Developmental changes in nuclear lamina components during germ cell differentiation

The nuclear lamina (NL) changes composition for regulation of nuclear events. We investigated changes that occur in Drosophila oogenesis, revealing switches in NL composition during germ cell differentiation. Germline stem cells (GSCs) express only LamB and predominantly emerin, whereas differentiating nurse cells predominantly express LamC and emerin2. A change in LamC-specific localization also occurs, wherein phosphorylated LamC redistributes to the nuclear interior only in the oocyte, prior to transcriptional reactivation of the meiotic genome. These changes support existing concepts that LamC promotes differentiation, a premise that was tested. Remarkably ectopic LamC production in GSCs did not promote premature differentiation. Increased LamC levels in differentiating germ cells altered internal nuclear structure, increased RNA production, and reduced female fertility due to defects in eggshell formation. These studies suggest differences between Drosophila lamins are regulatory, not functional, and reveal an unexpected robustness to level changes of a major scaffolding component of the NL.

Natural History of Dilated Cardiomyopathy Due to c.77T>C (p.Val26Ala) in Emerin Protein

(1) Introduction: Dilated cardiomyopathy (DCM) mainly affects young individuals and is the main indication of heart transplantation. The variant c.77T>C (p.Val26Ala) of the gene coding for emerin (EMD) in chromosome Xq28 has been catalogued as a pathogenic variant for the development of DCM, exhibiting an X-linked inheritance pattern. (2) Methods: A retrospective study was conducted covering the period 2015-2023 in patients with DCM of genetic origin. The primary endpoint was patient age at onset of the first composite major cardiac event, in the form of a first episode of heart failure, malignant ventricular arrhythmia, or end-stage heart failure, according to the presence of truncating variant in titin gene (TTNtv) versus the p.Val26Ala mutation in the EMD protein. (3) Results: A total of 31 and 22 patients were included in the EMD group and TTNtv group, respectively. The primary endpoint was significantly higher in the EMD group, with a hazard ratio of 4.16 (95% confidence interval: 1.83-9.46; p = 0.001). At 55 years of age, all the patients in the EMD group had already presented heart failure, nine presented malignant ventricular arrhythmia (29%), and 13 required heart transplantation (42%). (4) Conclusions: DCM secondary to the c.77T>C (p.Val26Ala) mutation in the EMD gene is associated to an increased risk of major cardiac events compared to patients with DCM due to TTNtv, with a large proportion of transplanted patients in the fifth decade of life.

Pharmacotherapeutic Approaches to Treatment of Muscular Dystrophies

Muscular dystrophies are a heterogeneous group of genetic muscle-wasting disorders that are subdivided based on the region of the body impacted by muscle weakness as well as the functional activity of the underlying genetic mutations. A common feature of the pathophysiology of muscular dystrophies is chronic inflammation associated with the replacement of muscle mass with fibrotic scarring. With the progression of these disorders, many patients suffer cardiomyopathies with fibrosis of the cardiac tissue. Anti-inflammatory glucocorticoids represent the standard of care for Duchenne muscular dystrophy, the most common muscular dystrophy worldwide; however, long-term exposure to glucocorticoids results in highly adverse side effects, limiting their use. Thus, it is important to develop new pharmacotherapeutic approaches to limit inflammation and fibrosis to reduce muscle damage and promote repair. Here, we examine the pathophysiology, genetic background, and emerging therapeutic strategies for muscular dystrophies.

Identification of PP2A-B55 targets uncovers regulation of emerin during nuclear envelope reassembly in Drosophila

Mitotic exit requires the dephosphorylation of many proteins whose phosphorylation was needed for mitosis. Protein phosphatase 2A with its B55 regulatory subunit (PP2A-B55) promotes this transition. However, the events and substrates that it regulates are incompletely understood. We used proteomic approaches in Drosophila to identify proteins that interact with and are dephosphorylated by PP2A-B55. Among several candidates, we identified emerin (otefin in Drosophila). Emerin resides in the inner nuclear membrane and interacts with the DNA-binding protein barrier-to-autointegration factor (BAF) via a LEM domain. We found that the phosphorylation of emerin at Ser50 and Ser54 near its LEM domain negatively regulates its association with BAF, lamin and additional emerin in mitosis. We show that dephosphorylation of emerin at these sites by PP2A-B55 determines the timing of nuclear envelope reformation. Genetic experiments indicate that this regulation is required during embryonic development. Phosphoregulation of the emerin-BAF complex formation by PP2A-B55 appears as a key event of mitotic exit that is likely conserved across species.

Genotype-Phenotype Correlations in Human Diseases Caused by Mutations of LINC Complex-Associated Genes: A Systematic Review and Meta-Summary

Mutations in genes encoding proteins associated with the linker of nucleoskeleton and cytoskeleton (LINC) complex within the nuclear envelope cause different diseases with varying phenotypes including skeletal muscle, cardiac, metabolic, or nervous system pathologies. There is some understanding of the structure of LINC complex-associated proteins and how they interact, but it is unclear how mutations in genes encoding them can cause the same disease, and different diseases with different phenotypes. Here, published mutations in LINC complex-associated proteins were systematically reviewed and analyzed to ascertain whether patterns exist between the genetic sequence variants and clinical phenotypes. This revealed LMNA is the only LINC complex-associated gene in which mutations commonly cause distinct conditions, and there are no clear genotype-phenotype correlations. Clusters of LMNA variants causing striated muscle disease are located in exons 1 and 6, and metabolic disease-associated LMNA variants are frequently found in the tail of lamin A/C. Additionally, exon 6 of the emerin gene, EMD, may be a mutation "hot-spot", and diseases related to SYNE1, encoding nesprin-1, are most often caused by nonsense type mutations. These results provide insight into the diverse roles of LINC-complex proteins in human disease and provide direction for future gene-targeted therapy development.

Shared and Distinctive Neighborhoods of Emerin and Lamin B Receptor Revealed by Proximity Labeling and Quantitative Proteomics

Emerin and lamin B receptor (LBR) are abundant transmembrane proteins of the nuclear envelope that are concentrated at the inner nuclear membrane (INM). Although both proteins interact with chromatin and nuclear lamins, they have distinctive biochemical and functional properties. Here, we have deployed proximity labeling using the engineered biotin ligase TurboID (TbID) and quantitative proteomics to compare the neighborhoods of emerin and LBR in cultured mouse embryonic fibroblasts. Our analysis revealed 232 high confidence proximity partners that interact selectively with emerin and/or LBR, 49 of which are shared by both. These included previously characterized NE-concentrated proteins, as well as a host of additional proteins not previously linked to emerin or LBR functions. Many of these are TM proteins of the ER, including two E3 ubiquitin ligases. Supporting these results, we found that 11/12 representative proximity relationships identified by TbID also were detected at the NE with the proximity ligation assay. Overall, this work presents methodology that may be used for large-scale mapping of the landscape of the INM and reveals a group of new proteins with potential functional connections to emerin and LBR.

Matrix remodeling controls a nuclear lamin A/C-emerin network that directs Wnt-regulated stem cell fate

Skeletal stem cells (SSCs) reside within a three-dimensional extracellular matrix (ECM) compartment and differentiate into multiple cell lineages, thereby controlling tissue maintenance and regeneration. Within this environment, SSCs can proteolytically remodel the surrounding ECM in response to growth factors that direct lineage commitment via undefined mechanisms. Here, we report that Mmp14-dependent ECM remodeling coordinates canonical Wnt signaling and guides stem cell fate by triggering an integrin-activated reorganization of the SCC cytoskeleton that controls nuclear lamin A/C levels via the linker of nucleoskeleton and cytoskeleton (LINC) complexes. In turn, SSC lamin A/C levels dictate the localization of emerin, an inner nuclear membrane protein whose ability to regulate β-catenin activity modulates Wnt signaling while directing lineage commitment in vitro and in vivo. These findings define a previously undescribed axis wherein SSCs use Mmp14-dependent ECM remodeling to control cytoskeletal and nucleoskeletal organization, thereby governing Wnt-dependent stem cell fate decisions.

