Defective Biomechanics and Pharmacological Rescue of Human Cardiomyocytes with Filamin C Truncations

Actin-binding filamin C (FLNC) is expressed in cardiomyocytes, where it localizes to Z-discs, sarcolemma, and intercalated discs. Although FLNC truncation variants (FLNCtv) are an established cause of arrhythmias and heart failure, changes in biomechanical properties of cardiomyocytes are mostly unknown. Thus, we investigated the mechanical properties of human-induced pluripotent stem cells-derived cardiomyocytes (hiPSC-CMs) carrying FLNCtv. CRISPR/Cas9 genome-edited homozygous FLNCKO-/- hiPSC-CMs and heterozygous knock-out FLNCKO+/- hiPSC-CMs were analyzed and compared to wild-type FLNC (FLNCWT) hiPSC-CMs. Atomic force microscopy (AFM) was used to perform micro-indentation to evaluate passive and dynamic mechanical properties. A qualitative analysis of the beating traces showed gene dosage-dependent-manner "irregular" peak profiles in FLNCKO+/- and FLNCKO-/- hiPSC-CMs. Two Young's moduli were calculated: E1, reflecting the compression of the plasma membrane and actin cortex, and E2, including the whole cell with a cytoskeleton and nucleus. Both E1 and E2 showed decreased stiffness in mutant FLNCKO+/- and FLNCKO-/- iPSC-CMs compared to that in FLNCWT. The cell adhesion force and work of adhesion were assessed using the retraction curve of the SCFS. Mutant FLNC iPSC-CMs showed gene dosage-dependent decreases in the work of adhesion and adhesion forces from the heterozygous FLNCKO+/- to the FLNCKO-/- model compared to FLNCWT, suggesting damaged cytoskeleton and membrane structures. Finally, we investigated the effect of crenolanib on the mechanical properties of hiPSC-CMs. Crenolanib is an inhibitor of the Platelet-Derived Growth Factor Receptor α (PDGFRA) pathway which is upregulated in FLNCtv hiPSC-CMs. Crenolanib was able to partially rescue the stiffness of FLNCKO-/- hiPSC-CMs compared to control, supporting its potential therapeutic role.

Filamin C Deficiency Impairs Sarcomere Stability and Activates Focal Adhesion Kinase through PDGFRA Signaling in Induced Pluripotent Stem Cell-Derived Cardiomyocytes

Truncating mutations in filamin C (FLNC) are associated with dilated cardiomyopathy and arrhythmogenic cardiomyopathy. FLNC is an actin-binding protein and is known to interact with transmembrane and structural proteins; hence, the ablation of FLNC in cardiomyocytes is expected to dysregulate cell adhesion, cytoskeletal organization, sarcomere structural integrity, and likely nuclear function. Our previous study showed that the transcriptional profiles of FLNC homozygous deletions in human pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are highly comparable to the transcriptome profiles of hiPSC-CMs from patients with FLNC truncating mutations. Therefore, in this study, we used CRISPR-Cas-engineered hiPSC-derived FLNC knockout cardiac myocytes as a model of FLNC cardiomyopathy to determine pathogenic mechanisms and to examine structural changes caused by FLNC deficiency. RNA sequencing data indicated the significant upregulation of focal adhesion signaling and the dysregulation of thin filament genes in FLNC-knockout (FLNCKO) hiPSC-CMs compared to isogenic hiPSC-CMs. Furthermore, our findings suggest that the complete loss of FLNC in cardiomyocytes led to cytoskeletal defects and the activation of focal adhesion kinase. Pharmacological inhibition of PDGFRA signaling using crenolanib (an FDA-approved drug) reduced focal adhesion kinase activation and partially normalized the focal adhesion signaling pathway. The findings from this study suggest the opportunity in repurposing FDA-approved drug as a therapeutic strategy to treat FLNC cardiomyopathy.

Tachycardia-induced metabolic rewiring as a driver of contractile dysfunction

Prolonged tachycardia-a risk factor for cardiovascular morbidity and mortality-can induce cardiomyopathy in the absence of structural disease in the heart. Here, by leveraging human patient data, a canine model of tachycardia and engineered heart tissue generated from human induced pluripotent stem cells, we show that metabolic rewiring during tachycardia drives contractile dysfunction by promoting tissue hypoxia, elevated glucose utilization and the suppression of oxidative phosphorylation. Mechanistically, a metabolic shift towards anaerobic glycolysis disrupts the redox balance of nicotinamide adenine dinucleotide (NAD), resulting in increased global protein acetylation (and in particular the acetylation of sarcoplasmic/endoplasmic reticulum Ca2+-ATPase), a molecular signature of heart failure. Restoration of NAD redox by NAD+ supplementation reduced sarcoplasmic/endoplasmic reticulum Ca2+-ATPase acetylation and accelerated the functional recovery of the engineered heart tissue after tachycardia. Understanding how metabolic rewiring drives tachycardia-induced cardiomyopathy opens up opportunities for therapeutic intervention.

Adverse events among persons with TB using in-person vs. electronic directly observed therapy

BACKGROUND: We evaluated patient safety within a randomized crossover trial comparing electronic directly observed therapy (eDOT) to in-person DOT (ipDOT) in persons undergoing TB treatment in New York City, NY, USA.METHODS: Participant symptoms, symptom severity, and clinical management were documented. We assessed adverse event reports (AERs) by DOT method during the two-period crossover. Using Cox proportional-hazards mixed-effects models, we estimated the adjusted hazard ratio (aHR) of participants reporting an adverse event (AE) vs. not reporting an AE.RESULTS: Of 211 participants, 57 (27.0%) reported AEs during the two-period crossover; of these, 54.4% (31/57) were reported while using eDOT vs. 45.6% (26/57) while using ipDOT. Controlling for study group and period, the aHR for eDOT vs. ipDOT was 0.98 (95% CI 0.49-1.93). Although statistically not significant, the wide confidence intervals suggest that a significant association cannot be entirely ruled out. Gastrointestinal symptoms were most frequently reported (42.1%, 24/57). AER types and severity did not differ significantly by DOT method. Days from symptom onset to medical attention was similar across DOT methods (median: 1.0 day, IQR 0.0-2.0). No participants switched DOT methods due to AERs or monitoring concerns.CONCLUSION: Further evaluation to ascertain whether AERs differ when patients use eDOT vs. ipDOT is warranted.

Biomechanical Impact of Pathogenic MYBPC3 Truncation Variant Revealed by Dynamically Tuning In Vitro Afterload

Engineered cardiac microtissues were fabricated using pluripotent stem cells with a hypertrophic cardiomyopathy associated c. 2827 C>T; p.R943x truncation variant in myosin binding protein C (MYBPC3+/-). Microtissues were mounted on iron-incorporated cantilevers, allowing manipulations of cantilever stiffness using magnets, enabling examination of how in vitro afterload affects contractility. MYPBC3+/- microtissues developed augmented force, work, and power when cultured with increased in vitro afterload when compared with isogenic controls in which the MYBPC3 mutation had been corrected (MYPBC3+/+(ed)), but weaker contractility when cultured with lower in vitro afterload. After initial tissue maturation, MYPBC3+/- CMTs exhibited increased force, work, and power in response to both acute and sustained increases of in vitro afterload. Together, these studies demonstrate that extrinsic biomechanical challenges potentiate genetically-driven intrinsic increases in contractility that may contribute to clinical disease progression in patients with HCM due to hypercontractile MYBPC3 variants.

Challenges associated with electronic and in-person directly observed therapy during a randomized trial

BACKGROUND: Electronic directly observed therapy (eDOT) has been proposed as an alternative to traditional in-person DOT (ipDOT) for monitoring TB treatment adherence. Information about the comparative performance and implementation of eDOT is limited.METHODS: The frequency of challenges during DOT, challenge type, and effect on medication observation were documented by DOT method during a crossover, noninferiority randomized controlled trial. A logistic mixed-effects model that adjusted for the study design was used to estimate the percentage of successfully observed doses when challenges occurred.RESULTS: A total of 20,097 medication doses were scheduled for observation with either eDOT (15,405/20,097; 76.7%) or ipDOT (4,692/20,097; 23.3%) for 213 study participants. In total, one or more challenges occurred during 17.3% (2,672/15,405) of eDOT sessions and 15.6% (730/4,692) of ipDOT sessions. Among 4,374 documented challenges, 27.3% (n = 1,192) were characterized as technical, 65.9% (n = 2,881) were patient-related, and 6.9% (n = 301) were program-related. Estimated from the logistic model (n = 6,782 doses, 173 participants), the adjusted percentage of doses successfully observed during problematic sessions was 21.7% (95% CI 11.2-37.8) for eDOT and 4.2% (95% CI 1.1-14.7) for ipDOT.CONCLUSION: Compared to ipDOT, challenges were encountered in a slightly higher percentage of eDOT sessions but were more often resolved to enable successful dose observation during problematic sessions.

