Evidence for Calcineurin-mediated Regulation of SERCA 2a Activity in Human Myocardium

Laboratory of Muscle Research and Molecular Cardiology, Klinik III für Innere Medizin, University of Cologne, Germany.
Journal of Molecular and Cellular Cardiology (Impact Factor: 4.66). 03/2002; 34(3):321-34. DOI: 10.1006/jmcc.2001.1515
Source: PubMed


Compromised SERCA 2a activity is a key malfunction leading to the Ca(2+) cycling alterations in failing human myocardium. SERCA 2a activity is regulated by the Ca(2+)/calmodulin-dependent protein kinase (CaM-kinase) but alterations of the CaM-kinase pathway regarding SERCA 2a in heart failure are unresolved. Therefore we investigated the CaM-kinase and phosphatase calcineurin mediated regulation of SERCA 2a in failing and non-failing human myocardium. We studied human myocardial preparations from explanted hearts from non-failing organ donors (NF, n=8) and from patients with terminal heart failure undergoing cardiac transplantation (dilated cardiomyopathy, DCM, n=8). SERCA 2a activity was determined using a NADH-coupled enzyme assay [expressed in nmol ATP/(mg protein x min)] and by(45)Ca(2+) uptake. Protein expression of SERCA 2a, phospholamban, calsequestrin and calcineurin was assessed by Western blotting (expressed as densitometric units/microg protein); phosphorylation of cardiac proteins was detected with specific phospho-antibodies for phospholamban at threonine-17 (PT17) or by incorporation of [gamma -(32)P] (expressed as pmol(32)P/mg). Maximal(45)Ca(2+) uptake (in pmol/mg/min) (NF: 3402+/-174; DCM: 2488+/-189) and maximal SERCA 2a activity were reduced in DCM compared to NF (V(max): NF: 125+/-9; DCM: 98+/-5). The V(max) reduction could be mimicked by calcineurin in vitro in NF (NF(control): 72.1+/-3.7; NF(+calcineurin): 49.8+/-2.9) and restored in DCM by CaM-kinase in vitro (DCM(control): 98+/-5; DCM(+CaM-kinase): 120+/-6). Protein expression of SERCA 2a, phospholamban and calsequestrin remained similar, but calcineurin expression was significantly increased in failing human hearts (NF: 11.6+/-1.5 v DCM: 17.1+/-1.6). Although the capacity of endogenous CaM-kinase to phosphorylate PT17 was significantly higher in DCM (DCM(control): 128+/-36; DCM(+endogenous CaM-kinase): 205+/-20) compared to NF myocardium (NF(control): 273+/-37; NF(+endogenous CaM-kinase): 254+/-31), net phosphorylation at threonine-17 phospholamban was significantly lower in DCM (DCM 130+/-11 v NF 170+/-11). A calcineurin-dependent dephosphorylation of phospholamban could be mimicked in vitro by incubation of NF preparations with calcineurin (NF(control) 80.7+/-4.4 v NF(+calcineurin) 30.7+/-4.1, P<0.05). In human myocardium, the V(max) of SERCA 2a and the phosphorylation of phospholamban is modulated by CaM-kinase and calcineurin, at least in vitro. In failing human myocardium, despite increased CaM-kinase activity, calcineurin dephosphorylation leads to decreased net phosphorylation of threonine-17 phospholamban in vivo. Increased calcineurin activity contributes to the impaired V(max) of SERCA 2a in failing human myocardium and the disorder in Ca(2+)-handling in heart failure.