Checkpoint activation drives global gene expression changes in Drosophila nuclear lamina mutants

The nuclear lamina (NL) lines the inner nuclear membrane. This extensive protein network organizes chromatin and contributes to the regulation of transcription, DNA replication, and repair. Lap2-emerin-MAN1 domain (LEM-D) proteins are key members of the NL, representing proteins that connect the NL to the genome through shared interactions with the chromatin-binding protein Barrier-to-Autointegration Factor (BAF). Functions of the LEM-D protein emerin and BAF are essential during Drosophila melanogaster oogenesis. Indeed, loss of either emerin or BAF blocks germ cell development and causes loss of germline stem cells, defects linked to the deformation of NL structure, and non-canonical activation of Checkpoint kinase 2 (Chk2). Here, we investigate the contributions of emerin and BAF to gene expression in the ovary. Profiling RNAs from emerin and baf mutant ovaries revealed that nearly all baf misregulated genes were shared with emerin mutants, defining a set of NL-regulated genes. Strikingly, loss of Chk2 restored the expression of most NL-regulated genes, identifying a large class of Chk2-dependent genes (CDGs). Nonetheless, some genes remained misexpressed upon Chk2 loss, identifying a smaller class of emerin-dependent genes (EDGs). Properties of EDGs suggest a shared role for emerin and BAF in the repression of developmental genes. Properties of CDGs demonstrate that Chk2 activation drives global misexpression of genes in the emerin and baf mutant backgrounds. Notably, CDGs were found upregulated in lamin-B mutant backgrounds. These observations predict that Chk2 activation might have a general role in gene expression changes found in NL-associated diseases, such as laminopathies.

Molecular Pathology of Laminopathies

The nuclear envelope is composed of the nuclear membranes, nuclear lamina, and nuclear pore complexes. Laminopathies are diseases caused by mutations in genes encoding protein components of the lamina and these other nuclear envelope substructures. Mutations in the single gene encoding lamin A and C, which are expressed in most differentiated somatic cells, cause diseases affecting striated muscle, adipose tissue, peripheral nerve, and multiple systems with features of accelerated aging. Mutations in genes encoding other nuclear envelope proteins also cause an array of diseases that selectively affect different tissues or organs. In some instances, the molecular and cellular consequences of laminopathy-causing mutations are known. However, even when these are understood, mechanisms explaining specific tissue or organ pathology remain enigmatic. Current mechanistic hypotheses focus on how alterations in the nuclear envelope may affect gene expression, including via the regulation of signaling pathways, or cellular mechanics, including responses to mechanical stress.

Nuclear Envelope Alterations in Myotonic Dystrophy Type 1 Patient-Derived Fibroblasts

Myotonic dystrophy type 1 (DM1) is a hereditary and multisystemic disease characterized by myotonia, progressive distal muscle weakness and atrophy. The molecular mechanisms underlying this disease are still poorly characterized, although there are some hypotheses that envisage to explain the multisystemic features observed in DM1. An emergent hypothesis is that nuclear envelope (NE) dysfunction may contribute to muscular dystrophies, particularly to DM1. Therefore, the main objective of the present study was to evaluate the nuclear profile of DM1 patient-derived and control fibroblasts and to determine the protein levels and subcellular distribution of relevant NE proteins in these cell lines. Our results demonstrated that DM1 patient-derived fibroblasts exhibited altered intracellular protein levels of lamin A/C, LAP1, SUN1, nesprin-1 and nesprin-2 when compared with the control fibroblasts. In addition, the results showed an altered location of these NE proteins accompanied by the presence of nuclear deformations (blebs, lobes and/or invaginations) and an increased number of nuclear inclusions. Regarding the nuclear profile, DM1 patient-derived fibroblasts had a larger nuclear area and a higher number of deformed nuclei and micronuclei than control-derived fibroblasts. These results reinforce the evidence that NE dysfunction is a highly relevant pathological characteristic observed in DM1.

Role of Lamin A and emerin in maintaining nuclear morphology in different subtypes of ovarian epithelial cancer

The nuclear lamina protein, Lamin A and inner nuclear membrane protein, emerin participate in maintaining nuclear morphology. However, their correlations with the nuclear shape in the four representative ovarian epithelial cancer subtypes, high-grade serous carcinoma (HGSCa), clear cell carcinoma (CCCa), endometrioid carcinoma (EMCa) and mucinous carcinoma (MUCa), remains unclear. The present study aimed to investigate the association between nuclear morphology and nuclear membrane protein expression in four histological subtypes of ovarian epithelial cancer. A total of 140 surgically resected ovarian cancer specimens were subjected to Feulgen staining to evaluate nuclear morphology, and immunohistochemistry analysis to assess Lamin A and emerin expression. The histological images were analyzed via computer-assisted image analysis (CAIA). The results demonstrated that the mean nuclear area of EMCa was significantly smaller compared with CCCa (P=0.0009). The standard deviation of the mean nuclear area was used to assess nuclear size variation, and the results indicated that EMCa lesions were significantly smaller than CCCa lesions (P=0.0006). Regarding the correlation between the Lamin A-positive rate and nuclear morphological factors, positive correlations were observed with nuclear area in CCCa and EMCa (R=0.2855 and R=0.2858, respectively) and nuclear perimeter in CCCa, EMCa and MUCa (R=0.2409, R=0.4054 and R=0.2370, respectively); however, a negative correlation with nuclear shape factor was observed in HGSCa and EMCa (R=-0.2079 and R=-0.3707, respectively). With regards to the correlation between emerin positivity and nuclear morphological factors, positive correlations were observed with nuclear shape factor in HGSCa (R=0.2673) and nuclear area in CCCa (R=0.3310). It is well-known that HGSCa and CCCa have conspicuous nuclear size variation, and EMCa has small nuclei without strong atypia. These findings were verified in the present study via CAIA. Taken together, the results of the present study suggest that Lamin A strongly contributes to the maintenance of nuclear morphology in ovarian epithelial cancer compared with emerin, although their contributions differ based on tumor subtype.

The Role of Emerin in Cancer Progression and Metastasis

It is commonly recognized in the field that cancer cells exhibit changes in the size and shape of their nuclei. These features often serve as important biomarkers in the diagnosis and prognosis of cancer patients. Nuclear size can significantly impact cell migration due to its incredibly large size. Nuclear structural changes are predicted to regulate cancer cell migration. Nuclear abnormalities are common across a vast spectrum of cancer types, regardless of tissue source, mutational spectrum, and signaling dependencies. The pervasiveness of nuclear alterations suggests that changes in nuclear structure may be crucially linked to the transformation process. The factors driving these nuclear abnormalities, and the functional consequences, are not completely understood. Nuclear envelope proteins play an important role in regulating nuclear size and structure in cancer. Altered expression of nuclear lamina proteins, including emerin, is found in many cancers and this expression is correlated with better clinical outcomes. A model is emerging whereby emerin, as well as other nuclear lamina proteins, binding to the nucleoskeleton regulates the nuclear structure to impact metastasis. In this model, emerin and lamins play a central role in metastatic transformation, since decreased emerin expression during transformation causes the nuclear structural defects required for increased cell migration, intravasation, and extravasation. Herein, we discuss the cellular functions of nuclear lamina proteins, with a particular focus on emerin, and how these functions impact cancer progression and metastasis.