Systems analysis of de novo mutations in congenital heart diseases identified a protein network in the hypoplastic left heart syndrome

Despite a strong genetic component, only a few genes have been identified in congenital heart diseases (CHDs). We introduced systems analyses to uncover the hidden organization on biological networks of mutations in CHDs and leveraged network analysis to integrate the protein interactome, patient exomes, and single-cell transcriptomes of the developing heart. We identified a CHD network regulating heart development and observed that a sub-network also regulates fetal brain development, thereby providing mechanistic insights into the clinical comorbidities between CHDs and neurodevelopmental conditions. At a small scale, we experimentally verified uncharacterized cardiac functions of several proteins. At a global scale, our study revealed developmental dynamics of the network and observed its association with the hypoplastic left heart syndrome (HLHS), which was further supported by the dysregulation of the network in HLHS endothelial cells. Overall, our work identified previously uncharacterized CHD factors and provided a generalizable framework applicable to studying many other complex diseases. A record of this paper's Transparent Peer Review process is included in the supplemental information.

Activation of PDGFRA signaling contributes to filamin C-related arrhythmogenic cardiomyopathy

FLNC truncating mutations (FLNCtv) are prevalent causes of inherited dilated cardiomyopathy (DCM), with a high risk of developing arrhythmogenic cardiomyopathy. We investigated the molecular mechanisms of mutant FLNC in the pathogenesis of arrhythmogenic DCM (a-DCM) using patient-specific induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). We demonstrated that iPSC-CMs from two patients with different FLNCtv mutations displayed arrhythmias and impaired contraction. FLNC ablation induced a similar phenotype, suggesting that FLNCtv are loss-of-function mutations. Coimmunoprecipitation and proteomic analysis identified β-catenin (CTNNB1) as a downstream target. FLNC deficiency induced nuclear translocation of CTNNB1 and subsequently activated the platelet-derived growth factor receptor alpha (PDGFRA) pathway, which were also observed in human hearts with a-DCM and FLNCtv. Treatment with the PDGFRA inhibitor, crenolanib, improved contractile function of patient iPSC-CMs. Collectively, our findings suggest that PDGFRA signaling is implicated in the pathogenesis, and inhibition of this pathway is a potential therapeutic strategy in FLNC-related cardiomyopathies.

The Potential of Gamma Secretase as a Therapeutic Target for Cardiac Diseases

Heart diseases are some of the most common and pressing threats to human health worldwide. The American Heart Association and the National Institute of Health jointly work to annually update data on cardiac diseases. In 2018, 126.9 million Americans were reported as having some form of cardiac disorder, with an estimated direct and indirect total cost of USD 363.4 billion. This necessitates developing therapeutic interventions for heart diseases to improve human life expectancy and economic relief. In this review, we look into gamma-secretase as a potential therapeutic target for cardiac diseases. Gamma-secretase, an aspartyl protease enzyme, is responsible for the cleavage and activation of a number of substrates that are relevant to normal cardiac development and function as found in mutation studies. Some of these substrates are involved in downstream signaling processes and crosstalk with pathways relevant to heart diseases. Most of the substrates and signaling events we explored were found to be potentially beneficial to maintain cardiac function in diseased conditions. This review presents an updated overview of the current knowledge on gamma-secretase processing of cardiac-relevant substrates and seeks to understand if the modulation of gamma-secretase activity would be beneficial to combat cardiac diseases.

Metabolic Maturation Media Improve Physiological Function of Human iPSC-Derived Cardiomyocytes

Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) have enormous potential for the study of human cardiac disorders. However, their physiological immaturity severely limits their utility as a model system and their adoption for drug discovery. Here, we describe maturation media designed to provide oxidative substrates adapted to the metabolic needs of human iPSC (hiPSC)-CMs. Compared with conventionally cultured hiPSC-CMs, metabolically matured hiPSC-CMs contract with greater force and show an increased reliance on cardiac sodium (Na⁺) channels and sarcoplasmic reticulum calcium (Ca²⁺) cycling. The media enhance the function, long-term survival, and sarcomere structures in engineered heart tissues. Use of the maturation media made it possible to reliably model two genetic cardiac diseases: long QT syndrome type 3 due to a mutation in the cardiac Na⁺ channel SCN5A and dilated cardiomyopathy due to a mutation in the RNA splicing factor RBM20. The maturation media should increase the fidelity of hiPSC-CMs as disease models.

Physiological immaturity of iPSC-derived cardiomyocytes limits their fidelity as disease models. Feyen et al. developed a low glucose, high oxidative substrate media that increase maturation of ventricular-like hiPSC-CMs in 2D and 3D cultures relative to standard protocols. Improved characteristics include a low resting V_m, rapid depolarization, and increased Ca²⁺ dependence and force generation.

Clinical Trial in a Dish: Using Patient-Derived Induced Pluripotent Stem Cells to Identify Risks of Drug-Induced Cardiotoxicity

Drug-induced cardiotoxicity is a significant clinical issue, with many drugs in the market being labeled with warnings on cardiovascular adverse effects. Treatments are often prematurely halted when cardiotoxicity is observed, which limits their therapeutic potential. Moreover, cardiotoxicity is a major reason for abandonment during drug development, reducing available treatment options for diseases and creating a significant financial burden and disincentive for drug developers. Thus, it is important to minimize the cardiotoxic effects of medications that are in use or in development. To this end, identifying patients at a higher risk of developing cardiovascular adverse effects for the drug of interest may be an effective strategy. The discovery of human induced pluripotent stem cells has enabled researchers to generate relevant cell types that retain a patient's own genome and examine patient-specific disease mechanisms, paving the way for precision medicine. Combined with the rapid development of pharmacogenomic analysis, the ability of induced pluripotent stem cell-derivatives to recapitulate patient-specific drug responses provides a powerful platform to identify subsets of patients who are particularly vulnerable to drug-induced cardiotoxicity. In this review, we will discuss the current use of patient-specific induced pluripotent stem cells in identifying populations who are at risk to drug-induced cardiotoxicity and their potential applications in future precision medicine practice. Graphic Abstract: A graphic abstract is available for this article.

Modelling diastolic dysfunction in induced pluripotent stem cell-derived cardiomyocytes from hypertrophic cardiomyopathy patients

AIMS

Diastolic dysfunction (DD) is common among hypertrophic cardiomyopathy (HCM) patients, causing major morbidity and mortality. However, its cellular mechanisms are not fully understood, and presently there is no effective treatment. Patient-specific induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) hold great potential for investigating the mechanisms underlying DD in HCM and as a platform for drug discovery.

METHODS AND RESULTS

In the present study, beating iPSC-CMs were generated from healthy controls and HCM patients with DD. Micropatterned iPSC-CMs from HCM patients showed impaired diastolic function, as evidenced by prolonged relaxation time, decreased relaxation rate, and shortened diastolic sarcomere length. Ratiometric Ca2+ imaging indicated elevated diastolic [Ca2+]i and abnormal Ca2+ handling in HCM iPSC-CMs, which were exacerbated by β-adrenergic challenge. Combining Ca2+ imaging and traction force microscopy, we observed enhanced myofilament Ca2+ sensitivity (measured as dF/Δ[Ca2+]i) in HCM iPSC-CMs. These results were confirmed with genome-edited isogenic iPSC lines that carry HCM mutations, indicating that cytosolic diastolic Ca2+ overload, slowed [Ca2+]i recycling, and increased myofilament Ca2+ sensitivity, collectively impairing the relaxation of HCM iPSC-CMs. Treatment with partial blockade of Ca2+ or late Na+ current reset diastolic Ca2+ homeostasis, restored diastolic function, and improved long-term survival, suggesting that disturbed Ca2+ signalling is an important cellular pathological mechanism of DD. Further investigation showed increased expression of L-type Ca2+channel (LTCC) and transient receptor potential cation channels (TRPC) in HCM iPSC-CMs compared with control iPSC-CMs, which likely contributed to diastolic [Ca2+]i overload.

