LMNA Mutations Research Articles

Progerin mRNA expression in non-HGPS patients is correlated with widespread shifts in transcript isoforms.

Hutchinson-Gilford Progeria Syndrome (HGPS) is a premature aging disease caused primarily by a C1824T mutation in LMNA. This mutation activates a cryptic splice donor site, producing a lamin variant called progerin. Interestingly, progerin has also been detected in cells and tissues of non-HGPS patients. Here, we investigated progerin expression using publicly available RNA-seq data from non-HGPS patients in the GTEx project. We found that progerin expression is present across all tissue types in non-HGPS patients and correlated with telomere shortening in the skin. Transcriptome-wide correlation analyses suggest that the level of progerin expression is correlated with switches in gene isoform expression patterns. Differential expression analyses show that progerin expression is correlated with significant changes in genes involved in splicing regulation and mitochondrial function. Interestingly, 5' splice sites whose use is correlated with progerin expression have significantly altered frequencies of consensus trinucleotides within the core 5' splice site. Furthermore, introns whose alternative splicing correlates with progerin have reduced GC content. Our study suggests that progerin expression in non-HGPS patients is part of a global shift in splicing patterns.

Lamin A/C deficiency-mediated ROS elevation contributes to pathogenic phenotypes of dilated cardiomyopathy in iPSC model

Mutations in the nuclear envelope (NE) protein lamin A/C (encoded by LMNA), cause a severe form of dilated cardiomyopathy (DCM) with early-onset life-threatening arrhythmias. However, molecular mechanisms underlying increased arrhythmogenesis in LMNA-related DCM (LMNA-DCM) remain largely unknown. Here we show that a frameshift mutation in LMNA causes abnormal Ca2+ handling, arrhythmias and disformed NE in LMNA-DCM patient-specific iPSC-derived cardiomyocytes (iPSC-CMs). Mechanistically, lamin A interacts with sirtuin 1 (SIRT1) where mutant lamin A/C accelerates degradation of SIRT1, leading to mitochondrial dysfunction and oxidative stress. Elevated reactive oxygen species (ROS) then activates the Ca2+/calmodulin-dependent protein kinase II (CaMKII)-ryanodine receptor 2 (RYR2) pathway and aggravates the accumulation of SUN1 in mutant iPSC-CMs, contributing to arrhythmias and NE deformation, respectively. Taken together, the lamin A/C deficiency-mediated ROS disorder is revealed as central to LMNA-DCM development. Manipulation of impaired SIRT1 activity and excessive oxidative stress is a potential future therapeutic strategy for LMNA-DCM.

Abstract Tu086: Repairing nuclear envelope ruptures to ameliorate Lamin-related cardiomyopathy

Heterozygous loss-of-function mutations in LMNA , encoding nuclear lamina protein Lamin A/C, cause severe adult-onset dilated cardiomyopathy. A prevailing hypothesis posits that LMNA insufficiency causes nuclear envelope structural defects that ultimately cause the disease. However, the mechanisms linking defective nuclear envelopes to cardiomyopathy remain undefined. To determine specific nuclear envelope defects and their consequences, we deleted Lmna in cardiomyocytes in adult mice ( Lmna CKO ). Strikingly, a modest (50%) reduction of Lamin A/C caused widespread localized ruptures of the nuclear envelope in cardiomyocytes (En et al. bioRxiv 2023). The nuclear envelope ruptures did not cause immediate cell death, but accompanied a strong inflammatory response in the heart, prior to fatal cardiomyopathy. We hypothesized that DNA leaked from ruptured nuclei might elicit the cGAS-STING cytosolic DNA sensing pathway of innate immunity. Contrary to this hypothesis, we did not observe cGAS-STING activation in Lmna CKO cardiomyocytes. This lack of cGAS-STING activation was likely due to the near absence of cGAS protein in adult cardiomyocytes. To investigate the mechanism underlying cardiac inflammation in Lmna CKO mice, we conducted time-course single-nucleus RNA-seq. This analysis nominated cardiac fibroblasts as the central mediator of the inflammatory response, receiving ECM-mediated signaling from Lmna CKO cardiomyocytes and recruiting immune cells to the mutant hearts. Finally, we found evidence suggesting that nuclear envelope repair activity counteracts nuclear envelope ruptures in Lmna CKO mice. We found that the envelope ruptured sites co-localized with the ESCRT-III membrane remodeling complex, previously implicated in nuclear envelope repair. We further found that overexpression of DNA-binding protein BANF1 promoted ESCRT-III recruitment to the ruptured sites. We are currently investigating whether facilitated nuclear envelope repair ameliorates cardiomyopathy in Lmna CKO mice. If it does, nuclear envelope repair may be a potential therapeutic strategy for LMNA -related dilated cardiomyopathy.