Defects in Emerin-Nucleoskeleton Binding Disrupt Nuclear Structure and Promote Breast Cancer Cell Motility and Metastasis

Nuclear envelope proteins play an important role in regulating nuclear size and structure in cancer. Altered expression of nuclear lamins are found in many cancers and its expression is correlated with better clinical outcomes. The nucleus is the largest organelle in the cell with a diameter between 10 and 20 μm. Nuclear size significantly impacts cell migration. Nuclear structural changes are predicted to impact cancer metastasis by regulating cancer cell migration. Here we show emerin regulates nuclear structure in invasive breast cancer cells to impact cancer metastasis. Invasive breast cancer cells had 40% to 50% less emerin than control cells, which resulted in decreased nuclear size. Overexpression of GFP-emerin in invasive breast cancer cells rescued nuclear size and inhibited migration through 3.0 and 8.0 μm pores. Mutational analysis showed emerin binding to nucleoskeletal proteins was important for its regulation of nuclear structure, migration, and invasion. Importantly, emerin expression inhibited lung metastasis by 91% in orthotopic mouse models of breast cancer. Emerin nucleoskeleton-binding mutants failed to inhibit metastasis. These results support a model whereby emerin binding to the nucleoskeleton regulates nuclear structure to impact metastasis. In this model, emerin plays a central role in metastatic transformation, because decreased emerin expression during transformation causes the nuclear structural defects required for increased cell migration, intravasation, and extravasation. IMPLICATIONS: Modulating emerin expression and function represents new targets for therapeutic interventions of metastasis, because increased emerin expression rescued cancer metastasis.

Emerin Represses STAT3 Signaling through Nuclear Membrane-Based Spatial Control

Emerin is the inner nuclear membrane protein involved in maintaining the mechanical integrity of the nuclear membrane. Mutations in EMD encoding emerin cause Emery–Dreifuss muscular dystrophy (EDMD). Evidence is accumulating that emerin regulation of specific gene expression is associated with this disease, but the exact function of emerin has not been fully elucidated. Here, we show that emerin downregulates Signal transducer and activators of transcription 3 (STAT3) signaling, activated exclusively by Janus kinase (JAK). Deletion mutation experiments show that the lamin-binding domain of emerin is essential for the inhibition of STAT3 signaling. Emerin interacts directly and co-localizes with STAT3 in the nuclear membrane. Emerin knockdown induces STAT3 target genes Bcl2 and Survivin to increase cell survival signals and suppress hydrogen peroxide-induced cell death in HeLa cells. Specifically, downregulation of BAF or lamin A/C increases STAT3 signaling, suggesting that correct-localized emerin, by assembling with BAF and lamin A/C, acts as an intrinsic inhibitor against STAT3 signaling. In C2C12 cells, emerin knockdown induces STAT3 target gene, Pax7, and activated abnormal myoblast proliferation associated with muscle wasting in skeletal muscle homeostasis. Our results indicate that emerin downregulates STAT3 signaling by inducing retention of STAT3 and delaying STAT3 signaling in the nuclear membrane. This mechanism provides clues to the etiology of emerin-related muscular dystrophy and may be a new therapeutic target for treatment.

Cardiac Arrhythmias in Muscular Dystrophies Associated with Emerinopathy and Laminopathy: A Cohort Study

Introduction: Cardiac involvement in patients with muscular dystrophy associated with Lamin A/C mutations (LMNA) is characterized by atrioventricular conduction abnormalities and life-threatening cardiac arrhythmias. Little is known about cardiac involvement in patients with emerin mutation (EMD). The aim of our study was to describe and compare the prevalence and time distribution of cardiac arrhythmias at extended follow-up. Patients and methods: 45 consecutive patients affected by muscular dystrophy associated to laminopathy or emerinopathy were examined. All patients underwent clinical evaluation, 12-lead surface electrocardiogram (ECG), 24 h electrocardiographic monitoring, and cardiac implanted device interrogation. Results: At the end of 11 (5.0–16.6) years of follow-up, 89% of the patients showed cardiac arrhythmias. The most prevalent was atrial standstill (AS) (31%), followed by atrial fibrillation/flutter (AF/Afl) (29%) and ventricular tachycardia (22%). EMD patients presented more frequently AF/AFl compared to LMNA (50% vs. 20%, p = 0.06). Half of the EMD patients presented with AS, whilst there was no occurrence of such in the LMNA (p = 0.001). Ventricular arrhythmias were found in 60% of patients with laminopathy compared to 3% in patients with emerinopathy (p < 0.001). The age of AVB occurrence was higher in the LMNA group (32.8 +/− 10.6 vs. 25.1 +/− 9.1, p = 0.03). Conclusions: Atrial arrhythmias are common findings in patients with muscular dystrophy associated with EMD/LMNA mutations; however, they occurred earlier in EMD patients. Ventricular arrhythmias were very common (60%) in LMNA and occurred definitely earlier compared to the EMD group.

Drosophila female germline stem cells undergo mitosis without nuclear breakdown

Stem cell homeostasis requires nuclear lamina (NL) integrity. In Drosophila germ cells, compromised NL integrity activates the ataxia telangiectasia and Rad3-related (ATR) and checkpoint kinase 2 (Chk2) checkpoint kinases, blocking germ cell differentiation and causing germline stem cell (GSC) loss. Checkpoint activation occurs upon loss of either the NL protein emerin or its partner barrier-to-autointegration factor, two proteins required for nuclear reassembly at the end of mitosis. Here, we examined how mitosis contributes to NL structural defects linked to checkpoint activation. These analyses led to the unexpected discovery that wild-type female GSCs utilize a non-canonical mode of mitosis, one that retains a permeable but intact nuclear envelope and NL. We show that the interphase NL is remodeled during mitosis for insertion of centrosomes that nucleate the mitotic spindle within the confines of the nucleus. We show that depletion or loss of NL components causes mitotic defects, including compromised chromosome segregation associated with altered centrosome positioning and structure. Further, in emerin mutant GSCs, centrosomes remain embedded in the interphase NL. Notably, these embedded centrosomes carry large amounts of pericentriolar material and nucleate astral microtubules, revealing a role for emerin in the regulation of centrosome structure. Epistasis studies demonstrate that defects in centrosome structure are upstream of checkpoint activation, suggesting that these centrosome defects might trigger checkpoint activation and GSC loss. Connections between NL proteins and centrosome function have implications for mechanisms associated with NL dysfunction in other stem cell populations, including NL-associated diseases, such as laminopathies.

The Molecular Basis and Biologic Significance of the β-Dystroglycan-Emerin Interaction

β-dystroglycan (β-DG) assembles with lamins A/C and B1 and emerin at the nuclear envelope (NE) to maintain proper nuclear architecture and function. To provide insight into the nuclear function of β-DG, we characterized the interaction between β-DG and emerin at the molecular level. Emerin is a major NE protein that regulates multiple nuclear processes and whose deficiency results in Emery–Dreifuss muscular dystrophy (EDMD). Using truncated variants of β-DG and emerin, via a series of in vitro and in vivo binding experiments and a tailored computational analysis, we determined that the β-DG–emerin interaction is mediated at least in part by their respective transmembrane domains (TM). Using surface plasmon resonance assays we showed that emerin binds to β-DG with high affinity (KD in the nanomolar range). Remarkably, the analysis of cells in which DG was knocked out demonstrated that loss of β-DG resulted in a decreased emerin stability and impairment of emerin-mediated processes. β-DG and emerin are reciprocally required for their optimal targeting within the NE, as shown by immunofluorescence, western blotting and immunoprecipitation assays using emerin variants with mutations in the TM domain and B-lymphocytes of a patient with EDMD. In summary, we demonstrated that β-DG plays a role as an emerin interacting partner modulating its stability and function.

