Dysferlin, a novel skeletal muscle gene, is mutated in Miyoshi myopathy and limb girdle muscular dystrophy

Dysferlinopathy: mitochondrial abnormalities in human skeletal muscle

PURPOSE

Mitochondrial defects have been associated with a series of muscular diseases. Dysferlinopathy, however, has been rarely reported with mitochondrial dysfunction. Here we report a cohort of dysferlinopathy patients with mitochondrial abnormalities found in muscle.

METHODS

Clinical data and muscle pathologies of nine cases with dysferlinopathy were retrospectively studied. mtDNA copy number, protein levels and activities of mitochondrial enzyme complexes were assayed.

RESULTS

Nine patients were diagnosed as having dysferlinopathy by DYSF sequencing and quantification of dysferlin levels in muscle homogenates. Muscle biopsies exhibited dystrophic changes (n = 9), ragged-red fibers (n = 9) and cytochrome c oxidase-deficient fibers (n = 9). mtDNA copy number increased significantly in 56% (15/27) of fibers with mitochondrial histology. Protein levels of complex IV subunits II (n = 5), complex III subunit core 2 (n = 2) and complex I NDUFB1 (n = 1) decreased. Impaired activities of complexes I, III and IV were observed in 56%, 33% and 78% of subjects and the activities were reduced by 21%, 18% and 40%, respectively. Besides, loss activities of complexes I/IV and decreased ATP level were also found in fibroblasts from dysferlinopathy.

CONCLUSION

Prominent mitochondrial abnormalities are common pathological findings in muscle from dysferlinopathy. Our data indicated that mitochondria may play a significant role in the progression of dysferlinopathy and also highlighted the potential of mitochondrial protective drugs in rescuing the symptoms of dysferlinopathy.

Nonsyndromic Early-Onset Cone-Rod Dystrophy and Limb-Girdle Muscular Dystrophy in a Consanguineous Israeli Family are Caused by Two Independent yet Linked Mutations in ALMS1 and DYSF

Genetic analysis of clinical phenotypes in consanguineous families is complicated by coinheritance of large DNA regions carrying independent variants. Here, we characterized a family with early onset cone-rod dystrophy (CRD) and muscular dystrophy. Homozygosity mapping (HM) followed by whole exome sequencing revealed a nonsense mutation, p.R270*, in ALMS1 and two novel potentially disease-causing missense variants, p.R1581C and p.Y2070C, in DYSF. ALMS1 and DYSF are genetically and physically linked on chromosome 2 in a genomic region suggested by HM and associated with Alström syndrome, which includes CRD, and with limb girdle muscular dystrophy, respectively. Affected family members lack additional systemic manifestations of Alström syndrome but exhibit mild muscular dystrophy. RNA-seq data did not reveal any significant variations in ALMS1 transcripts in the human retina. Our study thus implicates ALMS1 as a nonsyndromic retinal disease gene and suggests a potential role of variants in interacting cilia genes in modifying clinical phenotypes.

Inhibition of inflammation with celastrol fails to improve muscle function in dysferlin-deficient A/J mice

The dysferlin-deficient A/J mouse strain represents a homologous model for limb-girdle muscular dystrophy 2B. We evaluated the disease phenotype in 10 month old A/J mice compared to two dysferlin-sufficient, C57BL/6 and A/JOlaHsd, mouse lines to determine which functional end-points are sufficiently sensitive to define the disease phenotype for use in preclinical studies in the A/J strain. A/J mice had significantly lower open field behavioral activity (horizontal activity, total distance, movement time and vertical activity) when compared to C57BL/6 and A/JoIaHsd mice. Both A/J and A/JOIaHsd mice showed decreases in latency to fall with rotarod compared to C57BL/6. No changes were detected in grip strength, force measurements or motor coordination between these three groups. Furthermore, we have found that A/J muscle shows significantly increased levels of the pro-inflammatory cytokine TNF-α when compared to C57BL/6 mice, indicating an activation of NF-κB signaling as part of the inflammatory response in dysferlin-deficient muscle. Therefore, we assessed the effect of celastrol (a potent NF-κB inhibitor) on the disease phenotype in female A/J mice. Celastrol treatment for four months significantly reduced the inflammation in A/J muscle; however, it had no beneficial effect in improving muscle function, as assessed by grip strength, open field activity, and in vitro force contraction. In fact, celastrol treated mice showed a decrease in body mass, hindlimb grip strength and maximal EDL force. These findings suggest that inhibition of inflammation alone may not be sufficient to improve the muscle disease phenotype in dysferlin-deficient mice and may require combination therapies that target membrane stability to achieve a functional improvement in skeletal muscle.

sdf1 Expression reveals a source of perivascular-derived mesenchymal stem cells in zebrafish

There is accumulating evidence that mesenchymal stem cells (MSCs) have their origin as perivascular cells (PVCs) in vivo, but precisely identifying them has been a challenge, as they have no single definitive marker and are rare. We have developed a fluorescent transgenic vertebrate model in which PVC can be visualized in vivo based upon sdf1 expression in the zebrafish. Prospective isolation and culture of sdf1(DsRed) PVC demonstrated properties consistent with MSC including prototypical cell surface marker expression; mesodermal differentiation into adipogenic, osteogenic, and chondrogenic lineages; and the ability to support hematopoietic cells. Global proteomic studies performed by two-dimensional liquid chromatography and tandem mass spectrometry revealed a high degree of similarity to human MSC (hMSC) and discovery of novel markers (CD99, CD151, and MYOF) that were previously unknown to be expressed by hMSC. Dynamic in vivo imaging during fin regeneration showed that PVC may arise from undifferentiated mesenchyme providing evidence of a PVC-MSC relationship. This is the first model, established in zebrafish, in which MSC can be visualized in vivo and will allow us to better understand their function in a native environment.

