.

Methods:

Using next-generation sequencing, we analyzed 42 myopathy-associated genes, including DYSF, in 64 patients who were clinically or pathologically suspected of having dysferlinopathy. Putative pathogenic mutations were confirmed by Sanger sequencing. In addition, copy-number variations in DYSF were investigated using multiplex ligation-dependent probe amplification. We also analyzed the genetic profile for 90 patients with myopathy with dysferlin deficiency, as indicated by muscle specimen immunohistochemistry, including patients from a previous cohort.

Results:

We identified putative pathogenic mutations in 38 patients (59% of all investigated patients). Twenty-three patients had DYSF mutations, including 6 novel mutations. The remaining 16 patients, including a single patient who also carried the DYSF mutation, harbored putative pathogenic mutations in other genes. The genetic profile for 90 patients with dysferlin deficiency revealed that 70% had DYSF mutations (n = 63), 10% had CAPN3 mutations (n = 9), 2% had CAV3 mutations (n = 2), 3% had mutations in other genes (in single patients), and 16% did not have any identified mutations (n = 14).

Conclusions:

This study clarified the heterogeneous genetic profile for myopathies with dysferlin deficiency. Our results demonstrate the importance of a comprehensive analysis of related genes in improving the genetic diagnosis of dysferlinopathy as one of the most common subtypes of limb-girdle muscular dystrophy. Unresolved diagnoses should be investigated using whole-genome or whole-exome sequencing.

Quantitation of the calcium and membrane binding properties of the C2 domains of dysferlin

Dysferlin is a large membrane protein involved in calcium-triggered resealing of the sarcolemma after injury. Although it is generally accepted that dysferlin is Ca(2+) sensitive, the Ca(2+) binding properties of dysferlin have not been characterized. In this study, we report an analysis of the Ca(2+) and membrane binding properties of all seven C2 domains of dysferlin as well as a multi-C2 domain construct. Isothermal titration calorimetry measurements indicate that all seven dysferlin C2 domains interact with Ca(2+) with a wide range of binding affinities. The C2A and C2C domains were determined to be the most sensitive, with Kd values in the tens of micromolar, whereas the C2D domain was least sensitive, with a near millimolar Kd value. Mutagenesis of C2A demonstrates the requirement for negatively charged residues in the loop regions for divalent ion binding. Furthermore, dysferlin displayed significantly lower binding affinity for the divalent cations magnesium and strontium. Measurement of a multidomain construct indicates that the solution binding affinity does not change when C2 domains are linked. Finally, sedimentation assays suggest all seven C2 domains bind lipid membranes, and that Ca(2+) enhances but is not required for interaction. This report reveals for the first time, to our knowledge, that all dysferlin domains bind Ca(2+) albeit with varying affinity and stoichiometry.

Distal myopathies

In this article, distal myopathy syndromes are discussed. A discussion of the more traditional distal myopathies is followed by discussion of the myofibrillar myopathies. Other clinically and genetically distinctive distal myopathy syndromes usually based on single or smaller family cohorts are reviewed. Other neuromuscular disorders that are important to recognize are also considered, because they show prominent distal limb weakness.

New developments in exon skipping and splice modulation therapies for neuromuscular diseases

INTRODUCTION

Antisense oligonucleotide (AON) therapy is a form of treatment for genetic or infectious diseases using small, synthetic DNA-like molecules called AONs. Recent advances in the development of AONs that show improved stability and increased sequence specificity have led to clinical trials for several neuromuscular diseases. Impressive preclinical and clinical data are published regarding the usage of AONs in exon-skipping and splice modulation strategies to increase dystrophin production in Duchenne muscular dystrophy (DMD) and survival of motor neuron (SMN) production in spinal muscular atrophy (SMA).

AREAS COVERED

In this review, we focus on the current progress and challenges of exon-skipping and splice modulation therapies. In addition, we discuss the recent failure of the Phase III clinical trials of exon 51 skipping (drisapersen) for DMD.

EXPERT OPINION

The main approach of AON therapy in DMD and SMA is to rescue ('knock up' or increase) target proteins through exon skipping or exon inclusion; conversely, most conventional antisense drugs are designed to knock down (inhibit) the target. Encouraging preclinical data using this 'knock up' approach are also reported to rescue dysferlinopathies, including limb-girdle muscular dystrophy type 2B, Miyoshi myopathy, distal myopathy with anterior tibial onset and Fukuyama congenital muscular dystrophy.

Dysferlin stabilizes stress-induced Ca2+ signaling in the transverse tubule membrane

Dysferlinopathies, most commonly limb girdle muscular dystrophy 2B and Miyoshi myopathy, are degenerative myopathies caused by mutations in the DYSF gene encoding the protein dysferlin. Studies of dysferlin have focused on its role in the repair of the sarcolemma of skeletal muscle, but dysferlin's association with calcium (Ca(2+)) signaling proteins in the transverse (t-) tubules suggests additional roles. Here, we reveal that dysferlin is enriched in the t-tubule membrane of mature skeletal muscle fibers. Following experimental membrane stress in vitro, dysferlin-deficient muscle fibers undergo extensive functional and structural disruption of the t-tubules that is ameliorated by reducing external [Ca(2+)] or blocking L-type Ca(2+) channels with diltiazem. Furthermore, we demonstrate that diltiazem treatment of dysferlin-deficient mice significantly reduces eccentric contraction-induced t-tubule damage, inflammation, and necrosis, which resulted in a concomitant increase in postinjury functional recovery. Our discovery of dysferlin as a t-tubule protein that stabilizes stress-induced Ca(2+) signaling offers a therapeutic avenue for limb girdle muscular dystrophy 2B and Miyoshi myopathy patients.

