scholarly journals MCU Overexpression Rescues Inotropy and Reverses Heart Failure by Reducing SR Ca 2+ Leak

2021 ◽  
Author(s):  
Ting Liu ◽  
Ni Yang ◽  
Agnieszka Sidor ◽  
Brian O'Rourke
Keyword(s):  
Oxidative Stress ◽  
Heart Failure ◽  
Cardiac Function ◽  
Ventricular Myocytes ◽  
Interstitial Fibrosis ◽  
Left Ventricular ◽  
Viral Gene ◽  
Adrenergic Stimulation ◽  
Guinea Pig Model

Rationale: In heart failure (HF), impaired sarcoplasmic reticulum (SR) Ca 2+ release and cytosolic Na + overload depress mitochondrial Ca 2+ (mCa 2+ ) signaling, resulting in a diminished ability to maintain matrix NAD(P)H redox potential, leading to increased oxidative stress when workload increases. Enhancing mCa 2+ can reverse this defect but could potentially increase the likelihood of mitochondrial Ca 2+ overload. Objective: To determine if moderate mitochondrial Ca 2+ uniporter (MCU) overexpression has beneficial or detrimental effects on the development of HF and incident arrythmias in a guinea pig model (ACi) of HF and sudden cardiac death. Methods and Results: In vivo viral gene transfer was used to increase MCU levels by ~30% in ACi hearts. Left ventricular myocytes from hearts with MCU overexpression (ACi+MCU) displayed enhanced mCa 2+ uptake, decreased oxidative stress, and increased β‐adrenergic- and frequency-dependent augmentation of Ca 2+ transients and contractions, compared to myocytes from ACi hearts. MCU overexpression decreased SR Ca 2+ leak in the ACi group and mitigated the elevated ryanodine receptor disulfide crosslinks in HF. β‐adrenergic responses were blunted in isolated perfused ACi hearts and these deficiencies were normalized in ACI+MCU hearts. To examine the in vivo effects of MCU overexpression, ACi hearts were transduced with the MCU virus 2 3w after aortic constriction, at the onset of cardiac decompensation. Two weeks later, cardiac function worsened in the untreated ACi group (fractional shortening: 39{plus minus}1% at 2w and 32{plus minus}1% at 4w), whereas MCU overexpression significantly improved cardiac function (36{plus minus}1% at 2w and 42{plus minus}2% at 4w). MCU overexpression in the decompensating ACi heart also attenuated pulmonary edema and interstitial fibrosis and prevented triggered arrhythmias. Conclusions: Moderate MCU overexpression in failing hearts enhances contractility and responses to β-adrenergic stimulation in isolated myocytes and perfused hearts by inhibiting mitochondrial oxidative stress-induced SR Ca 2+ leak. MCU overexpression also reversed HF and inhibited ectopic ventricular arrhythmias.

The Pattern of Ventricular Remodeling Influences the Level of Oxidative Stress in Heart Failure Patients

2017 ◽  
Vol 68 (7) ◽  
pp. 1506-1511
Author(s):  
Cerasela Mihaela Goidescu ◽  
Anca Daniela Farcas ◽  
Florin Petru Anton ◽  
Luminita Animarie Vida Simiti
Keyword(s):  
Oxidative Stress ◽  
Heart Failure ◽  
Ventricular Remodeling ◽  
Clinical Laboratory ◽  
Left Ventricular ◽  
Control Group ◽  
Reactive Protein ◽  
Lv Mass ◽  
Few Data

