Cardiac Remodeling in Subclinical Hypertrophic Cardiomyopathy: The VANISH Randomized Clinical Trial

Importance

Valsartan has shown promise in attenuating cardiac remodeling in patients with early-stage sarcomeric hypertrophic cardiomyopathy (HCM). Genetic testing can identify individuals at risk of HCM in a subclinical stage who could benefit from therapies that prevent disease progression.

Objective

To explore the potential for valsartan to modify disease development, and to characterize short-term phenotypic progression in subclinical HCM.

Design, Setting, and Participants

The multicenter, double-blind, placebo-controlled Valsartan for Attenuating Disease Evolution in Early Sarcomeric Hypertrophic Cardiomyopathy (VANISH) randomized clinical trial was conducted from April 2014 to July 2019 at 17 sites in 4 countries (Brazil, Canada, Denmark, and the US), with 2 years of follow-up. The prespecified exploratory VANISH cohort studied here included sarcomere variant carriers with subclinical HCM and early phenotypic manifestations (reduced E' velocity, electrocardiographic abnormalities, or an increased left ventricular [LV] wall thickness [LVWT] to cavity diameter ratio) but no LV hypertrophy (LVH). Data were analyzed between March and December 2022.

Interventions

Treatment with placebo or valsartan (80 mg/d for children weighing <35 kg, 160 mg/d for children weighing ≥35 kg, or 320 mg/d for adults aged ≥18 years).

Main Outcomes and Measures

The primary outcome was a composite z score incorporating changes in 9 parameters of cardiac remodeling (LV cavity volume, LVWT, and LV mass; left atrial [LA] volume; E' velocity and S' velocity; and serum troponin and N-terminal prohormone of brain natriuretic peptide levels).

Results

This study included 34 participants, with a mean (SD) age of 16 (5) years (all were White). A total of 18 participants (8 female [44%] and 10 male [56%]) were randomized to valsartan and 16 (9 female [56%] and 7 male [44%]) were randomized to placebo. No statistically significant effects of valsartan on cardiac remodeling were detected (mean change in composite z score compared with placebo: -0.01 [95% CI, -0.29 to 0.26]; P = .92). Overall, 2-year phenotypic progression was modest, with only a mild increase in LA volume detected (increased by 3.5 mL/m2 [95% CI, 1.4-6.0 mL/m2]; P = .002). Nine participants (26%) had increased LVWT, including 6 (18%) who developed clinically overt HCM. Baseline LA volume index (LAVI; 35 vs 28 mL/m2; P = .01) and average interventricular septum thickness (8.5 vs 7.0 mm; P = .009) were higher in participants who developed HCM.

Conclusions and Relevance

In this exploratory cohort, valsartan was not proven to slow progression of subclinical HCM. Minimal changes in markers of cardiac remodeling were observed, although nearly one-fifth of patients developed clinically overt HCM. Transition to disease was associated with greater baseline interventricular septum thickness and LAVI. These findings highlight the importance of following sarcomere variant carriers longitudinally and the critical need to improve understanding of factors that drive disease penetrance and progression.

Trial Registration

ClinicalTrials.gov Identifier: NCT01912534.

The HCM - Linked Mutation Arg92Leu in TNNT2 Allosterically Alters the cTnC - cTnI Interface and Disrupts the PKA-mediated Regulation of Myofilament Relaxation

Background

Impaired left ventricular relaxation, high filling pressures, and dysregulation of Ca 2+ homeostasis are common findings contributing to diastolic dysfunction in hypertrophic cardiomyopathy (HCM). Studies have shown that impaired relaxation is an early observation in the sarcomere-gene-positive preclinical HCM cohort which suggests potential involvement of myofilament regulators of relaxation. Yet, a molecular level understanding of mechanism(s) at the level of the myofilament is lacking. We hypothesized that mutation-specific, allosterically mediated, changes to the cardiac troponin C-cardiac troponin I (cTnC-cTnI) interface can account for the development of early-onset diastolic dysfunction via decreased PKA accessibility to cTnI.

Methods

HCM mutations R92L-cTnT (Arg92Leu) and Δ160E-cTnT (Glu160 deletion) were studied in vivo , in vitro, and in silico via 2D echocardiography, western blotting, ex vivo hemodynamics, stopped-flow kinetics, time resolved fluorescence resonance energy transfer (TR-FRET), and molecular dynamics simulations.

Results

The HCM-causative mutations R92L-cTnT and Δ160E-cTnT result in different time-of-onset of diastolic dysfunction. R92L-cTnT demonstrated early-onset diastolic dysfunction accompanied by a localized decrease in phosphorylation of cTnI. Constitutive phosphorylation of cTnI (cTnI-D 23 D 24 ) was sufficient to recover diastolic function to Non-Tg levels only for R92L-cTnT. Mutation-specific changes in Ca 2+ dissociation rates associated with R92L-cTnT reconstituted with cTnI-D 23 D 24 led us to investigate potential involvement of structural changes in the cTnC-cTnI interface as an explanation for these observations. We probed the interface via TR-FRET revealing a repositioning of the N-terminus of cTnI, closer to cTnC, and concomitant decreases in distance distributions at sites flanking the PKA consensus sequence. Implementing TR-FRET distances as constraints into our atomistic model identified additional electrostatic interactions at the consensus sequence.

Conclusion

These data indicate that the early diastolic dysfunction observed in a subset of HCM is likely attributable to structural changes at the cTnC-cTnI interface that impair accessibility of PKA thereby blunting β-adrenergic responsiveness and identifying a potential molecular target for therapeutic intervention.

Alteration in tyrosine phosphorylation of cardiac proteome and EGFR pathway contribute to hypertrophic cardiomyopathy

Alterations of serine/threonine phosphorylation of the cardiac proteome are a hallmark of heart failure. However, the contribution of tyrosine phosphorylation (pTyr) to the pathogenesis of cardiac hypertrophy remains unclear. We use global mapping to discover and quantify site-specific pTyr in two cardiac hypertrophic mouse models, i.e., cardiac overexpression of ErbB2 (TgErbB2) and α myosin heavy chain R403Q (R403Q-αMyHC Tg), compared to control hearts. From this, there are significant phosphoproteomic alterations in TgErbB2 mice in right ventricular cardiomyopathy, hypertrophic cardiomyopathy (HCM), and dilated cardiomyopathy (DCM) pathways. On the other hand, R403Q-αMyHC Tg mice indicated that the EGFR1 pathway is central for cardiac hypertrophy, along with angiopoietin, ErbB, growth hormone, and chemokine signaling pathways activation. Surprisingly, most myofilament proteins have downregulation of pTyr rather than upregulation. Kinase-substrate enrichment analysis (KSEA) shows a marked downregulation of MAPK pathway activity downstream of k-Ras in TgErbB2 mice and activation of EGFR, focal adhesion, PDGFR, and actin cytoskeleton pathways. In vivo ErbB2 inhibition by AG-825 decreases cardiomyocyte disarray. Serine/threonine and tyrosine phosphoproteome confirm the above-described pathways and the effectiveness of AG-825 Treatment. Thus, altered pTyr may play a regulatory role in cardiac hypertrophic models.

