The BMAL1/HIF2A heterodimer modulates circadian variations of myocardial injury

Acute myocardial infarction stands as a prominent cause of morbidity and mortality worldwide 1-6 . Clinical studies have demonstrated that the severity of cardiac injury following myocardial infarction exhibits a circadian pattern, with larger infarct sizes and poorer outcomes in patients experiencing morning onset myocardial infarctions 7-14 . However, the molecular mechanisms that govern circadian variations of myocardial injury remain unclear. Here, we show that BMAL1 14-20 , a core circadian transcription factor, orchestrates diurnal variability in myocardial injury. Unexpectedly, BMAL1 modulates circadian-dependent cardiac injury by forming a transcriptionally active heterodimer with a non-canonical partner, hypoxia-inducible factor 2 alpha (HIF2A) 6,21-23 , in a diurnal manner. Substantiating this finding, we determined the cryo-EM structure of the BMAL1/HIF2A/DNA complex, revealing a previously unknown capacity for structural rearrangement within BMAL1, which enables the crosstalk between circadian rhythms and hypoxia signaling. Furthermore, we identified amphiregulin (AREG) as a rhythmic transcriptional target of the BMAL1/HIF2A heterodimer, critical for regulating circadian variations of myocardial injury. Finally, pharmacologically targeting the BMAL1/HIF2A-AREG pathway provides effective cardioprotection, with maximum efficacy when aligned with the pathway's circadian trough. Our findings not only uncover a novel mechanism governing the circadian variations of myocardial injury but also pave the way for innovative circadian-based treatment strategies, potentially shifting current treatment paradigms for myocardial infarction.

Oligogenic Architecture of Rare Noncoding Variants Distinguishes 4 Congenital Heart Disease Phenotypes

BACKGROUND

Congenital heart disease (CHD) is highly heritable, but the power to identify inherited risk has been limited to analyses of common variants in small cohorts.

METHODS

We performed reimputation of 4 CHD cohorts (n=55 342) to the TOPMed reference panel (freeze 5), permitting meta-analysis of 14 784 017 variants including 6 035 962 rare variants of high imputation quality as validated by whole genome sequencing.

RESULTS

Meta-analysis identified 16 novel loci, including 12 rare variants, which displayed moderate or large effect sizes (median odds ratio, 3.02) for 4 separate CHD categories. Analyses of chromatin structure link 13 of the genome-wide significant loci to key genes in cardiac development; rs373447426 (minor allele frequency, 0.003 [odds ratio, 3.37 for Conotruncal heart disease]; P=1.49×10^-8) is predicted to disrupt chromatin structure for 2 nearby genes BDH1 and DLG1 involved in Conotruncal development. A lead variant rs189203952 (minor allele frequency, 0.01 [odds ratio, 2.4 for left ventricular outflow tract obstruction]; P=1.46×10^-8) is predicted to disrupt the binding sites of 4 transcription factors known to participate in cardiac development in the promoter of SPAG9. A tissue-specific model of chromatin conformation suggests that common variant rs78256848 (minor allele frequency, 0.11 [odds ratio, 1.4 for Conotruncal heart disease]; P=2.6×10^-8) physically interacts with NCAM1 (P_FDR=1.86×10^-27), a neural adhesion molecule acting in cardiac development. Importantly, while each individual malformation displayed substantial heritability (observed h2 ranging from 0.26 for complex malformations to 0.37 for left ventricular outflow tract obstructive disease) the risk for different CHD malformations appeared to be separate, without genetic correlation measured by linkage disequilibrium score regression or regional colocalization.

CONCLUSIONS

We describe a set of rare noncoding variants conferring significant risk for individual heart malformations which are linked to genes governing cardiac development. These results illustrate that the oligogenic basis of CHD and significant heritability may be linked to rare variants outside protein-coding regions conferring substantial risk for individual categories of cardiac malformation.

Efficient in vivo genome editing prevents hypertrophic cardiomyopathy in mice

Dominant missense pathogenic variants in cardiac myosin heavy chain cause hypertrophic cardiomyopathy (HCM), a currently incurable disorder that increases risk for stroke, heart failure and sudden cardiac death. In this study, we assessed two different genetic therapies-an adenine base editor (ABE8e) and a potent Cas9 nuclease delivered by AAV9-to prevent disease in mice carrying the heterozygous HCM pathogenic variant myosin R403Q. One dose of dual-AAV9 vectors, each carrying one half of RNA-guided ABE8e, corrected the pathogenic variant in ≥70% of ventricular cardiomyocytes and maintained durable, normal cardiac structure and function. An additional dose provided more editing in the atria but also increased bystander editing. AAV9 delivery of RNA-guided Cas9 nuclease effectively inactivated the pathogenic allele, albeit with dose-dependent toxicities, necessitating a narrow therapeutic window to maintain health. These preclinical studies demonstrate considerable potential for single-dose genetic therapies to correct or silence pathogenic variants and prevent the development of HCM.

