Basal and IGF-I-dependent regulation of potassium channels by MAP kinases and PI3-kinase during eccentric cardiac hypertrophy

Declining Levels and Bioavailability of IGF-I in Cardiovascular Aging Associate With QT Prolongation-Results From the 1946 British Birth Cohort

Background

As people age, circulating levels of insulin-like growth factors (IGFs) and IGF binding protein 3 (IGFBP-3) decline. In rat cardiomyocytes, IGF-I has been shown to regulate sarcolemmal potassium channel activity and late sodium current thus impacting cardiac repolarization and the heart rate-corrected QT (QTc). However, the relationship between IGFs and IGFBP-3 with the QTc interval in humans, is unknown.

Objectives

To examine the association of IGFs and IGFBP-3 with QTc interval in an older age population-based cohort.

Methods

Participants were from the 1946 Medical Research Council (MRC) National Survey of Health and Development (NSHD) British birth cohort. Biomarkers from blood samples at age 53 and 60-64 years (y, exposures) included IGF-I/II, IGFBP-3, IGF-I/IGFBP-3 ratio and the change (Δ) in marker levels between the 60-64 and 53y sampled timepoints. QTc (outcome) was recorded from electrocardiograms at the 60-64y timepoint. Generalized linear multivariable models with adjustments for relevant demographic and clinical factors, were used for complete-cases and repeated after multiple imputation.

Results

One thousand four hundred forty-eight participants were included (48.3% men; QTc mean 414 ms interquartile range 26 ms). Univariate analysis revealed an association between low IGF-I and IGF-I/IGFBP-3 ratio at 60-64y with QTc prolongation [respectively: β -0.30 ms/nmol/L, (95% confidence intervals -0.44, -0.17), p < 0.001; β-28.9 ms/unit (-41.93, -15.50), p < 0.001], but not with IGF-II or IGFBP-3. No association with QTc was found for IGF biomarkers sampled at 53y, however both ΔIGF-I and ΔIGF-I/IGFBP-3 ratio were negatively associated with QTc [β -0.04 ms/nmol/L (-0.08, -0.008), p = 0.019; β -2.44 ms/unit (-4.17, -0.67), p = 0.007] while ΔIGF-II and ΔIGFBP-3 showed no association. In fully adjusted complete case and imputed models (reporting latter) low IGF-I and IGF-I/IGFBP-3 ratio at 60-64y [β -0.21 ms/nmol/L (-0.39, -0.04), p = 0.017; β -20.14 ms/unit (-36.28, -3.99), p = 0.015], steeper decline in ΔIGF-I [β -0.05 ms/nmol/L/10 years (-0.10, -0.002), p = 0.042] and shallower rise in ΔIGF-I/IGFBP-3 ratio over a decade [β -2.16 ms/unit/10 years (-4.23, -0.09), p = 0.041], were all independently associated with QTc prolongation. Independent associations with QTc were also confirmed for other previously known covariates: female sex [β 9.65 ms (6.65, 12.65), p < 0.001], increased left ventricular mass [β 0.04 ms/g (0.02, 0.06), p < 0.001] and blood potassium levels [β -5.70 ms/mmol/L (-10.23, -1.18) p = 0.014].

Conclusion

Over a decade, in an older age population-based cohort, declining levels and bioavailability of IGF-I associate with prolongation of the QTc interval. As QTc prolongation associates with increased risk for sudden death even in apparently healthy people, further research into the antiarrhythmic effects of IGF-I on cardiomyocytes is warranted.