Dysferlin rescue by spliceosome-mediated pre-mRNA trans-splicing targeting introns harbouring weakly defined 3' splice sites

The modification of the pre-mRNA cis-splicing process employing a pre-mRNA trans-splicing molecule (PTM) is an attractive strategy for the in situ correction of genes whose careful transcription regulation and full-length expression is determinative for protein function, as it is the case for the dysferlin (DYSF, Dysf) gene. Loss-of-function mutations of DYSF result in different types of muscular dystrophy mainly manifesting as limb girdle muscular dystrophy 2B (LGMD2B) and Miyoshi muscular dystrophy 1 (MMD1). We established a 3' replacement strategy for mutated DYSF pre-mRNAs induced by spliceosome-mediated pre-mRNA trans-splicing (SmaRT) by the use of a PTM. In contrast to previously established SmaRT strategies, we particularly focused on the identification of a suitable pre-mRNA target intron other than the optimization of the PTM design. By targeting DYSF pre-mRNA introns harbouring differentially defined 3' splice sites (3' SS), we found that target introns encoding weakly defined 3' SSs were trans-spliced successfully in vitro in human LGMD2B myoblasts as well as in vivo in skeletal muscle of wild-type and Dysf(-/-) mice. For the first time, we demonstrate rescue of Dysf protein by SmaRT in vivo. Moreover, we identified concordant qualities among the successfully targeted Dysf introns and targeted endogenous introns in previously reported SmaRT approaches that might facilitate a selective choice of target introns in future SmaRT strategies.

Targeted next-generation sequencing for the genetic diagnosis of dysferlinopathy

Dysferlinopathy comprises a group of autosomal recessive muscular dystrophies caused by mutations in the DYSF gene. Due to the large size of the gene and its lack of mutational hot spots, analysis of the DYSF gene is time-consuming and laborious using conventional sequencing methods. By next-generation sequencing (NGS), DYSF gene analysis has previously been validated through its incorporation in multi-gene panels or exome analyses. However, individual validation of NGS approaches for DYSF gene has not been performed. Here, we established and validated a hybridization capture-based target-enrichment followed by next-generation sequencing to detect mutations in patients with dysferlinopathy. With this approach, mean depth of coverage was approximately 450 fold and almost all (99.3%) of the targeted region had sequence coverage greater than 20 fold. When this approach was tested on samples from patients with known DYSF mutations, all known mutations were correctly retrieved. Using this method on 32 consecutive patient samples with dysferlinopathy, at least two pathogenic variants were detected in 28 (87.5%) samples and at least one pathogenic variant was identified in all samples. Our results suggested that the NGS-based screening method could facilitate efficient and accurate genetic diagnosis of dysferlinopathy.

DNA methylation dynamics in muscle development and disease

DNA methylation is an essential epigenetic modification for mammalian development and is crucial for the establishment and maintenance of cellular identity. Traditionally, DNA methylation has been considered as a permanent repressive epigenetic mark. However, the application of genome-wide approaches has allowed the analysis of DNA methylation in different genomic contexts revealing a more dynamic regulation than originally thought, since active DNA methylation and demethylation occur during cellular differentiation and tissue specification. Satellite cells are the primary stem cells in adult skeletal muscle and are responsible for postnatal muscle growth, hypertrophy, and muscle regeneration. This review outlines the published data regarding DNA methylation changes along the skeletal muscle program, in both physiological and pathological conditions, to better understand the epigenetic mechanisms that control myogenesis.

The limb-girdle muscular dystrophies

A collection of more than 30 genetic muscle diseases that share certain key features, limb-girdle muscular dystrophies are characterized by progressive weakness and muscle atrophy of the hips, shoulders, and proximal extremity muscles with postnatal onset. This article discusses clinical, laboratory, and histologic features of the 6 most prevalent limb-girdle dystrophies. In this large group of disorders, certain distinctive features often can guide clinicians to a correct diagnosis.

Review: Annexin-A5 and cell membrane repair

Annexins are soluble proteins that bind to biological membranes containing negatively charged phospholipids, principally phosphatidylserine, in a Ca(2+)-dependent manner. Annexin-A5 (AnxA5), the smallest member of the annexin family, presents unique properties of membrane binding and self-assembly into ordered two-dimensional (2D) arrays on membrane surfaces. We have previously reported that AnxA5 plays a central role in the machinery of membrane repair by enabling rapid resealing of plasma membrane disruption in murine perivascular cells. AnxA5 promotes membrane repair via the formation of a protective 2D bandage at membrane damaged site. Here, we review current knowledge on cell membrane repair and present recent findings on the role of AnxA5 in membrane resealing of human trophoblasts.

AAV.Dysferlin Overlap Vectors Restore Function in Dysferlinopathy Animal Models

OBJECTIVE

Dysferlinopathies are a family of untreatable muscle disorders caused by mutations in the dysferlin gene. Lack of dysferlin protein results in progressive dystrophy with chronic muscle fiber loss, inflammation, fat replacement, and fibrosis; leading to deteriorating muscle weakness. The objective of this work is to demonstrate efficient and safe restoration of dysferlin expression following gene therapy treatment.

METHODS

Traditional gene therapy is restricted by the packaging capacity limit of adeno-associated virus (AAV), however, use of a dual vector strategy allows for delivery of over-sized genes, including dysferlin. The two vector system (AAV.DYSF.DV) packages the dysferlin cDNA utilizing AAV serotype rh.74 through the use of two discrete vectors defined by a 1 kb region of homology. Delivery of AAV.DYSF.DV via intramuscular and vascular delivery routes in dysferlin deficient mice and nonhuman primates was compared for efficiency and safety.

RESULTS

Treated muscles were tested for dysferlin expression, overall muscle histology, and ability to repair following injury. High levels of dysferlin overexpression was shown for all muscle groups treated as well as restoration of functional outcome measures (membrane repair ability and diaphragm specific force) to wild-type levels. In primates, strong dysferlin expression was demonstrated with no safety concerns.

INTERPRETATION

Treated muscles showed high levels of dysferlin expression with functional restoration with no evidence of toxicity or immune response providing proof of principle for translation to dysferlinopathy patients.