Oxidative stress (OS) is increased in chronic diseases, including cardiovascular (CV), but there are few data on its effects on the heart and vessels. The isoprostanes (IsoP) are bioactive compounds, with 8-iso-PGF25a being the most representative in vivo marker of OS. They correlate with the severity of heart failure (HF), but because data regarding OS levels in different types of HF are scarce, our study was aimed to evaluate it by assessing the urinary levels of 8-iso-PGF2aand its correlations with various biomarkers and parameters. Our prospective study included 53 consecutive patients with HF secondary to ischemic heart disease or dilative cardiomyopathy, divided according to the type of HF (acute, chronic decompensated or chronic compensated HF). The control group included 13 hypertensive patients, effectively treated. They underwent clinical, laboratory - serum NT-proBNP, creatinine, uric acid, lipids, C reactive protein (CRP) and urinary 8-iso-PGF2a and echocardiographic assessment. HF patients, regardless the type of HF, had higher 8-iso-PGF2a than controls (267.32pg/�mol vs. 19.82pg/�mol, p[0.001). The IsoP level was directly correlated with ejection fraction (EF) (r=-0.31, p=0.01) and NT-proBNP level (r=0.29, p=0.019). The relative wall thickness (RWT) was negatively correlated with IsoP (r=-0.55, p[0.001). Also 8-iso-PGF25a was higher by 213.59pg/�mol in the eccentric left ventricular (LV) hypertrophy subgroup comparing with the concentric subgroup (p=0.014), and the subgroups with severe mitral regurgitation (MR) and moderate/severe pulmonary hypertension (PAH) had the highest 8-iso-PGF2a levels. Male sex, severe MR, moderate/severe PAH, high LV mass and low RWT values were predictive for high OS level in HF patients.Eccentric cardiac remodeling, MR severity and PAH severity are independent predictors of OS in HF patients.

scholarly journals p90 ribosomal S6 kinase 3 contributes to cardiac insufficiency in α-tropomyosin Glu180Gly transgenic mice

2013 ◽  
Vol 305 (7) ◽  
pp. H1010-H1019 ◽  
Author(s):  
Catherine L. Passariello ◽  
Marjorie Gayanilo ◽  
Michael D. Kritzer ◽  
Hrishikesh Thakur ◽  
Zoharit Cozacov ◽  
...  
Keyword(s):  
Heart Failure ◽  
Transgenic Mice ◽  
Cardiac Function ◽  
Interstitial Fibrosis ◽  
Cardiac Insufficiency ◽  
S6 Kinase ◽  
Transgenic Expression ◽  
P90 Ribosomal S6 Kinase ◽  
Ribosomal S6 Kinase

Myocardial interstitial fibrosis is an important contributor to the development of heart failure. Type 3 p90 ribosomal S6 kinase (RSK3) was recently shown to be required for concentric myocyte hypertrophy under in vivo pathological conditions. However, the role of RSK family members in myocardial fibrosis remains uninvestigated. Transgenic expression of α-tropomyosin containing a Glu180Gly mutation (TM180) in mice of a mixed C57BL/6:FVB/N background induces a cardiomyopathy characterized by a small left ventricle, interstitial fibrosis, and diminished systolic and diastolic function. Using this mouse model, we now show that RSK3 is required for the induction of interstitial fibrosis in vivo. TM180 transgenic mice were crossed to RSK3 constitutive knockout ( RSK3−/−) mice. Although RSK3 knockout did not affect myocyte growth, the decreased cardiac function and mild pulmonary edema associated with the TM180 transgene were attenuated by RSK3 knockout. The improved cardiac function was consistent with reduced interstitial fibrosis in the TM180; RSK3−/− mice as shown by histology and gene expression analysis, including the decreased expression of collagens. The specific inhibition of RSK3 should be considered as a potential novel therapeutic strategy for improving cardiac function and the prevention of sudden cardiac death in diseases in which interstitial fibrosis contributes to the development of heart failure.

scholarly journals Interaction of the Joining Region in Junctophilin-2 With the L-Type Ca 2+ Channel Is Pivotal for Cardiac Dyad Assembly and Intracellular Ca 2+ Dynamics

2021 ◽  
Vol 128 (1) ◽  
pp. 92-114
Author(s):  
Polina Gross ◽  
Jaslyn Johnson ◽  
Carlos M. Romero ◽  
Deborah M. Eaton ◽  
Claire Poulet ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Ventricular Myocytes ◽  
Close Association ◽  
Ryanodine Receptors ◽  
Left Ventricular ◽  
Induced Mutations ◽  
Adrenergic Stimulation ◽  
T Tubules ◽  
Junctional Sarcoplasmic Reticulum