Antisense therapy in neurology

Antisense therapy is an approach to fighting diseases using short DNA-like molecules called antisense oligonucleotides. Recently, antisense therapy has emerged as an exciting and promising strategy for the treatment of various neurodegenerative and neuromuscular disorders. Previous and ongoing pre-clinical and clinical trials have provided encouraging early results. Spinal muscular atrophy (SMA), Huntington’s disease (HD), amyotrophic lateral sclerosis (ALS), Duchenne muscular dystrophy (DMD), Fukuyama congenital muscular dystrophy (FCMD), dysferlinopathy (including limb-girdle muscular dystrophy 2B; LGMD2B, Miyoshi myopathy; MM, and distal myopathy with anterior tibial onset; DMAT), and myotonic dystrophy (DM) are all reported to be promising targets for antisense therapy. This paper focuses on the current progress of antisense therapies in neurology.

The phenotype of dysferlin-deficient mice is not rescued by adeno-associated virus-mediated transfer of anoctamin 5

Mutations in dysferlin and anoctamin 5 are the cause of muscular disorders, with the main presentations as limb-girdle muscular dystrophy or Miyoshi type of distal myopathy. Both these proteins have been implicated in sarcolemmal resealing. On the basis of similarities in associated phenotypes and protein functions, we tested the hypothesis that ANO5 protein could compensate for dysferlin absence. We first defined that the main transcript of ANO5 expressed in skeletal muscle is the 22-exon full-length isoform, and we demonstrated that dysferlin-deficient (Dysf (prmd)) mice have lower Ano5 expression levels, an observation that further enhanced the rational of the tested hypothesis. We then showed that AAV-mediated transfer of human ANO5 (hANO5) did not lead to apparent toxicity in wild-type mice. Finally, we demonstrated that AAV-hANO5 injection was not able to compensate for dysferlin deficiency in the Dysf (prmd) mouse model or improve the membrane repair defect seen in the absence of dysferlin. Consequently, overexpressing hANO5 does not seem to provide a valuable therapeutic strategy for dysferlin deficiency.

Dysferlin regulates cell adhesion in human monocytes

Dysferlin is mutated in a group of muscular dystrophies commonly referred to as dysferlinopathies. It is highly expressed in skeletal muscle, where it is important for sarcolemmal maintenance. Recent studies show that dysferlin is also expressed in monocytes. Moreover, muscle of dysferlinopathy patients is characterized by massive immune cell infiltrates, and dysferlin-negative monocytes were shown to be more aggressive and phagocytose more particles. This suggests that dysferlin deregulation in monocytes might contribute to disease progression, but the molecular mechanism is unclear. Here we show that dysferlin expression is increased with differentiation in human monocytes and the THP1 monocyte cell model. Freshly isolated monocytes of dysferlinopathy patients show deregulated expression of fibronectin and fibronectin-binding integrins, which is recapitulated by transient knockdown of dysferlin in THP1 cells. Dysferlin forms a protein complex with these integrins at the cell membrane, and its depletion impairs cell adhesion. Moreover, patient macrophages show altered adhesion and motility. These findings suggest that dysferlin is involved in regulating cellular interactions and provide new insight into dysferlin function in inflammatory cells.

Clinical features and a mutation with late onset of limb girdle muscular dystrophy 2B

OBJECTIVE AND METHODS

Dysferlin encoded by DYSF deficiency leads to two main phenotypes, limb girdle muscular dystrophy (LGMD) 2B and Miyoshi myopathy. To reveal in detail the mutational and clinical features of LGMD2B in Japan, we observed 40 Japanese patients in 36 families with LGMD2B in whom dysferlin mutations were confirmed.

RESULTS AND CONCLUSIONS

Three mutations (c.1566C>G, c.2997G>T and c.4497delT) were relatively more prevalent. The c.2997G>T mutation was associated with late onset, proximal dominant forms of dysferlinopathy, a high probability that muscle weakness started in an upper limb and lower serum creatine kinase (CK) levels. The clinical features of LGMD2B are as follows: (1) onset in the late teens or early adulthood, except patients homozygous for the c.2997G>T mutation; (2) lower limb weakness at onset; (3) distal change of lower limbs on muscle CT at an early stage; (4) impairment of lumbar erector spinal muscles on muscle CT at an early stage; (5) predominant involvement of proximal upper limbs; (6) preservation of function of the hands at late stage; (7) preservation of strength in neck muscles at late stage; (8) lack of facial weakness or dysphagia; (9) avoidance of scoliosis; (10) hyper-Ckaemia; (11) preservation of cardiac function; and (12) a tendency for respiratory function to decline with disease duration. It is important that the late onset phenotype is found with prevalent mutations.