CONCLUSION

In summary, this study recapitulated DD in HCM at the single-cell level, and revealed novel cellular mechanisms and potential therapeutic targets of DD using iPSC-CMs.

Human-Induced Pluripotent Stem Cell Model of Trastuzumab-Induced Cardiac Dysfunction in Patients With Breast Cancer

BACKGROUND

Molecular targeted chemotherapies have been shown to significantly improve the outcomes of patients who have cancer, but they often cause cardiovascular side effects that limit their use and impair patients' quality of life. Cardiac dysfunction induced by these therapies, especially trastuzumab, shows a distinct cardiotoxic clinical phenotype in comparison to the cardiotoxicity induced by conventional chemotherapies.

METHODS

We used the human induced pluripotent stem cell-derived cardiomyocyte (iPSC-CM) platform to determine the underlying cellular mechanisms in trastuzumab-induced cardiac dysfunction. We assessed the effects of trastuzumab on structural and functional properties in iPSC-CMs from healthy individuals and performed RNA-sequencing to further examine the effect of trastuzumab on iPSC-CMs. We also generated human induced pluripotent stem cells from patients receiving trastuzumab and examined whether patients' phenotype could be recapitulated in vitro by using patient-specific iPSC-CMs.

RESULTS

We found that clinically relevant doses of trastuzumab significantly impaired the contractile and calcium-handling properties of iPSC-CMs without inducing cardiomyocyte death or sarcomeric disorganization. RNA-sequencing and subsequent functional analysis revealed mitochondrial dysfunction and altered the cardiac energy metabolism pathway as primary causes of trastuzumab-induced cardiotoxic phenotype. Human iPSC-CMs generated from patients who received trastuzumab and experienced severe cardiac dysfunction were more vulnerable to trastuzumab treatment than iPSC-CMs generated from patients who did not experience cardiac dysfunction following trastuzumab therapy. It is important to note that metabolic modulation with AMP-activated protein kinase activators could avert the adverse effects induced by trastuzumab.

CONCLUSIONS

Our results indicate that alterations in cellular metabolic pathways in cardiomyocytes could be a key mechanism underlying the development of cardiac dysfunction following trastuzumab therapy; therefore, targeting the altered metabolism may be a promising therapeutic approach for trastuzumab-induced cardiac dysfunction.

A Premature Termination Codon Mutation in MYBPC3 Causes Hypertrophic Cardiomyopathy via Chronic Activation of Nonsense-Mediated Decay

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is frequently caused by mutations in myosin-binding protein C3 ( MYBPC3) resulting in a premature termination codon (PTC). The underlying mechanisms of how PTC mutations in MYBPC3 lead to the onset and progression of HCM are poorly understood. This study's aim was to investigate the molecular mechanisms underlying the pathogenesis of HCM associated with MYBPC3 PTC mutations by utilizing human isogenic induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs).

METHODS

Isogenic iPSC lines were generated from HCM patients harboring MYBPC3 PTC mutations (p.R943x; p.R1073P_Fsx4) using genome editing. Comprehensive phenotypic and transcriptome analyses were performed in the iPSC-CMs.

RESULTS

We observed aberrant calcium handling properties with prolonged decay kinetics and elevated diastolic calcium levels in the absence of structural abnormalities or contracile dysfunction in HCM iPSC-CMs as compared to isogenic controls. The mRNA expression levels of MYBPC3 were significantly reduced in mutant iPSC-CMs, but the protein levels were comparable among isogenic iPSC-CMs, suggesting that haploinsufficiency of MYBPC3 does not contribute to the pathogenesis of HCM in vitro. Furthermore, truncated MYBPC3 peptides were not detected. At the molecular level, the nonsense-mediated decay pathway was activated, and a set of genes involved in major cardiac signaling pathways was dysregulated in HCM iPSC-CMs, indicating an HCM gene signature in vitro. Specific inhibition of the nonsense-mediated decay pathway in mutant iPSC-CMs resulted in reversal of the molecular phenotype and normalization of calcium-handling abnormalities.

CONCLUSIONS

iPSC-CMs carrying MYBPC3 PTC mutations displayed aberrant calcium signaling and molecular dysregulations in the absence of significant haploinsufficiency of MYBPC3 protein. Here we provided the first evidence of the direct connection between the chronically activated nonsense-mediated decay pathway and HCM disease development.

Cost savings associated with video directly observed therapy for treatment of tuberculosis

OBJECTIVE: To calculate the per-session and annual direct program costs to implement directly observed therapy (DOT) for tuberculosis treatment and to conduct a cost attribution analysis under varying proportions of DOT utilization for four DOT types.DESIGN: Program data covering the study period from September 2014 to August 2015 in New York City (NYC) were used to conduct a retrospective bottom-up micro-costing economic evaluation. For each DOT type, potential per-session and annual program savings were estimated as the cost averted by adopting a uniform distribution of DOT alternatives. Sensitivity analyses explored aggregate cost impacts of unequal distributions.RESULTS: There was a total of 38 035 unique DOT visits, of which 12 002 (32%) were clinic-based (CDOT); 15 483 (41%) were field-based (FDOT); 7185 (19%) were live-video (LVDOT); and 3365 (9%) were recorded-video (RVDOT). The per-session direct costs (in 2016 $US) for DOT services delivered during the study period were $8.46 for CDOT; $19.83 for FDOT; $6.54 for LVDOT; and $5.35 for RVDOT. Sensitivity analyses supported the main findings.CONCLUSIONS: Significant cost savings were estimated with increased utilization of VDOT. Assuming equivalent treatment adherence, duration, completion, and adverse events across DOT types, RVDOT was the modality that most minimized cost.

Abstract 237: Identifying the Transcriptome Signature of Calcium Channel Blocker in Human iPSC-Derived Cardiomyocytes

Calcium channel blockers (CCBs) are important in treating cardiovascular diseases and the acute pharmacological actions of CCBs in the hearts have been extensively studied. However, we lack the knowledge of the drug-specific effect on human cardiomyocyte transcriptome and potential physiological change after long-term exposure as patients are usually prescribed with these medications for their lifetime after diagnosis. Thus, we aimed to simulate chronic CCB treatment in human cardiomyocytes and subsequently examine both the functional and transcriptomic alterations. We differentiated cardiomyocytes from three human induced pluripotent stem cell (iPSC) lines and exposed them to four different CCBs—nifedipine, amlodipine, diltiazem, and verapamil—at their physiological serum concentrations for two weeks. Without inducing cell death and damage to myofilament structure, CCBs elicited line specific inhibition on calcium kinetics and contractility. While all four CCBs exerted comparable inhibition on calcium kinetics, verapamil applied the strongest inhibition on cardiomyocyte contractile function. By examining cardiomyocyte transcriptome after treatment, we identified little overlap in their transcriptome signatures. Verapamil is the only inhibitor that reduced the expression of contraction related genes, such as myosin heavy chain and troponin I, consistent with its depressive effects on contractile function. Moreover, the alterations in these gene may help explain how HCM patients respond to verapamil in relieving outflow tract obstruction. In conclusion, we identified the distinct transcriptome signatures of different CCBs in human cardiomyocytes, suggesting that although the four inhibitors act on the same target, they may have distinct effects on normal cardiac cell physiology. The application of iPSC platform and transcriptomic findings may allow us to identify responders to verapamil treatment.

Activation of PDGF pathway links LMNA mutation to dilated cardiomyopathy

Lamin A/C (LMNA) is one of the most frequently mutated genes associated with dilated cardiomyopathy (DCM). DCM related to mutations in LMNA is a common inherited cardiomyopathy that is associated with systolic dysfunction and cardiac arrhythmias. Here we modelled the LMNA-related DCM in vitro using patient-specific induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). Electrophysiological studies showed that the mutant iPSC-CMs displayed aberrant calcium homeostasis that led to arrhythmias at the single-cell level. Mechanistically, we show that the platelet-derived growth factor (PDGF) signalling pathway is activated in mutant iPSC-CMs compared to isogenic control iPSC-CMs. Conversely, pharmacological and molecular inhibition of the PDGF signalling pathway ameliorated the arrhythmic phenotypes of mutant iPSC-CMs in vitro. Taken together, our findings suggest that the activation of the PDGF pathway contributes to the pathogenesis of LMNA-related DCM and point to PDGF receptor-β (PDGFRB) as a potential therapeutic target.