Navigating Lipodystrophy: Insights from Laminopathies and Beyond.

Recent research into laminopathic lipodystrophies-rare genetic disorders caused by mutations in the LMNA gene-has greatly expanded our knowledge of their complex pathology and metabolic implications. These disorders, including Hutchinson-Gilford progeria syndrome (HGPS), Mandibuloacral Dysplasia (MAD), and Familial Partial Lipodystrophy (FPLD), serve as crucial models for studying accelerated aging and metabolic dysfunction, enhancing our understanding of the cellular and molecular mechanisms involved. Research on laminopathies has highlighted how LMNA mutations disrupt adipose tissue function and metabolic regulation, leading to altered fat distribution and metabolic pathway dysfunctions. Such insights improve our understanding of the pathophysiological interactions between genetic anomalies and metabolic processes. This review merges current knowledge on the phenotypic classifications of these diseases and their associated metabolic complications, such as insulin resistance, hypertriglyceridemia, hepatic steatosis, and metabolic syndrome, all of which elevate the risk of cardiovascular disease, stroke, and diabetes. Additionally, a range of published therapeutic strategies, including gene editing, antisense oligonucleotides, and novel pharmacological interventions aimed at addressing defective adipocyte differentiation and lipid metabolism, will be explored. These therapies target the core dysfunctional lamin A protein, aiming to mitigate symptoms and provide a foundation for addressing similar metabolic and genetic disorders.

Recent insights in striated muscle laminopathies.

To highlight recent insights in different aspects of striated muscle laminopathies (SMLs) related to LMNA mutations. Clinical and genetic studies allow better patient management and diagnosis, with confirmation of ventricular tachyarrhythmias (VTA) risk prediction score to help with ICD implantation and development of models to help with classification of LMNA variants of uncertain significance. From a pathophysiology perspective, characterization of lamin interactomes in different contexts revealed new lamin A/C partners. Expression or function modulation of these partners evidenced them as potential therapeutic targets. After a positive phase 2, the first phase 3 clinical trial, testing a p38 inhibitor targeting the life-threatening cardiac disease of SML, has been recently stopped, thus highlighting the need for new therapeutic approaches together with new animal and cell models. Since the first LMNA mutation report in 1999, lamin A/C structure and functions have been actively explored to understand the SML pathophysiology. The latest discoveries of partners and altered pathways, highlight the importance of lamin A/C at the nuclear periphery and in the nucleoplasm. Modulation of altered pathways allowed some benefits, especially for cardiac involvement. However, additional studies are still needed to fully assess treatment efficacy and safety.

Missense and Non-Missense Lamin A/C Gene Mutations Are Similarly Associated with Major Arrhythmic Cardiac Events: A 20-Year Single-Centre Experience.

Arrhythmic risk stratification in patients with Lamin A/C gene (LMNA)-related cardiomyopathy influences clinical decisions. An implantable cardioverter defibrillator (ICD) should be considered in patients with an estimated 5-year risk of malignant ventricular arrhythmia (MVA) of ≥10%. The risk prediction score for MVA includes non-missense LMNA mutations, despite their role as an established risk factor for sudden cardiac death (SCD) has been questioned in several studies. The purpose of this study is to investigate cardiac features and find gene-phenotype correlations that would contribute to the evidence on the prognostic implications of non-missense vs. missense mutations in a cohort of LMNA mutant patients. An observational, prospective study was conducted in which 54 patients positive for a Lamin A/C mutation were enrolled, and 20 probands (37%) were included. The median age at first clinical manifestation was 41 (IQR 19) years. The median follow-up was 8 years (IQR 8). The type of LMNA gene mutation was distributed as follows: missense in 26 patients (48%), non-frameshift insertions in 16 (30%), frameshift deletions in 5 (9%), and nonsense in 7 (13%). Among the missense mutation carriers, two (8%) died and four (15%) were admitted onto the heart transplant list or underwent transplantation, with a major adverse cardiovascular event (MACE) rate of 35%. No statistically significant differences in MACE prevalence were identified according to the missense and non-missense mutation groups (p value = 0.847). Our data shift the spotlight on this considerable topic and could suggest that some missense mutations may deserve attention regarding SCD risk stratification in real-world clinical settings.