Rationale: Ca 2+ -induced Ca 2+ release (CICR) in normal hearts requires close approximation of L-type calcium channels (LTCCs) within the transverse tubules (T-tubules) and RyR (ryanodine receptors) within the junctional sarcoplasmic reticulum. CICR is disrupted in cardiac hypertrophy and heart failure, which is associated with loss of T-tubules and disruption of cardiac dyads. In these conditions, LTCCs are redistributed from the T-tubules to disrupt CICR. The molecular mechanism responsible for LTCCs recruitment to and from the T-tubules is not well known. JPH (junctophilin) 2 enables close association between T-tubules and the junctional sarcoplasmic reticulum to ensure efficient CICR. JPH2 has a so-called joining region that is located near domains that interact with T-tubular plasma membrane, where LTCCs are housed. The idea that this joining region directly interacts with LTCCs and contributes to LTCC recruitment to T-tubules is unknown. Objective: To determine if the joining region in JPH2 recruits LTCCs to T-tubules through direct molecular interaction in cardiomyocytes to enable efficient CICR. Methods and Results: Modified abundance of JPH2 and redistribution of LTCC were studied in left ventricular hypertrophy in vivo and in cultured adult feline and rat ventricular myocytes. Protein-protein interaction studies showed that the joining region in JPH2 interacts with LTCC-α1C subunit and causes LTCCs distribution to the dyads, where they colocalize with RyRs. A JPH2 with induced mutations in the joining region (mut PG1 JPH2) caused T-tubule remodeling and dyad loss, showing that an interaction between LTCC and JPH2 is crucial for T-tubule stabilization. mut PG1 JPH2 caused asynchronous Ca 2+ -release with impaired excitation-contraction coupling after β-adrenergic stimulation. The disturbed Ca 2+ regulation in mut PG1 JPH2 overexpressing myocytes caused calcium/calmodulin-dependent kinase II activation and altered myocyte bioenergetics. Conclusions: The interaction between LTCC and the joining region in JPH2 facilitates dyad assembly and maintains normal CICR in cardiomyocytes.

Role of inducible nitric oxide synthase in cardiac function and remodeling in mice with heart failure due to myocardial infarction

2005 ◽  
Vol 289 (6) ◽  
pp. H2616-H2623 ◽  
Author(s):  
Yun-He Liu ◽  
Oscar A. Carretero ◽  
Oscar H. Cingolani ◽  
Tang-Dong Liao ◽  
Ying Sun ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Nitric Oxide ◽  
Heart Failure ◽  
Cardiac Function ◽  
Systolic Function ◽  
Left Ventricular ◽  
Cross Sectional ◽  
Cardiac Reserve ◽  
Inos Knockout Mice ◽  
Inducible Nitric Oxide

Using inducible nitric oxide (NO) synthase (iNOS) knockout mice (iNOS−/−), we tested the hypotheses that 1) lack of iNOS attenuates cardiac remodeling and dysfunction and improves cardiac reserve postmyocardial infarction (MI), an effect that is partially mediated by reduction of oxidative stress due to reduced interaction between NO and reactive oxygen species (ROS); and 2) the cardioprotection afforded by iNOS deletion is eliminated by Nω-nitro-l-arginine methyl ester (l-NAME) due to inhibition of endothelial NOS (eNOS) and neuronal NOS (nNOS). MI was induced by ligating the left anterior descending coronary artery. Male iNOS−/− mice and wild-type controls (WT, C57BL/6J) were divided into sham MI, MI+vehicle, and MI+l-NAME (100 mg·kg−1·day−1 in drinking water for 8 wk). Cardiac function was evaluated by echocardiography. Left ventricular (LV) maximum rate of rise of ventricular pressure divided by pressure at the moment such maximum occurs (dP/d t/instant pressure) in response to isoproterenol (100 ng·kg−1·min−1 iv) was measured with a Millar catheter. Collagen deposition, myocyte cross-sectional area, and expression of nitrotyrosine and 4-hydroxy-2-nonenal (4-HNE), markers for ROS, were determined by histopathological and immunohistochemical staining. We found that the MI-induced increase in LV chamber dimension and the decrease in ejection fraction, an index of systolic function, were less severe in iNOS−/− compared with WT mice. l-NAME worsened LV remodeling and dysfunction further, and these detrimental effects were also attenuated in iNOS−/− mice, associated with better preservation of cardiac function. Lack of iNOS also reduced nitrotyrosine and 4-HNE expression after MI, indicating reduced oxidative stress. We conclude that iNOS does not seem to be a pathological mediator of heart failure; however, the lack of iNOS improves cardiac reserve post-MI, particularly when constitutive NOS isoforms are blocked. Decreased oxidative stress and other adaptive mechanisms independent of NOS may be partially responsible for such an effect, which needs to be studied further.

