Manuel Zarzoso

Extracellular Matrix–Mediated Maturation of Human Pluripotent Stem Cell–Derived Cardiac Monolayer Structure and Electrophysiological Function

Background—Human pluripotent stem cell–derived cardiomyocytes (hPSC-CMs) monolayers generated to date display an immature embryonic-like functional and structural phenotype that limits their utility for research and cardiac regeneration. In particular, the electrophysiological function of hPSC-CM monolayers and bioengineered constructs used to date are characterized by slow electric impulse propagation velocity and immature action potential profiles. Methods and Results—Here, we have identified an optimal extracellular matrix for significant electrophysiological and structural maturation of hPSC-CM monolayers. hPSC-CM plated in the optimal extracellular matrix combination have impulse propagation velocities ≈2× faster than previously reported (43.6±7.0 cm/s; n=9) and have mature cardiomyocyte action potential profiles, including hyperpolarized diastolic potential and rapid action potential upstroke velocity (146.5±17.7 V/s; n=5 monolayers). In addition, the optimal extracellular matrix promoted hypertrophic growth of cardiomyocytes and the expression of key mature sarcolemmal (SCN5A, Kir2.1, and connexin43) and myofilament markers (cardiac troponin I). The maturation process reported here relies on activation of integrin signaling pathways: neutralization of &bgr;1 integrin receptors via blocking antibodies and pharmacological blockade of focal adhesion kinase activation prevented structural maturation. Conclusions—Maturation of human stem cell–derived cardiomyocyte monolayers is achieved in a 1-week period by plating cardiomyocytes on PDMS (polydimethylsiloxane) coverslips rather than on conventional 2-dimensional cell culture formats, such as glass coverslips or plastic dishes. Activation of integrin signaling and focal adhesion kinase is essential for significant maturation of human cardiac monolayers.

Modifications of mechanoelectric feedback induced by 2,3-butanedione monoxime and Blebbistatin in Langendorff-perfused rabbit hearts.

Myocardial stretching is an arrhythmogenic factor. Optical techniques and mechanical uncouplers are used to study the mechanoelectric feedback. The aim of this study is to determine whether the mechanical uncouplers 2,3‐butanedione monoxime and Blebbistatin hinder or modify the electrophysiological effects of acute mechanical stretch.

Development and characterization of an experimental model of diet-induced metabolic syndrome in rabbit

Metabolic syndrome (MetS) has become one of the main concerns for public health because of its link to cardiovascular disease. Murine models have been used to study the effect of MetS on the cardiovascular system, but they have limitations for studying cardiac electrophysiology. In contrast, the rabbit cardiac electrophysiology is similar to human, but a detailed characterization of the different components of MetS in this animal is still needed. Our objective was to develop and characterize a diet-induced experimental model of MetS that allows the study of cardiovascular remodeling and arrhythmogenesis. Male NZW rabbits were assigned to control (n = 15) or MetS group (n = 16), fed during 28 weeks with high-fat, high-sucrose diet. We measured weight, morphological characteristics, blood pressure, glycaemia, standard plasma biochemistry and the metabolomic profile at weeks 14 and 28. Liver histological changes were evaluated using hematoxylin-eosin staining. A mixed model ANOVA or unpaired t-test were used for statistical analysis (P<0.05). Weight, abdominal contour, body mass index, systolic, diastolic and mean arterial pressure increased in the MetS group at weeks 14 and 28. Glucose, triglycerides, LDL, GOT-AST, GOT/GPT, bilirubin and bile acid increased, whereas HDL decreased in the MetS group at weeks 14 and 28. We found a 40% increase in hepatocyte area and lipid vacuoles infiltration in the liver from MetS rabbits. Metabolomic analysis revealed differences in metabolites related to fatty acids, energetic metabolism and microbiota, compounds linked with cardiovascular disease. Administration of high-fat and high-sucrose diet during 28 weeks induced obesity, glucose intolerance, hypertension, non-alcoholic hepatic steatosis and metabolic alterations, thus reproducing the main clinical manifestations of the metabolic syndrome in humans. This experimental model should provide a valuable tool for studies into the mechanisms of cardiovascular problems related to MetS, with special relevance in the study of cardiovascular remodeling, arrhythmias and SCD.