Relationship-based practice and digital technology in child and family social work: Learning from practice during the COVID-19 pandemic

Vital services provided by social workers to children in care or on the edge of care were largely delivered "online" during the COVID-19 pandemic. This paper explores the potential impact of these changes on vulnerable children and their families. Relationship-based practice is integral to social work and the shift to digital communication during the COVID-19 pandemic has led to accelerated practice changes and implications for relationship building both with and between service users. Going forward, social workers and other professionals are likely to move to an increasingly hybrid model of communication, combining both digital and face-to-face methods. This article identifies the impact of digital communication on relationships in professional practice, drawing on three studies of digital communication in the UK carried out at the University of East Anglia. The first considered how child protection social workers responded to the challenges of COVID-19, the second looked at how children in care were keeping in touch with their birth families and the third focused on the approaches being taken to moving children from foster care to adoptive families. Five themes related to relationships were identified across all three studies: the significance of the age and developmental stage of the child; the frequency of contact and communication; digital literacy/exclusion; the impact of the lack of sensory experience; and the importance of the relationship history. The article concludes with implications for utilising digital methods in building and maintaining relationships in practice and highlights the need to consider both the inner and outer worlds of those involved.

Valsartan in early-stage hypertrophic cardiomyopathy: a randomized phase 2 trial

Hypertrophic cardiomyopathy (HCM) is often caused by pathogenic variants in sarcomeric genes and characterized by left ventricular (LV) hypertrophy, myocardial fibrosis and increased risk of heart failure and arrhythmias. There are no existing therapies to modify disease progression. In this study, we conducted a multi-center, double-blind, placebo-controlled phase 2 clinical trial to assess the safety and efficacy of the angiotensin II receptor blocker valsartan in attenuating disease evolution in early HCM. In total, 178 participants with early-stage sarcomeric HCM were randomized (1:1) to receive valsartan (320 mg daily in adults; 80-160 mg daily in children) or placebo for 2 years ( NCT01912534 ). Standardized changes from baseline to year 2 in LV wall thickness, mass and volumes; left atrial volume; tissue Doppler diastolic and systolic velocities; and serum levels of high-sensitivity troponin T and N-terminal pro-B-type natriuretic protein were integrated into a single composite z-score as the primary outcome. Valsartan (n = 88) improved cardiac structure and function compared to placebo (n = 90), as reflected by an increase in the composite z-score (between-group difference +0.231, 95% confidence interval (+0.098, +0.364); P = 0.001), which met the primary endpoint of the study. Treatment was well-tolerated. These results indicate a key opportunity to attenuate disease progression in early-stage sarcomeric HCM with an accessible and safe medication.

Evaluating documentation of social history in paediatric medical notes at a regional paediatric centre - a quality improvement initiative

BACKGROUND

A child's home and family environment plays a vital role in neuro-cognitive and emotional development. Assessment of a child's home environment and social circumstances is an crucial part of holistic Paediatric assessment.

AIMS

Our aim is to achieve full compliance with comprehensive documentation of biopsychosocial history, for all children medically admitted to the children's inpatient unit in University Hospital Limerick.

METHODS

We performed a retrospective chart review to audit documentation within our department. This was followed by teaching interventions and a survey on knowledge, attitudes and behaviour of paediatric non-consultant hospital doctors (NCHDs) towards the social history. We performed two subsequent re-audits to assess response to our interventions, and provided educational sessions to seek improvement in quality of care.

RESULTS

Results showed a significant improvement in quality of documentation following interventions, demonstrated by a net increase of 53% in levels of documentation of some social history on first re-audit. Though this was not maintained at an optimum level throughout the course of the year with compliance reduced from 95% to 82.5% on second re-audit, there was nonetheless a sustained improvement from our baseline. Our qualitative survey suggested further initiatives and educational tools that may be helpful in supporting the ongoing optimisation of the quality of documentation of social history in our paediatric department.

CONCLUSION

We hope this quality improvement initiative will ultimately lead to sustained improvements in the quality of patient-centred care, and early identification and intervention for children at risk in our community.

Physical illnesses associated with childhood homelessness - a literature review

Background and aims

Childhood homelessness is a growing concern in Ireland creating a Pediatric subpopulation at increased risk of physical illnesses, many with life-long consequences. Our aim was to identify and categorize the physical morbidities prevalent in homeless children.

Methods

A review of the English-language literature on physical morbidities affecting homeless children (defined as &lt; 18 years of age), published from 1999-2019 was conducted. A total of 1194 articles were identified, 33 articles of which met our inclusion criteria.

Results

Respiratory issues were the most commonly cited illnesses affecting homeless children; including asthma, upper respiratory tract infections, and chronic cough. Homeless children were described as being at increased risk of contracting infectious diseases, many studies placing emphasis on STI and HIV/AIDS transmission. Dermatologic concerns comprised of scabies and head lice infestation, dermatitis, and abrasions. Malnutrition manifested as a range of physical morbidities; including childhood obesity, iron deficiency anemia, and stunted growth. Studies found a higher prevalence of poor dental and ocular health in this population as well. Many articles also commented on the risk factors predisposing homeless children to these physical health concerns, which can broadly be categorized as limited access to health care, poor living conditions, and lack of education.

Conclusions

This literature review summarized the physical illnesses prevalent among homeless children and the contributing factors leading to them. Gaps in the literature were also identified, and included a dearth of studies focusing on younger children compared to adolescents. We believe that the current issue of child homelessness is socially and medically unacceptable and that homelessness occurring today will be one of the scandals of the next generation. Further research into prevention and intervention programs for this vulnerable population is urgently needed.

Key messages

This literature review shows that homeless children are at an increased risk of several physical morbidities and identified the common themes among them. Based on this literature review, it is recommended that more research be done into developing appropriate intervention and prevention strategies to help this vulnerable population.

Baseline Characteristics of the VANISH Cohort

BACKGROUND

The VANISH trial (Valsartan for Attenuating Disease Evolution in Early Sarcomeric Hypertrophic Cardiomyopathy) targeted young sarcomeric gene mutation carriers with early-stage hypertrophic cardiomyopathy (HCM) to test whether valsartan can modify disease progression. We describe the baseline characteristics of the VANISH cohort and compare to previous trials evaluating angiotensin receptor blockers.