AKT and ERK1/2 activation via remote ischemic preconditioning prevents Kcne2-dependent sudden cardiac death

Sudden cardiac death (SCD) is the leading global cause of mortality. SCD often arises from cardiac ischemia reperfusion (IR) injury, pathologic sequence variants within ion channel genes, or a combination of the two. Alternative approaches are needed to prevent or ameliorate ventricular arrhythmias linked to SCD. Here, we investigated the efficacy of remote ischemic preconditioning (RIPC) of the limb versus the liver in reducing ventricular arrhythmias in a mouse model of SCD. Mice lacking the Kcne2 gene, which encodes a potassium channel β subunit associated with acquired Long QT syndrome were exposed to IR injury via coronary ligation. This resulted in ventricular arrhythmias in all mice (15/15) and SCD in 5/15 mice during reperfusion. Strikingly, prior RIPC (limb or liver) greatly reduced the incidence and severity of all ventricular arrhythmias and completely prevented SCD. Biochemical and pharmacological analysis demonstrated that RIPC cardioprotection required ERK1/2 and/or AKT phosphorylation. A lack of alteration in GSK‐3β phosphorylation suggested against conventional reperfusion injury salvage kinase (RISK) signaling pathway protection. If replicated in human studies, limb RIPC could represent a noninvasive, nonpharmacological approach to limit dangerous ventricular arrhythmias associated with ischemia and/or channelopathy‐linked SCD.

Alcohol-Mediated Organ Damages: Heart and Brain

Alcohol is one of the most commonly abused substances in the United States. Chronic consumption of ethanol has been responsible for numerous chronic diseases and conditions globally. The underlying mechanism of liver injury has been studied in depth, however, far fewer studies have examined other organs especially the heart and the central nervous system (CNS). The authors conducted a narrative review on the relationship of alcohol with heart disease and dementia. With that in mind, a complex relationship between inflammation and cardiovascular disease and dementia has been long proposed but inflammatory biomarkers have gained more attention lately. In this review we examine some of the consequences of the altered cytokine regulation that occurs in alcoholics in organs other than the liver. The article reviews the potential role of inflammatory markers such as TNF-α in predicting dementia and/or cardiovascular disease. It was found that TNF-α could promote and accelerate local inflammation and damage through autocrine/paracrine mechanisms. Unraveling the mechanisms linking chronic alcohol consumption with proinflammatory cytokine production and subsequent inflammatory signaling pathways activation in the heart and CNS, is essential to improve our understanding of the disease and hopefully facilitate the development of new remedies.

Cellular Communications in the Heart

Heart failure is one of the leading causes of morbidity and mortality worldwide. Cardiac remodelling is first an adaptive, becoming a maladaptive, compensatory mechanism that finally causes ventricular dysfunction independently of the etiology of the initial insult. In the present article the authors describe the elements of the human heart, examining their basic functions and their inter-communication under both normal and pathological circumstances. Cardiac myocytes carry out mechanical and electrical functions of the heart and cardiac fibroblasts maintain its structural integrity. Several factors can affect fibroblast activation and under pathological stress they transdifferentiate into myofibroblasts. Endothelial cells have complex biological functions, including the control of vascular permeability, vasomotion, regulation of haemostasis, immune responses and angiogenesis. The extracellular matrix is a complex architectural network consisting of a variety of proteins. Various routes using a plethora of products and mediators contribute to the cross-talk of the myocytes with endothelial cells, extracellular matrix and cardiac fibroblasts. A better understanding of the entire mechanism of cellular communication by the established or the more recently discovered agents will certainly emerge promising new perspectives when looking at the prevention of heart failure and leading to more substantial therapeutic interventions.

Control of cardiac repolarization by phosphoinositide 3-kinase signaling to ion channels