Multiplexed Single-Nucleus RNA Sequencing Using Lipid-Oligo Barcodes

This protocol describes a robust pipeline for simultaneously analyzing multiple samples by single-nucleus (sn)RNA-seq. cDNA obtained from each single sample are labeled with the same lipid-coupled oligonucleotide barcode (10X Genomics). Nuclei from as many as 12 individual samples can be pooled together and simultaneously processed for cDNA library construction and subsequent DNA sequencing. While previous protocols using lipid-coupled oligonucleotide barcodes were optimized for analysis of samples consisting of viable cells, this protocol is optimized for analyses of quick-frozen cell samples. The protocol ensures efficient recovery of nuclei both by incorporating high sucrose buffered solutions and by including a tracking dye (trypan blue) during nuclei isolation. The protocol also describes a procedure for removing single nuclei 'artifacts' by removing cell debris prior to single nuclear fractionation. This protocol informs the use of computational tools for filtering poorly labeled nuclei and assigning sample identity using barcode unique molecular identifier (UMI) read counts percentages. The computational pipeline is applicable to either cultured or primary, fresh or frozen cells, regardless of their cell types and species. Overall, this protocol reduces batch effects and experimental costs while enhancing sample comparison. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Labeling cells with lipid oligo barcodes and generating multiplexed single-nucleus RNA-seq libraries Basic Protocol 2: Bioinformatic deconvolution of the multiplexed snRNAseq libraries.

Genetic determinants of telomere length from 109,122 ancestrally diverse whole-genome sequences in TOPMed

Genetic studies on telomere length are important for understanding age-related diseases. Prior GWAS for leukocyte TL have been limited to European and Asian populations. Here, we report the first sequencing-based association study for TL across ancestrally-diverse individuals (European, African, Asian and Hispanic/Latino) from the NHLBI Trans-Omics for Precision Medicine (TOPMed) program. We used whole genome sequencing (WGS) of whole blood for variant genotype calling and the bioinformatic estimation of telomere length in n=109,122 individuals. We identified 59 sentinel variants (p-value <5×10-9) in 36 loci associated with telomere length, including 20 newly associated loci (13 were replicated in external datasets). There was little evidence of effect size heterogeneity across populations. Fine-mapping at OBFC1 indicated the independent signals colocalized with cell-type specific eQTLs for OBFC1 (STN1). Using a multi-variant gene-based approach, we identified two genes newly implicated in telomere length, DCLRE1B (SNM1B) and PARN. In PheWAS, we demonstrated our TL polygenic trait scores (PTS) were associated with increased risk of cancer-related phenotypes.

Mechanisms of Congenital Heart Disease Caused by NAA15 Haploinsufficiency

[Figure: see text].

Society of pediatric liver transplantation: Current registry status 2011-2018

BACKGROUND

SPLIT was founded in 1995 in order to collect comprehensive prospective data on pediatric liver transplantation, including waiting list data, transplant, and early and late outcomes. Since 2011, data collection of the current registry has been refined to focus on prospective data and outcomes only after transplant to serve as a foundation for the future development of targeted clinical studies.

OBJECTIVE

To report the outcomes of the SPLIT registry from 2011 to 2018.

METHODS

This is a multicenter, cross-sectional analysis characterizing patients transplanted and enrolled in the SPLIT registry between 2011 and 2018. All patients, <18 years of age, received a first liver-only, a combined liver-kidney, or a combined liver-pancreas transplant during this study period.

RESULTS

A total of 1911 recipients from 39 participating centers in North America were registered. Indications included biliary atresia (38.5%), metabolic disease (19.1%), tumors (11.7%), and fulminant liver failure (11.5%). Greater than 50% of recipients were transplanted as either Status 1A/1B or with a MELD/PELD exception score. Incompatible transplants were performed in 4.1%. Kaplan-Meier estimates of 1-year patient and graft survival were 97.3% and 96.6%. First 30 days of surgical complications included reoperation (31.7%), hepatic artery thrombosis (6.3%), and portal vein thrombosis (3.2%). In the first 90 days, biliary tract complications were reported in 13.6%. Acute cellular rejection during first year was 34.7%. At 1 and 2 years of follow-up, 39.2% and 50.6% had normal liver tests on monotherapy (tacrolimus or sirolimus). Further surgical, survival, allograft function, and complications are detailed.

Abstract 202: The R21C Mutation in Troponin I Has a Founder Effect in South Lebanon and Causes Malignant Hypertrophic Cardiomyopathy

Hypertrophic Cardiomyopathy (HCM) occurs in 1 of every 500 people and has a wide phenotypic variability. In the majority of cases, HCM is caused by known mutations in genes that code for sarcomere proteins. Although gene testing is widely available for HCM, knowing the phenotype caused by different gene mutations remains a challenging task. We recruited 28 families with HCM, of which 19 (67.8%) have at least one patient with pediatric onset. Index patients from 20 families received targeted sequencing for a panel of genes including TNNI3 , and 7 families received Sanger sequencing for the TNNI3 . We identified a missense mutation p.R21C in TNNI3 segregating with HCM in four families from South Lebanon. Through cascade screening, we identified 30 patients from the four families; twenty of them (67%) had a clinical diagnosis of HCM with a median age of 37 years, while 9 (30%), with a median age 21 years, had no evidence of HCM on echocardiography. An additional 27 members of the families had evidence of HCM, including 22 with SCD in the setting of no past medical history, and their carrier status for p.R21C was implied from the pedigrees. Survival analysis for 57 HCM patients with the mutation revealed a markedly decreased age at first adverse event as compared to 47 HCM patients with the MYBPC3 p.R502W mutation. Founder mutations in HCM that cause a severe phenotype are uncommon. The p.R21C mutation in TNNI3 is the first HCM mutation described in the Lebanese population and has a founder effect in South Lebanon. Early and more frequent screening with different imaging modalities as well as tailored management might be warranted for carriers of this mutation.