METHODS

Applying a randomized, double-blinded, placebo-controlled design, 178 participants with nonobstructive HCM (age, 23.3±10.1 years; 61% men) were randomized in the primary cohort and 34 (age, 16.5±4.9 years; 50% men) in the exploratory cohort of sarcomeric mutation carriers without left ventricular hypertrophy.

RESULTS

In the primary cohort, maximal left ventricular wall thickness was 17±4 mm for adults and Z score 7.0±4.5 for children. Nineteen percent had late gadolinium enhancement on cardiac magnetic resonance. Mean peak oxygen consumption was 33 mL/kg per minute, and 92% of participants were New York Heart Association functional class I. New York Heart Association class II was associated with older age, MYH7 variants, and more prominent imaging abnormalities. Six previous trials of angiotensin receptor blockers in HCM enrolled a median of 24 patients (range, 19-133) with mean age of 51.2 years; 42% of patients were in New York Heart Association class ≥II, and sarcomeric mutations were not required.

CONCLUSIONS

The VANISH cohort is much larger, younger, less heterogeneous, and has less advanced disease than prior angiotensin receptor blocker trials in HCM. Participants had relatively normal functional capacity and mild HCM features. New York Heart Association functional class II symptoms were associated with older age, more prominent imaging abnormalities, and MYH7 variants, suggesting both phenotype and genotype contribute to disease manifestations.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov. Unique identifier: NCT01912534.

Prevalence and Progression of Late Gadolinium Enhancement in Children and Adolescents With Hypertrophic Cardiomyopathy

BACKGROUND

Late gadolinium enhancement (LGE) on cardiac magnetic resonance imaging (CMR) is believed to represent dense replacement fibrosis. It is seen in ≈60% of adult patients with hypertrophic cardiomyopathy (HCM). However, the prevalence of LGE in children and adolescents with HCM is not well established. In addition, longitudinal studies describing the development and evolution of LGE in pediatric HCM are lacking. This study assesses the prevalence, progression, and clinical correlations of LGE in children and adolescents with, or genetically predisposed to, HCM.

METHODS

CMR scans from 195 patients ≤21 years of age were analyzed in an observational, retrospective study, including 155 patients with overt HCM and 40 sarcomere mutation carriers without left ventricular (LV) hypertrophy. The extent of LGE was quantified by measuring regions with signal intensity >6 SD above nulled remote myocardium.

RESULTS

Patients were 14.3±4.5 years of age at baseline and 68% were male. LGE was present in 70 (46%) patients with overt HCM (median extent, 3.3%; interquartile range, 0.8-7.1%), but absent in mutation carriers without LV hypertrophy. Thirty-one patients had >1 CMR (median interval between studies, 2.4 years; interquartile range, 1.5-3.2 years). LGE was detected in 13 patients (42%) at baseline and in 16 patients (52%) at follow-up CMR. The median extent of LGE increased by 2.4 g/y (range, 0-13.2 g/y) from 2.9% (interquartile range, 0.8-3.2%) of LV mass to 4.3% (interquartile range, 2.9-6.8%) ( P=0.02). In addition to LGE, LV mass and left atrial volume, indexed to body surface area, and z score for LV mass, as well, increased significantly from first to most recent CMR.

CONCLUSIONS

LGE was present in 46% of children and adolescents with overt HCM, in contrast to ≈60% typically reported in adult HCM. In the subset of patients with serial imaging, statistically significant increases in LGE, LV mass, and left atrial size were detected over 2.5 years, indicating disease progression over time. Further prospective studies are required to confirm these findings and to better understand the clinical implications of LGE in pediatric HCM.

The Burden of Early Phenotypes and the Influence of Wall Thickness in Hypertrophic Cardiomyopathy Mutation Carriers: Findings From the HCMNet Study

Importance

Sarcomere mutations and left ventricular (LV) hypertrophy (LVH) are cardinal features of hypertrophic cardiomyopathy (HCM). However, little is known about the full spectrum of phenotypic manifestations or how LVH influences disease expression.

Objectives

(1) To characterize and assess phenotypic burden in sarcomere mutation carriers (genotype positive [G+]) and (2) to investigate the correlation between LV wall thickness (LVWT) and other disease features in mutation carriers.

Design, Setting, and Participants

This investigation was a cross-sectional, multicenter observational study in the setting of the HCMNet network of HCM clinical centers. Mutation carriers with LVH (G+/LVH+), mutation carriers without LVH (G+/LVH-), and healthy related control individuals (G-/LVH-) were enrolled through HCMNet sites. A total of 193 participants were enrolled and underwent study procedures. Participants were enrolled between April 9, 2010, and January 30, 2012. Study analysis was performed between June 2015 and May 2016.

Exposures

The primary stratifying variables were the presence of a sarcomere mutation and measures of LVWT.

Main Outcomes and Measures

Variables from standardized exercise testing, echocardiography, cardiac magnetic resonance imaging, serum biomarker measurement, and electrocardiography were compared across study cohorts.

Results

Analyses were performed in 178 participants, including 81 G+/LVH+ (mean [SD] age at baseline, 27 [14] years), 55 G+/LVH- (20 [10] years), and 42 G-/LVH- (18 [8] years). All mutation carriers had smaller LV cavity, higher ratio of LVWT to diastolic diameter, and higher echocardiographic LV ejection fraction than controls. A phenotypic burden score was evaluated as the cumulative number of 7 traits (changes on electrocardiography; decreased LV systolic, diastolic diameter, or septal E' velocity; higher ratio of LVWT to diastolic diameter; serum troponin level; and natriuretic peptide level) in each individual. The mean (SE) phenotypic burden was 4.9 (0.2) phenotypes per individual in G+/LVH+, 2.4 (0.2) in G+/LVH-, and 1.3 (0.2) in controls (P < .001). Classification and regression tree analysis identified an LV end-diastolic dimension z score less than -1.85 or the combination of an LV end-diastolic dimension z score of -1.85 or higher and a septal E' velocity z score less than -0.52 as having 74% accuracy in discriminating G+/LVH- participants from controls. In mutation carriers, clinical variables demonstrated a continuous correlation with LVWT, generally without a clear cutoff signifying pathologic transition.

Conclusions and Relevance

G+/LVH- individuals demonstrated altered cardiac dimensions and function and a higher burden of early phenotypes than healthy G- controls. Two methods discriminated phenotypic subgroups, namely, a sum across 7 traits and a regression tree-based rule that identifies constellations of distinguishing factors. Greater LVWT is associated with more prominent cardiac abnormalities in a continuous, although not always linear, manner. A single value of LVWT could not dichotomize the presence or absence of disease.