Annexin-A5 promotes membrane resealing in human trophoblasts

Annexin-A5 (AnxA5) is the smallest member of the annexins, a group of soluble proteins that bind to membranes containing negatively-charged phospholipids, principally phosphatidylserine, in a Ca(2+)-dependent manner. AnxA5 presents unique properties of binding and self-assembling on membrane surfaces, forming highly ordered two-dimensional (2D) arrays. We showed previously that AnxA5 plays a central role in the machinery of cell membrane repair of murine perivascular cells, promoting the resealing of membrane damages via the formation of 2D protein arrays at membrane disrupted sites and preventing the extension of membrane ruptures. As the placenta is one of the richest source of AnxA5 in humans, we investigated whether AnxA5 was involved in membrane repair in this organ. We addressed this question at the level of human trophoblasts, either mononucleated cytotrophoblasts or multinucleated syncytiotrophoblasts, in choriocarcinoma cells and primary trophoblasts. Using established procedure of laser irradiation and fluorescence microscopy, we observed that both human cytotrophoblasts and syncytiotrophoblasts repair efficiently a μm²-size disruption. Compared to wild-type cells, AnxA5-deficient trophoblasts exhibit severe defect of membrane repair. Through specifically binding to the disrupted site as early as a few seconds after membrane wounding, AnxA5 promotes membrane resealing of injured human trophoblasts. In addition, we observed that a large membrane area containing the disrupted site was released in the extracellular milieu. We propose mechanisms ensuring membrane resealing and subsequent lesion removal in human trophoblasts. This article is part of a Special Issue entitled: 13th European Symposium on Calcium.

Skeletal myogenesis in the zebrafish and its implications for muscle disease modelling

Current evidence indicates that post-embryonic muscle growth and regeneration in amniotes is mediated almost entirely by stem cells derived from muscle progenitor cells (MPCs), known as satellite cells. Exhaustion and impairment of satellite cell activity is involved in the severe muscle loss associated with degenerative muscle diseases such as Muscular Dystrophies and is the main cause of age-associated muscle wasting. Understanding the molecular and cellular basis of satellite cell function in muscle generation and regeneration (myogenesis) is critical to the broader goal of developing treatments that may ameliorate such conditions. Considerable knowledge exists regarding the embryonic stages of amniote myogenesis. Much less is known about how post-embryonic amniote myogenesis proceeds, how adult myogenesis relates to embryonic myogenesis on a cellular or genetic level. Of the studies focusing on post-embryonic amniote myogenesis, most are post-mortem and in vitro analyses, precluding the understanding of cellular behaviours and genetic mechanisms in an undisturbed in vivo setting. Zebrafish are optically clear throughout much of their post-embryonic development, facilitating their use in live imaging of cellular processes. Zebrafish also possess a compartment of MPCs, which appear similar to satellite cells and persist throughout the post-embryonic development of the fish, permitting their use in examining the contribution of these cells to muscle tissue growth and regeneration.

Membrane Injury and Repair in the Muscular Dystrophies

Muscle cells have an elaborate plasma membrane and t-tubule system that has been evolutionarily refined to maximize electrical conductivity for synchronous muscle contraction. However, this elaborate plasma membrane network has intrinsic vulnerabilities to stretch-induced membrane injury, and thus requires ongoing maintenance and repair. Herein we discuss the types of membrane injuries encountered by myofibers in healthy muscle and in muscular dystrophy. We review the different mechanisms by which muscle fibers in patients with muscular dystrophy are rendered more susceptible to injury, and we summarize the latest developments in our understanding of how the muscular dystrophy protein dysferlin mediates satellite-cell independent membrane repair.

Gene therapy for muscular dystrophy: moving the field forward

Gene therapy for the muscular dystrophies has evolved as a promising treatment for this progressive group of disorders. Although corticosteroids and/or supportive treatments remain the standard of care for Duchenne muscular dystrophy, loss of ambulation, respiratory failure, and compromised cardiac function is the inevitable outcome. Recent developments in genetically mediated therapies have allowed for personalized treatments that strategically target individual muscular dystrophy subtypes based on disease pathomechanism and phenotype. In this review, we highlight the therapeutic progress with emphasis on evolving preclinical data and our own experience in completed clinical trials and others currently underway. We also discuss the lessons we have learned along the way and the strategies developed to overcome limitations and obstacles in this field.

A novel dysferlin mutant pseudoexon bypassed with antisense oligonucleotides

Objective

Mutations in dysferlin (DYSF), a Ca²⁺-sensitive ferlin family protein important for membrane repair, vesicle trafficking, and T-tubule function, cause Miyoshi myopathy, limb-girdle muscular dystrophy type 2B, and distal myopathy. More than 330 pathogenic DYSF mutations have been identified within exons or near exon–intron junctions. In ~17% of patients who lack normal DYSF, only a single disease-causing mutation has been identified. We studied one family with one known mutant allele to identify both the second underlying genetic defect and potential therapeutic approaches.

Methods

We sequenced the full DYSF cDNA and investigated antisense oligonucleotides (AONs) as a tool to modify splicing of the mRNA transcripts in order to process out mutant sequences.

Results

We identified a novel pseudoexon between exons 44 and 45, (pseudoexon 44.1, PE44.1), which inserts an additional 177 nucleotides into the mRNA and 59 amino acids within the conserved C2F domain of the DYSF protein. Two unrelated dysferlinopathy patients were also found to carry this mutation. Using AONs targeting PE44.1, we blocked the abnormal splicing event, yielding normal, full-length DYSF mRNA, and increased DYSF protein expression.

Interpretation

This is the first report of a deep intronic mutation in DYSF that alters mRNA splicing to include a mutant peptide fragment within a key DYSF domain. We report that AON-mediated exon-skipping restores production of normal, full-length DYSF in patients’ cells in vitro, offering hope that this approach will be therapeutic in this genetic context, and providing a foundation for AON therapeutics targeting other pathogenic DYSF alleles.

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.

