LMNA Mutations Research Articles

The structural and gene expression hypotheses in laminopathic diseases-not so different after all.

Laminopathies are a diverse group of rare diseases with various pathologies in different tissues, which are linked to mutations in the LMNA gene. Historically, the structural disease model proposed mechanical defects of the lamina and nuclear fragility, the gene expression model impairment of spatial chromatin organization and signaling pathways as underlying mechanisms leading to the pathologies. Exciting findings in the past few years showing that mechanical forces are directly transmitted into the nucleus, where they affect chromatin organization and mechanoresponsive signaling molecules, have led to a revised concept of an integrative unified disease model, in which lamin-mediated pathways in mechanotransduction and chromatin regulation are highly interconnected and mutually dependent. In this Perspective we highlight breakthrough findings providing new insight into lamin-linked mechanisms of mechanotransduction and chromatin regulation and discuss how a combined and interrelated impairment of these functions by LMNA mutations may impair the complex mechanosignaling network and cause tissue-specific pathologies in laminopathies.

INDICATIONS FOR IMPLANTATION AND EFFICIENCY OF CARDIOVERTER-DEFIBRILLATORS IN PATIENTS WITH DILATED CARDIOMYOPATHY

Purpose. To assess the frequency and predictors of appropriate shocks of cardioverter-defibrillators in patients with dilated cardiomyopathy (DCM) syndrome and the impact on the total mortality and sudden cardiac death (SCD).Material and Methods. A total of 275 patients with DCM syndrome (average age of 46.8 ± 12.5 years; 185 males and 90 females) were observed. Inclusion criteria were left ventricular (LV) end-diastolic diameter (EDD) more than 5.5 cm and LV ejection fraction (EF) less than 50%. Patients with coronary artery stenosis more than 50% were excluded. Implantable cardioverter-defibrillator (ICD) (n=44) and cardiac resynchronization therapy defibrillator (CRT-D) (n=32) were implanted in 76 (27.6%) patients (53 males and 23 females, average age of 48.9±12.9 years, LV EDD of 6.7±0.8 cm, and LV EF of 28.2±9.9%). A comparison group comprised 199 patients (72.4%) without devices (132 males and 67 females, average age of 46.0±12.3 years, LV EDD of 6.5±0.8 cm, and LV EF of 32.0±10.2%). The average follow-up was 27 (24; 30) months.Results. SCD in patients with DCM syndrome was recorded in 2.9% of cases; the total mortality rate was 18.9%; the rate of death + transplantation was 22.6%. The SCD, total mortality, and death+transplantation rates were 2.6% (4.6/0%), 23.7% (22.7/25.0%), and 32.9% (34.1/31.3%) in patients with devices (ICD/CRT-D) and 3.0%, 17.1%, and 16.6% in patients without devices, respectively. The rate of SCD+appropriate shocks (ASR) was significantly higher in study group: 26.3 vs 3.0% in comparison group (p<0.001). The nature of DCM syndrome was predominantly inflammatory (53%), primary (genetic) (19.6%), and multifactorial (25.1%). Genetic forms of DCM were represented by non-compaction cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy (ARVC), myopathies, and amyloidosis. The pathogenic mutations in the genes LMNA (n=1), DES (n=2), DSP (n=2), EMD (n=2), PKP2 (n=1), TTR (n=1), MUH7+MyBPC3 (n=1), and MyBPC3 (n=4) were detected. The ASR (ICD/CRT-D) rate was 23.7% (n=13/5). The only reliable predictor of ASR was the generic nature of DCM syndrome, identified in 100% of patients with shocks (in the presence of myocarditis in 77.8%/isolated in 22.2%) in comparison with 51.7% (29.3/22.4%) in patients without ASR (p<0.002, AUC 0.747, RR 1.66, 95% CI 0.711-3.885). Ventricular tachycardia (VT) was registered in 84% of patients with shocks (stable/unstable VT rates of 17/67%) vs 1.7/72%, in patients without shocks (р=0.06). In patients with shocks, low QRS voltage (39 vs 6.9%, р<0.05) and the absence of LV hypertrophy signs on the ECG (77.6 vs 58.6%, р>0.05) were registered more often. The average LV EF was higher in patients with ASR (34.4±9.7%) in comparison with patients without ASR (25.9±8.8%), р<0.005. Conclusions. The genetic nature of DCM syndrome is an important predictor of appropriate shocks and an independent selection criterion for ICD/CRT-D implantation. Age, NYHA class, and LV EF did not show prognostic significance. Additional predictors of appropriate shocks were sustained/unsustained VT, low QRS voltage, and the absence of LV hypertrophy signs on the ECG.

