Augmented phosphorylation of cardiac troponin I in hypertensive heart failure.

An altered cardiac myofilament response to activating Ca(2+) is a hallmark of human heart failure. Phosphorylation of cardiac troponin I (cTnI) is critical in modulating contractility and Ca(2+) sensitivity of cardiac muscle. cTnI can be phosphorylated by protein kinase A (PKA) at Ser(22/23) and protein kinase C (PKC) at Ser(22/23), Ser(42/44), and Thr(143). Whereas the functional significance of Ser(22/23) phosphorylation is well understood, the role of other cTnI phosphorylation sites in the regulation of cardiac contractility remains a topic of intense debate, in part, due to the lack of evidence of in vivo phosphorylation. In this study, we utilized top-down high resolution mass spectrometry (MS) combined with immunoaffinity chromatography to determine quantitatively the cTnI phosphorylation changes in spontaneously hypertensive rat (SHR) model of hypertensive heart disease and failure. Our data indicate that cTnI is hyperphosphorylated in the failing SHR myocardium compared with age-matched normotensive Wistar-Kyoto rats. The top-down electron capture dissociation MS unambiguously localized augmented phosphorylation sites to Ser(22/23) and Ser(42/44) in SHR. Enhanced Ser(22/23) phosphorylation was verified by immunoblotting with phospho-specific antibodies. Immunoblot analysis also revealed up-regulation of PKC-α and -δ, decreased PKCε, but no changes in PKA or PKC-ß levels in the SHR myocardium. This provides direct evidence of in vivo phosphorylation of cTnI-Ser(42/44) (PKC-specific) sites in an animal model of hypertensive heart failure, supporting the hypothesis that PKC phosphorylation of cTnI may be maladaptive and potentially associated with cardiac dysfunction.

Cardiac troponin T, a sarcomeric AKAP, tethers protein kinase A at the myofilaments.

Efficient and specific phosphorylation of PKA substrates, elicited in response to ß-adrenergic stimulation, require spatially confined pools of PKA anchored in proximity of its substrates. PKA-dependent phosphorylation of cardiac sarcomeric proteins has been the subject of intense investigations. Yet, the identity, composition, and function of PKA complexes at the sarcomeres have remained elusive. Here we report the identification and characterization of a novel sarcomeric AKAP (A-kinase anchoring protein), cardiac troponin T (cTnT). Using yeast two-hybrid technology in screening two adult human heart cDNA libraries, we identified the regulatory subunit of PKA as interacting with human cTnT bait. Immunoprecipitation studies show that cTnT is a dual specificity AKAP, interacting with both PKA-regulatory subunits type I and II. The disruptor peptide Ht31, but not Ht31P (control), abolished cTnT/PKA-R association. Truncations and point mutations identified an amphipathic helix domain in cTnT as the PKA binding site. This was confirmed by a peptide SPOT assay in the presence of Ht31 or Ht31P (control). Gelsolin-dependent removal of thin filament proteins also reduced myofilament-bound PKA-type II. Using a cTn exchange procedure that substitutes the endogenous cTn complex with a recombinant cTn complex we show that PKA-type II is troponin-bound in the myofilament lattice. Displacement of PKA-cTnT complexes correlates with a significant decrease in myofibrillar PKA activity. Taken together, our data propose a novel role for cTnT as a dual-specificity sarcomeric AKAP.

Cardiomyopathy-causing deletion K210 in cardiac troponin T alters phosphorylation propensity of sarcomeric proteins.

