The value of clinical routine blood biomarkers in predicting long-term mortality after stroke

Background:

Several blood biomarkers have been identified as predictors for poor outcome after ischemic stroke. However, recent studies mainly focused on single or experimental biomarkers and considered rather short follow-up intervals limiting their value for daily clinical practice. We, therefore, aimed to compare various clinical routine blood biomarkers for their predictive value on post-stroke mortality over a 5-year follow-up period.

Patients and methods:

This data analysis of a prospective single-center study included all consecutive ischemic stroke patients admitted to the stroke unit of our university hospital over a 1-year period. Various blood biomarkers of inflammation, heart failure, metabolic disorders, and coagulation were analyzed from standardized routine blood samples collected within 24 h of hospital admission. All patients underwent a thorough diagnostic workup and were followed for 5 years post-stroke.

Results:

Of 405 patients (mean age: 70.3 years), 72 deceased (17.8%) during the follow-up period. While various routine blood biomarkers were associated with post-stroke mortality in univariable analyses, only NT-proBNP remained an independent predictor (adjusted odds ratio 5.1; 95% CI 2.0–13.1; p < 0.001) for death after stroke. NT-proBNP levels ⩾794 pg/mL ( n = 169, 42%) had a sensitivity of 90% for post-stroke mortality with a negative predictive value of 97% and was additionally associated with cardioembolic stroke and heart failure (each p ⩽ 0.05).

Conclusion:

NT-proBNP represents the most relevant routine blood-based biomarker for the prediction of long-term mortality after ischemic stroke. Increased NT-proBNP levels indicate a vulnerable subgroup of stroke patients in which early and thorough cardiovascular assessment and consistent follow-ups could improve outcome after stroke.

miR-1183 Is a Key Marker of Remodeling upon Stretch and Tachycardia in Human Myocardium

Many cardiac insults causing atrial remodeling are linked to either stretch or tachycardia, but a comparative characterization of their effects on early remodeling events in human myocardium is lacking. Here, we applied isometric stretch or sustained tachycardia at 2.5 Hz in human atrial trabeculae for 6 h followed by microarray gene expression profiling. Among largely independent expression patterns, we found a small common fraction with the microRNA miR-1183 as the highest up-regulated transcript (up to 4-fold). Both, acute stretch and tachycardia induced down-regulation of the predicted miR-1183 target genes ADAM20 and PLA2G7. Furthermore, miR-1183 was also significantly up-regulated in chronically remodeled atrial samples from patients with persistent atrial fibrillation (3-fold up-regulation versus sinus rhythm samples), and in ventricular myocardium from dilative cardiomyopathy hearts (2-fold up-regulation) as compared to non-failing controls. In sum, although stretch and tachycardia show distinct transcriptomic signatures in human atrial myocardium, both cardiac insults consistently regulate the expression of miR-1183 and its downstream targets in acute and chronic remodeling. Thus, elevated expression of miR-1183 might serve as a tissue biomarker for atrial remodeling and might be of potential functional significance in cardiac disease.

Fine-Tuning Cardiac Insulin-Like Growth Factor 1 Receptor Signaling to Promote Health and Longevity

BACKGROUND

The insulin-like growth factor 1 (IGF1) pathway is a key regulator of cellular metabolism and aging. Although its inhibition promotes longevity across species, the effect of attenuated IGF1 signaling on cardiac aging remains controversial.

METHODS

We performed a lifelong study to assess cardiac health and lifespan in 2 cardiomyocyte-specific transgenic mouse models with enhanced versus reduced IGF1 receptor (IGF1R) signaling. Male mice with human IGF1R overexpression or dominant negative phosphoinositide 3-kinase mutation were examined at different life stages by echocardiography, invasive hemodynamics, and treadmill coupled to indirect calorimetry. In vitro assays included cardiac histology, mitochondrial respiration, ATP synthesis, autophagic flux, and targeted metabolome profiling, and immunoblots of key IGF1R downstream targets in mouse and human explanted failing and nonfailing hearts, as well.

RESULTS

Young mice with increased IGF1R signaling exhibited superior cardiac function that progressively declined with aging in an accelerated fashion compared with wild-type animals, resulting in heart failure and a reduced lifespan. In contrast, mice with low cardiac IGF1R signaling exhibited inferior cardiac function early in life, but superior cardiac performance during aging, and increased maximum lifespan, as well. Mechanistically, the late-life detrimental effects of IGF1R activation correlated with suppressed autophagic flux and impaired oxidative phosphorylation in the heart. Low IGF1R activity consistently improved myocardial bioenergetics and function of the aging heart in an autophagy-dependent manner. In humans, failing hearts, but not those with compensated hypertrophy, displayed exaggerated IGF1R expression and signaling activity.

CONCLUSIONS

Our findings indicate that the relationship between IGF1R signaling and cardiac health is not linear, but rather biphasic. Hence, pharmacological inhibitors of the IGF1 pathway, albeit unsuitable for young individuals, might be worth considering in older adults.

Electroanatomic mapping system guided his bundle pacemaker implantation: experience of the his bundle registry graz

Funding Acknowledgements

Type of funding sources: None.

Background

Patients with bradyarrhythmia in need for ventricular pacing may suffer from pacing-induced heart failure due to unphysiological right ventricular pacing. His bundle pacing (HBP) allows to overcome this common issue with a more physiologic approach but real-life procedural data using this technology is scarce.

Methods

We report a single centre experience of the first 44 consecutive patients being implanted with a His-bundle-based pacemaker 09/2020-11/2021 per 3D-mapping guided implantation due to different types of bradyarrhythmia, or for cardiac resynchronisation therapy in heart failure combined with a left-ventricular lead (HOT-CRT) ± a right ventricular defibrillator lead. The positioning of the His-bundle-lead was done by identifying the His-bundle-location with a 3D electroanatomic mapping system via an introducing sheath that is provided with electrodes at its tip.

Results

Mean age was 70 [16;86] years, 12/44 (27%) patients were female, mean baseline LVEF was 44±18%. Baseline ECG was captured: QRS width was 123±33ms, with typical LBBB in 14/44 (32%), typical RBBB in 4/44 (9%), alternating BBB in one patient (2%) and either no BBB or ventricular escape rhythm in 25/44 (57%). Indications for implantation were AV-block grade II-III in 19/44 (43%), primary prophylactic ICD indication in HFrEF in 13/44 (30%), atrial fibrillation with bradycardic conduction in 7/44 patients (16%), sick-sinus-syndrome in 4/44 (9%) and secondary prophylactic ICD indication in one patient (2%). In 41/44 (93%) a primary device was implanted, in 3/44 (7%) a pre-existent device was upgraded with a HB lead.

Therefore, 14 dual-chamber-pacemaker, 5 single-chamber-pacemaker, 8 single-chamber CRT-P, 11 dual-chamber CRT-P, 4 single-chamber CRT-D, 2 dual-chamber CRT-D were implanted. In 50 patients HBP was attempted, while in 6/50 (12%) patients outside of this analysis the attempt was not successful, these patients were consecutively implanted with a non-HBP-device and therefor excluded from the further analysis.