Estimated Weight of Paediatric Patients versus Measured Weight – A Prospective Comparison

Introduction Weight measurement is fundamental in the management of paediatric patients. Many methods have been described for estimating a patient’s weight. The aim of this study was to assess the accuracy of the APLS 2017 estimated weight guidelines. Methods 100 patient charts were analysed in University Hospital Limerick’s Paediatric unit. Measured weights were recorded, and estimated weights were calculated using the APLS 2017 charts. Estimated and measured weight was compared using Bland Altman plots. Results Of 100 subjects, 53 (53%) were female and 47 (47%) male. Fifty subjects (50%) were Pre-School, 32 (32%) Primary School and 18 (18%) Secondary School. Estimated weight was a good predictor for measured weight, however weight was underestimated by between 2.34% and 16.39% of measured weight. Discussion The current APLS guidelines are reasonably accurate; but accuracy decreases with increasing age. Estimation cannot replace an accurate measurement, which is not always feasible in the acute setting.

Coming of Age in Ireland: the Twilight Zone!

Aim To describe the healthcare needs of adolescent patients inhabiting the ‘seventh age of childhood’ in our region with a view towards future workforce and infrastructure planning. Methods This is a retrospective descriptive study of patients aged between 14 and 16 years presenting to each of the six hospitals in our hospital group over a 10 year period (01.07.2006-1.07.2016) using electronic databases. Results There were 10,992 hospital admissions, 41,456 outpatient appointments and an average of 1,847 attendances per year at our Emergency Department in this age group. Seventeen percent (n=1,873) of patients were admitted to age appropriate wards. Only 11.3% (n=1,242) of our cohort were admitted under the care of a Paediatrician. Conclusion The Irish healthcare agenda needs to be advanced to ensure the optimal health for this valuable, yet vulnerable generation. Further investment will help shape the fledgling discipline of ‘adolescent health’ in Ireland.

Juvenile Idiopathic Arthritis Associated with Combined JP-HHT Syndrome: A Novel Phenotype Associated with a Novel Variant in SMAD4

Juvenile polyposis (JP) syndrome is characterized by multiple hamartomatous polyps of the gastrointestinal tract. Hereditary hemorrhagic telangiectasia (HHT) is a vascular dysplasia characterized by telangiectasia in the skin, mucous membranes, and arteriovenous malformations in other organs. Individuals with JP-HHT syndrome have variable features of both rare disorders, attributed to heterozygous mutations in the SMAD4 gene. Systemic juvenile idiopathic arthritis (JIA) is a severe, chronic disease marked by arthritis and systemic inflammation for which the cause remains unknown. JIA has never been described in association with SMAD4 -related disease. We describe a case of JP-HHT syndrome with a novel SMAD4 variant, c.1052A > T (p.D351V), in which the child also had JIA manifestation.

The Expressed Genome in Cardiovascular Diseases and Stroke: Refinement, Diagnosis, and Prediction: A Scientific Statement From the American Heart Association

There have been major advances in our knowledge of the contribution of DNA sequence variations to cardiovascular disease and stroke. However, the inner workings of the body reflect the complex interplay of factors beyond the DNA sequence, including epigenetic modifications, RNA transcripts, proteins, and metabolites, which together can be considered the "expressed genome." The emergence of high-throughput technologies, including epigenomics, transcriptomics, proteomics, and metabolomics, is now making it possible to address the contributions of the expressed genome to cardiovascular disorders. This statement describes how the expressed genome can currently and, in the future, potentially be used to diagnose diseases and to predict who will develop diseases such as coronary artery disease, stroke, heart failure, and arrhythmias.

Heart Failure-Related Hyperphosphorylation in the Cardiac Troponin I C Terminus Has Divergent Effects on Cardiac Function In Vivo

BACKGROUND

In human heart failure, Ser199 (equivalent to Ser200 in mouse) of cTnI (cardiac troponin I) is significantly hyperphosphorylated, and in vitro studies suggest that it enhances myofilament calcium sensitivity and alters calpain-mediated cTnI proteolysis. However, how its hyperphosphorylation affects cardiac function in vivo remains unknown.

METHODS AND RESULTS

To address the question, 2 transgenic mouse models were generated: a phospho-mimetic cTnIS200D and a phospho-silenced cTnIS200A, each driven by the cardiomyocyte-specific α-myosin heavy chain promoter. Cardiac structure assessed by echocardiography and histology was normal in both transgenic models compared with littermate controls (n=5). Baseline in vivo hemodynamics and isolated muscle studies showed that cTnIS200D significantly prolonged relaxation and lowered left ventricular peak filling rate, whereas ejection fraction and force development were normal (n=5). However, with increased heart rate or β-adrenergic stimulation, cTnIS200D mice had less enhanced ejection fraction or force development versus controls, whereas relaxation improved similarly to controls (n=5). By contrast, cTnIS200A was functionally normal both at baseline and under the physiological stresses. To test whether either mutation impacted cardiac response to ischemic stress, isolated hearts were subjected to ischemia/reperfusion. cTnIS200D were protected, recovering 88±8% of contractile function versus 35±15% in littermate controls and 28±8% in cTnIS200A (n=5). This was associated with less cTnI proteolysis in cTnIS200D hearts.

CONCLUSIONS

Hyperphosphorylation of this serine in cTnI C terminus impacts heart function by depressing diastolic function at baseline and limiting systolic reserve under physiological stresses. However, paradoxically, it preserves heart function after ischemia/reperfusion injury, potentially by decreasing proteolysis of cTnI.

Gene expression profiles predictive of cold-induced sweetening in potato

Cold storage (2-4 °C) used in potato production to suppress diseases and sprouting during storage can result in cold-induced sweetening (CIS), where reducing sugars accumulate in tuber tissue leading to undesirable browning, production of bitter flavors, and increased levels of acrylamide with frying. Potato exhibits genetic and environmental variation in resistance to CIS. The current study profiles gene expression in post-harvest tubers before cold storage using transcriptome sequencing and identifies genes whose expression is predictive for CIS. A distance matrix for potato clones based on glucose levels after cold storage was constructed and compared to distance matrices constructed using RNA-seq gene expression data. Congruence between glucose and gene expression distance matrices was tested for each gene. Correlation between glucose and gene expression was also tested. Seventy-three genes were found that had significant p values in the congruence and correlation tests. Twelve genes from the list of 73 genes also had a high correlation between glucose and gene expression as measured by Nanostring nCounter. The gene annotations indicated functions in protein degradation, nematode resistance, auxin transport, and gibberellin response. These 12 genes were used to build models for prediction of CIS using multiple linear regression. Nine linear models were constructed that used different combinations of the 12 genes. An F-box protein, cellulose synthase, and a putative Lax auxin transporter gene were most frequently used. The findings of this study demonstrate the utility of gene expression profiles in predictive diagnostics for severity of CIS.