Identification of COMMD1 as a novel lamin A binding partner.

Lamin A, which is encoded by the LMNA gene, regulates gene expression and genome stability through interactions with a variety of proteins. Mutations in LMNA lead to a diverse set of inherited human diseases, collectively referred to as laminopathies. To gain insight into the protein interactions of lamin A, a yeast two-hybrid screen was conducted using the carboxy-terminus of lamin A. The screen identified copper metabolism MURR1 domain-containing 1 (COMMD1) as a novel lamin A binding partner. Colocalization experiments using fluorescent confocal microscopy revealed that COMMD1 colocalized with lamin A in 293 cells. Furthermore, the COMMD1-lamin A protein interaction was also demonstrated in co-immunoprecipitation experiments. Collectively, the present study demonstrated a physical interaction between COMMD1 and lamin A, which may aid to elucidate the mechanisms of lamin A in the aging process.

Modeling of LMNA-Related Dilated Cardiomyopathy Using Human Induced Pluripotent Stem Cells.

Dilated cardiomyopathy (DCM) is one of the leading causes of heart failure and heart transplantation. A portion of familial DCM is due to mutations in the LMNA gene encoding the nuclear lamina proteins lamin A and C and without adequate treatment these patients have a poor prognosis. To get better insights into pathobiology behind this disease, we focused on modeling LMNA-related DCM using human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CM). Primary skin fibroblasts from DCM patients carrying the most prevalent Finnish founder mutation (p.S143P) in LMNA were reprogrammed into hiPSCs and further differentiated into cardiomyocytes (CMs). The cellular structure, functionality as well as gene and protein expression were assessed in detail. While mutant hiPSC-CMs presented virtually normal sarcomere structure under normoxia, dramatic sarcomere damage and an increased sensitivity to cellular stress was observed after hypoxia. A detailed electrophysiological evaluation revealed bradyarrhythmia and increased occurrence of arrhythmias in mutant hiPSC-CMs on β-adrenergic stimulation. Mutant hiPSC-CMs also showed increased sensitivity to hypoxia on microelectrode array and altered Ca2+ dynamics. Taken together, p.S143P hiPSC-CM model mimics hallmarks of LMNA-related DCM and provides a useful tool to study the underlying cellular mechanisms of accelerated cardiac degeneration in this disease.

Congenital muscular dystrophies in China.

Congenital muscular dystrophies (CMDs) are clinically and genetically heterogeneous conditions. We launched a nationwide study to determine the frequency of CMD in the Chinese population and assess the status of diagnosis and disease management for CMD in China. Cases were chosen from databases in 34 tertiary academic hospitals from 29 first-level administrative divisions (provinces, municipalities, autonomous regions, and special administrative regions), and medical records were reviewed to confirm the diagnoses. The study included 409 patients, of those patients who consented to genetic testing (n = 340), mutations were identified in 286 of them. The most common forms identified were LAMA2-related CMD (36.4%), followed by COL6-related CMD (23.2%) and α-dystroglycanopathy (21.0%). The forms of CMD related to mutations in LMNA and SEPN1 were less frequent (12.5% and 2.4%, respectively). We also recorded a significant difference in the diagnostic capabilities and disease management of CMD, with this being relatively backward in research centers from less developed regions. We provide, for the first time, comprehensive epidemiologic information of CMD in a large cohort of Chinese people. To our knowledge, this is the largest sample size of its kind so far highlighting the prevalence of CMD in China.