In the 44 patients included in this analysis with primary successful HBP, 4/44 (9%) his-bundle-leads dislocated within the first 48 hours, leading to a secondary success rate of 91%. There were two post-procedural pneumothorax that needed drainage, no major procedure-related complications occurred. Median skin-to skin procedure time was 109±50 minutes. The paced QRS width at the post-implantation follow up was 115±32ms with a change in QRS width of -10ms (+72;-92ms). When excluding the secondary lead dislocations and including only the successful HB paced QRS complexes, the paced QRS width was 105±30ms and the change in QRS width was -12±42ms. The mean his-bundle threshold was 1,2±1V over 0,5ms (0,5;1,5ms). The proportion of ventricular pacing was 69±38%.

Conclusion

Electroanatomic-guided His bundle pacing is feasible, with high implantation success rate and electric impact, both regarding QRS width and pacing threshold.

Liver Fibrosis-4 index indicates atrial fibrillation in acute ischemic stroke

Background

Non‐alcoholic fatty liver disease and particularly liver fibrosis are related to cardiovascular disease and may indicate an increased risk for atrial fibrillation (AF), but this association has not yet been systematically investigated in a cohort of ischemic stroke patients.

Methods

We analyzed data from a prospective single‐center study enrolling all consecutive ischemic stroke patients admitted to our stroke unit over a 1‐year period. All patients received a thorough etiological workup. For evaluation of liver fibrosis, we determined the Fibrosis‐4 (FIB‐4) index, a well‐established noninvasive liver fibrosis test. Laboratory results were analyzed from a uniform blood sample taken at stroke unit admission.

Results

Of 414 included patients (mean age 70.2 years, 57.7% male), FIB‐4 indicated advanced liver fibrosis in 92 (22.2%). AF as the underlying stroke mechanism was present in 28.0% (large vessel disease: 25.6%, small vessel disease: 11.4%, cryptogenic: 29.2%). Patients with FIB‐4 ≥ 2.67 had higher rates of AF (53.3% vs. 20.8%, p < 0.001), and this association remained significant after correction for established AF risk factors (odds ratio 2.53, 95% confidence interval 1.44–4.46, p = 0.001). FIB‐4 was further associated with worse functional outcome 3 months (p < 0.001) and higher mortality 4 years post‐stroke (p < 0.02), but these relationships were no longer present after correction for age and initial stroke severity. Moreover, FIB‐4 was not associated with long‐term recurrent vascular events.

Conclusions

Liver fibrosis assessed by the FIB‐4 index is independently associated with AF in acute ischemic stroke patients. Further studies should evaluate whether adding the FIB‐4 index to AF risk scores increases their precision.

Predicting atrial fibrillation after cryptogenic stroke via a clinical risk score-a prospective observational study

Background and purpose

Atrial fibrillation (AF) often remains undiagnosed in cryptogenic stroke (CS), mostly because of limited availability of cardiac long‐term rhythm monitoring. There is an unmet need for a pre‐selection of CS patients benefitting from such work‐up. A clinical risk score was therefore developed for the prediction of AF after CS and its performance was evaluated over 1 year of follow‐up.

Methods

Our proposed risk score ranges from 0 to 16 points and comprises variables known to be associated with occult AF in CS patients including age, N‐terminal pro‐brain natriuretic peptide, electrocardiographic and echocardiographic features (supraventricular premature beats, atrial runs, atrial enlargement, left ventricular ejection fraction) and brain imaging markers (multi‐territory/prior cortical infarction). All CS patients admitted to our Stroke Unit between March 2018 and August 2019 were prospectively followed for AF detection over 1 year after discharge.

Results

During the 1‐year follow‐up, 24 (16%) out of 150 CS patients with AF (detected via electrocardiogram controls, n = 18; loop recorder monitoring, n = 6) were diagnosed. Our predefined AF Risk Score (cutoff ≥4 points; highest Youden's index) had a sensitivity of 92% and a specificity of 67% for 1‐year prediction of AF. Notably, only two CS patients with <4 score points were diagnosed with AF later on (negative predictive value 98%).

Conclusions

A clinical risk score for 1‐year prediction of AF in CS with high sensitivity, reasonable specificity and excellent negative predictive value is presented. Generalizability of our score needs to be tested in external cohorts with continuous cardiac rhythm monitoring.

Expert consensus on acute management of ventricular arrhythmias - VT network Austria

The Arrhythmia Working Group of the Austrian Society of Cardiology (ÖKG) has set the goal of systematically structuring and organizing the acute care of patients with ventricular arrhythmias (VA), i.e. ventricular tachycardia (VT) or ventricular fibrillation (VF) in Austria. Within a consensus paper, national recommendations on the basic diagnostic work-up of VA (12-lead ECG, medical history, family history, laboratory analyses, echocardiography, search for reversible causes, ICD interrogation), as well as further medical treatment and therapeutic measures (indication of coronary angiography, ablation therapy) are established. Since acute ablation of VT is indicated in the current ESC guidelines as a class IB indication for scar-associated incessant VT or electrical storm (ES; ≥ 3 ICD therapies in 24 h) as well as for ischemic cardiomyopathy (iCMP) with recurrent ICD shocks, organizational measures must be taken to ensure that these guidelines can be implemented. Therefore, a VT network will be established covering all areas in Austria, consisting of primary and secondary VT centers. Organizational aspects of an acute VT network are defined and should subsequently be implemented by the participating hospitals. All electrophysiologic centers in Austria that deal with VT ablation are to be integrated into the network in the medium-term. Centers that co-operate in the network are divided into primary and secondary VT centers according to predefined criteria.

Impact of electric cardioversion on platelet activation

Introduction

Atrial fibrillation (AF) comes along with high risk of stroke. This risk continues even after re-establishing sinus rhythm with cardioversion. Aim of this study is to evaluate the contribution of electric cardioversion (EC) to platelet activation and procoagulatory tendency.

Methods

Extent of platelet activation before and after electric cardioversion was quantified using flow cytometry, impedance aggregation measurements with Multiplate®, and quantification of serum levels of platelet factor 4 (PF4) and ß-thromboglobulin (ß-TG) in patients with AF (N = 10).

Results

No significant differences were observed in any of the measured parameters comparing the values from before and after cardioversion. Geometric means of P-selectin expression and integrin αIIbβ3 activation were 0.27 (+/- 0.07) and 2.30 (+/- 2.61) before EC and 0.28 (+/- 0.17) and 1.67 (+/- 1.82) after EC. Levels of ß-TG were 110.11 ng/ml (+/- 3.78) before and 110.51 ng/ml (+/- 2.56) after EC, levels of PF4 were 35.64 ng/ml (+/- 12.94) before and 32.40 ng/ml (+/- 4.95) after EC. Platelet aggregation triggered with adenosine diphosphate (ADP), arachidonic acid, collagen, Ristocetin, or thrombin receptor activating peptide (TRAP) revealed results within the normally expected ranges without significant changes before and after EC.

Discussion

Electric cardioversion has no influence on platelet activation markers which is in agreement with other studies reporting electrical cardioversion to be safe.

No antiarrhythmic effect of direct oral anticoagulants versus vitamin K antagonists in paroxysmal atrial fibrillation patients undergoing catheter ablation

INTRODUCTION

Direct oral anticoagulants (DOACs) are superior to vitamin K antagonists (VKAs) for the prevention of stroke in atrial fibrillation (AF) patients with elevated stroke risk. Possible antiarrhythmic effects of DOACs have been discussed. We analyzed impact of DOAC treatment on recurrence-free survival after AF catheter ablation.