Comprehensive Versus Targeted Genetic Testing in Children with Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a genetic disease of the sarcomere that can be found in both children and adults and is associated with many causative mutations. In children who are not the index case of HCM in their families, current recommendations call only for targeted genetic testing for familial mutations. However, clinical experience suggests that de novo mutations are possible, as are mutations inherited from apparently an unaffected parent. A chart review was conducted of all patients who received HCM genetic testing at Johns Hopkins from 2004 to 2013. In total, 239 patient charts were analyzed for personal and familial genetic findings. Eighty-one patients with sarcomere gene mutations were identified, of which 66 had a clinical diagnosis of HCM. Importantly, eight patients had >1 pathogenic or likely pathogenic mutation, including six patients who were diagnosed with HCM as children (18 or younger). In this analysis, when a sarcomere mutation is identified in a family, the likelihood of a child with HCM having >1 mutation is 25 % (6/24), compared to 4.8 % (2/42) for adults. The large number of children with multiple mutations suggests that broad panel rather than targeted genetic testing should be considered in HCM presenting during childhood even if the child is not the index case.

The Establishment of a Pilot Paediatric Obesity Clinic at the University Hospital, Limerick

This study describes the establishment of a pilot Paediatric Obesity Clinic (POC) in the University Hospital Limerick (UHL). Referrals were received from consultant paediatricians in the catchment areas of UHL for paediatric patients with high levels of excess adiposity. Fifteen patients and their families were invited to the POC in 2012. An initial medical assessment was conducted by 2 consultant paediatricians. Patients were also reviewed by a dietitian, a physiotherapist and physical activity experts from local Sports Partnerships. Twelve children and their families attended the POC (mean age = 8.08 years; Range = 3.6-13.6): 11/12 were overweight and 9/12 were obese. Abnormalities in blood work were detected as follows: 1/7 had elevated LDL-cholesterol; 2/8 had elevated triglyceride levels; 4/8 had elevated fasting insulin; 2/8 had elevated fasting glucose. With the current prevalence of obesity in paediatric populations, initiatives such as UHL's POC need to be established, funded and supported, to try to meet complex, multidisciplinary patient needs and to prevent future complex and expensive health complications.

Removal of Abnormal Myofilament O-GlcNAcylation Restores Ca2+ Sensitivity in Diabetic Cardiac Muscle

Contractile dysfunction and increased deposition of O-linked β-N-acetyl-d-glucosamine (O-GlcNAc) in cardiac proteins are a hallmark of the diabetic heart. However, whether and how this posttranslational alteration contributes to lower cardiac function remains unclear. Using a refined β-elimination/Michael addition with tandem mass tags (TMT)-labeling proteomic technique, we show that CpOGA, a bacterial analog of O-GlcNAcase (OGA) that cleaves O-GlcNAc in vivo, removes site-specific O-GlcNAcylation from myofilaments, restoring Ca(2+) sensitivity in streptozotocin (STZ) diabetic cardiac muscles. We report that in control rat hearts, O-GlcNAc and O-GlcNAc transferase (OGT) are mainly localized at the Z-line, whereas OGA is at the A-band. Conversely, in diabetic hearts O-GlcNAc levels are increased and OGT and OGA delocalized. Consistent changes were found in human diabetic hearts. STZ diabetic hearts display increased physical interactions of OGA with α-actin, tropomyosin, and myosin light chain 1, along with reduced OGT and increased OGA activities. Our study is the first to reveal that specific removal of O-GlcNAcylation restores myofilament response to Ca(2+) in diabetic hearts and that altered O-GlcNAcylation is due to the subcellular redistribution of OGT and OGA rather than to changes in their overall activities. Thus, preventing sarcomeric OGT and OGA displacement represents a new possible strategy for treating diabetic cardiomyopathy.

Transformative Impact of Proteomics on Cardiovascular Health and Disease: A Scientific Statement From the American Heart Association

The year 2014 marked the 20th anniversary of the coining of the term proteomics. The purpose of this scientific statement is to summarize advances over this period that have catalyzed our capacity to address the experimental, translational, and clinical implications of proteomics as applied to cardiovascular health and disease and to evaluate the current status of the field. Key successes that have energized the field are delineated; opportunities for proteomics to drive basic science research, facilitate clinical translation, and establish diagnostic and therapeutic healthcare algorithms are discussed; and challenges that remain to be solved before proteomic technologies can be readily translated from scientific discoveries to meaningful advances in cardiovascular care are addressed. Proteomics is the result of disruptive technologies, namely, mass spectrometry and database searching, which drove protein analysis from 1 protein at a time to protein mixture analyses that enable large-scale analysis of proteins and facilitate paradigm shifts in biological concepts that address important clinical questions. Over the past 20 years, the field of proteomics has matured, yet it is still developing rapidly. The scope of this statement will extend beyond the reaches of a typical review article and offer guidance on the use of next-generation proteomics for future scientific discovery in the basic research laboratory and clinical settings.

Abstract 268: Myofilament Tyrosine Phosphorylation by Src Kinase is upregulated in ErbB2 Transgenic Mice

Objectives: Tyrosine (Tyr) phosphorylation of the myofilament is an emerging, and potentially important, post-translational modification in cardiomyopathy. ErbB2, a Tyr receptor kinase, was overexpressed in transgenic mice (ErbB2-Tg) resulting in significant cardiac hypertrophy. We hypothesize that the development of cardiac hypertrophy in ErbB2-Tg is associated with increased myofilament Tyr phosphorylation and may implicate myofilament Tyr phosphorylation in cardiac hypertrophy.

Methods: Proteins were isolated from ErbB2-Tg and Ntg heart homogenates ( n =4 per group). Reduction/alkylation was followed by trypsinization. Resulting peptides were desalted in C 18 columns and lyophilized. Phosphorylated Tyr (p-Tyr) enrichment was performed on 20 mg of peptides using a p-Tyr Mouse mAb kit (Cell Signaling). Immuno-precipitated and desalted peptides were analyzed by LC-MS/MS (Orbitrap Elite, Thermo). Raw data were searched with Mascot 2.3. Label-free quantification with MS1 extracted ion chromatograms was performed using Skyline. Western blot analysis for total and phosphorylated Src kinase was performed per manufacturer’s protocol (Cell Signaling).