Upregulation of phosphoinositide 3-kinase (PI3K) signaling is a common alteration in human cancer, and numerous drugs that target this pathway have been developed for cancer treatment. However, recent studies have implicated inhibition of the PI3K signaling pathway as the cause of a drug-induced long-QT syndrome in which alterations in several ion currents contribute to arrhythmogenic drug activity. Surprisingly, some drugs that were thought to induce long-QT syndrome by direct block of the rapid delayed rectifier (IKr) also seem to inhibit PI3K signaling, an effect that may contribute to their arrhythmogenicity. The importance of PI3K in regulating cardiac repolarization is underscored by evidence that QT interval prolongation in diabetes mellitus also may result from changes in multiple currents because of decreased insulin activation of PI3K in the heart. How PI3K signaling regulates ion channels to control the cardiac action potential is poorly understood. Hence, this review summarizes what is known about the effect of PI3K and its downstream effectors, including Akt, on sodium, potassium, and calcium currents in cardiac myocytes. We also refer to some studies in noncardiac cells that provide insight into potential mechanisms of ion channel regulation by this signaling pathway in the heart. Drug development and safety could be improved with a better understanding of the mechanisms by which PI3K regulates cardiac ion channels and the extent to which PI3K inhibition contributes to arrhythmogenic susceptibility.

Alcohol and inflammatory responses: summary of the 2013 Alcohol and Immunology Research Interest Group (AIRIG) meeting

Loyola University Chicago, Health Sciences Campus in Maywood, Illinois hosted the 18th annual Alcohol and Immunology Research Interest Group (AIRIG) meeting on November 22, 2013. This year's meeting emphasized alcohol's effect on inflammatory responses in diverse disease states and injury conditions. The meeting consisted of three plenary sessions demonstrating the adverse effects of alcohol, specifically, liver inflammation, adverse systemic effects, and alcohol's role in infection and immunology. Researchers also presented insight on modulation of microRNAs and stress proteins following alcohol consumption. Additionally, researchers revealed sex- and concentration-dependent differences in alcohol-mediated pathologies.

Crosstalk between mitogen-activated protein kinases and mitochondria in cardiac diseases: therapeutic perspectives

Cardiovascular diseases cause more mortality and morbidity worldwide than any other diseases. Although many intracellular signaling pathways influence cardiac physiology and pathology, the mitogen-activated protein kinase (MAPK) family has garnered significant attention because of its vast implications in signaling and crosstalk with other signaling networks. The extensively studied MAPKs ERK1/2, p38, JNK, and ERK5, demonstrate unique intracellular signaling mechanisms, responding to a myriad of mitogens and stressors and influencing the signaling of cardiac development, metabolism, performance, and pathogenesis. Definitive relationships between MAPK signaling and cardiac dysfunction remain elusive, despite 30 years of extensive clinical studies and basic research of various animal/cell models, severities of stress, and types of stimuli. Still, several studies have proven the importance of MAPK crosstalk with mitochondria, powerhouses of the cell that provide over 80% of ATP for normal cardiomyocyte function and play a crucial role in cell death. Although many questions remain unanswered, there exists enough evidence to consider the possibility of targeting MAPK-mitochondria interactions in the prevention and treatment of heart disease. The goal of this review is to integrate previous studies into a discussion of MAPKs and MAPK-mitochondria signaling in cardiac diseases, such as myocardial infarction (ischemia), hypertrophy and heart failure. A comprehensive understanding of relevant molecular mechanisms, as well as challenges for studies in this area, will facilitate the development of new pharmacological agents and genetic manipulations for therapy of cardiovascular diseases.

Calcitonin Gene-Related Peptide Regulates Cardiomyocyte Survival through Regulation of Oxidative Stress by PI3K/Akt and MAPK Signaling Pathways

CGRP and specific CGRP receptors are found in the heart where they produce positive-inotropic and anti-apoptotic effects, key adaptations to exercise and cardiovascular disease. PI3K/Akt and MAPK signaling imbalances are associated with cardiomyocyte pathologies; however, the effects of CGRP on these pathways are unclear. Therefore, we hypothesized that CGRP modulates inotropic and apoptotic adaptations of cardiomyocytes by regulating PI3K/Akt and MAPK/ERK signaling balances. We treated cardiomyocytes with combinations of CGRP, PI3K/Akt and MAPK signaling agonists and antagonists. We evaluated expression of the mRNA and proteins levels of survival signaling molecules related to the PI3K/Akt and MAPK and measured apoptosis by caspase 3/7 activity. CGRP_1-37 decreased Akt, NFκB, SOD-3 and increased ERK1/2 and p38 MAPK expressions, which was antagonized by CGRP_8-37. Akt-negative construct transfection, Ad.Akt(K179M), inhibited the CGRP_1-37-induced increment in MAPK expressions. A PI3K-antagonist treatment with LY294002 or CGRP_1-37/Ad.Akt(K179M) co-treatment alleviated the CGRP-increased caspase activity and -decrements in SOD-3. These findings demonstrate a CGRP negative effect on the PI3K/Akt signaling pathway and CGRP receptor-induced crosstalk between PI3K/Akt and MAPK in normal cardiomyocytes. Future studies to differentiate CGRP effects on intracellular signal transduction mechanisms in pathological conditions will elucidate the significance of CGRP in, and provide novel therapeutic targets for, heart failure.