METHODS

Two-hundred and thirty-nine consecutive patients (median age 57 [IQR 48-64] years, 26.4% female) undergoing ablation for paroxysmal AF were included into this study. 68.6% of them received DOACs (DOAC group), 31.4% VKA (VKA group). The primary outcome was arrhythmia-free one-year survival.

RESULTS

DOAC patients had lower BMI, shorter history of AF, less arterial hypertension, less vascular disease, less use of antiarrhythmics and consequently lower CHA₂DS₂-VASc and HAS-BLED Scores. There was no difference in arrhythmia-free survival between DOAC and VKA groups (DOAC: 86.6%, VKA: 76.7%, p = 0.286).

CONCLUSIONS

Despite baseline characteristics favouring a better outcome of DOAC patients, arrhythmia-free survival was similar in both groups. Consequently, DOAC treatment did not have clinically relevant antiarrhythmic properties in these patients.

MIR1183 as a new tissue biomarker with triggered acute response and upregulation in chronic atrial and ventricular remodeling

Background and purpose

Cardiac remodeling can be caused by a variety of insults linked to either stretch or tachycardia as a triggering mechanism. We aimed to investigate similarities and differences of the transcriptomic profiles in response to either acute stretch or tachycardia in isolated human atrial myocardium. In addition, we tested the highest acutely regulated target for its chronic regulation in human tissue with atrial or ventricular cardiac remodeling.

Methods

For acute trigger testing we applied either stretch (high pre- and afterload) or sustained tachycardia (2.5 Hz) for 6 hours in isolated atrial human trabeculae from cardiac surgery patients (all in sinus rhythm, SR). We performed gene expression profiling by RNA microarrays (n=5 per group) as a remodeling readout. For chronic regulation we performed qPCR of selected genes of interest in right atrial appendage tissue obtained from cardiac surgery patients with persistent atrial fibrillation compared to control patients with SR (n=6 per group), and also in ventricular tissue samples from failing hearts (from transplanted dilative cardiomyopathy patients) or non-failing control hearts (from multi-organ donors denied for transplantation), n=6 per group.

Results

The expression patterns of stretch and tachycardia were largely independent with 1305 transcripts regulated solely by stretch and 1837 transcripts by tachycardia with p&lt;0.05. In contrast, the fraction of commonly regulated genes was small (65 transcripts with p&lt;0.05). However, this fraction contained the strongest upregulated transcript, the microRNA precursor gene MIR1183, which was similarly upregulated by both triggers (4.1fold in stretch and 2.7fold in tachycardia, both p&lt;0.05). MIR1183 also showed upregulation in two important chronic remodeling settings: In atrial samples with persistent atrial fibrillation in comparison to sinus rhythm, it was 2.8fold upregulated, and in ventricular samples from dilative cardiomyopathy hearts it was 1.6fold upregulated (p&lt;0.05 for both). A functional role of MIR1183 in remodeling was also suggested by significant downregulation of its predicted downstream target genes ADAM20 and PLA2G7. Our ongoing research aims to confirm upregulation also in the circulating expression levels of the mature form of MIR1183 in human plasma samples in a cohort of atrial fibrillation patients with diseased atria, these findings will also be presented at scientific sessions.

Conclusion

Stretch and tachycardia show distinct transcriptomic signatures in human atrial trabeculae but share the strongest upregulated gene MIR1183 and consistent regulation of its downstream targets. This is present in an acute as well as chronic remodeling setting. Expression levels of MIR1183 might serve as a biomarker for atrial remodeling and to some extend ventricular remodeling and have potential functional significance in cardiac disease.

Funding Acknowledgement

Type of funding source: Public Institution(s). Main funding source(s): Medical University of Graz

The role of stretch, tachycardia and sodium-calcium exchanger in induction of early cardiac remodelling

Stretch and tachycardia are common triggers for cardiac remodelling in various conditions, but a comparative characterization of their role in the excitation‐transcription coupling (ETC) and early regulation of gene expression and structural changes is lacking. Here, we show that stretch and tachycardia directly induced hypertrophy of neonatal rat cardiac myocytes and also of non‐myocytes. Both triggers induced similar patterns of hypertrophy but had largely distinct gene expression profiles. ACTA1 served as good hypertrophy marker upon stretch, while RCAN1 was found increased in response to tachycardia in a rate‐dependent fashion. Mechanistically, several calcium‐handling proteins, including the sodium‐calcium exchanger (NCX), contributed to ETC. Phosphorylation of the calcium/calmodulin‐dependent protein kinase II (CaMKII) was elevated and occurred downstream of NCX activation upon tachycardia, but not stretch. Microarray profiling revealed that stretch and tachycardia regulated around 33% and 20% genes in a NCX‐dependent manner, respectively. In conclusion, our data show that hypertrophy induction by stretch and tachycardia is associated with different gene expression profiles with a significant contribution of the NCX.

Wearable cardioverter-defibrillator as bridging to ICD in pediatric hypertrophic cardiomyopathy with myocardial bridging - a case report

Background

There is only limited experience with wearable cardioverter-defibrillators (WCD) in pediatric patients. We report on the successful application of a WCD in an adolescent patient with hypertrophic cardiomyopathy and myocardial bridging.

Case presentation

A 15-year-old girl presented with a history of recurrent syncope, dyspnea, and vertigo with exercise. Diagnostic work-up revealed non-obstructive hypertrophic cardiomyopathy and signs of myocardial ischemia with exercise. Given this high-risk constellation, the patient was scheduled for prophylactic implantation of an implantable cardioverter-defibrillator (ICD). One month after initial presentation and days prior to the planned ICD implantation, the patient collapsed during an episode of sustained ventricular tachycardia (VT) while running. VT was terminated by WCD shock delivery. Following this event, computerized tomography scan revealed myocardial bridging of the left anterior descending coronary artery causing a 90% stenosis in systole. After coronary surgery, life threatening arrhythmias have not recurred, but due to progressive heart failure, the patient underwent successful heart transplantation after 2 years.

Conclusions

The reported case highlights the importance and applicability of WCDs and the potentially malign nature of myocardial bridging in pediatric high-risk patients.