Abstract 18575: The Transcriptional Cofactor Eyes Absent 4 is a Critical Regulator for Maintaining Normal Cardiac Function

Circulation ◽  
2014 ◽  
Vol 130 (suppl_2) ◽  
Author(s):  
Tatjana Williams ◽  
Moritz Hundertmark ◽  
Peter Nordbeck ◽  
Sabine Voll ◽  
Anahi Paula Arias-Loza ◽  
...  
Keyword(s):  
Heart Failure ◽  
Cardiac Function ◽  
Interstitial Fibrosis ◽  
Critical Role ◽  
Cardiac Physiology ◽  
Eyes Absent ◽  
Age Dependent ◽  
Normal Cardiac Function

Introduction: E193, a human mutation in the transcription cofactor Eyes absent 4 (EYA4) causes hearing impairment followed by terminal heart failure, defining an important role for Eya4 in maintaining normal cardiac function. METHODS AND RESULTS: First, in-vitro experiments show that overexpression of Eya4 and the mutant isoform alter the expression of p27kip1 on both, transcript and protein levels. Next, we generated transgenic mice with cardiomyocyte-specific Eya4 or E193 overexpression to elucidate the in vivo function of Eya4 upon cardiac physiology. Luciferase and CHIP assays revealed that Eya4 and E193 bind to and regulate p27 expression in a contradictory manner, as already seen in vitro. Activity and phoshorylation of the downstream molecules CK2α and HDAC2 were significantly elevated in Eya4 mice, whereas they were significantly reduced in E193 animals compared to WT littermates. MRI and hemodynamic analysis indicate that a constitutive overexpression of Eya4 results in the age-dependent development of hypertrophy already under baseline conditions with no obvious functional effects, whereas E193 overexpressing animals develop onset of dilative cardiomyopathy as seen in human patients carrying the E193 mutation. Morphometric analysis proved ventricular hypertrophy or dilation of the LV associated with a thinning of the myocardial wall, interstitial fibrosis of myocardial tissue and alterations in cell size. Re-activation of fetal genes also occured in both TG models, characteristic for cardiac disease. Both cardiac phenotypes were aggravated upon pressure overload. Finally, we identified a new human heterozygous truncating Eya4 mutation, E215, which leads to similar clinical features of disease and a stable myocardial expression of the mutant protein. Conclusion: Our results implicate that Eya4 plays a critical role in regulating normal cardiac physiology and function via Six1/p27/CK2α/HDAC2 and that an imbalance within the Eya4/Six1 transcriptional complex leads to an age dependent onset of cardiomyopthy and heart failure.