Evaluation of the Complexity of Myocardial Activation During Ventricular Fibrillation. An Experimental Study

INTRODUCTION AND OBJECTIVES An experimental model is used to analyze the characteristics of ventricular fibrillation in situations of variable complexity, establishing relationships among the data produced by different methods for analyzing the arrhythmia. METHODS In 27 isolated rabbit heart preparations studied under the action of drugs (propranolol and KB-R7943) or physical procedures (stretching) that produce different degrees of change in the complexity of myocardial activation during ventricular fibrillation, use was made of spectral, morphological, and mapping techniques to process the recordings obtained with epicardial multielectrodes. RESULTS The complexity of ventricular fibrillation assessed by mapping techniques was related to the dominant frequency, normalized spectral energy, signal regularity index, and their corresponding coefficients of variation, as well as the area of the regions of interest identified on the basis of these parameters. In the multivariate analysis, we used as independent variables the area of the regions of interest related to the spectral energy and the coefficient of variation of the energy (complexity index=-0.005×area of the spectral energy regions -2.234×coefficient of variation of the energy+1.578; P=.0001; r=0.68). CONCLUSIONS The spectral and morphological indicators and, independently, those derived from the analysis of normalized energy regions of interest provide a reliable approach to the evaluation of the complexity of ventricular fibrillation as an alternative to complex mapping techniques.

Cardiac Kir2.1 and NaV1.5 Channels Traffic Together to the Sarcolemma to Control Excitability

Rationale: In cardiomyocytes, NaV1.5 and Kir2.1 channels interact dynamically as part of membrane bound macromolecular complexes. Objective: The objective of this study was to test whether NaV1.5 and Kir2.1 preassemble during early forward trafficking and travel together to common membrane microdomains. Methods and Results: In patch-clamp experiments, coexpression of trafficking-deficient mutants Kir2.1&Dgr;314-315 or Kir2.1R44A/R46A with wild-type (WT) NaV1.5WT in heterologous cells reduced inward sodium current compared with NaV1.5WT alone or coexpressed with Kir2.1WT. In cell surface biotinylation experiments, expression of Kir2.1&Dgr;314-315 reduced NaV1.5 channel surface expression. Glycosylation analysis suggested that NaV1.5WT and Kir2.1WT channels associate early in their biosynthetic pathway, and fluorescence recovery after photobleaching experiments demonstrated that coexpression with Kir2.1 increased cytoplasmic mobility of NaV1.5WT, and vice versa, whereas coexpression with Kir2.1&Dgr;314-315 reduced mobility of both channels. Viral gene transfer of Kir2.1&Dgr;314-315 in adult rat ventricular myocytes and human induced pluripotent stem cell–derived cardiomyocytes reduced inward rectifier potassium current and inward sodium current, maximum diastolic potential and action potential depolarization rate, and increased action potential duration. On immunostaining, the AP1 (adaptor protein complex 1) colocalized with NaV1.5WT and Kir2.1WT within areas corresponding to t-tubules and intercalated discs. Like Kir2.1WT, NaV1.5WT coimmunoprecipitated with AP1. Site-directed mutagenesis revealed that NaV1.5WT channels interact with AP1 through the NaV1.5Y1810 residue, suggesting that, like for Kir2.1WT, AP1 can mark NaV1.5 channels for incorporation into clathrin-coated vesicles at the trans-Golgi. Silencing the AP1 υ-adaptin subunit in human induced pluripotent stem cell–derived cardiomyocytes reduced inward rectifier potassium current, inward sodium current, and maximum diastolic potential and impaired rate-dependent action potential duration adaptation. Conclusions: The NaV1.5-Kir2.1 macromolecular complex pre-assembles early in the forward trafficking pathway. Therefore, disruption of Kir2.1 trafficking in cardiomyocytes affects trafficking of NaV1.5, which may have important implications in the mechanisms of arrhythmias in inheritable cardiac diseases.