Creatine and l-carnitine attenuate muscular laminopathy in the LMNA mutation transgenic zebrafish

Lamin A/C gene (LMNA) mutations contribute to severe striated muscle laminopathies, affecting cardiac and skeletal muscles, with limited treatment options. In this study, we delve into the investigations of five distinct LMNA mutations, including three novel variants and two pathogenic variants identified in patients with muscular laminopathy. Our approach employs zebrafish models to comprehensively study these variants. Transgenic zebrafish expressing wild-type LMNA and each mutation undergo extensive morphological profiling, swimming behavior assessments, muscle endurance evaluations, heartbeat measurement, and histopathological analysis of skeletal muscles. Additionally, these models serve as platform for focused drug screening. We explore the transcriptomic landscape through qPCR and RNAseq to unveil altered gene expression profiles in muscle tissues. Larvae of LMNA(L35P), LMNA(E358K), and LMNA(R453W) transgenic fish exhibit reduced swim speed compared to LMNA(WT) measured by DanioVision. All LMNA transgenic adult fish exhibit reduced swim speed compared to LMNA(WT) in T-maze. Moreover, all LMNA transgenic adult fish, except LMNA(E358K), display weaker muscle endurance than LMNA(WT) measured by swimming tunnel. Histochemical staining reveals decreased fiber size in all LMNA mutations transgenic fish, excluding LMNA(WT) fish. Interestingly, LMNA(A539V) and LMNA(E358K) exhibited elevated heartbeats. We recognize potential limitations with transgene overexpression and conducted association calculations to explore its effects on zebrafish phenotypes. Our results suggest lamin A/C overexpression may not directly impact mutant phenotypes, such as impaired swim speed, increased heart rates, or decreased muscle fiber diameter. Utilizing LMNA zebrafish models for drug screening, we identify l-carnitine treatment rescuing muscle endurance in LMNA(L35P) and creatine treatment reversing muscle endurance in LMNA(R453W) zebrafish models. Creatine activates AMPK and mTOR pathways, improving muscle endurance and swim speed in LMNA(R453W) fish. Transcriptomic profiling reveals upstream regulators and affected genes contributing to motor dysfunction, cardiac anomalies, and ion flux dysregulation in LMNA mutant transgenic fish. These findings faithfully mimic clinical manifestations of muscular laminopathies, including dysmorphism, early mortality, decreased fiber size, and muscle dysfunction in zebrafish. Furthermore, our drug screening results suggest l-carnitine and creatine treatments as potential rescuers of muscle endurance in LMNA(L35P) and LMNA(R453W) zebrafish models. Our study offers valuable insights into the future development of potential treatments for LMNA-related muscular laminopathy.

Distribution of myocardial fibrosis in patients with nonischemic cardiomyopathy and ventricular tachycardia based on genetic variant