Identifying the Transcriptome Signatures of Calcium Channel Blockers in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

RATIONALE

Calcium channel blockers (CCBs) are an important class of drugs in managing cardiovascular diseases. Patients usually rely on these medications for the remainder of their lives after diagnosis. Although the acute pharmacological actions of CCBs in the hearts are well-defined, little is known about the drug-specific effects on human cardiomyocyte transcriptomes and physiological alterations after long-term exposure.

OBJECTIVE

This study aimed to simulate chronic CCB treatment and to examine both the functional and transcriptomic changes in human cardiomyocytes.

METHODS AND RESULTS

We differentiated cardiomyocytes and generated engineered heart tissues from 3 human induced pluripotent stem cell lines and exposed them to 4 different CCBs-nifedipine, amlodipine, diltiazem, and verapamil-at their physiological serum concentrations for 2 weeks. Without inducing cell death and damage to myofilament structure, CCBs elicited line-specific inhibition on calcium kinetics and contractility. While all 4 CCBs exerted similar inhibition on calcium kinetics, verapamil applied the strongest inhibition on cardiomyocyte contractile function. By profiling cardiomyocyte transcriptome after CCB treatment, we identified little overlap in their transcriptome signatures. Verapamil is the only inhibitor that reduced the expression of contraction-related genes, such as MYH (myosin heavy chain) and troponin I, consistent with its depressive effects on contractile function. The reduction of these contraction-related genes may also explain the responsiveness of patients with hypertrophic cardiomyopathy to verapamil in managing left ventricular outflow tract obstruction.

CONCLUSIONS

This is the first study to identify the transcriptome signatures of different CCBs in human cardiomyocytes. The distinct gene expression patterns suggest that although the 4 inhibitors act on the same target, they may have distinct effects on normal cardiac cell physiology.

Determining the Pathogenicity of a Genomic Variant of Uncertain Significance Using CRISPR/Cas9 and Human-Induced Pluripotent Stem Cells

BACKGROUND

The progression toward low-cost and rapid next-generation sequencing has uncovered a multitude of variants of uncertain significance (VUS) in both patients and asymptomatic "healthy" individuals. A VUS is a rare or novel variant for which disease pathogenicity has not been conclusively demonstrated or excluded, and thus cannot be definitively annotated. VUS, therefore, pose critical clinical interpretation and risk-assessment challenges, and new methods are urgently needed to better characterize their pathogenicity.

METHODS

To address this challenge and showcase the uncertainty surrounding genomic variant interpretation, we recruited a "healthy" asymptomatic individual, lacking cardiac-disease clinical history, carrying a hypertrophic cardiomyopathy (HCM)-associated genetic variant (NM_000258.2:c.170C>A, NP_000249.1:p.Ala57Asp) in the sarcomeric gene MYL3, reported by the ClinVar database to be "likely pathogenic." Human-induced pluripotent stem cells (iPSCs) were derived from the heterozygous VUS MYL3_(170C>A) carrier, and their genome was edited using CRISPR/Cas9 to generate 4 isogenic iPSC lines: (1) corrected "healthy" control; (2) homozygous VUS MYL3_(170C>A); (3) heterozygous frameshift mutation MYL3^(170C>A/fs); and (4) known heterozygous MYL3 pathogenic mutation (NM_000258.2:c.170C>G), at the same nucleotide position as VUS MYL3_(170C>A), lines. Extensive assays including measurements of gene expression, sarcomere structure, cell size, contractility, action potentials, and calcium handling were performed on the isogenic iPSC-derived cardiomyocytes (iPSC-CMs).

RESULTS

The heterozygous VUS MYL3_(170C>A)-iPSC-CMs did not show an HCM phenotype at the gene expression, morphology, or functional levels. Furthermore, genome-edited homozygous VUS MYL3_(170C>A)- and frameshift mutation MYL3^(170C>A/fs)-iPSC-CMs lines were also asymptomatic, supporting a benign assessment for this particular MYL3 variant. Further assessment of the pathogenic nature of a genome-edited isogenic line carrying a known pathogenic MYL3 mutation, MYL3_(170C>G), and a carrier-specific iPSC-CMs line, carrying a MYBPC3_(961G>A) HCM variant, demonstrated the ability of this combined platform to provide both pathogenic and benign assessments.

CONCLUSIONS

Our study illustrates the ability of clustered regularly interspaced short palindromic repeats/Cas9 genome-editing of carrier-specific iPSCs to elucidate both benign and pathogenic HCM functional phenotypes in a carrier-specific manner in a dish. As such, this platform represents a promising VUS risk-assessment tool that can be used for assessing HCM-associated VUS specifically, and VUS in general, and thus significantly contribute to the arsenal of precision medicine tools available in this emerging field.

Abstract 243: Modeling of Diastolic Dysfunction in Induced Pluripotent Stem Cell-derived Cardiomyocytes From Hypertrophic Cardiomyopathy Patients

Aims: Diastolic dysfunction (DD) is common among hypertrophic cardiomyopathy (HCM) patients, causing major morbidity and mortality. Yet its cellular mechanisms are not fully understood, and presently, there is no effective treatment. Patient-specific induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) hold great potential for investigating the mechanisms underlying DD and as a platform for drug discovery.

Methods and results: In the present study, beating iPSC-CMs were generated from healthy recruits and HCM patients with evident DD. Micropatterned iPSC-CMs from HCM patients showed impaired diastolic function, as evidenced by prolonged relaxation time, retarded relaxation rate, and shortened diastolic sarcomere length. Ratiometric Ca 2+ imaging indicated elevated diastolic [Ca 2+ ] i and abnormal Ca 2+ handling in HCM iPSC-CMs, which were exacerbated by β-adrenergic challenge. Combining Ca 2+ imaging and traction force microscopy (TFM), we observed enhanced myofilament Ca 2+ sensitivity (measured as dF/Δ[Ca 2+ ] i ) in HCM iPSC-CMs. These results indicated that cytosolic diastolic Ca 2+ overload, slowed [Ca 2+ ] i decline and increased myofilament Ca 2+ sensitivity, collectively impair the relaxation of HCM cells. Treating HCM iPSC-CMs with partial blockade of Ca 2+ or late Na + current reset diastolic Ca 2+ homeostasis, restored diastolic function and improved long-term survival, suggesting disturbed Ca 2+ signaling is an important cellular pathological mechanism of DD. Further investigation showed increased expression of L-type calcium channel (LTCC) and transient receptor potential channels (TRPCs) in HCM iPSC-CMs, which likely contribute to diastolic [Ca 2+ ] i overload.

Conclusion: In summary, this study recapitulated DD at the single cell level, and revealed novel mechanisms and potential therapeutic targets of DD using HCM iPSC-CMs.

High Incidence of Thrombophilia Detected in Chinese Patients with Venous Thrombosis

Venous thromboembolism is rare in Chinese. To determine the incidence and disease profile of thrombophilia in Chinese patients with thrombosis, 52 unselected Chinese patients with documented venous thrombosis were studied for the presence of thrombophilia. Levels of antithrombin III (AT III), protein C (PC) and protein S (PS) as well as the presence of acquired lupus anticoagulant (LA) and anticardiolipin antibody (ACA) were investigated. Thirty patients were found to be abnormal. These consisted of 5 AT III deficiencies, 9 PC deficiencies, 10 PS deficiencies, 1 combined PC & PS deficiency (all in the heterozygous range), and 5 patients with LA and/or ACA. When the patients with LA and/or ACA are excluded, the incidence of hereditary thrombophilia is 25/47 i.e. 53.2%' which is much higher than those reported in studies of Caucasian patients selected under strict criteria. Family studies performed in 16 cases ot hereditary thrombophilia revealed involvement in 11 cases (68.7%); a total of 36 heterozygous family members were affected, most of which remain asymptomatic. Although 35 events predisposing to thrombosis (27 pregnancies, 1 oral contraceptive consumption and 7 surgical operations) were identified among these index patients, and the heterozygous family members, thrombosis was observed on only 6 occasions (17.1%). The data suggest that pregnancy and surgery do not carry the same degree of thrombotic risk in Chinese as in the Caucasian population with heterozygous AT III, PC and PS deficiency.