Lack of correlation between outcomes of membrane repair assay and correction of dystrophic changes in experimental therapeutic strategy in dysferlinopathy

Mutations in the dysferlin gene are the cause of Limb-girdle Muscular Dystrophy type 2B and Miyoshi Myopathy. The dysferlin protein has been implicated in sarcolemmal resealing, leading to the idea that the pathophysiology of dysferlin deficiencies is due to a deficit in membrane repair. Here, we show using two different approaches that fullfiling membrane repair as asseyed by laser wounding assay is not sufficient for alleviating the dysferlin deficient pathology. First, we generated a transgenic mouse overexpressing myoferlin to test the hypothesis that myoferlin, which is homologous to dysferlin, can compensate for the absence of dysferlin. The myoferlin overexpressors show no skeletal muscle abnormalities, and crossing them with a dysferlin-deficient model rescues the membrane fusion defect present in dysferlin-deficient mice in vitro. However, myoferlin overexpression does not correct muscle histology in vivo. Second, we report that AAV-mediated transfer of a minidysferlin, previously shown to correct the membrane repair deficit in vitro, also fails to improve muscle histology. Furthermore, neither myoferlin nor the minidysferlin prevented myofiber degeneration following eccentric exercise. Our data suggest that the pathogenicity of dysferlin deficiency is not solely related to impairment in sarcolemmal repair and highlight the care needed in selecting assays to assess potential therapies for dysferlinopathies.

Lysosome fusion to the cell membrane is mediated by the dysferlin C2A domain in coronary arterial endothelial cells

Dysferlin has recently been reported to participate in cell membrane repair in muscle and other cells through lysosome fusion. Given that lysosome fusion is a crucial mechanism that leads to membrane raft clustering, the present study attempted to determine whether dysferlin is involved in this process and its related signalling, and explores the mechanism underlying dysferlin-mediated lysosome fusion in bovine coronary arterial endothelial cells (CAECs). We found that dysferlin is clustered in membrane raft macrodomains after Fas Ligand (FasL) stimulation as detected by confocal microscopy and membrane fraction flotation. Small-interfering RNA targeted to dysferlin prevented membrane raft clustering. Furthermore, the translocation of acid sphingomyelinase (ASMase) to membrane raft clusters, whereby local ASMase activation and ceramide production--an important step that mediates membrane raft clustering--was attenuated. Functionally, silencing of the dysferlin gene reversed FasL-induced impairment of endothelium-dependent vasodilation in isolated small coronary arteries. By monitoring fluorescence quenching or dequenching, silencing of the dysferlin gene was found to almost completely block lysosome fusion to plasma membrane upon FasL stimulation. Further studies to block C2A binding and silencing of AHNAK (a dysferlin C2A domain binding partner), showed that the dysferlin C2A domain is required for FasL-induced lysosome fusion to the cell membrane, ASMase translocation and membrane raft clustering. We conclude that dysferlin determines lysosome fusion to the plasma membrane through its C2A domain and it is therefore implicated in membrane-raft-mediated signaling and regulation of endothelial function in coronary circulation.

Childhood onset of limb-girdle muscular dystrophy

Limb-girdle muscular dystrophies comprise a rare heterogeneous group of genetic muscular dystrophies, involving 15 autosomal recessive subtypes and seven autosomal dominant subtypes. Autosomal recessive dystrophy is far more common than autosomal dominant dystrophy. Typical clinical features include progressive limb muscle weakness and atrophy (proximal greater than distal), varying from very mild to severe. Significant overlap of clinical phenotypes, with genetic and clinical heterogeneity, constitutes the rule for this group of diseases. Muscle biopsies are useful for histopathologic and immunolabeling studies, and DNA analysis is the gold standard to establish the specific form of muscular dystrophy. A definitive diagnosis among various subtypes is challenging, and the data presented here provide neuromuscular clinicians with additional information to help attain that goal.

Preclinical studies with umbilical cord mesenchymal stromal cells in different animal models for muscular dystrophy

Umbilical cord mesenchymal stromal cells (MSC) have been widely investigated for cell-based therapy studies as an alternative source to bone marrow transplantation. Umbilical cord tissue is a rich source of MSCs with potential to derivate at least muscle, cartilage, fat, and bone cells in vitro. The possibility to replace the defective muscle cells using cell therapy is a promising approach for the treatment of progressive muscular dystrophies (PMDs), independently of the specific gene mutation. Therefore, preclinical studies in different models of muscular dystrophies are of utmost importance. The main objective of the present study is to evaluate if umbilical cord MSCs have the potential to reach and differentiate into muscle cells in vivo in two animal models of PMDs. In order to address this question we injected (1) human umbilical cord tissue (hUCT) MSCs into the caudal vein of SJL mice; (2) hUCT and canine umbilical cord vein (cUCV) MSCs intra-arterially in GRMD dogs. Our results here reported support the safety of the procedure and indicate that the injected cells could engraft in the host muscle in both animal models but could not differentiate into muscle cells. These observations may provide important information aiming future therapy for muscular dystrophies.

Distal muscular dystrophies

Distal muscular dystrophies are a group of inherited primary muscle disorders showing progressive weakness and atrophy preferentially in the hands, forearm, lower legs, or feet. Extensive progress in understanding the molecular genetic background has changed the classification and extended the list of confirmed entities to almost 20 different disorders, making the differential diagnostic procedure both easier and more difficult. Distal phenotypes first have to be differentiated from neurogenic disorders. The axonal form of Charcot-Marie-Tooth disease with late-onset distal weakness and distal forms of chronic spinal muscular atrophy may mimic those of the distal dystrophies. Increasing numbers of reports suggest increasing awareness of distal phenotypes in muscular dystrophy. Some disorders regularly progress eventually to involve proximal muscle, whereas others, such as tibial muscular dystrophy titinopathy (Udd), Welander distal myopathy, and distal myosinopathy (Laing), remain distal throughout the patient's lifetime. Pathologically there is a gradual degeneration and loss of muscle fibers with replacement by fibrous and fatty connective tissue, similar to the proximal forms of muscular dystrophy, frequently, but not always with rimmed vacuolar degenerative change. Strikingly, many of the genes involved in distal dystrophies code for sarcomeric proteins. However, the genetic programs leading to preferential involvement of distal muscles have remained unknown.