BackgroundMany genetic nonischemic dilated cardiomyopathies (NICMs) cause ventricular tachycardias (VTs) originating from scar substrate identified as areas of low electrogram voltage. Substrate locations vary, and the causes of scar are not well defined. ObjectiveThis study evaluated VT substrate locations in genetic NICM patients undergoing VT ablation to evaluate spatial relationships between specific variants and substrate locations. MethodsIn this retrospective case series analysis, 32 patients (aged 55 ± 16 years; 94% male; left ventricular ejection fraction, 34% ± 13%) with genetic NICM referred for VT ablation between October 2018 and November 2022 at a single medical center were evaluated. Scar locations were defined as areas of low unipolar or bipolar voltage. ResultsOf the 32 patients evaluated, mutations in TTN (n = 11), LMNA (n = 6), PKP2 (n = 5), MYBPC3 (n = 3), DSP (n = 2), TTR (n = 1), FLNC (n = 1), AGL (n = 1), DES (n = 1), and DSG2 (n = 1) were observed. Substrates associated with mutations in TTN were observed only in basal subregions, predominantly anterior (100%) and septal (50%) regions. LMNA mutations were associated with fibrosis in mid inferolateral (60%) and apical inferolateral (60%) regions. Substrate location for individuals with PKP2 mutations was solely observed in the right ventricle, predominantly basal inferolateral regions. ConclusionUnderstanding spatial relationships between genetic variants causing NICM and VT substrate locations can help lead to generalizable regions in patients with genetically related NICM presenting in VT, which can be investigated during ablation procedures.

Generation of isogenic allelic series of LMNA-mutated hiPSC lines using the novel and highly-efficient targeting platform, STRAIGHT-IN

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): The Netherlands Organisation for Health Research and Development ZonMW Background Human induced pluripotent stem cells (hiPSCs) have demonstrated enormous potential for advancing in vitro disease modelling and genetically modified hiPSCs carrying disease-associated variants are particularly useful tools for this purpose. Until now, strategies for efficient and rapid integration of large DNA payloads (>10 kb) into specific genomic regions are still limited, thus precluding efficient and rapid targeting of hiPSC lines. Purpose and Methods To overcome this, the STRAIGHT-IN platform (Serine and Tyrosine Recombinase Assisted Integration of Genes for High-Throughput INvestigation) was developed that combined different classes of site-specific recombinases with CRISPR-Cas9 mediated homologous recombination and allowed stringent site-specific replacement of large genomic fragments in hiPSCs. Here, we use STRAIGHT-IN to simultaneously generate a library of genetically matched hiPSC lines carrying multiple heterozygous mutations in LMNA gene. Mutations in LMNA, encoding Lamin A/C protein, have been associated with 5-10% cases of dilated cardiomyopathy (DCM) with conduction defects. Results Through detailed online searches of the LMNA database and literature, we identified and selected 11 LMNA mutations to insert into a wild-type hiPSC line based on the following criteria: (i) mutations associated with cardiac abnormalities, in terms of structural (DCM/heart failure) and arrhythmic phenotypes; (ii) mutations with known familiar/pedigree-relationship; (iii) different types of mutations (missense and nonsense). We then applied the workflow of STRAIGHT-IN consisting of: (1) replacing the entire LMNA genomic locus (33 kb) on one allele with a Landing Pad (LP) cassette containing Serine Recombinase (Bxb1) recognition sites; (2) reintroducing LMNA gene into the LP cassette through integration of Bxb1-Donor plasmids carrying the LMNA variants of interest via Bxb1 expression; (3) expressing a tyrosine recombinase (Cre) to excise the majority of the auxiliary exogenous DNA sequences. Conclusions STRAIGHT-IN allows simultaneous generation of a panel of 11 isogenic hiPSC lines carrying selected LMNA mutations rapidly (5-6 weeks), efficiently and cost-effectively, thus facilitating the production of specific mutated hiPSC lines for disease modelling and personalized medicine applications.