EDMD-Causing Emerin Mutant Myogenic Progenitors Exhibit Impaired Differentiation Using Similar Mechanisms

Mutations in the gene encoding emerin (EMD) cause Emery–Dreifuss muscular dystrophy (EDMD1), an inherited disorder characterized by progressive skeletal muscle wasting, irregular heart rhythms and contractures of major tendons. The skeletal muscle defects seen in EDMD are caused by failure of muscle stem cells to differentiate and regenerate the damaged muscle. However, the underlying mechanisms remain poorly understood. Most EDMD1 patients harbor nonsense mutations and have no detectable emerin protein. There are three EDMD-causing emerin mutants (S54F, Q133H, and Δ95–99) that localize correctly to the nuclear envelope and are expressed at wildtype levels. We hypothesized these emerin mutants would share in the disruption of key molecular pathways involved in myogenic differentiation. We generated myogenic progenitors expressing wildtype emerin and each EDMD1-causing emerin mutation (S54F, Q133H, Δ95–99) in an emerin-null (EMD^−/y) background. S54F, Q133H, and Δ95–99 failed to rescue EMD^−/y myogenic differentiation, while wildtype emerin efficiently rescued differentiation. RNA sequencing was done to identify pathways and networks important for emerin regulation of myogenic differentiation. This analysis significantly reduced the number of pathways implicated in EDMD1 muscle pathogenesis.

Emerin Phosphorylation during the Early Phase of the Oxidative Stress Response Influences Emerin-BAF Interaction and BAF Nuclear Localization

Reactive Oxygen Species (ROS) are reactive molecules required for the maintenance of physiological functions. Oxidative stress arises when ROS production exceeds the cellular ability to eliminate such molecules. In this study, we showed that oxidative stress induces post-translational modification of the inner nuclear membrane protein emerin. In particular, emerin is phosphorylated at the early stages of the oxidative stress response, while protein phosphorylation is abolished upon recovery from stress. A finely tuned balance between emerin phosphorylation and O-GlcNAcylation seems to govern this dynamic and modulates emerin–BAF interaction and BAF nucleoplasmic localization during the oxidative stress response. Interestingly, emerin post-translational modifications, similar to those observed during the stress response, are detected in cells bearing LMNA gene mutations and are characterized by a free radical generating environment. On the other hand, under oxidative stress conditions, a delay in DNA damage repair and cell cycle progression is found in cells from Emery–Dreifuss Muscular Dystrophy type 1, which do not express emerin. These results suggest a role of the emerin–BAF protein platform in the DNA damage response aimed at counteracting the detrimental effects of elevated levels of ROS.

Histone acetyltransferase inhibition rescues differentiation of emerin-deficient myogenic progenitors

INTRODUCTION

Emery-Dreifuss muscular dystrophy (EDMD) is a disease characterized by skeletal muscle wasting, major tendon contractures, and cardiac conduction defects. Mutations in the gene encoding emerin cause EDMD1. Our previous studies suggested that emerin activation of histone deacetylase 3 (HDAC3) to reduce histone 4-lysine 5 (H4K5) acetylation (ac) is important for myogenic differentiation.

METHODS

Pharmacological inhibitors (Nu9056, L002) of histone acetyltransferases targeting acetylated H4K5 were used to test whether increased acetylated H4K5 was responsible for the impaired differentiation seen in emerin-deficient myogenic progenitors.

RESULTS

Nu9056 and L002 rescued impaired differentiation in emerin deficiency. SRT1720, which inhibits the nicotinamide adenine dinucleotide (NAD)⁺ -dependent deacetylase sirtuin 1 (SIRT1), failed to rescue myotube formation.

DISCUSSION

We conclude that emerin regulation of HDAC3 activity to affect H4K5 acetylation dynamics is important for myogenic differentiation. Targeting H4K5ac dynamics represents a potential new strategy for ameliorating the skeletal muscle wasting seen in EDMD1.

Probing the Environment of Emerin by Enhanced Ascorbate Peroxidase 2 (APEX2)-Mediated Proximity Labeling

Emerin is one of the best characterized proteins of the inner nuclear membrane, but can also occur at the level of the endoplasmic reticulum. We now use enhanced ascorbate peroxidase 2 (APEX2) to probe the environment of emerin. APEX2 can be used as a genetic tag that produces short-lived yet highly reactive biotin species, allowing the modification of proteins that interact with or are in very close proximity to the tagged protein. Biotinylated proteins can be isolated using immobilized streptavidin and analyzed by mass spectrometry. As an alternative to the standard approach with a genetic fusion of APEX2 to emerin, we also used RAPIDS (rapamycin- and APEX-dependent identification of proteins by SILAC), a method with improved specificity, where the peroxidase interacts with the protein of interest (i.e., emerin) only upon addition of rapamycin to the cells. We compare these different approaches, which, together, identify well-known interaction partners of emerin like lamin A and the lamina associated polypeptide 1 (LAP1), as well as novel proximity partners.

Nuclear architecture as an intrinsic regulator of Drosophila female germline stem cell maintenance

Homeostasis of Drosophila germline stem cells (GSC) depends upon the integration of intrinsic and extrinsic signals. This review highlights emerging data that support nuclear architecture as an intrinsic regulator of GSC maintenance and germ cell differentiation. Here, we focus on the nuclear lamina (NL) and the nucleolus, two compartments that undergo alterations in composition upon germ cell differentiation. Loss of NL or nucleolar components leads to GSC loss, resulting from activation of GSC quality control checkpoint pathways. We suggest that the NL and nucleolus integrate signals needed for the switch between GSC maintenance and germ cell differentiation, and propose regulation of nuclear actin pools as one mechanism that connects these compartments.

Emery-Dreifuss muscular dystrophy

Emery-Dreifuss muscular dystrophy (EDMD) is a rare muscular dystrophy, but is particularly important to diagnose due to frequent life-threatening cardiac complications. EDMD classically presents with muscle weakness, early contractures, cardiac conduction abnormalities and cardiomyopathy, although the presence and severity of these manifestations vary by subtype and individual. Associated genes include EMD, LMNA, SYNE1, SYNE2, FHL1, TMEM43, SUN1, SUN2, and TTN, encoding emerin, lamin A/C, nesprin-1, nesprin-2, FHL1, LUMA, SUN1, SUN2, and titin, respectively. The Online Mendelian Inheritance in Man database recognizes subtypes 1 through 7, which captures most but not all of the associated genes. Genetic diagnosis is essential whenever available, but traditional diagnostic tools can help steer the evaluation toward EDMD and assist with interpretation of equivocal genetic test results. Management is primarily supportive, but it is important to monitor patients closely, especially for potential cardiac complications. There is a high potential for progress in the treatment of EDMD in the coming years.

A Micropatterning Strategy to Study Nuclear Mechanotransduction in Cells

Micropatterning techniques have been widely used in biology, particularly in studies involving cell adhesion and proliferation on different substrates. Cell micropatterning approaches are also increasingly employed as in vitro tools to investigate intracellular mechanotransduction processes. In this report, we examined how modulating cellular shapes on two-dimensional rectangular fibronectin micropatterns of different widths influences nuclear mechanotransduction mediated by emerin, a nuclear envelope protein implicated in Emery-Dreifuss muscular dystrophy (EDMD). Fibronectin microcontact printing was tested onto glass coverslips functionalized with three different silane reagents (hexamethyldisilazane (HMDS), (3-Aminopropyl)triethoxysilane (APTES) and (3-Glycidyloxypropyl)trimethoxysilane (GPTMS)) using a vapor-phase deposition method. We observed that HMDS provides the most reliable printing surface for cell micropatterning, notably because it forms a hydrophobic organosilane monolayer that favors the retainment of surface antifouling agents on the coverslips. We showed that, under specific mechanical cues, emerin-null human skin fibroblasts display a significantly more deformed nucleus than skin fibroblasts expressing wild type emerin, indicating that emerin plays a crucial role in nuclear adaptability to mechanical stresses. We further showed that proper nuclear responses to forces involve a significant relocation of emerin from the inner nuclear envelope towards the outer nuclear envelope and the endoplasmic reticulum membrane network. Cell micropatterning by fibronectin microcontact printing directly on HMDS-treated glass represents a simple approach to apply steady-state biophysical cues to cells and study their specific mechanobiology responses in vitro.