Download full-text


Available from: Götz Münch, Mar 05, 2014
  • Source
    • "These findings may be due to the attenuation of β1-adrenergic cascade, due to receptor desensitization, down-regulation and uncoupling, typical of the disease progression (Bristow et al., 1982; Dash et al., 2001; Port and Bristow, 2001), and/or the increase in PP1 activity, described in HF (Bibb et al., 2001; Carr et al., 2002; Gupta et al., 2003). Indeed, in human failing myocardium, phosphorylation of Ser16 in PLN decreased because of increases in PP1 activity (Schwinger et al., 1999), whereas phosphorylation of Thr17 decreased due to increased activity of PP2B (calcineurin; Münch et al., 2002). Interestingly, this decrease occurred despite an increase in CaMKII activity characteristic of HF. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Phospholamban (PLN) is a phosphoprotein in cardiac sarcoplasmic reticulum (SR) that is a reversible regulator of the Ca2+-ATPase (SERCA2a) activity and cardiac contractility. Dephosphorylated PLN inhibits SERCA2a and PLN phosphorylation, at either Ser16 by PKA or Thr17 by Ca2+-calmodulin-dependent protein kinase (CaMKII), reverses this inhibition. Through this mechanism, PLN is a key modulator of SR Ca2+ uptake, Ca2+ load, contractility, and relaxation. PLN phosphorylation is also the main determinant of β1-adrenergic responses in the heart. Although phosphorylation of Thr17 by CaMKII contributes to this effect, its role is subordinate to the PKA-dependent increase in cytosolic Ca2+, necessary to activate CaMKII. Furthermore, the effects of PLN and its phosphorylation on cardiac function are subject to additional regulation by its interacting partners, the anti-apoptotic HAX-1 protein and Gm or the anchoring unit of protein phosphatase 1. Regulation of PLN activity by this multimeric complex becomes even more important in pathological conditions, characterized by aberrant Ca2+-cycling. In this scenario, CaMKII-dependent PLN phosphorylation has been associated with protective effects in both acidosis and ischemia/reperfusion. However, the beneficial effects of increasing SR Ca2+ uptake through PLN phosphorylation may be lost or even become deleterious, when these occur in association with alterations in SR Ca2+ leak. Moreover, a major characteristic in human and experimental heart failure (HF) is depressed SR Ca2+ uptake, associated with decreased SERCA2a levels and dephosphorylation of PLN, leading to decreased SR Ca2+ load and impaired contractility. Thus, the strategy of altering SERCA2a and/or PLN levels or activity to restore perturbed SR Ca2+ uptake is a potential therapeutic tool for HF treatment. We will review here the role of CaMKII-dependent phosphorylation of PLN at Thr17 on cardiac function under physiological and pathological conditions.
    Frontiers in Pharmacology 01/2014; 5:5. DOI:10.3389/fphar.2014.00005 · 3.80 Impact Factor
  • Source
    • "Thus the frequency dependence of the maximal rate of uptake by the SERCA pump (Figure 5B) shares its characteristics with peak ICa,L current (Figure 4B) linked together by activated-CaMKII (Figure 5C). It is important to note that rate-dependent enhancement in SERCA activty by CaMKII significantly overrides the inhibitory influence of CaN in a non-failing heart [54]. Figure 5B also shows the underlying rate-dependent decline in unphosphorylated PLB responsible for rate-dependent increase in SR uptake. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Rate-dependent effects on the Ca2+ sub-system in a rat ventricular myocyte are investigated. Here, we employ a deterministic mathematical model describing various Ca2+ signalling pathways under voltage clamp (VC) conditions, to better understand the important role of calmodulin (CaM) in modulating the key control variables Ca2+/calmodulin-dependent protein kinase-II (CaMKII), calcineurin (CaN), and cyclic adenosine monophosphate (cAMP) as they affect various intracellular targets. In particular, we study the frequency dependence of the peak force generated by the myofilaments, the force-frequency response (FFR). Our cell model incorporates frequency-dependent CaM-mediated spatially heterogenous interaction of CaMKII and CaN with their principal targets (dihydropyridine (DHPR) and ryanodine (RyR) receptors and the SERCA pump). It also accounts for the rate-dependent effects of phospholamban (PLB) on the SERCA pump; the rate-dependent role of cAMP in up-regulation of the L-type Ca2+ channel (ICa;L); and the enhancement in SERCA pump activity via phosphorylation of PLB. Our model reproduces positive peak FFR observed in rat ventricular myocytes during voltage-clamp studies both in the presence/absence of cAMP mediated beta-adrenergic stimulation. This study provides quantitative insight into the rate-dependence of Ca2+-induced Ca2+-release (CICR) by investigating the frequency-dependence of the trigger current (ICa;L) and RyR-release. It also highlights the relative role of the sodium-calcium exchanger (NCX) and the SERCA pump at higher frequencies, as well as the rate-dependence of sarcoplasmic reticulum (SR) Ca2+ content. A rigorous Ca2+ balance imposed on our investigation of these Ca2+ signalling pathways clarifies their individual roles. Here, we present a coupled electromechanical study emphasizing the rate-dependence of isometric force developed and also investigate the temperature-dependence of FFR. Our model provides mechanistic biophysically based explanations for the rate-dependence of CICR, generating useful and testable hypotheses. Although rat ventricular myocytes exhibit a positive peak FFR in the presence/absence of beta-adrenergic stimulation, they show a characteristic increase in the positive slope in FFR due to the presence of Norepinephrine or Isoproterenol. Our study identifies cAMP-mediated stimulation, and rate-dependent CaMKII-mediated up-regulation of ICa;L as the key mechanisms underlying the aforementioned positive FFR.