Results: We found a total of 286 p-Tyr modified peptides in ErbB2-Tg compared to 226 in control NTg mice. Over 70 p-Tyr sites on myofilament protein were up-regulated in ErbB2-Tg, including troponin I, myosin heavy chain, titin, α-tropomyosin, myosin-binding protein-C3, myosin regulatory light chain-2 and myosin light chain-1. We used PhosphoMotif Finder to search the potential responsible kinase. Most of the p-Tyr sites were consistent with Src kinase motifs. Furthermore, Western blot analysis showed that total, and phospho-Src (Y416) expression was increased in ErbB2-Tg mice.

Conclusion: We concluded that these novel p-Tyr sites on myofilament proteins are increased in ErbB2-Tg mice and correlate with up-regulated Src kinase activity. Thus increased tyrosine myofilament phosphorylation may be involved in the development of cardiac hypertrophy. Since ErbB2 is a therapeutic target of trastuzumab therapy this may also have translational implications to ameliorate off target effects of cancer treatment.

A novel phosphorylation site, Serine 199, in the C-terminus of cardiac troponin I regulates calcium sensitivity and susceptibility to calpain-induced proteolysis

Phosphorylation of cardiac troponin I (cTnI) by protein kinase C (PKC) is implicated in cardiac dysfunction. Recently, Serine 199 (Ser199) was identified as a target for PKC phosphorylation and increased Ser199 phosphorylation occurs in end-stage failing compared with non-failing human myocardium. The functional consequences of cTnI-Ser199 phosphorylation in the heart are unknown. Therefore, we investigated the impact of phosphorylation of cTnI-Ser199 on myofilament function in human cardiac tissue and the susceptibility of cTnI to proteolysis. cTnI-Ser199 was replaced by aspartic acid (199D) or alanine (199A) to mimic phosphorylation and dephosphorylation, respectively, with recombinant wild-type (Wt) cTn as a negative control. Force development was measured at various [Ca(2+)] and at sarcomere lengths of 1.8 and 2.2 μm in demembranated cardiomyocytes in which endogenous cTn complex was exchanged with the recombinant human cTn complexes. In idiopathic dilated cardiomyopathy samples, myofilament Ca(2+)-sensitivity (pCa50) at 2.2 μm was significantly higher in 199D (pCa50 = 5.79 ± 0.01) compared to 199A (pCa50 = 5.65 ± 0.01) and Wt (pCa50 = 5.66 ± 0.02) at ~63% cTn exchange. Myofilament Ca(2+)-sensitivity was significantly higher even with only 5.9 ± 2.5% 199D exchange compared to 199A, and saturated at 12.3 ± 2.6% 199D exchange. Ser199 pseudo-phosphorylation decreased cTnI binding to both actin and actin-tropomyosin. Moreover, altered susceptibility of cTnI to proteolysis by calpain I was found when Ser199 was pseudo-phosphorylated. Our data demonstrate that low levels of cTnI-Ser199 pseudo-phosphorylation (~6%) increase myofilament Ca(2+)-sensitivity in human cardiomyocytes, most likely by decreasing the binding affinity of cTnI for actin-tropomyosin. In addition, cTnI-Ser199 pseudo-phosphorylation or mutation regulates calpain I mediated proteolysis of cTnI.

Cardiac troponin I Pro82Ser variant induces diastolic dysfunction, blunts β-adrenergic response, and impairs myofilament cooperativity

Troponin I (TnI) variant Pro82Ser (cTnIP82S) was initially considered a disease-causing mutation; however, later studies suggested the contrary. We tested the hypothesis of whether a causal link exists between cTnIP82S and cardiac structural and functional remodeling, such as during aging or chronic pressure overload. A cardiac-specific transgenic (Tg) mouse model of cTnIP82S was created to test this hypothesis. During aging, Tg cTnIP82S displayed diastolic dysfunction, characterized by longer isovolumetric relaxation time, and impaired ejection and relaxation time. In young, Tg mice in vivo pressure-volume loops and intact trabecular preparations revealed normal cardiac contractility at baseline. However, upon β-adrenergic stimulation, a blunted contractile reserve and no hastening in left ventricle relaxation were evident in vivo, whereas, in isolated muscles, Ca(2+) transient amplitude isoproterenol dose-response was blunted. In addition, when exposed to chronic pressure overload, Tg mice show exacerbated hypertrophy and decreased contractility compared with age-matched non-Tg littermates. At the molecular level, this mutation significantly impairs myofilament cooperative activation. Importantly, this occurs in the absence of alterations in TnI or myosin-binding protein C phosphorylation. The cTnIP82S variant occurs near a region of interactions with troponin T; therefore, structural changes in this region could explain its meaningful effects on myofilament cooperativity. Our data indicate that cTnIP82S mutation modifies age-dependent diastolic dysfunction and impairs overall contractility after β-adrenergic stimulation or chronic pressure overload. Thus cTnIP82S variant should be regarded as a disease-modifying factor for dysfunction and adverse remodeling with aging and chronic pressure overload.

Troponin I phosphorylation in human myocardium in health and disease

Cardiac troponin I (cTnI) is well known as a biomarker for the diagnosis of myocardial damage. However, because of its central role in the regulation of contraction and relaxation in heart muscle, cTnI may also be a potential target for the treatment of heart failure. Studies in rodent models of cardiac disease and human heart samples showed altered phosphorylation at various sites on cTnI (i.e. site-specific phosphorylation). This is caused by altered expression and/or activity of kinases and phosphatases during heart failure development. It is not known whether these (transient) alterations in cTnI phosphorylation are beneficial or detrimental. Knowledge of the effects of site-specific cTnI phosphorylation on cardiomyocyte contractility is therefore of utmost importance for the development of new therapeutic strategies in patients with heart failure. In this review we focus on the role of cTnI phosphorylation in the healthy heart upon activation of the beta-adrenergic receptor pathway (as occurs during increased stress and exercise) and as a modulator of the Frank-Starling mechanism. Moreover, we provide an overview of recent studies which aimed to reveal the functional consequences of changes in cTnI phosphorylation in cardiac disease.

Obstructive sleep apnea in pregnancy: reliability of prevalence and prediction estimates

OBJECTIVE

We sought to ascertain the validity of two screening scales for obstructive sleep apnea (OSA) in pregnancy and to establish the prevalence of OSA in pregnancy.

STUDY DESIGN

In this prospective observational study, two screening scales were administered. Screen positive subjects were referred for diagnostic polysomnography (PSG); if admitted for antepartum care, screen positive subjects underwent a modified study with a type 3 device (T3D).