Genome Editing of Induced Pluripotent Stem Cells to Decipher Cardiac Channelopathy Variant

BACKGROUND

The long QT syndrome (LQTS) is an arrhythmogenic disorder of QT interval prolongation that predisposes patients to life-threatening ventricular arrhythmias such as Torsades de pointes and sudden cardiac death. Clinical genetic testing has emerged as the standard of care to identify genetic variants in patients suspected of having LQTS. However, these results are often confounded by the discovery of variants of uncertain significance (VUS), for which there is insufficient evidence of pathogenicity.

OBJECTIVES

The purpose of this study was to demonstrate that genome editing of patient-specific induced pluripotent stem cells (iPSCs) can be a valuable approach to delineate the pathogenicity of VUS in cardiac channelopathy.

METHODS

Peripheral blood mononuclear cells were isolated from a carrier with a novel missense variant (T983I) in the KCNH2 (LQT2) gene and an unrelated healthy control subject. iPSCs were generated using an integration-free Sendai virus and differentiated to iPSC-derived cardiomyocytes (CMs).

RESULTS

Whole-cell patch clamp recordings revealed significant prolongation of the action potential duration (APD) and reduced rapidly activating delayed rectifier K+ current (IKr) density in VUS iPSC-CMs compared with healthy control iPSC-CMs. ICA-105574, a potent IKr activator, enhanced IKr magnitude and restored normal action potential duration in VUS iPSC-CMs. Notably, VUS iPSC-CMs exhibited greater propensity to proarrhythmia than healthy control cells in response to high-risk torsadogenic drugs (dofetilide, ibutilide, and azimilide), suggesting a compromised repolarization reserve. Finally, the selective correction of the causal variant in iPSC-CMs using CRISPR/Cas9 gene editing (isogenic control) normalized the aberrant cellular phenotype, whereas the introduction of the homozygous variant in healthy control cells recapitulated hallmark features of the LQTS disorder.

CONCLUSIONS

The results suggest that the KCNH2T983I VUS may be classified as potentially pathogenic.

A novel human S10F-Hsp20 mutation induces lethal peripartum cardiomyopathy

Heat shock protein 20 (Hsp20) has been shown to be a critical regulator of cardiomyocyte survival upon cardiac stress. In this study, we investigated the functional significance of a novel human Hsp20 mutation (S10F) in peripartum cardiomyopathy. Previous findings showed that cardiac-specific overexpression of this mutant were associated with reduced autophagy, left ventricular dysfunction and early death in male mice. However, this study indicates that females have normal function with no alterations in autophagy but died within a week after 1-4 pregnancies. Further examination of mutant females revealed left ventricular chamber dilation and hypertrophic remodelling. Echocardiography demonstrated increases in left ventricular end-systolic volume and left ventricular end-diastolic volume, while ejection fraction and fractional shortening were depressed following pregnancy. Subsequent studies revealed that cardiomyocyte apoptosis was elevated in mutant female hearts after the third delivery, associated with decreases in the levels of Bcl-2/Bax and Akt phosphorylation. These results indicate that the human S10F mutant is associated with dysregulation of cell survival signalling, accelerated heart failure and early death post-partum.

Regulation of BECN1-mediated autophagy by HSPB6: Insights from a human HSPB6S10F mutant

HSPB6/Hsp20 (heat shock protein family B [small] member 6) has emerged as a novel cardioprotector against stress-induced injury. We identified a human mutant of HSPB6 (HSPB6^S10F) exclusively present in dilated cardiomyopathy (DCM) patients. Cardiac expression of this mutant in mouse hearts resulted in remodeling and dysfunction, which progressed to heart failure and early death. These detrimental effects were associated with reduced interaction of mutant HSPB6^S10F with BECN1/Beclin 1, leading to BECN1 ubiquitination and its proteosomal degradation. As a result, autophagy flux was substantially inhibited and apoptosis was increased in HSPB6^S10F-mutant hearts. In contrast, overexpression of wild-type HSPB6 (HSPB6 WT) not only increased BECN1 levels, but also competitively suppressed binding of BECN1 to BCL2, resulting in stimulated autophagy. Indeed, preinhibition of autophagy attenuated the cardioprotective effects of HSPB6 WT. Taken together, these findings reveal a new regulatory mechanism of HSPB6 in cell survival through its interaction with BECN1. Furthermore, Ser10 appears to be crucial for the protective effects of HSPB6 and transversion of this amino acid to Phe contributes to cardiomyopathy.

HAX-1 regulates SERCA2a oxidation and degradation

Ischemia/reperfusion injury is associated with contractile dysfunction and increased cardiomyocyte death. Overexpression of the hematopoietic lineage substrate-1-associated protein X-1 (HAX-1) has been shown to protect from cellular injury but the function of endogenous HAX-1 remains obscure due to early lethality of the knockout mouse. Herein we generated a cardiac-specific and inducible HAX-1 deficient model, which uncovered an unexpected role of HAX-1 in regulation of sarco/endoplasmic reticulum Ca-ATPase (SERCA2a) in ischemia/reperfusion injury. Although ablation of HAX-1 in the adult heart elicited no morphological alterations under non-stress conditions, it diminished contractile recovery and increased infarct size upon ischemia/reperfusion injury. These detrimental effects were associated with increased loss of SERCA2a. Enhanced SERCA2a degradation was not due to alterations in calpain and calpastatin levels or calpain activity. Conversely, HAX-1 overexpression improved contractile recovery and maintained SERCA2a levels. The regulatory effects of HAX-1 on SERCA2a degradation were observed at multiple levels, including intact hearts, isolated cardiomyocytes and sarcoplasmic reticulum microsomes. Mechanistically, HAX-1 ablation elicited increased production of reactive oxygen species at the sarco/endoplasic reticulum compartment, resulting in SERCA2a oxidation and a predisposition to its proteolysis. This effect may be mediated by NAPDH oxidase 4 (NOX4), a novel binding partner of HAX-1. Accordingly, NOX inhibition with apocynin abrogated the effects of HAX-1 ablation in hearts subjected to ischemia/reperfusion injury. Taken together, our findings reveal a role of HAX-1 in the regulation of oxidative stress and SERCA2a degradation, implicating its importance in calcium homeostasis and cell survival pathways.

Abstract 6: Restoration of Impaired Diastolic Function in Hypertrophic Cardiomyopathy Induced Pluripotent Stem Cell-derived Cardiomyocytes by Re-balancing the Calcium Homeostasis

Background: Diastolic dysfunction is commonly seen in hypertrophic cardiomyopathy (HCM). However, the cellular mechanism is not fully understood, and no effective treatment so far has been developed. We hypothesize here that HCM patient-specific induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) can recapitulate the cellular mechanism, and provide us a platform for mechanistic study and for drug screening of diastolic dysfunctions in HCM.

Methods and Results: We generated beating iPSC-CMs from healthy individuals and HCM patients carrying familial mutations (MYH7 R663H (n=2 lines) and MYBPC3 R943ter (n=2 lines)). Sarcomere shortening measurement in patterned iPSC-CMs with live cell confocal imaging showed significantly prolonged diastolic phase and slower relaxation velocity in HCM iPSC-CMs compared to WT cells. To elucidate the cellular mechanism, Fura-2 AM ratiometric calcium imaging showed marked elevation of resting calcium level and increased abnormal calcium handlings in HCM iPSC-CMs, which were exaggerated by β-adrenergic activation with isoproterenol. By applying calcium transient and contractile force simultaneous recording, we defined a “risk index of diastolic dysfunction” (measured as transient-contraction gain factor), which was significantly increased in HCM iPSC-CMs. Thus, both elevated basal calcium level and increased calcium sensitivity of myofilament contribute to the abnormal diastolic function in HCM iPSC-CMs. Gene expression profiling of HCM and WT iPSC-CMs indicated that increased calcium channels may underlie the increased basal calcium concentration in HCM cells. Indeed, partially blocking the calcium influx by calcium blockers reset the basal calcium level, attenuated calcium mishandling, and restored the diastolic function in HCM iPSC-CMs. Moreover, re-balancing calcium homeostasis significantly improved long-term survival rate of HCM iPSC-CMs at both basal level and under β-adrenergic stress.

Conclusion: The iPSC-CM models carrying patient-specific HCM mutations recapitulated diastolic dysfunction on single cell level. Future studies using these platform may reveal additional novel cellular mechanisms and therapeutic targets of diastolic dysfunction in HCM disease.

