Development Of Dilated Cardiomyopathy Research Articles

Screening for dilated cardiomyopathy in immediate family members: to whom, how, when (and where).

Dilated cardiomyopathy (DCM) is defined by the presence of left ventricular dilation and systolic dysfunction in the absence of coronary artery disease, valvular disease, congenital heart disease, or altered haemodynamic conditions. Dilated cardiomyopathy can recognize multiple aetiologies, including infectious processes, effect of toxic substances, immunological mechanisms, and genetic causes. In recent years, many genes coding for proteins involved in the structure and function of the cardiomyocytes have been associated with the development of DCM, making the identification of familial forms increasingly frequent. At the same time, an ever-increasing use of cardiac magnetic resonance imaging has made it possible to identify early morpho-functional alterations in subjects with initial forms of the disease, or carriers of pathogenic genetic variants. The increasingly in-depth understanding of the genetic and molecular mechanisms operating in DCM has also favoured the development of new therapeutic strategies including drugs with molecular targets and gene therapies. In this panorama, screening of family members of patients affected by DCM represents an important tool for early diagnosis, treatment, and prognostic stratification. In relation to its clinical relevance and its complexity, it is important that family screening and follow-up of identified patients are carried out in units dedicated to the treatment and study of cardiomyopathies.

HOIL-1L deficiency induces cell cycle alteration which causes immaturity of skeletal muscle and cardiomyocytes

HOIL-1L deficiency was recently reported to be one of the causes of myopathy and dilated cardiomyopathy (DCM). However, the mechanisms by which myopathy and DCM develop have not been clearly elucidated. Here, we sought to elucidate these mechanisms using the murine myoblast cell line C2C12 and disease-specific human induced pluripotent stem cells (hiPSCs). Myotubes differentiated from HOIL-1L-KO C2C12 cells exhibited deteriorated differentiation and mitotic cell accumulation. CMs differentiated from patient-derived hiPSCs had an abnormal morphology with a larger size and were excessively multinucleated compared with CMs differentiated from control hiPSCs. Further analysis of hiPSC-derived CMs showed that HOIL-1L deficiency caused cell cycle alteration and mitotic cell accumulation. These results demonstrate that abnormal cell maturation possibly contribute to the development of myopathy and DCM. In conclusion, HOIL-1L is an important intrinsic regulator of cell cycle-related myotube and CM maturation and cell proliferation.

Epidermal Growth Factor-Like Repeats and Discoidin I-Like Domains 3 Deficiency Attenuates Dilated Cardiomyopathy by Inhibiting Ubiquitin Specific Peptidase 10 Dependent Smad4 Deubiquitination.

Dilated cardiomyopathy (DCM) is the leading cause of heart failure with a poor prognosis. Recent studies suggest that endothelial to mesenchymal transition (EndMT) may be involved in the pathogenesis and cardiac remodeling during DCM development. EDIL3 (epidermal growth factor-like repeats and discoidin I-like domains 3) is an extracellular matrix glycoprotein that has been reported to promote EndMT in various diseases. However, the roles of EDIL3 in DCM still remain unclear. A mouse model of DCM and human umbilical vein endothelial cells were used to explore the roles and mechanisms of EDIL3 in DCM. The results indicated that EndMT and EDIL3 were activated in DCM mice. EDIL3 deficiency attenuated cardiac dysfunction and remodeling in DCM mice. EDIL3 knockdown alleviated EndMT by inhibiting USP10 (ubiquitin specific peptidase 10) dependent Smad4 deubiquitination invivo and invitro. Recombinant human EDIL3 promoted EndMT via reinforcing deubiquitination of Smad4 in human umbilical vein endothelial cells treated with IL-1β (interleukin 1β) and TGF-β (transforming growth factor beta). Inhibiting USP10 abolished EndMT exacerbated by EDIL3. In addition, recombinant EDIL3 also aggravates doxorubicin-induced EndMT by promoting Smad4 deubiquitination in HUVECs. Taken together, these results indicate that EDIL3 deficiency attenuated EndMT by inhibiting USP10 dependent Smad4 deubiquitination in DCM mice.

Ryanodine receptor dysfunction causes senescence and fibrosis in Duchenne dilated cardiomyopathy.

