Proteomic characterization of human LMNA-related congenital muscular dystrophy muscle cells

LMNA-related congenital muscular dystrophy (L-CMD) is caused by mutations in the LMNA gene, encoding lamin A/C. To further understand the molecular mechanisms of L-CMD, proteomic profiling using DIA mass spectrometry was conducted on immortalized myoblasts and myotubes from controls and L-CMD donors each harbouring a different LMNA mutation (R249W, del.32 K and L380S). Compared to controls, 124 and 228 differentially abundant proteins were detected in L-CMD myoblasts and myotubes, respectively, and were associated with enriched canonical pathways including synaptogenesis and necroptosis in myoblasts, and Huntington's disease and insulin secretion in myotubes. Abnormal nuclear morphology and reduced lamin A/C and emerin abundance was evident in all L-CMD cell lines compared to controls, while nucleoplasmic aggregation of lamin A/C was restricted to del.32 K cells, and mislocalization of emerin was restricted to R249W cells. Abnormal nuclear morphology indicates loss of nuclear lamina integrity as a common feature of L-CMD, likely rendering muscle cells vulnerable to mechanically induced stress, while differences between L-CMD cell lines in emerin and lamin A localization suggests that some molecular alterations in L-CMD are mutation specific. Nonetheless, identifying common proteomic alterations and molecular pathways across all three L-CMD lines has highlighted potential targets for the development of non-mutation specific therapies.

Effect of β-Estradiol on Adipogenesis in a 3T3-L1 Cell Model of Prelamin A Accumulation

The accumulation of farnesylated prelamin A has been suggested as one of the mechanisms responsible for the loss of fat in type 2 familial partial lipodystrophy due to variants in the LMNA gene. In this rare disease, fat loss appears in women after puberty, affecting sex-hormone-dependent anatomical areas. This study investigated the impact of 17-β-estradiol on adipogenesis in murine preadipocytes subjected to a pharmacologically induced accumulation of farnesylated and non-farnesylated prelamin A. To induce the accumulation of non-farnesylated or farnesylated prelamin A, 3T3-L1 cells were treated with the farnesyltransferase inhibitor 277 or the methyltransferase inhibitor N-acetyl-S-farnesyl-l-cysteine methylester. Subsequently, the cells were induced to undergo adipocyte differentiation in the presence or absence of 17-β-estradiol. Prelamin A accumulation was assessed through immunofluorescence, while real-time PCR and Western blot techniques were used to quantify several adipogenic genes and evaluate protein levels, respectively. The results showed that 17-β-estradiol increased adipogenesis, although the combination of this hormone plus farnesylated prelamin A led to a reduction in the number of mature adipocytes and the expression of the different genes involved in adipogenesis. In conclusion, the influence of farnesylated prelamin A accumulation on adipogenesis manifested only in the presence of estradiol. These in vitro findings suggest a potential mechanism that could explain the characteristic phenotype in women suffering type 2 familial partial lipodystrophy.

Nuclear Abnormalities in LMNA p.(Glu2Lys) Variant Segregating with LMNA-Associated Cardiocutaneous Progeria Syndrome

The LMNA gene encodes lamin A and lamin C, which play important roles in nuclear organization. Pathogenic variants in LMNA cause laminopathies, a group of disorders with diverse phenotypes. There are two main groups of disease-causing variants: missense variants affecting dimerization and intermolecular interactions, and heterozygous substitutions activating cryptic splice sites. These variants lead to different disorders, such as dilated cardiomyopathy and Hutchinson-Gilford progeria (HGP). Among these, the phenotypic terms for LMNA-associated cardiocutaneous progeria syndrome (LCPS), which does not alter lamin A processing and has an older age of onset, have been described. Here, we present the workup of an LMNA variant of uncertain significance, NM_170707.2 c. 4G>A, p.(Glu2Lys), in a 36-year-old female with severe calcific aortic stenosis, a calcified mitral valve, premature aging, and a family history of similar symptoms. Due to the uncertainty of in silico predictions for this variant, an assessment of nuclear morphology was performed using the immunocytochemistry of stable cell lines to indicate whether the p.(Glu2Lys) had a similar pathogenic mechanism as a previously described pathogenic variant associated with LCPS, p.Asp300Gly. Indirect immunofluorescence analysis of nuclei from stable cell lines showed abnormal morphology, including lobulation and occasional ringed nuclei. Relative to the controls, p.Glu2Lys and p.Asp300Gly nuclei had significantly (p < 0.001) smaller average nuclear areas than controls (mean = 0.10 units, SD = 0.06 for p.Glu2Lys; and mean = 0.09 units, SD = 0.05 for p.Asp300Gly versus mean = 0.12, SD = 0.05 for WT). After functional studies and segregation studies, this variant was upgraded to likely pathogenic. In summary, our findings suggest that p.Glu2Lys impacts nuclear morphology in a manner comparable to what was observed in p.Asp300Gly cells, indicating that the variant is the likely cause of the LCPS segregating within this family.

Characterization of cardiac involvement in patients with LMNA splice-site mutation-related dilated cardiomyopathy and sudden cardiac death

Introduction: LMNA splicing mutations occur in 9.1% of cases with cardiac involvement cases, but the phenotype and severity of disease they cause have not yet been systematically studied. The aim of this study was to understand the clinical and pathogenic characteristics of the LMNA splice-site mutation phenotype in patients with LMNA-related dilated cardiomyopathy (DCM) and sudden cardiac death (SCD). Methods and Results: First, we reported a novel family with LMNA-related DCM and SCD, and the clinical characteristics of all current patients with LMNA splicing mutations were further summarized through the ClinVar database. Seventeen families with a total of 134 individuals, containing a total of 15 LMNA splicing mutation sites, were enrolled. A total of 42 subjects (31.3%) had SCD. Compared without with the non-DCM group (n = 56), the patients within the DCM group (n = 78) presented a lower incidence of atrioventricular block (AVB) (p = 0.015) and a higher incidence rates of non-sustained ventricular tachycardia (p = 0.004),) and implantable cardioverter defibrillator (ICD) implantation (p = 0.005). Kaplan‒Meier survival analysis showed that the patients with pacemaker (PM) implantation had a significantly reduced the occurrence of SCD compared to patientswith those without PM implantation (log-rank p < 0.001), while there was no significant difference in ICD implantation between the two groups (log-rank p = 0.73). Second, we identified the family that we reported with a mutation in an LMNA c.513+1 G>A mutation in the reported family, and pathogenic prediction analysis showed that the mutation site was extremely harmful. Next, we conducted gene expression levels and cardiac pathological biopsy studies on the proband of this family. We found that the expression of normal LMNA mRNA from the proband was significantly downregulated in peripheral blood mononuclear cells than incompared with healthy individuals. Finally, we comprehensively summarized the pathological characteristics of LMNA-related DCM, including hypertrophy, atrophy, fibrosis, white blood cell infiltration, intercalated disc remodeling, and downregulation of desmin and connexin 43 (Cx43) expression. Discussion: Above all, Cardiaccardiac involvement in patients with LMNA splice-site mutation presented with a high rate of SCD. Implanting a pacemaker significantly reduced the SCD rate in non-DCM patients with AVB. The pathogenic characterization was not only haveinvolved suppressed the expression of the healthy LMNA allele, but was also associated with abnormal expression and distribution of desmin and Cx43.

The upregulation of lamin A/C as a compensatory mechanism during tight junction disruption in renal tubular cells mediated by calcium oxalate crystals

Calcium oxalate monohydrate (COM), the most important crystal causing kidney stone disease, upregulates lamin A/C but downregulates zonula occludens-1 (ZO-1) in renal tubular cells. While roles for F-actin and α-tubulin and their association with ZO-1 are known to regulate COM-mediated tight junction (TJ) disruption, roles of lamin A/C and its interplay with ZO-1 in COM kidney stone model remain unclear and are thus the objectives of this study. Lamin A/C was knocked down in MDCK cells by silencing RNA specific for LMNA (siLMNA). Both wild-type (WT) and siLMNA cells were treated with COM for 48-h compared with the untreated (control) cells. Western blotting and immunofluorescence staining revealed upregulated lamin A/C and downregulated ZO-1 in the COM-treated WT cells. siLMNA successfully reduced lamin A/C expression in both control and COM-treated cells. Nonetheless, siLMNA did not reverse the effect of COM on the decreases in ZO-1 and transepithelial resistance, but further reduced their levels in both control and COM-treated cells. Protein-protein interaction analysis demonstrated that two cytoskeletal proteins (actin and tubulin) served as the linkers to connect lamin A/C with ZO-1 and occludin (both of which are the TJ proteins). Altogether, these data implicate that lamin A/C and ZO-1 are indirectly associated to control TJ function, and ZO-1 expression is regulated by lamin A/C. Moreover, COM-induced upregulation of lamin A/C most likely serves as a compensatory mechanism to cope with the downregulation of ZO-1 during COM-mediated TJ disruption.