Patient-Specific and Genome-Edited Induced Pluripotent Stem Cell-Derived Cardiomyocytes Elucidate Single-Cell Phenotype of Brugada Syndrome

BACKGROUND

Brugada syndrome (BrS), a disorder associated with characteristic electrocardiogram precordial ST-segment elevation, predisposes afflicted patients to ventricular fibrillation and sudden cardiac death. Despite marked achievements in outlining the organ level pathophysiology of the disorder, the understanding of human cellular phenotype has lagged due to a lack of adequate human cellular models of the disorder.

OBJECTIVES

The objective of this study was to examine single cell mechanism of Brugada syndrome using induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs).

METHODS

This study recruited 2 patients with type 1 BrS carrying 2 different sodium voltage-gated channel alpha subunit 5 variants as well as 2 healthy control subjects. We generated iPSCs from their skin fibroblasts by using integration-free Sendai virus. We used directed differentiation to create purified populations of iPSC-CMs.

RESULTS

BrS iPSC-CMs showed reductions in inward sodium current density and reduced maximal upstroke velocity of action potential compared with healthy control iPSC-CMs. Furthermore, BrS iPSC-CMs demonstrated increased burden of triggered activity, abnormal calcium (Ca²⁺) transients, and beating interval variation. Correction of the causative variant by genome editing was performed, and resultant iPSC-CMs showed resolution of triggered activity and abnormal Ca²⁺ transients. Gene expression profiling of iPSC-CMs showed clustering of BrS compared with control subjects. Furthermore, BrS iPSC-CM gene expression correlated with gene expression from BrS human cardiac tissue gene expression.

CONCLUSIONS

Patient-specific iPSC-CMs were able to recapitulate single-cell phenotype features of BrS, including blunted inward sodium current, increased triggered activity, and abnormal Ca²⁺ handling. This novel human cellular model creates future opportunities to further elucidate the cellular disease mechanism and identify novel therapeutic targets.

HAX-1 regulates cyclophilin-D levels and mitochondria permeability transition pore in the heart

The major underpinning of massive cell death associated with myocardial infarction involves opening of the mitochondrial permeability transition pore (mPTP), resulting in disruption of mitochondria membrane integrity and programmed necrosis. Studies in human lymphocytes suggested that the hematopoietic-substrate-1 associated protein X-1 (HAX-1) is linked to regulation of mitochondrial membrane function, but its role in controlling mPTP activity remains obscure. Herein we used models with altered HAX-1 expression levels in the heart and uncovered an unexpected role of HAX-1 in regulation of mPTP and cardiomyocyte survival. Cardiac-specific HAX-1 overexpression was associated with resistance against loss of mitochondrial membrane potential, induced by oxidative stress, whereas HAX-1 heterozygous deficiency exacerbated vulnerability. The protective effects of HAX-1 were attributed to specific down-regulation of cyclophilin-D levels leading to reduction in mPTP activation. Accordingly, cyclophilin-D and mPTP were increased in heterozygous hearts, but genetic ablation of cyclophilin-D in these hearts significantly alleviated their susceptibility to ischemia/reperfusion injury. Mechanistically, alterations in cyclophilin-D levels by HAX-1 were contributed by the ubiquitin-proteosomal degradation pathway. HAX-1 overexpression enhanced cyclophilin-D ubiquitination, whereas proteosomal inhibition restored cyclophilin-D levels. The regulatory effects of HAX-1 were mediated through interference of cyclophilin-D binding to heat shock protein-90 (Hsp90) in mitochondria, rendering it susceptible to degradation. Accordingly, enhanced Hsp90 expression in HAX-1 overexpressing cardiomyocytes increased cyclophilin-D levels, as well as mPTP activation upon oxidative stress. Taken together, our findings reveal the role of HAX-1 in regulating cyclophilin-D levels via an Hsp90-dependent mechanism, resulting in protection against activation of mPTP and subsequent cell death responses.

Up-regulation of micro-RNA765 in human failing hearts is associated with post-transcriptional regulation of protein phosphatase inhibitor-1 and depressed contractility

AIMS

Impaired sarcoplasmic reticulum (SR) Ca(2+) cycling and depressed contractility, a hallmark of human and experimental heart failure, has been partially attributed to increased protein phosphatase 1 (PP-1) activity, associated with down-regulation of its endogenous inhibitor-1. The levels and activity of inhibitor-1 are reduced in failing hearts, contributing to dephosphorylation and inactivation of key calcium cycling proteins. Therefore, we investigated the mechanisms that mediate decreases in inhibitor-1 by post-transcriptional modification.

METHODS AND RESULTS

Bioinformatics revealed that 17 human microRNAs may serve as modulators of inhibitor-1. However, real-time PCR analysis identified only one of these microRNAs, miR-765, as being increased in human failing hearts concomitant with decreased inhibitor-1 levels. Expression of miR-765 in HEK293 cells or mouse ventricular myocytes confirmed suppression of inhibitor-1 levels through binding of this miR-765 to the 3'-untranslated region of inhibitor-1 mRNA. To determine the functional significance of miR-765 in Ca(2+) cycling, pri-miR-765 as well as a non-translated nucleotide sequence (miR-Ctrl) were expressed in adult mouse ventricular myocytes. The inhibitor-1 expression levels were decreased, accompanied by enhanced PP-1 activity in the miR-765 cardiomyocytes, and these reflected depressed contractile mechanics and Ca(2+) transients, compared with the miR-Ctrl group. The depressive effects were associated with decreases in the phosphorylation of phospholamban and SR Ca(2+) load. These miR-765 negative inotropic effects were abrogated in inhibitor-1-deficient cardiomyocytes, suggesting its apparent specificity for inhibitor-1.

CONCLUSIONS

miR-765 levels are increased in human failing hearts. Such increases may contribute to depressed cardiac function through reduced inhibitor-1 expression and enhanced PP-1 activity, associated with reduced SR Ca(2+) load.

A novel human R25C-phospholamban mutation is associated with super-inhibition of calcium cycling and ventricular arrhythmia

AIMS

Depressed sarcoplasmic reticulum (SR) Ca(2+) cycling, a universal characteristic of human and experimental heart failure, may be associated with genetic alterations in key Ca(2+)-handling proteins. In this study, we identified a novel PLN mutation (R25C) in dilated cardiomyopathy (DCM) and investigated its functional significance in cardiomyocyte Ca(2+)-handling and contractility.

METHODS AND RESULTS

Exome sequencing identified a C73T substitution in the coding region of PLN in a family with DCM. The four heterozygous family members had implantable cardiac defibrillators, and three developed prominent ventricular arrhythmias. Overexpression of R25C-PLN in adult rat cardiomyocytes significantly suppressed the Ca(2+) affinity of SR Ca(2+)-ATPase (SERCA2a), resulting in decreased SR Ca(2+) content, Ca(2+) transients, and impaired contractile function, compared with WT-PLN. These inhibitory effects were associated with enhanced interaction of R25C-PLN with SERCA2, which was prevented by PKA phosphorylation. Accordingly, isoproterenol stimulation relieved the depressive effects of R25C-PLN in cardiomyocytes. However, R25C-PLN also elicited increases in the frequency of Ca(2+) sparks and waves as well as stress-induced aftercontractions. This was accompanied by increased Ca(2+)/calmodulin-dependent protein kinase II activity and hyper-phosphorylation of RyR2 at serine 2814.

CONCLUSION

The findings demonstrate that human R25C-PLN is associated with super-inhibition of SERCA2a and Ca(2+) transport as well as increased SR Ca(2+) leak, promoting arrhythmogenesis under stress conditions. This is the first mechanistic evidence that increased PLN inhibition may impact both SR Ca(2+) uptake and Ca(2+) release activities and suggests that the human R25C-PLN may be a prognostic factor for increased ventricular arrhythmia risk in DCM carriers.

Novel role of HAX-1 in ischemic injury protection involvement of heat shock protein 90

RATIONALE

Ischemic heart disease is characterized by contractile dysfunction and increased cardiomyocyte death, induced by necrosis and apoptosis. Increased cell survival after an ischemic insult is critical and depends on several cellular pathways, which have not been fully elucidated.

OBJECTIVE

To test the hypothesis that the anti-apoptotic hematopoietic lineage substrate-1-associated protein X-1 (HAX-1), recently identified as regulator of cardiac Ca cycling, also may ameliorate cellular injury with an ischemic insult.

