Catecholaminergic-induced arrhythmias in failing cardiomyocytes associated with human HRCS96A variant overexpression

Article (PDF Available)inAJP Heart and Circulatory Physiology 301(4):H1588-95 · July 2011with18 Reads
DOI: 10.1152/ajpheart.01153.2010 · Source: PubMed
The histidine-rich calcium binding protein (HRC) Ser96Ala polymorphism was shown to correlate with ventricular arrhythmias and sudden death only in dilated cardiomyopathy patients but not in healthy human carriers. In the present study, we assessed the molecular and cellular mechanisms underlying human arrhythmias by adenoviral expression of the human wild-type (HRC(WT)) or mutant HRC (HRC(S96A)) in adult rat ventricular cardiomyocytes. Total HRC protein was increased by ∼50% in both HRC(WT)- and HRC(S96A)-infected cells. The HRC(S96A) mutant exacerbated the inhibitory effects of HRC(WT) on the amplitude of Ca(2+) transients, prolongation of Ca(2+) decay time, and caffeine-induced sarcoplasmic reticulum Ca(2+) release. Consistent with these findings, HRC(S96A) reduced maximal sarcoplasmic reticulum calcium uptake rate to a higher extent than HRC(WT). Furthermore, the frequency of spontaneous Ca(2+) sparks, which was reduced by HRC(WT), was increased by mutant HRC(S96A) under resting conditions although there were no spontaneous Ca(2+) waves under stress conditions. However, expression of the HRC(S96A) genetic variant in cardiomyocytes from a rat model of postmyocardial infarction heart failure induced dramatic disturbances of rhythmic Ca(2+) transients. These findings indicate that the HRC Ser96Ala variant increases the propensity of arrhythmogenic Ca(2+) waves in the stressed failing heart, suggesting a link between this genetic variant and life-threatening ventricular arrhythmias in human carriers.
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    • c o m / l o c a t e / i j c a r d (i) The increase in oxygen consumption in the myocardium that arises because of the increased need for re-internalization of calcium during diastole can lead to increased risk for ischemic patients ; this may foster energy starvation in cardiac cells owing to increased ATP consumption in order to support an increased SERCA activity; (ii) A further increase in oxygen demand is induced by the chronotropic effect induced by some of the calcium mobilizers (especially those which acts via an increase in intracellular cAMP level); (iii) Drugs acting through modulation of cyclic AMP (e.g. cathecolamines, PDE inhibitors) also induce the phosphorylation of troponin I [9] and thus promote calcium desensitization of the contractile apparatus [10] leading to a less efficient contraction; (iv) Disturbed intracellular calcium homeostasis can lead to ventricular arrhythmia [11] due to early and delayed afterdepolarizations, while unstable intracellular calcium dynamics can promote ventricular extrasystoles and increase the incidence of wave breaks during ventricular fibrillation [12]; (v) The increase in intracellular calcium has been associated with acceleration of myocardial remodeling, and with apoptosis [13]; (vi) Diastolic abnormalities, seen as impaired relaxation and increased diastolic wall stress, are also detrimental consequence of Ca 2+ overload [14]; (vii) The overall worse prognosis in the mid-term to long-term, whereby the use of dobutamine and PDE inhibitors was specifically investigated in two focused meta-analyses by Tacon et al. [15] and by Nony et al. [16], respectively. Their conclusion was that these drugs do not provide any benefits in terms of patient survival.
    [Show abstract] [Hide abstract] ABSTRACT: The use of inotropes for correcting hemodynamic dysfunction in patients with congestive heart failure has been described over many decades. Drugs such as cardiac glycosides, cathecolamines, phosphodiestherase inhibitors, and calcium sensitizers have been in turn proposed. However, the number of new chemical entities in this therapeutic field has been surprisingly low, and the current selection of drugs is limited. One of the paradigm shifts in the discovery for new inotropes was to focus on 'calcium sensitizers' instead of 'calcium mobilizers'. This was designed to lead to the development of safer inotropes, devoid of the complications that arise due to increased intracellular calcium levels. However, only three such calcium sensitizers have been fully developed over the lat-est 30 years. Moreover, two of these, levosimendan and pimobendan, have multiple molecular targets and other pharmacologic effects in addition to inotropy, such as peripheral vasodilation. More recently, omecamtiv mecarbil was described, which is believed to have a pure inotropy action that is devoid of pleiotropic effects. When the clinical data of these three calcium sensitizers are compared, it appears that the less pure inotropes have the cutting edge over the purer inotrope, due to additional effects during the treatment of a complex syndrome such as acute congested heart failure. This review aims to answer the question whether calcium sensitization per se is a sufficient strategy for bringing required clinical benefits to patients with heart failure. This review is dedicated to the memory of Heimo Haikala, a true and passionate innovator in this challenging field.