Knockdown of LMNA inhibits Akt/β-catenin-mediated cell invasion and migration in clear cell renal cell carcinoma cells

The LMNA gene encoding lamin A/C is amplified in some clear cell renal cell carcinoma (ccRCC) samples. Our data showed that depletion of the tumor suppressor PBRM1 can upregulate lamin A/C levels, and lamin A/C could interact with PBRM1. However, the role of lamin A/C in ccRCC is not yet fully understood. Our functional assays showed that although the proliferation ability was slightly impaired after LMNA depletion, the migration and invasion of ccRCC cells were significantly inhibited. This suppression was accompanied by a reduction in MMP2, MMP9, AKT/p-AKT, and Wnt/β-catenin protein levels. Our data therefore suggest that lamin A/C, as an interaction partner of the tumor suppressor PBRM1, plays a crucial role in tumor invasion and metastasis in ccRCC.

An alpha-helix variant p.Arg156Pro in LMNA as a cause of hereditary dilated cardiomyopathy: genetics and bioinfomatics exploration

LMNA gene encodes lamin A/C protein which participates in the construction of nuclear lamina, the mutations of LMNA result in a wide variety of diseases known as laminopathies. LMNA-related dilated cardiomyopathy(LMNA-DCM) is one of the more common laminopathy which characterized by progressive heart failure and arrhythmia. However, the mutation features of LMNA-DCM are yet to be elucidated. Herein we described a dilated cardiomyopathy family carrying novel variant c.467G > C(p.Arg156Pro) of LMNA as heterozygous pathogenic variant identified by whole-exome sequencing. With the help of Alphafold2, we predicted mutant protein structure and found an interrupted α-helix region in lamin A/C. In the analysis of 49 confirmed pathogenic missense of laminopathies, Chi-square test showed the DCM phenotype was related to the α-helix region mutation (p < 0.017). After screening the differentially expressed genes (DEGs) in both mice models and human patients in Gene Expression Omnibus database, we found the variation of α-helix-coding region in LMNA caused abnormal transcriptomic features in cell migration, collagen-containing extracellular matrix, and PI3K-Akt signaling pathway. Subsequently we constructed (TF)-mRNA-microRNA (miRNA) regulatory network and identified 7 key genes (FMOD, CYP1B1, CA3, F2RL1, HAPLIN1, SNAP91, and KANSL1) as potential biomarkers or therapeutic targets in LMNA-DCM patients.

Med25 Limits Master Regulators That Govern Adipogenesis

Mediator 25 (Med25) is a member of the mediator complex that relays signals from transcription factors to the RNA polymerase II machinery. Multiple transcription factors, particularly those involved in lipid metabolism, utilize the mediator complex, but how Med25 is involved in this context is unclear. We previously identified Med25 in a translatome screen of adult cardiomyocytes (CMs) in a novel cell type-specific model of LMNA cardiomyopathy. In this study, we show that Med25 upregulation is coincident with myocardial lipid accumulation. To ascertain the role of Med25 in lipid accumulation, we utilized iPSC-derived and neonatal CMs to recapitulate the in vivo phenotype by depleting lamins A and C (lamin A/C) in vitro. Although lamin A/C depletion elicits lipid accumulation, this effect appears to be mediated by divergent mechanisms dependent on the CM developmental state. To directly investigate Med25 in lipid accumulation, we induced adipogenesis in Med25-silenced 3T3-L1 preadipocytes and detected enhanced lipid accumulation. Assessment of pertinent mediators driving adipogenesis revealed that C/EBPα and PPARγ are super-induced by Med25 silencing. Our results indicate that Med25 limits adipogenic potential by suppressing the levels of master regulators that govern adipogenesis. Furthermore, we caution the use of early-developmental-stage cardiomyocytes to model adult-stage cells, particularly for dissecting metabolic perturbations emanating from LMNA mutations.

Epigenetics in LMNA-Related Cardiomyopathy

Mutations in the gene for lamin A/C (LMNA) cause a diverse range of diseases known as laminopathies. LMNA-related cardiomyopathy is a common inherited heart disease and is highly penetrant with a poor prognosis. In the past years, numerous investigations using mouse models, stem cell technologies, and patient samples have characterized the phenotypic diversity caused by specific LMNA variants and contributed to understanding the molecular mechanisms underlying the pathogenesis of heart disease. As a component of the nuclear envelope, LMNA regulates nuclear mechanostability and function, chromatin organization, and gene transcription. This review will focus on the different cardiomyopathies caused by LMNA mutations, address the role of LMNA in chromatin organization and gene regulation, and discuss how these processes go awry in heart disease.

Clinical Spectrum of LMNA-Associated Type 2 Familial Partial Lipodystrophy: A Systematic Review

Type 2 familial partial lipodystrophy (FPLD2) is a laminopathic lipodystrophy due to pathogenic variants in the LMNA gene. Its rarity implies that it is not well-known. The aim of this review was to explore the published data regarding the clinical characterisation of this syndrome in order to better describe FPLD2. For this purpose, a systematic review through a search on PubMed until December 2022 was conducted and the references of the retrieved articles were also screened. A total of 113 articles were included. FPLD2 is characterised by the loss of fat starting around puberty in women, affecting limbs and trunk, and its accumulation in the face, neck and abdominal viscera. This adipose tissue dysfunction conditions the development of metabolic complications associated with insulin resistance, such as diabetes, dyslipidaemia, fatty liver disease, cardiovascular disease, and reproductive disorders. However, a great degree of phenotypical variability has been described. Therapeutic approaches are directed towards the associated comorbidities, and recent treatment modalities have been explored. A comprehensive comparison between FPLD2 and other FPLD subtypes can also be found in the present review. This review aimed to contribute towards augmenting knowledge of the natural history of FPLD2 by bringing together the main clinical research in this field.

Genomic analysis of a novel pathogenic variant in the gene LMNA associated with cardiac laminopathies found in Ecuadorian siblings: A case report

Introduction

Cardiac laminopathies are caused by mutations in the LMNA gene and include a wide range of clinical manifestations involving electrical and mechanical changes in cardiomyocytes. In Ecuador, cardiovascular diseases were the primary cause of death in 2019, accounting for 26.5% of total deaths. Cardiac laminopathy-associated mutations involve genes coding for structural proteins with functions related to heart development and physiology.

Family description

Two Ecuadorian siblings, self-identified as mestizos, were diagnosed with cardiac laminopathies and suffered embolic strokes. Moreover, by performing Next-Generation Sequencing, a pathogenic variant (NM_170707.3:c.1526del) was found in the gene LMNA.

Discussion and conclusion

Currently, genetic tests are an essential step for disease genetic counseling, including cardiovascular disease diagnosis. Identification of a genetic cause that may explain the risk of cardiac laminopathies in a family can help the post-test counseling and recommendations from the cardiologist. In the present report, a pathogenic variant ((NM_170707.3:c.1526del) has been identified in two Ecuadorian siblings with cardiac laminopathies. The LMNA gene codes for A-type laminar proteins that are associated with gene transcription regulation. Mutations in the LMNA gene cause laminopathies, disorders with diverse phenotypic manifestations. Moreover, understanding the molecular biology of the disease-causing mutations is essential in deciding the correct type of treatment.

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.