Inotropic and lusitropic effects of calcitonin gene-related peptide in the heart

Previous studies have demonstrated positive-inotropic effects of calcitonin gene-related peptide (CGRP), but the mechanisms remain unclear. Therefore, two experiments were performed to determine the physiological correlates of the positive-inotropic effects of CGRP. Treatments designed to antagonize the effects of physiologically active CGRP₁₋₃₇ included posttreatment with CGRP₈₋₃₇ and pretreatment with LY-294002 (LY, an inhibitor of phosphatidylinositol 3-kinase), 17β-estradiol (E), and progesterone (P) were also used to modulate the effects of CGRP₁₋₃₇. Experiment 1 was in vitro studies on sarcomeres and cells of isolated adult rat cardiac myocytes. CGRP₁₋₃₇, alone and in combination with E and P, decreased sarcomere shortening velocities and increased shortening percentages, effects that were antagonized by CGRP₈₋₃₇, but not by LY. CGRP₁₋₃₇ increased resting intracellular calcium ion concentrations and Ca(2+) influxes, effects that were also antagonized by both CGRP₈₋₃₇ and LY. Experiment 2 was in vivo studies on left ventricular pressure-volume (PV) loops. CGRP₁₋₃₇ increased end-systolic pressure, ejection fraction, and velocities of contraction and relaxation while decreasing stroke volume, cardiac output, stroke work, PV area, and compliance. After partial occlusion of the vena cava, CGRP₁₋₃₇ increased the slope of the end-systolic PV relationship. CGRP₈₋₃₇ and LY attenuated most of the CGRP-induced changes. These findings suggest that CGRP-induced positive-inotropic effects may be increased by treatments with estradiol and progesterone and inhibited by LY. The physiological correlates of CGRP-induced positive inotropy observed in rat sarcomeres, cells, and intact hearts are likely to reveal novel mechanisms of heart failure in humans.

Cross talk between cardiac myocytes and fibroblasts: from multiscale investigative approaches to mechanisms and functional consequences

The heart is comprised of a syncytium of cardiac myocytes (CM) and surrounding nonmyocytes, the majority of which are cardiac fibroblasts (CF). CM and CF are highly interspersed in the myocardium with one CM being surrounded by one or more CF. Bidirectional cross talk between CM and CF plays important roles in determining cardiac mechanical and electrical function in both normal and diseased hearts. Genetically engineered animal models and in vitro studies have provided evidence that CM and CF can regulate each other's function. Their cross talk contributes to structural and electrical remodeling in both atria and ventricles and appears to be involved in the pathogenesis of various heart diseases that lead to heart failure and arrhythmia disorders. Mechanisms of CM-CF cross talk, which are not yet fully understood, include release of paracrine factors, direct cell-cell interactions via gap junctions and potentially adherens junctions and nanotubes, and cell interactions with the extracellular matrix. In this article, we provide an overview of the existing multiscale experimental and computational approaches for the investigation of cross talk between CM and CF and review recent progress in our understanding of the functional consequences and underlying mechanisms. Targeting cross talk between CM and CF could potentially be used therapeutically for the modulation of the cardiac remodeling response in the diseased heart and may lead to new strategies for the treatment of heart failure or rhythm disturbances.