Abstract 341: Efficient Large-scale Sarcomere Tracking (sarctrack) to Assess HCM Variants in iPSC-CMs

Variants that drive HCM and associated adverse patient outcomes are found in the cardiac sarcomere. These variants range from those that are known to be pathogenic to those that are likely pathogenic or even variants of unknown significance (VUS). CRISPR/Cas-9 engineering has accelerated our ability to generate variants in iPSC to probe changes in cellular function and assess cellular pathogenicity in VUSs. However, iPSC-CMs are not as functionally mature as adult cardiomyocytes. For this reason we have developed a platform to assess contractile function directly at the level of the sarcomere. We use a custom built MatLab algorithm to assess sarcomere length, contraction time, relaxation time, and beat rate of individual sarcomeres within iPSC-CMs. Sarcomeres are visualised using reporter lines that have been engineered with an N-terminal TTN-GFP. We assess the contractile function of thick filament variants in MYH7 and MYBPC3. We show the ability to detect changes in key contractile parameters. This platform allows the screening of pharmacological compounds against these reporter lines with engineered variants.

Multilayer Myocardial Mechanics in Genotype-Positive Left Ventricular Hypertrophy-Negative Patients With Hypertrophic Cardiomyopathy

It is unknown whether the presence of a sarcomeric mutation alone is sufficient to result in abnormal myocardial force generation, or whether additional changes in myocardial architecture (hypertrophy, disarray, and fibrosis) are required to impair systolic function. Speckle tracking echocardiography allows quantification of global strain/strain rates, twist, and dyssynchrony. In the present study we sought to further elucidate early abnormalities of myocardial mechanics in sarcomeric mutation carriers without evidence of clinical disease. Sixty genotype-positive left ventricular hypertrophy-negative (G+left ventricular hypertrophy [LVH]-) patients and 60 normal controls were studied. Velocity vector imaging was applied retrospectively to echocardiographic images to quantify global longitudinal and circumferential strain/strain rate, and rotation parameters. The G+LVH- group demonstrated both smaller left ventricular diastolic cavity dimensions (4.5 ± 0.6 cm vs 4.8 ± 0.4 cm) and a higher LVEF (66 ± 6% vs 60 ± 5%) compared with controls. An increase in circumferential subendocardial systolic strain (-30 ± 5 vs -27 ± 3%) and both systolic and diastolic subendocardial strain rate was seen in the G+LVH- group. Peak rotation angles were higher at the base and apex, with an increase in total twist (9.0 ± 3.8 vs 6.9 ± 2.9). In the control group, global and average segmental strain were similar, suggesting no/minimal dyssynchrony (global mechanical synchrony index [GMSi] 0.97-0.98). In the G+LVH- group GMSi was significantly lower (subendocardial GMSi 0.95; subepicardial GMSi 0.60), suggesting increasing subendocardial to subepicardial dyssynchrony. In conclusion, utilizing multilayer strain analysis, we demonstrate that G+LVH- subjects have enhanced subendocardial systolic strain rate and twist, as well as mechanical dyssynchrony within the left ventricular myocardium. These results demonstrate that abnormalities in myocardial mechanics precede the development of clinical hypertrophy.

Abstract 571: MYBPC3 Mutations Cause Hypertrophic Cardiomyopathy by Dysregulating Myosin: Implications for Therapy

The mechanisms by which truncating mutations in MYBPC3 (encoding cardiac myosin binding protein-C; cMyBPC) or myosin missense mutations cause hyper-contractility and poor relaxation in hypertrophic cardiomyopathy (HCM) are incompletely understood. Using genetic and biochemical approaches we explored how depletion of cMyBPC altered sarcomere function. We demonstrate that stepwise loss of cMyBPC resulted in reciprocal augmentation of myosin contractility. Direct attenuation of myosin function, via a damaging missense variant (F764L) that causes dilated cardiomyopathy (DCM) normalized the increased contractility from cMyBPC depletion. Depletion of cMyBPC also altered dynamic myosin conformations during relaxation - enhancing the myosin state that enables ATP hydrolysis and thin filament interactions while reducing the super relaxed conformation associated with energy conservation. MYK-461, a pharmacologic inhibitor of myosin ATPase, rescued relaxation deficits and restored normal contractility in mouse and human cardiomyocytes with MYBPC3 mutations. These data define dosage-dependent effects of cMyBPC on myosin that occur across all phases of the cardiac cycle as the pathophysiologic mechanisms by which MYBPC3 truncations cause HCM. Therapeutic strategies to attenuate cMyBPC activity may rescue depressed cardiac contractility in DCM patients, while inhibiting myosin by MYK-461 should benefit the substantial proportion of HCM patients with MYBPC3 mutations.