Duchenne muscular dystrophy (DMD) is an X-linked disorder characterized by progressive muscle weakness due to the absence of functional dystrophin. DMD patients also develop dilated cardiomyopathy (DCM). We have previously shown that DMD (mdx) mice and a canine DMD model (GRMD) exhibit abnormal intracellular calcium (Ca2+) cycling related to early-stage pathological remodelling of the ryanodine receptor intracellular calcium release channel (RyR2) on the sarcoplasmic reticulum (SR) contributing to age-dependent DCM. Here, we used hiPSC-CMs from DMD patients selected by Speckle-tracking echocardiography and canine DMD cardiac biopsies to assess key early-stage Duchenne DCM features. Dystrophin deficiency was associated with RyR2 remodelling and SR Ca2+ leak (RyR2 Po of 0.03±0.01 for HC vs. 0.16±0.01 for DMD, P<0.01), which led to early-stage defects including senescence. We observed higher levels of senescence markers including p15 (2.03±0.75 for HC vs. 13.67±5.49 for DMD, P<0.05) and p16 (1.86±0.83 for HC vs. 10.71±3.00 for DMD, P<0.01) in DMD hiPSC-CMs and in the canine DMD model. The fibrosis was increased in DMD hiPSC-CMs. We observed cardiac hypocontractility in DMD hiPSC-CMs. Stabilizing RyR2 pharmacologically by S107 prevented most of these pathological features, including the rescue of the contraction amplitude (1.65±0.06μm for DMD vs. 2.26±0.08μm for DMD+S107, P<0.01). These data were confirmed by proteomic analyses, in particular ECM remodelling and fibrosis. We identified key cellular damages that are established earlier than cardiac clinical pathology in DMD patients, with major perturbation of the cardiac ECC. Our results demonstrated that cardiac fibrosis and premature senescence are induced by RyR2 mediated SR Ca2+ leak in DMD cardiomyocytes. We revealed that RyR2 is an early biomarker of DMD-associated cardiac damages in DMD patients. The progressive and later DCM onset could be linked with the RyR2-mediated increased fibrosis and premature senescence, eventually causing cell death and further cardiac fibrosis in a vicious cycle leading to further hypocontractility as a major feature of DCM. The present study provides a novel understanding of the pathophysiological mechanisms of the DMD-induced DCM. By targeting RyR2 channels, it provides a potential pharmacological treatment.

Diet-Mediated Dilated Cardiomyopathy in the Canine

Dilated cardiomyopathy (DCM) is a disease of the heart muscle resulting in decreased myocardial function and is the second most common myopathy in canine. Previously, canine dilated cardiomyopathy was considered to be an inherited disease among large and giant breeds, however, recent reports suggest a possible link between certain grain-free diets and this condition. Several investigations into the incidence of this condition in relationship to grain-free diet consumption have been conducted in recent years. The most recent research shows a static overall trend in the incidence of DCM despite a five-fold increase in the sales of grain-free pet foods. Inadequate intake of protein, taurine, and specific sulfur-containing amino acids may have a potential role in the development of DCM, as these nutrients are crucial for cardiac muscle development and function. However, significant research remains to be done on the topic to discern any potential definitive causation.

Comprehensive review on gene mutations contributing to dilated cardiomyopathy.

Dilated cardiomyopathy (DCM) is one of the most common primary myocardial diseases. However, to this day, it remains an enigmatic cardiovascular disease (CVD) characterized by ventricular dilatation, which leads to myocardial contractile dysfunction. It is the most common cause of chronic congestive heart failure and the most frequent indication for heart transplantation in young individuals. Genetics and various other factors play significant roles in the progression of dilated cardiomyopathy, and variants in more than 50 genes have been associated with the disease. However, the etiology of a large number of cases remains elusive. Numerous studies have been conducted on the genetic causes of dilated cardiomyopathy. These genetic studies suggest that mutations in genes for fibronectin, cytoskeletal proteins, and myosin in cardiomyocytes play a key role in the development of DCM. In this review, we provide a comprehensive description of the genetic basis, mechanisms, and research advances in genes that have been strongly associated with DCM based on evidence-based medicine. We also emphasize the important role of gene sequencing in therapy for potential early diagnosis and improved clinical management of DCM.