    Theoretical Biology and Medical Modelling 09/2013; 10(1):54. DOI:10.1186/1742-4682-10-54 · 0.95 Impact Factor
  • Source
    • "Phosphorylation of phospholamban increases sarcoplasmic reticulum Ca 2+ -ATPase activity (Tada et al., 1975). In vitro sarcoplasmic reticulum Ca 2+ -ATPase activity can be depressed by calcineurin-mediated dephosphorylation in non-failing tissue (Münch et al., 2002). When sarcoplasmic reticulum Ca 2+ -ATPase activity is decreased , reuptake of calcium into the sarcoplasmic reticulum is decreased, which result in the Ca 2+ overload in the myocardium cytoplasm and calcineurin as well as initiate hypertrophy in cardiomyocytes . "
    [Show abstract] [Hide abstract]
    ABSTRACT: To observe effects of angiotensin (Ang) II receptor antagonist (AT1) irbesartan and angiotensin-converting enzyme (ACE) inhibitor perindopril on rat myocardium calcineurin expression and sarcoplasmic reticulum Ca(2+)-ATPase activity in the model of pressure-overload cardiac hypertrophy. Forty male adult Sprague Dawley rats were divided into 5 groups. One group was treated by sham operation; four groups were myocardium hypertrophy cases caused by banding aortic above renal artery. Drugs were given one week after operation. Group 1: sham group, rats (n=8) were gavaged with normal saline 2 ml/(kg.d) (ig); Group 2: control group, rats (n=8) were treated with normal saline 2 ml/(kg.d) (ig); Group 3: rats (n=8) were given perindopril 2 mg/(kg.d) (ig); Group 4: rats (n=8) were treated with irbesartan 20 mg/(kg.d) (ig); Group 5: rats (n=8) were given irbesartan 20 mg/(kg.d) plus perindopril 2 mg/(kg.d) (ig). Morphometric determination, calcineurin expression and sarcoplasmic reticulum Ca(2+)-ATPase activity were done at the end of 6 week of drug intervention. Expression of calcineurin in myocardium was detected by immunohistochemistry. Left ventricular mass index (LVMI), transverse diameter of myocardial cell (TDM), calcineurin activity were remarkably decreased after drug intervention and this decrease was most remarkable in the combination drug therapy group. Sarcoplasmic reticulum Ca(2+)-ATPase activity was increased after drug intervention, especially in the combined drug therapy group. Calcineurin expression in myocardium was remarkably decreased after drug intervention. LVMI was positively correlated with TDM and calcineurin, negatively correlated with sarcoplasmic reticulum Ca(2+)-ATPase. These data suggest that irbesartan and perindopril inhibit cardiac hypertrophy through the increased activity of sarcoplasmic reticulum Ca(2+)-ATPase and decreased expression of calcineurin. Their combination had better effects on regressing of ventricular hypertrophy.
    Journal of Zhejiang University SCIENCE B 04/2006; 7(3):228-34. DOI:10.1631/jzus.2006.B0228 · 1.28 Impact Factor
Show more