Blood Biomarkers of Heart Failure and Hypercoagulation to Identify Atrial Fibrillation-Related Stroke

Background and Purpose- Occult atrial fibrillation (AF) causes a relevant proportion of initially cryptogenic stroke (CS), but prolonged rhythm monitoring is difficult to apply to all such patients. We hypothesized that blood biomarkers indicating heart failure (NT-proBNP [N-terminal pro-brain natriuretic peptide]) and hypercoagulability (D-dimer, AT-III [antithrombin-III]) were associated with AF-related stroke and could serve to predict the likelihood of AF detection in CS patients early on. Methods- Over a 1-year period, we prospectively applied a defined etiologic work-up to all ischemic stroke patients admitted to our stroke unit. If no clear stroke cause was detected (CS), patients underwent extended in-hospital cardiac rhythm monitoring (≥72 hours). Blood to determine biomarker levels was drawn within 24 hours after admission. Results- Of 429 patients, 103 had AF-related stroke. Compared with noncardiac stroke patients (n=171), they had higher NT-proBNP (1867 versus 263 pg/ml) and D-dimer levels (1.1 versus 0.6 µg/ml), and lower AT-III concentration (89% versus 94%). NT-proBNP ≥505 pg/ml distinguished AF-related from noncardiac stroke with a sensitivity of 93% and a specificity of 72%. D-dimer and AT-III cutoffs had lower sensitivities (61% and 53%) and specificities (58% and 69%) for AF-related stroke. Of all initially 143 CS patients, 14 were diagnosed with AF during in-hospital monitoring. The preidentified NT-proBNP cutoff ≥505 pg/ml correctly predicted AF in 12 of them (86%, negative predictive value: 98%), while D-dimer and AT-III cutoffs were noncontributory. Conclusions- This study supports the association of NT-proBNP and to a lesser extent of hypercoagulation markers with AF-related stroke. NT-proBNP seems helpful in selecting CS patients for immediate extended cardiac rhythm monitoring to detect occult AF whereby levels <505 pg/ml seem to have a high-negative predictive value.

Is there a difference in rhythm outcome between patients undergoing first line versus second line paroxysmal atrial fibrillation ablation?

BACKGROUND

Catheter ablation of atrial fibrillation (AF) is an established second line therapy for patients with symptomatic paroxysmal AF (PAF) and may be considered as a first line therapy in selected patients who are highly symptomatic, considering patient choice, benefit, and risk, according to recent guidelines. Our study investigated whether a first line vs. second line ablation approach may result in improved sinus rhythm maintenance after ablation.

METHODS

A total of 153 patients undergoing pulmonary vein isolation for PAF were included in the study (age 55±12 years, 29% female). Seventy-nine patients underwent first line AF ablation and 74 patients underwent second line AF ablation after failed antiarrhythmic drug therapy. There was no significant difference in baseline characteristics such as age, history of AF, left atrial size or LVEF between groups. Success was defined as atrial tachyarrhythmia free survival during a 12-month follow-up by means of serial ECG Holter monitoring.

RESULTS

There was no significant difference in cumulative arrhythmia-free survival between those patients who received AF ablation as a first or second line therapy. Single procedure success was 78% in the first line group vs. 81% in the second line group; multiple procedure success was 90 vs. 91%, (n.s.). Complication rate was 1.3% vs. 1.4% (n.s.).

CONCLUSION

Success of AF ablation did not differ between patients who receive ablation as first vs. second line therapy. Based on these data, a trial of AAD therapy before AF ablation may be justified in most patients with symptomatic PAF eligible for rhythm control.

Crosstalk between FGF23- and angiotensin II-mediated Ca2+ signaling in pathological cardiac hypertrophy

Heart failure (HF) manifestation and progression are driven by systemic activation of neuroendocrine signaling cascades, such as the renin-angiotensin aldosterone system (RAAS). Fibroblast growth factor 23 (FGF23), an endocrine hormone, is linked to HF and cardiovascular mortality. It is also a mediator of left-ventricular hypertrophy (LVH). In vivo, high circulating levels of FGF23 are associated with an altered systemic RAAS response. FGF23 is proposed to trigger pathological signaling mediated by Ca2+-regulated transcriptional pathways. In the present study, we investigated Ca2+-dependent signaling of FGF23 in ventricular cardiomyocytes and its association with angiotensin II (ATII). In neonatal rat ventricular myocytes (NRVMs), both ATII and FGF23 induced hypertrophy as observed by an increase in cell area and hypertrophic gene expression. Furthermore, FGF23 activates nuclear Ca2+-regulated CaMKII-HDAC4 pathway, similar to ATII. In addition to a global increase in cytoplasmic Ca2+, FGF23, like ATII, induced inositol 1, 4, 5-triphosphate (IP3)-induced Ca2+ release from the nucleoplasmic Ca2+ store, associated with cellular hypertrophy. Interestingly, ATII receptor antagonist, losartan, significantly attenuated FGF23-induced changes in Ca2+ homeostasis and cellular hypertrophy suggesting an involvement of ATII receptor-mediated signaling. In addition, application of FGF23 increased intracellular expression of ATII peptide and its secretion in NRVMs, confirming the participation of ATII. In conclusion, FGF23 and ATII share a common mechanism of IP3-nuclear Ca2+-dependent cardiomyocyte hypertrophy. FGF23-mediated cellular hypertrophy is associated with increased production and secretion of ATII by cardiomyocytes. These findings indicate a pathophysiological role of the cellular angiotensin system in FGF23-induced hypertrophy in ventricular cardiomyocytes.

Large-scale genome-wide analysis identifies genetic variants associated with cardiac structure and function

BACKGROUND

Understanding the genetic architecture of cardiac structure and function may help to prevent and treat heart disease. This investigation sought to identify common genetic variations associated with inter-individual variability in cardiac structure and function.

METHODS

A GWAS meta-analysis of echocardiographic traits was performed, including 46,533 individuals from 30 studies (EchoGen consortium). The analysis included 16 traits of left ventricular (LV) structure, and systolic and diastolic function.

RESULTS

The discovery analysis included 21 cohorts for structural and systolic function traits (n = 32,212) and 17 cohorts for diastolic function traits (n = 21,852). Replication was performed in 5 cohorts (n = 14,321) and 6 cohorts (n = 16,308), respectively. Besides 5 previously reported loci, the combined meta-analysis identified 10 additional genome-wide significant SNPs: rs12541595 near MTSS1 and rs10774625 in ATXN2 for LV end-diastolic internal dimension; rs806322 near KCNRG, rs4765663 in CACNA1C, rs6702619 near PALMD, rs7127129 in TMEM16A, rs11207426 near FGGY, rs17608766 in GOSR2, and rs17696696 in CFDP1 for aortic root diameter; and rs12440869 in IQCH for Doppler transmitral A-wave peak velocity. Findings were in part validated in other cohorts and in GWAS of related disease traits. The genetic loci showed associations with putative signaling pathways, and with gene expression in whole blood, monocytes, and myocardial tissue.

CONCLUSION

The additional genetic loci identified in this large meta-analysis of cardiac structure and function provide insights into the underlying genetic architecture of cardiac structure and warrant follow-up in future functional studies.

FUNDING

For detailed information per study, see Acknowledgments.

Effect of high-dose vitamin D3 on hospital length of stay in critically ill patients with vitamin D deficiency: the VITdAL-ICU randomized clinical trial

IMPORTANCE

Low vitamin D status is linked to increased mortality and morbidity in patients who are critically ill. It is unknown if this association is causal.

OBJECTIVE

To investigate whether a vitamin D3 treatment regimen intended to restore and maintain normal vitamin D status over 6 months is of health benefit for patients in ICUs.

DESIGN, SETTING, AND PARTICIPANTS

A randomized double-blind, placebo-controlled, single-center trial, conducted from May 2010 through September 2012 at 5 ICUs that included a medical and surgical population of 492 critically ill adult white patients with vitamin D deficiency (≤20 ng/mL) assigned to receive either vitamin D3 (n = 249) or a placebo (n = 243).

INTERVENTIONS

Vitamin D3 or placebo was given orally or via nasogastric tube once at a dose of 540,000 IU followed by monthly maintenance doses of 90,000 IU for 5 months.