The role of TBX20 truncating variants in dilated and left ventricular non-compaction cardiomyopathy

Abstract Background The genetic cause of dilated cardiomyopathy (DCM) remains unexplained in a considerable proportion of cases. TBX20, the T-Box transcription factor 20 gene, has been linked to cardiac septal defects. Although only a few case reports have described an association between TBX20 and DCM/left ventricular non-compaction (LVNC), there are no case-control studies available, and TBX20 is still considered a gene with limited evidence for these phenotypes. Objectives This study sought to investigate the relationship between truncating variants in TBX20 (TBX20tv) and the development of DCM and LVNC. Methods TBX20 was sequenced using massive parallel sequencing in 7,463 unrelated probands with DCM/LVNC and 22,773 probands with other diagnoses (e.g., hypertrophic or arrhythmogenic cardiomyopathy, channelopathies, or aortic diseases) as internal controls. It was tested for enrichment and cosegregation of TBX20tv in DCM/LVNC, and clinical characteristics and outcomes in carriers were analyzed. Results Twenty-four probands with 22 TBX20tv were identified. Variant frequencies were significantly higher in patients with DCM/LVNC (24/7,463; 0.29%) than in internal controls (2/22,773; 0.008%) or controls from the gnomAD database (4/124,098; 0.003%), with an OR of 70.18 (CI95%: 9.48 to 519.8; p &amp;lt;0.0001) and 95.61 (CI95%: 33.06-276.55; p &amp;lt;0.0001), respectively. Cosegregation was studied in 21 families, identifying 57 carriers, of whom 43 (75.4%) had cardiac involvement. A combined LODs score of 4.41 was obtained, which is indicative of very strong segregation. Regarding clinical characteristics, the mean age at diagnosis was 37 years old, and 50% of carriers were female. Forty-six percent developed left-ventricular dysfunction, which was moderate to severe in half of the cases. Three carriers received a heart transplant, and another carrier died due to heart failure. Congenital heart defects were present in 16 patients (28.1%). Valvular involvement was the most frequent congenital abnormality (5 cases had bicuspid aortic valve, and another 5 had mitral valve defects), followed by heart septal defects (3 atrial and 3 ventricular); coronary anomalies (2) and aortic coarctation (2) were also detected. In some patients, these defects presented as complex congenital heart disease. Conclusions TBX20tv are associated with the development of dilated and non-compaction cardiomyopathy, and the presence of congenital heart defects is also common. Although some carriers, particularly younger ones, may not present the phenotype, nearly half of them experience ventricular dysfunction, and significant cardiac events, such as cardiac death or transplantation, are not uncommon. Therefore, the TBX20 gene should be routinely included in genetic testing panels for DCM and LVNC.

Abstract 14241: Alcohol Exposure Among Patients With Dilated Cardiomyopathy: A Report From the DCM Precision Medicine Study

Introduction: Alcohol-related cardiomyopathy is characterized by cardiac dysfunction and dilatation due to prolonged and excessive alcohol (ETOH) consumption. This study aims to determine the prevalence, use patterns and genetic associations of ETOH exposure in patient with dilated cardiomyopathy (DCM) and their first-degree relatives (FDR). Hypothesis: 1. There is increased prevalence of EOTH use among patients who develop DCM. 2. Non-genetic co-morbidities are more common in patients who use ETOH and developed DCM. 3. Probands and FDR who use ETOH and develop DCM are more likely to have genetic variants. Methods: We analyzed clinical and genetic data on individuals aged 18 and older enrolled in the US DCM Precision Medicine Study. Partial and full DCM phenotypic expression were included in the analysis. The AUDIT-C score was used to evaluate the intensity of ETOH use. ETOH use and presence of DCM-related rare genetic variants were examined in FDRs using GEE type logistic mixed models adjusted for intra-family correlation and site heterogeneity. Results: A total of 2,595 subjects (1,188 probands and 1,407 FDRs) were included. Prior and current ETOH users were 270 (23%) and 546 (46%) for probands, and 30 (10%) and 168 (54%) for FDRs with DCM/partial DCM. Avg. years of drinking were 25.2 for probands and 24.0 for FDRs with DCM/partial DCM; the percent with AUDIT-C positive scores were 31.5 for probands and 32.7 for FDRs with DCM/partial DCM. In probands, moderate or high/severe ETOH use was more likely to be in men, white, Hispanic and those with &lt;/=12 yrs. of education (p&amp;lt;0.001). Patients drinking heavily were more likely to have hypertension, diabetes, hypercholesterolemia, and history of arrhythmia/conduction disease. Among FDRs, DCM/partial DCM was associated with the presence of DCM-related variants but not with moderate-severe drinking years in quartile after controlling for demographics and comorbidities. ETOH use did not modify the genetic effect on DCM/partial DCM. Conclusions: There is a high prevalence of prior or current ETOH use among probands and FDRs with DCM/partial DCM with an average ETOH use between 24-25 yrs. ETOH use was not found to associate with DCM or to modify the association between the presence of genetic variants and development of DCM.

