Eya4 Induces Hypertrophy via Regulation of p27kip1

BACKGROUND

E193, a heterozygous truncating mutation in the human transcription cofactor Eyes absent 4 (Eya4), causes hearing impairment followed by dilative cardiomyopathy.

METHODS AND RESULTS

In this study, we first show Eya4 and E193 alter the expression of p27(kip1) in vitro, suggesting Eya4 is a negative regulator of p27. Next, we generated transgenic mice with cardiac-specific overexpression of Eya4 or E193. Luciferase and chromatin immunoprecipitation assays confirmed Eya4 and E193 bind and regulate p27 expression in a contradictory manner. Activity and phosphorylation status of the downstream molecules casein kinase-2α and histone deacetylase 2 were significantly elevated in Eya4- but significantly reduced in E193-overexpressing animals compared with wild-type littermates. Magnetic resonance imaging and hemodynamic analysis indicate Eya4-overexpression results in an age-dependent development of hypertrophy already under baseline conditions with no obvious functional effects, whereas E193 animals develop onset of dilative cardiomyopathy as seen in human E193 patients. Both cardiac phenotypes were aggravated on pressure overload. Finally, we identified a new heterozygous truncating Eya4 mutation, E215, which leads to similar clinical features of disease and a stable myocardial expression of the mutant protein as seen with E193.

CONCLUSIONS

Our results implicate Eya4/Six1 regulates normal cardiac function via p27/casein kinase-2α/histone deacetylase 2 and indicate that mutations within this transcriptional complex and signaling cascade lead to the development of cardiomyopathy.

Abstract 271: Nos1ap Alters Qtc Intervals Upon Overexpression in Mice

Rationale: The QT interval duration (QTc) reflects cardiac depolarization. It may predispose individuals to ventricular tachycardia and sudden cardiac death if prolonged (long QTc), shortened (short QTc) or otherwise unregularly. Whole-genome association studies have linked genetic variations in the neuronal nitric oxide synthase adapter protein NOS1AP to variations in QTc intervals and sudden cardiac death.

Hypothesis: We hypothesize NOS1AP functions as an L-type-Ca2+ channel modulator via its interaction with the neuronal nitric oxide synthase NOS1. Therefore, alterations in myocardial NOS1AP expression should temper with QTc intervals and increase susceptibility to rhythm disorders.

Methods and results: We generated conditional double transgenic mice by crossbreeding pTRE-6xHN-Nos1AP animals with α-MHC-tTA mice; NOS1AP expression is therefore restricted to cardiomyocytes and under control of doxycycline (Tet-Off system). Double transgenic animals were investigated with the main focus upon electrical alterations. Heart rates were similar in NOS1AP overexpressing and non-induced animals. Atrial programmed stimulation repeatedly caused atrial tachycardia, while ventricular programmed stimulation caused VT in NOS1AP overexpressing mice. There was a clear decrease of QTc intervals in NOS1AP overexpressing mice paralleld by a significantly reduced survival (only 56% after 12 weeks vs 100% in non-induced mice. Induced QTc alterations and accompanied deaths subsided upon readministration of doxycycline.

We also investigated the functional effect of the human SNP rs16847548 (T/C). We found that this SNP decreased NOS1AP transcriptional activity in vitro and therefore suggest this leads to a decrease in NOS1AP expression in humans.

Conclusion: Myocardial overexpression of NOS1AP leads to short QTc syndrome with increased susceptibility to atrial and ventricular rhythm disorders and cardiac death. SNP rs16847548 in NOS1AP resulted in less NOS1AP promoter activity in vitro which could explain the alteration in QTc intervals.

In summary, not only mutations in ion channels themselves but also genetic alterations in the expression of ion channel modulators such as NOS1AP, have an impact on QTc intervals.

Abstract 270: The Eya4/six1 Signalling Cascade is Activated in Acquired Heart Disease

Rationale: We previously identified a mutation in the human transcriptional cofactor Eya4 as cause of familial dilated cardiomyopathy (DCM). We now provide evidence that the Eya4/Six1 signalling cascade also is crucial in acquired heart disease.