Translational research and therapeutic perspectives in dysferlinopathies

Dysferlinopathies are autosomal recessive disorders caused by mutations in the dysferlin (DYSF) gene, encoding the dysferlin protein. DYSF mutations lead to a wide range of muscular phenotypes, with the most prominent being Miyoshi myopathy (MM) and limb girdle muscular dystrophy type 2B (LGMD2B) and the second most common being LGMD. Symptoms generally appear at the end of childhood and, although disease progression is typically slow, walking impairments eventually result. Dysferlin is a modular type II transmembrane protein for which numerous binding partners have been identified. Although dysferlin function is only partially elucidated, this large protein contains seven calcium sensor C2 domains, shown to play a key role in muscle membrane repair. On the basis of this major function, along with detailed clinical observations, it has been possible to design various therapeutic approaches for dysferlin-deficient patients. Among them, exon-skipping and minigene transfer strategies have been evaluated at the preclinical level and, to date, represent promising approaches for clinical trials. This review aims to summarize the pathophysiology of dysferlinopathies and to evaluate the therapeutic potential for treatments currently under development.

Dysferlin deficiency and the development of cardiomyopathy in a mouse model of limb-girdle muscular dystrophy 2B

Limb-girdle muscular dystrophy 2B, Miyoshi myopathy, and distal myopathy of anterior tibialis are severely debilitating muscular dystrophies caused by genetically determined dysferlin deficiency. In these muscular dystrophies, it is the repair, not the structure, of the plasma membrane that is impaired. Though much is known about the effects of dysferlin deficiency in skeletal muscle, little is known about the role of dysferlin in maintenance of cardiomyocytes. Recent evidence suggests that dysferlin deficiency affects cardiac muscle, leading to cardiomyopathy when stressed. However, neither the morphological location of dysferlin in the cardiomyocyte nor the progression of the disease with age are known. In this study, we examined a mouse model of dysferlinopathy using light and electron microscopy as well as echocardiography and conscious electrocardiography. We determined that dysferlin is normally localized to the intercalated disk and sarcoplasm of the cardiomyocytes. In the absence of dysferlin, cardiomyocyte membrane damage occurs and is localized to the intercalated disk and sarcoplasm. This damage results in transient functional deficits at 10 months of age, but, unlike in skeletal muscle, the cell injury is sublethal and causes only mild cardiomyopathy even at advanced ages.

Caveolinopathies: from the biology of caveolin-3 to human diseases

In muscle tissue the protein caveolin-3 forms caveolae--flask-shaped invaginations localized on the cytoplasmic surface of the sarcolemmal membrane. Caveolae have a key role in the maintenance of plasma membrane integrity and in the processes of vesicular trafficking and signal transduction. Mutations in the caveolin-3 gene lead to skeletal muscle pathology through multiple pathogenetic mechanisms. Indeed, caveolin-3 deficiency is associated to sarcolemmal membrane alterations, disorganization of skeletal muscle T-tubule network and disruption of distinct cell-signaling pathways. To date, there have been 30 caveolin-3 mutations identified in the human population. Caveolin-3 defects lead to four distinct skeletal muscle disease phenotypes: limb girdle muscular dystrophy, rippling muscle disease, distal myopathy, and hyperCKemia. In addition, one caveolin-3 mutant has been described in a case of hypertrophic cardiomyopathy. Many patients show an overlap of these symptoms and the same mutation can be linked to different clinical phenotypes. This variability can be related to additional genetic or environmental factors. This review will address caveolin-3 biological functions in muscle cells and will describe the muscle and heart disease phenotypes associated with caveolin-3 mutations.

ANNIE: integrated de novo protein sequence annotation

Function prediction of proteins with computational sequence analysis requires the use of dozens of prediction tools with a bewildering range of input and output formats. Each of these tools focuses on a narrow aspect and researchers are having difficulty obtaining an integrated picture. ANNIE is the result of years of close interaction between computational biologists and computer scientists and automates an essential part of this sequence analytic process. It brings together over 20 function prediction algorithms that have proven sufficiently reliable and indispensable in daily sequence analytic work and are meant to give scientists a quick overview of possible functional assignments of sequence segments in the query proteins. The results are displayed in an integrated manner using an innovative AJAX-based sequence viewer. ANNIE is available online at: http://annie.bii.a-star.edu.sg. This website is free and open to all users and there is no login requirement.

Changes in skeletal muscle expression of AQP1 and AQP4 in dystrophinopathy and dysferlinopathy patients

Transmembrane water transport is mediated by aquaporins (AQPs), of which AQP1 and AQP4 are expressed in skeletal muscle. AQP4 expression is reduced in Duchenne muscular dystrophy (DMD) patients, and is reported to correlate with decreased alpha1-syntrophin and altered osmotic permeability. In this study, we assessed the relationship between AQP1, AQP4, dystrophin and alpha1-syntrophin in dystrophinopathy and dysferlinopathy patients. Muscle biopsies of patients with DMD (n = 8) and limb-girdle muscular dystrophy type 2B (LGMD2B; n = 5) were screened for AQP1 and AQP4 expression by real-time quantitative RT-PCR or Western blot and immunohistochemistry. AQP expression was further analyzed in primary myotubes derived from DMD and LGMD2B patients by cell culture and immunohistochemistry. AQP1 transcript and protein expression was significantly elevated in DMD biopsies, and was localized to the sarcolemma of muscle fibers and endothelia of muscle capillaries. AQP4 was significantly reduced despite normal dystrophin and alpha1-syntrophin in dysferlinopathy patients, while expression of AQP1 was variably upregulated. Expression of AQP1 and AQP4 was normal in patient-derived primary myotubes, suggesting that altered AQPs observed in biopsies are likely secondary to the dystrophic process. Our study shows that AQP4 downregulation can occur in muscular dystrophies with either normal or disrupted expression of dystrophin-associated proteins, and that this might be associated with upregulation of AQP1.