Bedside Back to Bench: Building Bridges between Basic and Clinical Genomic Research

Genome sequencing has revolutionized the diagnosis of genetic diseases. Close collaborations between basic scientists and clinical genomicists are now needed to link genetic variants with disease causation. To facilitate such collaborations, we recommend prioritizing clinically relevant genes for functional studies, developing reference variant-phenotype databases, adopting phenotype description standards, and promoting data sharing.

Phenotype and prognostic correlations of the converter region mutations affecting the β myosin heavy chain

Objectives

The prognostic value of genetic studies in cardiomyopathies is still controversial. Our objective was to evaluate the outcome of patients with cardiomyopathy with mutations in the converter domain of β myosin heavy chain (MYH7).

Methods

Clinical characteristics and survival of 117 affected members with mutations in the converter domain of MYH7 were compared with 409 patients described in the literature with mutations in the same region.

Results

Twenty-five mutations were evaluated (9 in our families including 3 novel (Ile730Asn, Asp717Gly and Arg719Pro)). Clinical diagnoses were hypertrophic (n=407), dilated (n=15), non-compaction (n=4) and restrictive (n=5) cardiomyopathies, unspecified cardiomyopathy (n=11), sudden death (n=50) and 35 healthy carriers. One hundred eighty-four had events (cardiovascular death or transplant). Median event-free survival was 50±2 years in our patients and 53±3 years in the literature (p=0.27). There were significant differences in the outcome between mutation: Ile736Thr had fewer events than other mutations in the region (p=0.01), while Arg719Gln (p<0.01) had reduced event-free survival.

Conclusions

Mutations in the converter region are generally associated with adverse prognosis although there are differences between mutations. The identification of a mutation in this particular region provides important prognostic information that should be considered in the clinical management of affected patients.

Increased frequency of de novo copy number variants in congenital heart disease by integrative analysis of single nucleotide polymorphism array and exome sequence data

RATIONALE

Congenital heart disease (CHD) is among the most common birth defects. Most cases are of unknown pathogenesis.

OBJECTIVE

To determine the contribution of de novo copy number variants (CNVs) in the pathogenesis of sporadic CHD.

METHODS AND RESULTS

We studied 538 CHD trios using genome-wide dense single nucleotide polymorphism arrays and whole exome sequencing. Results were experimentally validated using digital droplet polymerase chain reaction. We compared validated CNVs in CHD cases with CNVs in 1301 healthy control trios. The 2 complementary high-resolution technologies identified 63 validated de novo CNVs in 51 CHD cases. A significant increase in CNV burden was observed when comparing CHD trios with healthy trios, using either single nucleotide polymorphism array (P=7×10(-5); odds ratio, 4.6) or whole exome sequencing data (P=6×10(-4); odds ratio, 3.5) and remained after removing 16% of de novo CNV loci previously reported as pathogenic (P=0.02; odds ratio, 2.7). We observed recurrent de novo CNVs on 15q11.2 encompassing CYFIP1, NIPA1, and NIPA2 and single de novo CNVs encompassing DUSP1, JUN, JUP, MED15, MED9, PTPRE SREBF1, TOP2A, and ZEB2, genes that interact with established CHD proteins NKX2-5 and GATA4. Integrating de novo variants in whole exome sequencing and CNV data suggests that ETS1 is the pathogenic gene altered by 11q24.2-q25 deletions in Jacobsen syndrome and that CTBP2 is the pathogenic gene in 10q subtelomeric deletions.

CONCLUSIONS

We demonstrate a significantly increased frequency of rare de novo CNVs in CHD patients compared with healthy controls and suggest several novel genetic loci for CHD.

A common genetic variant within SCN10A modulates cardiac SCN5A expression

Variants in SCN10A, which encodes a voltage-gated sodium channel, are associated with alterations of cardiac conduction parameters and the cardiac rhythm disorder Brugada syndrome; however, it is unclear how SCN10A variants promote dysfunctional cardiac conduction. Here we showed by high-resolution 4C-seq analysis of the Scn10a-Scn5a locus in murine heart tissue that a cardiac enhancer located in Scn10a, encompassing SCN10A functional variant rs6801957, interacts with the promoter of Scn5a, a sodium channel-encoding gene that is critical for cardiac conduction. We observed that SCN5A transcript levels were several orders of magnitude higher than SCN10A transcript levels in both adult human and mouse heart tissue. Analysis of BAC transgenic mouse strains harboring an engineered deletion of the enhancer within Scn10a revealed that the enhancer was essential for Scn5a expression in cardiac tissue. Furthermore, the common SCN10A variant rs6801957 modulated Scn5a expression in the heart. In humans, the SCN10A variant rs6801957, which correlated with slowed conduction, was associated with reduced SCN5A expression. These observations establish a genomic mechanism for how a common genetic variation at SCN10A influences cardiac physiology and predisposes to arrhythmia.