A Novel Mutation Of The EMD Gene In A Family With Cardiac Conduction Abnormalities And A High Incidence Of Sudden Cardiac Death

Background

Emery-Dreifuss muscular dystrophy, caused by mutations in genes such as emerin (EMD) or lamin A/C (LMNA), is a disorder affecting the joints, muscles, and heart, with a wide spectrum of patient phenotypes including muscle wasting and cardiac conduction defects.

Methods and results

Here we report a multi-generation family from the Hunan Province of China. Affected family members displayed an uncommon clinical presentation of serious cardiac conduction abnormalities at an early age and a high incidence of sudden cardiac death along with mild skeletal muscular atrophy and joint contracture. Clinical analysis of affected members provided evidence of X-linked recessive inheritance. Consequently, using Sanger sequencing of X chromosome exomes, we identified a novel duplication mutation (c.405dup/p.Asp136X) in the EMD gene as the cause for the disease in this family. This variant is a novel mutation that has not been previously reported in Pubmed, Clinvar or other cases reported in the Human Gene Mutation Database.

Conclusion

Our finding expands the mutation spectrum of Emery-Dreifuss muscular dystrophy and provides a rationale for EMD mutation testing in cases of X-linked inherited cardiac conduction disease and sudden cardiac death, even in those lacking pathognomonic neuromuscular features.

Clinical aspects of Emery-Dreifuss muscular dystrophy

Emery-Dreifuss muscular dystrophy (EDMD), clinically characterized by scapulo-humero-peroneal muscle atrophy and weakness, multi-joint contractures with spine rigidity and cardiomyopathy with conduction defects, is associated with structural/functional defect of genes that encode the proteins of nuclear envelope, including lamin A and several lamin-interacting proteins. This paper presents clinical aspects of EDMD in context to causative genes, genotype-phenotype correlation and its emplacement within phenotypic spectrum of skeletal muscle diseases associated with envelopathies.

Proteomic mapping by rapamycin-dependent targeting of APEX2 identifies binding partners of VAPB at the inner nuclear membrane

Vesicle-associated membrane protein-associated protein B (VAPB) is a tail-anchored protein that is present at several contact sites of the endoplasmic reticulum (ER). We now show by immunoelectron microscopy that VAPB also localizes to the inner nuclear membrane (INM). Using a modified enhanced ascorbate peroxidase 2 (APEX2) approach with rapamycin-dependent targeting of the peroxidase to a protein of interest, we searched for proteins that are in close proximity to VAPB, particularly at the INM. In combination with stable isotope labeling with amino acids in cell culture (SILAC), we confirmed many well-known interaction partners at the level of the ER with a clear distinction between specific and nonspecific hits. Furthermore, we identified emerin, TMEM43, and ELYS as potential interaction partners of VAPB at the INM and the nuclear pore complex, respectively.

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 K37 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 K37. 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 K37 is to perturb emerin function within the LINC complex in response to mechanical stress.

Rare BANF1 Alleles and Relatively Frequent EMD Alleles Including 'Healthy Lipid' Emerin p.D149H in the ExAC Cohort

Emerin (EMD) and barrier to autointegration factor 1 (BANF1) each bind A-type lamins (LMNA) as fundamental components of nuclear lamina structure. Mutations in LMNA, EMD and BANF1 are genetically linked to many tissue-specific disorders including Emery-Dreifuss muscular dystrophy and cardiomyopathy (LMNA, EMD), lipodystrophy, insulin resistance and type 2 diabetes (LMNA) and progeria (LMNA, BANF1). To explore human genetic variation in these genes, we analyzed EMD and BANF1 alleles in the Exome Aggregation Consortium (ExAC) cohort of 60,706 unrelated individuals. We identified 13 rare heterozygous BANF1 missense variants (p.T2S, p.H7Y, p.D9N, p.S22R, p.G25E, p.D55N, p.D57Y, p.L63P, p.N70T, p.K72R, p.R75W, p.R75Q, p.G79R), and one homozygous variant (p.D9H). Several variants are known (p.G25E) or predicted (e.g., p.D9H, p.D9N, p.L63P) to perturb BANF1 and warrant further study. Analysis of EMD revealed two previously identified variants associated with adult-onset cardiomyopathy (p.K37del, p.E35K) and one deemed 'benign' in an Emery-Dreifuss patient (p.D149H). Interestingly p.D149H was the most frequent emerin variant in ExAC, identified in 58 individuals (overall allele frequency 0.06645%), of whom 55 were East Asian (allele frequency 0.8297%). Furthermore, p.D149H associated with four 'healthy' traits: reduced triglycerides (-0.336; p = 0.0368), reduced waist circumference (-0.321; p = 0.0486), reduced cholesterol (-0.572; p = 0.000346) and reduced LDL cholesterol (-0.599; p = 0.000272). These traits are distinct from LMNA-associated metabolic disorders and provide the first insight that emerin influences metabolism. We also identified one novel in-frame deletion (p.F39del) and 62 novel emerin missense variants, many of which were relatively frequent and potentially disruptive including p.N91S and p.S143F (∼0.041% and ∼0.034% of non-Finnish Europeans, respectively), p.G156S (∼0.39% of Africans), p.R204G (∼0.18% of Latinx), p.R207P (∼0.08% of South Asians) and p.R221L (∼0.15% of Latinx). Many novel BANF1 variants are predicted to disrupt dimerization or binding to DNA, histones, emerin or A-type lamins. Many novel emerin variants are predicted to disrupt emerin filament dynamics or binding to BANF1, HDAC3, A-type lamins or other partners. These new human variants provide a foundational resource for future studies to test the molecular mechanisms of BANF1 and emerin function, and to understand the link between emerin variant p.D149H and a 'healthy' lipid profile.

Emerin Is Required for Proper Nucleus Reassembly after Mitosis: Implications for New Pathogenetic Mechanisms for Laminopathies Detected in EDMD1 Patients

Emerin is an essential LEM (LAP2, Emerin, MAN1) domain protein in metazoans and an integral membrane protein associated with inner and outer nuclear membranes. Mutations in the human EMD gene coding for emerin result in the rare genetic disorder: Emery–Dreifuss muscular dystrophy type 1 (EDMD1). This disease belongs to a broader group called laminopathies—a heterogeneous group of rare genetic disorders affecting tissues of mesodermal origin. EDMD1 phenotype is characterized by progressive muscle wasting, contractures of the elbow and Achilles tendons, and cardiac conduction defects. Emerin is involved in many cellular and intranuclear processes through interactions with several partners: lamins; barrier-to-autointegration factor (BAF), β-catenin, actin, and tubulin. Our study demonstrates the presence of the emerin fraction which associates with mitotic spindle microtubules and centrosomes during mitosis and colocalizes during early mitosis with lamin A/C, BAF, and membranes at the mitotic spindle. Transfection studies with cells expressing EGFP-emerin protein demonstrate that the emerin fusion protein fraction also localizes to centrosomes and mitotic spindle microtubules during mitosis. Transient expression of emerin deletion mutants revealed that the resulting phenotypes vary and are mutant dependent. The most frequent phenotypes include aberrant nuclear shape, tubulin network mislocalization, aberrant mitosis, and mislocalization of centrosomes. Emerin deletion mutants demonstrated different chromatin binding capacities in an in vitro nuclear assembly assay and chromatin-binding properties correlated with the strength of phenotypic alteration in transfected cells. Aberrant tubulin staining and microtubule network phenotype appearance depended on the presence of the tubulin binding region in the expressed deletion mutants. We believe that the association with tubulin might help to “deliver” emerin and associated membranes to decondensing chromatin. Preliminary analyses of cells from Polish patients with EDMD1 revealed that for several mutations thought to be null for emerin protein, a truncated emerin protein was present. We infer that the EDMD1 phenotype may be strengthened by the toxicity of truncated emerin expressed in patients with certain nonsense mutations in EMD.