Abstract 14975: SIRT1 Ameliorates Cardiac Dysfunction Caused by Lamin A/C Deficiency via Mitochondrial Bioenergetics Improvement

Background: The LMNA gene encodes lamin A/C and is the second most frequently mutated gene associated with dilated cardiomyopathy (DCM) but lacks effective therapeutic options. Recent transcriptomic studies have shown that mutation of LMNA leads to abnormal expression of genes related to mitochondrial function, however, the mechanisms have not been investigated further. Hypothesis: LMNA protects against cardiac dysfunction via mitochondrial bioenergetics maintenance. Aims To decipher the mechanism by which LMNA mediates mitochondrial bioenergetics and DCM phenotype. Methods: Proteomics was performed to decipher the pathogenesis of DCM in Lmna -/- mice. Neonatal rat ventricular myocytes (NRVMs) were used to dissect molecular mechanisms. Adenovirus and adeno-associated virus (AAV) were constructed to overexpress SIRT1 in vitro and in vivo , respectively. Results: Lmna -/- mice at 1 month of age showed obvious cardiac dysfunction, while 2-week-old Lmna -/- mice showed no obvious cardiac phenotype. Proteomics revealed downregulated mitochondrial function-related pathways in Lmna -/- hearts. Early injured mitochondria with decreased cristae density were detected and the only reduced mitochondrial biogenesis regulator SIRT1 was found in 2 week-old Lmna -/- hearts. Overexpression of SIRT1 in lamin A/C knockdown NRVMs effectively improved mitochondrial oxidative respiration capacity. AAV-SIRT1 injection significantly alleviated mitochondrial injury, DCM phenotype of Lmna -/- mice, and prolonged lifespan (Figure 1). Mechanistically, LMNA maintains mitochondrial bioenergetics through SIRT1-PARKIN axis. Conclusions: Lamin A/C deficiency leads to mitochondrial damage in cardiomyocytes and promotes the development of DCM through SIRT1 downregulation. Targeting SIRT1 ameliorates mitochondrial injury and DCM phenotype in Lmna -/- mice, which may provide a novel therapeutic strategy for LMNA mutation-associated DCM.

OPA1, a molecular regulator of dilated cardiomyopathy.

Dilated cardiomyopathy (DCM) is a disease with no specific treatment, poor prognosis and high mortality. During DCM development, there is apoptosis, mitochondrial dynamics imbalance and changes in cristae structure. Optic atrophy 1 (OPA1) appears at high frequency in these three aspects. DCM LMNA (LaminA/C) gene mutation can activate TP53, and the study of P53 shows that P53 affects OPA1 through Bak/Bax and OMA1 (a metalloprotease). OPA1 can be considered the missing link between DCMp53 and DCM apoptosis, mitochondrial dynamics imbalance and changes in cristae structure. OPA1 regulates apoptosis by regulating the release of cytochrome c from the mitochondrial matrix through CJs (crisp linkages, located in the inner mitochondrial membrane) and unbalances mitochondrial fusion and fission by affecting mitochondrial inner membrane (IM) fusion. OPA1 is also associated with the formation and maintenance of mitochondrial cristae. OPA1 is not the root cause of DCM, but it is an essential mediator in P53 mediating the occurrence and development of DCM, so OPA1 also becomes a molecular regulator of DCM. This review discusses the implication of OPA1 for DCM from three aspects: apoptosis, mitochondrial dynamics and ridge structure.

Abstract P2043: Loss Of Full-length Mylk3 Causes Dilated Cardiomyopathy Via A Myl2-independent Mechanism

Introduction: We recently discovered C57BL/6N male mice develop dilated cardiomyopathy (DCM) at 12 months, while the closely related C57BL/6J do not. We identified a variant (Chr8:85365179A&gt;T, c.-5T&gt;A) in myosin light chain kinase 3 ( Mylk3 ) in the B/6N substrain that abolishes translation of the predominant transcript (ENSMUST00000034133). MYLK3 phosphorylates many sarcomere proteins, in particular myosin light chain 2 (MYL2), vital for cardiac development and function. We therefore hypothesise this variant drives the DCM in the B/6N mice. Results: To determine whether the Mylk3 variant alone can cause DCM in mice, we generated two novel isogenic mouse lines. The first carries the Mylk3 c.-5T&gt;A variant on the C57BL/6J background. The second carries the ‘wildtype’ Mylk3 variant on the C57BL/6N background (c.-5A&gt;T, C57BL/6N Mylk3.6J ). While wildtype male C57BL/6J mice developed normally, male littermates expressing the mutant Mylk3 allele (C57BL/6J Mylk3.6N ) show signs of DCM at just 4 weeks old, with increased left ventricular diameter and volume, thinning of the posterior wall and a reduced ejection fraction. In contrast, the C57BL/6N mice develop DCM symptoms, but the C57BL/6N Mylk3.6J mice have smaller left ventricles, thicker left ventricular posterior wall and elevated ejection fraction. We assessed MYL2 phosphorylation by western blot, and contradictory to previous reports, found no difference between any of our mice lines. This may be due to the persistence of a shorter Mylk3 isoform that is unaffected by the variant due to a distinct N-terminus (ENSMUST00000122452; D3Z630). There was no difference between the isoforms in their ability to phosphorylate MYL2 suggesting the shorter isoform could compensate. Phosphoproteomics identified over 500 differentially phosphorylated peptides in 3-day old C57BL/6J and C57BL/6J Mylk3.6N mice. These include many key cardiac transcription factors, such as NFATC2 and FOXK1. Conclusion: We hypothesise that loss of MYLK3 may cause dilated cardiomyopathy in our mice by a MYL2-independent mechanism, possibly by altering vital cardiac transcription causing altered heart development.

