X-linked Emery-Dreifuss Muscular Dystrophy Research Articles

X-linked Emery-Dreifuss muscular dystrophy is associated with a high risk of malignant ventricular arrhythmia

Abstract Background Emery-Dreifuss muscular dystrophy (EDMD) is caused by variants in EMD (X-linked) and LMNA (autosomal dominant). LMNA variants are known to cause end-stage heart failure (ESHF) and malignant ventricular arrhythmia (MVA) [1], but the risk of cardiac complications in EMD variant-carriers is unknown. Purpose To determine the incidence of MVA and ESHF in EMD variant-carriers. Methods Consecutively referred individuals carrying EMD variants were recruited from 12 cardiomyopathy units in Europe and the USA. The incidence of MVA and ESHF in male and female EMD variant-carriers was determined. Male EMD variant-carriers with a cardiac phenotype at baseline (EMDcardiac) were compared to consecutively recruited male LMNA variant-carriers with a cardiac phenotype (LMNAcardiac). Results Longitudinal follow-up data were available for 38 male and 21 female EMD variant-carriers (mean (SD) ages 33.4 (13.3) and 43.3 (16.8) years, respectively; Table 1). Nine (23.6%) males developed MVA and five (13.2%) developed ESHF during a median follow-up time of 65.0 [24.3, 109.5] months. No female EMD variant-carrier had MVA or ESHF, but nine (42.8%) developed a mild cardiac phenotype at a median [IQR] age of 58.6 [53.2, 60.4] years. Incidence rates for MVA were similar for EMDcardiac and LMNAcardiac (4.8 versus 6.6 per hundred person-years, respectively; log-rank test p = 0.49; Figure 1). Incidence rates for ESHF were 2.4 per hundred person-years for EMDcardiac and 5.9 per hundred person-years for LMNAcardiac (log-rank test p = 0.09; Figure 1). Conclusions Male EMD variant-carriers have a high risk of progressive heart failure and ventricular arrhythmias similar to that of male LMNA variant-carriers. These data suggest that early ICD implantation and heart failure drug therapy should be considered in male EMD variant-carriers with cardiac disease.Table 1Figure 1

Emerin interacts with histone methyltransferases to regulate repressive chromatin at the nuclear periphery.

X-Linked Emery-Dreifuss muscular dystrophy is caused by mutations in the gene encoding emerin. Emerin is an inner nuclear membrane protein important for repressive chromatin organization at the nuclear periphery. Myogenic differentiation is a tightly regulated process characterized by genomic reorganization leading to coordinated temporal expression of key transcription factors, including MyoD, Pax7, and Myf5. Emerin was shown to interact with repressive histone modification machinery, including HDAC3 and EZH2. Using emerin-null myogenic progenitor cells we established several EDMD-causing emerin mutant lines in the effort to understand how the functional interaction of emerin with HDAC3 regulates histone methyltransferase localization or function to organize repressive chromatin at the nuclear periphery. We found that, in addition to its interaction with HDAC3, emerin interacts with the histone methyltransferases EZH2 and G9a in myogenic progenitor cells. Further, we show enhanced binding of emerin HDAC3-binding mutants S54F and Q133H to EZH2 and G9a. Treatment with small molecule inhibitors of EZH2 and G9a reduced H3K9me2 or H3K27me3 throughout differentiation. EZH2 and G9a inhibitors impaired cell cycle withdrawal, differentiation commitment, and myotube formation in wildtype progenitors, while they had no effect on emerin-null progenitors. Interestingly, these inhibitors exacerbated the impaired differentiation of emerin S54F and Q133H mutant progenitors. Collectively, these results suggest the functional interaction between emerin and HDAC3, EZH2, and G9a are important for myogenic differentiation.

Emerin self-assembly and nucleoskeletal coupling regulate nuclear envelope mechanics against stress.

