Showing papers by "Mark E. Anderson published in 2005"

Calmodulin kinase II inhibition protects against structural heart disease

Abstract: Beta-adrenergic receptor (betaAR) stimulation increases cytosolic Ca(2+) to physiologically augment cardiac contraction, whereas excessive betaAR activation causes adverse cardiac remodeling, including myocardial hypertrophy, dilation and dysfunction, in individuals with myocardial infarction. The Ca(2+)-calmodulin-dependent protein kinase II (CaMKII) is a recently identified downstream element of the betaAR-initiated signaling cascade that is linked to pathological myocardial remodeling and to regulation of key proteins involved in cardiac excitation-contraction coupling. We developed a genetic mouse model of cardiac CaMKII inhibition to test the role of CaMKII in betaAR signaling in vivo. Here we show CaMKII inhibition substantially prevented maladaptive remodeling from excessive betaAR stimulation and myocardial infarction, and induced balanced changes in excitation-contraction coupling that preserved baseline and betaAR-stimulated physiological increases in cardiac function. These findings mark CaMKII as a determinant of clinically important heart disease phenotypes, and suggest CaMKII inhibition can be a highly selective approach for targeting adverse myocardial remodeling linked to betaAR signaling.

Oxidative Mediated Lipid Peroxidation Recapitulates Proarrhythmic Effects on Cardiac Sodium Channels

Abstract: Sudden cardiac death attributable to ventricular tachycardia/fibrillation (VF) remains a catastrophic outcome of myocardial ischemia and infarction. At the same time, conventional antagonist drugs targeting ion channels have yielded poor survival benefits. Although pharmacological and genetic models suggest an association between sodium (Na + ) channel loss-of-function and sudden cardiac death, molecular mechanisms have not been identified that convincingly link ischemia to Na + channel dysfunction and ventricular arrhythmias. Because ischemia can evoke the generation of reactive oxygen species, we explored the effect of oxidative stress on Na + channel function. We show here that oxidative stress reduces Na + channel availability. Both the general oxidant tert-butyl-hydroperoxide and a specific, highly reactive product of the isoprostane pathway of lipid peroxidation, E 2 -isoketal, potentiate inactivation of cardiac Na + channels in human embryonic kidney (HEK)-293 cells and cultured atrial (HL-1) myocytes. Furthermore, E 2 -isoketals were generated in the epicardial border zone of the canine healing infarct, an arrhythmogenic focus where Na + channels exhibit similar inactivation defects. In addition, we show synergistic functional effects of flecainide, a proarrhythmic Na + channel blocker, and oxidative stress. These data suggest Na + channel dysfunction evoked by lipid peroxidation is a candidate mechanism for ischemia-related conduction abnormalities and arrhythmias.

Atrial Fibrillation in KCNE1-Null Mice

Abstract: Although atrial fibrillation is the most common serious cardiac arrhythmia, the fundamental molecular pathways remain undefined. Mutations in KCNQ1 , one component of a sympathetically activated cardiac potassium channel complex, cause familial atrial fibrillation, although the mechanisms in vivo are unknown. We show here that mice with deletion of the KCNQ1 protein partner KCNE1 have spontaneous episodes of atrial fibrillation despite normal atrial size and structure. Isoproterenol abolishes these abnormalities, but vagomimetic interventions have no effect. Whereas loss of KCNE1 function prolongs ventricular action potentials in humans, KCNE1 −/− mice displayed unexpectedly shortened atrial action potentials, and multiple potential mechanisms were identified: (1) K + currents (total and those sensitive to the KCNQ1 blocker chromanol 293B) were significantly increased in atrial cells from KCNE1 −/− mice compared with controls, and (2) when CHO cells expressing KCNQ1 and KCNE1 were pulsed very rapidly (at rates comparable to the normal mouse heart and to human atrial fibrillation), the sigmoidicity of I Ks activation prevented current accumulation, whereas cells expressing KCNQ1 alone displayed marked current accumulation at these very rapid rates. Thus, KCNE1 deletion in mice unexpectedly leads to increased outward current in atrial myocytes, shortens atrial action potentials, and enhances susceptibility to atrial fibrillation.

A dynamic α-β inter-subunit agonist signaling complex is a novel feedback mechanism for regulating L-type Ca2+ channel opening

Abstract: SPECIFIC AIMSCalmodulin binding peptides modeled after the L-type Ca2+ channel (CaV1.2) pore-forming α subunit cytoplasmic C terminus increase channel openings when applied to the cytoplasmic face of native L-type Ca2+ channels voltage-clamped in excised cell membrane patches, suggesting these sequences are endogenous agonist ligands. The aim of this study was to test the hypothesis that the cytoplasmic β subunit, which itself increases CaV1.2 channel opening probability and is constitutively bound to the α subunit, was the receptor for these endogenous ligands.PRINCIPAL FINDINGS1. The α subunit C terminus binds to the β subunit through embedded calmodulin interacting motifsWe coexpressed various flag-tagged CaV1.2 α subunit C terminus constructs (Fig. 1⤻ a) with full-length myc-tagged β subunits (β2a) in tsA-201 cells. Cell lysates were assayed for protein expression by immunoblotting (Fig. 1b⤻ , input) and run over anti-flag agarose to immunoprecipitate (IP) the α subunit C terminus-derived proteins. IP...

The Fire From Within The Biggest Ca2+ Channel Erupts and Dribbles

Abstract: See related article, pages 1314–1322 The multifunctional Ca2+ and calmodulin (CaM)-dependent protein kinase II (CaMKII) is a serine threonine kinase that is abundant in heart where it phosphorylates Ca2+i homeostatic proteins. It seems likely that CaMKII plays an important role in cardiac physiology because these target proteins significantly overlap with the more extensively studied serine threonine kinase, protein kinase A (PKA), which is a key arbiter of catecholamine responses in heart. However, the physiological functions of CaMKII remain poorly understood, whereas the potential role of CaMKII in signaling myocardial dysfunction and arrhythmias has become an area of intense focus. CaMKII activity and expression are upregulated in failing human hearts and in many animal models of structural heart disease.1 CaMKII inhibitory drugs can prevent cardiac arrhythmias2,3 and suppress afterdepolarizations4 that are a probable proximate focal cause of arrhythmias in heart failure. CaMKII inhibition in mice reduces left ventricular dilation and prevents disordered intracellular Ca2+ (Ca2+i) homeostasis after myocardial infarction.5 CaMKII overexpression in mouse heart causes severe cardiac hypertrophy, dysfunction, and sudden death that is heralded by increased SR Ca2+ leak6; these findings go a long way to making a case for CaMKII as a causative signal in heart disease and arrhythmias but do not identify critical molecular targets or test the potential role of CaMKII in a large non-rodent animal model. The work by Ai et al in this issue of Circulation Research makes an important contribution by demonstrating CaMKII upregulation causes increased Ca2+ leak from ryanodine receptor (RyR) Ca2+ release channels in a clinically-relevant model of structural heart disease.7 Ca2+i release controls cardiac contraction, and most of the Ca2+i for contraction is released from the intracellular sarcoplasmic reticulum (SR) …