Limb-girdle muscular dystrophy subtypes: First-reported cohort from northeastern China

The relative frequencies of different subtypes of limb-girdle muscular dystrophies vary widely among different populations. We estimated the percentage of limb-girdle muscular dystrophy subtypes in Chinese people based on 68 patients with limb-girdle muscular dystrophy from the Myology Clinic, Neurology Department, First Hospital of Jilin University, China. A diagnosis of calpainopathy was made in 12 cases (17%), and dysferlin deficiency in 10 cases (15%). Two biopsies revealed α-sarcoglycan deficiency (3%), and two others revealed a lack of caveolin-3 (3%). A diagnosis of unclassified limb-girdle muscular dystrophy was made in the remaining patients (62%). The appearances of calpain 3- and dysferlin-deficient biopsies were similar, though rimmed vacuoles were unique to dysferlinopathy, while inflammatory infiltrates were present in both these limb-girdle muscular dystrophy type 2D biopsies. Macrophages were detected in seven dysferlinopathy biopsies. The results of this study suggest that the distribution of limb-girdle muscular dystrophy subtypes in the Han Chinese population is similar to that reported in the West. The less necrotic, regenerating and inflammatory appearance of limb-girdle muscular dystrophy type 2A, but with more lobulated fibers, supports the idea that calpainopathy is a less active, but more chronic disease than dysferlinopathy. Unusual features indicated an extended limb-girdle muscular dystrophy disease spectrum. The use of acid phosphatase stain should be considered in suspected dysferlinopathies. To the best of our knowledge, this is the first report to define the relative proportions of the various forms of limb-girdle muscular dystrophy in China, based on protein testing.

Calpain cleavage within dysferlin exon 40a releases a synaptotagmin-like module for membrane repair

The muscular dystrophy protein dysferlin plays a key role in the calcium-activated vesicle fusion of membrane repair. This study establishes calpains as upstream regulators of dysferlin in the membrane repair cascade and further demonstrates that similar C-terminal modules are enzymatically released from other ferlin family members.

Dysferlin and calpain are important mediators of the emergency response to repair plasma membrane injury. Our previous research revealed that membrane injury induces cleavage of dysferlin to release a synaptotagmin-like C-terminal module we termed mini-dysferlin_C72. Here we show that injury-activated cleavage of dysferlin is mediated by the ubiquitous calpains via a cleavage motif encoded by alternately spliced exon 40a. An exon 40a–specific antibody recognizing cleaved mini-dysferlin_C72 intensely labels the circumference of injury sites, supporting a key role for dysferlin_Exon40a isoforms in membrane repair and consistent with our evidence suggesting that the calpain-cleaved C-terminal module is the form specifically recruited to injury sites. Calpain cleavage of dysferlin is a ubiquitous response to membrane injury in multiple cell lineages and occurs independently of the membrane repair protein MG53. Our study links calpain and dysferlin in the calcium-activated vesicle fusion of membrane repair, placing calpains as upstream mediators of a membrane repair cascade that elicits cleaved dysferlin as an effector. Of importance, we reveal that myoferlin and otoferlin are also cleaved enzymatically to release similar C-terminal modules, bearing two C2 domains and a transmembrane domain. Evolutionary preservation of this feature highlights its functional importance and suggests that this highly conserved C-terminal region of ferlins represents a functionally specialized vesicle fusion module.

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.

Improved immunoblotting methods provide critical insights into phenotypic differences between two murine dysferlinopathy models

INTRODUCTION

We adopted a proteomics-based approach to gain insights into phenotypic differences between A/J and B10.SJL murine dysferlinopathy models.

METHODS

We optimized immunoblotting of dysferlin by preparing homogenates of the tibialis anterior (TA) muscle under several different conditions. We compared TA muscles of control, A/J, and B10.SJL mice for levels of dysferlin; dysferlin's partners MG53, annexin-A2, and caveolin-3; and the endoplasmic reticulum (ER) stress marker CHOP. We performed immunoelectron microscopy on control rat TA muscle to determine the precise location of dysferlin.

RESULTS

RIPA (radioimmunoprecipitation assay) buffer and sonication improves immunoblotting of dysferlin. The ER stress marker CHOP is elevated in A/J muscle. Dysferlin is localized mostly to membranes close to the Z-disk that have been reported to be part of the Golgi, ER, and sarcoplasmic reticulum (SR) networks.

CONCLUSIONS

ER stress might underlie phenotypic differences between A/J and B10.SJL mice and play a role in human dysferlinopathies.

Dysferlin regulates cell membrane repair by facilitating injury-triggered acid sphingomyelinase secretion

Dysferlin deficiency compromises the repair of injured muscle, but the underlying cellular mechanism remains elusive. To study this phenomenon, we have developed mouse and human myoblast models for dysferlinopathy. These dysferlinopathic myoblasts undergo normal differentiation but have a deficit in their ability to repair focal injury to their cell membrane. Imaging cells undergoing repair showed that dysferlin-deficit decreased the number of lysosomes present at the cell membrane, resulting in a delay and reduction in injury-triggered lysosomal exocytosis. We find repair of injured cells does not involve formation of intracellular membrane patch through lysosome-lysosome fusion; instead, individual lysosomes fuse with the injured cell membrane, releasing acid sphingomyelinase (ASM). ASM secretion was reduced in injured dysferlinopathic cells, and acute treatment with sphingomyelinase restored the repair ability of dysferlinopathic myoblasts and myofibers. Our results provide the mechanism for dysferlin-mediated repair of skeletal muscle sarcolemma and identify ASM as a potential therapy for dysferlinopathy.

Diagnostic overview of blood-based dysferlin protein assay for dysferlinopathies

INTRODUCTION

Dysferlin deficiency causes dysferlinopathies. Among peripheral blood mononuclear cells (PBMCs), the dysferlin protein is expressed specifically in CD14(+) monocytes.

METHODS

We quantified dysferlin protein levels in PBMC lysates of 77 individuals suspected clinically of having a dysferlinopathy to screen for true positives. Subsequent molecular confirmation was done by Sanger sequencing and comparative genomic hybridization arrays to establish diagnosis.

RESULTS

Of the 44 individuals who had significantly reduced dysferlin levels (≤10%), 41 underwent molecular testing. We identified at least 1 mutation in 85% (35 of 41), and 2 mutations, establishing a dysferlinopathy diagnosis, in 61% (25 of 41) of these individuals. Among those with dysferlin protein levels of >10% (33 of 77), only 1 individual (of 14 who underwent molecular testing) had a detectable mutation.

CONCLUSIONS

Our results suggest that dysferlin protein levels of ≤10% in PBMCs, are highly indicative of primary dysferlinopathies. However, this assay may not distinguish carriers from those with secondary dysferlin reduction.