Image analysis of the nuclear characteristics of emerin protein and the correlation with nuclear grooves and intranuclear cytoplasmic inclusions in lung adenocarcinoma

Nuclear size and shape are important components in the diagnosis of pathological specimens. However, a qualitative evaluation is typically applied rather than a quantitative evaluation technique. In the present study, we sought to evaluate the nuclear morphological characteristics of lung adenocarcinoma using whole-slide imaging (WSI) and computer-assisted image analysis (IA). We evaluated the nuclear characteristics of 106 cases of surgically resected lung adenocarcinoma according to Feulgen staining and immunohistochemistry (IHC) for the inner nuclear membrane protein emerin. According to the Feulgen reaction, although the nuclear area (size) of the carcinoma cells was correlated with the nuclear perimeter (NP) (R=0.8973), the nuclear staining intensity of carcinoma cells was not correlated with the nuclear area. Using emerin IHC, we used IA software that was able to detect both the NP and the emerin-stained nuclear membrane length (ENML) in the nucleus, and found that the more nuclei exhibited a longer ENML relative to the NP, the more nuclear grooves and intranuclear cytoplasmic inclusions were present. In addition, the nuclear area was correlated with the percentage of nuclei that had a longer ENML compared to the NP against the total nuclei (R=0.7759). Furthermore, the emerin low expression group showed an enlarged nuclear area (P=0.0264), elongated NP (P=0.0091), and lower shape factor (P=0.0486) compared with the normal emerin expression group. Our data indicated the usefulness of WSI and IA for pathological specimen analysis. In addition, this study is the first to report that the low expression of emerin in cancer cell results in an oval shape of nuclei and nuclear enlargement in clinical samples.

The Pathogenesis and Therapies of Striated Muscle Laminopathies

Emery-Dreifuss muscular dystrophy (EDMD) is a genetic condition characterized by early contractures, skeletal muscle weakness, and cardiomyopathy. During the last 20 years, various genetic approaches led to the identification of causal genes of EDMD and related disorders, all encoding nuclear envelope proteins. By their respective localization either at the inner nuclear membrane or the outer nuclear membrane, these proteins interact with each other and establish a connection between the nucleus and the cytoskeleton. Beside this physical link, these proteins are also involved in mechanotransduction, responding to environmental cues, such as increased tension of the cytoskeleton, by the activation or repression of specific sets of genes. This ability of cells to adapt to environmental conditions is altered in EDMD. Increased knowledge on the pathophysiology of EDMD has led to the development of drug or gene therapies that have been tested on mouse models. This review proposed an overview of the functions played by the different proteins involved in EDMD and related disorders and the current therapeutic approaches tested so far.

Risk stratification in laminopathies and Emery Dreifuss muscular dystrophy

Laminopathies are genetic disorders due to gene mutation encoding for proteins of the nuclear envelope. Patients are at risk of conduction defect, arrhythmia, sudden death and heart failure. The authors summarize predictive factors for cardiac events reported in the literature in this group of disease.

FHL1B Interacts with Lamin A/C and Emerin at the Nuclear Lamina and is Misregulated in Emery-Dreifuss Muscular Dystrophy

BACKGROUND

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 a nuclear 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.

OBJECTIVE

To gain insight into the pathophysiology of EDMD, we focused our attention on the poorly characterized FHL1B isoform.

METHODS

The amount and the localisation of FHL1B were evaluated in control and diseased human primary myoblasts using immunofluorescence and western blotting.

RESULTS

We found that in addition to a cytoplasmic 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 a major 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.

CONCLUSIONS

Altogether, the specific localization of FHL1B and its modulation in disease-patient's myoblasts confirmed FHL1-related EDMD as a nuclear envelope disease.

Cardiolaminopathies from bench to bedside: challenges in clinical decision-making with focus on arrhythmia-related outcomes

Lamin A/C gene mutations can be associated with cardiac diseases, usually referred to as 'cardiolaminopathies' characterized by arrhythmic disorders and/or left ventricular or biventricular dysfunction up to an overt picture of heart failure. The phenotypic cardiac manifestations of laminopathies are frequently mixed in complex clinical patterns and specifically may include bradyarrhythmias (sinus node disease or atrioventricular blocks), atrial arrhythmias (atrial fibrillation, atrial flutter, atrial standstill), ventricular tachyarrhythmias and heart failure of variable degrees of severity. Family history, physical examination, laboratory findings (specifically serum creatine phosphokinase values) and ECG findings are often important 'red flags' in diagnosing a 'cardiolaminopathy'. Sudden arrhythmic death, thromboembolic events or stroke and severe heart failure requiring heart transplantation are the most dramatic complications of the evolution of cardiolaminopathies and appropriate risk stratification is clinically needed combined with clinical follow-up. Treatment with cardiac electrical implantable devices is indicated in case of bradyarrhythmias (implant of a device with pacemaker functions), risk of life-threatening ventricular tachyarrhythmias (implant of an ICD) or in case of heart failure with wide QRS interval (implant of a device for cardiac resynchronization). New technologies introduced in the last 5 years can help physicians to reduce device-related complications, thanks to the extension of device longevity and availability of leadless pacemakers or defibrillators, to be implanted in appropriately selected patients. An improved knowledge of the complex pathophysiological pathways involved in cardiolaminopathies and in the determinants of their progression to more severe forms will help to improve clinical management and to better target pharmacological and non-pharmacological treatments.

Expression Profiling of Differentiating Emerin-Null Myogenic Progenitor Identifies Molecular Pathways Implicated in Their Impaired Differentiation

Mutations in the gene encoding emerin cause Emery-Dreifuss muscular dystrophy (EDMD), a disorder causing progressive skeletal muscle wasting, irregular heart rhythms and contractures of major tendons. RNA sequencing was performed on differentiating wildtype and emerin-null myogenic progenitors to identify molecular pathways implicated in EDMD, 340 genes were uniquely differentially expressed during the transition from day 0 to day 1 in wildtype cells. 1605 genes were uniquely expressed in emerin-null cells; 1706 genes were shared among both wildtype and emerin-null cells. One thousand and forty-seven transcripts showed differential expression during the transition from day 1 to day 2. Four hundred and thirty-one transcripts showed altered expression in both wildtype and emerin-null cells. Two hundred and ninety-five transcripts were differentially expressed only in emerin-null cells and 321 transcripts were differentially expressed only in wildtype cells. DAVID, STRING and Ingenuity Pathway Analysis identified pathways implicated in impaired emerin-null differentiation, including cell signaling, cell cycle checkpoints, integrin signaling, YAP/TAZ signaling, stem cell differentiation, and multiple muscle development and myogenic differentiation pathways. Functional enrichment analysis showed biological functions associated with the growth of muscle tissue and myogenesis of skeletal muscle were inhibited. The large number of differentially expressed transcripts upon differentiation induction suggests emerin functions during transcriptional reprograming of progenitors to committed myoblasts.