Loss of Mature Lamin A/C Triggers a Shift in Intracellular Metabolic Homeostasis via AMPKα Activation

The roles of lamin A/C in adipocyte differentiation and skeletal muscle lipid metabolism are associated with familial partial lipodystrophy of Dunnigan (FPLD). We confirmed that LMNA knockdown (KD) in mouse adipose-derived mesenchymal stem cells (AD-MSCs) prevented adipocyte maturation. Importantly, in in vitro experiments, we discovered a significant increase in phosphorylated lamin A/C levels at serine 22 or 392 sites (pLamin A/C-S22/392) accompanying increased lipid synthesis in a liver cell line (7701 cells) and two hepatocellular carcinoma (HCC) cell lines (HepG2 and MHCC97-H cells). Moreover, HCC cells did not survive after LMNA knockout (KO) or even KD. Evidently, the functions of lamin A/C differ between the liver and adipose tissue. To date, the mechanism of hepatocyte lipid metabolism mediated by nuclear lamin A/C remains unclear. Our in-depth study aimed to identify the molecular connection between lamin A/C and pLamin A/C, hepatic lipid metabolism and liver cancer. Gain- and loss-of-function experiments were performed to investigate functional changes and the related molecular pathways in 7701 cells. Adenosine 5' monophosphate-activated protein kinase α (AMPKα) was activated when abnormalities in functional lamin A/C were observed following lamin A/C depletion or farnesyltransferase inhibitor (FTI) treatment. Active AMPKα directly phosphorylated acetyl-CoA-carboxylase 1 (ACC1) and subsequently inhibited lipid synthesis but induced glycolysis in both HCC cells and normal cells. According to the mass spectrometry analysis, lamin A/C potentially regulated AMPKα activation through its chaperone proteins, ATPase or ADP/ATP transporter 2. Lonafarnib (an FTI) combined with low-glucose conditions significantly decreased the proliferation of the two HCC cell lines more efficiently than lonafarnib alone by inhibiting glycolysis or the maturation of prelamin A.

LMNA Reduced Acquired Resistance to Erlotinib in NSCLC by Reversing the Epithelial-Mesenchymal Transition via the FGFR/MAPK/c-fos Signaling Pathway

For patients exhibiting non-small-cell lung cancer (NSCLC) with activating epidermal growth factor receptor (EGFR) mutations, epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) are a first-line treatment. However, most patients who initially responded to EGFR-TKIs eventually developed acquired resistance, limiting the effectiveness of therapy. It has long been known that epithelial-mesenchymal transition (EMT) leads to acquired resistance to EGFR-TKIs in NSCLC. However, the mechanisms underlying the resistance dependent on EMT are unknown. This research aimed to reveal the effects of LMNA in the regulation of acquired resistance to erlotinib by EMT in NSCLC. The acquired erlotinib-resistant cells (HCC827/ER) were induced by gradual increase of concentrations of erlotinib in erlotinib-sensitive HCC827 cells. RNA sequencing and bioinformatics analysis were performed to uncover the involvement of LMNA in the EMT process that induced acquired resistance to erlotinib. The effect of LMNA on cell proliferation and migration was measured by clone-formation, wound-healing, and transwell assays, respectively. The EMT-related protein, nuclear shape and volume, and cytoskeleton changes were examined by immunofluorescence. Western blot was used to identify the underlying molecular mechanism of LMNA regulation of EMT. HCC827/ER cells with acquired resistance to erlotinib underwent EMT and exhibited lower LMNA expression compared to parental sensitive cells. LMNA negatively regulated the expression of EMT markers; HCC827/ER cells showed a significant up-regulation of mesenchymal markers, such as CDH2, SNAI2, VIM, ZEB1, and TWIST1. The overexpression of LMNA in HCC827/ER cells significantly inhibited EMT and cell proliferation, and this inhibitory effect of LMNA was enhanced in the presence of 2.5 μM erlotinib. Furthermore, a decrease in LMNA expression resulted in a higher nuclear deformability and cytoskeletal changes. In HCC827/ER cells, AKT, FGFR, ERK1/2, and c-fos phosphorylation levels were higher than those in HCC827 cells; Furthermore, overexpression of LMNA in HCC827/ER cells reduced the phosphorylation of AKT, ERK1/2, c-fos, and FGFR. In conclusion, our findings first demonstrated that downregulation of LMNA promotes acquired EGFR-TKI resistance in NSCLC with EGFR mutations by EMT. LMNA inhibits cell proliferation and migration of erlotinib-resistant cells via inhibition of the FGFR/MAPK/c-fos signaling pathway. These findings indicated LMNA as a driver of acquired resistance to erlotinib and provided important information about the development of resistance to erlotinib treatment in NSCLC patients with EGFR mutations.

Autosomal dominant Emery-Dreifuss muscular dystrophy caused by a mutation in the lamin A/C gene identified by exome sequencing: a case report

Background

Emery-Dreifuss Muscular Dystrophy (EDMD) is an uncommon genetic disease among the group of muscular dystrophies. EDMD is clinically heterogeneous and resembles other muscular dystrophies. Mutation of the lamin A/C (LMNA) gene, which causes EDMD, also causes many other diseases. There is inter and intrafamilial variability in clinical presentations. Precise diagnosis can help in patient surveillance, especially before they present with cardiac problems. Hence, this paper shows how a molecular work-out by next-generation sequencing can help this group of disorders.

Case presentation

A 2-year-10-month-old Javanese boy presented to our clinic with weakness in lower limbs and difficulty climbing stairs. The clinical features of the boy were Gower's sign, waddling gait and high CK level. His father presented with elbow contractures and heels, toe walking and weakness of limbs, pelvic, and peroneus muscles. Exome sequencing on this patient detected a pathogenic variant in the LMNA gene (NM_170707: c.C1357T: NP_733821: p.Arg453Trp) that has been reported to cause Autosomal Dominant Emery-Dreifuss muscular dystrophy. Further examination showed total atrioventricular block and atrial fibrillation in the father.

Conclusion

EDMD is a rare disabling muscular disease that poses a diagnostic challenge. Family history work-up and thorough neuromuscular physical examinations are needed. Early diagnosis is essential to recognize orthopaedic and cardiac complications, improving the clinical management and prognosis of the disease. Exome sequencing could successfully determine pathogenic variants to provide a conclusive diagnosis.

The most severe form of LMNA-associated congenital muscular dystrophy

Alterations in the LMNA gene cause a wide spectrum of diseases collectively called laminopathies. LMNA-associated congenital muscular dystrophy is a form of laminopathy, which usually causes infantile onset of muscle weakness, predominantly in the cervical-axial muscles, and motor developmental retardation. Cardiac symptoms during the first decade of life are rare. We report a case of LMNA-associated congenital muscular dystrophy in which the patient did not achieve head control and experienced facial muscle weakness. Cardiac dysrhythmias were observed at 5 years with development of dilated cardiomyopathy and ischemic strokes at 7 years. Despite intensive medical intervention, he died suddenly at 9 years. This report broadens the spectrum of phenotypes of this disorder with the most severe symptoms during the first decade of life. Our case underscores the need for early genetic testing for LMNA in patients with congenital muscular dystrophy to screen for cardiac manifestations and intervene as necessary.

A Novel Type I Interferon Primed Dendritic Cell Subpopulation in TREX1 Mutant Chilblain Lupus Patients

Heterozygous TREX1 mutations are associated with monogenic familial chilblain lupus and represent a risk factor for developing systemic lupus erythematosus. These interferonopathies originate from chronic type I interferon stimulation due to sensing of inadequately accumulating nucleic acids. We here analysed the composition of dendritic cell (DC) subsets, central stimulators of immune responses, in patients with TREX1 deficiency. We performed single-cell RNA-sequencing of peripheral blood DCs and monocytes from two patients with familial chilblain lupus and heterozygous mutations in TREX1 and from controls. Type I interferon pathway genes were strongly upregulated in patients. Cell frequencies of the myeloid and plasmacytoid DC and of monocyte populations in patients and controls were similar, but we describe a novel DC subpopulation highly enriched in patients: a myeloid DC CD1C⁺ subpopulation characterized by the expression of LMNA, EMP1 and a type I interferon- stimulated gene profile. The presence of this defined subpopulation was confirmed in a second cohort of patients and controls by flow cytometry, also revealing that an increased percentage of patient's cells in the subcluster express costimulatory molecules. We identified a novel type I interferon responsive myeloid DC subpopulation, that might be important for the perpetuation of TREX1-induced chilblain lupus and other type I interferonopathies.