Emerin is an integral nuclear envelope protein that participates in the maintenance of nuclear shape. When mutated or absent, emerin causes X-linked Emery-Dreifuss muscular dystrophy (EDMD). To understand how emerin takes part in molecular --scaffolding at the nuclear envelope and helps protect the nucleus against mechanical stress, we established its nanoscale organization using single-molecule tracking and super-resolution microscopy. We show that emerin monomers form localized oligomeric nanoclusters stabilized by both lamin A/C and the SUN1-containing linker of nucleoskeleton and cytoskeleton (LINC) complex. Interactions of emerin with nuclear actin and BAF (also known as BANF1) additionally modulate its membrane mobility and its ability to oligomerize. In nuclei subjected to mechanical challenges, the mechanotransduction functions of emerin are coupled to changes in its oligomeric state, and the incremental self-assembly of emerin determines nuclear shape adaptation against mechanical forces. We also show that the abnormal nuclear envelope deformations induced by EDMD emerin mutants stem from improper formation of lamin A/C and LINC complex-stabilized emerin oligomers. These findings place emerin at the center of the molecular processes that regulate nuclear shape remodeling in response to mechanical challenges.

Historical aspects of muscle research in the Dubowitz Neuromuscular Centre: the Hammersmith days

Historical aspects of muscle research in the Dubowitz Neuromuscular Centre: the Hammersmith days

Novel FHL1 mutation variant identified in a patient with nonobstructive hypertrophic cardiomyopathy and myopathy \u2013 a case report

BackgroundHypertrophic cardiomyopathy (HCM) is a genetic disorder mostly caused by sarcomeric gene mutations, but almost 10% of cases are attributed to inherited metabolic and neuromuscular disorders. First described in 2008 in an American-Italian family with scapuloperoneal myopathy, FHL1 gene encodes four-and-a-half LIM domains 1 proteins which are involved in sarcomere formation, assembly and biomechanical stress sensing both in cardiac and skeletal muscle, and its mutations are responsible for a large spectrum of neuromuscular disorders (mostly myopathies) and cardiac disease, represented by HCM, either isolated, or in conjunction with neurologic and skeletal muscle impairment. We thereby report a novel mutation variant in FHL1 structure, associated with HCM and type 6 Emery-Dreifuss muscular dystrophy (EDMD).Case presentationWe describe the case of a 40 year old male patient, who was referred to our department for evaluation in the setting of NYHA II heart failure symptoms and was found to have HCM. The elevated muscular enzymes raised the suspicion of a neuromuscular disease. Rigid low spine and wasting of deltoidus, supraspinatus, infraspinatus and calf muscles were described by the neurological examination. Electromyography and muscle biopsy found evidence of chronic myopathy. Diagnosis work-up was completed by next-generation sequencing genetic testing which found a likely pathogenic mutation in the FHL1 gene (c.157-1G > A, hemizygous) involved in the development of X-linked EDMD type 6.ConclusionThis case report highlights the importance of multimodality diagnostic approach in a patient with a neuromuscular disorder and associated hypertrophic cardiomyopathy by identifying a novel mutation variant in FHL1 gene. Raising awareness of non-sarcomeric gene mutations which can lead to HCM is fundamental, because of diagnostic and clinical risk stratification challenges.

Mapping the Emerin Interactome by Apex Proximity Labeling

Emerin is a highly conserved LEM-domain protein expressed mostly at the inner nuclear envelope of mammalian cells. Mutations in the EMD gene encoding for emerin cause X-linked Emery-Dreifuss muscular dystrophy (EDMD). Through its interaction with a variety of nuclear binding partners, emerin has a number of biological functions that include regulation of gene expression, nucleo-cytoskeleton mechanotransduction and maintenance of nuclear shape. The molecular pathogenesis of EDMD remains unclear and mapping the protein interaction network of emerin can potentially help elucidate the molecular mechanisms behind the disease. Here we used a proximity-dependent biotinylation method based on an engineered ascorbate peroxidase (APEX2) to obtain proteomic profiles of emerin interactions at the nuclear envelope and the endoplasmic reticulum in cells. We generated constructs of APEX2 fused to the N- or the C-terminus of emerin to study its interacting partners across the inner nuclear envelope, the outer nuclear envelope and the endoplasmic reticulum membrane. We also optimized proximity biotin labeling in both live and fixed cells, and showed that biotinylation patterns vary significantly between emerin fusions and for cells micropatterned on fibronectin strips of decreasing widths that we use to apply increasing mechanical perturbation to the cell nuclei. These data indicate that emerin explores different microenvironments and interacts with distinct partners as a function of nuclear strain. Using APEX2 quantitative proteomics, we also started to identify key interacting partners of emerin and their subcompartmental localizations for cells subjected to increasing mechanical challenges.