    Full-text · Article · Dec 2015
    • The Histidine Rich Ca 2? (HRC)-binding protein is a SR protein that, similarly to calsequestrin, functions as Ca 2? buffer. HRC over-expression results in a significant inhibition of the SR Ca 2? uptake, a decrease in Ca 2? transient amplitude and a reduction in Ca 2? spark frequency, suggesting that HRC may buffer the SR luminal Ca 2? , thus inhibiting Ca 2? release (Han et al. 2011). Alternatively, it may act as a negative regulator of RyR opening, directly or through its binding to triadin.
    [Show abstract] [Hide abstract] ABSTRACT: The sarcoplasmic reticulum (SR) of striated muscles is specialized for releasing Ca(2+) following sarcolemma depolarization in order to activate muscle contraction. To this end, the SR forms a network of longitudinal tubules and cisternae that surrounds the myofibrils and, at the same time, participates to the assembly of the triadic junctional membrane complexes formed by the close apposition of one t-tubule, originated from the sarcolemma, and two SR terminal cisternae. Advancements in understanding the molecular basis of the SR structural organization have identified an interaction between sAnk1, a transmembrane protein located on the longitudinal SR (l-SR) tubules, and obscurin, a myofibrillar protein. The direct interaction between these two proteins results in molecular contacts that have the overall effect to stabilize the l-SR tubules along myofibrils in skeletal muscle fibers. Less known is the structural organization of the sites in the SR that are specialized for Ca(2+) release and are positioned at the junctional SR (j-SR), i.e. the region of the terminal cisternae that faces the t-tubule at triads. At the j-SR, several trans-membrane proteins like triadin, junctin, or intra-luminal SR proteins like calsequestrin, are assembled together with the ryanodine receptor, the SR Ca(2+) release channel, into a macromolecular complex specialized in releasing Ca(2+). At triads, the 12 nm-wide gap between the t-tubule and the j-SR allows the ryanodine receptor on the j-SR to be functionally coupled with the voltage-gated L-type calcium channel on the t-tubule in order to allow the transduction of the voltage-induced signal into Ca(2+) release through the ryanodine receptor channels. The muscle-specific junctophilin isoforms (JPH1 and JPH2) are anchored to the j-SR with a trans-membrane segment present at the C-terminus and are capable to bind the sarcolemma with a series of phospholipid-binding motifs localized at the N-terminus. Accordingly, through this dual interaction, JPH1 and JPH2 are responsible for the assembly of the triadic junctional membrane complexes. Recent data indicate that junctophilins seem also to interact with other proteins of the excitation-contraction machinery, suggesting that they may contribute to hold excitation-contraction coupling proteins to the sites where the j-SR is being organized.
    Full-text · Article · Sep 2015
    • The protein levels of HRC have been shown to be significantly reduced in human and animal models of heart failure (Fan et al., 2004), which may be a compensatory mechanism that increases calcium release from the SR in an attempt to improve cardiac contraction. More recently, a HRC mutation (Ser96Ala) was found to cause defects in regulation, as evidenced by depressed calcium transients and prolonged calcium decay, which lead to DCM and ventricular arrhythmias (Arvanitis et al., 2008; Han et al., 2011) (Table 1). S100A1 is a calcium-binding protein that has recently emerged as a key regulator of calcium homeostasis in cardiac muscle.
    [Show abstract] [Hide abstract] ABSTRACT: Cardiomyocyte function depends on coordinated movements of calcium into and out of the cell and the proper delivery of ATP to energy-utilizing enzymes. Defects in calcium-handling proteins and abnormal energy metabolism are features of heart failure. Recent discoveries have led to gene-based therapies targeting calcium-transporting or -binding proteins, such as the cardiac sarco(endo)plasmic reticulum calcium ATPase (SERCA2a), leading to improvements in calcium homeostasis and excitation-contraction coupling. Here we review impaired calcium cycling and energetics in heart failure, assessing their roles from both a mutually exclusive and interdependent viewpoint, and discuss therapies that may improve the failing myocardium. Copyright © 2015 Elsevier Inc. All rights reserved.