MAIN OUTCOMES AND MEASURES

The primary outcome was hospital length of stay. Secondary outcomes included, among others, length of ICU stay, the percentage of patients with 25-hydroxyvitamin D levels higher than 30 ng/mL at day 7, hospital mortality, and 6-month mortality. A predefined severe vitamin D deficiency (≤12 ng/mL) subgroup analysis was specified before data unblinding and analysis.

RESULTS

A total of 475 patients were included in the final analysis (237 in the vitamin D3 group and 238 in the placebo group). The median (IQR) length of hospital stay was not significantly different between groups (20.1 days [IQR, 11.1-33.3] for vitamin D3 vs 19.3 days [IQR, 11.1-34.9] for placebo; P = .98). Hospital mortality and 6-month mortality were also not significantly different (hospital mortality: 28.3% [95% CI, 22.6%-34.5%] for vitamin D3 vs 35.3% [95% CI, 29.2%-41.7%] for placebo; hazard ratio [HR], 0.81 [95% CI, 0.58-1.11]; P = .18; 6-month mortality: 35.0% [95% CI, 29.0%-41.5%] for vitamin D3 vs 42.9% [95% CI, 36.5%-49.4%] for placebo; HR, 0.78 [95% CI, 0.58-1.04]; P = .09). For the severe vitamin D deficiency subgroup analysis (n = 200), length of hospital stay was not significantly different between the 2 study groups: 20.1 days (IQR, 12.9-39.1) for vitamin D3 vs 19.0 days (IQR, 11.6-33.8) for placebo. Hospital mortality was significantly lower with 28 deaths among 98 patients (28.6% [95% CI, 19.9%-38.6%]) for vitamin D3 compared with 47 deaths among 102 patients (46.1% [95% CI, 36.2%-56.2%]) for placebo (HR, 0.56 [95% CI, 0.35-0.90], P for interaction = .04), but not 6-month mortality (34.7% [95% CI, 25.4%-45.0%] for vitamin D3 vs 50.0% [95% CI, 39.9%-60.1%] for placebo; HR, 0.60 [95% CI, 0.39-0.93], P for interaction = .12).

CONCLUSIONS AND RELEVANCE

Among critically ill patients with vitamin D deficiency, administration of high-dose vitamin D3 compared with placebo did not reduce hospital length of stay, hospital mortality, or 6-month mortality. Lower hospital mortality was observed in the severe vitamin D deficiency subgroup, but this finding should be considered hypothesis generating and requires further study.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT01130181.

Early remodeling of perinuclear Ca2+ stores and nucleoplasmic Ca2+ signaling during the development of hypertrophy and heart failure

BACKGROUND

A hallmark of heart failure is impaired cytoplasmic Ca(2+) handling of cardiomyocytes. It remains unknown whether specific alterations in nuclear Ca(2+) handling via altered excitation-transcription coupling contribute to the development and progression of heart failure.

METHODS AND RESULTS

Using tissue and isolated cardiomyocytes from nonfailing and failing human hearts, as well as mouse and rabbit models of hypertrophy and heart failure, we provide compelling evidence for structural and functional changes of the nuclear envelope and nuclear Ca(2+) handling in cardiomyocytes as remodeling progresses. Increased nuclear size and less frequent intrusions of the nuclear envelope into the nuclear lumen indicated altered nuclear structure that could have functional consequences. In the (peri)nuclear compartment, there was also reduced expression of Ca(2+) pumps and ryanodine receptors, increased expression of inositol-1,4,5-trisphosphate receptors, and differential orientation among these Ca(2+) transporters. These changes were associated with altered nucleoplasmic Ca(2+) handling in cardiomyocytes from hypertrophied and failing hearts, reflected as increased diastolic Ca(2+) levels with diminished and prolonged nuclear Ca(2+) transients and slowed intranuclear Ca(2+) diffusion. Altered nucleoplasmic Ca(2+) levels were translated to higher activation of nuclear Ca(2+)/calmodulin-dependent protein kinase II and nuclear export of histone deacetylases. Importantly, the nuclear Ca(2+) alterations occurred early during hypertrophy and preceded the cytoplasmic Ca(2+) changes that are typical of heart failure.

CONCLUSIONS

During cardiac remodeling, early changes of cardiomyocyte nuclei cause altered nuclear Ca(2+) signaling implicated in hypertrophic gene program activation. Normalization of nuclear Ca(2+) regulation may therefore be a novel therapeutic approach to prevent adverse cardiac remodeling.

Subclinical abnormalities in sarcoplasmic reticulum Ca(2+) release promote eccentric myocardial remodeling and pump failure death in response to pressure overload

OBJECTIVES

This study sought to explore whether subclinical alterations of sarcoplasmic reticulum (SR) Ca(2+) release through cardiac ryanodine receptors (RyR2) aggravate cardiac remodeling in mice carrying a human RyR2(R4496C+/-) gain-of-function mutation in response to pressure overload.

BACKGROUND

RyR2 dysfunction causes increased diastolic SR Ca(2+) release associated with arrhythmias and contractile dysfunction in inherited and acquired cardiac diseases, such as catecholaminergic polymorphic ventricular tachycardia and heart failure (HF).

METHODS

Functional and structural properties of wild-type and catecholaminergic polymorphic ventricular tachycardia-associated RyR2(R4496C+/-) hearts were characterized under conditions of pressure overload induced by transverse aortic constriction (TAC).

RESULTS

Wild-type and RyR2(R4496C+/-) hearts had comparable structural and functional properties at baseline. After TAC, RyR2(R4496C+/-) hearts responded with eccentric hypertrophy, substantial fibrosis, ventricular dilation, and reduced fractional shortening, ultimately resulting in overt HF. RyR2(R4496C+/-)-TAC cardiomyocytes showed increased incidence of spontaneous SR Ca(2+) release events, reduced Ca(2+) transient peak amplitude, and SR Ca(2+) content as well as reduced SR Ca(2+)-ATPase 2a and increased Na(+)/Ca(2+)-exchanger protein expression. HF phenotype in RyR2(R4496C+/-)-TAC mice was associated with increased mortality due to pump failure but not tachyarrhythmic events. RyR2-stabilizer K201 markedly reduced Ca(2+) spark frequency in RyR2(R4496C+/-)-TAC cardiomyocytes. Mini-osmotic pump infusion of K201 prevented deleterious remodeling and improved survival in RyR2(R4496C+/-)-TAC mice.

CONCLUSIONS

The combination of subclinical congenital alteration of SR Ca(2+) release and pressure overload promoted eccentric remodeling and HF death in RyR2(R4496C+/-) mice, and pharmacological RyR2 stabilization prevented this deleterious interaction. These findings suggest potential clinical relevance for patients with acquired or inherited gain-of-function of RyR2-mediated SR Ca(2+) release.

Spongious Hypertrophic Cardiomyopathy in Patients With Mutations in the Four-and-a-Half LIM Domain 1 Gene

Background—

X-linked myopathy with postural muscle atrophy is a novel X-linked myopathy caused by mutations in the four-and-a-half LIM domain 1 gene (FHL1). Cardiac involvement was suspected in initial publications. We now systematically analyzed the association of the FHL1 genotype with the cardiac phenotype to establish a potential cardiac involvement in the disease.