Abstract P1182: The Genetic Dissection Of Rpl3l As A Causal Gene For Neonatal Dilated Cardiomyopathy And Left Ventricular Noncompaction

Background: Cardiomyopathies are responsible for nearly 10% of cardiac deaths in neonates. Recently, biallelic variants in ribosomal protein L3-like ( RPL3L , NM_005061.2) have been reported in neonates with dilated cardiomyopathy (DCM) and heart failure (HF). This study is aimed to study RPL3L induced genetic pathways and mechanisms involved in the development of DCM. Methods: Whole exome and RNA sequencing, histology, immunohistochemistry, and Western blotting were performed in a human explanted heart. Genetic correlation, expression quantitative trait loci (eQTL) mapping and functional analysis were performed using cardiac gene expression data from the patient as well as human and murine genetic reference populations (GRPs). Results: Two-month-old patient with DCM and HF carrying compound heterozygous RPL3L variants, p.A51T and p.V231F, has been managed on an INTERMACS profile 2 with continuous-flow ventricular assist device and successfully bridged to heart transplantation at the age of 4 months. Morphology of the explanted heart displayed apical deep intertrabecular recesses consistent with left ventricular noncompaction (LVNC). Histology revealed interstitial fibrosis and myocardial hypertrophy. No signs of myocarditis and glycogen or mucopolysaccharides deposits were detected. Immunohistochemistry revealed abnormal clusters of RPL3L protein in the cytosol of cardiomyocytes and disruption of F-actin, Z-disk proteins, MYL4 and dystrophin was evident. In a mouse heart, the Rpl3l level was of 33.45 RPKM, while levels of RPL3L appeared to be 32 RPKM in a human heart compared to its mean expression in other adult tissues of 2.54 (mouse) and 2.36 (human). Systems genetics analysis identified high expression values ranged from 11.31 to 12.16 across murine GRPs of BXD mice with the ~1.8-fold difference. Pathways such as “thermogenesis”, “diabetic cardiomyopathy” and “DCM” significantly associated with RPL3L. e QTL mapping suggested Myl4 (Chr 11) and Sdha (Chr 13) as the upstream regulators of Rpl3l . Conclusions: Compound RPL3L heterozygosity is causal for neonatal DCM and LVNC. The RPL3L is highly expressed in the heart tissue of humans and mice. Genes, Myl4 and Sdha, are strong candidates that regulate expression of Rpl3l in murine heart.