Experimental Study of the Effects of EIPA, Losartan, and BQ-123 on Electrophysiological Changes Induced by Myocardial Stretch

INTRODUCTION AND OBJECTIVES Mechanical response to myocardial stretch has been explained by various mechanisms, which include Na(+)/H(+) exchanger activation by autocrine-paracrine system activity. Drug-induced changes were analyzed to investigate the role of these mechanisms in the electrophysiological responses to acute myocardial stretch. METHODS Multiple epicardial electrodes and mapping techniques were used to analyze changes in ventricular fibrillation induced by acute myocardial stretch in isolated perfused rabbit hearts. Four series were studied: control (n = 9); during perfusion with the angiotensin receptor blocker losartan (1 μM, n = 8); during perfusion with the endothelin A receptor blocker BQ-123 (0.1 μM, n = 9), and during perfusion with the Na(+)/H(+) exchanger inhibitor EIPA (5-[N-ethyl-N-isopropyl]-amiloride) (1 μM, n = 9). RESULTS EIPA attenuated the increase in the dominant frequency of stretch-induced fibrillation (control=40.4%; losartan=36% [not significant]; BQ-123=46% [not significant]; and EIPA=22% [P<.001]). During stretch, the activation maps were less complex (P<.0001) and the spectral concentration of the arrhythmia was greater (greater regularity) in the EIPA series: control=18 (3%); EIPA = 26 (9%) (P < .02); losartan=18 (5%) (not significant); and BQ-123=18 (4%) (not significant). CONCLUSIONS The Na(+)/H(+) exchanger inhibitor EIPA attenuated the electrophysiological effects responsible for the acceleration and increased complexity of ventricular fibrillation induced by acute myocardial stretch. The angiotensin II receptor antagonist losartan and the endothelin A receptor blocker BQ-123 did not modify these effects.

QT Interval Heterogeneities Induced Through Local Epicardial Warming/Cooling. An Experimental Study

INTRODUCTION AND OBJECTIVES Abnormal QT interval durations and dispersions have been associated with increased risk of ventricular arrhythmias. The present study examines the possible arrhythmogenic effect of inducing QT interval variations through local epicardial cooling and warming. METHODS In 10 isolated rabbit hearts, the temperatures of epicardial regions of the left ventricle were modified in a stepwise manner (from 22°C to 42°C) with simultaneous electrogram recording in these regions and in others of the same ventricle. QT and activation-recovery intervals were determined during sinus rhythm, whereas conduction velocity and ventricular arrhythmia induction were determined during programmed stimulation. RESULTS In the area modified from baseline temperature (37°C), the QT (standard deviation) was prolonged with maximum hypothermia (195 [47] vs 149 [12] ms; P<.05) and shortened with hyperthermia (143 [18] vs 152 [27] ms; P<.05). The same behavior was displayed for the activation-recovery interval. The conduction velocity decreased with hypothermia and increased with hyperthermia. No changes were seen in the other unmodified area. Repetitive responses were seen in 5 experiments, but no relationship was found between their occurrence and hypothermia or hyperthermia (P>.34). CONCLUSIONS In the experimental model employed, local variations in the epicardial temperature modulate the QT interval, activation-recovery interval, and conduction velocity. Induction of heterogeneities did not promote ventricular arrhythmia occurrence.

An Experimental Model of Diet-Induced Metabolic Syndrome in Rabbit: Methodological Considerations, Development, and Assessment

In recent years, obesity and metabolic syndrome (MetS) have become a growing problem for public health and clinical practice, given their increased prevalence due to the rise of sedentary lifestyles and unhealthy eating habits. Thanks to animal models, basic research can investigate the mechanisms underlying pathological processes such as MetS. Here, we describe the methods used to develop an experimental rabbit model of diet-induced MetS and its assessment. After a period of acclimation, animals are fed a high-fat (10% hydrogenated coconut oil and 5% lard), high-sucrose (15% sucrose dissolved in water) diet for 28 weeks. During this period, several experimental procedures were performed to evaluate the different components of MetS: morphological and blood pressure measurements, glucose tolerance determination, and the analysis of several plasma markers. At the end of the experimental period, animals developed central obesity, mild hypertension, pre-diabetes, and dyslipidemia with low HDL, high LDL, and an increase of triglyceride (TG) levels, thus reproducing the main components of human MetS. This chronic model allows new perspectives for understanding the underlying mechanisms in the progression of the disease, the detection of preclinical and clinical markers that allow the identification of patients at risk, or even the testing of new therapeutic approaches for the treatment of this complex pathology.