Ca(2+) desensitization of myofilaments is indicated as a primary mechanism for the pathogenesis of familial dilated cardiomyopathy (DCM) associated with the deletion of lysine 210 (DeltaK210) in cardiac troponin T (cTnT). DeltaK210 knock-in mice closely recapitulate the clinical phenotypes documented in patients with this mutation. Considerable evidence supports the proposition that phosphorylation of cardiac sarcomeric proteins is a key modulator of function and may exacerbate the effect of the deletion. In this study we investigate the impact of K210 deletion on phosphorylation propensity of sarcomeric proteins. Analysis of cardiac myofibrils isolated from DeltaK210 hearts identified a decrease in phosphorylation of cTnI (46%), cTnT (30%) and MyBP-C (32%) compared with wild-type controls. Interestingly, immunoblot analyses with phospho-specific antibodies show augmented phosphorylation of cTnT-Thr(203) (28%) and decreased phosphorylation of cTnI-Ser(23/24) (41%) in mutant myocardium. In vitro kinase assays indicate that DeltaK210 increases phosphorylation propensity of cTnT-Thr(203) three-fold, without changing cTnI-Ser(23/24) phosphorylation. Molecular modeling of cTnT-DeltaK210 structure reveals changes in the electrostatic environment of cTnT helix (residues 203-224) that lead to a more basic environment around Thr(203), which may explain the enhanced PKC-dependent phosphorylation. In addition, yeast two-hybrid assays indicate that cTnT-DeltaK210 binds stronger to cTnI compared with cTnT-wt. Collectively, our observations suggest that cardiomyopathy-causing DeltaK210 has far-reaching effects influencing cTnI-cTnT binding and posttranslational modifications of key sarcomeric proteins.

Funding opportunities for investigators in the early stages of career development.

Many sources of advice and guidance are available to the early career investigator. Generally, mentors serve as the primary source of information, although program and review officers are the most underutilized resources. This article organizes these opportunities to enable early career investigators to plot a rational trajectory for career success. A list of the major agencies that provide grant support for early career investigators is included. In addition, funding opportunities are organized on the basis of the stage in career development pathway and the type of terminal degree.

Early development of intracellular calcium cycling defects in intact hearts of spontaneously hypertensive rats.

Defects in excitation-contraction coupling have been reported in failing hearts, but little is known about the relationship between these defects and the development of heart failure (HF). We compared the early changes in intracellular Ca(2+) cycling to those that underlie overt pump dysfunction and arrhythmogenesis found later in HF. Laser-scanning confocal microscopy was used to measure Ca(2+) transients in myocytes of intact hearts in Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs) at different ages. Early compensatory mechanisms include a positive inotropic effect in SHRs at 7.5-9 mo compared with 6 mo. Ca(2+) transient duration increased at 9 mo in SHRs, indicating changes in Ca(2+) reuptake during decompensation. Cell-to-cell variability in Ca(2+) transient duration increased at 7.5 mo, decreased at 9 mo, and increased again at 22 mo (overt HF), indicating extensive intercellular variability in Ca(2+) transient kinetics during disease progression. Vulnerability to intercellular concordant Ca(2+) alternans increased at 9-22 mo in SHRs and was mirrored by a slowing in Ca(2+) transient restitution, suggesting that repolarization alternans and the resulting repolarization gradients might promote reentrant arrhythmias early in disease development. Intercellular discordant and subcellular Ca(2+) alternans increased as early as 7.5 mo in SHRs and may also promote arrhythmias during the compensated phase. The incidence of spontaneous and triggered Ca(2+) waves was increased in SHRs at all ages, suggesting a higher likelihood of triggered arrhythmias in SHRs compared with WKY rats well before HF develops. Thus serious and progressive defects in Ca(2+) cycling develop in SHRs long before symptoms of HF occur. Defective Ca(2+) cycling develops early and affects a small number of myocytes, and this number grows with age and causes the transition from asymptomatic to overt HF. These defects may also underlie the progressive susceptibility to Ca(2+) alternans and Ca(2+) wave activity, thus increasing the propensity for arrhythmogenesis in HF.

Calcium handling in human embryonic stem cell-derived cardiomyocytes.