Development and Validation of a New Risk Prediction Score for Life-Threatening Ventricular Tachyarrhythmias in Laminopathies.

An accurate estimation of the risk of life-threatening (LT) ventricular tachyarrhythmia (VTA) in patients with LMNA mutations is crucial to select candidates for implantable cardioverter-defibrillator implantation. We included 839 adult patients with LMNA mutations, including 660 from a French nationwide registry in the development sample, and 179 from other countries, referred to 5 tertiary centers for cardiomyopathies, in the validation sample. LTVTA was defined as (1) sudden cardiac death or (2) implantable cardioverter defibrillator-treated or hemodynamically unstable VTA. The prognostic model was derived using the Fine-Gray regression model. The net reclassification was compared with current clinical practice guidelines. The results are presented as means (SD) or medians [interquartile range]. We included 444 patients, 40.6 (14.1) years of age, in the derivation sample and 145 patients, 38.2 (15.0) years, in the validation sample, of whom 86 (19.3%) and 34 (23.4%) experienced LTVTA over 3.6 [1.0-7.2] and 5.1 [2.0-9.3] years of follow-up, respectively. Predictors of LTVTA in the derivation sample were: male sex, nonmissense LMNA mutation, first degree and higher atrioventricular block, nonsustained ventricular tachycardia, and left ventricular ejection fraction (https://lmna-risk-vta.fr). In the derivation sample, C-index (95% CI) of the model was 0.776 (0.711-0.842), and the calibration slope 0.827. In the external validation sample, the C-index was 0.800 (0.642-0.959), and the calibration slope was 1.082 (95% CI, 0.643-1.522). A 5-year estimated risk threshold ≥7% predicted 96.2% of LTVTA and net reclassified 28.8% of patients with LTVTA in comparison with the guidelines-based approach. In comparison with the current standard of care, this risk prediction model for LTVTA in laminopathies significantly facilitated the choice of candidates for implantable cardioverter defibrillators. URL: https://www.clinicaltrials.gov. Unique identifier: NCT03058185.

The K219T-Lamin mutation induces conduction defects through epigenetic inhibition of SCN5A in human cardiac laminopathy

Mutations in LMNA, which encodes the nuclear proteins Lamin A/C, can cause cardiomyopathy and conduction disorders. Here, we employ induced pluripotent stem cells (iPSCs) generated from human cells carrying heterozygous K219T mutation on LMNA to develop a disease model. Cardiomyocytes differentiated from these iPSCs, and which thus carry K219T-LMNA, have altered action potential, reduced peak sodium current and diminished conduction velocity. Moreover, they have significantly downregulated Nav1.5 channel expression and increased binding of Lamin A/C to the promoter of SCN5A, the channel’s gene. Coherently, binding of the Polycomb Repressive Complex 2 (PRC2) protein SUZ12 and deposition of the repressive histone mark H3K27me3 are increased at SCN5A. CRISPR/Cas9-mediated correction of the mutation re-establishes sodium current density and SCN5A expression. Thus, K219T-LMNA cooperates with PRC2 in downregulating SCN5A, leading to decreased sodium current density and slower conduction velocity. This mechanism may underlie the conduction abnormalities associated with LMNA-cardiomyopathy.

Phenotypic diversity and glucocorticoid sensitivity in patients with familial partial lipodystrophy type 2.