Increased burden of cardiovascular disease in carriers of APOL1 genetic variants

RATIONALE

Two distinct alleles in the gene encoding apolipoprotein L1 (APOL1), a major component of high-density lipoprotein, confer protection against Trypanosoma brucei rhodesiense infection and also increase risk for chronic kidney disease. Approximately 14% of Americans with African ancestry carry 2 APOL1 risk alleles, accounting for the high chronic kidney disease burden in this population.

OBJECTIVE

We tested whether APOL1 risk alleles significantly increase risk for atherosclerotic cardiovascular disease (CVD) in African Americans.

METHODS AND RESULTS

We sequenced APOL1 in 1959 randomly selected African American participants in the Jackson Heart Study (JHS) and evaluated associations between APOL1 genotypes and renal and cardiovascular phenotypes. Previously identified association between APOL1 genotypes and chronic kidney disease was confirmed (P=2.4×10(-6)). Among JHS participants with 2 APOL1 risk alleles, we observed increased risk for CVD (50/763 events among participants without versus 37/280 events among participants with 2 risk alleles; odds ratio, 2.17; P=9.4×10(-4)). We replicated this novel association of APOL1 genotype with CVD in Women's Health Initiative (WHI) participants (66/292 events among participants without versus 37/101 events among participants with 2 risk alleles; odds ratio, 1.98; P=8.37×10(-3); JHS and WHI combined, P=8.5×10(-5); odds ratio, 2.12). The increased risk for CVD conferred by APOL1 alleles was robust to correction for both traditional CVD risk factors and chronic kidney disease.

CONCLUSIONS

APOL1 variants contribute to atherosclerotic CVD risk, indicating a genetic component to cardiovascular health disparities in individuals of African ancestry. The considerable population of African Americans with 2 APOL1 risk alleles may benefit from intensive interventions to reduce CVD.

The Congenital Heart Disease Genetic Network Study: rationale, design, and early results

Congenital heart defects (CHD) are the leading cause of infant mortality among birth defects, and later morbidities and premature mortality remain problematic. Although genetic factors contribute significantly to cause CHD, specific genetic lesions are unknown for most patients. The National Heart, Lung, and Blood Institute-funded Pediatric Cardiac Genomics Consortium established the Congenital Heart Disease Genetic Network Study to investigate relationships between genetic factors, clinical features, and outcomes in CHD. The Pediatric Cardiac Genomics Consortium comprises 6 main and 4 satellite sites at which subjects are recruited, and medical data and biospecimens (blood, saliva, cardiovascular tissue) are collected. Core infrastructure includes an administrative/data-coordinating center, biorepository, data hub, and core laboratories (genotyping, whole-exome sequencing, candidate gene evaluation, and variant confirmation). Eligibility includes all forms of CHD. Annual follow-up is obtained for probands <1-year-old. Parents are enrolled whenever available. Enrollment from December 2010 to June 2012 comprised 3772 probands. One or both parents were enrolled for 72% of probands. Proband median age is 5.5 years. The one third enrolled at age <1 year are contacted annually for follow-up information. The distribution of CHD favors more complex lesions. Approximately, 11% of probands have a genetic diagnosis. Adequate DNA is available from 97% and 91% of blood and saliva samples, respectively. Genomic analyses of probands with heterotaxy, atrial septal defects, conotruncal, and left ventricular outflow tract obstructive lesions are underway. The scientific community's use of Pediatric Cardiac Genomics Consortium resources is welcome.

Burden of rare sarcomere gene variants in the Framingham and Jackson Heart Study cohorts

Rare sarcomere protein variants cause dominant hypertrophic and dilated cardiomyopathies. To evaluate whether allelic variants in eight sarcomere genes are associated with cardiac morphology and function in the community, we sequenced 3,600 individuals from the Framingham Heart Study (FHS) and Jackson Heart Study (JHS) cohorts. Out of the total, 11.2% of individuals had one or more rare nonsynonymous sarcomere variants. The prevalence of likely pathogenic sarcomere variants was 0.6%, twice the previous estimates; however, only four of the 22 individuals had clinical manifestations of hypertrophic cardiomyopathy. Rare sarcomere variants were associated with an increased risk for adverse cardiovascular events (hazard ratio: 2.3) in the FHS cohort, suggesting that cardiovascular risk assessment in the general population can benefit from rare variant analysis.

Abstract 323: Growth Differentiation Factor-15 Is Upregulated in Profibrotic States of Dilated Cardiomyopathy and Not Hypertrophic Cardiomyopathy

Introduction: Dilated cardiomyopathy (DCM) and hypertrophic cardiomyopathy (HCM) are leading causes of morbidity and mortality in the adult population. Both DCM and HCM arise from structural perturbations and remodeling of the heart, and many cases have been found to result from underlying familial mutations. The signaling pathways by which these mutations lead to pathological ventricular remodeling, fibrosis, and heart failure remain unknown.

Methods: In this study we attempt to identify molecular pathways in a DCM mouse model and compare and contrast the results with those previously observed in HCM mouse models. We use a transgenic mouse expressing an arginine-to-cysteine (R9C) mutation in phospholamban (PLN), previously identified in DCM patients. To define molecules involved in disease progression, we generated expression profiles using high-throughput sequencing and assessed genes of interest by immunostaining.