SJL dystrophic mice express a significant amount of human muscle proteins following systemic delivery of human adipose-derived stromal cells without immunosuppression

Limb-girdle muscular dystrophies (LGMDs) are a heterogeneous group of disorders characterized by progressive degeneration of skeletal muscle caused by the absence of or defective muscular proteins. The murine model for limb-girdle muscular dystrophy 2B (LGMD2B), the SJL mice, carries a deletion in the dysferlin gene that causes a reduction in the protein levels to 15% of normal. The mice show muscle weakness that begins at 4-6 weeks and is nearly complete by 8 months of age. The possibility of restoring the defective muscle protein and improving muscular performance by cell therapy is a promising approach for the treatment of LGMDs or other forms of progressive muscular dystrophies. Here we have injected human adipose stromal cells (hASCs) into the SJL mice, without immunosuppression, aiming to assess their ability to engraft into recipient dystrophic muscle after systemic delivery; form chimeric human/mouse muscle fibers; express human muscle proteins in the dystrophic host and improve muscular performance. We show for the first time that hASCs are not rejected after systemic injection even without immunosuppression, are able to fuse with the host muscle, express a significant amount of human muscle proteins, and improve motor ability of injected animals. These results may have important applications for future therapy in patients with different forms of muscular dystrophies.

Caveolin-3 T78M and T78K missense mutations lead to different phenotypes in vivo and in vitro

Caveolins are the principal protein components of caveolae, invaginations of the plasma membrane involved in cell signaling and trafficking. Caveolin-3 (Cav-3) is the muscle-specific isoform of the caveolin family and mutations in the CAV3 gene lead to a large group of neuromuscular disorders. In unrelated patients, we identified two distinct CAV3 mutations involving the same codon 78. Patient 1, affected by dilated cardiomyopathy and limb girdle muscular dystrophy (LGMD)-1C, shows an autosomal recessive mutation converting threonine to methionine (T78M). Patient 2, affected by isolated familiar hyperCKemia, shows an autosomal dominant mutation converting threonine to lysine (T78K). Cav-3 wild type (WT) and Cav-3 mutations were transiently transfected into Cos-7 cells. Cav-3 WT and Cav-3 T78M mutant localized at the plasma membrane, whereas Cav-3 T78K was retained in a perinuclear compartment. Cav-3 T78K expression was decreased by 87% when compared with Cav-3 WT, whereas Cav-3 T78M protein levels were unchanged. To evaluate whether Cav-3 T78K and Cav-3 T78M mutants behaved with a dominant negative pattern, Cos-7 cells were cotransfected with green fluorescent protein (GFP)-Cav-3 WT in combination with either mutant or WT Cav-3. When cotransfected with Cav-3 WT or Cav-3 T78M, GFP-Cav-3 WT was localized at the plasma membrane, as expected. However, when cotransfected with Cav-3 T78K, GFP-Cav-3 WT was retained in a perinuclear compartment, and its protein levels were reduced by 60%, suggesting a dominant negative action. Accordingly, Cav-3 protein levels in muscles from a biopsy of patient 2 (T78K mutation) were reduced by 80%. In conclusion, CAV3 T78M and T78K mutations lead to distinct disorders showing different clinical features and inheritance, and displaying distinct phenotypes in vitro.

Dysferlin deficiency enhances monocyte phagocytosis: a model for the inflammatory onset of limb-girdle muscular dystrophy 2B

Dysferlin deficiency causes limb-girdle muscular dystrophy type 2B (LGMD2B; proximal weakness) and Miyoshi myopathy (distal weakness). Muscle inflammation is often present in dysferlin deficiency, and patients are frequently misdiagnosed as having polymyositis. Because monocytes normally express dysferlin, we hypothesized that monocyte/macrophage dysfunction in dysferlin-deficient patients might contribute to disease onset and progression. We therefore examined phagocytic activity, in the presence and absence of cytokines, in freshly isolated peripheral blood monocytes from LGMD2B patients and in the SJL dysferlin-deficient mouse model. Dysferlin-deficient monocytes showed increased phagocytic activity compared with control cells. siRNA-mediated inhibition of dysferlin expression in the J774 macrophage cell line resulted in significantly enhanced phagocytosis, both at baseline and in response to tumor necrosis factor-alpha. Immunohistochemical analysis revealed positive staining for several mononuclear cell activation markers in LGMD2B human muscle and SJL mouse muscle. SJL muscle showed strong up-regulation of endocytic proteins CIMPR, clathrin, and adaptin-alpha, and LGMD2B muscle exhibited decreased expression of decay accelerating factor, which was not dysferlin-specific. We further showed that expression levels of small Rho family GTPases RhoA, Rac1, and Cdc 42 were increased in dysferlin-deficient murine immune cells compared with control cells. Therefore, we hypothesize that mild myofiber damage in dysferlin-deficient muscle stimulates an inflammatory cascade that may initiate, exacerbate, and possibly perpetuate the underlying myofiber-specific dystrophic process.