To evaluate the phenotypic heterogeneity and glucocorticoid sensitivity in FPLD2 patients exhibiting the p.R482W or p.R644C LMNA mutations. Prospective study with FPLD2 patients (n=24) and controls (n=24), who underwent anthropometric, body composition, metabolic profile and adipokines/cytokine plasma measurements. Plasma and salivary cortisol were measured in basal conditions and after 0.25, 0.5 and 1.0mg of dexamethasone (DEX) given at 23:00hours. Glucocorticoid receptor (GR) and 11βHSD isoforms expression were assessed by qPCR. Familial partial lipodystrophy type 2 individuals presented increased waist and neck circumferences, decreased hip circumference, peripheral skinfold thickness and fat mass. Patients presented increased HOMA-IR, triglycerides, TNF-α, IL-1β, IL-6 and IL-10, and decreased adiponectin and leptin plasma levels. FPLD2 patients showed decreased ability to suppress the HPA axis compared with controls after 0.5mg DEX. The phenotype was more pronounced in patients harbouring the p.R482W LMNA mutation. GRβ overexpression in PBMC was observed in female patients compared with female controls. Familial partial lipodystrophy type 2 patients exhibited anthropometric, clinical and biochemical phenotypic heterogeneity related to LMNA mutation sites and to gender. LMNA mutations affecting both lamin A and lamin C lead to more severe phenotype. FPLD2 patients also showed blunted HPA axis response to DEX, probably due to the association of increased levels of proinflammatory cytokines with GRβ overexpression leading to a more severe phenotype in female.

SUN-135 Dual Energy X-Ray Absorptiometry (DEXA) as a Diagnostic Tool for Familial Partial Lipodystrophy, Dunnigan Variety (FPLD2)

FPLD2 is a rare autosomal dominant disorder characterized by loss of subcutaneous (sc) fat from the extremities but increased fat deposition in the face, neck and abdomen. Most FPLD2 patients (~75%) have “typical” heterozygous missense LMNA mutations affecting the arginine 482 residue and have severe loss of sc fat from the extremities and develop moderate to severe metabolic complications. Other patients have “atypical” mutations with variable loss of sc fat from the extremities and mild to severe metabolic complications. Since genetic testing is expensive, the diagnosis of FPLD2 is usually missed or delayed. Thus, there exists a need for an objective screening tool which can aid in the diagnosis of FPLD2. Therefore, we determined the predictive value of skinfold thickness measurements and various DEXA-based regional body fat parameters for diagnosis of FPLD2. We compared body fat data of 49 adult females (F) and 5 males (M) with FPLD2 to the sex- and age-matched controls (2,459 F, 3,459 M) from the National Health and Nutrition Examination Survey (NHANES) 2005-2010. Thirty nine patients had “typical” heterozygous p.R482W or p.R482Q LMNA mutation. The other heterozygous LMNA mutations included p.R582S (n = 1), p.R582H (n = 1), p.S583L (n = 3), p.R349W (n = 1), p.R25L (n = 1), p.G523R (n = 2), p.D192V (n = 1), p.L241P (n = 1), p.R62G (n = 2) and p.K515E (n = 2). The mean ± SD age and body mass index of affected F was 42 ± 13.5 y and 25.6 ± 4.5 kg/m2, respectively; and of affected M was 45.4 ± 11.6 y and 29.2 ± 7.0 kg/m2, respectively. Hypertriglyceridemia and diabetes mellitus were present in 74% and 52% of the FPLD2 patients, respectively. Our data revealed that the lower limb fat %, as well as the ratio of lower limb fat %/ truncal fat %, in all affected females were ≤ 1st percentile (%ile) of the controls, except in two patients, one of whom had a p.G523R mutation, and the other had a p.R482Q mutation but had an unusual excess fat accumulation in the medial part of the thighs and knees. All FPLD2 females had triceps skinfold thickness values ≤ 1st %ile of NHANES except in three patients. The subscapular skinfold thickness values in females on the other hand, were between the 5th to 99th %ile of NHANES. Unfortunately, data for thigh skinfold thickness were not available from NHANES. The lower limb fat % in affected males was below 25th %ile of controls. We conclude that DEXA-derived lower limb fat % and the ratio of lower limb fat %/ truncal fat % are the best predictors of FPLD2 diagnosis in females but not in males. Women with values of lower limb fat % (~ 20% or less) and the ratio of lower limb fat %/ truncal fat % (~ 0.85 or less), both of which are below the 1st %ile of NHANES data, should be further evaluated for diagnosis of FPLD2, especially if presenting with metabolic complications.