LMNA Variants and Risk of Adult-Onset Cardiac Disease

BACKGROUND

Genetic variants in LMNA may cause cardiac disease, but population-level contributions of variants to cardiac disease burden are not well-characterized.

OBJECTIVES

We sought to determine the frequency and contribution of rare LMNA variants to cardiomyopathy and arrhythmia risk among ambulatory adults.

METHODS

We included 185,990 UK Biobank participants with whole-exome sequencing. We annotated rare loss-of-function and missense LMNA variants for functional effect using 30 in silico prediction tools. We assigned a predicted functional effect weight to each variant and calculated a score for each carrier. We tested associations between the LMNA score and arrhythmia (atrial fibrillation, bradyarrhythmia, ventricular arrhythmia) or cardiomyopathy outcomes (dilated cardiomyopathy and heart failure). We also examined associations for variants located upstream vs downstream of the nuclear localization signal.

RESULTS

Overall, 1,167 (0.63%) participants carried an LMNA variant and 15,079 (8.11%) had an arrhythmia or cardiomyopathy event during a median follow-up of 10.9 years. The LMNA score was associated with arrhythmia or cardiomyopathy (OR: 2.21; P < 0.001) and the association was more significant when restricted to variants upstream of the nuclear localization signal (OR: 5.05; P < 0.001). The incidence rate of arrhythmia or cardiomyopathy was 8.43 per 1,000 person-years (95% CI: 6.73-10.12 per 1,000 person-years) among LMNA variant carriers and 6.38 per 1,000 person-years (95% CI: 6.27-6.50 per 1,000 person-years) among noncarriers. Only 3 (1.2%) of the variants were reported as pathogenic in ClinVar.

CONCLUSIONS

Middle-aged adult carriers of rare missense or loss-of-function LMNA variants are at increased risk for arrhythmia and cardiomyopathy.

Emery-Dreifuss muscular dystrophy with dilated cardiomyopathy preceding skeletal muscle symptoms

Emery-Dreifuss muscular dystrophy is a slowly progressive skeletal muscle and joint disorder associated with cardiac complications. Dilated cardiomyopathy was the initial manifestation of Emery-Dreifuss muscular dystrophy in an 8-year-old girl. Despite normal muscle and myocardial biopsies, genetic testing revealed LMNA mutations. As Emery-Dreifuss muscular dystrophy is associated with minimal skeletal muscle weakness, cardiac complications can facilitate its diagnosis.

PRMT6/LMNA/CXCL12 signaling pathway regulated the osteo/odontogenic differentiation ability in dental stem cells isolated from apical papilla

Tooth loss and maxillofacial bone defect are common diseases, which seriously affect people's health. Effective tooth and maxillofacial bone tissue regeneration is a key problem that need to be solved. In the present study, we investigate the role of PRMT6 in osteo/odontogenic differentiation and migration capacity by using SCAPs. Our results showed that knockdown of PRMT6 promoted the osteo/odontogenic differentiation compared with the control group, as detected by alkaline phosphatase activity, alizarin red staining, and the indicators of osteo/odontogenic differentiation measured by Western blot. In addition, overexpression of PRMT6 inhibited the osteo/odontogenic differentiation potentials of SCAPs. Then, knockdown of PRMT6 promoted the migration ability and overexpression of PRMT6 inhibited the migration ability in SCAPs. Mechanically, we discovered that the depletion of PRMT6 promoted the expression of CXCL12 by decreasing H3R2 methylation in the promoter region of CXCL12. In addition, PRMT6 formed a protein complex with LMNA, a nuclear structural protein. Depletion of LMNA inhibited the osteo/odontogenic differentiation and CXCL12 expression and increased the intranucleus PRMT6 in SCAPs. To sum up, PRMT6 might inhibit the osteo/odontogenic differentiation and migration ability of SCAPs via inhibiting CXCL12. And LMNA might be a negative regulator of PRMT6. It is suggested that PRMT6 may be a key target for SCAP-mediated bone and tooth tissue regeneration.

Red herring pathogenic variants: a case report of premature ventricular contraction-triggered ventricular fibrillation with an incidental pathogenic LMNA variant

Background

Pathogenic variants in the lamin A/C gene (LMNA) can lead to a wide range of phenotypes from dilated and arrhythmogenic cardiomyopathies and conduction abnormalities to partial lipodystrophies. This case highlights a coincidental pathogenic LMNA variant identified in a patient with sudden cardiac arrest (SCA). We demonstrate the need for careful interpretation of pathogenic variants identified in cardiomyopathy genes by highlighting a case in which a coincidental pathogenic LMNA variant was found in a patient with premature ventricular complex (PVC)-induced ventricular fibrillation (VF).

Case summary

We present the case of a 16-year-old male with SCA secondary to VF. Genetic testing identified a maternally inherited pathogenic variant in LMNA annotated c.1961dup; p.T655Nfs*49. The patient received an implantable cardiac defibrillator and was discharged on nadolol. The patient's two brothers were also variant-positive. However, the patient and both brothers had normal chamber dimensions on echocardiogram and no late gadolinium enhancement on cardiac magnetic resonance imaging. The family members with the variant were recommended to have prophylactic implantable cardiac defibrillators and thus sought a second opinion. The patient received an appropriate shock and device interrogation identified PVCs. Electrophysiology study identified PVC-induced VF which was ablated with no recurrent ventricular arrhythmias/implantable cardioverter defibrillator therapies over 8 months of follow-up. Although the variant in LMNA could lead to cardiac arrest, the clinical phenotype was consistent with a non-genetic aetiology. The family members were told to have periodic cardiac evaluation.

Discussion

This case demonstrates the identification of a coincidental pathogenic variant in a cardiomyopathy gene in a patient with cardiac arrest. Although this variant could lead to cardiomyopathy, it appears the cardiac arrest was not due to the pathogenic variant. This highlights the need to consider the clinical phenotype when interpreting genetic test results for cardiomyopathies even in the presence of a positive genetic test result.

Diagnostic Yield of Genetic Testing in Young Patients With Atrioventricular Block of Unknown Cause

Background

The cause of atrioventricular block (AVB) remains unknown in approximately half of young patients with the diagnosis. Although variants in several genes associated with cardiac conduction diseases have been identified, the contribution of genetic variants in younger patients with AVB is unknown.

Methods and Results

Using the Danish Pacemaker and Implantable Cardioverter Defibrillator (ICD) Registry, we identified all patients younger than 50 years receiving a pacemaker because of AVB in Denmark in the period from January 1, 1996 to December 31, 2015. From medical records, we identified patients with unknown cause of AVB at time of pacemaker implantation. These patients were invited to a genetic screening using a panel of 102 genes associated with inherited cardiac diseases. We identified 471 living patients with AVB of unknown cause, of whom 226 (48%) accepted participation. Median age at the time of pacemaker implantation was 39 years (interquartile range, 32–45 years), and 123 (54%) were men. We found pathogenic or likely pathogenic variants in genes associated with or possibly associated with AVB in 12 patients (5%). Most variants were found in the LMNA gene (n=5). LMNA variant carriers all had a family history of either AVB and/or sudden cardiac death.

Conclusions

In young patients with AVB of unknown cause, we found a possible genetic cause in 1 out of 20 participating patients. Variants in the LMNA gene were most common and associated with a family history of AVB and/or sudden cardiac death, suggesting that genetic testing should be a part of the diagnostic workup in these patients to stratify risk and screen family members.

Mechanisms of A-Type Lamin Targeting to Nuclear Ruptures Are Disrupted in LMNA- and BANF1-Associated Progerias

Mutations in the genes LMNA and BANF1 can lead to accelerated aging syndromes called progeria. The protein products of these genes, A-type lamins and BAF, respectively, are nuclear envelope (NE) proteins that interact and participate in various cellular processes, including nuclear envelope rupture and repair. BAF localizes to sites of nuclear rupture and recruits NE-repair machinery, including the LEM-domain proteins, ESCRT-III complex, A-type lamins, and membranes. Here, we show that it is a mobile, nucleoplasmic population of A-type lamins that is rapidly recruited to ruptures in a BAF-dependent manner via BAF’s association with the Ig-like β fold domain of A-type lamins. These initially mobile lamins become progressively stabilized at the site of rupture. Farnesylated prelamin A and lamin B1 fail to localize to nuclear ruptures, unless that farnesylation is inhibited. Progeria-associated LMNA mutations inhibit the recruitment affected A-type lamin to nuclear ruptures, due to either permanent farnesylation or inhibition of BAF binding. A progeria-associated BAF mutant targets to nuclear ruptures but is unable to recruit A-type lamins. Together, these data reveal the mechanisms that determine how lamins respond to nuclear ruptures and how progeric mutations of LMNA and BANF1 impair recruitment of A-type lamins to nuclear ruptures.