Hypothesis: We hypothesize that the transcriptional complex Eya4/Six1 regulates targets relevant in normal cardiac function. We speculate it, amongst others, regulates expression of p27kip1, a known inhibitor of hypertrophy in adult cardiomyocytes, upon hypertrophic stimuli.

Methods and results: We first examined the correlation of Eya4 and p27 in regards to phosphorylation and cellular distribution in failing and normal human hearts. Immunhistology revealed Eya4 is mainly distributed in the cytoplasm while p27 predominantly resides in the nucleus of healthy myocardial tissue. In sections of failing human hearts, Eya4 accumulated in the perinuclear and nuclear region; nuclear p27 levels were significantly diminished, phosphorylated p27 was evenly distributed in the cytoplasm. In a murine model of MI, IH showed Eya4 translocates in a time-dependent manner. WB analyses for p27 showed an age dependent decrease in p27 protein levels upon MI compared to control littermates. We generated transgenic mice with constitutive myocardial overexpression of Eya4 and E193. As judged by MRI, hemodynamic and morphometric analysis both transgenic mouse models developed cardiac phenotypes compared to age-matched wildtype littermates already under basal conditions in an age dependent manner. p27 expression and downstream factors were also altered in both transgenic lines as a result of Eya4, and accordingly, E193 overexpression. In summary, we provide evidence that the Eya4/Six1 signalling cascade is not only relevant in a rare version of heritable DCM but also in more common forms of acquired heart disease. Eya4/Six1 seems to regulate p27, which was shown to be an important regulator of cardiac physiology in postmitotic cardiomyocytes.

Magnetic resonance imaging safety in pacemaker and implantable cardioverter defibrillator patients: how far have we come?

Magnetic resonance imaging (MRI) has long been regarded a general contraindication in patients with cardiovascular implanted electronic devices such as cardiac pacemakers or cardioverter defibrillators (ICDs) due to the risk of severe complications and even deaths caused by interactions of the magnetic resonance (MR) surrounding and the electric devices. Over the last decade, a better understanding of the underlying mechanisms responsible for such potentially life-threatening complications as well as technical advances have allowed an increasing number of pacemaker and ICD patients to safely undergo MRI. This review lists the key findings from basic research and clinical trials over the last 20 years, and discusses the impact on current day clinical practice. With ‘MR-conditional’ devices being the new standard of care, MRI in pacemaker and ICD patients has been adopted to clinical routine today. However, specific precautions and specifications of these devices should be carefully followed if possible, to avoid patient risks which might appear with new MR technology and further increasing indications and patient numbers.

Abstract 165: The Transcriptional Cofactor Eyes Absent 4 Is A Critical Regulator In Cardiac Physiology

Introduction: Eyes absent 4 (Eya4) is a transcription cofactor involved in a number of cellular and developmental processes. We have previously shown that a truncating mutation in Eya4, E193, causes hearing impairment followed by terminal heart failure suggesting Eya4 is a regulator in cardiac physiology.

Methods and Results: Transgene- or adenovirus mediated overexpression of Eya4 or E193 altered the expression of p27kip1, a critical mediator of cardiac hypertrophy in adult cardiomyocytes.

Luciferase reporter and EMSA assays revealed that Eya4 directly binds to and suppresses p27kip1 promoter activity, while E193 exerts an opposing effect, respectively. Activity and phosphorylation of downstream molecules were significantly altered in Eya4 and E193 transgenic (TG) mice in a contradictory manner. Cardiac phenotypes evolved in both TG models already under basal conditions. Eya4 TG hearts developed hypertrophy as judged by increases in heart weight and cross-sectional cell surfaces and re-activation of fetal genes as well as fibrosis. E193 TG animals showed onset of DCM along with wall thinning, ventricular dilation, fibrosis and slightly compromised cardiac function. These two distinct cardiac phenotypes were even more aggravated upon pressure overload or Angiotensin II infusion.