FHL1-related myopathy may not be classified by reducing bodies in muscle biopsy

FHL1-related myopathies, including reducing body myopathy (RBM), X-linked scapulo-axio-peroneal myopathy, rigid spine syndrome, X-linked myopathy with postural muscle atrophy (XMPMA), X-linked Emery–Dreifuss muscular dystrophy and hypertrophic cardiomyopathy, are clinically and pathologically heterogeneous disorders caused by FHL1 gene mutations. According to previous reports, the first three types are myopathies with reducing bodies observed in biopsies, and the last three are myopathies without reducing bodies. We report four FHL1-related myopathy patients, including an XMPMA patient and a RBM family with three patients. Clinical information, muscle biopsies, electromyograms and genetic testing were obtained. Muscle weakness and atrophy, spinal rigidity, and joint contracture were present in the RBM family. The XMPMA patient showed a pseudoathletic appearance with muscle weakness and atrophy, spinal rigidity and deformity. The index patient of the RBM family underwent two muscle biopsies to find reducing bodies. Interestingly, these muscle biopsies revealed reducing bodies and rimmed vacuoles not only in the RBM family but also in the XMPMA patient. Next-generation sequencing identified a reported single missense mutation c.448 C>T (p. C150R) in the RBM family and a novel mutation c.814T>C (p. S272P) in the XMPMA patient. Therefore, FHL1-related myopathies overlap substantially and may not be simply classified into subtypes depending on reducing bodies. Biopsies of additional affected muscles can aid in finding reducing bodies. We report the first XMPMA patient with a novel FHL1 mutation and reducing bodies in a muscle biopsy in China.

An Emerin LEM-Domain Mutation Impairs Cell Response to Mechanical Stress.

Emerin is a nuclear envelope protein that contributes to genome organization and cell mechanics. Through its N-terminal LAP2-emerin-MAN1 (LEM)-domain, emerin interacts with the DNA-binding protein barrier-to-autointegration (BAF). Emerin also binds to members of the linker of the nucleoskeleton and cytoskeleton (LINC) complex. Mutations in the gene encoding emerin are responsible for the majority of cases of X-linked Emery-Dreifuss muscular dystrophy (X-EDMD). Most of these mutations lead to an absence of emerin. A few missense and short deletion mutations in the disordered region of emerin are also associated with X-EDMD. More recently, missense and short deletion mutations P22L, ∆K37 and T43I were discovered in emerin LEM-domain, associated with isolated atrial cardiac defects (ACD). Here we reveal which defects, at both the molecular and cellular levels, are elicited by these LEM-domain mutations. Whereas ΔK37 mutation impaired the correct folding of the LEM-domain, P22L and T43I had no impact on the 3D structure of emerin. Surprisingly, all three mutants bound to BAF, albeit with a weaker affinity in the case of ΔK37. In human myofibroblasts derived from a patient’s fibroblasts, emerin ∆K37 was correctly localized at the inner nuclear membrane, but was present at a significantly lower level, indicating that this mutant is abnormally degraded. Moreover, SUN2 was reduced, and these cells were defective in producing actin stress fibers when grown on a stiff substrate and after cyclic stretches. Altogether, our data suggest that the main effect of mutation ΔK37 is to perturb emerin function within the LINC complex in response to mechanical stress.

FHL1B Interacts with Lamin A/C andEmerin at the Nuclear Lamina andisMisregulated in Emery-Dreifuss Muscular Dystrophy.

Emery-Dreifuss muscular dystrophy (EDMD) is associated with mutations in EMD and LMNA genes, encoding for the nuclear envelope proteins emerin and lamin A/C, indicating that EDMD is anuclear envelope disease. We recently reported mutations in FHL1 gene in X-linked EDMD. FHL1 encodes FHL1A, and the two minor isoforms FHL1B and FHL1C. So far, none have been described at the nuclear envelope. To gain insight into the pathophysiology of EDMD, we focused our attention on the poorly characterized FHL1B isoform. The amount and the localisation of FHL1B were evaluated in control and diseased human primary myoblasts using immunofluorescence and western blotting. We found that in addition to acytoplasmic localization, this isoform strongly accumulated at the nuclear envelope of primary human myoblasts, like but independently of lamin A/C and emerin. During myoblast differentiation, we observed amajor reduction of FHL1B protein expression, especially in the nucleus. Interestingly, we found elevated FHL1B expression level in myoblasts from an FHL1-related EDMD patient where the FHL1 mutation only affects FHL1A, as well as in myoblasts from an LMNA-related EDMD patient. Altogether, the specific localization of FHL1B and its modulation in disease-patient's myoblasts confirmed FHL1-related EDMD as anuclear envelope disease.