Caveolin regulates endocytosis of the muscle repair protein, dysferlin

Dysferlin and Caveolin-3 are plasma membrane proteins associated with muscular dystrophy. Patients with mutations in the CAV3 gene show dysferlin mislocalization in muscle cells. By utilizing caveolin-null cells, expression of caveolin mutants, and different mutants of dysferlin, we have dissected the site of action of caveolin with respect to dysferlin trafficking pathways. We now show that Caveolin-1 or -3 can facilitate exit of a dysferlin mutant that accumulates in the Golgi complex of Cav1(-/-) cells. In contrast, wild type dysferlin reaches the plasma membrane but is rapidly endocytosed in Cav1(-/-) cells. We demonstrate that the primary effect of caveolin is to cause surface retention of dysferlin. Caveolin-1 or Caveolin-3, but not specific caveolin mutants, inhibit endocytosis of dysferlin through a clathrin-independent pathway colocalizing with internalized glycosylphosphatidylinositol-anchored proteins. Our results provide new insights into the role of this endocytic pathway in surface remodeling of specific surface components. In addition, they highlight a novel mechanism of action of caveolins relevant to the pathogenic mechanisms underlying caveolin-associated disease.

Proteomic analysis of plasma membrane and secretory vesicles from human neutrophils

Background

Polymorphonuclear neutrophils (PMN) constitute an essential cellular component of innate host defense against microbial invasion and exhibit a wide array of responses both to particulate and soluble stimuli. As the cells recruited earliest during acute inflammation, PMN respond rapidly and release a variety of potent cytotoxic agents within minutes of exposure to microbes or their products. PMN rely on the redistribution of functionally important proteins, from intracellular compartments to the plasma membrane and phagosome, as the means by which to respond quickly. To determine the range of membrane proteins available for rapid recruitment during PMN activation, we analyzed the proteins in subcellular fractions enriched for plasma membrane and secretory vesicles recovered from the light membrane fraction of resting PMN after Percoll gradient centrifugation and free-flow electrophoresis purification using mass spectrometry-based proteomics methods.

Results

To identify the proteins light membrane fractions enriched for plasma membrane vesicles and secretory vesicles, we employed a proteomic approach, first using MALDI-TOF (peptide mass fingerprinting) and then by HPLC-MS/MS using a 3D ion trap mass spectrometer to analyze the two vesicle populations from resting PMN. We identified several proteins that are functionally important but had not previously been recovered in PMN secretory vesicles. Two such proteins, 5-lipoxygenase-activating protein (FLAP) and dysferlin were further validated by immunoblot analysis.

Conclusion

Our data demonstrate the broad array of proteins present in secretory vesicles that provides the PMN with the capacity for remarkable and rapid reorganization of its plasma membrane after exposure to proinflammatory agents or stimuli.

Mouse behavioral tasks relevant to autism: phenotypes of 10 inbred strains

Three defining clinical symptoms of autism are aberrant reciprocal social interactions, deficits in social communication, and repetitive behaviors, including motor stereotypies and insistence on sameness. We developed a set of behavioral tasks designed to model components of these core symptoms in mice. Male mice from 10 inbred strains were characterized in assays for sociability, preference for social novelty, and reversal of the spatial location of the reinforcer in T-maze and Morris water maze tasks. Six strains, C57BL/6J, C57L/J, DBA/2J, FVB/NJ, C3H/HeJ, and AKR/J, showed significant levels of sociability, while A/J, BALB/cByJ, BTBR T(+)tf/J, and 129S1/SvImJ mice did not. C57BL/6J, C57L/J, DBA/2J, FVB/NJ, BALB/cByJ, and BTBR T(+)tf/J showed significant preference for social novelty, while C3H/HeJ, AKR/J, A/J, and 129S1/SvImJ did not. Normal scores on relevant control measures confirmed general health and physical abilities in all strains, ruling out artifactual explanations for social deficits. Elevated plus maze scores confirmed high anxiety-like behaviors in A/J, BALB/cByJ, and 129S1/SvImJ, which could underlie components of their low social approach. Strains that showed high levels of performance on acquisition of a T-maze task were also able to reach criterion for reversal learning. On the Morris water maze task, DBA/2J, AKR/J, BTBR T(+)tf/J, and 129S1/SvImJ failed to show significant quadrant preference during the reversal probe trial. These results highlight a dissociation between social task performance and reversal learning. BTBR T(+)tf/J is a particularly interesting strain, displaying both low social approach and resistance to change in routine on the water maze, consistent with an autism-like phenotype. Our multitask strategy for modeling symptoms of autism will be useful for investigating targeted and random gene mutations, QTLs, and microarray analyses.

Painful enlargement of the calf muscles in limb girdle muscular dystrophy type 2B (LGMD2B) with a novel compound heterozygous mutation in DYSF

Limb girdle muscular dystrophy type 2B (LGMD2B) and Miyoshi Myopathy are caused by mutations in the dysferlin gene. The phenotype of these allelic disease variants can vary considerably. We report on an adolescent female with a severe and rapidly progressing clinical course of LGMD2B which has been suggested by the muscle histopathology and Western blot and proven by mutation analysis in the Dysferlin gene. We detected a novel compound heterozygous mutation of which one affects the extracellular part of the protein. This is the first report on a mutation in this region of dysferlin and might explain the unusual phenotype of the patient.