Results: PLN R9C/+ hearts exhibit increasing fibrosis, with proliferation of non-myocyte cells occurring throughout the disease spectrum. Losartan treatment, which effectively blocks the HCM phenotype, does not block the emergence of DCM and neither reduces fibrosis nor increases lifespan in PLN R9C/+ mice. Growth differentiation factor-15 (GDF15) RNA and protein levels are significantly upregulated in the left ventricles of PLN R9C/+ mice during DCM and heart failure. GDF15 is predominantly expressed in non-myocytes in WT mice, but in PLN R9C/+ mice, is upregulated almost 25-fold in myocytes and less than 1.5-fold in non-myocytes.

Conclusion: Both fibrosis and the proliferation of non-myocytes in PLN R9C/+ mouse hearts increase as the DCM phenotype worsens, similar to that observed in HCM mouse models. However, losartan has no effect on the DCM phenotype suggesting that the molecular pathways of DCM and HCM may be different. This study identifies GDF15 as a signaling molecule that may play a unique role in DCM. GDF15 is upregulated in myocytes during DCM, but remains relatively unchanged in HCM. Understanding the genetic mechanisms underlying the progression of disease and fibrosis in both DCM and HCM will help us to characterize the distinct pathways of both diseases, as well as identify new, more specific targets for therapy.

Abstract 73: Aberrant Activation of γ2-AMPK Increases Cardiac Growth Through Cellular Hypertrophy and Hyperplasia

AMP-activated protein kinase (AMPK) is an energy sensor and a key regulator of cell metabolism, hence a promising drug target. Point mutations in the regulatory γ2-subunit (encoded by PRKAG2 gene) have been shown to cause a unique form of cardiomyopathy in humans characterized by cardiac growth, arrhythmias and glycogen storage. In previous studies, we demonstrated that the mutation of prkag2 (N488I) caused aberrant activation of AMPK leading to glycogen storage. However, elimination of glycogen storage by inhibiting glycogen synthase activity failed to normalize heart weight (HW) of the mutant mice. Here, we aimed to determine whether cardiac growth in PRKAG2 ardiomyopathy was dueto cellular hypertrophy or hyperplasia. We used transgenic mice expressing a mutant PRKAG2 (N488I) in the heart (TGγ2 N488I ) that faithfully recapitulated PRKAG2 cardiomyopathy. We determined HW and cardiac myocyte size in adult (2 months) and postnatal (2 weeks) hearts in WT and TGγ2 N488I . At 2 months, TGγ2 N488I hearts show a 2.4-fold increase in HW/BW (body weight) (10.3 ± 1.44 vs. 4.3± 0.17 mg/g) as well as cross-sectional cell surface area compared WT hearts (325 ± 13 vs. 155 ± 5.4 μm 2 ,p<0.01), suggesting cellular hypertrophy in adult TGγ2 N488I heart. Furthermore, we observed increased mTOR activity evidenced by enhanced phosphorylation of mTOR (Ser2448) as well as its downstream targets S6 and 4E-BP. The HW of TGγ2 N488I was partially inhibited by treatment with rapamycin, an inhibitor of mTOR. Interestingly, the length and width of isolated cardiomyocytes from 2 weeks old mice were not different between the WT and TGγ2 N488I heart in spite of a 50% increase of HW of TGγ2 N488I mice. We observed a 2- fold increase in the expression of a proliferation marker, proliferating cell nuclear antigen (PCNA) during postnatal cardiac growth. Expression of Cyclin genes including cyclin D1, D2 and E1 was greatly increased in TGγ2 N488I hearts (2.4 - 4 fold, p<0.01 vs. WT). Taken together, these data indicate that aberrant γ2-AMPK activation stimulates cardiac growth through increased cell number during postnatal growth period and increased cell size at adulthood. These results suggest a novel role of γ2-AMPK in the growth of cardiac myocytes.

CD36 overexpression predisposes to arrhythmias but reduces infarct size in spontaneously hypertensive rats: gene expression profile analysis