Effects of IGF-1 on I(K) and I(K1) Channels via PI3K/Akt Signaling in Neonatal Cardiac Myocytes

Previous studies suggest that sarcolemmal potassium currents play important roles in cardiac hypertrophy. IGF-1 contributes to cardiac hypertrophy via activation of PI3K/Akt signaling. However, the relationships between IGF-1, PI3K/Akt signaling and sarcolemmal potassium currents remain unknown. Therefore, we tested the hypothesis that IGF-1 and PI3K/Akt signaling, independently, decrease sarcolemmal potassium currents in cardiac myocytes of neonatal rats. We compared the delayed outward rectifier (I_K) and the inward rectifier (I_K) current densities resulting from IGF-1 treatments to those resulting from simulation of PI3K/Akt signaling using adenoviral (Ad) BD110 and wild-type Akt and to those resulting from inhibition of PI3K signaling by LY294002. Ad.BD110 and Ad.Akt decreased I_K and these decrements were attenuated by LY 294002. The IGF-1 treatments decreased both I_K and I_K1 but only the I_K decrement was attenuated by LY294002. These findings demonstrate that IGF-1 may contribute to cardiac hypertrophy by PI3K/Akt signal transduction mechanisms in neonatal rat cardiomyocytes. Failure of LY294002 to effectively antagonize IGF-1 induced decrements in I_K1 suggests that a signal pathway adjunct to PI3K/Akt contributes to IGF-1 protection against arrhythmogenesis in these myocytes. Our findings imply that sarcolemmal outward and inward rectifier potassium channels are substrates for IGF-1/PI3K/Akt signal transduction molecules.

IGF-1 deficiency resists cardiac hypertrophy and myocardial contractile dysfunction: role of microRNA-1 and microRNA-133a

This study was designed to examine the impact of insulin-like growth factor-1 (IGF-1) deficiency on abdominal aortic constriction (AAC)-induced cardiac geometric and functional changes with a focus on microRNA-1, 133a and 208, which are specially expressed in hearts and govern cardiac hypertrophy and stress-dependent cardiac growth. Liver-specific IGF-1-deficient (LID) and C57/BL6 mice were subject to AAC. Echocardiographic and cardiomyocyte function were assessed 4 wks later. Haematoxylin and eosin staining was used to monitor myocardial morphology. Western blot and real-time PCR were used to detect protein and miR expression, respectively. Neonatal rat cardiomyocytes (NRCMs) were transfected with miRs prior to IGF-1 exposure to initiate cell proliferation. Immunohistochemistry and [³H] Leucine incorporation were used to detect cell surface area and protein abundance. C57 mice subject to AAC displayed increased ventricular wall thickness, decreased left ventricular end diastolic and end systolic dimensions and elevated cardiomyocyte shortening capacity, all of which were attenuated in LID mice. In addition, IGF-1 deficiency mitigated AAC-induced increase in atrial natriuretic factor, GATA binding protein 4, glucose transporter 4 (GLUT4) and Akt phosphorylation. In contrast, neither AAC treatment nor IGF-1 deficiency affected glycogen synthase kinase 3b, mammalian target of rapamycin, the Glut-4 translocation mediator Akt substrate of 160 kD (AS160) and protein phosphatase. Levels of miR-1 and -133a (but not miR-208) were significantly attenuated by AAC in C57 but not LID mice. Transfection of miR-1 and -133a obliterated IGF-1-induced hypertrophic responses in NRCMs. Our data suggest that IGF-1 deficiency retards AAC-induced cardiac hypertrophic and contractile changes via alleviating down-regulation of miR-1 and miR-133a in response to left ventricular pressure overload.