Differential sex-dependent role of lncRNAs in cardiomyopathy

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Ministry of Education and Science Cardiovascular diseases are one of the most prevalent causes of mortality and morbidity worldwide. Structural diseases such as dilated and hypertrophic cardiomyopathy significantly contributed to it. In recent years, several studies have pinpointed the importance of non-coding genome in the pathogenesis of cardiomyopathy. We have previously reported the role of distinct lncRNAs in atrial fibrillation. We now explored the plausible role of these lncRNAs in cardiomyopathy by analyzing their expression in two different mouse mutant models of lamin (LMNA) - LMNAR249W and αMHCCreLMNAFF, a cardiac hypertrophic MyBPC3 mutant model as well as in experimental myocardial infarction mice. Importantly, both LMNA mutant models developed a dilated cardiomyopathy, a condition distinctly observed in males but not in females. Our data demonstrated that Walras, Gm26533, Wallrd, Walaa and Walrad are downregulated in females, but not males. Furthermore, differential deregulation is also observed in MyBPC3 mutant model but not in myocardial infarction. In vitro analyses demonstrated an estrogen-dependent regulation. In addition, expression analyses in distinct cardiovascular cell lines revealed enriched myocardial expression of Walras and Gm26533 while Wallrd and Walaa are preferentially expressed in endocardial cells. These data were further validated by in situ hybridization in embryonic cardiac tissues. Walras overexpression resulted in enhanced expression of two key factors of UPR signaling pathway, i.e. Atf6 and Ire1, while Walras inhibition downregulated them. Upregulation of both UPR factors in Walrasgain-of-function assays is accompanied by increased cardiomyocyte apoptosis. In contrast, Walras inhibition resulted in increased Bcl2 expression and therefore increased cell viability. Mechanistically, Walras directly interacts with calumenin protein, a known protective factor against UPR-associated apoptosis, as demonstrated by pulldown assays. In sum, we demonstrated sex-dependent regulation of distinct lncRNAs in different cardiomyopathic mouse models and at least one of them, i.e. Walras contributes to UPR-associated apoptosis regulation, providing a causative link to the development of distinct cardiomyopathies.

Troponin T Assessment Allows for Identification of Mutation Carriers among Young Relatives of Patients with LMNA-Related Dilated Cardiomyopathy.

Background:LMNA-related dilated cardiomyopathy (LMNA-DCM) caused by mutations in the lamin A/C gene (LMNA) is one of the most common forms of hereditary DCM. Due to the high risk of mutation transmission to offspring and the high incidence of ventricular arrhythmia and sudden death even before the onset of heart failure symptoms, it is very important to identify LMNA-mutation carriers. However, many relatives of LMNA-DCM patients do not report to specialized centers for clinical or genetic screening. Therefore, an easily available tool to identify at-risk subjects is needed. Methods: We compared two cohorts of young, asymptomatic relatives of DCM patients who reported for screening: 29 LMNA mutation carriers and 43 individuals from the control group. Receiver operating characteristic (ROC) curves for potential indicators of mutation carriership status were analyzed. Results: PR interval, N-terminal pro-B-type natriuretic peptide (NT-proBNP), and high-sensitivity cardiac troponin T (hscTnT) serum levels were higher in the LMNA mutation carrier cohort. Neither group differed significantly with regard to creatinine concentration or left ventricular ejection fraction. The best mutation carriership discriminator was hscTnT level with an optimal cut-off value at 5.5 ng/L, for which sensitivity and specificity were 86% and 93%, respectively. The median hscTnT level was 11.0 ng/L in LMNA mutation carriers vs. <3.0 ng/L in the control group, p < 0.001. Conclusions: Wherever access to genetic testing is limited, LMNA mutation carriership status can be assessed reliably using the hscTnT assay. Among young symptomless relatives of LMNA-DCM patients, a hscTnT level >5.5 ng/L strongly suggests mutation carriers.

Eliminating elevated p53 signaling fails to rescue skeletal muscle defects or extend survival in lamin A/C-deficient mice.

Lamins A and C, encoded by the LMNA gene, are nuclear intermediate filaments that provide structural support to the nucleus and contribute to chromatin organization and transcriptional regulation. LMNA mutations cause muscular dystrophies, dilated cardiomyopathy, and other diseases. The mechanisms by which many LMNA mutations result in muscle-specific diseases have remained elusive, presenting a major hurdle in the development of effective treatments. Previous studies using striated muscle laminopathy mouse models found that cytoskeletal forces acting on mechanically fragile Lmna-mutant nuclei led to transient nuclear envelope rupture, extensive DNA damage, and activation of DNA damage response (DDR) pathways in skeletal muscle cells in vitro and in vivo. Furthermore, hearts of Lmna mutant mice have elevated activation of the tumor suppressor protein p53, a central regulator of DDR signaling. We hypothesized that elevated p53 activation could present a pathogenic mechanism in striated muscle laminopathies, and that eliminating p53 activation could improve muscle function and survival in laminopathy mouse models. Supporting a pathogenic function of p53 activation in muscle, stabilization of p53 was sufficient to reduce contractility and viability in wild-type muscle cells in vitro. Using three laminopathy models, we found that increased p53 activity in Lmna-mutant muscle cells primarily resulted from mechanically induced damage to the myonuclei, and not from altered transcriptional regulation due to loss of lamin A/C expression. However, global deletion of p53 in a severe muscle laminopathy model did not reduce the disease phenotype or increase survival, indicating that additional drivers of disease must contribute to the disease pathogenesis.