Methods and Results—

Seventeen male patients and 23 female mutation carriers were compared with healthy controls. Every patient underwent a comprehensive clinical and cardiovascular workup. ECG abnormalities occurred frequently in affected males and were less frequent in heterozygous females. Both male and female mutation carriers had increased myocardial mass (affected males=115.1±25.3 g/m 2 ; heterozygous females=95.1±19.6 g/m 2 ; controls=89.0±15.6 g/m 2 and 72.6±12.6 g/m 2 ; respectively) with increased wall thickness (typically midventricular and apical segments) mainly in affected males. Longitudinal systolic function was reduced in affected males (radial systolic strain: affected males=24.6±11.8%; male controls=43.2±14.8%; P =0.002). Diastolic dysfunction occurred in both affected males and heterozygous females. Cardiac MRI revealed a morphological hallmark of X-linked myopathy with postural muscle atrophy; a characteristic spongious structure and replacement fibrosis indicated by late enhancement could be detected in most affected males. X-linked myopathy with postural muscle atrophy was associated with reduced exercise capacity in affected males but not in heterozygous female mutation carriers.

Conclusions—

X-linked myopathy with postural muscle atrophy patients consistently showed electrical, functional, and characteristic morphological cardiac abnormalities that translate into reduced exercise capacity. Reduced systolic and diastolic function is associated with a novel type of spongious hypertrophic cardiomyopathy. An unexpected finding was that some cardiac abnormalities were also present in heterozygous female mutation carriers.

Transcription factor GATA4 is activated but not required for insulin-like growth factor 1 (IGF1)-induced cardiac hypertrophy

Insulin-like growth factor 1 (IGF1) promotes a physiological type of cardiac hypertrophy and has therapeutic effects in heart disease. Here, we report the relationship of IGF1 to GATA4, an essential transcription factor in cardiac hypertrophy and cell survival. In cultured neonatal rat ventricular myocytes, we compared the responses to IGF1 (10 nmol/liter) and phenylephrine (PE, 20 μmol/liter), a known GATA4 activator, in concentrations promoting a similar extent of hypertrophy. IGF1 and PE both increased nuclear accumulation of GATA4 and phosphorylation at Ser(105) (PE, 2.4-fold; IGF1, 1.8-fold; both, p < 0.05) and increased GATA4 DNA binding activity as indicated by ELISA and by chromatin IP of selected promoters. Although IGF1 and PE each activated GATA4 to the same degree, GATA4 knockdown by RNA interference only blocked hypertrophy by PE but not by IGF1. PE induction of a panel of GATA4 target genes (Nppa, Nppb, Tnni3, Myl1, and Acta1) was inhibited by GATA4 knockdown. In contrast, IGF1 regulated only Acta1 in a GATA4-dependent fashion. Consistent with the in vitro findings, Gata4 haploinsufficiency in mice did not alter cardiac structure, hyperdynamic function, or antifibrotic effects induced by myocardial overexpression of the IGF1 receptor. Our data indicate that GATA4 is activated by the IGF1 pathway, but although it is required for responses to pathological stimuli, it is not necessary for the effects of IGF1 on cardiac structure and function.

Functional effects of glucose transporters in human ventricular myocardium

AIMS

Insulin-dependent positive inotropic effects (PIE) are partially Ca(2+) independent. This mechanism is potentially glucose dependent. In contrast to most animal species, human myocardium expresses high levels of sodium-glucose-transporter-1 (SGLT-1) mRNA besides the common glucose-transporters-1 and -4 (GLUT1, GLUT4).

METHODS AND RESULTS

We used ventricular myocardium from 61 end-stage failing human hearts (ischaemic cardiomyopathy, ICM and dilated cardiomyopathy, DCM) and 13 non-failing donor hearts. The effect of insulin on isometric twitch force was examined with or without blocking of PI3-kinase, GLUT4-translocation, or SGLT-1. Substrate-dependent (glucose vs. pyruvate vs. palmitoyl-carnitine) effects were tested in atrial myocardium. mRNA expression of glucose transporters was analysed. Insulin increased developed force by 122 + or - 7.4, 121.7 + or - 2.5, and 134.1 + or - 5.7% in non-failing, DCM, and ICM (P < 0.05 vs. DCM), respectively. Positive inotropic effect was partially blunted by inhibition of PI-3-kinase, GLUT4, or SGLT1. Combined inhibition of PI3-kinase and glucose-transport completely abolished PIE. Positive inotropic effect was significantly stronger in glucose-containing solution compared with pyruvate or palmitoyl-carnitine containing. mRNA expression showed only a tendency towards elevated GLUT4-expression in ICM.

CONCLUSIONS

Positive inotropic effect of insulin is pronounced in ICM, but underlying mechanisms are unaltered. The Ca(2+)-independent PIE of insulin is mediated via glucose-transporters. Together with the Ca(2+)-dependent PI-3-kinase mediated pathway, it is responsible for the entire PIE. Substrate-dependency affirms a glucose-dependent part of the PIE.

Heart failure-associated changes in RNA splicing of sarcomere genes

BACKGROUND

Alternative mRNA splicing is an important mechanism for regulation of gene expression. Altered mRNA splicing occurs in association with several types of cancer, and a small number of disease-associated changes in splicing have been reported in heart disease. However, genome-wide approaches have not been used to study splicing changes in heart disease. We hypothesized that mRNA splicing is different in diseased hearts compared with control hearts.

METHODS AND RESULTS

We used the Affymetrix Exon array to globally evaluate mRNA splicing in left ventricular myocardial RNA from controls (n=15) and patients with ischemic cardiomyopathy (n=15). We observed a broad and significant decrease in mRNA splicing efficiency in heart failure, which affected some introns to a greater extent than others. The profile of mRNA splicing separately clustered ischemic cardiomyopathy and control samples, suggesting distinct changes in mRNA splicing between groups. Reverse transcription-polymerase chain reaction validated 9 previously unreported alternative splicing events. Furthermore, we demonstrated that splicing of 4 key sarcomere genes, cardiac troponin T (TNNT2), cardiac troponin I (TNNI3), myosin heavy chain 7 (MYH7), and filamin C, gamma (FLNC), was significantly altered in ischemic cardiomyopathy and in dilated cardiomyopathy and aortic stenosis. In aortic stenosis samples, these differences preceded the onset of heart failure. Remarkably, the ratio of minor to major splice variants of TNNT2, MYH7, and FLNC classified independent test samples as control or disease with >98% accuracy.

CONCLUSIONS

Our data indicate that mRNA splicing is broadly altered in human heart disease and that patterns of aberrant RNA splicing accurately assign samples to control or disease classes.

Long-term cardiac-targeted RNA interference for the treatment of heart failure restores cardiac function and reduces pathological hypertrophy

BACKGROUND

RNA interference (RNAi) has the potential to be a novel therapeutic strategy in diverse areas of medicine. Here, we report on targeted RNAi for the treatment of heart failure, an important disorder in humans that results from multiple causes. Successful treatment of heart failure is demonstrated in a rat model of transaortic banding by RNAi targeting of phospholamban, a key regulator of cardiac Ca(2+) homeostasis. Whereas gene therapy rests on recombinant protein expression as its basic principle, RNAi therapy uses regulatory RNAs to achieve its effect.