Duplication in the microtubule-actin cross-linking factor 1 gene causes a novel neuromuscular condition

Spectrins and plakins are important communicators linking cytoskeletal components to each other and to cellular junctions. Microtubule-actin cross-linking factor 1 (MACF1) belongs to the spectraplakin family and is involved in control of microtubule dynamics. Complete knock out of MACF1 in mice is associated with developmental retardation and embryonic lethality. Here we present a family with a novel neuromuscular condition. Genetic analyses show a heterozygous duplication resulting in reduced MACF1 gene product. The functional consequence is affected motility observed as periodic hypotonia, lax muscles and diminished motor skills, with heterogeneous presentation among the affected family members. To corroborate these findings we used RNA interference to knock down the VAB-10 locus containing the MACF1 homologue in C. elegans, and we could show that this also causes movement disturbances. These findings suggest that changes in the MACF1 gene is implicated in this neuromuscular condition, which is an important observation since MACF1 has not previously been associated with any human disease and thus presents a key to understanding the essential nature of this gene.

Rapid actin-cytoskeleton-dependent recruitment of plasma membrane-derived dysferlin at wounds is critical for muscle membrane repair

Deficits in membrane repair may contribute to disease progression in dysferlin-deficient muscular dystrophy. Dysferlin, a type-II transmembrane phospholipid-binding protein, is hypothesized to regulate fusion of repair vesicles with the sarcolemma to facilitate membrane repair, but the dysferlin-containing compartments involved in membrane repair and the mechanism by which these compartments contribute to resealing are unclear. A dysferlin-pHluorin [dysf-pH-sensitive green fluorescent protein (pHGFP)] muscle-specific transgenic mouse was developed to examine the dynamic behavior and subcellular localization of dysferlin during membrane repair in adult skeletal muscle fibers. Live-cell confocal microscopy of uninjured adult dysf-pHGFP muscle fibers revealed that dysferlin is highly enriched in the sarcolemma and transverse tubules. Laser-wounding induced rapid recruitment of ∼30 μm of local dysferlin-containing sarcolemma, leading to formation of stable dysferlin accumulations surrounding lesions, endocytosis of dysferlin, and formation of large cytoplasmic vesicles from distal regions of the fiber. Disruption of the actin cytoskeleton decreased recruitment of sarcolemma-derived dysferlin to lesions in dysf-pHGFP fibers without affecting endocytosis and impaired membrane resealing in wild-type fibers, similar to findings in dysferlin deficiency (a 2-fold increase in FM1-43 uptake). Our data support a new mechanism whereby recruitment of sarcolemma-derived dysferlin creates an active zone of high lipid-binding activity at wounds to interact with repair vesicles and facilitate membrane resealing in skeletal muscle.

Adaptive plasticity in the mouse mandible

Background

Plasticity, i.e. non-heritable morphological variation, enables organisms to modify the shape of their skeletal tissues in response to varying environmental stimuli. Plastic variation may also allow individuals to survive in the face of new environmental conditions, enabling the evolution of heritable adaptive traits. However, it is uncertain whether such a plastic response of morphology constitutes an evolutionary adaption itself. Here we investigate whether shape differences due to plastic bone remodelling have functionally advantageous biomechanical consequences in mouse mandibles. Shape characteristics of mandibles from two groups of inbred laboratory mice fed either rodent pellets or ground pellets mixed with jelly were assessed using geometric morphometrics and mechanical advantage measurements of jaw adductor musculature.

Results

Mandibles raised on diets with differing food consistency showed significant differences in shape, which in turn altered their biomechanical profile. Mice raised on a soft food diet show a reduction in mechanical advantage relative to mice of the same inbred strain raised on a typical hard food diet. Further, the soft food eaters showed lower levels of integration between jaw regions, particularly between the molar and angular region relative to hard food eaters.

Conclusions

Bone remodelling in mouse mandibles allows for significant shifts in biomechanical ability. Food consistency significantly influences this process in an adaptive direction, as mice raised on hard food develop jaws better suited to handle hard foods. This remodelling also affects the organisation of the mandible, as mice raised on soft food appear to be released from developmental constraints showing less overall integration than those raised on hard foods, but with a shift of integration towards the most solicited regions of the mandible facing such a food, namely the incisors. Our results illustrate how environmentally driven plasticity can lead to adaptive functional changes that increase biomechanical efficiency of food processing in the face of an increased solicitation. In contrast, decreased demand in terms of food processing seems to release developmental interactions between jaw parts involved in mastication, and may generate new patterns of co-variation, possibly opening new directions to subsequent selection. Overall, our results emphasize that mandible shape and integration evolved as parts of a complex system including mechanical loading food resource utilization and possibly foraging behaviour.

Fam65b is important for formation of the HDAC6-dysferlin protein complex during myogenic cell differentiation

Previously, we identified family with sequence similarity 65, member B (Fam65b), as a protein transiently up-regulated during differentiation and fusion of human myogenic cells. Silencing of Fam65b expression results in severe reduction of myogenin expression and consequent lack of myoblast fusion. The molecular function of Fam65b and whether misregulation of its expression could be causative of muscle diseases are unknown. Protein pulldowns were used to identify Fam65b-interacting proteins in differentiating human muscle cells and regenerating muscle tissue. In vitro, human muscle cells were treated with histone-deacetylase (HDAC) inhibitors, and expression of Fam65b and interacting proteins was studied. Nontreated cells were used as controls. In vivo, expression of Fam65b was down-regulated in developing zebrafish to determine the effects on muscle development. Fam65b binds to HDAC6 and dysferlin, the protein mutated in limb girdle muscular dystrophy 2B. The tricomplex Fam65b-HDAC6-dysferlin is transient, and Fam65b expression is necessary for the complex to form. Treatment of myogenic cells with pan-HDAC or HDAC6-specific inhibitors alters Fam65b expression, while dysferlin expression does not change. Inhibition of Fam65b expression in developing zebrafish results in abnormal muscle, with low birefringence, tears at the myosepta, and increased embryo lethality. Fam65b is an essential component of the HDAC6-dysferlin complex. Down-regulation of Fam65b in developing muscle causes changes consistent with muscle disease.-Balasubramanian, A., Kawahara, G., Gupta, V. A., Rozkalne, A., Beauvais, A., Kunkel, L. M., Gussoni, E. Fam65b is important for formation of the HDAC6-dysferlin protein complex during myogenic cell differentiation.