Abstract 278: Domain-specific Roles for GRK2 in Cardiac Hypertrophy and Heart Failure

2016 ◽  
Vol 119 (suppl_1) ◽  
Author(s):  
Sarah M Schumacher ◽  
Erhe Gao ◽  
J. Kurt Chuprun ◽  
Walter J. Koch
Keyword(s):  
Heart Failure ◽  
Interstitial Fibrosis ◽  
Heart Function ◽  
Pressure Overload ◽  
Left Ventricular ◽  
Cross Sectional ◽  
Amino Terminal ◽  
Domain Specific ◽  
Rgs Domain

During heart failure (HF), cardiac levels and activity of the G protein-coupled receptor (GPCR) kinase (GRK) GRK2 are elevated and contribute to adverse remodeling and contractile dysfunction, while inhibition via a carboxyl-terminal peptide, βARKct, enhances heart function and can prevent HF. Mounting evidence supports the idea of a dynamic “interactome” in which GRK2 can uncouple GPCRs via novel protein-protein interactions. Several GRK2 interacting partners are important for adaptive and maladaptive myocyte growth; therefore, an understanding of domain-specific interactions with signaling and regulatory molecules could lead to novel targets for HF therapy. For instance, GRK2 contains a putative amino-terminal R egulator of G protein S ignaling (RGS) domain (βARKrgs) that directly interacts with Gαq and inhibits signaling. Previously, our lab investigated cardiac-specific transgenic expression of a fragment of this RGS domain (βARKnt), that did not reduce acute hypertrophy after pressure overload or demonstrate RGS activity in vivo against Gαq-mediated signaling. In contrast, βARKnt induced hypertrophy and elevated β-adrenergic receptor (βAR) density without altering agonist-induced contractility or adenylyl cyclase activity, due to a compensatory increase in GRK2 activity. Importantly, βAR downregulation in response to chronic agonist administration was attenuated by βARKnt expression, indicating a novel regulation of βAR receptor density. Herein, we investigated the effect of βARKnt expression during chronic pressure overload post trans-aortic constriction (TAC). Echocardiographic analysis revealed increased posterior wall thickness and left-ventricular mass 4 weeks post-TAC compared to non-transgenic littermate controls. Importantly, despite enhanced hypertrophy, the progression to HF was inhibited in βARKnt mice 14 weeks post-TAC. Histological analysis of interstitial fibrosis and cross-sectional area is underway to determine alterations in maladaptive remodeling. Further, cardiomyocyte signaling and βARKnt protein-binding partners are a focus, since our data indicate that βARKnt-mediated regulation of βAR density may provide a novel means of cardioprotection during pressure-overload induced HF.

scholarly journals Interferon-γ ablation exacerbates myocardial hypertrophy in diastolic heart failure

2012 ◽  
Vol 303 (5) ◽  
pp. H587-H596 ◽  
Author(s):  
Anthony G. Garcia ◽  
Richard M. Wilson ◽  
Joline Heo ◽  
Namita R. Murthy ◽  
Simoni Baid ◽  
...  
Keyword(s):  
Heart Failure ◽  
Cardiac Hypertrophy ◽  
Ventricular Myocytes ◽  
Salt Water ◽  
Diastolic Heart Failure ◽  
Velocity Ratio ◽  
Interleukin 10 ◽  
Interferon Γ ◽  
Left Ventricular

Diastolic heart failure (HF) accounts for up to 50% of all HF admissions, with hypertension being the major cause of diastolic HF. Hypertension is characterized by left ventricular (LV) hypertrophy (LVH). Proinflammatory cytokines are increased in LVH and hypertension, but it is unknown if they mediate the progression of hypertension-induced diastolic HF. We sought to determine if interferon-γ (IFNγ) plays a role in mediating the transition from hypertension-induced LVH to diastolic HF. Twelve-week old BALB/c (WT) and IFNγ-deficient (IFNγKO) mice underwent either saline ( n = 12) or aldosterone ( n = 16) infusion, uninephrectomy, and fed 1% salt water for 4 wk. Tail-cuff blood pressure, echocardiography, and gene/protein analyses were performed. Isolated adult rat ventricular myocytes were treated with IFNγ (250 U/ml) and/or aldosterone (1 μM). Hypertension was less marked in IFNγKO-aldosterone mice than in WT-aldosterone mice (127 ± 5 vs. 136 ± 4 mmHg; P < 0.01), despite more LVH (LV/body wt ratio: 4.9 ± 0.1 vs. 4.3 ± 0.1 mg/g) and worse diastolic dysfunction (peak early-to-late mitral inflow velocity ratio: 3.1 ± 0.1 vs. 2.8 ± 0.1). LV ejection fraction was no different between IFNγKO-aldosterone vs. WT-aldosterone mice. LV end systolic dimensions were decreased significantly in IFNγKO-aldosterone vs. WT-aldosterone hearts (1.12 ± 0.1 vs. 2.1 ± 0.3 mm). Myocardial fibrosis and collagen expression were increased in both IFNγKO-aldosterone and WT-aldosterone hearts. Myocardial autophagy was greater in IFNγKO-aldosterone than WT-aldosterone mice. Conversely, tumor necrosis factor-α and interleukin-10 expressions were increased only in WT-aldosterone hearts. Recombinant IFNγ attenuated cardiac hypertrophy in vivo and modulated aldosterone-induced hypertrophy and autophagy in cultured cardiomyocytes. Thus IFNγ is a regulator of cardiac hypertrophy in diastolic HF and modulates cardiomyocyte size possibly by regulating autophagy. These findings suggest that IFNγ may mediate adaptive downstream responses and challenge the concept that inflammatory cytokines mediate only adverse effects.