CD36 fatty acid translocase plays a key role in supplying heart with its major energy substrate, long-chain fatty acids (FA). Previously, we found that the spontaneously hypertensive rat (SHR) harbors a deletion variant of Cd36 gene that results in reduced transport of long-chain FA into cardiomyocytes and predisposes the SHR to cardiac hypertrophy. In the current study, we analyzed the effects of mutant Cd36 on susceptibility to ischemic ventricular arrhythmias and myocardial infarction in adult SHR-Cd36 transgenic rats with wild-type Cd36 compared with age-matched SHR controls. Using an open-chest model of coronary artery occlusion, we found that SHR-Cd36 transgenic rats showed profound arrhythmogenesis resulting in significantly increased duration of tachyarrhythmias (207 ± 48 s vs. 55 ± 21 s, P < 0.05), total number of premature ventricular complexes (2,623 ± 517 vs. 849 ± 250, P < 0.05) and arrhythmia score (3.86 ± 0.18 vs. 3.13 ± 0.13, P < 0.001). On the other hand, transgenic SHR compared with SHR controls showed significantly reduced infarct size (52.6 ± 4.3% vs. 72.4 ± 2.9% of area at risk, P < 0.001). Similar differences were observed in isolated perfused hearts, and the increased susceptibility of transgenic SHR to arrhythmias was abolished by reserpine, suggesting the involvement of catecholamines. To further search for possible molecular mechanisms of altered ischemic tolerance, we compared gene expression profiles in left ventricles dissected from 6-wk-old transgenic SHR vs. age-matched controls using Illumina-based sequencing. Circadian rhythms and oxidative phosphorylation were identified as the top KEGG pathways, while circadian rhythms, VDR/RXR activation, IGF1 signaling, and HMGB1 signaling were the top IPA canonical pathways potentially important for Cd36-mediated effects on ischemic tolerance. It can be concluded that transgenic expression of Cd36 plays an important role in modulating the incidence and severity of ischemic and reperfusion ventricular arrhythmias and myocardial infarct size induced by coronary artery occlusion. The proarrhythmic effect of Cd36 transgene appears to be dependent on adrenergic stimulation.

Genome-wide association study identifies a susceptibility locus for thoracic aortic aneurysms and aortic dissections spanning FBN1 at 15q21.1

Although thoracic aortic aneurysms and dissections (TAAD) can be inherited as a single-gene disorder, the genetic predisposition in the majority of affected people is poorly understood. In a multistage genome-wide association study (GWAS), we compared 765 individuals who had sporadic TAAD (STAAD) with 874 controls and identified common SNPs at a 15q21.1 locus that were associated with STAAD, with odds ratios of 1.6-1.8 that achieved genome-wide significance. We followed up 107 SNPs associated with STAAD with P < 1 × 10(-5) in the region, in two separate STAAD cohorts. The associated SNPs fall into a large region of linkage disequilibrium encompassing FBN1, which encodes fibrillin-1. FBN1 mutations cause Marfan syndrome, whose major cardiovascular complication is TAAD. This study shows that common genetic variants at 15q21.1 that probably act via FBN1 are associated with STAAD, suggesting a common pathogenesis of aortic disease in Marfan syndrome and STAAD.

Hypertrophic and dilated cardiomyopathy mutations differentially affect the molecular force generation of mouse α-cardiac myosin in the laser trap assay

Point mutations in cardiac myosin, the heart's molecular motor, produce distinct clinical phenotypes: hypertrophic (HCM) and dilated (DCM) cardiomyopathy. Do mutations alter myosin's molecular mechanics in a manner that is predictive of the clinical outcome? We have directly characterized the maximal force-generating capacity (Fmax) of two HCM (R403Q, R453C) and two DCM (S532P, F764L) mutant myosins isolated from homozygous mouse models using a novel load-clamped laser trap assay. Fmaxwas 50% (R403Q) and 80% (R453C) greater for the HCM mutants compared with the wild type, whereas Fmaxwas severely depressed for one of the DCM mutants (65% S532P). Although Fmaxwas normal for the F764L DCM mutant, its actin-activated ATPase activity and actin filament velocity ( Vactin) in a motility assay were significantly reduced (Schmitt JP, Debold EP, Ahmad F, Armstrong A, Frederico A, Conner DA, Mende U, Lohse MJ, Warshaw D, Seidman CE, Seidman JG. Proc Natl Acad Sci USA 103: 14525–14530, 2006.). These Fmaxdata combined with previous Vactinmeasurements suggest that HCM and DCM result from alterations to one or more of myosin's fundamental mechanical properties, with HCM-causing mutations leading to enhanced but DCM-causing mutations leading to depressed function. These mutation-specific changes in mechanical properties must initiate distinct signaling cascades that ultimately lead to the disparate phenotypic responses observed in HCM and DCM.

Compound and double mutations in patients with hypertrophic cardiomyopathy: implications for genetic testing and counselling

OBJECTIVE

To report the frequency of single and multiple gene mutations in an Australian cohort of patients with hypertrophic cardiomyopathy (HCM).

METHODS

Genetic screening of seven HCM genes (beta-MHC, MyBP-C, cTnT, cTnI, ACTC, MYL2, and MYL3) was undertaken in 80 unrelated probands. Screening was by denaturing high performance liquid chromatography and direct DNA sequencing. Clinical data were collected on all patients and on genotyped family members.

RESULTS

26 mutations were identified in 23 families (29%). Nineteen probands (24%) had single mutations (11 beta-MHC, 4 MyBP-C, 3 cTnI, 1 cTnT). Multiple gene mutations were identified in four probands (5%): one had a double mutation and the others had compound mutations. Six of 14 affected individuals from multiple mutation families (43%) experienced a sudden cardiac death event, compared with 10 of 55 affected members (18%) from single mutation families (p = 0.05). There was an increase in septal wall thickness in patients with compound mutations (mean (SD): 30.7 (3.1) v 24.4 (7.4) mm; p<0.05).

CONCLUSIONS

Multiple gene mutations occurring in HCM families may result in a more severe clinical phenotype because of a "double dose" effect. This highlights the importance of screening the entire panel of HCM genes even after a single mutation has been identified.