METHODS AND RESULTS

We report that cardiac ischemia/reperfusion injury is associated with significant decreases in HAX-1 levels ex vivo and in vivo. Accordingly, overexpression of HAX-1 improved contractile recovery, coupled with reduced infarct size, plasma troponin I level, and apoptosis. The beneficial effects were associated with decreased endoplasmic reticulum (ER) stress response through specific inhibition of the inositol-requiring enzyme (IRE-1) signaling pathway, including its downstream effectors caspase-12 and the transcription factor C/EBP homologous protein. Conversely, HAX-1 heterozygous-deficient hearts exhibited increases in infarct size and IRE-1 activity. The inhibitory effects of HAX-1 were mediated by its binding to the N-terminal fragment of the heat shock protein 90 (Hsp90). Moreover, HAX-1 sequestered Hsp90 from IRE-1 to the phospholamban-sarcoplasmic/endoplasmic reticulum calcium ATPase complex. The HAX-1 regulation was further supported by loss of IRE-1 inhibition in presence of the Hsp90 inhibitor, 17-N-allylamino-17-demethoxygeldanamycin.

CONCLUSIONS

Cardiac ischemia-reperfusion injury is associated with decreases in HAX-1 levels. Consequently, overexpression of HAX-1 promotes cardiomyocyte survival, mediated by its interaction with Hsp90 and specific inhibition of IRE-1 signaling at the ER/sarcoplasmic reticulum.

Abstract P084: Cardiac-Specific Overexpression of Human Histidine-Rich Calcium Binding Protein (HRC-S96A) Genetic Variant Impairs Sarcoplasmic Ca 2+ Handling, Resulting in Arrhythmias

Disturbed Ca-homeostasis in the cardiomyocyte is a hallmark of human and experimental heart failure. The histidine-rich Ca binding protein (HRC), an intraluminal SR protein is an additional regulator of SR Ca2+ cycling. Previous biochemical studies have shown that HRC can bind to triadin (a component of ryanodine receptors complex) and SERCA2a, suggesting that HRC may be involved in the regulation of SR Ca2+ release and Ca2+ uptake. We recently identified a human HRC genetic variant (S96A), which appears to correlate with ventricular arrhythmias and sudden death in dilated cardiomyopathy (DCM) patients. To gain insight into the physiological and pathological significance of the S96A-HRC variant, we generated transgenic mice with cardiac-specific overexpression of human HRC wild-type (HRC-WT) and S96A mutant (HRC-S96A) in the HRC null (HRC KO) background. We obtained lines with similar expression levels of HRC-S96A and HRC-WT for further characterization. Overexpression of human HRC-S96A resulted in decreased fractional shortening by 22% (7.7 ± 0.5% in HRC-WTs vs. 6.0 ± 0.4% in HRC-S96A), rates of contraction by 20% (75 ± 5 µm/sec in HRC-WTs vs. 60 ± 4 µm/sec in HRC-S96A) and rates of relaxation by 20% (87 ± 6 µm/sec in HRC-WTs vs. 70 ± 4.5 µm/sec in HRC-S96A) compared with HRC-WT. Myocytes isolated from HRC-S96A mice had diminished Ca2+ transient amplitude and delayed half-decay time of the Ca2+ transient. In addition, the frequency of Ca2+ sparks was significantly higher although caffeine-induced SR Ca2+ release (SR load) was reduced in HRC-S96A cells. To determine the effect of S96A-HRC under stress conditions, 5 Hz field stimulation in the presence of 1 µmol/L Isoproterenol was applied: after-contractions were developed in 46% (16 of 35) of HRC-S96A cardiomyocytes, compared to 12% (4 of 33) of HRC-WTs mice. The findings of the present study demonstrate that the human HRC-S96A variant results in impaired myocytes Ca2+ handling, associated with depressed SR Ca2+-uptake rate and increased rate of SR Ca2+ leak, which may destabilize the cells, promoting aftercontractions under stress conditions. Thus, there appears to be a link between this genetic variant and ventricular arrhythmias in DCM human carriers.

Catecholaminergic-induced arrhythmias in failing cardiomyocytes associated with human HRCS96A variant overexpression

The histidine-rich calcium binding protein (HRC) Ser96Ala polymorphism was shown to correlate with ventricular arrhythmias and sudden death only in dilated cardiomyopathy patients but not in healthy human carriers. In the present study, we assessed the molecular and cellular mechanisms underlying human arrhythmias by adenoviral expression of the human wild-type (HRC(WT)) or mutant HRC (HRC(S96A)) in adult rat ventricular cardiomyocytes. Total HRC protein was increased by ∼50% in both HRC(WT)- and HRC(S96A)-infected cells. The HRC(S96A) mutant exacerbated the inhibitory effects of HRC(WT) on the amplitude of Ca(2+) transients, prolongation of Ca(2+) decay time, and caffeine-induced sarcoplasmic reticulum Ca(2+) release. Consistent with these findings, HRC(S96A) reduced maximal sarcoplasmic reticulum calcium uptake rate to a higher extent than HRC(WT). Furthermore, the frequency of spontaneous Ca(2+) sparks, which was reduced by HRC(WT), was increased by mutant HRC(S96A) under resting conditions although there were no spontaneous Ca(2+) waves under stress conditions. However, expression of the HRC(S96A) genetic variant in cardiomyocytes from a rat model of postmyocardial infarction heart failure induced dramatic disturbances of rhythmic Ca(2+) transients. These findings indicate that the HRC Ser96Ala variant increases the propensity of arrhythmogenic Ca(2+) waves in the stressed failing heart, suggesting a link between this genetic variant and life-threatening ventricular arrhythmias in human carriers.

Perceptions of insulin therapy amongst Asian patients with diabetes in Singapore

AIMS

The objective of this study was to determine the prevalence of insulin refusal amongst Singaporean patients with Type 2 diabetes mellitus, to compare perceptions regarding insulin therapy use between patients who were willing to use insulin and those who were not and to identify demographic factors that might predict insulin refusal.

METHODS

A cross-sectional interviewer-administered survey incorporating demographic variables and 17 perceptions regarding insulin use (14 negative and three positive) was conducted among a sample of 265 patients attending a public primary healthcare centre.

RESULTS

Seven of every 10 patients expressed unwillingness to use insulin therapy (70.6%). The greatest differences in perceptions between patients willing to use insulin therapy and those who were not included fear of not being able to inject insulin correctly (47.4 vs. 70.6%), fear of pain (44.9 vs. 65.8%), belief that insulin therapy would make it difficult to fulfil responsibilities at work and home (46.2 vs. 66.8%) and belief that insulin therapy improved diabetes control (82.1 vs. 58.3%). A tertiary level of education was associated with willingness to use insulin (odds ratio 3.3, confidence interval 1.8-6.1), and significant differences in perceptions were present in patients with different educational levels.

CONCLUSIONS

Insulin refusal is an important problem amongst our patients with Type 2 diabetes mellitus. Findings of this study suggest that interventions aimed at increasing insulin therapy use should focus on injection-related concerns, perceived lifestyle adaptations and correction of misconceptions. Different interventions may also be required for patients of different educational groups.

SERCA2a superinhibition by human phospholamban triggers electrical and structural remodeling in mouse hearts

Phospholamban (PLN), the reversible inhibitor of the sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA2a), is a key regulator of myocyte Ca(2+) cycling with a significant role in heart failure. We previously showed that the single amino acid difference between human and mouse PLN results in increased inhibition of Ca(2+) cycling and cardiac remodeling and attenuated stress responses in transgenic mice expressing the human PLN (hPLN) in the null background. Here we dissect the molecular and electrophysiological processes triggered by the superinhibitory hPLN in the mouse. Using a multidisciplinary approach, we performed global gene expression analysis, electrophysiology, and mathematical simulations on hPLN mice. We identified significant changes in a series of Na(+) and K(+) homeostasis genes/proteins (including Kcnd2, Scn9a, Slc8a1) and ionic conductance (including L-type Ca(2+) current, Na(+)/Ca(2+) exchanger, transient outward K(+) current). Simulation analysis suggests that this electrical remodeling has a critical role in rescuing cardiac function by improving sarcoplasmic reticulum Ca(2+) load and overall Ca(2+) dynamics. Furthermore, multiple structural and transcription factor gene expression changes indicate an ongoing structural remodeling process, favoring hypertrophy and myogenesis while suppressing apoptosis and progression to heart failure. Our findings expand current understanding of the hPLN function and provide additional insights into the downstream implications of SERCA2a superinhibition in the mammalian heart.