Relationship between cardiomyocyte cell death and cardiac function during hypertensive cardiac remodelling in Dahl rats

2002 ◽  
Vol 102 (3) ◽  
pp. 329-335 ◽  
Author(s):  
Shuntaro IKEDA ◽  
Mareomi HAMADA ◽  
Peng QU ◽  
Go HIASA ◽  
Hidetoshi HASHIDA ◽  
...  
Keyword(s):  
Heart Failure ◽  
Cell Death ◽  
Cardiac Function ◽  
Apoptotic Cell ◽  
Mrna Level ◽  
Northern Blotting ◽  
Left Ventricular ◽  
Cardiomyocyte Apoptosis ◽  
Terminal Deoxynucleotidyl Transferase

The exact mechanisms responsible for the progression of heart failure remain unclear. We investigated the in vivo relationship between the incidence of apoptotic cell death and left ventricular function serially from the beginning of hypertension to decompensated heart failure in Dahl salt-sensitive rats. Dahl salt-resistant and Dahl salt-sensitive rats were fed on a high-salt diet from 6 weeks of age. Systolic blood pressure was recorded by the tail-cuff method every week. Cardiac function in vivo was evaluated by echocardiography and cardiac catheterization. Cardiomyocyte apoptosis was detected by the TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling) method. The gene expression of Bax, Bcl-2 and Bcl-xL was analysed by Northern blotting. The TUNEL method revealed that the incidence of cardiomyocyte apoptosis was significantly increased in the hearts of 18-week-old Dahl salt-sensitive rats (apoptotic index 1.3±0.1%). Northern blot analysis revealed that the Bcl-xL mRNA level increased gradually during the progression towards heart failure. In conclusion, these data suggest that cardiomyocyte apoptosis is a terminal event, and plays a role as an aggravating factor in the vicious cycle of heart failure.

In vivo gene delivery of HSP70i by adenovirus and adeno-associated virus preserves contractile function in mouse heart following ischemia-reperfusion

2006 ◽  
Vol 291 (6) ◽  
pp. H2905-H2910 ◽  
Author(s):  
Darrell D. Belke ◽  
Bernd Gloss ◽  
John M. Hollander ◽  
Eric A. Swanson ◽  
Hervé Duplain ◽  
...  
Keyword(s):  
Cardiac Function ◽  
Viral Vector ◽  
Contractile Function ◽  
Ischemia Reperfusion ◽  
Left Ventricular ◽  
Viral Gene ◽  
Mouse Heart ◽  
Adeno Associated Virus