Aged induced pluripotent stem cell (iPSCs) as a new cellular model for studying premature aging

Nuclear integrity and mechanical stability of the nuclear envelope (NE) are conferred by the nuclear lamina, a meshwork of intermediate filaments composed of A- and B-type lamins, supporting the inner nuclear membrane and playing a pivotal role in chromatin organization and epigenetic regulation. During cell senescence, nuclear alterations also involving NE architecture are widely described. In the present study, we utilized induced pluripotent stem cells (iPSCs) upon prolonged in vitro culture as a model to study aging and investigated the organization and expression pattern of NE major constituents. Confocal and four-dimensional imaging combined with molecular analyses, showed that aged iPSCs are characterized by nuclear dysmorphisms, nucleoskeletal components (lamin A/C-prelamin isoforms, lamin B1, emerin, and nesprin-2) imbalance, leading to impaired nucleo-cytoplasmic MKL1 shuttling, actin polymerization defects, mitochondrial dysfunctions, SIRT7 downregulation and NF-kBp65 hyperactivation. The observed age-related NE features of iPSCs closely resemble those reported for premature aging syndromes (e.g., Hutchinson-Gilford progeria syndrome) and for somatic cell senescence. These findings validate the use of aged iPSCs as a suitable cellular model to study senescence and for investigating therapeutic strategies aimed to treat premature aging.

Semaphorin 3A promotes activation of Pax7, Myf5, and MyoD through inhibition of emerin expression in activated satellite cells

We previously showed that Semaphorin 3A (Sema3A) expression was induced when quiescent muscle satellite cells were stimulated by hepatocyte growth factor and became activated satellite cells (ASCs). However, how Sema3A regulates genes in the early phase of ASCs remains unclear. In this study, we investigated whether Sema3A signaling can regulate the early phase of ASCs, an important satellite cell stage for postnatal growth, repair, and maintenance of skeletal muscle. We showed that expression of the myogenic proliferation regulatory factors Pax7 and Myf5 was decreased in myoblasts transfected with Sema3A siRNA. These cells failed to activate expression MyoD, another myogenic proliferation regulatory factor, during differentiation. Interestingly, some of the Sema3A-depleted cells did not express Pax7 and MyoD and had enlarged nuclei and very large cytoplasmic areas. We also observed that Pax7 and Myf5 expression was increased in Myc-Sema3A overexpressing myoblasts. BrdU analysis indicated that Sema3A regulated proliferation of ASCs. These findings suggest that Sema3A signaling can modulate expression of Pax7, Myf5, and MyoD. Moreover, we found that expression of emerin, an inner nuclear membrane protein, was regulated by Sema3A signaling. Emerin was identified by positional cloning as the gene responsible for the X-linked form of Emery-Dreifuss muscular dystrophy (X-EDMD). In conclusion, our results support a role for Sema3A in maintaining ASCs through regulation, via emerin, of Pax7, Myf5, and MyoD expression.

The nuclear lamina in health and disease

The nuclear lamina (NL) is a structural component of the nuclear envelope and makes extensive contacts with integral nuclear membrane proteins and chromatin. These interactions are critical for many cellular processes, such as nuclear positioning, perception of mechanical stimuli from the cell surface, nuclear stability, 3-dimensional organization of chromatin and regulation of chromatin-binding proteins, including transcription factors. The NL is present in all nucleated metazoan cells but its composition and interactome differ between tissues. Most likely, this contributes to the broad spectrum of disease manifestations in humans with mutations in NL-related genes, ranging from muscle dystrophies to neurological disorders, lipodystrophies and progeria syndromes. We review here exciting novel insight into NL function at the cellular level, in particular in chromatin organization and mechanosensation. We also present recent observations on the relation between the NL and metabolism and the special relevance of the NL in muscle tissues. Finally, we discuss new therapeutic approaches to treat NL-related diseases.

Nuclear envelope proteins modulate proliferation of vascular smooth muscle cells during cyclic stretch application

Cyclic stretch is an important inducer of vascular smooth muscle cell (VSMC) proliferation, which is crucial in vascular remodeling during hypertension. However, the molecular mechanism remains unclear. We studied the effects of emerin and lamin A/C, two important nuclear envelope proteins, on VSMC proliferation in hypertension and the underlying mechano-mechanisms. In common carotid artery of hypertensive rats in vivo and in cultured cells subjected to high (15%) cyclic stretch in vitro, VSMC proliferation was increased significantly, and the expression of emerin and lamin A/C was repressed compared with normotensive or normal (5%) cyclic stretch controls. Using targeted siRNA to mimic the repressed expression of emerin or lamin A/C induced by 15% stretch, we found that VSMC proliferation was enhanced under static and 5%-stretch conditions. Overexpression of emerin or lamin A/C reversed VSMC proliferation induced by 15% stretch. Hence, emerin and lamin A/C play critical roles in suppressing VSMC hyperproliferation induced by hyperstretch. ChIP-on-chip and MOTIF analyses showed that the DNAs binding with emerin contain three transcription factor motifs: CCNGGA, CCMGCC, and ABTTCCG; DNAs binding with lamin A/C contain the motifs CVGGAA, GCCGCYGC, and DAAGAAA. Protein/DNA array proved that altered emerin or lamin A/C expression modulated the activation of various transcription factors. Furthermore, accelerating local expression of emerin or lamin A/C reversed cell proliferation in the carotid artery of hypertensive rats in vivo. Our findings establish the pathogenetic role of emerin and lamin A/C repression in stretch-induced VSMC proliferation and suggest mechanobiological mechanism underlying this process that involves the sequence-specific binding of emerin and lamin A/C to specific transcription factor motifs.

Emery-Dreifuss muscular dystrophy: a test case for precision medicine

Emery-Dreifuss muscular dystrophy (EDMD) is characterized by the clinical triad of scapulohumeroperoneal muscle weakness, joint contractures, and cardiac defects that include arrhythmias and dilated cardiomyopathy. Although there is a defining group of clinical findings, the proteins responsible and their underlying gene defects leading to EDMD are varied. A common aspect of the gene defects is their involvement in, or with, the nuclear envelope. Treatment approaches are largely based on clinical symptoms. The genetic diversity of EDMD predicts that a cure will ultimately depend upon the individual's defect at the gene level, making this an ideal candidate for a precision medicine approach.

Sigma-1 receptor mediates cocaine-induced transcriptional regulation by recruiting chromatin-remodeling factors at the nuclear envelope

The sigma-1 receptor (Sig-1R) chaperone at the endoplasmic reticulum (ER) plays important roles in cellular regulation. Here we found a new function of Sig-1R, in that it translocates from the ER to the nuclear envelope (NE) to recruit chromatin-remodeling molecules and regulate the gene transcription thereof. Sig-1Rs mainly reside at the ER-mitochondrion interface. However, on stimulation by agonists such as cocaine, Sig-1Rs translocate from ER to the NE, where Sig-1Rs bind NE protein emerin and recruit chromatin-remodeling molecules, including lamin A/C, barrier-to-autointegration factor (BAF), and histone deacetylase (HDAC), to form a complex with the gene repressor specific protein 3 (Sp3). Knockdown of Sig-1Rs attenuates the complex formation. Cocaine was found to suppress the gene expression of monoamine oxidase B (MAOB) in the brain of wild-type but not Sig-1R knockout mouse. A single dose of cocaine (20 mg/kg) in rats suppresses the level of MAOB at nuclear accumbens without affecting the level of dopamine transporter. Daily injections of cocaine in rats caused behavioral sensitization. Withdrawal from cocaine in cocaine-sensitized rats induced an apparent time-dependent rebound of the MAOB protein level to about 200% over control on day 14 after withdrawal. Treatment of cocaine-withdrawn rats with the MAOB inhibitor deprenyl completely alleviated the behavioral sensitization to cocaine. Our results demonstrate a role of Sig-1R in transcriptional regulation and suggest cocaine may work through this newly discovered genomic action to achieve its addictive action. Results also suggest the MAOB inhibitor deprenyl as a therapeutic agent to block certain actions of cocaine during withdrawal.

LMO7-null mice exhibit phenotypes consistent with emery-dreifuss muscular dystrophy

INTRODUCTION

Mutations in the inner nuclear envelope protein emerin cause Emery-Dreifuss muscular dystrophy (EDMD), which is characterized by progressive skeletal muscle wasting, cardiac conduction defects, and tendon contractures. We previously showed that emerin binds directly to the transcription regulator Lmo7 and attenuates its activity to regulate the proper temporal expression of important myogenic differentiation genes.