Clinical and genetic insights into non-compaction: a meta-analysis and systematic review on 7598 individuals.

Left ventricular non-compaction has been increasingly diagnosed in recent years. However, it is still debated whether non-compaction is a pathological condition or a physiological trait. In this meta-analysis and systematic review, we compare studies, which investigated these two different perspectives. Furthermore, we provide a comprehensive overview on the clinical outcome as well as genetic background of left ventricular non-compaction cardiomyopathy in adult patients. We retrieved PubMed/Medline literatures in English language from 2000 to 19/09/2018 on clinical outcome and genotype of patients with non-compaction. We summarized and extensively reviewed all studies that passed selection criteria and performed a meta-analysis on key phenotypic parameters. Altogether, 35 studies with 2271 non-compaction patients were included in our meta-analysis. The mean age at diagnosis was the mid of their fifth decade. Two-thirds of patients were male. Congenital heart diseases including atrial or ventricular septum defect or Ebstein anomaly were reported in 7% of patients. Twenty-four percent presented with family history of cardiomyopathy. The mean frequency of neuromuscular diseases was 5%. Heart rhythm abnormalities were reported frequently: conduction disease in 26%, supraventricular tachycardia in 17%, and sustained or non-sustained ventricular tachycardia in 18% of patients. Three important outcome measures were reported including systemic thromboembolic events with a mean frequency of 9%, heart transplantation with 4%, and adequate ICD therapy with 15%. Nine studies investigated the genetics of non-compaction cardiomyopathy. The most frequently mutated gene was TTN with a pooled frequency of 11%. The average frequency of MYH7 mutations was 9%, for MYBPC3 mutations 5%, and for CASQ2 and LDB3 3% each. TPM1, MIB1, ACTC1, and LMNA mutations had an average frequency of 2% each. Mutations in PLN, HCN4, TAZ, DTNA, TNNT2, and RBM20 were reported with a frequency of 1% each. We also summarized the results of eight studies investigating the non-compaction in altogether 5327 athletes, pregnant women, patients with sickle cell disease, as well as individuals from population-based cohorts, in which the presence of left ventricular hypertrabeculation ranged from 1.3 to 37%. The summarized data indicate that non-compaction may lead to unfavorable outcome in different cardiomyopathy entities. The presence of key features in a multimodal diagnostic approach could distinguish between benign morphological trait and manifest cardiomyopathy.

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.

Tissue-Specific Influence of Lamin A Mutations on Notch Signaling and Osteogenic Phenotype of Primary Human Mesenchymal Cells.

Lamin A is involved in many cellular functions due to its ability to bind chromatin and transcription factors and affect their properties. Mutations of LMNA gene encoding lamin A affect the differentiation capacity of stem cells, but the mechanisms of this influence remain largely unclear. We and others have reported recently an interaction of lamin A with Notch pathway, which is among the main developmental regulators of cellular identity. The aim of this study was to explore the influence of LMNA mutations on the proosteogenic response of human cells of mesenchymal origin and to further explore the interaction of LMNA with Notch pathway. Mutations R527C and R471C in LMNA are associated with mandibuloacral dysplasia type A, a highly penetrant disease with a variety of abnormalities involving bone development. We used lentiviral constructs bearing mutations R527C and R471C and explored its influence on proosteogenic phenotype expression and Notch pathway activity in four types of human cells: umbilical vein endothelial cells (HUVEC), cardiac mesenchymal cells (HCMC), aortic smooth muscle cells (HASMC), and aortic valve interstitial cells (HAVIC). The proosteogenic response of the cells was induced by the addition of either LPS or specific effectors of osteogenic differentiation to the culture medium; phenotype was estimated by the expression of osteogenic markers by qPCR; activation of Notch was assessed by expression of Notch-related and Notch-responsive genes by qPCR and by activation of a luciferase CSL-reporter construct. Overall, we observed different reactivity of all four cell lineages to the stimulation with either LPS or osteogenic factors. R527C had a stronger influence on the proosteogenic phenotype. We observed the inhibiting action of LMNA R527C on osteogenic differentiation in HCMC in the presence of activated Notch signaling, while LMNA R527C caused the activation of osteogenic differentiation in HAVIC in the presence of activated Notch signaling. Our results suggest that the effect of a LMNA mutation is strongly dependent not only on a specific mutation itself, but also might be influenced by the intrinsic molecular context of a cell lineage.