An LMNA synonymous variant associated with severe dilated cardiomyopathy: Case report

Dilated cardiomyopathy (DCM) is one of the most common cardiac phenotypes caused by mutations of lamin A/C (LMNA) gene in humans. In our study, a cohort of 57 patients who underwent heart transplant for dilated cardiomyopathy was screened for variants in LMNA. We identified a synonymous variant c.936G>A in the last nucleotide of exon 5 of LMNA in a DCM family. Clinically, the LMNA variant carriers presented with severe familial DCM, conduction disease, and high creatine-kinase level. The LMNA c.936G>A variant is novel and has not been reported in current genetic variant databases. Sanger sequencing results showed the presence of LMNA c.936G>A variant in the genomic DNA but not in the cDNA derived from one family member's heart tissue. Real-time quantitative polymerase chain reaction showed significantly lower LMNA mRNA levels in the patient's heart compared to the controls, suggesting that the c.936G>A LMNA variant resulted in reduced mRNA and possibly lower protein expression of LMNA. These findings expand the understanding on the association between synonymous variant of LMNA and the molecular pathogenesis in DCM patients.

Hutchinson-Gilford progeria syndrome complicated with stroke: A report of 2 cases and literature review

BACKGROUND

Hutchinson-Gilford Progeria Syndrome (HGPS) is a ultrarare, fatal autosomal dominant disorder. The pathogenesis of the disease is a mutation in LMNA, which leads to the accumulation of progerin in cells, impairing the normal physiological functions. Stroke and transient ischemic attack seriously affect the survival rate and quality of life of HGPS children, although the literature of this aspect is limited. This study summarizes the clinical manifestations and related imaging features of HGPS children with stroke to improve pediatric clinicians' understanding of this disease.

CASE PRESENTATION

Both children have a de novo heterozygous mutation of LMNA [c.1824C > T ( p.G608G)]. Case 1. At the age of 4 years, the child had a cerebral infarction, which manifested as blurred vision and communication disturbance. Multiple abnormal signals were observed on the head MRI in the bilateral frontoparietal cortex, bilateral semiovale center, lateral ventricle, and deep frontal and parietal lobes. Multiple abnormal white matter signals on head MRA: bilateral internal carotid artery stenosis with basilar artery, and bilateral thickening of the posterior communicating artery. Case 2. At the age of 8.5 years, the child presented with cerebral infarction, which manifested as decreased muscle strength and choking after drinking water. MRI of the head showed that the bilateral frontal lobes were small with multiple abnormal signal shadows in the bilateral center of the semiovale and the lateral ventricle. Brain MRA revealed that the bilateral internal carotid arteries (C5-7) were narrow and uneven in thickness, and the A1 segment of the left anterior cerebral artery was narrower than the contralateral one. After symptomatic and supportive treatment, the two children improved.

CONCLUSION

Hemiplegia and physical weakness are the most prevalent stroke symptoms in children with HGPS, followed by headache, epilepsy, dysarthria, and psychosis as the primary manifestation in some children. Stroke in children with HGPS is mostly ischemic cerebral infarction caused by an insufficient cerebral blood supply. Pediatric cerebral infarction mainly occurs in the large vascular area, involving all vascular areas, with the internal carotid artery and middle cerebral artery being the most commonly accumulated.

Case report: Focal segmental glomerulosclerosis in a pediatric atypical progeroid syndrome

Atypical progeroid syndrome (APS) is a rare type of progeroid syndrome mainly caused by heterozygous missense mutations in the LMNA (MIM 150330) gene. APS has heterogeneous clinical manifestations, and its kidney manifestations, particularly in children, are rarely documented. Here, we report the first pediatric case of APS with focal segmental glomerulosclerosis (FSGS). A 10-year-old boy with progeroid features was referred to the nephrology clinic because of hyperuricemia. He had dark skin, protruding eyes, and beaked nose and was very thin, suggesting lipodystrophy. He had been treated for recurrent urinary tract infection during infancy, and liver biopsy for persisting hepatitis showed steatohepatitis. He also had hypertrophic cardiomyopathy (HCMP) with mitral and tricuspid valve regurgitation. Genetic studies were performed considering his multisystem symptoms, and he was diagnosed as having APS according to exome sequencing findings (c.898G > C, p.Asp300His of LMNA). During the first visit to the nephrology clinic, he had minimal proteinuria (urine protein/creatinine ratio of 0.23 mg/mg), which worsened during follow-up. In three years, his urine protein/creatinine ratio and N-acetyl-b-D-glucosaminidase/creatinine ratio increased to 1.52 and 18.7, respectively. The kidney biopsy result was consistent with findings of FSGS, peri-hilar type, showing segmental sclerosis of 1 (5%) glomerulus out of 21 glomeruli. An angiotensin receptor blocker was added to manage his proteinuria. This is the first pediatric report of FSGS in an APS patient with confirmed LMNA defect, who manifested progeroid features, lipodystrophy, HCMP with heart valve dysfunction, and steatohepatitis. Our case suggests that screening for proteinuric nephropathy is essential for managing APS patients since childhood.

Familial atrial myopathy in a large multigenerational heart-hand syndrome pedigree carrying an LMNA missense variant in rod 2B domain (p.R335W)

BACKGROUND

The literature on laminopathy with ventricular phenotype is extensive. However, the pathogenicity of LMNA variations in atrial lesions still lacks research.

OBJECTIVE

The purpose of this study was to characterize the atrial phenotypes and possible mechanisms in a large Chinese family with heart-hand syndrome carrying a LMNA missense variant in rod 2B domain (c.1003C>T p.R335W).

METHODS

Clinical characteristics were collected on the basis of the pedigree investigation. Comprehensive functional analyses, including molecular dynamic (MD) simulation, cellular, and animal functional assays, determined the pathogenicity in atrial myopathy.

RESULTS

In the pedigree investigation, 6 of 13 of the mutation carriers showed heterogeneous cardiac phenotypes and 8 carriers also had brachydactyly. In silico molecular dynamics simulations predicted increased binding energy of the R335W mutant lamin A. Atrial cardiomyocytes (HL-1, human induced pluripotent stem cell-derived atrial cardiomyocytes) expressing R335W showed abnormal nuclear morphology, compromised DNA repair, and dysfunctional contraction. Adult zebrafish expressing mutant lamin A showed increased P wave duration in the electrocardiogram, decreased peak A wave velocity in echocardiography, and atrial lesions under the transmission electron microscope.

CONCLUSION

LMNA p.R335W mutation leads to familial heart-hand syndrome characterized by an overlapping phenotype of prominent atrial lesions and brachydactyly. The unstable lamin dimerization and impaired DNA repair are possible mechanisms underlying cardiac phenotypes. Our findings consolidated the genetic role in the course of atrial arrhythmias and cardiac aging, which is helpful in the diagnosis and treatment of cardiac laminopathy.

Predictors of mortality and cardiovascular outcomes in Emery-Dreifuss Muscular Dystrophy in a long-term follow-up

BACKGROUND

Emery-Dreifuss Muscular Dystrophy (EDMD) is an extremely rare muscular dystrophy due to either emerinopathy (EMD) or laminopathy (LMNA). The main risk for patients is that of cardiovascular complications.

AIMS

The aim of this study was to identify predictors of adverse clinical events in patients with EDMD in long-term follow-up observation.

METHODS

A total of 45 patients with confirmed EMD or LMNA mutation were included in the study. The relationships between clinical parameters, the overall survival rate, and risk factors for disease progression were assessed. The primary endpoint was defined as death, while the secondary endpoint comprised death, resuscitated cardiac arrest (RCA), heart transplant (HTX), stroke, end-stage heart failure (ESHF), and hospitalization due to heart failure (HF).