RESULT

A total of 1509 subjects underwent OSA screening; 58 completed diagnostic testing. Neither measure was a reliable diagnostic tool for OSA as determined by T3D or PSG (detection rates of 10.3% and 18.0%, respectively). Among screen positive subjects undergoing PSG or T3D testing, 15.5% ultimately met 'gold standard' OSA diagnostic criteria for an estimated point prevalence of 4.9%.

CONCLUSION

In this prospective trial, screening positive on the Berlin questionnaire or Epworth sleepiness scale was poorly predictive of OSA among gravidae and was associated with a high false referral rate.

Phosphorylation of protein kinase C sites Ser42/44 decreases Ca(2+)-sensitivity and blunts enhanced length-dependent activation in response to protein kinase A in human cardiomyocytes

Protein kinase C (PKC)-mediated phosphorylation of troponin I (cTnI) at Ser42/44 is increased in heart failure. While studies in rodents demonstrated that PKC-mediated Ser42/44 phosphorylation decreases maximal force and ATPase activity, PKC incubation of human cardiomyocytes did not affect maximal force. We investigated whether Ser42/44 pseudo-phosphorylation affects force development and ATPase activity using troponin exchange in human myocardium. Additionally, we studied if pseudo-phosphorylated Ser42/44 modulates length-dependent activation of force, which is regulated by protein kinase A (PKA)-mediated cTnI-Ser23/24 phosphorylation. Isometric force was measured in membrane-permeabilized cardiomyocytes exchanged with human recombinant wild-type troponin or troponin mutated at Ser42/44 or Ser23/24 into aspartic acid (D) or alanine (A) to mimic phosphorylation and dephosphorylation, respectively. In troponin-exchanged donor cardiomyocytes experiments were repeated after PKA incubation. ATPase activity was measured in troponin-exchanged cardiac muscle strips. Compared to wild-type, 42D/44D decreased Ca(2+)-sensitivity without affecting maximal force in failing and donor cardiomyocytes. In donor myocardium, 42D/44D did not affect maximal ATPase activity or tension cost. Interestingly, 42D/44D blunted the length-dependent increase in Ca(2+)-sensitivity induced upon PKA-mediated phosphorylation. Since the drop in Ca(2+)-sensitivity at physiological Ca(2+)-concentrations is relatively large phosphorylation of Ser42/44 may result in a decrease of force and associated ATP utilization in the human heart.

Length-dependent activation is modulated by cardiac troponin I bisphosphorylation at Ser23 and Ser24 but not by Thr143 phosphorylation

Frank-Starling's law reflects the ability of the heart to adjust the force of its contraction to changes in ventricular filling, a property based on length-dependent myofilament activation (LDA). The threonine at amino acid 143 of cardiac troponin I (cTnI) is prerequisite for the length-dependent increase in Ca(2+) sensitivity. Thr143 is a known target of protein kinase C (PKC) whose activity is increased in cardiac disease. Thr143 phosphorylation may modulate length-dependent myofilament activation in failing hearts. Therefore, we investigated if pseudo-phosphorylation at Thr143 modulates length dependence of force using troponin exchange experiments in human cardiomyocytes. In addition, we studied effects of protein kinase A (PKA)-mediated cTnI phosphorylation at Ser23/24, which has been reported to modulate LDA. Isometric force was measured at various Ca(2+) concentrations in membrane-permeabilized cardiomyocytes exchanged with recombinant wild-type (WT) troponin or troponin mutated at the PKC site Thr143 or Ser23/24 into aspartic acid (D) or alanine (A) to mimic phosphorylation and dephosphorylation, respectively. In troponin-exchanged donor cardiomyocytes experiments were repeated after incubation with exogenous PKA. Pseudo-phosphorylation of Thr143 increased myofilament Ca(2+) sensitivity compared with WT without affecting LDA in failing and donor cardiomyocytes. Subsequent PKA treatment enhanced the length-dependent shift in Ca(2+) sensitivity after WT and 143D exchange. Exchange with Ser23/24 variants demonstrated that pseudo-phosphorylation of both Ser23 and Ser24 is needed to enhance the length-dependent increase in Ca(2+) sensitivity. cTnI pseudo-phosphorylation did not alter length-dependent changes in maximal force. Thus phosphorylation at Thr143 enhances myofilament Ca(2+) sensitivity without affecting LDA, while Ser23/24 bisphosphorylation is needed to enhance the length-dependent increase in myofilament Ca(2+) sensitivity.

PKCα-specific phosphorylation of the troponin complex in human myocardium: a functional and proteomics analysis

Aims

Protein kinase Cα (PKCα) is one of the predominant PKC isoforms that phosphorylate cardiac troponin. PKCα is implicated in heart failure and serves as a potential therapeutic target, however, the exact consequences for contractile function in human myocardium are unclear. This study aimed to investigate the effects of PKCα phosphorylation of cardiac troponin (cTn) on myofilament function in human failing cardiomyocytes and to resolve the potential targets involved.

Methods and Results

Endogenous cTn from permeabilized cardiomyocytes from patients with end-stage idiopathic dilated cardiomyopathy was exchanged (∼69%) with PKCα-treated recombinant human cTn (cTn (DD+PKCα)). This complex has Ser23/24 on cTnI mutated into aspartic acids (D) to rule out in vitro cross-phosphorylation of the PKA sites by PKCα. Isometric force was measured at various [Ca²⁺] after exchange. The maximal force (F_max) in the cTn (DD+PKCα) group (17.1±1.9 kN/m²) was significantly reduced compared to the cTn (DD) group (26.1±1.9 kN/m²). Exchange of endogenous cTn with cTn (DD+PKCα) increased Ca²⁺-sensitivity of force (pCa₅₀ = 5.59±0.02) compared to cTn (DD) (pCa₅₀ = 5.51±0.02). In contrast, subsequent PKCα treatment of the cells exchanged with cTn (DD+PKCα) reduced pCa₅₀ to 5.45±0.02. Two PKCα-phosphorylated residues were identified with mass spectrometry: Ser198 on cTnI and Ser179 on cTnT, although phosphorylation of Ser198 is very low. Using mass spectrometry based-multiple reaction monitoring, the extent of phosphorylation of the cTnI sites was quantified before and after treatment with PKCα and showed the highest phosphorylation increase on Thr143.

Conclusion

PKCα-mediated phosphorylation of the cTn complex decreases F_max and increases myofilament Ca²⁺-sensitivity, while subsequent treatment with PKCα in situ decreased myofilament Ca²⁺-sensitivity. The known PKC sites as well as two sites which have not been previously linked to PKCα are phosphorylated in human cTn complex treated with PKCα with a high degree of specificity for Thr143.