Inducible heat shock protein 70 (HSP70i) has been shown to exert a protective effect in hearts subjected to ischemia-reperfusion. Although studied in heat-shocked animals and in transgenic mice that constitutively overexpress the protein, the therapeutic application of the protein in the form of a viral vector-mediated HSP70i expression has not been widely examined. Accordingly, we have examined the effects of HSP70i delivered in vivo to the left ventricular free wall of the heart via viral gene therapy in mice. The affect of virally mediated HSP70i expression in preserving cardiac function following ischemia-reperfusion was examined after short-term expression (5-day adenovirus mediated) and long-term expression (8-mo adeno-associated virus mediated) in mice by subjecting ex vivo Langendorff perfused hearts to a regime of ischemia-reperfusion. Both vectors were capable of increasing HSP70i expression in the heart, and neither vector had any effect on cardiac function during aerobic (preischemic) perfusion when compared with corresponding controls. In contrast, both adenovirus-mediated and adeno-associated virus-mediated expression of HSP70i improved the contractile recovery of the heart after 120 min of reperfusion following ischemia. This study demonstrates the feasibility of using both short- and long-term expression of virally mediated HSP70i as a therapeutic intervention against cardiac ischemia-reperfusion injury.

scholarly journals Genetic Loss of I K1 Causes Adrenergic-Induced Phase 3 Early Afterdepolariz ations and Polymorphic and Bidirectional Ventricular Tachycardia

2020 ◽  
Vol 13 (9) ◽  
Author(s):  
Louise Reilly ◽  
Francisco J. Alvarado ◽  
Di Lang ◽  
Sara Abozeid ◽  
Hannah Van Ert ◽  
...  
Keyword(s):  
Ventricular Tachycardia ◽  
Action Potential ◽  
Cardiac Function ◽  
Ventricular Myocytes ◽  
Optical Mapping ◽  
Adrenergic Stimulation ◽  
Phase 3 ◽  
Early Afterdepolarizations ◽  
Whole Heart

Background: Arrhythmia syndromes associated with KCNJ2 mutations have been described clinically; however, little is known of the underlying arrhythmia mechanism. We create the first patient inspired KCNJ2 transgenic mouse and study effects of this mutation on cardiac function, I K1 , and Ca 2+ handling, to determine the underlying cellular arrhythmic pathogenesis. Methods: A cardiac-specific KCNJ2 -R67Q mouse was generated and bred for heterozygosity (R67Q +/− ). Echocardiography was performed at rest, under anesthesia. In vivo ECG recording and whole heart optical mapping of intact hearts was performed before and after adrenergic stimulation in wild-type (WT) littermate controls and R67Q +/− mice. I K1 measurements, action potential characterization, and intracellular Ca 2+ imaging from isolated ventricular myocytes at baseline and after adrenergic stimulation were performed in WT and R67Q +/− mice. Results: R67Q +/− mice (n=17) showed normal cardiac function, structure, and baseline electrical activity compared with WT (n=10). Following epinephrine and caffeine, only the R67Q +/− mice had bidirectional ventricular tachycardia, ventricular tachycardia, frequent ventricular ectopy, and/or bigeminy and optical mapping demonstrated high prevalence of spontaneous and sustained ventricular arrhythmia. Both R67Q +/− (n=8) and WT myocytes (n=9) demonstrated typical n-shaped I K1 IV relationship; however, following isoproterenol, max outward I K1 increased by ≈20% in WT but decreased by ≈24% in R67Q +/− ( P <0.01). R67Q +/− myocytes (n=5) demonstrated prolonged action potential duration at 90% repolarization and after 10 nmol/L isoproterenol compared with WT (n=7; P <0.05). Ca 2+ transient amplitude, 50% decay rate, and sarcoplasmic reticulum Ca 2+ content were not different between WT (n=18) and R67Q +/− (n=16) myocytes. R67Q +/− myocytes (n=10) under adrenergic stimulation showed frequent spontaneous development of early afterdepolarizations that occurred at phase 3 of action potential repolarization. Conclusions: KCNJ2 mutation R67Q +/− causes adrenergic-dependent loss of I K1 during terminal repolarization and vulnerability to phase 3 early afterdepolarizations. This model clarifies a heretofore unknown arrhythmia mechanism and extends our understanding of treatment implications for patients with KCNJ2 mutation.

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