FHL1 protein isoforms in Emery-Dreifuss muscular dystrophy

Emery-Dreifuss muscular dystrophy (EDMD) is a hereditary muscular disorder characterized by early joint contractures, progressive muscular wasting and weakness of scapuloperoneal distribution, and at adult age, patients develop cardiac abnormalities with a high risk of sudden death[1]. EDMD encompasses both X-linked and autosomal inheritance due to mutations in the genes encoding the nuclear envelope proteins emerin, lamin A/C[2-4]. First mutations in the Four-and-a-half LIM domain 1 gene (FHL1) being responsible for X-linked EDMD were described by Gueneau et al.[5]. The human FHL1 gene encodes three alternatively spliced isoforms, named FHL1A, FHL1B and FHL1C, with FHL1A being the most abundantly expressed protein isoform in striated muscle. There is still little known about the precise localization and functions of the three different FHL1 isoforms in human skeletal muscle. Here, we describe for the first time the subcellular localization of FHL1A, FHL1B, and FHL1C in vitro in differentiating human primary myoblasts. Localization of FHL1 protein isoforms was studied at the myoblast and myotube stages by confocal microscope analysis. Endogenous FHL1B protein localization was detected by an anti-FHL1B specific antibody, while for FHL1A and FHL1C, as no efficient isoform-specific antibodies were available, an anti-Flag antibody was used to follow Flag-tagged FHL1A and Flag-tagged FHL1C protein expression, after lentiviral transduction of human primary myoblasts. Successful transduction was confirmed by western blotting of whole extracts from myoblasts and myotubes using an anti-Flag antibody. In human myoblasts, Flag-FHL1A and Flag-FHL1C showed both a cytoplasmic and a nuclear distribution, while the nuclear staining was more pronounced in Flag-FHL1C transduced myoblasts. Endogenous FHL1B protein gave a moderate cytoplasmic and a strong nuclear staining. During 6- and 12-days of human myoblast differentiation, localization of all three FHL1 protein isoforms shifted from the nucleus to the cytoplasm. In addition, all FHL1 protein isoforms were observed to co-localize with phalloidin-stained actin fibers. Collectively, these results indicate differentiation-related changes in expression and subcellular localization of the human FHL1 protein isoforms.

Muscular Dystrophy Mutations Impair the Nuclear Envelope Emerin Self-assembly Properties.

More than 100 genetic mutations causing X-linked Emery-Dreifuss muscular dystrophy have been identified in the gene encoding the integral inner nuclear membrane protein emerin. Most mutations are nonsense or frameshift mutations that lead to the absence of emerin in cells. Only very few cases are due to missense or short in-frame deletions. Molecular mechanisms explaining the corresponding emerin variants' loss of function are particularly difficult to identify because of the mostly intrinsically disordered state of the emerin nucleoplasmic region. We now demonstrate that this EmN region can be produced as a disordered monomer, as revealed by nuclear magnetic resonance, but rapidly self-assembles in vitro. Increases in concentration and temperature favor the formation of long curvilinear filaments with diameters of approximately 10 nm, as observed by electron microscopy. Assembly of these filaments can be followed by fluorescence through Thioflavin-T binding and by Fourier-transform Infrared spectrometry through formation of β-structures. Analysis of the assembly properties of five EmN variants reveals that del95-99 and Q133H impact filament assembly capacities. In cells, these variants are located at the nuclear envelope, but the corresponding quantities of emerin-emerin and emerin-lamin proximities are decreased compared to wild-type protein. Furthermore, variant P183H favors EmN aggregation in vitro, and variant P183T provokes emerin accumulation in cytoplasmic foci in cells. Substitution of residue Pro183 might systematically favor oligomerization, leading to emerin aggregation and mislocalization in cells. Our results suggest that emerin self-assembly is necessary for its proper function and that a loss of either the protein itself or its ability to self-assemble causes muscular dystrophy.