The objective of the current study was to characterize calcium handling in developing human embryonic stem cell-derived cardiomyocytes (hESC-CMs). To this end, real-time polymerase chain reaction (PCR), immunocytochemistry, whole-cell voltage-clamp, and simultaneous patch-clamp/laser scanning confocal calcium imaging and surface membrane labeling with di-8-aminonaphthylethenylpridinium were used. Immunostaining studies in the hESC-CMs demonstrated the presence of the sarcoplasmic reticulum (SR) calcium release channels, ryanodine receptor-2, and inositol-1,4,5-trisphosphate (IP3) receptors. Store calcium function was manifested as action-potential-induced calcium transients. Time-to-target plots showed that these action-potential-initiated calcium transients traverse the width of the cell via a propagated wave of intracellular store calcium release. The hESC-CMs also exhibited local calcium events ("sparks") that were localized to the surface membrane. The presence of caffeine-sensitive intracellular calcium stores was manifested following application of focal, temporally limited puffs of caffeine in three different age groups: early-stage (with the initiation of beating), intermediate-stage (10 days post-beating [dpb]), and late-stage (30-40 dpb) hESC-CMs. Calcium store load gradually increased during in vitro maturation. Similarly, ryanodine application decreased the amplitude of the spontaneous calcium transients. Interestingly, the expression and function of an IP3-releasable calcium pool was also demonstrated in the hESC-CMs in experiments using caged-IP3 photolysis and antagonist application (2 microM 2-Aminoethoxydiphenyl borate). In summary, our study establishes the presence of a functional SR calcium store in early-stage hESC-CMs and shows a unique pattern of calcium handling in these cells. This study also stresses the importance of the functional characterization of hESC-CMs both for developmental studies and for the development of future myocardial cell replacement strategies. Disclosure of potential conflicts of interest is found at the end of this article.

Regional differences in the expression of tetrodotoxin-sensitive inward Ca2+ and outward Cs+/K+ currents in mouse and human ventricles.

Tetrodotoxin (TTX) sensitive inward Ca2+ currents, ICa(TTX), have been identified in cardiac myocytes from several species, although it is unclear if ICa(TTX) is expressed in all cardiac cell types, and if ICa(TTX) reflects Ca2+ entry through the main, Nav1.5-encoded, cardiac Na+ (Nav) channels. To address these questions, recordings were obtained with 2 mm Ca2+ and 0 mm Na+ in the bath and 120 mm Cs+ in the pipettes from myocytes isolated from adult mouse interventricular septum (IVS), left ventricular (LV) endocardium, apex, and epicardium and from human LV endocardium and epicardium. On membrane depolarizations from a holding potential of -100 mV, ICa(TTX) was identified in mouse IVS and LV endocardial myocytes and in human LV endocardial myocytes, whereas only TTX-sensitive outward Cs+/K+ currents were observed in mouse LV apex and epicardial myocytes and human LV epicardial myocytes. The inward Ca2+, but not the outward Cs+/K+, currents were blocked by mm concentrations of MTSEA, a selective blocker of cardiac Nav1.5-encoded Na+ channels. In addition, in Nav1.5-expressing tsA-201 cells, ICa(TTX) was observed in 3 (of 20) cells, and TTX-sensitive outward Cs+/K+ currents were observed in the other (17) cells. The time- and voltage-dependent properties of the TTX-sensitive inward Ca2+ and outward Cs+/K+ currents recorded in Nav1.5-expressing tsA-201 were indistinguishable from native currents in mouse and human cardiac myocytes. Overall, the results presented here suggest marked regional, cell type-specific, differences in the relative ion selectivity, and likely the molecular architecture, of native SCN5A-/Scn5a- (Nav1.5-) encoded cardiac Na+ channels in mouse and human ventricles.

Left ventricular dysfunction and associated cellular injury in rats exposed to chronic intermittent hypoxia.

Obstructive sleep apnea (OSA) increases cardiovascular morbidity and mortality. We have reported that chronic intermittent hypoxia (CIH), a direct consequence during OSA, leads to left ventricular (LV) remodeling and dysfunction in rats. The present study is to determine LV myocardial cellular injury that is possibly associated with LV global dysfunction. Fifty-six rats were exposed either to CIH (nadir O(2) 4-5%) or sham (handled normoxic controls, HC), 8 h/day for 6 wk. At the end of the exposure, we studied LV global function by cardiac catheterization, and LV myocardial cellular injury by in vitro analyses. Compared with HC, CIH animals demonstrated elevations in mean arterial pressure and LV end-diastolic pressure, but reductions in cardiac output (CIH 141.3 +/- 33.1 vs. HC 184.4 +/- 21.2 ml x min(-1) x kg(-1), P < 0.01), maximal rate of LV pressure rise in systole (+dP/dt), and maximal rate of LV pressure fall in diastole (-dP/dt). CIH led to significant cell injury in the left myocardium, including elevated LV myocyte size, measured by cell surface area (CIH 3,564 +/- 354 vs. HC 2,628 +/- 242 microm(2), P < 0.05) and cell length (CIH 148 +/- 23 vs. HC 115 +/- 16 microm, P < 0.05), elevated terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL)-stained positive cell number (CIH 98 +/- 45 vs. HC 15 +/- 13, P < 0.01), elevated caspase-3 activity (906 +/- 249 vs. 2,275 +/- 1,169 pmol x min(-1) x mg(-1), P < 0.05), and elevated expression of several remodeling gene markers, including c-fos, atrial natriuretic peptide, beta-myosin heavy chain, and myosin light chain-2. However, there was no difference between groups in sarcomere contractility of isolated LV myocytes, or in LV collagen deposition on trichrome-stained slices. In conclusion, CIH-mediated LV global dysfunction is associated with myocyte hypertrophy and apoptosis at the cellular level.