Circulating cardiac MicroRNAs safeguard against dilated cardiomyopathy

Cardiac-resident or -enriched microRNAs (miRNAs) could be released into the bloodstream becoming circulating cardiac miRNAs, which are increasingly recognized as non-invasive and accessible biomarkers of multiple heart diseases. However, dilated cardiomyopathy (DCM)-associated circulating miRNAs (DACMs) and their roles in DCM pathogenesis remain largely unexplored. Two human cohorts, consisting of healthy individuals and DCM patients, were enrolled for serum miRNA sequencing (10vs. 10) and quantitative polymerase chain reaction validation (46vs. 54), respectively. Rigorous screening strategy was enacted to define DACMs and their potentials for diagnosis. DCM mouse model, different sources of cardiomyocytes, adeno-associated virus 9 (AAV9), gene knockout, RNAscope miRNA in situ hybridization, mRFP-GFP-LC3B reporter, echocardiography and transmission electron microscopy were adopted for mechanistic explorations. Serum miRNA sequencing revealed a unique expression pattern for DCM circulating miRNAs. DACMs miR-26a-5p, miR-30c-5p, miR-126-5p and miR-126-3p were found to be depleted in DCM circulation as well as heart tissues. Their expressions in circulation and heart tissues were proven to be correlated significantly, and a combination of these miRNAs was suggested potential values for DCM diagnosis. FOXO3, a predicted common target, was experimentally demonstrated to be co-repressed within cardiomyocytes by these DACMs except miR-26a-5p. Delivery of a combination of miR-30c-5p, miR-126-5p and miR-126-3p into the murine myocardium via AAV9 carrying an expression cassette driven by cTnT promoter, or cardiac-specific knockout of FOXO3 (Myh6-CreERT2 , FOXO3 flox+/+ ) dramatically attenuated cardiac apoptosis and autophagy involved in DCM progression. Moreover, competitively disrupting the interplay between DACMs and FOXO3 mRNA by specifically introducing their interacting regions into murine myocardium crippled the cardioprotection of DACMs against DCM. Circulating cardiac miRNA-FOXO3 axis plays a pivotal role in safeguarding against myocardial apoptosis and excessive autophagy in DCM development, which may provide serological cues for DCM non-invasive diagnosis and shed light on DCM pathogenesis and therapeutic targets.

Role of Coxsackievirus B3-Induced Immune Responses in the Transition from Myocarditis to Dilated Cardiomyopathy and Heart Failure.

Dilated cardiomyopathy (DCM) is a cardiac disease marked by the stretching and thinning of the heart muscle and impaired left ventricular contractile function. While most patients do not develop significant cardiac diseases from myocarditis, disparate immune responses can affect pathological outcomes, including DCM progression. These altered immune responses, which may be caused by genetic variance, can prolong cytotoxicity, induce direct cleavage of host protein, or encourage atypical wound healing responses that result in tissue scarring and impaired mechanical and electrical heart function. However, it is unclear which alterations within host immune profiles are crucial to dictating the outcomes of myocarditis. Coxsackievirus B3 (CVB3) is a well-studied virus that has been identified as a causal agent of myocarditis in various models, along with other viruses such as adenovirus, parvovirus B19, and SARS-CoV-2. This paper takes CVB3 as a pathogenic example to review the recent advances in understanding virus-induced immune responses and differential gene expression that regulates iron, lipid, and glucose metabolic remodeling, the severity of cardiac tissue damage, and the development of DCM and heart failure.

Correlation Analysis of CTSB Promoter Polymorphism and Function in Patients with Dilated Cardiomyopathy

Dilated cardiomyopathy (DCM) is caused by a combination of genetic susceptibility and environmental factors. Cathepsin B affects the pathogenesis of DCM; however, its molecular mechanism is still unclear. In this study, we examined the association of rare CTSB variants with the occurrence of DCM. This case-control study involved 394 participants: 142 patients with DCM and 252 healthy controls. DNA was extracted from the peripheral leukocytes of all participants, and CTSB variants were analyzed and identified using polymerase chain reaction amplification. Functional analysis was performed using the dual-luciferase reporter assay, and the ability of genetic CTSB variants to bind to transcription factors (TFs) was analyzed and validated using the electrophoretic mobility shift assay (EMSA). Two single-nucleotide polymorphisms (SNPs) were identified in the study population. One SNP, g.4803 T > C (rs1293312), was more common in patients with DCM. A second SNP, g.4954 T > A (rs942670850), was identified in two patients with DCM. Both SNPs significantly enhanced the transcriptional activity of CTSB promoters. An analysis using the TRANSFAC database revealed that these SNPs affect TF binding, which was confirmed using the EMSA. Our results demonstrate that within the CTSB promoter, the genetic variants g.4803T>C (rs1293312) and g.4954 T > A (rs942670850) are rare risk factors for DCM development.

Structural basis of domain destabilization by dilated-cardiomyopathy-causing missense mutations in titin.

Truncating variants in the titin gene are the most common cause of familial dilated cardiomyopathy (DCM), accounting for 25% of the genotype-positive cases. Similar to other genetic diseases triggered by gene loss of function, it has been proposed that destabilizing titin missense mutations can also result in DCM. Indeed, the highly destabilizing C3575S mutation targeting immunoglobulin-like (Ig) 21 domain of cardiac titin has been recently identified as a cause of DCM. However, the effects of the mutation on the structure of the parent domain and whether altered disulfide bond formation contribute to the destabilizing properties of the mutation remain unexplored. Here, using high-resolution X-ray crystallography, we report that the structure of the C3575S mutant domain is largely unperturbed (RMSD: 0.538 Å). In addition, using gel-shift assays, we have ruled out that the lower thermal stability of the mutant domain results from its inability to establish intramolecular disulfide bonds. Instead, we propose that the lower hydrophobicity of serine is not well accommodated in the core of mutant domains, causing their destabilization. Finally, we have observed that similar missense mutations, which cause a decrease in hydrophobicity in buried positions of titin Ig domains, are enriched in DCM patients. Altogether, our results illustrate that subtle physicochemical changes induced by titin missense mutations can cause domain destabilization, even in the absence of remarkable structural alterations, resulting in development of DCM.

