Abstract 1463: Titin Isoform Phosphorylation in Failing Human Myocardium
Titin lowers myocardial diastolic stiffness by shifting its isoform expression from the stiff N2B to the compliant N2BA isoform and by increasing its phosphorylation. Resting tension (RT) of cardiomyocytes (CM), expression and phosphorylation of titin isoforms were compared in myocardial biopsies of controls (CON) (n=10) and of patients with dilated cardiomyopathy (DCMP) (n=23), hypertensive heart disease (HT) (n=17) and aortic stenosis (AS) (n=20). No patient had coronary artery disease. CM were isolated, treated with Triton X-100 and stretched to a sarcomere length of 2.2 microm to measure RT. Expression and phosphorylation of titin isoforms were analysed by gel electrophoresis with SYPRO Ruby and Pro-Q Diamond Phosphoprotein Stain and reported as ratio of titin isoforms (N2BA/N2B) or as ratio of phosphorylated titin isoforms (P-N2BA/P-N2B). CM RT was low in CON (3.7±0.5 kN/m2), DCMP (4.7±0.2) and AS (2.4±0.2) but high in HT (6.6±0.6; p<0.01 vs. CON, DCMP or AS). When CM RT was low, P-N2BA/P-N2B ratio was lower than when CM RT was high (0.53±0.06 vs. 0.77±0.05; p<0.05). When CM RT was low, P-N2BA/P-N2B ratio correlated with N2BA/N2B ratio (Figure⇓; r=0.80, p<0.02). When CM RT was high, P-N2BA/P-N2B ratio and N2BA/N2B ratio no longer correlated because of excessive P-N2BA and deficient P-N2B.
Phosphorylation of titin isoforms modulates RT of CM;
As observed in CON, DCMP and AS, CM RT remains low when titin isoform phosphorylation correlates with titin isoform expression;
As observed in HT, CM RT rises when there is high phosphorylation but low expression of the compliant N2BA titin isoform and low phosphorylation but high expression of the stiff N2B titin isoform.