Application of blebbistatin as an excitation-contraction uncoupler for electrophysiologic study of rat and rabbit hearts.

BACKGROUND: Application of fluorescence imaging of cardiac electrical activity is limited by motion artifacts and/or side effects of currently available pharmacologic excitation-contraction uncoupling agents. OBJECTIVES: The purpose of this study was to test whether blebbistatin, a recently discovered inhibitor of myosin II isoforms, can be used as an excitation-contraction uncoupler. METHODS: The specificity and potency of blebbistatin were examined by assaying the effects of blebbistatin on the contraction and basic cardiac electrophysiologic parameters of Langendorff-perfused rabbit hearts, isolated rabbit right ventricle and right atrium, and single rat ventricular myocytes using conventional ECG, surface electrograms, microelectrode recordings, and optical imaging with voltage-sensitive and Ca(2+)-sensitive dyes. Action potential morphology, ECG parameters, cardiac conduction, and refractoriness were determined after perfusion with 0.1-10 microM blebbistatin. RESULTS: Blebbistatin 5-10 microM completely eliminated contraction in all cardiac preparations but did not have any effect on electrical activity, including ECG parameters, atrial and ventricular effective refractory periods, and atrial and ventricular activation patterns. Blebbistatin 10 microM had no effects on action potential morphology in rabbit cardiac tissue. Blebbistatin inhibited single cellular contraction in a dose-dependent manner with half-maximal inhibitory concentration (IC(50)) = 0.43 microM, without altering the morphologies of intracellular calcium transients. The blebbistatin effect was completely reversible by simultaneous washout and photobleaching by ultraviolet light CONCLUSION: Blebbistatin is a promising novel selective excitation-contraction uncoupler that can be used for optical imaging of cardiac tissues.

Enhanced G(i) signaling selectively negates beta2-adrenergic receptor (AR)--but not beta1-AR-mediated positive inotropic effect in myocytes from failing rat hearts.

BACKGROUND: Myocardial contractile response to beta1- and beta2-adrenergic receptor (AR) stimulation is severely impaired in chronic heart failure, in which G(i) signaling and the ratio of beta2/beta1 are often increased. Because beta2-AR but not beta1-AR couples to G(s) and G(i) with the G(i) coupling negating the G(s)-mediated contractile response, we determined whether the heart failure-associated augmentation of G(i) signaling contributes differentially to the defects of these beta-AR subtypes and, if so, whether inhibition of G(i) or selective activation of beta2-AR/G(s) by ligands restores beta2-AR contractile response in the failing heart. METHODS AND RESULTS: Cardiomyocytes were isolated from 18- to 24-month-old failing spontaneously hypertensive (SHR) or age-matched Wistar-Kyoto (WKY) rat hearts. In SHR cardiomyocytes, either beta-AR subtype-mediated inotropic effect was markedly diminished, whereas G(i) proteins and the beta2/beta1 ratio were increased. Disruption of G(i) signaling by pertussis toxin (PTX) enabled beta2- but not beta1-AR to induce a full positive inotropic response in SHR myocytes. Furthermore, screening of a panel of beta2-AR ligands revealed that the contractile response mediated by most beta2-AR agonists, including zinterol, salbutamol, and procaterol, was potentiated by PTX, indicating concurrent G(s) and G(i) activation. In contrast, fenoterol, another beta2-AR agonist, induced a full positive inotropic effect in SHR myocytes even in the absence of PTX. CONCLUSIONS: We conclude that enhanced G(i) signaling is selectively involved in the dysfunction of beta2- but not beta1-AR in failing SHR hearts and that disruption of G(i) signaling by PTX or selective activation of beta2-AR/G(s) signaling by fenoterol restores the blunted beta2-AR contractile response in the failing heart.