Generation of two human iPSC lines with Exon 3 mutations in BCL2-Associated Athanogene 3 (BAG3) from dilated cardiomyopathy patients

Dilated cardiomyopathies (DCM) are one of the main causes of heart failure as one ages. BAG3 is a chaperone protein that is heavily implicated in the development of DCM and speed of progression toward heart failure. Here we generate two human iPSC lines from individuals with mutations in exon 3 of BAG3 and provide validation of their pluripotency and ability to differentiate toward the three primary germ layers. These two cell lines can help our understanding of BAG3 and its role in DCM by providing a good model for BAG3 inactivation and insufficiency.

198 ROLE OF CARDIAC MAGNETIC RESONANCE IMAGING IN ARRHYTMICH RISK STRATIFICATION

Abstract Introduction Danon disease (DD) is a rare multi-systemic disorder firstly described by Danon et al. in 1981 and characterized by a triad consisting with hypertrophic cardiomyopathy, skeletal myopathy, and intellectual disability. It is an inherited dominant X-linked condition, due to mutations in the lysosome-associated membrane protein 2 (LAMP2) gene. Typically, males present a more severe phenotype with earlier onset and rapid heart failure progression with extracardiac manifestations; female patients manifest a milder phenotype with later onset and isolated cardiac involvement. Female carriers may develop dilated cardiomyopathy (DCM). In recent years, it has been described a severe arrhythmogenic phenotype, particularly in women, with a high risk of sudden cardiac death (SCD). Case presentation Case 1 is a 16 y.o. woman referred to our outpatient cardiomyopathies clinic, diagnosed with left ventricle (LV) hypertrophy on the basis of ECG and echocardiography, performed in 2016, in view of cutaneous nevus surgical exeresis. At echocardiographic evaluation we found an asymmetric LV hypertrophy with preserved LV ejection fraction (LVEF 65%). A cMRI was performed, showing mild LV thickening and left ventricular hypertrabeculation morphology, mainly in the LV lateral wall, but not all criteria for LV noncompaction (NC) were satisfied. There was no late gadolinium enhancement (LGE) accumulation. She underwent a genetic screening with inconclusive results, so we started a clinical outpatient follow-up showing no significant arrhythmias at ECG Holter and no limitation of physical activities. In 2021, when she was 21 yo, her father died suddenly and no autoptic examination was performed. A genetic exam was repeated, highlighting a LAMP2 gene mutation. In 2016 her 3 years older sister, Case 2, underwent a familiar screening. She had a long history of mild dyspnea occurring during exertion. Echocardiography showed asymmetric hypertrophy with marked thickening of infero-lateral wall (25 mm,) with normal systolic function (EF 70%). She underwent a cMRI, highlighting diffuse asymmetric hypertrophy (max 24 mm) with LGE in lateral wall and lower septum. First genetic test was nonconclusive but after her father's death another test was performed, demonstrating LAMP2 gene mutation. In 2021 a follow-up cMRI showed markedly reduced myocardial thickness of the apex, with a pattern of noncompaction myocardial. We found a LVEF at lower limits, depressed longitudinal function (MAPSE 8 mm) and manly severe progression of fibrotic degeneration. ECG Holter revealed premature ventricular complex, in absence of nonsustained ventricular tachycardia. Following the evolution of fibrosis, cardioverter defibrillator (ICD) implantation was performed. Case 1 was clinically stable during strict follow-up. Conclusion Cardiac magnetic resonance imaging (cMRI) may be useful in arrhythmic risk stratification, accurate systolic dysfunction evaluation, and proper timing and indication for ICD implantation.