Limb-girdle muscular dystrophies: where next after six decades from the first proposal (Review)

Limb-girdle muscular dystrophies (LGMD) are a heterogeneous group of disorders, which has led to certain investigators disputing its rationality. The mutual feature of LGMD is limb-girdle affection. Magnetic resonance imaging (MRI), perioral skin biopsies, blood-based assays, reverse-protein arrays, proteomic analyses, gene chips and next generation sequencing are the leading diagnostic techniques for LGMD and gene, cell and pharmaceutical treatments are the mainstay therapies for these genetic disorders. Recently, more highlights have been shed on disease biomarkers to follow up disease progression and to monitor therapeutic responsiveness in future trials. In this study, we review LGMD from a variety of aspects, paying specific attention to newly evolving research, with the purpose of bringing this information into the clinical setting to aid the development of novel therapeutic strategies for this hereditary disease. In conclusion, substantial progress in our ability to diagnose and treat LGMD has been made in recent decades, however enhancing our understanding of the detailed pathophysiology of LGMD may enhance our ability to improve disease outcome in subsequent years.

Cis-splicing and translation of the pre-trans-splicing molecule combine with efficiency in spliceosome-mediated RNA trans-splicing

Muscular dystrophies are a group of genetically distinct diseases for which no treatment exists. While gene transfer approach is being tested for several of these diseases, such strategies can be hampered when the size of the corresponding complementary DNA (cDNA) exceeds the packaging capacity of adeno-associated virus vectors. This issue concerns, in particular, dysferlinopathies and titinopathies that are due to mutations in the dysferlin (DYSF) and titin (TTN) genes. We investigated the efficacy of RNA trans-splicing as a mode of RNA therapy for these two types of diseases. Results obtained with RNA trans-splicing molecules designed to target the 3' end of mouse titin and human dysferlin pre-mRNA transcripts indicated that trans-splicing of pre-mRNA generated from minigene constructs or from the endogenous genes was achieved. Collectively, these results provide the first demonstration of DYSF and TTN trans-splicing reprogramming in vitro and in vivo. However, in addition to these positive results, we uncovered a possible issue of the technique in the form of undesirable translation of RNA pre-trans-splicing molecules, directly from open reading frames present on the molecule or associated with internal alternative cis-splicing. These events may hamper the efficiency of the trans-splicing process and/or lead to toxicity.

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.

Achilles tendon lengthening for equinus foot with Miyoshi myopathy: a case report

A 17-year-old male presented with reduced muscle strength in both lower limbs and demonstrated equinus foot (ankle equinus) in the right lower limb. Using dysferlin immunostaining, the patient was diagnosed with Miyoshi myopathy by the neurologist. Achilles tendon lengthening was performed, and a plantigrade foot without ankle equinus was achieved.

Crystal structures of the human Dysferlin inner DysF domain

BACKGROUND

Mutations in dysferlin, the first protein linked with the cell membrane repair mechanism, causes a group of muscular dystrophies called dysferlinopathies. Dysferlin is a type two-anchored membrane protein, with a single C terminal trans-membrane helix, and most of the protein lying in cytoplasm. Dysferlin contains several C2 domains and two DysF domains which are nested one inside the other. Many pathogenic point mutations fall in the DysF domain region.

RESULTS

We describe the crystal structure of the human dysferlin inner DysF domain with a resolution of 1.9 Ångstroms. Most of the pathogenic mutations are part of aromatic/arginine stacks that hold the domain in a folded conformation. The high resolution of the structure show that these interactions are a mixture of parallel ring/guanadinium stacking, perpendicular H bond stacking and aliphatic chain packing.

CONCLUSIONS

The high resolution structure of the Dysferlin DysF domain gives a template on which to interpret in detail the pathogenic mutations that lead to disease.

Dysferlin and other non-red cell proteins accumulate in the red cell membrane of Diamond-Blackfan Anemia patients

Diamond Blackfan Anemia (DBA) is a congenital anemia usually caused by diverse mutations in ribosomal proteins. Although the genetics of DBA are well characterized, the mechanisms that lead to macrocytic anemia remain unclear. We systematically analyzed the proteomes of red blood cell membranes from multiple DBA patients to determine whether abnormalities in protein translation or erythropoiesis contribute to the observed macrocytosis or alterations in the mature red blood cell membrane. In depth proteome analysis of red cell membranes enabled highly reproducible identification and quantitative comparisons of 1100 or more proteins. These comparisons revealed clear differences between red cell membrane proteomes in DBA patients and healthy controls that were consistent across DBA patients with different ribosomal gene mutations. Proteins exhibiting changes in abundance included those known to be increased in DBA such as fetal hemoglobin and a number of proteins not normally found in mature red cell membranes, including proteins involved in the major histocompatibility complex class I pathway. Most striking was the presence of dysferlin in the red blood cell membranes of DBA patients but absent in healthy controls. Immunoblot validation using red cell membranes isolated from additional DBA patients and healthy controls confirmed a distinct membrane protein signature specific to patients with DBA.

Mechanisms of muscle injury, repair, and regeneration

Skeletal muscle continuously adapts to changes in its mechanical environment through modifications in gene expression and protein stability that affect its physiological function and mass. However, mechanical stresses commonly exceed the parameters that induce adaptations, producing instead acute injury. Furthermore, the relatively superficial location of many muscles in the body leaves them further vulnerable to acute injuries by exposure to extreme temperatures, contusions, lacerations or toxins. In this article, the molecular, cellular, and mechanical factors that underlie muscle injury and the capacity of muscle to repair and regenerate are presented. Evidence shows that muscle injuries that are caused by eccentric contractions result from direct mechanical damage to myofibrils. However, muscle pathology following other acute injuries is largely attributable to damage to the muscle cell membrane. Many feaures in the injury-repair-regeneration cascade relate to the unregulated influx of calcium through membrane lesions, including: (i) activation of proteases and hydrolases that contribute muscle damage, (ii) activation of enzymes that drive the production of mitogens and motogens for muscle and immune cells involved in injury and repair, and (iii) enabling protein-protein interactions that promote membrane repair. Evidence is also presented to show that the myogenic program that is activated by acute muscle injury and the inflammatory process that follows are highly coordinated, with myeloid cells playing a central role in modulating repair and regeneration. The early-invading, proinflammatory M1 macrophages remove debris caused by injury and express Th1 cytokines that play key roles in regulating the proliferation, migration, and differentiation of satellite cells. The subsequent invasion by anti-inflammatory, M2 macrophages promotes tissue repair and attenuates inflammation. Although this system provides an effective mechanism for muscle repair and regeneration following acute injury, it is dysregulated in chronic injuries. In this article, the process of muscle injury, repair and regeneration that occurs in muscular dystrophy is used as an example of chronic muscle injury, to highlight similarities and differences between the injury and repair processes that occur in acutely and chronically injured muscle.