Patients with a non-dysferlin Miyoshi myopathy have a novel membrane repair defect

Two autosomal recessive muscle diseases, limb girdle muscular dystrophy type 2B (LGMD2B) and Miyoshi myopathy (MM), are caused by mutations in the dysferlin gene. These mutations result in poor ability to repair cell membrane damage, which is suggested to be the cause for this disease. However, many patients who share clinical features with MM-type muscular dystrophy do not carry mutations in dysferlin gene. To understand the basis of MM that is not due to mutations in dysferlin gene, we analyzed cells from patients in one such family. In these patients, we found no defects in several potential candidates - annexin A2, caveolin-3, myoferlin and the MMD2 locus on chromosome 10p. Similar to dysferlinopathy, these cells also exhibit membrane repair defects and the severity of the defect correlated with severity of their disease. However, unlike dysferlinopathy, none of the conventional membrane repair pathways are defective in these patient cells. These results add to the existing evidence that cell membrane repair defect may be responsible for MM-type muscular dystrophy and indicate that a previously unsuspected genetic lesion that affects cell membrane repair pathway is responsible for the disease in the non-dysferlin MM patients.

Histological and Immunohistological Changes of the Skeletal Muscles in Older SJL/J Mice

SJL/J mice have been studied as the model animals for autoimmunological diseases. Recently it was clarified that SJL/J mice have a defect of dysferlin. Human limb girdle muscular dystrophy 2B and Miyoshi myopathy also have a defect of dysferlin. In this study we present the histological and immunohistological changes in the natural course. Histological study revealed that SJL/J mice had inflammatory, degenerative changes, and neurogenic changes in later ages. As for interstitial inflammatory cells, the macrophages were dominant in any age, and in the T cell subset, the CD4+ T cells were more abundant than the CD8+ T cells, and few B cells were seen. The laboratory data showed a high level of creatine kinase in all ages. It is suspected that the inflammatory changes were induced by the primary immunological abnormality or by the defect of dysferlin in SJL/J mice.

The inflammatory reaction pattern distinguishes primary dysferlinopathies from idiopathic inflammatory myopathies: an important role for the membrane attack complex

Degenerative muscle changes in dysferlinopathies are often accompanied by inflammatory infiltrates and may even mimic primary idiopathic inflammatory myopathies. In the present study, the inflammatory reaction pattern with respect to the cellular composition of the infiltrates and the expression of potent cytokines was characterized in dysferlinopathies and in idiopathic inflammatory myopathies. Cellular infiltrates in dysferlinopathies mainly consisted of CD4+CD25- T cells and macrophages. We noted a prominent expression of interferon-gamma which may contribute to the marked upregulation of MHC class I antigen observed on the vast majority of muscle fibres. Furthermore, membrane attack complex positive deposits were found on intact as well as necrotic muscle fibres. Collectively, our study indicates that the inflammatory reaction pattern in dysferlinopathies is distinct from the one in idiopathic inflammatory myopathies. In particular, membrane attack complex deposits and a pro-inflammatory milieu in the absence of interleukin-10 expression may contribute to progressive muscle damage in dysferlinopathies.

Molecular biology of distal muscular dystrophies--sarcomeric proteins on top

During the last 10 years several muscular dystrophies within the group of distal myopathies have been clarified as to the molecular genetic cause of the disease. Currently, the next steps are carried out to identify the molecular pathogenesis downstream of the gene defects. Some early ideas on what is going on in the muscle cells based on the defect proteins are emerging. However, in no single distal muscular dystrophy these efforts have yet reached the point where direct trials for therapy would have been launched, and in many distal dystrophies the causative gene is still lacking. When comparing the gene defects in the distal dystrophies with the more common proximal muscular dystrophies such as dystrophinopathies or limb-girdle muscular dystrophies, there is a striking difference: the genes for distal dystrophies encode sarcomere proteins whereas the genes for proximal dystrophies more often encode sarcolemmal proteins.

Identification and characterization of a novel human dysferlin transcript: dysferlin_v1

Mutations in the dysferlin (DYSF) gene are associated with limb girdle muscular dystrophy type 2B and Miyoshi myopathy. In this study, we report the identification and characterization of a novel dysferlin transcript that we named DYSF_v1 (GenBank accession: DQ267935). This transcript differs from the currently known dysferlin transcript (GenBank accession: AF075575) in the sequence of the entire first exon which spans 232 bases. This unique first exon is derived from intron 1 of DYSF, and has an immediate upstream 5' untranslated region containing CpG islands and sequences consistent with transcription factor binding sites. Exon 1 of DYSF_v1 shares 85% sequence homology and has similar genomic organization with the first exon of mouse dysferlin. Northern blot analysis showed that the DYSF_v1 transcript spans 7.5 kb and is expressed in human skeletal muscle, heart, placenta, brain, spleen, kidney, intestine, and lung tissues. DYSF_v1 retains phylogenic conservancy and shows similar expression pattern as the currently known human dysferlin.

Sarcolemmopathy: muscular dystrophies with cell membrane defects

In this article, we review the molecular pathology of muscular dystrophies caused by defects of proteins located within or near cell membranes. These disorders include Bethlem myopathy, merosinopathy, dystrophinopathy, sarcoglycanopathies, integrinopathy, dysferlinopathy and caveolinopathy. We refer to these diseases collectively as sarcolemmopathy. Here, we describe the biological functions of these proteins in the context of muscular contractions and their roles in the infrastructure of muscle; defects of muscle infrastructures cause those diseases. As an example, in dystrophinopathy, cell membranes have mechanical defects due to the absence of dystrophin. Cracks of the cell membrane induced by muscle contraction may allow the influx and efflux of substances that trigger muscle cell degeneration. However, such cracks may be resealed on relaxation. In addition, dystrophinopathy causes secondary defects of various dystrophin-associated proteins suggesting that defects in cell signaling participate in the pathologic process. With regard to other sarcolemmopathies, we discuss pathological mechanisms based on available data.

