title: Evidence for calcineurin-mediated regulation of SERCA 2a activity in human myocardium.
abstract: 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.
authors.affiliation: Laboratory of Muscle Research and Molecular Cardiology, Klinik III für Innere Medizin, University of Cologne, Germany.
authors.forename: Götz
authors.initials: G
authors.lastname: Münch
authors.forename: Birgit
authors.initials: B
authors.lastname: Bölck
authors.forename: Peter
authors.initials: P
authors.lastname: Karczewski
authors.forename: Robert H G
authors.initials: RH
authors.lastname: Schwinger
mesh_terms: D000328:Adult; D015153:Blotting, Western; D019703:Calcineurin / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002155:Calsequestrin / Q000378:metabolism; D005260:Female; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D009206:Myocardium / Q000201:enzymology* / Q000378:metabolism* / Q000473:pathology; D010766:Phosphorylation; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000099211:Phospholamban
chemical_list: D019703:Calcineurin; D002118:Calcium; D002135:Calcium-Binding Proteins; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D000252:Calcium-Transporting ATPases; D002155:Calsequestrin; D007527:Isoenzymes; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000099211:Phospholamban