Characterization of the cardiac myosin binding protein-C phosphoproteome in healthy and failing human hearts

INTRODUCTION

Cardiac myosin binding protein-C (cMyBP-C) becomes dephosphorylated in the failing heart and reduced phosphorylation-dependent regulation of cMyBP-C has been implicated in contractile dysfunction. To date, several phosphorylation sites have been identified for human cMyBP-C; however, a comprehensive characterization of the cMyBP-C phosphoproteome is lacking. This study aimed to characterize the cMyBP-C phosphoproteome using two different proteomic-based methods in explanted donor and end-stage failing hearts.

METHODS

The first approach used to characterize the cMyBP-C phosphoproteome employed a strong-cation exchange chromatography (SCX) fractionation method (10 pooled samples, technical replicates=4) and the second employed a sodium dodecylsulfate polyacrylamide gel electrophoresis method (n=10; technical replicates=2). Each subsequently underwent titanium dioxide (TiO2) affinity chromatography to enrich for the tryptic phosphopeptides, which were analyzed using an LTQ-Orbitrap mass spectrometer. Moreover, recombinant C0-C2 fragment of mouse cMyBP-C incubated with PKA, PKC, CaMKII and CK2 was analyzed to identify the kinases involved with phosphorylation of cMyBP-C.

RESULTS

Seventeen phosphorylation sites on cMyBP-C were identified in vivo, with the majority localized in the N-terminal domains C0-C2. The three most abundant phosphorylated sites, Ser284, Ser286 and Thr290, are located in the regulatory M-domain of cMyBP-C. Ser284 showed a significant reduction in phosphorylation in HF.

CONCLUSION

This study demonstrates that cMyBP-C harbors more phosphorylation sites than previously known, with a total of 17 (9 novel) identified phosphorylation sites in vivo. Most sites were primarily located within the N-terminal side of the protein. The most highly phosphorylated site on cMyBP-C was Ser284 and this site showed decreased phosphorylation in the failing heart, which implicates importance for fine-tuning contractility. To date, the functional importance of Ser286 and Thr290 is unknown. In addition, 16 sites were identified after in vitro kinase incubation. The data have been deposited to the ProteomeXchange with identifier PXD000158.

Perturbed length-dependent activation in human hypertrophic cardiomyopathy with missense sarcomeric gene mutations

RATIONALE

High-myofilament Ca(2+) sensitivity has been proposed as a trigger of disease pathogenesis in familial hypertrophic cardiomyopathy (HCM) on the basis of in vitro and transgenic mice studies. However, myofilament Ca(2+) sensitivity depends on protein phosphorylation and muscle length, and at present, data in humans are scarce.

OBJECTIVE

To investigate whether high myofilament Ca(2+) sensitivity and perturbed length-dependent activation are characteristics for human HCM with mutations in thick and thin filament proteins.

METHODS AND RESULTS

Cardiac samples from patients with HCM harboring mutations in genes encoding thick (MYH7, MYBPC3) and thin (TNNT2, TNNI3, TPM1) filament proteins were compared with sarcomere mutation-negative HCM and nonfailing donors. Cardiomyocyte force measurements showed higher myofilament Ca(2+) sensitivity in all HCM samples and low phosphorylation of protein kinase A (PKA) targets compared with donors. After exogenous PKA treatment, myofilament Ca(2+) sensitivity was similar (MYBPC3mut, TPM1mut, sarcomere mutation-negative HCM), higher (MYH7mut, TNNT2mut), or even significantly lower (TNNI3mut) compared with donors. Length-dependent activation was significantly smaller in all HCM than in donor samples. PKA treatment increased phosphorylation of PKA-targets in HCM myocardium and normalized length-dependent activation to donor values in sarcomere mutation-negative HCM and HCM with truncating MYBPC3 mutations but not in HCM with missense mutations. Replacement of mutant by wild-type troponin in TNNT2mut and TNNI3mut corrected length-dependent activation to donor values.

CONCLUSIONS

High-myofilament Ca(2+) sensitivity is a common characteristic of human HCM and partly reflects hypophosphorylation of PKA targets compared with donors. Length-dependent sarcomere activation is perturbed by missense mutations, possibly via posttranslational modifications other than PKA hypophosphorylation or altered protein-protein interactions, and represents a common pathomechanism in HCM.

Impact of site-specific phosphorylation of protein kinase A sites Ser23 and Ser24 of cardiac troponin I in human cardiomyocytes

PKA-mediated phosphorylation of contractile proteins upon β-adrenergic stimulation plays an important role in the regulation of cardiac performance. Phosphorylation of the PKA sites (Ser(23)/Ser(24)) of cardiac troponin (cTn)I results in a decrease in myofilament Ca(2+) sensitivity and an increase in the rate of relaxation. However, the relation between the level of phosphorylation of the sites and the functional effects in the human myocardium is unknown. Therefore, site-directed mutagenesis was used to study the effects of phosphorylation at Ser(23) and Ser(24) of cTnI on myofilament function in human cardiac tissue. Serines were replaced by aspartic acid (D) or alanine (A) to mimic phosphorylation and dephosphorylation, respectively. cTnI-DD mimics both sites phosphorylated, cTnI-AD mimics Ser(23) unphosphorylated and Ser(24) phosphorylated, cTnI-DA mimics Ser(23) phosphorylated and Ser(24) unphosphorylated, and cTnI-AA mimics both sites unphosphorylated. Force development was measured at various Ca(2+) concentrations in permeabilized cardiomyocytes in which the endogenous troponin complex was exchanged with these recombinant human troponin complexes. In donor cardiomyocytes, myofilament Ca(2+) sensitivity (pCa(50)) was significantly lower in cTnI-DD (pCa(50): 5.39 ± 0.01) compared with cTnI-AA (pCa(50): 5.50 ± 0.01), cTnI-AD (pCa(50): 5.48 ± 0.01), and cTnI-DA (pCa(50): 5.51 ± 0.01) at ~70% cTn exchange. No effects were observed on the rate of tension redevelopment. In cardiomyocytes from idiopathic dilated cardiomyopathic tissue, a linear decline in pCa(50) with cTnI-DD content was observed, saturating at ~55% bisphosphorylation. Our data suggest that in the human myocardium, phosphorylation of both PKA sites on cTnI is required to reduce myofilament Ca(2+) sensitivity, which is maximal at ~55% bisphosphorylated cTnI. The implications for in vivo cardiac function in health and disease are detailed in the DISCUSSION in this article.