LMNA–RELATED DILATED CARDIOMYOPATHY PRESENTING WITH REGIONAL WALL AKINESIS AND TRANSMURAL LATE GADOLINIUM ENHANCEMENT

Abstract A 26–year–old girl was admitted at hospital in December 2022 for a syncopal episode. She referred fatigue and dyspnea in the last 2 months. EKG was markedly abnormal showing peripheral low voltages, poor R wave progression in prechordial leads, negative T waves V4–V6, DII, DIII and aVF, fragmented QRS (Fig.1). Echo showed moderately dilated left ventricle (LV) with apical akinesia and apical aneurysm (no thrombi) and hypo–akinesia and hyperechoic appearance of the middle segments of the infero–posterior and lateral wall (Fig.2a). EF was 38%. There was no family history for sudden cardiac death and cardiomyopathy. Creatine kinase and neurological examination were normal. The diagnostic work–up included: myocardial scintigraphy which showed fixed tracer uptake deficit at apical and posterolateral levels (Fig.2b); cardiac magnetic resonance (CMR): apical aneurysm with extended late gadolinium enhancement (LGE) due to fibrosis, focally transmural, on the left ventricle’s midapical and infero–lateral thinned–hypokinetic myocardial walls (Fig.3a, 3b); Coronary angiography showed no stenosis. Due to myocardial aneurysm in absence of CAD, Chagas disease was excluded. We performed LV endomyocardial biopsy which showed cardiomyopathic changes and replacement fibrosis. Due to fibrosis extension, complex ventricular extrasystoles detected on monitoring and syncope, ICD was implanted. Finally genetic testing showed c.1621C&amp;gt;Tp.Arg541Cys LMNA pathogenetic mutation leading to the diagnosis of LMNA–related LV cardiomyopathy, with extensive fibrosis in multiple areas of left ventricle including the apical segments at a very young age. Patients with LMNA mutation-related heart disease are characterized by conduction abnormalities, ventricular tachyarrhythmias (VA) and high risk of sudden cardiac death with mildly impaired systolic function, often without chamber dilation. About 88% LMNA– cardiomyopathy have typical myocardial fibrosis, predominantly in the mid-myocardium of the basal septum. However, our patient and previous reported cases with the same p.R541 LMNA mutation presents with a specific phenotype including regional LV akinesis, segmental transmural LGE, significant LV dilatation and systolic dysfunction and VA without conduction abnormality. Of note, EKG shows normal A–V conduction but low voltage and negative T waves in precordial and inferior leads. These features are not typical for LMNA–disease and underline the phenotypic variability of cardiomyopathies.

Perinuclear damage from nuclear envelope deterioration elicits stress responses that contribute to LMNA cardiomyopathy.

Mutations in the LMNA gene encoding lamins A/C cause an array of tissue-selective diseases, with the heart being the most commonly affected organ. Despite progress in understanding the perturbations emanating from LMNA mutations, an integrative understanding of the pathogenesis underlying cardiac dysfunction remains elusive. Using a novel conditional deletion model capable of translatome profiling, we observed that cardiomyocyte-specific Lmna deletion in adult mice led to rapid cardiomyopathy with pathological remodeling. Before cardiac dysfunction, Lmna-deleted cardiomyocytes displayed nuclear abnormalities, Golgi dilation/fragmentation, and CREB3-mediated stress activation. Translatome profiling identified MED25 activation, a transcriptional cofactor that regulates Golgi stress. Autophagy is disrupted in the hearts of these mice, which can be recapitulated by disrupting the Golgi. Systemic administration of modulators of autophagy or ER stress significantly delayed cardiac dysfunction and prolonged survival. These studies support a hypothesis wherein stress responses emanating from the perinuclear space contribute to the LMNA cardiomyopathy development.