National Institutes of Health Career Development Awards for Cardiovascular Physician-Scientists: Recent Trends and Strategies for Success.

Nurturing the development of cardiovascular physician-scientist investigators is critical for sustained progress in cardiovascular science and improving human health. The transition from an inexperienced trainee to an independent physician-scientist is a multifaceted process requiring a sustained commitment from the trainee, mentors, and institution. A cornerstone of this training process is a career development (K) award from the National Institutes of Health (NIH). These awards generally require 75% of the awardee's professional effort devoted to research aims and diverse career development activities carried out in a mentored environment over a 5-year period. We report on recent success rates for obtaining NIH K awards, provide strategies for preparing a successful application and navigating the early career period for aspiring cardiovascular investigators, and offer cardiovascular division leadership perspectives regarding K awards in the current era. Our objective is to offer practical advice that will equip trainees considering an investigator path for success.

Arrhythmia triggers in heart failure: the smoking gun of [Ca2+]i dysregulation.

Among the most serious problems associated with heart failure is the increased likelihood of life-threatening arrhythmias. Both triggered and reentrant arrhythmias in heart failure may arise as a result of aberrant intracellular Ca cycling. This article presents some new ideas, based on recent studies, about how altered Ca cycling in heart failure might serve as the cellular basis for arrhythmogenesis.

Commentary: Improving participant recruitment in clinical and translational research.

In this issue of Academic Medicine, Kitterman and colleagues report the results of an evaluation of the prevalence and cost of low-enrolling studies (zero or one participant enrolled) conducted at Oregon Health & Science University (OHSU). They found that one-third of all studies terminated between 2005 and 2009 at OHSU had low enrollment and that these low-enrolling studies cost the institution almost $1 million annually. The recruitment of research participants is critical to conducting clinical and translational research. Failure to recruit research participants has a negative financial impact, but, more importantly, underenrolled studies do not contribute to scientific or clinical knowledge. In this commentary, the authors describe four areas in which academic health centers (AHCs) could invest more effort and resources to improve the recruitment of research participants. First, more planning and resources should be put into determining the feasibility of participant recruitment. Second, studies that are underenrolling should be terminated early to prevent unethical research, to save financial and other resources, and to allow these resources to be applied to successful research. Third, AHCs should professionalize, centralize, and automate participant recruitment. Fourth, AHCs should take a leadership role in partnering with the public to improve participation in clinical research. Participant recruitment must be improved if clinical and translational research is to meet its promise of improving health.

Age-associated disruption of molecular clock expression in skeletal muscle of the spontaneously hypertensive rat.

It is well known that spontaneously hypertensive rats (SHR) develop muscle pathologies with hypertension and heart failure, though the mechanism remains poorly understood. Woon et al. (2007) linked the circadian clock gene Bmal1 to hypertension and metabolic dysfunction in the SHR. Building on these findings, we compared the expression pattern of several core-clock genes in the gastrocnemius muscle of aged SHR (80 weeks; overt heart failure) compared to aged-matched control WKY strain. Heart failure was associated with marked effects on the expression of Bmal1, Clock and Rora in addition to several non-circadian genes important in regulating skeletal muscle phenotype including Mck, Ttn and Mef2c. We next performed circadian time-course collections at a young age (8 weeks; pre-hypertensive) and adult age (22 weeks; hypertensive) to determine if clock gene expression was disrupted in gastrocnemius, heart and liver tissues prior to or after the rats became hypertensive. We found that hypertensive/hypertrophic SHR showed a dampening of peak Bmal1 and Rev-erb expression in the liver, and the clock-controlled gene Pgc1α in the gastrocnemius. In addition, the core-clock gene Clock and the muscle-specific, clock-controlled gene Myod1, no longer maintained a circadian pattern of expression in gastrocnemius from the hypertensive SHR. These findings provide a framework to suggest a mechanism whereby chronic heart failure leads to skeletal muscle pathologies; prolonged dysregulation of the molecular clock in skeletal muscle results in altered Clock, Pgc1α and Myod1 expression which in turn leads to the mis-regulation of target genes important for mechanical and metabolic function of skeletal muscle.

