title: Hypophosphorylation of the Stiff N2B titin isoform raises cardiomyocyte resting tension in failing human myocardium.
abstract: High diastolic stiffness of failing myocardium results from interstitial fibrosis and elevated resting tension (F(passive)) of cardiomyocytes. A shift in titin isoform expression from N2BA to N2B isoform, lower overall phosphorylation of titin, and a shift in titin phosphorylation from N2B to N2BA isoform can raise F(passive) of cardiomyocytes. In left ventricular biopsies of heart failure (HF) patients, aortic stenosis (AS) patients, and controls (CON), we therefore related F(passive) of isolated cardiomyocytes to expression of titin isoforms and to phosphorylation of titin and titin isoforms. Biopsies were procured by transvascular technique (44 HF, 3 CON), perioperatively (25 AS, 4 CON), or from explanted hearts (4 HF, 8 CON). None had coronary artery disease. Isolated, permeabilized cardiomyocytes were stretched to 2.2-microm sarcomere length to measure F(passive). Expression and phosphorylation of titin isoforms were analyzed using gel electrophoresis with ProQ Diamond and SYPRO Ruby stains and reported as ratio of titin (N2BA/N2B) or of phosphorylated titin (P-N2BA/P-N2B) isoforms. F(passive) was higher in HF (6.1+/-0.4 kN/m(2)) than in CON (2.3+/-0.3 kN/m(2); P<0.01) or in AS (2.2+/-0.2 kN/m(2); P<0.001). Titin isoform expression differed between HF (N2BA/N2B=0.73+/-0.06) and CON (N2BA/N2B=0.39+/-0.05; P<0.001) and was comparable in HF and AS (N2BA/N2B=0.59+/-0.06). Overall titin phosphorylation was also comparable in HF and AS, but relative phosphorylation of the stiff N2B titin isoform was significantly lower in HF (P-N2BA/P-N2B=0.77+/-0.05) than in AS (P-N2BA/P-N2B=0.54+/-0.05; P<0.01). Relative hypophosphorylation of the stiff N2B titin isoform is a novel mechanism responsible for raised F(passive) of human HF cardiomyocytes.
authors.affiliation: Laboratory of Physiology, VU University Medical Center Amsterdam, Van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands.
authors.forename: Attila
authors.initials: A
authors.lastname: Borbély
authors.forename: Ines
authors.initials: I
authors.lastname: Falcao-Pires
authors.forename: Loek
authors.initials: L
authors.lastname: van Heerebeek
authors.forename: Nazha
authors.initials: N
authors.lastname: Hamdani
authors.forename: István
authors.initials: I
authors.lastname: Edes
authors.forename: Cristina
authors.initials: C
authors.lastname: Gavina
authors.forename: Adelino F
authors.initials: AF
authors.lastname: Leite-Moreira
authors.forename: Jean G F
authors.initials: JG
authors.lastname: Bronzwaer
authors.forename: Zoltán
authors.initials: Z
authors.lastname: Papp
authors.forename: Jolanda
authors.initials: J
authors.lastname: van der Velden
authors.forename: Ger J M
authors.initials: GJ
authors.lastname: Stienen
authors.forename: Walter J
authors.initials: WJ
authors.lastname: Paulus
mesh_terms: D000368:Aged; D001706:Biopsy; D064211:Connectin; D004548:Elasticity; D005260:Female; D006333:Heart Failure / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009124:Muscle Proteins / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000473:pathology; D010766:Phosphorylation; D020033:Protein Isoforms / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism*; D012518:Sarcomeres / Q000378:metabolism* / Q000473:pathology
chemical_list: D064211:Connectin; D009124:Muscle Proteins; D020033:Protein Isoforms; C577285:TTN protein, human; D011494:Protein Kinases