Tissue inhibitors of matrix metalloproteinases in serum are cardiac biomarkers in Emery-Dreifuss muscular dystrophy

Tissue inhibitors of matrix metalloproteinases (TIMPs) are known to be involved in cardiovascular diseases. Hitherto, they have not been examined in dilated cardiomyopathy in the course of Emery-Dreifuss muscular dystrophy (EDMD). To define TIMPs in serum because they might help in defining cardiac dysfunction at the early cardiological stages of this disease and detect preclinical stages of cardiomyopathy. Twenty-five EDMD patients connected with lamin A/C (AD-EDMD) or emerin (X-EDMD) deficiency and 20 healthy age-matched controls were examined. The serum levels of the tissue inhibitors TIMP-1, -2, -3 were quantified using the ELISA sandwich immunoassay procedure with appropriate antibodies. Serum levels of TIMP-1 were normal in autosomal AD-EDMD and increased in the majority of X-linked EDMD. The level of TIMP-2 was decreased in 25%/21% of AD-EDMD/X-EDMD cases. TIMP-3 serum level was significantly reduced in all the examined patients. Receiver operating curves indicated that in terms of sensitivity and specificity characteristics the performance of TIMP-3 (less that of TIMP-2) makes them the best markers of cardiac involvement among the examined TIMPs. Evidence shows that the levels of TIMP-3, and in some cases also TIMP-2, are decreased in EDMD. The decrease might be associated with an adverse effect on matrix metalloproteinases and remodelling of the myocardial matrix. The specific decrease of TIMP-3 indicates that this biomarker might help in early detection of cardiac involvement in EDMD. Up-regulation of TIMP-1 in the majority of patients with X-EDMD indicates increased myocardial extracellular matrix turnover, early onset of tissue remodelling, and may contribute to arrhythmia, frequently occurring in this form of the disease.

Update of Emerinopathies’ clinical-genetic spectrum: the French network experience

Emerinopathies include diseases caused by EMD gene mutations localized on chromosome X and encoding emerin, an integral protein of the nuclear envelope. The most frequent emerinopathy is the X-linked EmeryDreifuss muscular dystrophy (X-EDMD) that was first reported in the 60ths by Emery and Dreifuss [1]. The disease is characterized by muscle weakness and wasting usually with a humeroperoneal distribution in the first stages, early joint contractures involving Achilles tendons, elbows, neck and the whole spine, and cardiac involvement featuring conduction defects, arrhythmias, subsequent cardiomyopathy (usually dilated) and frequently responsible of sudden death. Bione et al. [2] identified the first mutations of EMD gene encoding emerin to be responsible of X-EDMD. These mutations usually lead to absence or reduced level of emerin in different tissues of affected males including skeletal muscle, skin, oral mucosa cells and lymphocytes as it is demonstrated by immunocytochemical and histochemical methods [3,4]. Female carriers exhibit mosaic expression patterns with usually normal emerin amounts [3]. These methods may thus be used in the diagnostic strategy of X-EDMD prior to EMD gene analysis. In a recent study (unpublished work from the French network and LBGM) aiming to assess the diagnostic utility of emerin study by western blot on lymphoblastoid cell lines, we looked at EMD mutation rate observed in a cohort of 269 male and female patients with variable emerin amounts. In male patients, absence or severe reduction of emerin (<5%) lead to EMD mutation identification in all cases, while moderate emerin amount reduction revealed EMD mutation in 75% of the patients. Interestingly, in all cases where emerin amounts were considered as normal, no EMD mutations were found. In female cases, all cases with emerin moderate or severe reduction harbored EMD mutation. When emerin is normal, EMD mutation was found in 58% of female cases. These results suggest that a diagnostic rate of 100% may be reached if emerin study by western blot is performed prior to EMD gene screening in male patients. Moreover, emerin gene mutations have been rarely observed in rare cases of isolated cardiac disease [5,6] and limb girdle muscular dystrophies with cardiac disease and without joint contractures [7,8].

Identification of a novel human LAP1 isoform that is regulated by protein phosphorylation.