METHODS

The skeletal muscle and cardiac phenotypes were analyzed in a newly generated Lmo7-null mouse using histological analysis, echocardiography, and various neuromuscular tests to determine if Lmo7 was important for skeletal muscle and cardiac function.

RESULTS

Lmo7-null mice had growth retardation, decreased fiber size, and impaired skeletal muscle and cardiac function. Lmo7-null mice also had lower levels of phosphorylated retinoblastoma (Rb), extracellular signal-regulated kinase, and c-Jun N-terminal kinase, which is consistent with altered Rb and mitogen-activated protein kinase signaling.

CONCLUSIONS

These findings demonstrate that loss of Lmo7 in mice causes myopathic phenotypes similar to those seen in other EDMD mouse models.

Nuclear localization signal deletion mutants of lamin A and progerin reveal insights into lamin A processing and emerin targeting

Lamin A is a major component of the lamina, which creates a dynamic network underneath the nuclear envelope. Mutations in the lamin A gene (LMNA) cause severe genetic disorders, one of which is Hutchinson-Gilford progeria syndrome (HGPS), a disease triggered by a dominant mutant named progerin. Unlike the wild-type lamin A, whose farnesylated C-terminus is excised during post-translational processing, progerin retains its farnesyl tail and accumulates on the nuclear membrane, resulting in abnormal nuclear morphology during interphase. In addition, membrane-associated progerin forms visible cytoplasmic aggregates in mitosis. To examine the potential effects of cytoplasmic progerin, nuclear localization signal (NLS) deleted progerin and lamin A (PGΔNLS and LAΔNLS, respectively) have been constructed. We find that both ΔNLS mutants are farnesylated in the cytosol and associate with a sub-domain of the ER via their farnesyl tails. While the farnesylation on LAΔNLS can be gradually removed, which leads to its subsequent release from the ER into the cytoplasm, PGΔNLS remains permanently farnesylated and membrane-bounded. Moreover, both ΔNLS mutants dominantly affect emerin’s nuclear localization. These results reveal new insights into lamin A biogenesis and lamin A-emerin interaction.

Heterogeneous Immunoreactivity of Emerin, a Nuclear Envelope LEM-domain Protein, in Normal Thyroid Follicles

Emerin is a LEM domain-containing integral membrane protein of the vertebrate nuclear envelope. Recently it has been reported that emerin regulates tissue-specific gene/protein expression. We studied the relationship between emerin expression and follicle function in normal and hyperplastic human thyroid tissues using immunohistochemistry and statistical methods. Emerin immunoreactivity was heterogeneous among follicular cells and follicles in normal thyroid tissue. It tended to be strong in the nuclei of tall follicular cells of small follicles and weak or negative in the nuclei of flat follicular cells of large follicles. Follicles with strong expression of emerin were also strongly positive for thyroglobulin (Tg) and thyroxine (T4) in follicular cells and colloid substance, suggesting active functioning follicles. In contrast, large follicles with weak expression of emerin were also weak or negative for Tg and T4. Emerin immunoreactivity was strong in almost all nuclei of hyperplastic follicular cells in Graves' disease tissues. These findings suggest that emerin expression may be related with follicular function and may contribute to the understanding of hormonogenesis in normal thyroid follicles.

The nuclear envelope LEM-domain protein emerin

Emerin, a conserved LEM-domain protein, is among the few nuclear membrane proteins for which extensive basic knowledge—biochemistry, partners, functions, localizations, posttranslational regulation, roles in development and links to human disease—is available. This review summarizes emerin and its emerging roles in nuclear “lamina” structure, chromatin tethering, gene regulation, mitosis, nuclear assembly, development, signaling and mechano-transduction. We also highlight many open questions, exploration of which will be critical to understand how this intriguing nuclear membrane protein and its “family” influence the genome.

The nuclear envelope protein emerin binds directly to histone deacetylase 3 (HDAC3) and activates HDAC3 activity

Organization of the genome is critical for maintaining cell-specific gene expression, ensuring proper cell function. It is well established that the nuclear lamina preferentially associates with repressed chromatin. However, the molecular mechanisms underlying repressive chromatin formation and maintenance at the nuclear lamina remain poorly understood. Here we show that emerin binds directly to HDAC3, the catalytic subunit of the nuclear co-repressor (NCoR) complex, and recruits HDAC3 to the nuclear periphery. Emerin binding stimulated the catalytic activity of HDAC3, and emerin-null cells exhibit increased H4K5 acetylation, which is the preferred target of the NCoR complex. Emerin-null cells exhibit an epigenetic signature similar to that seen in HDAC3-null cells. Emerin-null cells also had significantly less HDAC3 at the nuclear lamina. Collectively, these data support a model whereby emerin facilitates repressive chromatin formation at the nuclear periphery by increasing the catalytic activity of HDAC3.

Emerinopathy and laminopathy clinical, pathological and molecular features of muscular dystrophy with nuclear envelopathy in Japan

Mutations in the genes for nuclear envelope proteins of emerin (EMD) and lamin A/C (LMNA) are known to cause Emery-Dreifuss muscular dystrophy (EDMD) and limb girdle muscular dystrophy (LGMD). We compared clinical features of the muscular dystrophy patients associated with mutations in EMD (emerinopathy) and LMNA (laminopathy) in our series. The incidence of laminopathy was slightly higher than that of emerinopathy. The age at onset of the disease in emerinopathy was variable and significantly older than in laminopathy. The initial symptom of emerinopathy was also variable, whereas nearly all laminopathy patients presented initially with muscle weakness. Calf hypertrophy was often seen in laminopathy, underscoring the importance of mutation screening for LMNA in childhood muscular dystrophy with calf hypertrophy. The clinical spectrum of emerinopathy is actually wider than previously known including EDMD, LGMD, conduction defects with minimal muscle/joint involvement, and their intermittent forms. Pathologically, no marked difference was observed between emerinopathy and laminopathy. Increased number and variation in size of myonuclei were detected. More precise observations using electron microscopy is warranted to characterize the detailed nuclear changes in nuclear envelopathy.

Cardiac dysrhythmias,cardiomyopathy and muscular dystrophy in patients with Emery-Dreifuss muscular dystrophy and limb-girdle muscular dystrophy type 1B

Emery-Dreifuss muscular dystrophy (EDMD) and limb-girdle muscular dystrophy type 1B (LGMD1B) are characterized by cardiac dysrhythmias, late-onset cardiomyopathy, slowly progressive skeletal myopathy and contractures of the neck, elbows and ankles. The causative mutation is either in the emerin gene (X-linked recessive EDMD) or lamin A/C gene (autosomal dominant EDMD2 or LGMD1B). We report three cases of EDMD, EDMD2 and LGMD1B. A 14-yr-old boy showed limitation of cervical flexion and contractures of both elbows and ankles. Sinus arrest with junctional escape beats was noted. He was diagnosed as X-linked recessive EDMD (MIM 310300). A 28-yr-old female showed severe wasting and weakness of humeroperoneal muscles. Marked limitation of cervical flexion and contractures of both elbows and ankles were noted. Varying degrees of AV block were noted. She was diagnosed as autosomal dominant EDMD2 (MIM 181350). A 41-yr-old female had contractures of both ankles and limb-girdle type muscular dystrophy. ECG revealed atrial tachycardia with high grade AV block. She was diagnosed as autosomal dominant LGMD1B (MIM 159001). Cardiac dysrhythmias in EDMD and LGMD1B include AV block, bradycardia, atrial tachycardia, atrial fibrillation, and atrial standstill, causing sudden death necessitating pacemaker implantation. Cardiologists should know about these unusual genetic diseases with conduction defects, especially in young adults.