Presence of extensive intraductal component in patients undergoing breast conservative surgery predicts presence of residual disease in subsequent completion mastectomy

BACKGROUND

Local recurrence remains a serious problem among patients undergoing breast conservative surgery. This study aimed at identifying risk factors for residual disease after breast conservative surgery.

METHODS

This retrospective study was based on patients with invasive breast cancer who have received breast conservative surgery and subsequent completion mastectomy. All patients had a clear resection margin in the initial operation. We analyzed the association between the presence of residual disease during completion mastectomy and the following risk factors: T staging, young age, and presence of extensive intraductal component (EIC), a close margin, lymphovascular permeation (LVP), positivity of estrogen receptor, progesterone receptor, and c-erbB-2.

RESULTS

Residual disease was encountered in 21 (45.7%) of 46 patients; EIC was present in 28 patients (60.9%), of whom 17 had residual disease. Presence of EIC during breast conservation surgery was associated with a higher risk of residual disease during completion mastectomy (P = 0.011). Other variables were not statistically significant risk factors for presence of residual disease. No local recurrence was recorded in our cohort, and the disease-free survival and overall survival after completion mastectomy were similar for patients who had residual disease and those who had not.

CONCLUSIONS

The presence of EIC is a significant risk factor for residual disease in patients after breast conservative surgery. Our findings may suggest the indicated value of completion mastectomy in patients with EIC during initial breast conservative surgery to decrease the risk of subsequent local failure.

Living donor liver transplantation for hepatitis C related hepatocellular carcinoma in a haemophilia A patient

We report the first case of unrelated living liver transplantation for hepatitis C related hepatocellular carcinoma (HCC) in a Chinese patient with haemophilia A. The development of cirrhosis and HCC was insidious in this patient, who has previously failed interferon treatment despite low viral load and genotype 6a. With factor VIII and novoseven support, there were no operative complications and there was no need for blood transfusion. Postoperative pegulated interferon treatment resulted in viral clearance with no increased cellular rejection. The use of living donors represent a potential life saving therapeutic options for hepatitis C virus related complications in haemophiliac, especially in countries of organ shortage. Careful patient and donor choice, meticulous surgical expertise and proper counselling, however, are prudent requirements.

Characterising atherothrombosis in Hong Kong: results of the Hong Kong data from a global atherothrombosis epidemiological survey

OBJECTIVES

To describe the characteristics of patients in Hong Kong with or at risk of atherothrombosis, to determine the proportion of symptomatic patients with more than one vascular bed affected, and to assess the relationship between ankle brachial index and disease severity.

DESIGN

Local participation in an international prevalence study.

SETTING

Five centres in Hong Kong.

PARTICIPANTS

A total of 210 subjects were recruited (105 women and 105 men). Patients were divided into the symptomatic group (with current or previous atherothrombotic symptoms, n=101) and at-risk group (with no current or previous symptoms, but aged over 55 years with at least two specified risk factors, n=109).

MAIN OUTCOME MEASURES

Patient characteristics were described, including the number of arterial beds affected, ankle brachial index, presence of risk factors, and medications taken.

RESULTS

Of the symptomatic patients, 30% had more than one arterial bed involved. A total of 55.4% of the symptomatic group and 18.4% of the at-risk group had abnormal ankle brachial index values. Lower ankle brachial indices were associated with a greater number of affected arterial beds. Diabetes mellitus and hypertension were the most prevalent risk factors in the at-risk group. Symptomatic patients were commonly treated with antihypertensive and antiplatelet agents, whereas at-risk patients were mostly treated with antihypertensive and antidiabetic agents. Only 20% of at-risk patients were taking antiplatelet agents.

CONCLUSIONS

Ankle brachial index is a useful tool for predicting those at risk of atherothrombosis. This simple measurement can be used as part of the screening process in the general practice. The role of antiplatelet agents in primary prevention of atherothrombotic events in at-risk patients deserves further attention.

Sentinel lymph node technique for breast cancer: radiation safety issues

The radiation safety issues in the application of radioguided sentinel lymph node (SLN) biopsy are discussed, particularly the effective dose (ED) for patients undergoing lymphoscintigraphy by taking into account both the internal emission and the external transmission dose. The quantitative result can be compared with other common radiological examinations. Whole body and finger doses of surgical and pathology staff were determined by direct measurement using high-sensitivity thermoluminescent dosimeters (TLDs) and compared with the annual dose limits recommended by the International Commission on Radiological Protection (ICRP). These dosimetric observations for personnel also provide reference information to implement guidelines for the safe handling, storage, and transport of radioactive specimens at all stages of the radioguided surgery effort in order to maintain good work practices while dealing with unsealed radioactive substances.

Red blood cell alloantibodies and liver transplantation in Chinese patients

BACKGROUND

Red blood cell (RBC) alloantibodies are present in up to 14% of white recipients of liver transplants and can cause severe delayed hemolysis.

METHODS

A retrospective survey showed 17 cases (8.8%) of RBC alloantibodies in 192 consecutive Chinese recipients of liver transplants compared with a background hospital incidence of 3.7%.

RESULTS

The spectrum of RBC alloantibodies in Chinese patients was different than in white patients, with no anti-D or anti-K antibodies but a significant incidence of anti-Mi (29%) antibodies. There was a significantly increased incidence of transfusions in RBC alloantibody positive cases. Delayed hemolysis also resulted in higher day-7 bilirubin levels. A total of 7 to 86 antigen-positive units were issued in five RBC alloantibody cases, including three early deaths. Seven cases in the RBC alloantibody negative group, but none in the positive group, were salvaged by regraft.

CONCLUSIONS

Blood banks servicing transplant centers should be aware of ethnic patterns in RBC alloantibodies. Delayed hemolysis may jeopardize patient survival as the result of difficult postoperative stabilization, especially in cases requiring massive transfusion.

Red blood cell alloantibodies and liver transplantation in Chinese patients

Red blood cell (RBC) alloantibodies are present in up to 14% of white recipients of liver transplants and can cause severe delayed hemolysis. A retrospective survey showed 17 cases (8.8%) of RBC alloantibodies in 192 consecutive Chinese recipients of liver transplants, compared with a 3.7% background hospital incidence. The spectrum of RBC alloantibodies was different from that in white recipients, with no anti-D or anti-K antibodies but with a significant incidence of anti-Mi (29%) antibodies. There was significantly increased transfusion in RBC alloantibody positive cases. Delayed hemolysis also resulted in higher day-7 bilirubin levels. A total of 7 to 86 antigen-positive units were issued in five RBC alloantibody cases, including three early deaths. Seven cases in the RBC alloantibody negative group, but none in the positive group, were salvaged by regraft. Blood banks servicing transplant centers should be aware of ethnic patterns in RBC alloantibodies. Delayed hemolysis may jeopardize patient survival as a result of difficult postoperative stabilization, especially in cases requiring massive transfusion.

Synthesis and studies of 1,4,5,8,9,12,13,16-octamethoxytetraphenylene

[structure: see text] The synthesis of 1,4,5,8,9,12,13,16-octamethoxytetraphenylene (6) is accomplished in five steps from 3,6-dimethoxy-2-nitroaniline (8). Its inclusion property and the electrochemical data of the corresponding tetraquinone 7 are presented.

Vitamin B12 deficiency--need for a new guideline

OBJECTIVES

Many patients with vitamin B12 deficiency do not have anemia or macrocytosis, but the prevalence of B12 deficiency in patients without macrocytosis is not known.

METHODS

We investigated the prevalence of B12 deficiency among patients with normocytosis and microcytosis and recommended a screening strategy. All patients (n = 3714) with serum B12 measured at the Prince of Wales Hospital in 1996 were reviewed. The prevalence of serum B12 less than 140 pmol/L was determined for the following patient subgroups: younger than 70 y, older than 70 y, anemic, non-anemic, macrocytic, normocytic, microcytic, documented iron deficiency, and documented thalassemia.

RESULTS

The prevalence of B12 deficiency (<140 pmol/L) ranged from 4.8% to 9.8% among the different subgroups.

CONCLUSIONS

Whatever screening criteria were used, a significant number of B12-deficient patients will be missed. Therefore, there may be a case for universal vitamin B12 screening.

Rhodizonate and croconate dianions as divergent hydrogen-bond acceptors in the self-assembly of supramolecular structures

The C5O5(2-) and relatively unstable C6O6(2-) dianions, each serving as a hub for binding with a set of convergent NH donor groups of four phenylurea molecules, have been generated in situ and stabilized in nearly isostructural hydrogen-bonded host lattices.