RESULTS

During a median length of follow-up observation of ten years (interquartile range, 5-15), ten patients (22%) died, one suffered RCA, two had HTX, and six suffered ischemic strokes (13%). Seven patients developed ESHF and eight were hospitalized due to HF. The secondary endpoint occurred in 16 patients (36%). LMNA mutation (hazard ratio [HR], 6.01; 95% confidence interval [CI], 1.61-22.4; P = 0.008) and higher serum N-terminal fragment of B-type natriuretic peptide (NT-proBNP) concentration (HR, 1.29; 95% CI, 1.06-1.56 per 100 pg/ml; P = 0.01) increased the risk of death. Higher tricuspid annular plane systolic excursion (TAPSE) decreased the risk for the secondary endpoint (HR, 0.78; 95% CI, 0.68-0.90 mm; P <0.001). NT-proBNP >257 pg/ml and TAPSE <21 mm may be assumed as the best cut-off values for the primary and secondary endpoints, respectively.

CONCLUSIONS

LMNA mutation and higher NT-proBNP concentration were associated with increased mortality in EDMD. Lower TAPSE was a predictor of a composite secondary endpoint in EDMD.

Clinical Features of LMNA-Related Cardiomyopathy in 18 Patients and Characterization of Two Novel Variants

Dilated cardiomyopathy (DCM) refers to a spectrum of heterogeneous myocardial disorders characterized by ventricular dilation and depressed myocardial performance in the absence of hypertension, valvular, congenital, or ischemic heart disease. Mutations in LMNA gene, encoding for lamin A/C, account for 10% of familial DCM. LMNA-related cardiomyopathies are characterized by heterogeneous clinical manifestations that vary from a predominantly structural heart disease, mainly mild-to-moderate left ventricular (LV) dilatation associated or not with conduction system abnormalities, to highly pro-arrhythmic profiles where sudden cardiac death (SCD) occurs as the first manifestation of disease in an apparently normal heart. In the present study, we select, among 77 DCM families referred to our center for genetic counselling and molecular screening, 15 patient heterozygotes for LMNA variants. Segregation analysis in the relatives evidences other eight heterozygous patients. A genotype-phenotype correlation has been performed for symptomatic subjects. Lastly, we perform in vitro functional characterization of two novel LMNA variants using dermal fibroblasts obtained from three heterozygous patients, evidencing significant differences in terms of lamin expression and nuclear morphology. Due to the high risk of SCD that characterizes patients with lamin A/C cardiomyopathy, genetic testing for LMNA gene variants is highly recommended when there is suspicion of laminopathy.

[A case of laminopathy with the mutation of LMNA gene identified by the exome analysis of disease-related genes]

Laminopathy, caused by mutations in the LMNA gene, include a variety of diseases, such as Emery-Dreifuss muscular dystrophy. A Japanese woman developed progressive muscle weakness, muscle atrophy and joint contractures of upper and lower limbs after the age of two years old. She had restrictive respiratory dysfunction, and developed both supraventricular and ventricular arrhythmias after the fourth decade of life. At 55 years old, she had tracheostomy, required mechanical ventilation and was implanted with the implantable cardioverter defibrillator. The serum level of creatine kinase was within normal range. Electromyography showed polyphasic or large motor unit potentials and reduced interference pattern, while relatively normal recruitment. The exome analysis of disease-related genes revealed a heterozygous pathogenic variant c.1072G>A (p.E358K) in the LMNA gene, which contributed to the diagnosis of laminopathy.

Preclinical Advances of Therapies for Laminopathies

Laminopathies are a group of rare disorders due to mutation in LMNA gene. Depending on the mutation, they may affect striated muscles, adipose tissues, nerves or are multisystemic with various accelerated ageing syndromes. Although the diverse pathomechanisms responsible for laminopathies are not fully understood, several therapeutic approaches have been evaluated in patient cells or animal models, ranging from gene therapies to cell and drug therapies. This review is focused on these therapies with a strong focus on striated muscle laminopathies and premature ageing syndromes.

Two Decades after Mandibuloacral Dysplasia Discovery: Additional Cases and Comprehensive View of Disease Characteristics

Pathogenic variants in the LMNA gene cause a group of heterogeneous genetic disorders, called laminopathies. In particular, homozygous or compound heterozygous variants in LMNA have been associated with “mandibuloacral dysplasia type A” (MADA), an autosomal recessive disorder, characterized by mandibular hypoplasia, growth retardation mainly postnatal, pigmentary skin changes, progressive osteolysis of the distal phalanges and/or clavicles, and partial lipodystrophy. The detailed characteristics of this multisystemic disease have yet to be specified due to its rarity and the limited number of cases described. Here, we report three unrelated Egyptian patients with variable severity of MAD features. Next-generation sequencing using a gene panel revealed a homozygous c.1580G>A-p.Arg527His missense variant in LMNA exon 9 in an affected individual with a typical MADA phenotype. Another homozygous c.1580G>T-p.Arg527Leu variant affecting the same amino acid was identified in two additional patients, who both presented with severe manifestations very early in life. We combined our observations together with data from all MADA cases reported in the literature to get a clearer picture of the phenotypic variability in this disease. This work raises the number of reported MADA families, argues for the presence of the founder effect in Egypt, and strengthens genotype–phenotype correlations.

The diagnostic applicability of A-type Lamin in non-muscle invasive bladder cancer

PURPOSE

Lamin A is a major component of the nuclear lamina maintaining nuclear integrity, regulation of gene expression, cell proliferation, and apoptosis. Its deregulation in cancer has been recently reported to be associated with its prognosis. However, its clinical significance in non-muscle invasive bladder cancer (NMIBC) remains to be defined.

MATERIAL/METHODS

Immunohistochemical staining and RT-qPCR were performed to screen the expression patterns of Lamin A/C protein and Lamin A mRNA respectively in 58 high and low grade NMIBC specimens.

RESULTS

Lamin A/C protein was expressed only in the nucleus and less exhibited in NMIBC tissues compared to non-tumoral ones. On the other side, Lamin A mRNA was up-regulated in NMIBC compared to controls. Nevertheless, both expression patterns (protein and mRNA) were not correlated to clinical prognosis factors and were not able to predict the overall survival of patients with high-grade NMIBC.

CONCLUSIONS

The deregulation of A-type Lamin is not associated with the prognosis of NMIBC, but it could serve as a diagnostic biomarker distinguishing NMIBC patients from healthy subjects suggesting its involvement as an initiator event of tumorigenesis in our cohort.

Multiple G-quadruplexes in the LMNA promoter regulate LMNA variant 6 transcription and promote colon cancer cell growth

Lamin A/C proteins, major components of the nuclear lamina, are encoded by the LMNA gene. These proteins have multiple cellular functions, including DNA transcription and replication, chromatin organization, regulation of the cell cycle, and apoptosis. Mutations in LMNA are associated with a variety of diseases called laminopathies. LMNA has implications in cancer; however, its mechanisms of dysregulation in cancer cells are not yet fully understood. In this study, among the LMNA transcript variants, we focused on a transcriptional variant 6 (termed LMNA-V6), which contains unique 3 exons upstream of exon 1 of LMNA. The promoter region of LMNA-V6 formed multiple G-quadruplexes and increased its transcriptional activity. Moreover, LMNA-V6 negatively regulated other LMNA mRNA variants, lamin A and lamin C, via direct interaction with their promoter. Knockdown of LMNA-V6 decreased the proliferation of colon cancer cells, whereas overexpression of the unique 3 exons of LMNA-V6 increased cell growth. Furthermore, microarray gene expression profiling showed that alteration of LMNA-V6 levels influenced the expression of p53 in colon cancer cells. Taken together, the results suggest that LMNA-V6 may be a novel functional RNA whose expression is regulated through multiple G-quadruplexes in colon cancer cells.