Dysferlin is essential for endocytosis in the sea star oocyte

Dysferlin is a calcium-binding transmembrane protein involved in membrane fusion and membrane repair. In humans, mutations in the dysferlin gene are associated with muscular dystrophy. In this study, we isolated plasma membrane-enriched fractions from full-grown immature oocytes of the sea star, and identified dysferlin by mass spectrometry analysis. The full-length dysferlin sequence is highly conserved between human and the sea star. We learned that in the sea star Patiria miniata, dysferlin RNA and protein are expressed from oogenesis to gastrulation. Interestingly, the protein is highly enriched in the plasma membrane of oocytes. Injection of a morpholino against dysferlin leads to a decrease of endocytosis in oocytes, and to a developmental arrest during gastrulation. These results suggest that dysferlin is critical for normal endocytosis during oogenesis and for embryogenesis in the sea star and that this animal may be a useful model for studying the relationship of dysferlin structure as it relates to its function.

Trophoblast cell fusion and differentiation are mediated by both the protein kinase C and a pathways

The syncytiotrophoblast of the human placenta is an epithelial barrier that interacts with maternal blood and is a key for the transfer of nutrients and other solutes to the developing fetus. The syncytiotrophoblast is a true syncytium and fusion of progenitor cytotrophoblasts is the cardinal event leading to the formation of this layer. BeWo cells are often used as a surrogate for cytotrophoblasts, since they can be induced to fuse, and then express certain differentiation markers associated with trophoblast syncytialization. Dysferlin, a syncytiotrophoblast membrane repair protein, is up-regulated in BeWo cells induced to fuse by treatment with forskolin; this fusion is thought to occur through cAMP/protein kinase A-dependent mechanisms. We hypothesized that dysferlin may also be up-regulated in response to fusion through other pathways. Here, we show that BeWo cells can also be induced to fuse by treatment with an activator of protein kinase C, and that this fusion is accompanied by increased expression of dysferlin. Moreover, a dramatic synergistic increase in dysferlin expression is observed when both the protein kinase A and protein kinase C pathways are activated in BeWo cells. This synergy in fusion is also accompanied by dramatic increases in mRNA for the placental fusion proteins syncytin 1, syncytin 2, as well as dysferlin. Dysferlin, however, was shown to be dispensable for stimulus-induced BeWo cell syncytialization, since dysferlin knockdown lines fused to the same extent as control cells. The classical trophoblast differentiation marker human chorionic gonadotropin was also monitored and changes in the expression closely parallel that of dysferlin in all of the experimental conditions employed. Thus different biochemical markers of trophoblast fusion behave in concert supporting the hypothesis that activation of both protein kinase C and A pathways lead to trophoblastic differentiation.

Membrane damage-induced vesicle-vesicle fusion of dysferlin-containing vesicles in muscle cells requires microtubules and kinesin

Mutations in the dysferlin gene resulting in dysferlin-deficiency lead to limb-girdle muscular dystrophy 2B and Myoshi myopathy in humans. Dysferlin has been proposed as a critical regulator of vesicle-mediated membrane resealing in muscle fibers, and localizes to muscle fiber wounds following sarcolemma damage. Studies in fibroblasts and urchin eggs suggest that trafficking and fusion of intracellular vesicles with the plasma membrane during resealing requires the intracellular cytoskeleton. However, the contribution of dysferlin-containing vesicles to resealing in muscle and the role of the cytoskeleton in regulating dysferlin-containing vesicle biology is unclear. Here, we use live-cell imaging to examine the behavior of dysferlin-containing vesicles following cellular wounding in muscle cells and examine the role of microtubules and kinesin in dysferlin-containing vesicle behavior following wounding. Our data indicate that dysferlin-containing vesicles move along microtubules via the kinesin motor KIF5B in muscle cells. Membrane wounding induces dysferlin-containing vesicle-vesicle fusion and the formation of extremely large cytoplasmic vesicles, and this response depends on both microtubules and functional KIF5B. In non-muscle cell types, lysosomes are critical mediators of membrane resealing, and our data indicate that dysferlin-containing vesicles are capable of fusing with lysosomes following wounding which may contribute to formation of large wound sealing vesicles in muscle cells. Overall, our data provide mechanistic evidence that microtubule-based transport of dysferlin-containing vesicles may be critical for resealing, and highlight a critical role for dysferlin-containing vesicle-vesicle and vesicle-organelle fusion in response to wounding in muscle cells.

The effects of MyD88 deficiency on disease phenotype in dysferlin-deficient A/J mice: role of endogenous TLR ligands

An absence of dysferlin leads to activation of innate immune receptors such as Toll-like receptors (TLRs) and skeletal muscle inflammation. Myeloid differentiation primary response gene 88 (MyD88) is a key mediator of TLR-dependent innate immune signalling. We hypothesized that endogenous TLR ligands released from the leaking dysferlin-deficient muscle fibres engage TLRs on muscle and immune cells and contribute to disease progression. To test this hypothesis, we generated and characterized dysferlin and MyD88 double-deficient mice. Double-deficient mice exhibited improved body weight, grip strength, and maximum muscle contractile force at 6-8 months of age when compared to MyD88-sufficient, dysferlin-deficient A/J mice. Double-deficient mice also showed a decrease in total fibre number, which contributed to the observed increase in the number of central nuclei/fibres. These results indicate that there was less regeneration in the double-deficient mice. We next tested the hypothesis that endogenous ligands, such as single-stranded ribonucleic acids (ssRNAs), released from damaged muscle cells bind to TLR-7/8 and perpetuate the disease progression. We found that injection of ssRNA into the skeletal muscle of pre-symptomatic mice (2 months old) resulted in a significant increase in degenerative fibres, inflammation, and regenerating fibres in A/J mice. In contrast, characteristic histological features were significantly decreased in double-deficient mice. These data point to a clear role for the TLR pathway in the pathogenesis of dysferlin deficiency and suggest that TLR-7/8 antagonists may have therapeutic value in this disease.

