January 30, 2009Circulation Research366 citationsOpen Access
Hypophosphorylation of the Stiff N2B Titin Isoform Raises Cardiomyocyte Resting Tension in Failing Human Myocardium
Key Points
- To evaluate how titin isoform shifts and isoform-specific phosphorylation contribute to elevated cardiomyocyte resting tension in failing human myocardium.
- Obtained left ventricular biopsies from patients with heart failure (n=48), aortic stenosis (n=25), and non-failing controls (n=15) without coronary artery disease.
Structured PICO
P
Population
88 human subjects (48 with heart failure [27 HFREF, 17 HFNEF, 4 end-stage], 25 with aortic stenosis, 15 controls). None had significant coronary artery disease. Left ventricular biopsies were procured transvascularly, perioperatively, or from explanted hearts.
I
Intervention
Ex vivo analysis of isolated, permeabilized cardiomyocytes stretched to 2.2-microm sarcomere length, with in vitro administration of protein kinase A (PKA), protein kinase G (PKG), gelsolin, or 2,3-butanedione monoxime (BDM).
C
Comparator
Cardiomyocytes from control patients (normal LV function) and aortic stenosis patients, as well as baseline measurements before in vitro kinase administration.
O
Outcome
Cardiomyocyte resting tension (Fpassive), titin isoform expression (N2BA/N2B ratio), and titin isoform phosphorylation (P-N2BA/P-N2B ratio).surrogate
Relative hypophosphorylation of the stiff N2B titin isoform is a key mechanism underlying elevated cardiomyocyte resting tension and diastolic dysfunction 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.
Cite This Study
Borbély et al. (2009) studied this question.