The role of genetic mutations in genes LMNA, PPARG, PLIN1, AKT2, CIDEC in Köbberling–Dunnigan Syndrome

The role of genetic mutations in genes LMNA, PPARG, PLIN1, AKT2, CIDEC in Köbberling–Dunnigan Syndrome

The Cutting Edge: The Role of mTOR Signaling in Laminopathies.

The mechanistic target of rapamycin (mTOR) is a ubiquitous serine/threonine kinase that regulates anabolic and catabolic processes, in response to environmental inputs. The existence of mTOR in numerous cell compartments explains its specific ability to sense stress, execute growth signals, and regulate autophagy. mTOR signaling deregulation is closely related to aging and age-related disorders, among which progeroid laminopathies represent genetically characterized clinical entities with well-defined phenotypes. These diseases are caused by LMNA mutations and feature altered bone turnover, metabolic dysregulation, and mild to severe segmental progeria. Different LMNA mutations cause muscular, adipose tissue and nerve pathologies in the absence of major systemic involvement. This review explores recent advances on mTOR involvement in progeroid and tissue-specific laminopathies. Indeed, hyper-activation of protein kinase B (AKT)/mTOR signaling has been demonstrated in muscular laminopathies, and rescue of mTOR-regulated pathways increases lifespan in animal models of Emery-Dreifuss muscular dystrophy. Further, rapamycin, the best known mTOR inhibitor, has been used to elicit autophagy and degradation of mutated lamin A or progerin in progeroid cells. This review focuses on mTOR-dependent pathogenetic events identified in Emery-Dreifuss muscular dystrophy, LMNA-related cardiomyopathies, Hutchinson-Gilford Progeria, mandibuloacral dysplasia, and type 2 familial partial lipodystrophy. Pharmacological application of mTOR inhibitors in view of therapeutic strategies is also discussed.

A humanized yeast system to analyze cleavage of prelamin A by ZMPSTE24.

The nuclear lamins A, B, and C are intermediate filament proteins that form a nuclear scaffold adjacent to the inner nuclear membrane in higher eukaryotes, providing structural support for the nucleus. In the past two decades it has become evident that the final step in the biogenesis of the mature lamin A from its precursor prelamin A by the zinc metalloprotease ZMPSTE24 plays a critical role in human health. Defects in prelamin A processing by ZMPSTE24 result in premature aging disorders including Hutchinson Gilford Progeria Syndrome (HGPS) and related progeroid diseases. Additional evidence suggests that defects in prelamin A processing, due to diminished ZMPSTE24 expression or activity, may also drive normal physiological aging. Because of the important connection between prelamin A processing and human aging, there is increasing interest in how ZMPSTE24 specifically recognizes and cleaves its substrate prelamin A, encoded by LMNA. Here, we describe two humanized yeast systems we have recently developed to examine ZMPSTE24 processing of prelamin A. These systems differ from one another slightly. Version 1.0 is optimized to analyze ZMPSTE24 mutations, including disease alleles that may affect the function or stability of the protease. Using this system, we previously showed that some ZMPSTE24 disease alleles that affect stability can be rescued by the proteasome inhibitor bortezomib, which may have therapeutic implications. Version 2.0 is designed to analyze LMNA mutations at or near the ZMPSTE24 processing site to assess whether they permit or impede prelamin A processing. Together these systems offer powerful methodology to study ZMPSTE24 disease alleles and to dissect the specific residues and features of the lamin A tail that are required for recognition and cleavage by the ZMPSTE24 protease.