Regulation of the instantaneous inward rectifier and the delayed outward rectifier potassium channels by Captopril and Angiotensin II via the Phosphoinositide-3 kinase pathway in volume-overload-induced hypertrophied cardiac myocytes

Background

Early development of cardiac hypertrophy may be beneficial but sustained hypertrophic activation leads to myocardial dysfunction. Regulation of the repolarizing currents can be modulated by the activation of humoral factors, such as angiotensin II (ANG II) through protein kinases. The aim of this work is to assess the regulation of I_K and I_K1 by ANG II through the PI3-K pathway in hypertrophied ventricular myocytes.

Material/Methods

Cardiac eccentric hypertrophy was induced through volume-overload in adult male rats by aorto-caval shunt (3 weeks). After one week half of the rats were given captopril (2 weeks; 0.5 g/l/day) and the other half served as control. The voltage-clamp and western blot techniques were used to measure the delayed outward rectifier potassium current (I_K) and the instantaneous inward rectifier potassium current (I_K1) and Akt activity, respectively.

Results

Hypertrophied cardiomyocytes showed reduction in I_K and I_K1. Treatment with captopril alleviated this difference seen between sham and shunt cardiomyocytes. Acute administration of ANG II (10⁻⁶M) to cardiocytes treated with captopril reduced I_K and I_K1 in shunts, but not in sham. Captopril treatment reversed ANG II effects on I_K and I_K1 in a PI3-K-independent manner. However in the absence of angiotensin converting enzyme inhibition, ANG II increased both I_K and I_K1 in a PI3-K-dependent manner in hypertrophied cardiomyocytes.

Conclusions

Thus, captopril treatment reveals a negative effect of ANG II on I_K and I_K1, which is PI3-K independent, whereas in the absence of angiotensin converting enzyme inhibition I_K and I_K1 regulation is dependent upon PI3-K.

ATP-Sensitive Potassium Channel Currents in Eccentrically Hypertrophied Cardiac Myocytes of Volume-Overloaded Rats

ATP-sensitive potassium channels (K(ATP)) protect the myocardium from hypertrophy induced by pressure-overloading. In this study, we determined the effects of these channels in volume-overloading. We compared the effects of a K(ATP) agonist and a K(ATP) antagonist on sarcolemmal transmembrane current density (pA/pF) clamped at 20 mV increments of membrane potential from -80 to +40 mV in ventricular cardiac myocytes. The basal outward potassium pA/pF in myocytes of volume-overloaded animals was significantly smaller than that in the myocytes of sham-operated controls. Treatment of the control myocytes with the K(ATP) agonist cromakalim increased pA/pF significantly. This increase was blocked by the K(ATP) antagonist glibenclamide. Treatment of the hypertrophied myocytes from volume-overloaded animals with cromakalim and in the presence and absence of glibenclamide did not change pA/pF significantly. These findings suggest that eccentrically hypertrophied cardiac myocytes from volume-overloading may be unresponsive to specific activation/inactivation of K(ATP) and that dysfunctional K(ATP) may fail to protect the myocardium from left ventricular hypertrophy associated with volume-overloading.

Cardiac fibroblasts in cell culture systems: myofibroblasts all along?

The cytoarchitecture of the working myocardium is characterized by densely packed cardiomyocytes that are embedded in a three-dimensional network of numerous fibroblasts. Although the importance of cardiac fibroblasts in maintaining an orderly structured extracellular matrix is well recognized, less is known about their potential paracrine and electrotonic interactions with cardiomyocytes. This is partly the result of the complex intermingling of both cell types in vivo that tends to preclude a direct investigation of heterocellular crosstalk. It is for that reason that most of our present knowledge regarding stromal-parenchymal cell interactions is based on culture systems that permit direct access to either cell type. An often disregarded feature of such studies is that cardiac fibroblasts in standard two-dimensional cell culture have a pronounced tendency to undergo a phenotype switch to myofibroblasts. This cell type typically appears in injured hearts where it contributes importantly to fibrotic remodeling. The present review focuses on recent insights into electrical and paracrine crosstalk between myofibroblasts and cardiomyocytes while acknowledging that a comprehensive understanding of stromal-parenchymal cell interactions will depend on future methodological developments that permit retaining the fibroblast phenotype in cell culture systems and that will, most importantly, allow direct investigations of heterocellular crosstalk in intact tissue.