    Full-text · Article · Feb 2015
    • The functional importance of HRC is highlighted by the identification of a human genetic variant (Ser96Ala) that was linked to life‐threatening ventricular arrhythmias and sudden death in a well‐characterized cohort of patients with idiopathic DCM.14 Furthermore, the percentage of homozygous Ala/Ala patients with an implantable cardioverter‐defibrillator was almost double that of the Ser/Ala heterozygotes, suggesting a strong dosage effect of this HRC genetic variant on ventricular arrhythmias. Indeed, acute overexpression of the human Ala96 HRC variant in isolated adult rat cardiomyocytes by adenoviral gene transfer resulted in aberrant Ca2+ transient kinetics and increased frequency of Ca2+ sparks.15
    [Show abstract] [Hide abstract] ABSTRACT: A human genetic variant (Ser96Ala) in the sarcoplasmic reticulum (SR) histidine-rich Ca(2+)-binding (HRC) protein has been linked to ventricular arrhythmia and sudden death in dilated cardiomyopathy. However, the precise mechanisms affecting SR function and leading to arrhythmias remain elusive. We generated transgenic mice with cardiac-specific expression of human Ala96 HRC or Ser96 HRC in the null background to assess function in absence of endogenous protein. Ala96 HRC decreased (25% to 30%) cardiomyocyte contractility and Ca(2+) kinetics compared with Ser96 HRC in the absence of any structural or histological abnormalities. Furthermore, the frequency of Ca(2+) waves was significantly higher (10-fold), although SR Ca(2+) load was reduced (by 27%) in Ala96 HRC cells. The underlying mechanisms involved diminished interaction of Ala96 HRC with triadin, affecting ryanodine receptor (RyR) stability. Indeed, the open probability of RyR, assessed by use of ryanodine binding, was significantly increased. Accordingly, stress conditions (5 Hz plus isoproterenol) induced aftercontractions (65% in Ala96 versus 12% in Ser96) and delayed afterdepolarizations (70% in Ala96 versus 20% in Ser96). The increased SR Ca(2+) leak was accompanied by hyperphosphorylation (1.6-fold) of RyR at Ser2814 by calmodulin-dependent protein kinase II. Accordingly, inclusion of the calmodulin-dependent protein kinase II inhibitor KN93 prevented Ser2814 phosphorylation and partially reversed the increases in Ca(2+) spark frequency and wave production. Parallel in vivo studies revealed ventricular ectopy on short-term isoproterenol challenge and increased (4-fold) propensity to arrhythmias, including nonsustained ventricular tachycardia, after myocardial infarction in Ala96 HRC mice. These findings suggest that aberrant SR Ca(2+) release and increased susceptibility to delayed afterdepolarizations underlie triggered arrhythmic activity in human Ala96 HRC carriers.
    Full-text · Article · Aug 2013
  • [Show abstract] [Hide abstract] ABSTRACT: Calsequestrin is the most abundant Ca-binding protein of the specialized endoplasmic reticulum found in muscle, the sarcoplasmic reticulum (SR). Calsequestrin binds Ca with high capacity and low affinity and importantly contributes to the mobilization of Ca during each contraction both in skeletal and cardiac muscle. Surprisingly, mutations in the gene encoding the cardiac isoform of calsequestrin (Casq2) have been associated with an inherited form of ventricular arrhythmia triggered by emotional or physical stress termed catecholaminergic polymorphic ventricular tachycardia (CPVT). Despite normal cardiac contractility and normal resting ECG, CPVT patients present with a high risk of sudden death at a young age. Here, we review recent new insights regarding the role of calsequestrin in genetic and acquired arrhythmia disorders. Mouse models of CPVT have shed light on the pathophysiological mechanism underlying CPVT. Casq2 is not only a Ca-storing protein as initially hypothesized, but it has a far more complex function in Ca handling and regulating SR Ca release channels. The functional importance of Casq2 interactions with other SR proteins and the importance of alterations in Casq2 trafficking are also being investigated. Reports of altered Casq2 trafficking in animal models of acquired heart diseases such as heart failure suggest that Casq2 may contribute to arrhythmia risk beyond genetic forms of Casq2 dysfunction.
    Article · Dec 2011
  • [Show abstract] [Hide abstract] ABSTRACT: Cardiac calsequestrin (Casq2) is the major Ca2+ binding protein in the sarcoplasmic reticulum, which is the principle Ca2+ storage organelle of cardiac muscle. During the last decade, experimental studies have provided new concepts on the role of Casq2 in the regulation of cardiac muscle Ca2+ handling. Furthermore, mutations in the gene encoding for cardiac calsequestrin, CASQ2, cause a rare but severe form of catecholaminergic polymorphic ventricular tachycardia (CPVT). Here, we review the physiology of Casq2 in cardiac Ca2+ handling and discuss pathophysiological mechanisms that lead to CPVT caused by CASQ2 mutations. We also describe the clinical aspects of CPVT and provide an update of its contemporary clinical management.
    Full-text · Article · Mar 2012
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