METHODS AND RESULTS

We describe structural requirements to obtain high RNAi activity from adenoviral and adeno-associated virus (AAV9) vectors and show that an adenoviral short hairpin RNA vector (AdV-shRNA) silenced phospholamban in cardiomyocytes (primary neonatal rat cardiomyocytes) and improved hemodynamics in heart-failure rats 1 month after aortic root injection. For simplified long-term therapy, we developed a dimeric cardiotropic adeno-associated virus vector (rAAV9-shPLB) to deliver RNAi activity to the heart via intravenous injection. Cardiac phospholamban protein was reduced to 25%, and suppression of sacroplasmic reticulum Ca(2+) ATPase in the HF groups was rescued. In contrast to traditional vectors, rAAV9 showed high affinity for myocardium but low affinity for liver and other organs. rAAV9-shPLB therapy restored diastolic (left ventricular end-diastolic pressure, dp/dt(min), and tau) and systolic (fractional shortening) functional parameters to normal ranges. The massive cardiac dilation was normalized, and cardiac hypertrophy, cardiomyocyte diameter, and cardiac fibrosis were reduced significantly. Importantly, no evidence was found of microRNA deregulation or hepatotoxicity during these RNAi therapies.

CONCLUSIONS

Our data show for the first time the high efficacy of an RNAi therapeutic strategy in a cardiac disease.

Atrial myocardium is the predominant inotropic target of adrenomedullin in the human heart

Adrenomedullin (ADM) is an endogenous peptide with favorable hemodynamic effects in vivo. In this study, we characterized the direct functional effects of ADM in isolated preparations from human atria and ventricles. In electrically stimulated human nonfailing right atrial trabeculae, ADM (0.0001–1 μmol/l) increased force of contraction in a concentration-dependent manner, with a maximal increase by 35 ± 8% (at 1 μmol/l; P < 0.05). The positive inotropic effect was accompanied by a disproportionate increase in calcium transients assessed by aequorin light emission [by 76 ± 20%; force/light ratio (ΔF/ΔL) 0.58 ± 0.15]. In contrast, elevation of extracellular calcium (from 2.5 to 3.2 mmol/l) proportionally increased force and aequorin light emission (ΔF/ΔL 1.0 ± 0.1; P < 0.05 vs. ADM). Consistent with a cAMP-dependent mechanism, ADM (1 μmol/l) increased atrial cAMP levels by 90 ± 12%, and its inotropic effects could be blocked by the protein kinase A (PKA) inhibitor H-89. ADM also exerted positive inotropic effects in failing atrial myocardium and in nonfailing and failing ventricular myocardium. The inotropic response was significantly weaker in ventricular vs. atrial myocardium and in failing vs. nonfailing myocardium. In conclusion, ADM exerts Ca2+-dependent positive inotropic effects in human atrial and less-pronounced effects in ventricular myocardium. The inotropic effects are related to increased cAMP levels and stimulation of PKA. In heart failure, the responsiveness to ADM is reduced in atria and ventricles.

Altered microRNA expression in human heart disease

MicroRNAs are recently discovered regulators of gene expression and are becoming increasingly recognized as important regulators of heart function. Genome-wide profiling of microRNAs in human heart failure has not been reported previously. We measured expression of 428 microRNAs in 67 human left ventricular samples belonging to control (n = 10), ischemic cardiomyopathy (ICM, n = 19), dilated cardiomyopathy (DCM, n = 25), or aortic stenosis (AS, n = 13) diagnostic groups. miRNA expression between disease and control groups was compared by ANOVA with Dunnett's post hoc test. We controlled for multiple testing by estimating the false discovery rate. Out of 428 microRNAs measured, 87 were confidently detected; 43 were differentially expressed in at least one disease group. In supervised clustering, microRNA expression profiles correctly grouped samples by their clinical diagnosis, indicating that microRNA expression profiles are distinct between diagnostic groups. This was further supported by class prediction approaches, in which the class (control, ICM, DCM, AS) predicted by a microRNA-based classifier matched the clinical diagnosis 69% of the time (P < 0.001). These data show that expression of many microRNAs is altered in heart disease and that different types of heart disease are associated with distinct changes in microRNA expression. These data will guide further studies of the contribution of microRNAs to heart disease pathogenesis.

Uncoupling protein 2 modulates cell viability in adult rat cardiomyocytes

Uncoupling protein 2 (UCP2) is an inner mitochondrial membrane proton carrier that uncouples ATP synthesis. The aim of this study was to determine whether UCP2 plays a role in survival of adult rat cardiac myocytes. We first studied the effects of UCP2 overexpression in vitro. Overexpression of UCP2 in primary cardiomyocytes led to a significant decline in ATP level and the development of acidosis but had no observable effect on cell survival. When cardiomyocytes were challenged with hypoxia-reoxygenation, cells overexpressing UCP2 survived significantly less compared with control. This finding was associated with upregulation of proapoptotic protein Bcl-2 and 19-kDa interacting protein 3 (BNIP3). Furthermore, UCP2 short interfering RNA prevented both the increase in cell death and BNIP3 expression. To examine the in vivo role of UCP2 in the heart, we used the Dahl salt-sensitive rat heart-failure model. Northern blot analysis revealed that UCP2 mRNA level was significantly upregulated in rat heart failure along with BNIP3 protein level. In conclusion, UCP2 increases sensitivity of adult rat cardiac myocytes to hypoxia-reoxygenation by way of ATP depletion and acidosis, which in turn causes accumulation of prodeath protein BNIP3.

Dilated cardiomyopathy resulting from high-level myocardial expression of Cre-recombinase

BACKGROUND

Conditional gene inactivation in mice using the bacteriophage P1 Cre-loxP recombination system requires transgenic expression of Cre-recombinase driven by a tissue-specific or inducible promoter.

METHODS AND RESULTS

Using the cardiac alpha-myosin-heavy-chain promoter, the most commonly used myocardial-specific transgenic promoter, we created transgenic mice expressing Cre-recombinase in the heart. Seven transgenic lines developed dilated cardiomyopathy and premature death from congestive heart failure. One founder line that survived long enough to propagate had extremely high-level Cre recombinase expression. Transgenic lines that expressed low levels remained healthy. The high-expressing strain developed heart failure over a very predictable and reproducible time course. Detailed examination of the high-expressing strain revealed important molecular, cellular, and pharmacologic hallmarks of cardiomyopathy. First, "fetal genes" such as atrial natriuretic factor and brain natriuretic protein were expressed, a marker of pathologic cardiac hypertrophy and heart failure. Second, an increased incidence of cardiac myocyte apoptosis was present. Third, treatment of mice with captopril or metoprolol, drugs that delay the progression of heart failure, improved survival.

CONCLUSION

Cre-recombinase when expressed at high levels may cause organ dysfunction, which could be mistaken for an effect of conditional gene inactivation. In addition, the stereotypic cardiomyopathy and disease progression in the characterized, high-expressing transgenic strain suggests its utility as a model to study the effects of pharmacologic or genetic manipulations in heart failure.