Distal myopathies

PURPOSE OF REVIEW

The distal myopathies are a heterogeneous group of disorders that pose a challenge to both the clinician and geneticist. This article summarizes the findings of recent clinical, genetic and molecular studies and the current diagnostic approach to this group of patients.

RECENT FINDINGS

Publications over the past 5 years describe a number of new clinical phenotypes and genetic loci and further emphasize the overlap in clinical phenotype between a number of these disorders and between the distal and limb girdle myopathies and hereditary inclusion body myopathies. Recent studies have led to the identification of the genes and mutations responsible for early onset (Laing) myopathy and tibial (Udd) myopathy, and for distal myopathy with rimmed vacuoles (Nonaka), which has been shown to be allelic with quadriceps sparing hereditary inclusion body myopathy (IBM2), and have elucidated the underlying pathogenetic mechanisms in these conditions. New diagnostic approaches using magnetic resonance imaging, and a blood-based assay for dysferlin deficiency, have also been reported.

SUMMARY

These findings have important implications for future genetic linkage and gene expression studies and for the diagnostic approach to patients with a distal myopathy phenotype. They also hold promise for the eventual development of therapies for this group of disorders.

Aberrant dysferlin trafficking in cells lacking caveolin or expressing dystrophy mutants of caveolin-3

Mutations in the dysferlin (DYSF) and caveolin-3 (CAV3) genes are associated with muscle disease. Dysferlin is mislocalized, by an unknown mechanism, in muscle from patients with mutations in caveolin-3 (Cav-3). To examine the link between Cav-3 mutations and dysferlin mistargeting, we studied their localization at high resolution in muscle fibers, in a model muscle cell line, and upon heterologous expression of dysferlin in muscle cell lines and in wild-type or caveolin-null fibroblasts. Dysferlin shows only partial overlap with Cav-3 on the surface of isolated muscle fibers but co-localizes with Cav-3 in developing transverse (T)-tubules in muscle cell lines. Heterologously expressed dystrophy-associated mutant Cav3R26Q accumulates in the Golgi complex of muscle cell lines or fibroblasts. Cav3R26Q and other Golgi-associated mutants of both Cav-3 (Cav3P104L) and Cav-1 (Cav1P132L) caused a dramatic redistribution of dysferlin to the Golgi complex. Heterologously expressed epitope-tagged dysferlin associates with the plasma membrane in primary fibroblasts and muscle cells. Transport to the cell surface is impaired in the absence of Cav-1 or Cav-3 showing that caveolins are essential for dysferlin association with the PM. These results suggest a functional role for caveolins in a novel post-Golgi trafficking pathway followed by dysferlin.

Dysferlin mutation in a Chinese pedigree with Miyoshi myopathy

OBJECTIVES

Mutations in the dysferlin gene cause two autosomal recessive forms of muscular dystrophy: Miyoshi myopathy and limb-girdle muscular dystrophy type 2B. The purpose of this study was to diagnose a Chinese pedigree with the autosomal recessive form of muscular dystrophy and conduct mutational screening.

METHODS

The pedigree was diagnosed accurately by using two-point linkage analysis and multi-Western blot analysis. Mutations were determined by reverse transcriptase polymerase chain reaction (RT-PCR) followed by DNA sequencing.

RESULTS

Two-point linkage analysis showed significant LOD scores with makers from chromosome 2p13. Multi-Western blot analysis confirmed dysferlin deficiency of muscle specimen from the propositus. Mutation analysis of the dysferlin gene revealed a novel mutation, 6429delG, on exon 53.

CONCLUSIONS

We identified an inbred Chinese pedigree with Miyoshi myopathy caused by the 6429delG mutation in the dysferlin gene. This mutation is predicted to result in premature termination of translation contributing to Miyoshi myopathy.

Autophagic vacuoles with sarcolemmal features delineate Danon disease and related myopathies

Among the autophagic vacuolar myopathies (AVMs), a subgroup is characterized pathologically by unusual autophagic vacuoles with sarcolemmal features (AVSF) and includes Danon disease and X-linked myopathy with excessive autophagy. The diagnostic importance and detailed morphologic features of AVSF in different AVMs have not been well established, and the mechanism of AVSF formation is not known. To address these issues, we have performed detailed histologic studies of myopathies with AVSF and other AVMs. In Danon disease and related AVMs, at the light microscopic level, autophagic vacuoles appeared to be accumulations of lysosomes, which, by electron microscopy consisted of clusters of autophagic vacuoles, indicative of autolysosomes. Some autolysosomes were surrounded by membranes with sarcolemmal proteins, acetylcholinesterase activity, and basal lamina. In Danon disease, the number of fibers with AVSF increased linearly with age while the number with autolysosomal accumulations decreased slightly, suggesting that AVSF are produced secondarily in response to autolysosomes. Most of the AVSF form enclosed spaces, indicating that the vacuolar membranes may be formed in situ rather than through sarcolemmal indentation. This unique intracytoplasmic membrane structure was not found in other AVMs. In conclusion, AVSF with acetylcholinesterase activity are autolysosomes surrounded by secondarily generated intracytoplasmic sarcolemma-like structure and delineates a subgroup of AVMs.