Sarcomere protein gene mutations and inherited heart disease: a beta-cardiac myosin heavy chain mutation causing endocardial fibroelastosis and heart failure

Inherited human cardiomyopathies often lead to heart failure. A common feature of these conditions is that affected individuals can express the disease causing mutations for many years without showing clinical signs of the disease. Previous studies have demonstrated that sarcomere protein gene mutations can cause either dilated cardiomyopathy or hypertrophic cardiomyopathy. Here we demonstrate that the Arg442His missense mutation in beta-cardiac myosin heavy chain (betaMHC) causes dilated cardiomyopathy, endocardial fibroelastosis and heart failure at a very early age. Using standard genetic engineering tools we and others have made murine models by introducing human disease causing mutations into mice. The central hypothesis of these studies has been that by identifying the pathophysiological pathways activated by these mutations we can define enzymatic activities that are modified during the disease process and which may be involved in pathways that involve more common forms of cardiac disease. Murine models bearing different mutant myosins are being used to address whether each disease causing mutant betaMHC activates the same or different cellular pathways. Dissecting the molecular pathways modulated by mutations in sarcomere protein genes as well as other genes has already demonstrated that there are multiple pathways leading to cardiac remodelling and heart failure. Defining the mechanisms by which mutations in the same genes activate different cellular pathways remains an important question.

Clinical and genetic linkage analysis of a large Venezuelan kindred with Usher syndrome

OBJECTIVE

To undertake a comprehensive investigation into the very high incidence of congenital deafness on the Macano peninsula of Margarita Island, Venezuela.

METHODS

Numerous visits were made to the isolated island community over a 4-year-period. During these visits, it became apparent that a significant number of individuals complained of problems with hearing and vision. Socioeconomic assessments, family pedigrees and clinical histories were recorded on standard questionnaires. All individuals underwent thorough otolaryngologic and ophthalmologic examinations. Twenty milliliters of peripheral venous blood was obtained from each participant. A genome-wide linkage analysis study was performed. Polymorphic microsatellite markers were amplified by polymerase chain reaction and separated on polyacrylamide gels. An ABI 377XL sequencer was used to separate fragments and LOD scores were calculated by using published software.

RESULTS

Twenty-four families were identified, comprising 329 individuals, age range 1-80 years, including 184 children. All families were categorized in the lower two (least affluent) socioeconomic categories. A high incidence of consanguinity was detected. Fifteen individuals (11 adults, 4 children) had profound congenital sensorineural hearing loss, vestibular areflexia and retinitis pigmentosa. A maximum LOD score of 6.76 (Linkage >3.0), between markers D11s4186 and D11s911, confirmed linkage to chromosome 11q13.5. The gene myosin VIIA (MYO7A) was confirmed in the interval. Clinical and genetic findings are consistent with a diagnosis of Usher syndrome 1B for those with hearing and vision problems.

CONCLUSIONS

We report 15 Usher syndrome 1B individuals from a newly detected Latin American socio-demographic origin, with a very high prevalence of 76 per 100,000 population.

Genetic causes of inherited cardiac hypertrophy: Robert L. Frye Lecture

Cardiac hypertrophy is well recognized as a cardiac manifestation of systemic disorders such as hypertension or intrinsic myocardial disease, but it can also reflect an underlying genetic defect. Molecular studies of inherited forms of cardiac hypertrophy have defined 2 novel pathways that lead to cardiac remodeling in adults, discoveries that increasingly provide insights relevant for both diagnosis and management. This article reviews the genetic studies that led to the current molecular understanding of hypertrophic cardiomyopathy and discusses more recently discovered causes of inherited cardiac hypertrophy.

Mutations of TTN, encoding the giant muscle filament titin, cause familial dilated cardiomyopathy

Congestive heart failure (CHF) can result from various disease states with inadequate cardiac output. CHF due to dilated cardiomyopathy (DCM) is a familial disease in 20-30% of cases and is associated with mutations in genes encoding cytoskeletal, contractile or inner-nuclear membrane proteins. We show that mutations in the gene encoding giant-muscle filament titin (TTN) cause autosomal dominant DCM linked to chromosome 2q31 (CMD1G; MIM 604145). Titin molecules extend from sarcomeric Z-discs to M-lines, provide an extensible scaffold for the contractile machinery and are crucial for myofibrillar elasticity and integrity. In a large DCM kindred, a segregating 2-bp insertion mutation in TTN exon 326 causes a frameshift, truncating A-band titin. The truncated protein of approximately 2 mD is expressed in skeletal muscle, but western blot studies with epitope-specific anti-titin antibodies suggest that the mutant protein is truncated to a 1.14-mD subfragment by site-specific cleavage. In another large family with DCM linked to CMD1G, a TTN missense mutation (Trp930Arg) is predicted to disrupt a highly conserved hydrophobic core sequence of an immunoglobulin fold located in the Z-disc-I-band transition zone. The identification of TTN mutations in individuals with CMD1G should provide further insights into the pathogenesis of familial forms of CHF and myofibrillar titin turnover.