Abstract 3105: Lamin Mutations: Single Nuclei Multiomic Analysis Reveals Endothelial Cell Dysfunction And Its Cardiovascular Implications

Background: LMNA-related dilated cardiomyopathy (DCM) or cardiolaminopathy is an autosomal dominant trait with complete penetrance resulting in left ventricular enlargement and cardiac dysfunction. LMNA mutations in DCM have been shown to cause to ventricular arrythmias and conduction deficits. The interplay between the LMNA gene and other cell types have yet to be fully elucidated. Notably, cardiolaminopathy patients present with prominent cardiac fibrosis, but the mechanistic link between LMNA mutations and the development of fibrosis remains inconclusive. Additionally, LMNA is expressed in the endothelium, and patients with cardiolaminopathy exhibit distinct endothelial dysfunction. Hypothesis: We hypothesize that LMNA mutations prompt a cascade of pathological alterations on the endothelium, causing vascular dysfunction and fibrosis through endothelial to mesenchymal transition (EndoMT). Aims: Next generation sequencing platforms are critical to identifying these epigenetic and transcriptomic changes in the endothelium. Combining sequencing technology with our iPSC platform, we aim to unravel the mechanism behind vascular dysfunction and fibrosis in LMNA-DCM to uncover novel therapeutic targets and treatment strategies. Methods: We performed single nuclei multiome (RNA and ATAC) on cardiac tissue from one patient with LMNA-dilated cardiomyopathy. Frozen tissues were minced into pieces before digestion. We then utilized patient-specific induced pluripotent stem cells (iPSCs) and CRISPR-generated isogenic controls. We differentiated to endothelial cells (iPSC-ECs) and nuclei capture was performed after 24hr flow. Results: Endothelial cell clusters from cardiac tissue exhibit increased stress and mesenchymal markers. Phenotypic shift and EC dysfunction was corroborated with iPSC-ECs derived from two LMNA-DCM patients. Conclusion: These results present important considerations highlighting vascular dysfunction in LMNA-DCM and notes the importance of the endothelium in cardiac health. By analyzing these datasets produced from LMNA-DCM cardiac tissue and our iPSC-EC platform, there is opportunity to both define the mechanisms that causes cardiac fibrosis and to develop new therapeutic strategies.

The Influence of a Genetic Variant in CCDC78 on LMNA-Associated Skeletal Muscle Disease.

Mutations in the LMNA gene-encoding A-type lamins can cause Limb-Girdle muscular dystrophy Type 1B (LGMD1B). This disease presents with weakness and wasting of the proximal skeletal muscles and has a variable age of onset and disease severity. This variability has been attributed to genetic background differences among individuals; however, such variants have not been well characterized. To identify such variants, we investigated a multigeneration family in which affected individuals are diagnosed with LGMD1B. The primary genetic cause of LGMD1B in this family is a dominant mutation that activates a cryptic splice site, leading to a five-nucleotide deletion in the mature mRNA. This results in a frame shift and a premature stop in translation. Skeletal muscle biopsies from the family members showed dystrophic features of variable severity, with the muscle fibers of some family members possessing cores, regions of sarcomeric disruption, and a paucity of mitochondria, not commonly associated with LGMD1B. Using whole genome sequencing (WGS), we identified 21 DNA sequence variants that segregate with the family members possessing more profound dystrophic features and muscle cores. These include a relatively common variant in coiled-coil domain containing protein 78 (CCDC78). This variant was given priority because another mutation in CCDC78 causes autosomal dominant centronuclear myopathy-4, which causes cores in addition to centrally positioned nuclei. Therefore, we analyzed muscle biopsies from family members and discovered that those with both the LMNA mutation and the CCDC78 variant contain muscle cores that accumulated both CCDC78 and RyR1. Muscle cores containing mislocalized CCDC78 and RyR1 were absent in the less profoundly affected family members possessing only the LMNA mutation. Taken together, our findings suggest that a relatively common variant in CCDC78 can impart profound muscle pathology in combination with a LMNA mutation and accounts for variability in skeletal muscle disease phenotypes.