Finally, we just recently identified a new mutation in Eya4, E215, which also causes hearing impairment and heart failure.

Conclusion: Our data indicate that Eya4, in a physical complex with Six1, plays a critical role in regulating normal cardiac function via p27/CK2-α/HDAC2 and allude that mutations within the Exa4/Six1 transcriptional complex interfere with this newly established signalling pathway, finally leading to age-related onset of cardiomyopathy.

Clinical Perspective: Gaining a better understanding of this disease mechanism could help identify new treatment options for heart failure patients.

Untersuchung der Streuung von Positronen an Elektronen in der Wilsonschen Nebelkammer

In einer "langsamen", mit Methan gefüllten Wilson-Kammer, die hier beschrieben wird, wird die Streuung von Positronen aus Cu64 an Elektronen untersucht. Aus 5000 Aufnahmen mit 2900 m ausgewerteter Positronenbahnlänge wird die Häufigkeit von Stößen mit verschiedener Energieübertragung im Energiebereich 100-400 ekV bestimmt und mit der Theorie von Möller-Bhabha verglichen. Innerhalb der experimentellen Unsicherheit besteht Übereinstimmung zwischen den beobachteten und den berechneten Absolutwerten. Ein Dreierstoß zwischen einem Positron und zwei Elektronen wurde beobachtet.

Abstract 080: Eya4 Induces Hypertrophy Via Regulation Of p27kip1

Introduction: E193, a truncating mutation in the transcription cofactor Eyes absent 4 (Eya4) causes hearing impairment followed by heart failure. Here we identified the Eya4 dependent molecular mechanisms leading to the cardiac phenotype in the E193 mutation.

Methods and Results: First we showed in vitro that the cyclin-dependent kinase inhibitor protein p27kip1 is a direct target of Eya4/Six1 and is suppressed upon Eya4 overexpression, whereas E193 has a dominant negative effect, releasing Eya4 mediated suppression of p27. We next generated transgenic mice with cardiac specific constitutive overexpression of full-length Eya4 or the mutant form E193. While E193 transgenic mice developed age-dependent DCM, Eya4 mice displayed cardiac hypertrophy already under basal conditions as judged by increases in heart weight and cardiomyocyte cross-sectional areas along with increases in myocardial dimension and mass. These two distinct cardiac phenotypes were even more aggravated upon pressure overload suggesting Eya4 is a regulator of cardiac hypertrophy. We also observed that the activity of Casein Kinase 2-α and the phosphorylation status of HDAC2 were significantly upregulated in the Eya4 transgenic mice, while they were significantly reduced in E193 mice, under baseline conditions and pressure overload. We were also able to identify a new human mutation (E215) with a phenotype comparable to the one seen in E193 patients.

Conclusion: Our results implicate that Eya4/Six1 regulates cardiac hypertrophic reactions via p27/CK2-α/HDAC2 and indicate that truncating mutations in Eya4 interfere with this newly established signalling pathway.

MRI-guided ablation of wide complex tachycardia in a univentricular heart

Magnetic resonance imaging can be used for preprocedural assessment of complex anatomy for radiofrequency (RF) ablations, e.g., in a univentricular heart. This case report features the treatment of a young patient with a functionally univentricular heart who suffered from persistent sudden onset tachycardia with wide complexes that required RF ablation as treatment.

Abstract 270: The Core Function of Calcineurin

Background: Recent evidence demonstrates that not only NFAT, but also calcineurin is translocated into the nucleus upon hypertrophic stimulation. Previously it was also demonstrated that calpain-mediated degradation caused a constitutive active calcineurin. We hypothesised that nuclear calcineurin is an intranuclear Ca 2+ sensor hypertrophied myocardium and that inhibition of nuclear translocation of calcineurin is a therapeutic strategy to prevent hypertrophy.

Methods: Employing a transgene mouse model with conditional calpastatin overexpression (”tet-off”, resulting in calpain inhibition), different adenoviral calcineurin mutants and confocal microscopy in isolated adult cardiac myocytes we investigated calcineurin translocation and nuclear Ca 2+ transients. Assessment of cardiac function if transgenic animals was performed by 7T MRI.