Dysferlin and myoferlin regulate transverse tubule formation and glycerol sensitivity

Dysferlin is a membrane-associated protein implicated in muscular dystrophy and vesicle movement and function in muscles. The precise role of dysferlin has been debated, partly because of the mild phenotype in dysferlin-null mice (Dysf). We bred Dysf mice to mice lacking myoferlin (MKO) to generate mice lacking both myoferlin and dysferlin (FER). FER animals displayed progressive muscle damage with myofiber necrosis, internalized nuclei, and, at older ages, chronic remodeling and increasing creatine kinase levels. These changes were most prominent in proximal limb and trunk muscles and were more severe than in Dysf mice. Consistently, FER animals had reduced ad libitum activity. Ultrastructural studies uncovered progressive dilation of the sarcoplasmic reticulum and ectopic and misaligned transverse tubules in FER skeletal muscle. FER muscle, and Dysf- and MKO-null muscle, exuded lipid, and serum glycerol levels were elevated in FER and Dysf mice. Glycerol injection into muscle is known to induce myopathy, and glycerol exposure promotes detachment of transverse tubules from the sarcoplasmic reticulum. Dysf, MKO, and FER muscles were highly susceptible to glycerol exposure in vitro, demonstrating a dysfunctional sarcotubule system, and in vivo glycerol exposure induced severe muscular dystrophy, especially in FER muscle. Together, these findings demonstrate the importance of dysferlin and myoferlin for transverse tubule function and in the genesis of muscular dystrophy.

FER-1/Dysferlin promotes cholinergic signaling at the neuromuscular junction in C. elegans and mice

Dysferlin is a member of the evolutionarily conserved ferlin gene family. Mutations in Dysferlin lead to Limb Girdle Muscular Dystrophy 2B (LGMD2B), an inherited, progressive and incurable muscle disorder. However, the molecular mechanisms underlying disease pathogenesis are not fully understood. We found that both loss-of-function mutations and muscle-specific overexpression of C. elegans fer-1, the founding member of the Dysferlin gene family, caused defects in muscle cholinergic signaling. To determine if Dysferlin-dependent regulation of cholinergic signaling is evolutionarily conserved, we examined the in vivo physiological properties of skeletal muscle synaptic signaling in a mouse model of Dysferlin-deficiency. In addition to a loss in muscle strength, Dysferlin −/− mice also exhibited a cholinergic deficit manifested by a progressive, frequency-dependent decrement in their compound muscle action potentials following repetitive nerve stimulation, which was observed in another Dysferlin mouse model but not in a Dysferlin-independent mouse model of muscular dystrophy. Oral administration of Pyridostigmine bromide, a clinically used acetylcholinesterase inhibitor (AchE.I) known to increase synaptic efficacy, reversed the action potential defect and restored in vivo muscle strength to Dysferlin −/− mice without altering muscle pathophysiology. Our data demonstrate a previously unappreciated role for Dysferlin in the regulation of cholinergic signaling and suggest that such regulation may play a significant pathophysiological role in LGMD2B disease.

Full-length dysferlin expression driven by engineered human dystrophic blood derived CD133+ stem cells

The protein dysferlin is abundantly expressed in skeletal and cardiac muscles, where its main function is membrane repair. Mutations in the dysferlin gene are involved in two autosomal recessive muscular dystrophies: Miyoshi myopathy and limb-girdle muscular dystrophy type 2B. Development of effective therapies remains a great challenge. Strategies to repair the dysferlin gene by skipping mutated exons, using antisense oligonucleotides (AONs), may be suitable only for a subset of mutations, while cell and gene therapy can be extended to all mutations. AON-treated blood-derived CD133+ stem cells isolated from patients with Miyoshi myopathy led to partial dysferlin reconstitution in vitro but failed to express dysferlin after intramuscular transplantation into scid/blAJ dysferlin null mice. We thus extended these experiments producing the full-length dysferlin mediated by a lentiviral vector in blood-derived CD133+ stem cells isolated from the same patients. Transplantation of engineered blood-derived CD133+ stem cells into scid/blAJ mice resulted in sufficient dysferlin expression to correct functional deficits in skeletal muscle membrane repair. Our data suggest for the first time that lentivirus-mediated delivery of full-length dysferlin in stem cells isolated from Miyoshi myopathy patients could represent an alternative therapeutic approach for treatment of dysferlinopathies.

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.

Bone marrow transplantation in dysferlin-deficient mice results in a mild functional improvement

Dysferlinopathies are caused by mutations in the DYSF gene. Dysferlin is a protein mainly expressed in the skeletal muscle and monocytes. Cell therapy constitutes a promising tool for the treatment of muscular dystrophies. The aim of our study was to evaluate the effect of bone marrow transplantation (BMT) using the A/J Dysf(prmd) mouse model of dysferlinopathy. For that purpose, we studied dysferlin expression by western blot and/or immunohistochemistry in transplanted mice and controls. Computerized analyses of locomotion and electrophysiological techniques were also performed to test the functional improvement. We observed dysferlin expression in splenocytes, but not in the skeletal muscle of the transplanted mice. However, the locomotion test, electromyography studies, and muscle histology showed an improvement in all transplanted mice that was more significant in the animals transplanted with dysferlin⁺/⁺ cells. In conclusion, although BMT restores dysferlin expression in monocytes, but not in skeletal muscle, muscle function was partially recovered. We propose that the slight improvement observed in the functional studies could be related with factors, such as the hepatocyte growth factor, released after BMT that prevented muscle degeneration.