Effects of JTV-519 on stretch-induced manifestations of mechanoelectric feedback

JTV‐519 is a 1,4‐benzothiazepine derivative with multichannel effects that inhibits Ca2+ release from the sarcoplasmic reticulum and stabilizes the closed state of the ryanodine receptor, preventing myocardial damage and the induction of arrhythmias during Ca2+ overload. Mechanical stretch increases cellular Na+ inflow, activates the reverse mode of the Na+/Ca2+ exchanger, and modifies Ca2+ handling and myocardial electrophysiology, favoring arrhythmogenesis. This study aims to determine whether JTV‐519 modifies the stretch‐induced manifestations of mechanoelectric feedback. The ventricular fibrillation (VF) modifications induced by acute stretch were studied in Langendorff‐perfused rabbit hearts using epicardial multiple electrodes under control conditions (n=9) or during JTV‐519 perfusion: 0.1 μmol/L (n=9) and 1 μmol/L (n=9). Spectral and mapping techniques were used to establish the baseline, stretch and post‐stretch VF characteristics. JTV‐519 slowed baseline VF and decreased activation complexity. These effects were dose‐dependent (baseline VF dominant frequency: control=13.9±2.2 Hz; JTV 0.1 μmol/L=11.1±1.1 Hz, P<.01; JTV 1 μmol/L=6.6±1.1 Hz, P<.0001). The stretch‐induced acceleration of VF (control=38.8%) was significantly reduced by JTV‐519 0.1 μmol/L (19.8%) and abolished by JTV 1 μmol/L (−1.5%). During stretch, the VF activation complexity index was reduced in both JTV‐519 series (control=1.60±0.15; JTV 0.1 μmol/L=1.13±0.3, P<.0001; JTV 1 μmol/L=0.57±0.21, P<.0001), and was independently related to VF dominant frequency (R=.82; P<.0001). The fifth percentile of the VF activation intervals, conduction velocity and wavelength entered the multiple linear regression model using dominant frequency as the dependent variable (R=−.84; P<.0001). In conclusion, JTV‐519 slowed and simplified the baseline VF activation patterns and abolished the stretch‐induced manifestations of mechanoelectric feedback.

Epicardial-limited electrophysiological heterogeneities do not facilitate ventricular arrhythmia induction. An experimental study

The electrophysiological heterogeneities of the myocardium are associated with vulnerability to arrhythmias. This study presents an experimental heterogeneity model based on local epicardial cooling/warming. The ventricular activation-recovery interval (ARl), conduction velocity (CV) and arrhythmogenic response to electrical pacing were determined. Electrical mapping was carried out on isolated rabbit hearts (n=8), using a specific electrode device for epicardial temperature control. With respect to baseline, ARl in the modified zone was prolonged (137 ± 22 ms vs 111 ± 13 ms, p<;0.05) under maximum hypothermia (22.3 ± 0.6 °C vs 36.7 ± 0.8 DC), and was shortened (98 ± 13 ms vs 107 ± 16 ms, p<;0.05) under conditions of hyperthermia (41.8 ± 0.3 °C vs 37.3 ± 0.4 DC). CV decreased (70 ± 17 cm/s vs 76 ± 17 cm/s, p<;0.05) under hypothermia and increased (79 ± 20 cm/s vs 75 ± 21 cm/s, p<;0.05) under hyperthermia. There were no changes in the unmodified zone. Repetitive responses were observed in four hearts, with no dependency between the appearance of responses and the induced modifications. Thermally induced dispersion of ARl and CV did not favor the induction of ventricular arrhythmias, probably because only a limited zone of the ventricular epicardium was affected.