Circadian profiles in the embryonic chick heart: L-type voltage-gated calcium channels and signaling pathways

Circadian clocks exist in the heart tissue and modulate multiple physiological events, from cardiac metabolism to contractile function and expression of circadian oscillator and metabolic-related genes. Ample evidence has demonstrated that there are endogenous circadian oscillators in adult mammalian cardiomyocytes. However, mammalian embryos cannot be entrained independently to light-dark (LD) cycles in vivo without any maternal influence, but circadian genes are well expressed and able to oscillate in embryonic stages. The authors took advantage of using chick embryos that are independent of maternal influences to investigate whether embryonic hearts could be entrained under LD cycles in ovo. The authors found circadian regulation of L-type voltage-gated calcium channels (L-VGCCs), the ion channels responsible for the production of cardiac muscle contraction in embryonic chick hearts. The mRNA levels and protein expression of VGCCα1C and VGCCα1D are under circadian control, and the average L-VGCC current density is significantly larger when cardiomyocytes are recorded during the night than day. The phosphorylation states of several kinases involved in insulin signaling and cardiac metabolism, including extracellular signal-regulated kinase (Erk), stress-activated protein kinase (p38), protein kinase B (Akt), and glycogen synthase kinase-3β (GSK-3β), are also under circadian control. Both Erk and p38 have been implicated in regulating cardiac contractility and in the development of various pathological states, such as cardiac hypertrophy and heart failure. Even though both Erk and phosphoinositide 3-kinase (PI3K)-Akt signaling pathways participate in complex cellular processes regarding physiological or pathological states of cardiomyocytes, the circadian oscillators in the heart regulate these pathways independently, and both pathways contribute to the circadian regulation of L-VGCCs.

Role of apoptosis signal-regulating kinase-1-c-Jun NH2-terminal kinase-p38 signaling in voltage-gated K+ channel remodeling of the failing heart: regulation by thioredoxin

c-Jun NH(2)-terminal kinase (JNK) and p38 kinase are key regulators of cardiac hypertrophy and apoptosis during pathological stress, but their role in regulating ion channels in the diseased heart is unclear. Thus, we compared the kinase profile and electrophysiological phenotype of the rat ventricle 6-8 weeks after myocardial infarction (MI). Molecular analyses showed that JNK and p38 activities were markedly increased in post-MI hearts, while parallel voltage-clamp studies in ventricular myocytes revealed a characteristic downregulation of transient outward K(+) current (I(to)) density. When post-MI myocytes were treated with JNK or p38 inhibitors, I(to) density increased to control levels. Upregulation of I(to) was also elicited by insulin-like growth factor-1, which decreased JNK/p38 activity in post-MI hearts, and these changes were blocked by the thioredoxin (Trx) reductase inhibitor auranofin. Consistent with activation of JNK-p38 signaling, binding of apoptosis signal-regulating kinase-1 with Trx1 was also markedly decreased post-MI, and was reversed by insulin-like growth factor-1 in an auranofin-sensitive manner. We conclude that expression of ventricular K(+) channels is redox regulated and that chronic impairment of the Trx system in the post-MI heart contributes to I(to) remodeling through sustained activation of apoptosis signal-regulating kinase-1-JNK-p38 signaling. The cardiac Trx system may thus be a novel therapeutic target to reverse or prevent ventricular arrhythmias in the failing heart.