Results: We could demonstrate that chronic Ang II stimulation of mice caused calpain-mediated degradation of calcineurin resulting in a constitutive active calcineurin with nuclear translocation. The constitutive active calcineurin in the nucleus escaped further degradation by the UPS and sustained an ongoing hypertrophic response, even after removal of Ang II. Inhibition of nuclear translocation of activated calcineurin by a small inhibitory peptide prevented myocardial hypertrophy in vivo. Transgenic inhibition of calpain activity by calpastatin overexpression prevented proteolysis of calcineurin and allowed for relocation of calcineurin from the nucleus back to the cytosol and regression hypertrophy after removal of Ang II. We were also able to demonstrate that Ang II increases nuclear Ca 2+ transients via InsP3 receptors and that calcineurin is able to act as nuclear Ca 2+ sensor detecting local Ca 2+ release from the nuclear envelope via InsP3R. Nuclear calcineurin mutants that are defective for Ca 2+ activation failed to activate NFAT dependent transcription.

Conclusion: This provides an explanation how Ca 2+ and calcineurin can regulate transcription in cardiomyocytes in response to neurohumoral signals apart from Ca 2+ changes in contraction regulation.

Abstract 27: The Transcription Cofactor Eya4 Mediates the Development of Acquired Cardiac Hypertrophy

Introduction: Eyes absent 4 (Eya4) is a transcription cofactor involved in a number of cellular and developmental processes. We have previously shown that a mutation in Eya4 (E193) leads to late-onset familial dilated cardiomyopathy and heart failure. A precise role for Eya4 in the myocardium has not yet been identified. It appears to regulate the cyclin dependent kinase inhibitor p27 kip1 (p27), a protein shown to regulate hypertrophic responses in the adult cardiomyocyte. This study was aimed to explore the role of Eya4 in induced cardiac hypertrophy.

Methods and results: We generated transgenic mice with cardiac-specific overexpression of HA-tagged Eya4 or E193 to elucidate the function of these proteins in the development of heart failure in vivo . These and wildtype littermates were challenged with angiotensin II (ATII) or subjected to transaortic constriction (TAC). Magnetic resonance imaging to visualize cardiac structures in detail showed that in response to sustained ATII stimulation and TAC, Eya4 mice exhibited a phenotype with significantly increased parameters of hypertrophy compared to WT and E193 overexpressing animals as judged by increases in heart weight and LV free wall diameter, cross-sectional cell surface areas and fibrosis. MRI also showed mild cardiac hypertrophy in Eya4 transgenic mice already under baseline conditions in an age dependent fashion. Moreover, Eya4 overexpression induced a significant suppression of p27 protein expression and resulted in increased levels of phosphorylated histone deacetylase 2 (HDAC2). E193 overexpression induced age dependent wall thinning and ventricular dilation under baseline conditions with no obvious structural or functional defects. ATII or TAC induced significant changes in HW/BW ratio, IVS, fibrosis, hemodynamic and cell size measurements, albeit to a lesser extent than seen with Eya4 mice. p27 expression and pHDAC2 levels were only slightly altered.

Conclusion: In summary, we have demonstrated a mutation in Eya4 to disturb cardiac physiology. We now provide evidence that Eya4 is also involved in forms of acquired heart disease. It seems to suppress p27, which leads to phosphorylation and activation of HDAC2 and results in the development of cardiac hypertrophy.