Lamina associated polypeptide 1 (LAP1) is an integral protein of the inner nuclear membrane that is ubiquitously expressed. LAP1 binds to lamins and chromatin, probably contributing to the maintenance of the nuclear envelope architecture. Moreover, LAP1 also interacts with torsinA and emerin, proteins involved in DYT1 dystonia and X-linked Emery-Dreifuss muscular dystrophy disorder, respectively. Given its relevance to human pathological conditions, it is important to better understand the functional diversity of LAP1 proteins. In rat, the LAP1 gene (TOR1AIP1) undergoes alternative splicing to originate three LAP1 isoforms (LAP1A, B and C). However, it remains unclear if the same occurs with the human TOR1AIP1 gene, since only the LAP1B isoform had thus far been identified in human cells. In silico analysis suggested that, across different species, potential new LAP1 isoforms could be generated by alternative splicing. Using shRNA to induce LAP1 knockdown and HPLC-mass spectrometry analysis the presence of two isoforms in human cells was described and validated: LAP1B and LAP1C; the latter is putatively N-terminal truncated. LAP1B and LAP1C expression profiles appear to be dependent on the specific tissues analyzed and in cultured cells LAP1C was the major isoform detected. Moreover, LAP1B and LAP1C expression increased during neuronal maturation, suggesting that LAP1 is relevant in this process. Both isoforms were found to be post-translationally modified by phosphorylation and methionine oxidation and two LAP1B/LAP1C residues were shown to be dephosphorylated by PP1. This study permitted the identification of the novel human LAP1C isoform and partially unraveled the molecular basis of LAP1 regulation.

Abnormal proliferation and spontaneous differentiation of myoblasts from a symptomatic female carrier of X-linked Emery–Dreifuss muscular dystrophy

The paper by Meinke et al. (in this issue) [1] is a reminder of how much useful information can be obtained from detailed molecular studies of unusual neuromuscular patients, provided you have resources, persistence and a co-operative family.

Abnormal proliferation and spontaneous differentiation of myoblasts from a symptomatic female carrier of X-linked Emery–Dreifuss muscular dystrophy

Emery–Dreifuss muscular dystrophy (EDMD) is a neuromuscular disease characterized by early contractures, slowly progressive muscular weakness and life-threatening cardiac arrhythmia that can develop into cardiomyopathy. In X-linked EDMD (EDMD1), female carriers are usually unaffected. Here we present a clinical description and in vitro characterization of a mildly affected EDMD1 female carrying the heterozygous EMD mutation c.174_175delTT; p.Y59* that yields loss of protein. Muscle tissue sections and cultured patient myoblasts exhibited a mixed population of emerin-positive and -negative cells; thus uneven X-inactivation was excluded as causative. Patient blood cells were predominantly emerin-positive, but considerable nuclear lobulation was observed in non-granulocyte cells – a novel phenotype in EDMD. Both emerin-positive and emerin-negative myoblasts exhibited spontaneous differentiation in tissue culture, though emerin-negative myoblasts were more proliferative than emerin-positive cells. The preferential proliferation of emerin-negative myoblasts together with the high rate of spontaneous differentiation in both populations suggests that loss of functional satellite cells might be one underlying mechanism for disease pathology. This could also account for the slowly developing muscle phenotype.

Attenuation of Wnt/β-catenin activity reverses enhanced generation of cardiomyocytes and cardiac defects caused by the loss of emerin.

Mutations in EMD, encoding emerin cause skeletal muscle and heart defects in patients with X-linked Emery-Dreifuss muscular dystrophy (X-EDMD) but the underlying mechanisms leading to cardiac defects are poorly understood. Here, we investigated the role of emerin in controlling cardiomyocyte proliferation and cardiac remodeling and explored its function in regulation of the Wnt/β-catenin pathway. We observed a remarkable increase of cardiomyocytes in emerin-null adult mice accompanied with decreased numbers of multinucleated cells. Depletion of emerin in mouse ES cell-derived cardiomyocytes by shRNA caused hyperactivation of Wnt/β-catenin signaling, increased proliferation and abrogated timely cardiac differentiation. Likewise, emerin-null mice exhibited increased Wnt/β-catenin signaling, cardiac dysfunction and perturbed hypertrophic remodeling following pressure overload. Pharmacological inhibition of β-catenin normalized proliferation and differentiation of ES cell-derived cardiomyocytes while inactivation of a single allele of β-catenin efficiently rescued cardiac dysfunction in emerin-null mice. We conclude that emerin constrains β-catenin signaling in the heart providing tight control of cardiomyocyte numbers. Enhanced Wnt/β-catenin signaling seems to contribute to cardiac defects observed in X-EDMD. Hence, therapeutic inhibition of Wnt/β-catenin signaling might be beneficial for X-EDMD patients.