Investigating LMNA-Related Dilated Cardiomyopathy Using Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

LMNA-related dilated cardiomyopathy is an inherited heart disease caused by mutations in the LMNA gene encoding for lamin A/C. The disease is characterized by left ventricular enlargement and impaired systolic function associated with conduction defects and ventricular arrhythmias. We hypothesized that LMNA-mutated patients' induced Pluripotent Stem Cell-derived cardiomyocytes (iPSC-CMs) display electrophysiological abnormalities, thus constituting a suitable tool for deciphering the arrhythmogenic mechanisms of the disease, and possibly for developing novel therapeutic modalities. iPSC-CMs were generated from two related patients (father and son) carrying the same E342K mutation in the LMNA gene. Compared to control iPSC-CMs, LMNA-mutated iPSC-CMs exhibited the following electrophysiological abnormalities: (1) decreased spontaneous action potential beat rate and decreased pacemaker current (I_f) density; (2) prolonged action potential duration and increased L-type Ca²⁺ current (I_Ca,L) density; (3) delayed afterdepolarizations (DADs), arrhythmias and increased beat rate variability; (4) DADs, arrhythmias and cessation of spontaneous firing in response to β-adrenergic stimulation and rapid pacing. Additionally, compared to healthy control, LMNA-mutated iPSC-CMs displayed nuclear morphological irregularities and gene expression alterations. Notably, KB-R7943, a selective inhibitor of the reverse-mode of the Na⁺/Ca²⁺ exchanger, blocked the DADs in LMNA-mutated iPSC-CMs. Our findings demonstrate cellular electrophysiological mechanisms underlying the arrhythmias in LMNA-related dilated cardiomyopathy.

Dilated cardiomyopathy in the era of precision medicine: latest concepts and developments

Dilated cardiomyopathy (DCM) is an umbrella term entailing a wide variety of genetic and non-genetic etiologies, leading to left ventricular systolic dysfunction and dilatation, not explained by abnormal loading conditions or coronary artery disease. The clinical presentation can vary from asymptomatic to heart failure symptoms or sudden cardiac death (SCD) even in previously asymptomatic individuals. In the last 2 decades, there has been striking progress in the understanding of the complex genetic basis of DCM, with the discovery of additional genes and genotype-phenotype correlation studies. Rigorous clinical work-up of DCM patients, meticulous family screening, and the implementation of advanced imaging techniques pave the way for a more efficient and earlier diagnosis as well as more precise indications for implantable cardioverter defibrillator implantation and prevention of SCD. In the era of precision medicine, genotype-directed therapies have started to emerge. In this review, we focus on updates of the genetic background of DCM, characteristic phenotypes caused by recently described pathogenic variants, specific indications for prevention of SCD in those individuals and genotype-directed treatments under development. Finally, the latest developments in distinguishing athletic heart syndrome from subclinical DCM are described.

Hutchinson-Gilford Progeria Syndrome: An Overview of the Molecular Mechanism, Pathophysiology and Therapeutic Approach

Lamin A/C encoded by the LMNA gene is an essential component for maintaining the nuclear structure. Mutation in the lamin A/C leads to a group of inherited disorders is known as laminopathies. In the human body, there are several mutations in the LMNA gene that have been identified. It can affect diverse organs or tissues or can be systemic, causing different diseases. In this review, we mainly focused on one of the most severe laminopathies, Hutchinson-Gilford progeria syndrome (HGPS). HGPS is an immensely uncommon, deadly, metameric ill-timed laminopathies caused by the abnormal splicing of the LMNA gene and production of an aberrant protein known as progerin. Here, we also presented the currently available data on the molecular mechanism, pathophysiology, available treatment, and future approaches to this deadly disease. Due to the production of progerin, an abnormal protein leads to an abnormality in nuclear structure, defects in DNA repair, shortening of telomere, and impairment in gene regulation which ultimately results in aging in the early stage of life. Now some treatment options are available for this disease, but a proper understanding of the molecular mechanism of this disease will help to develop a more appropriate treatment which makes it an emerging area of research.

Case Reports: Emery-Dreifuss Muscular Dystrophy Presenting as a Heart Rhythm Disorders in Children

Emery-Dreifuss muscular dystrophy (EDMD) is inherited muscle dystrophy often accompanied by cardiac abnormalities in the form of supraventricular arrhythmias, conduction defects and sinus node dysfunction. Cardiac phenotype typically arises years after skeletal muscle presentation, though, could be severe and life-threatening. The defined clinical manifestation with joint contractures, progressive muscle weakness and atrophy, as well as cardiac symptoms are observed by the third decade of life. Still, clinical course and sequence of muscle and cardiac signs may be variable and depends on the genotype. Cardiac abnormalities in patients with EDMD in pediatric age are not commonly seen. Here we describe five patients with different forms of EDMD (X-linked and autosomal-dominant) caused by the mutations in EMD and LMNA genes, presented with early onset of cardiac abnormalities and no prominent skeletal muscle phenotype. The predominant forms of cardiac pathology were atrial arrhythmias and conduction disturbances that progress over time. The presented cases discussed in the light of therapeutic strategy, including radiofrequency ablation and antiarrhythmic devices implantation, and the importance of thorough neurological and genetic screening in pediatric patients presenting with complex heart rhythm disorders.

International retrospective natural history study of LMNA-related congenital muscular dystrophy

Muscular dystrophies due to heterozygous pathogenic variants in LMNA gene cover a broad spectrum of clinical presentations and severity with an age of onset ranging from the neonatal period to adulthood. The natural history of these conditions is not well defined, particularly in patients with congenital or early onset who arguably present with the highest disease burden. Thus the definition of natural history endpoints along with clinically revelant outcome measures is essential to establishing both clinical care planning and clinical trial readiness for this patient group. We designed a large international cross-sectional retrospective natural history study of patients with genetically proven muscle laminopathy who presented with symptoms before two years of age intending to identify and characterize an optimal clinical trial cohort with pertinent motor, cardiac and respiratory endpoints. Quantitative statistics were used to evaluate associations between LMNA variants and distinct clinical events. The study included 151 patients (median age at symptom onset 0.9 years, range: 0.0–2.0). Age of onset and age of death were significantly lower in patients who never acquired independent ambulation compared to patients who achieved independent ambulation. Most of the patients acquired independent ambulation (n = 101, 66.9%), and subsequently lost this ability (n = 86; 85%). The age of ambulation acquisition (median: 1.2 years, range: 0.8–4.0) and age of ambulation loss (median: 7 years, range: 1.2–38.0) were significantly associated with the age of the first respiratory interventions and the first cardiac symptoms. Respiratory and gastrointestinal interventions occurred during first decade while cardiac interventions occurred later. Genotype–phenotype analysis showed that the most common mutation, p.Arg249Trp (20%), was significantly associated with a more severe disease course. This retrospective natural history study of early onset LMNA-related muscular dystrophy confirms the progressive nature of the disorder, initially involving motor symptoms prior to onset of other symptoms (respiratory, orthopaedic, cardiac and gastrointestinal). The study also identifies subgroups of patients with a range of long-term outcomes. Ambulatory status was an important mean of stratification along with the presence or absence of the p.Arg249Trp mutation. These categorizations will be important for future clinical trial cohorts. Finally, this study furthers our understanding of the progression of early onset LMNA-related muscular dystrophy and provides important insights into the anticipatory care needs of LMNA-related respiratory and cardiac manifestations.

Variable Expressivity and Allelic Heterogeneity in Type 2 Familial Partial Lipodystrophy: The p.(Thr528Met) LMNA Variant

Type 2 familial partial lipodystrophy, or Dunnigan disease, is a metabolic disorder characterized by abnormal subcutaneous adipose tissue distribution. This rare condition results from variants principally affecting exons 8 and 11 of the LMNA gene. In this study, five FPLD2-diagnosed patients carrying the c.1583C>T, p.(Thr528Met) variant in exon 9 of the LMNA gene and with obvious clinical heterogeneity were evaluated. Specific polymorphisms in LMNA and in PPARG were also detected. Exhaustive clinical course, physical examination, biochemical features and family history were recorded, along with the assessment of anthropometric features and body composition by dual-energy X-ray absorptiometry. Preadipocytes obtained from a T528M patient were treated with the classic adipose differentiation medium with pioglitazone. Various adipogenes were evaluated by real-time PCR, and immunofluorescence was used to study intracellular localization of emerin, lamin A and its precursors. As demonstrated with Oil red O staining, the preadipocytes of the T528M patient failed to differentiate, the expression of various adipogenic genes was reduced in the lipodystrophic patient and immunofluorescence studies showed an accumulation of farnesylated prelamin A in T528M cells. We conclude that the T528M variant in LMNA could lead to FPLD2, as the adipogenic machinery is compromised.