MTOR Inhibition Prolongs Survival and Has Beneficial Effects on Heart Function After Onset of Lamin A/C Gene Mutation Cardiomyopathy in Mice.

Mutations in LMNA encoding nuclear envelope proteins lamin A/C cause dilated cardiomyopathy. Activation of the AKT/mTOR (RAC-α serine/threonine-protein kinase/mammalian target of rapamycin) pathway is implicated as a potential pathophysiologic mechanism. The aim of this study was to assess whether pharmacological inhibition of mTOR signaling has beneficial effects on heart function and prolongs survival in a mouse model of the disease, after onset of heart failure. We treated male LmnaH222P/H222P mice, after the onset of heart failure, with placebo or either of 2 orally bioavailable mTOR inhibitors: everolimus or NV-20494, a rapamycin analog highly selective against mTORC1. We examined left ventricular remodeling, and the cell biological, biochemical, and histopathologic features of cardiomyopathy, potential drug toxicity, and survival. Everolimus treatment (n=17) significantly reduced left ventricular dilatation and increased contractility on echocardiography, with a 7% (P=0.018) reduction in left ventricular end-diastolic diameter and a 39% (P=0.0159) increase fractional shortening compared with placebo (n=17) after 6 weeks of treatment. NV-20494 treatment (n=15) yielded similar but more modest and nonsignificant changes. Neither drug prevented the development of cardiac fibrosis. Drug treatment reactivated suppressed autophagy and inhibited mTORC1 signaling in the heart, although everolimus was more potent. With regards to drug toxicity, everolimus alone led to a modest degree of glucose intolerance during glucose challenge. Everolimus (n=20) and NV-20494 (n=20) significantly prolonged median survival in LmnaH222P/H222P mice, by 9% (P=0.0348) and 11% (P=0.0206), respectively, compared with placebo (n=20). These results suggest that mTOR inhibitors may be beneficial in patients with cardiomyopathy caused by LMNA mutations and that further study is warranted.

A CASE OF PROGRESSIVE ARRHYTHMIAS AND CARDIOMYOPATHY ASSOCIATED WITH LMNA MUTATIONS IDENTIFIED WITH GENETIC TESTING

A CASE OF PROGRESSIVE ARRHYTHMIAS AND CARDIOMYOPATHY ASSOCIATED WITH LMNA MUTATIONS IDENTIFIED WITH GENETIC TESTING

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.

Lamin A K97E leads to NF-κB-mediated dysfunction of inflammatory responses in dilated cardiomyopathy.

Lamins are type V intermediate filament proteins underlying the inner nuclear membrane which provide structural rigidity to the nucleus, tether the chromosomes, maintain nuclear homeostasis, and remain dynamically associated with developmentally regulated regions of the genome. A large number of mutations particularly in the LMNA gene encoding lamin A/C results in a wide array of human diseases, collectively termed as laminopathies. Dilated Cardiomyopathy (DCM) is one such laminopathic cardiovascular disease which is associated with systolic dysfunction of left or both ventricles leading to cardiac arrhythmia which ultimately culminates into myocardial infarction. In this work, we have unraveled the epigenetic landscape to address the regulation of gene expression in mouse myoblast cell line in the context of the missense mutation LMNA 289A<G (Lys97Glu) that is found in DCM-afflicted patient with severe symptoms. Significant changes in H3-specific epigenetic modifications indicated a dysregulation in transcription machinery which was investigated by RNA sequencing analysis. The major pathways involved in IL-17 signaling, cellular response to interferon-beta and gamma, cytokine production, and related pathways are found to be downregulated. Analysis of the promoter sequences of the genes in the abovementioned pathways led us to the master regulator NF-κB and its regulatory network. We report here for the first time that there is a significant downregulation of the NF-κB pathway, which has been implicated in cardio-protection elsewhere. This provides a new pathophysiological explanation that correlates an LMNA mutation and dilated cardiomyopathy.