Crossing the chasm: information technology to biomedical informatics.

Accelerating the translation of new scientific discoveries to improve human health and disease management is the overall goal of a series of initiatives integrated in the National Institutes of Health (NIH) "Roadmap for Medical Research." The Clinical and Translational Science Award (CTSA) program is, arguably, the most visible component of the NIH Roadmap providing resources to institutions to transform their clinical and translational research enterprises along the goals of the Roadmap. The CTSA program emphasizes biomedical informatics as a critical component for the accomplishment of the NIH's translational objectives. To be optimally effective, emerging biomedical informatics programs must link with the information technology platforms of the enterprise clinical operations within academic health centers.This report details one academic health center's transdisciplinary initiative to create an integrated academic discipline of biomedical informatics through the development of its infrastructure for clinical and translational science infrastructure and response to the CTSA mechanism. This approach required a detailed informatics strategy to accomplish these goals. This transdisciplinary initiative was the impetus for creation of a specialized biomedical informatics core, the Center for Biomedical Informatics (CBI). Development of the CBI codified the need to incorporate medical informatics including quality and safety informatics and enterprise clinical information systems within the CBI. This article describes the steps taken to develop the biomedical informatics infrastructure, its integration with clinical systems at one academic health center, successes achieved, and barriers encountered during these efforts.

"Oh, the places you'll go": transformation of the nation's biomedical research enterprise in the 21st century.

The postgenomic era and heightened public expectations for tangible improvements in the public health have stimulated a complete transformation of the nation's biomedical research enterprise. The National Institutes of Health (NIH) "Roadmap for Medical Research" has catalyzed this transformation. The NIH roadmap consists of several interrelated initiatives, of which the Clinical and Translational Science Award (CTSA) program is the most relevant for rehabilitation specialists. This article reviews the evolution of this transformation and highlights the unprecedented opportunities the CTSA program provides rehabilitation specialists to play leadership roles in improving the clinical care of their patients.

Multiple defects in intracellular calcium cycling in whole failing rat heart.

BACKGROUND: A number of defects in excitation-contraction coupling have been identified in failing mammalian hearts. The goal of this study was to measure the defects in intracellular Ca(2+) cycling in left ventricular epicardial myocytes of the whole heart in an animal model of congestive heart failure (CHF). METHODS AND RESULTS: Intracellular Ca(2+) transients were measured using confocal microscopy in whole rat hearts from age-matched Wistar-Kyoto control rats and spontaneously hypertensive rats at approximately 23 months of age. Basal Ca(2+) transients in myocytes in spontaneously hypertensive rats were smaller in amplitude and longer in duration than Wistar-Kyoto control rats. There was also greater variability in transient characteristics associated with duration between myocytes of CHF than Wistar-Kyoto controls. Approximately 21% of CHF myocytes demonstrated spontaneous Ca(2+) waves compared with very little of this activity in Wistar-Kyoto control rats. A separate population of spontaneously hypertensive rat myocytes showed Ca(2+) waves that were triggered during pacing and were absent at rest (triggered waves). Rapid pacing protocols caused Ca(2+) alternans to develop at slower heart rates in CHF. CONCLUSIONS: Epicardial cells demonstrate both serious defects and greater cell-to-cell variability in Ca(2+) cycling in CHF. The defects in Ca(2+) cycling include both spontaneous and triggered waves of Ca(2+) release, which promote triggered activity. The slowing of Ca(2+) repriming in the sarcoplasmic reticulum is probably responsible for the increased vulnerability to Ca(2+) alternans in CHF. Our results suggest that defective Ca(2+) cycling could contribute both to reduced cardiac output in CHF and to the establishment of repolarization gradients, thus creating the substrate for reentrant arrhythmias.