Variable Expressivity in Type 2 Familial Partial Lipodystrophy Related to R482 and N466 Variants in the LMNA Gene

Patients with Dunnigan disease (FPLD2) with a pathogenic variant affecting exon 8 of the LMNA gene are considered to have the classic disease, whereas those with variants in other exons manifest the "atypical" disease. The aim of this study was to investigate the degree of variable expressivity when comparing patients carrying the R482 and N466 variants in exon 8. Thus, 47 subjects with FPLD2 were studied: one group of 15 patients carrying the N466 variant and the other group of 32 patients with the R482 variant. Clinical, metabolic, and body composition data were compared between both groups. The thigh skinfold thickness was significantly decreased in the R482 group in comparison with the N466 group (4.2 ± 1.8 and 5.6 ± 2.0 mm, respectively, p = 0.002), with no other differences in body composition. Patients with the N466 variant showed higher triglyceride levels (177.5 [56-1937] vs. 130.0 [55-505] mg/dL, p = 0.029) and acute pancreatitis was only present in these subjects (20%). Other classic metabolic abnormalities related with the disease were present regardless of the pathogenic variant. Thus, although FPLD2 patients with the R482 and N466 variants share most of the classic characteristics, some phenotypic and metabolic differences suggest possible heterogeneity even within exon 8 of the LMNA gene.

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.

Mandibuloacral dysplasia type A in five tunisian patients

Mandibuloacral dysplasia with type A lipodystrophy is a rare autosomal recessive disorder characterized by craniofacial dysmorphism, type A lipodystrophy, clavicular dysplasia, and acroostelolysis. It is caused by homozygous or compound heterozygous missense mutations in LMNA gene. We report five Tunisian patients harboring the same homozygous c.1580G > A; p. (Arg527His) mutation in LMNA gene. The patients presented with typical features of mandibuloacral dysplasia including, prominent eyes, thin or beaked nose, dental overcrowding, mandibular hypoplasia, short and broad finger's distal phalanges with round tips and lipodystrophy type A. Newly recognized signs are growth hormone deficiency and dilated cardiomyopathy. Genotype-phenotype correlation found that at least one of the disease's LMNA mutant alleles involve one of the highly conserved aminoacids, residing in a key site domain for protein function within the C-terminal globular domain of A-type lamins. Also, the severity of the disease depends on the position in the protein's domain and on the type of substitution of the concerned aminoacid.

Integrated analysis reveals the alterations that LMNA interacts with euchromatin in LMNA mutation-associated dilated cardiomyopathy

BACKGROUND

Dilated cardiomyopathy (DCM) is a serious cardiac heterogeneous pathological disease, which may be caused by mutations in the LMNA gene. Lamins interact with not only lamina-associated domains (LADs) but also euchromatin by alone or associates with the lamina-associated polypeptide 2 alpha (LAP2α). Numerous studies have documented that LMNA regulates gene expression by interacting with LADs in heterochromatin. However, the role of LMNA in regulating euchromatin in DCM is poorly understood. Here, we determine the differential binding genes on euchromatin in DCM induced by LMNA mutation by performing an integrated analysis of bioinformatics and explore the possible molecular pathogenesis mechanism.

RESULTS

Six hundred twenty-three and 4484 differential binding genes were identified by ChIP-seq technology. The ChIP-seq analysis results and matched RNA-Seq transcriptome data were integrated to further validate the differential binding genes of ChIP-seq. Five and 60 candidate genes involved in a series of downstream analysis were identified. Finally, 4 key genes (CREBBP, PPP2R2B, BMP4, and BMP7) were harvested, and these genes may regulate LMNA mutation-induced DCM through WNT/β-catenin or TGFβ-BMP pathways.

CONCLUSIONS

We identified four key genes that may serve as potential biomarkers and novel therapeutic targets. Our study also illuminates the possible molecular pathogenesis mechanism that the abnormal binding between LMNA or LAP2α-lamin A/C complexes and euchromatin DNA in LMNA mutations, which may cause DCM through the changes of CREBBP, PPP2R2B, BMP4, BMP7 expressions, and the dysregulation of WNT/β-catenin or TGFβ-BMP pathways, providing valuable insights to improve the occurrence and development of DCM.

Site specificity determinants for prelamin A cleavage by the zinc metalloprotease ZMPSTE24

The integral membrane zinc metalloprotease ZMPSTE24 is important for human health and longevity. ZMPSTE24 performs a key proteolytic step in maturation of prelamin A, the farnesylated precursor of the nuclear scaffold protein lamin A. Mutations in the genes encoding either prelamin A or ZMPSTE24 that prevent cleavage cause the premature aging disease Hutchinson–Gilford progeria syndrome (HGPS) and related progeroid disorders. ZMPSTE24 has a novel structure, with seven transmembrane spans that form a large water-filled membrane chamber whose catalytic site faces the chamber interior. Prelamin A is the only known mammalian substrate for ZMPSTE24; however, the basis of this specificity remains unclear. To define the sequence requirements for ZMPSTE24 cleavage, we mutagenized the eight residues flanking the prelamin A scissile bond (TRSY↓LLGN) to all other 19 amino acids, creating a library of 152 variants. We also replaced these eight residues with sequences derived from putative ZMPSTE24 cleavage sites from amphibian, bird, and fish prelamin A. Cleavage of prelamin A variants was assessed using an in vivo yeast assay that provides a sensitive measure of ZMPSTE24 processing efficiency. We found that residues on the C-terminal side of the cleavage site are most sensitive to changes. Consistent with other zinc metalloproteases, including thermolysin, ZMPSTE24 preferred hydrophobic residues at the P1’ position (Leu647), but in addition, showed a similar, albeit muted, pattern at P2’. Our findings begin to define a consensus sequence for ZMPSTE24 that helps to clarify how this physiologically important protease functions and may ultimately lead to identifying additional substrates.

Whole-exome sequencing in patients with protein aggregate myopathies reveals causative mutations associated with novel atypical phenotypes

Background

Myofibrillar myopathies (MFM) are a subgroup of protein aggregate myopathies (PAM) characterized by a common histological picture of myofibrillar dissolution, Z-disk disintegration, and accumulation of degradation products into inclusions. Mutations in genes encoding components of the Z-disk or Z-disk-associated proteins occur in some patients whereas in most of the cases, the causative gene defect is still unknown. We aimed to search for pathogenic mutations in genes not previously associated with MFM phenotype.

Methods

We performed whole-exome sequencing in four patients from three unrelated families who were diagnosed with PAM without aberrations in causative genes for MFM.

Results

In the first patient and her affected daughter, we identified a heterozygous p.(Arg89Cys) missense mutation in LMNA gene which has not been linked with PAM pathology before. In the second patient, a heterozygous p.(Asn4807Phe) mutation in RYR1 not previously described in PAM represents a novel, candidate gene with a possible causative role in the disease. Finally, in the third patient and his symptomatic daughter, we found a previously reported heterozygous p.(Cys30071Arg) mutation in TTN gene that was clinically associated with cardiac involvement.

Conclusions

Our study identifies a new genetic background in PAM pathology and expands the clinical phenotype of known pathogenic mutations.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10072-020-04876-7.

Phosphorylated Lamin A/C in the Nuclear Interior Binds Active Enhancers Associated with Abnormal Transcription in Progeria

LMNA encodes nuclear Lamin A/C that tethers lamina-associated domains (LADs) to the nuclear periphery. Mutations in LMNA cause degenerative disorders including the premature aging disorder Hutchinson-Gilford progeria, but the mechanisms are unknown. We report that Ser22-phosphorylated (pS22) Lamin A/C was localized to the nuclear interior in human fibroblasts throughout the cell cycle. pS22-Lamin A/C interacted with a subset of putative active enhancers, not LADs, at locations co-bound by the transcriptional activator c-Jun. In progeria-patient fibroblasts, a subset of pS22-Lamin A/C-binding sites were lost, whereas new pS22-Lamin A/C-binding sites emerged in normally quiescent loci. New pS22-Lamin A/C binding was accompanied by increased histone acetylation, increased c-Jun binding, and upregulation of nearby genes implicated in progeria pathophysiology. These results suggest that Lamin A/C regulates gene expression by enhancer binding. Disruption of the gene regulatory rather than LAD tethering function of Lamin A/C may underlie the pathogenesis of disorders caused by LMNA mutations.