Diabetes mellitus coexisted with progeria: a case report of atypical Werner syndrome with novel LMNA mutations and literature review

Werner syndrome (WS) is a rare, adult-onset progeroid syndrome. Classic WS is caused by WRN mutation and partial atypical WS (AWS) is caused by LMNA mutation. A 19-year-old female patient with irregular menstruation and hyperglycemia was admitted. Physical examination revealed characteristic faces of progeria, graying and thinning of the hair scalp, thinner and atrophic skin over the hands and feet, as well as lipoatrophy of the extremities, undeveloped breasts at Tanner stage 3, and short stature. The patient also suffered from severe insulin-resistant diabetes mellitus, hyperlipidemia, fatty liver, and polycystic ovarian morphology. Possible WS was considered and both WRN and LMNA genes were analyzed. A novel missense mutation p.L140Q (c.419T>A) in the LMNA gene was identified and confirmed the diagnosis of AWS. Her father was a carrier of the same mutation. We carried out therapy for lowering blood glucose and lipid and improving insulin resistance, et al. The fasting glucose, postprandial glucose and triglyceride level was improved after treatment for 9 days. Literature review of AWS was performed to identify characteristics of the disease. Diabetes mellitus is one of the clinical manifestations of WS and attention must give to the differential diagnosis. Gene analysis is critical in the diagnosis of WS. According to the literature, classic and atypical WS differ in incidence, pathogenic gene, and clinical manifestations. Characteristic dermatological pathology may be significantly more important for the initial identification of AWS. Early detection, appropriate treatments, and regular follow-up may improve prognosis and survival of WS patients.

External validation of risk factors for malignant ventricular arrhythmias in lamin a/c mutation carriers

International recommendations state that implantable cardiovertor defibrillator should be considered early in patients with a confirmed disease-causing LMNA mutation with clinical risk factors, especially in the presence of non-sustained ventricular tachycardia, LVEF < 45%, male sex or non-missense mutations. The prognostic model derived from these recommendations hasn’t been validated on a separate external sample of patients. To evaluate the performance of the 4 prognosis factors on a separate external cohort of LMNA patients. We identified 101 consecutive LMNA mutation carriers who have been managed and genotyped in our center between 2004 and 2015. We recorded for all patients the values of the 4 previous identified predictive factors and whether they experienced a malignant ventricular aarhythmia (MVA) or not. The mean follow-up was 4.7 years. MVA was oberserved in 16 patients. Four risk groups were defined from the four previous predictive factors and log-rank test showed statistical significance ( P < 0,001) of MVA occurrence rates between groups (See Fig. 1 ). The 4 risk factors (non-sustained ventricular tachycardia, LVEF < 45%, male sex and non-missense mutations) derived from a previous work showed good performance on predicting malignant ventricular arrhythmia on an external cohort. Further studies are needed to identify other potential risk factors that could be even more accurate to predict sudden cardiac death.

Induced Pluripotent Stem Cells to Study Mechanisms of Laminopathies: Focus on Epigenetics.