954 DILATED CARDIOMYOPATHY AND ATRIOVENTRICULAR BLOCK RELATED TO THE MUTATION IN THE LMNE GENE: DESCRIPTION OF A FAMILY

Abstract The proband was patient A2, suffering by severe left ventricular dysfunction (EF 20%) and II degree Mobitz type 1 atrioventricular block, requiring dual chamber ICD implantation, and retinitis pigmentosa. He had three brothers A1, A4, A5 suffering also by dilated cardiomyopathy and ICD/CRTD recipients. His sister A3, his daughter B1 and the firstborn brother A1 were also affected by retinitis pigmentosa. Genetic analysis was performed in A2 by NGS of a panel of genes related to heart disease and retinitis pigmentosa. It documented the presence of a missense pathogenetic variant (class 4) of the LMNA gene in heterozygosis (c.949G&amp;gt;A). This variant has been described in several scientific papers as associated with cardiac impairment in patients suffering from atrioventricular block and dilated cardiomyopathy. Laminin A/C is a fundamental protein of the nuclear envelope of the cell. Germline mutations in the LMNA gene, present on chromosome 22 (1q22), encoding the A/C lamina, have been causally linked to four different diseases with 42 reported mutations: Dilated cardiomyopathy (DCM) with disease of the conduction system; Limb girdle muscular dystrophy (LGMD); Autosomal dominant variant of Emery-Dreifuss muscular dystrophy (EDMD); Autosomal dominant partial lipodystrophy. LMNA-related dilated cardiomyopathy (DCM) is characterized by left ventricular enlargement and/or reduced systolic function frequently preceded or accompanied by significant conduction system disease. Family studies suggest that conduction system disease commonly precedes the development of DCM by a few years to a decade or more. Conduction system involvement usually starts with disease of the sinus node and/or atrioventricular node that can manifest as sinus bradycardia, sinus node arrest with junctional rhythms, or heart block (commonly first-degree heart block that progresses to second- and third-degree block). The following are also common: symptomatic bradyarrhythmias requiring cardiac pacemakers, supraventricular arrhythmias including atrial flutter, atrial fibrillation, supraventricular tachycardia, and the sick sinus syndrome (i.e., tachycardia-bradycardia syndrome), ventricular arrhythmias including frequent premature ventricular contractions and ventricular tachycardia Sudden cardiac death may occur with progressive disease. Although more malignant, life-threatening arrhythmias may occur with longstanding and usually previously symptomatic DCM, sudden cardiac death can also be the presenting manifestation of LMNA-related DCM, with minimal or no left ventricular dysfunction. In the cardiological setting, the AVB associated with DCM is a reliable marker for LMNA gene molecular screening. Regarding retinitis pigmentosa, the variant in heterozygosis c538C&amp;gt;G was found in the RHO gene in the proband, classifiable as pathogenetic. This gene encodes a protein necessary for the function of retinal photoreceptors and pathogenic mutations have been found in 30-40% of hereditary forms of retinitis pigmentosa. In conclusion, we believe that the tests carried out confirmed the hypothesis of a hereditary form of cardiomyopathy and retinitis pigmentosa, which seem to segregate independently in the family. Both mutations can be transmitted in 50% of cases, regardless of sex. For this reason we recommended to extend genetic analysis to all the first-degree relatives (siblings and children).

Calsyntenin-1 Promotes Doxorubicin-induced Dilated Cardiomyopathy in Rats

PurposeDoxorubicin is an important cancer chemotherapeutic agent with severe cardiotoxic effects that eventually lead to dilated cardiomyopathy (DCM). Calsyntenin-1(CLSTN1) plays a critical role in the nervous system, but its relevance in cardiovascular diseases is unknown. We investigated the significance of CLSTN1 in doxorubicin-induced DCM.MethodsCLSTN1 expression in doxorubicin-induced DCM rats and H9c2 cells was determined using western blotting. To further explore the functions of CLSTN1, a cardiac-specific CLSTN1 overexpression rat model was constructed. The rats were subjected to analysis using echocardiographic, hemodynamic, and electrocardiographic parameters. Potential downstream molecules in CLSTN1 overexpression heart tissue were investigated using proteomics and western blotting. Finally, a knockdown of CLSTN1 was constructed to investigate the rescue function on doxorubicin-induced cell toxicity.ResultsCLSTN1 protein expression increased drastically in doxorubicin-induced DCM rats and H9c2 cells. Under doxorubicin treatment, CLSTN1 protein-specific overexpression in the heart muscle promoted cardiac chamber enlargement and heart failure, while the knockdown of CLSTN1 reduced doxorubicin-induced cardiomyocyte toxicity in vitro. At the mechanistic level, overexpression of CLSTN1 downregulated SERCA2 expression and increased the phosphorylation levels of PI3K-Akt and CaMK2.ConclusionOur findings demonstrated that CLSTN1 promotes the pathogenesis of doxorubicin-induced DCM. CLSTN1 could be a therapeutic target to prevent the development of doxorubicin-induced DCM.