Minimizing risk of nephrogenic systemic fibrosis in cardiovascular magnetic resonance

Nephrogenic Systemic Fibrosis is a rare condition appearing only in patients with severe renal impairment or failure and presents with dermal lesions and involvement of internal organs. Although many cases are mild, an estimated 5% have a progressive debilitating course. To date, there is no known effective treatment thus stressing the necessity of ample prevention measures. An association with the use of Gadolinium based contrast agents (GBCA) makes Nephrogenic Systemic Fibrosis a potential side effect of contrast enhanced magnetic resonance imaging and offers the opportunity for prevention by limiting use of gadolinium based contrast agents in renal failure patients. In itself toxic, Gadolinium is embedded into chelates that allow its safe use as a contrast agent. One NSF theory is that Gadolinium chelates distribute into the extracellular fluid compartment and set Gadolinium ions free, depending on multiple factors among which the duration of chelates exposure is directly related to the renal function. Major medical societies both in Europe and in North America have developed guidelines for the usage of GBCA. Since the establishment of these guidelines and the increased general awareness of this condition, the occurrence of NSF has been nearly eliminated. Giving an overview over the current knowledge of NSF pathobiochemistry, pathogenesis and treatment options this review focuses on the guidelines of the European Medicines Agency, the European Society of Urogenital Radiology, the FDA and the American College of Radiology from 2008 up to 2011 and the transfer of this knowledge into every day practice.

Reducing RF-related heating of cardiac pacemaker leads in MRI: implementation and experimental verification of practical design changes

There are serious concerns regarding safety when performing magnetic resonance imaging in patients with implanted conductive medical devices, such as cardiac pacemakers, and associated leads, as severe incidents have occurred in the past. In this study, several approaches for altering an implant's lead design were systematically developed and evaluated to enhance the safety of implanted medical devices in a magnetic resonance imaging environment. The individual impact of each design change on radiofrequency heating was then systematically investigated in functional lead prototypes at 1.5 T. Radiofrequency-induced heating could be successfully reduced by three basic changes in conventional pacemaker lead design: (1) increasing the lead tip area, (2) increasing the lead conductor resistance, and (3) increasing outer lead insulation conductivity. The findings show that radiofrequency energy pickup in magnetic resonance imaging can be reduced and, therefore, patient safety can be improved with dedicated construction changes according to a "safe by design" strategy. Incorporation of the described alterations into implantable medical devices such as pacemaker leads can be used to help achieve favorable risk-benefit-ratios when performing magnetic resonance imaging in the respective patient group.

Direct cooling of the catheter tip increases safety for CMR-guided electrophysiological procedures

BACKGROUND

One of the safety concerns when performing electrophysiological (EP) procedures under magnetic resonance (MR) guidance is the risk of passive tissue heating due to the EP catheter being exposed to the radiofrequency (RF) field of the RF transmitting body coil. Ablation procedures that use catheters with irrigated tips are well established therapeutic options for the treatment of cardiac arrhythmias and when used in a modified mode might offer an additional system for suppressing passive catheter heating.

METHODS

A two-step approach was chosen. Firstly, tests on passive catheter heating were performed in a 1.5 T Avanto system (Siemens Healthcare Sector, Erlangen, Germany) using a ASTM Phantom in order to determine a possible maximum temperature rise. Secondly, a phantom was designed for simulation of the interface between blood and the vascular wall. The MR-RF induced temperature rise was simulated by catheter tip heating via a standard ablation generator. Power levels from 1 to 6 W were selected. Ablation duration was 120 s with no tip irrigation during the first 60 s and irrigation at rates from 2 ml/min to 35 ml/min for the remaining 60 s (Biotronik Qiona Pump, Berlin, Germany). The temperature was measured with fluoroscopic sensors (Luxtron, Santa Barbara, CA, USA) at a distance of 0 mm, 2 mm, 4 mm, and 6 mm from the catheter tip.

RESULTS

A maximum temperature rise of 22.4°C at the catheter tip was documented in the MR scanner. This temperature rise is equivalent to the heating effect of an ablator's power output of 6 W at a contact force of the weight of 90 g (0.883 N). The catheter tip irrigation was able to limit the temperature rise to less than 2°C for the majority of examined power levels, and for all examined power levels the residual temperature rise was less than 8°C.

CONCLUSION

Up to a maximum of 22.4°C, the temperature rise at the tissue surface can be entirely suppressed by using the catheter's own irrigation system. The irrigated tip system can be used to increase MR safety of EP catheters by suppressing the effects of unwanted passive catheter heating due to RF exposure from the MR scanner.