Mitogen-activated protein kinase signaling in the heart: angels versus demons in a heart-breaking tale

Among the myriad of intracellular signaling networks that govern the cardiac development and pathogenesis, mitogen-activated protein kinases (MAPKs) are prominent players that have been the focus of extensive investigations in the past decades. The four best characterized MAPK subfamilies, ERK1/2, JNK, p38, and ERK5, are the targets of pharmacological and genetic manipulations to uncover their roles in cardiac development, function, and diseases. However, information reported in the literature from these efforts has not yet resulted in a clear view about the roles of specific MAPK pathways in heart. Rather, controversies from contradictive results have led to a perception that MAPKs are ambiguous characters in heart with both protective and detrimental effects. The primary object of this review is to provide a comprehensive overview of the current progress, in an effort to highlight the areas where consensus is established verses the ones where controversy remains. MAPKs in cardiac development, cardiac hypertrophy, ischemia/reperfusion injury, and pathological remodeling are the main focuses of this review as these represent the most critical issues for evaluating MAPKs as viable targets of therapeutic development. The studies presented in this review will help to reveal the major challenges in the field and the limitations of current approaches and point to a critical need in future studies to gain better understanding of the fundamental mechanisms of MAPK function and regulation in the heart.

Myricetin reduces voltage activated potassium channel currents in DRG neurons by a p38 dependent mechanism

Myricetin is a naturally occurring flavonoid known for its anti-neoplastic, anti-oxidant and anti-inflammatory effects. Currently, potential analgesic effects are proposed for several animal models of acute and chronic pain. Pilot studies show a flavonoid-induced modulation of intracellular mitogen-activated protein kinases (MAPK) as p38 and interactions with voltage activated potassium channel currents (I(K(V))). The aim of this study was to investigate the underlying modulation of I(K(V)) and the influence of MAPK phosphorylation in an in vitro cell model. Whole cell patch-clamp recordings of rat dorsal root ganglion neurons were performed and I(K(V)) isolated. I(K(V)) were concentration-dependently reduced by myricetin (1-75μM myricetin; reduction range 18-78%) with no voltage dependency (-80 to +60mV). The reduction of I(K(V)) was enhanced by blocking p38 with the p38 inhibitor SB203580 (40±20% without SB203580 vs. 62±5% with 5μM SB203580 or 83±7% with 10μM SB203580), but abolished by activation of p38 using anisomycin (40±20% without anisomycin vs. 0.73±17% with 5μM anisomycin). We conclude that myricetin reduces I(K(V)) by p38 dependent mechanisms in sensory neurons. Since a reduction of I(K(V)) rather increases neuronal excitability, it is unlikely that this effect of myricetin contributes to its analgesic effects.

Cross-talk between MAPKs and PI-3K pathways alters the functional density of I(K) channels in hypertrophied hearts

Mitogen activated protein kinases (MAPK), such as ERK1/2 and p38 MAPK and phosphatidylinositol-3 phosphate kinase (PI-3K) play a major role in the development of cardiac hypertrophy. Recently, we have shown their crucial role in the regulation of the myocardial function through their effects on crucial ion channels. It is the focus of this study to resolve the interaction between these pathways and its implication on the function of the normal and hypertrophied cardiomyocytes. To that end, we created arteriovenous fistula in the adult rat that developed volume-overload eccentric cardiac hypertrophy over a 3-week period. We measured the relative activity of ERK1/2, p38 MAPKs and Akt through western blot analysis and assessed the functional density of the outward rectifier potassium current (I(K)) using the patch-clamp technique. The results showed a mutual negative autoregulation between ERK1/2 and p38 in normal cardiomyocytes, which disappears during cardiac hypertrophy. In addition, PI-3K seems to assume a greater role in mediating IGF-1 effects on the MAPKs during cardiac hypertrophy. This was also relevant to I(K) functional density which was reduced by activation of both MAPKs and Akt by angiotensin II (ANG II) and insulin-like growth factor-1 (IGF-1), respectively; however, this reduction was reversed by inhibition of PI-3K alone in hypertrophied myocytes but not in normal ones. This raises an important implication relative to the role of IGF-1-dependent activation of PI-3K, which may translate into a differential prognostic for cardiac hypertrophy among ethnic groups. This is true in African Americans, having higher circulating IGF-1 levels, and especially true for the athletes among them.