G.P.142: A new EMD gene missense mutation in exon 1 leads to absence of emerin and is responsible for X-linked dilated cardiomyopathy with conduction defects and arrhythmias and almost elusive skeletal muscle features

Mutations in the EMD gene, encoding emerin, lead to X-linked Emery-Dreifuss muscular dystrophy (EDMD). Although always associated with EDMD, an almost exclusive cardiac involvement was found in exceptional patients carrying EMD gene mutations. We here report 2 brothers belonging to a family where 9 affected male subjects developed dilated cardiomyopathy (DCM) with conduction defects and arrhythmias. The oldest brother of 53years developed DCM since 49years and requiring implantable cardioverter defibrillator (ICD) implantation. He subsequently developed atrio-ventricular and ventricular conduction defects as well as ventricular arrhythmias at 52years that required ICD upgrading and additional pacemaker implantation. His youngest brother aged 45years was also affected. The family history showed several affected members: a third brother who died after cardiac transplantation at 38years, a fourth brother who died suddenly at 50years, two maternal uncles and cousins died in their 5th or 6th decades among them 2 were diagnosed as arrhythmogenic right ventricular dysplasia. An X-linked mode of inheritance was therefore suspected and DMD gene analysis did not show any exonic deletion or duplication or exon 1 point mutation. Further neurological assessment of the oldest brother showed neither muscle weakness nor joint contractures whereas hands and legs were slightly hypotrophic. CPK were at normal level and needle electromyography examination showed normal pattern. Deltoid muscle biopsy was normal as were protein immunohistochemical studies including dystrophin, desmin, myotilin and caveolin 3 while emerin staining was totally absent. Subsequent EMD gene analysis revealed a new missense mutation in exon 1 (c.65C>T, p.Pro22Leu). In addition to the 2 previously reported families with a close emerin mutation (p.delK37) and an exclusive cardiac disease, our family further indicates that emerin protein is crucial for correct cardiac function.

Lamina-Associated Polypeptide-1 Interacts with the Muscular Dystrophy Protein Emerin and Is Essential for Skeletal Muscle Maintenance

X-linked Emery-Dreifuss muscular dystrophy is caused by loss of function of emerin, an integral protein of the inner nuclear membrane. Yet emerin null mice are essentially normal, suggesting the existence of a critical compensating factor. We show that the lamina-associated polypeptide1 (LAP1) interacts with emerin. Conditional deletion of LAP1 from striated muscle causes muscular dystrophy; this pathology is worsened in the absence of emerin. LAP1 levels are significantly higher in mouse than human skeletal muscle, and reducing LAP1 by approximately half in mice also induces muscle abnormalities in emerin null mice. Conditional deletion of LAP1 from hepatocytes yields mice that exhibit normal liver function and are indistinguishable from littermate controls. These results establish that LAP1 interacts physically and functionally with emerin and plays an essential and selective role in skeletal muscle maintenance. They also highlight how dissecting differences between mouse and human phenotypes can provide fundamental insights into disease mechanisms.

The emerin-binding transcription factor Lmo7 is regulated by association with p130Cas at focal adhesions

Loss of function mutations in the nuclear inner membrane protein, emerin, cause X-linked Emery-Dreifuss muscular dystrophy (X-EDMD). X-EDMD is characterized by contractures of major tendons, skeletal muscle weakening and wasting, and cardiac conduction system defects. The transcription factor Lmo7 regulates muscle- and heart-relevant genes and is inhibited by binding to emerin, suggesting Lmo7 misregulation contributes to EDMD disease. Lmo7 associates with cell adhesions and shuttles between the plasma membrane and nucleus, but the regulation and biological consequences of this dual localization were unknown. We report endogenous Lmo7 also associates with focal adhesions in cells, and both co-localizes and co-immunoprecipitates with p130Cas, a key signaling component of focal adhesions. Lmo7 nuclear localization and transcriptional activity increased significantly in p130Cas-null MEFs, suggesting Lmo7 is negatively regulated by p130Cas-dependent association with focal adhesions. These results support EDMD models in which Lmo7 is a downstream mediator of integrin-dependent signaling that allows tendon cells and muscles to adapt to and withstand mechanical stress.