Gata4 is required for maintenance of postnatal cardiac function and protection from pressure overload-induced heart failure

An important event in the pathogenesis of heart failure is the development of pathological cardiac hypertrophy. In cultured cardiomyocytes, the transcription factor Gata4 is required for agonist-induced hypertrophy. We hypothesized that, in the intact organism, Gata4 is an important regulator of postnatal heart function and of the hypertrophic response of the heart to pathological stress. To test this hypothesis, we studied mice heterozygous for deletion of the second exon of Gata4 (G4D). At baseline, G4D mice had mild systolic and diastolic dysfunction associated with reduced heart weight and decreased cardiomyocyte number. After transverse aortic constriction (TAC), G4D mice developed overt heart failure and eccentric cardiac hypertrophy, associated with significantly increased fibrosis and cardiomyocyte apoptosis. Inhibition of apoptosis by overexpression of the insulin-like growth factor 1 receptor prevented TAC-induced heart failure in G4D mice. Unlike WT-TAC controls, G4D-TAC cardiomyocytes hypertrophied by increasing in length more than width. Gene expression profiling revealed up-regulation of genes associated with apoptosis and fibrosis, including members of the TGF-beta pathway. Our data demonstrate that Gata4 is essential for cardiac function in the postnatal heart. After pressure overload, Gata4 regulates the pattern of cardiomyocyte hypertrophy and protects the heart from load-induced failure.

Overexpression of HAX-1 Protects Cardiac Myocytes From Apoptosis Through Caspase-9 Inhibition

Caspase-9 is a critical regulator of mitochondria-mediated apoptosis. We found that adult cardiac myocytes, but not nonmyocytes, have high caspase-9 expression, and exhibit relative resistance to caspase-9–induced cell death. Thus, we hypothesized that cardiac myocytes possess factors that resist apoptosis. Through a yeast two-hybrid screening of adult human heart cDNA library, we identified HS-1 associated protein-1 (HAX-1), a 35-kD BH-domain containing protein localized to the mitochondria as one of the molecules that interacts with caspase-9. Recombinant HAX-1 protein inhibited caspase-9 processing in a dose-dependent manner in a cell-free caspase activation assay. Overexpression of HAX-1 in adult cardiac myocytes conferred 30% protection from apoptosis as compared with the control. Suppression of HAX-1 expression using siRNA-HAX-1 resulted in significant cell death in adult cardiac myocytes, suggesting the importance of HAX-1 in cardiac myocyte resistance to apoptotic stimulation. On apoptotic stimulation, some caspase-9 translocated to the mitochondria and co-localized with HAX-1, confirming the spatial proximity of caspase-9 and HAX-1. In summary, HAX-1 is a newly identified anti-apoptotic factor and its mechanism of action is through caspase-9 inhibition.

Transcription factor gata4 regulates cardiac BCL2 gene expression in vitro and in vivo

The transcription factor GATA-4 protects cardiomyocytes against doxorubicin-induced cardiotoxicity. Here, we report the identification of Bcl2 as a direct target gene of GATA4 that may mediate the prosurvival function of GATA4 in cardiomyocytes. Bcl2 transcript and protein levels were reduced by doxorubicin in neonatal rat ventricular cardiomyocytes (NRVC) and in mouse heart as determined by RT-PCR and Western blot analysis. The reduction in Bcl2 was prevented by overexpression of GATA4 in NRVC and in transgenic mouse heart. Also, expression of GATA4 increased baseline Bcl2 levels by 30% in NRVC and 2.7-fold in transgenic heart, indicating the sufficiency of GATA4 to up-regulate Bcl2 gene expression. GATA4 knockdown by siRNA reduced Bcl2 levels by 48% in NRVC, suggesting that GATA4 is required for Bcl2 constitutive gene expression. Transfection of HEK cells with GATA4 plasmids activated Bcl2 promoter and elevated Bcl2 protein levels. Deletion and mutagenesis analysis revealed that a consensus GATA motif at base -266 on the promoter conserved across multiple species is partially responsible for the promoter activity. Electrophoretic mobility shift and chromatin immunoprecipitation assays demonstrate that GATA4 directly bound to this GATA site. Together, these results indicate that GATA4 positively regulates cardiac Bcl2 gene expression in vitro and in vivo.

The insulin-like growth factor 1 receptor induces physiological heart growth via the phosphoinositide 3-kinase(p110alpha) pathway

Insulin-like growth factor 1 (IGF1) was considered a potential candidate for the treatment of heart failure. However, some animal studies and clinical trials have questioned whether elevating IGF1 chronically is beneficial. Secondary effects of increased serum IGF1 levels on other tissues may explain these unfavorable results. The aim of the current study was to examine the role of IGF1 in cardiac myocytes in the absence of secondary effects, and to elucidate downstream signaling pathways and transcriptional regulatory effects of the IGF1 receptor (IGF1R). Transgenic mice overexpressing IGF1R in the heart displayed cardiac hypertrophy, which was the result of an increase in myocyte size, and there was no evidence of histopathology. IGF1R transgenics also displayed enhanced systolic function at 3 months of age, and this was maintained at 12-16 months of age. The phosphoinositide 3-kinase (PI3K)-Akt-p70S6K1 pathway was significantly activated in hearts from IGF1R transgenics. Cardiac hypertrophy induced by overexpression of IGF1R was completely blocked by a dominant negative PI3K(p110alpha) mutant, suggesting IGF1R promotes compensated cardiac hypertrophy in a PI3K(p110alpha)-dependent manner. This study suggests that targeting the cardiac IGF1R-PI3K(p110alpha) pathway could be a potential therapeutic strategy for the treatment of heart failure.

Influence of mild hypothermia on myocardial contractility and circulatory function

Myocardial contractility depends on temperature. We investigated the influence of mild hypothermia (37-31 degrees C) on isometric twitch force, sarcoplasmic reticulum (SR) Ca2+-content and intracellular Ca2+-transients in ventricular muscle strips from human and porcine myocardium, and on in vivo hemodynamic parameters in pigs. In vitro experiments: muscle strips from 5 nonfailing human and 8 pig hearts. Electrical stimulation (1 Hz), simultaneous recording of isometric force and rapid cooling contractures (RCCs) as an indicator of SR Ca2+-content, or intracellular Ca2+-transients (aequorin method). In vivo experiments: 8 pigs were monitored with Millar-Tip (left ventricle) and Swan-Ganz catheter (pulmonary artery). Hemodynamic parameters were assessed at baseline conditions (37 degrees C), and after stepwise cooling on cardiopulmonary bypass to 35, 33 and 31 degrees C. Hypothermia increased isometric twitch force significantly by 91 +/- 16 % in human and by 50 +/- 9 % in pig myocardium (31 vs. 37 degrees C; p < 0.05, respectively). RCCs or aequorin light emission did not change significantly. In anesthetized pigs, mild hypothermia resulted in an increase in hemodynamic parameters of myocardial contractility. While heart rate decreased from 111 +/- 3 to 73 +/- 1 min(-1), cardiac output increased from 2.4 +/- 0.1 to 3.1 +/- 0.31/min, and stroke volume increased from 21 +/- 1 to 41 +/- 3 ml. +dP/dtmax increased by 25 +/- 8% (37 vs. 31 degrees C; p < 0.05 for all values). Systemic and pulmonary vascular resistance did not change significantly during cooling. Mild hypothermia exerts significant positive inotropic effects in human and porcine myocardium without increasing intracellular Ca2+-transients or SR Ca2+-content. These effects translate into improved hemodynamic parameters of left ventricular function.