Laminopathies are a group of rare degenerative disorders that manifest with a wide spectrum of clinical phenotypes, including both systemic multi-organ disorders, such as the Hutchinson-Gilford Progeria Syndrome (HGPS), and tissue-restricted diseases, such as Emery-Dreifuss muscular dystrophy, dilated cardiomyopathy and lipodystrophies, often overlapping. Despite their clinical heterogeneity, which remains an open question, laminopathies are commonly caused by mutations in the LMNA gene, encoding the nuclear proteins Lamin A and C. These two proteins are main components of the nuclear lamina and are involved in several biological processes. Besides the well-known structural function in the nucleus, their role in regulating chromatin organization and transcription has emerged in the last decade, supporting the hypothesis that the disruption of this layer of regulation may be mechanism underlying the disease. Indeed, recent studies that show various epigenetic defects in cells carrying LMNA mutations, such as loss of heterochromatin, changes in gene expression and chromatin remodeling, strongly support this view. However, those findings are restricted to few cell types in humans, mainly because of the limited accessibility of primary cells and the difficulties to culture them ex-vivo. On the other hand, animal models might fail to recapitulate phenotypic hallmarks of the disease as of humans. To fill this gap, models based on induced pluripotent stem cell (iPSCs) technology have been recently generated that allowed investigations on diverse cells types, such as mesenchymal stem cells (MSCs), vascular and smooth muscle cells and cardiomyocytes, and provided a platform for investigating mechanisms underlying the pathogenesis of laminopathies in a cell-type specific human context. Nevertheless, studies on iPSC-based models of laminopathy have expanded only in the last few years and, with the advancement of reprogramming and differentiation protocols, their number is expecting to further increase over time. This review will give an overview of models developed thus far, with a focus on the novel insights on epigenetic mechanisms underlying the disease in different human cellular contexts. Perspectives and future directions of the field will be also given, highlighting the potential of those models for preclinical studies for identifying molecular targets and their translational impact on patients' cure.

Endothelial progerin expression causes cardiovascular pathology through an impaired mechanoresponse.

Hutchinson-Gilford progeria syndrome (HGPS) is a premature aging disorder characterized by accelerated cardiovascular disease with extensive fibrosis. It is caused by a mutation in LMNA leading to expression of truncated prelamin A (progerin) in the nucleus. To investigate the contribution of the endothelium to cardiovascular HGPS pathology, we generated an endothelium-specific HGPS mouse model with selective endothelial progerin expression. Transgenic mice develop interstitial myocardial and perivascular fibrosis and left ventricular hypertrophy associated with diastolic dysfunction and premature death. Endothelial cells show impaired shear stress response and reduced levels of endothelial nitric oxide synthase (eNOS) and NO. On the molecular level, progerin impairs nucleocytoskeletal coupling in endothelial cells through changes in mechanoresponsive components at the nuclear envelope, increased F-actin/G-actin ratios, and deregulation of mechanoresponsive myocardin-related transcription factor-A (MRTFA). MRTFA binds to the Nos3 promoter and reduces eNOS expression, thereby mediating a profibrotic paracrine response in fibroblasts. MRTFA inhibition rescues eNOS levels and ameliorates the profibrotic effect of endothelial cells in vitro. Although this murine model lacks the key anatomical feature of vascular smooth muscle cell loss seen in HGPS patients, our data show that progerin-induced impairment of mechanosignaling in endothelial cells contributes to excessive fibrosis and cardiovascular disease in HGPS patients.

Cardiac Involvement in Emery-Dreifuss Muscular Dystrophy and Related Management Strategies.

Emery-Dreifuss muscular dystrophy (EDMD) is a group of hereditary muscular dystrophy syndrome caused by deficiency of genes encoding nuclear envelope proteins. Patients having EDMD show the triad of muscle dystrophy, joint contracture, and cardiac disease. In almost all patients, cardiac involvement is prevalent and is the most severe aspect of EDMD. Cardiac disease is predominantly shown by conduction defects, atrial fibrillation/flutter, and atrial standstill. Sudden death and heart failure because of left ventricular dysfunction are important causes of mortality, particularly in those patients that have the LMNA mutation. Medical treatment of EDMD is limited to addressing symptoms and ambulation support; moreover, pacemaker implantation is necessary when there are severe conduction defects and bradycardia occurs. Note that automated defibrillation devices may be considered for those patients who have a high risk of sudden death, rate, or rhythm control. Also, anticoagulation should be initiated in those patients who have atrial fibrillation/flutter. Thus, for optimal management, a multidisciplinary approach is required.