Abstract 3577: Titin-Actin Interaction Contributes to High Resting Tension of Failing Human Cardiomyocytes
Cardiomyocytes isolated from failing human hearts have elevated resting tension (RT), which is attributed to altered spring characteristics of titin resulting from changes in isoform expression and/or hypophosphorylation. The present study investigated the role of the 100 nm wide titin-actin overlap region at the Z-discs, which presets tension on the extensible titin segments. Left ventricular (LV) myocardium was procured from explanted donor hearts (Control), from surgical biopsies in aortic stenosis (AS) patients and from LV transvascular endomyocardial biopsies in heart failure patients (HF). Cardiomyocytes were mechanically isolated, triton permeabilized, attached between a force transducer and a piezoelectric motor and stretched to a sarcomere length of 2.2 μm to measure resting tension (RT). Following baseline measurements, protein kinase A (PKA) and gelsolin treatments were applied. Gelsolin severs the thin filament, thereby reducing titin-actin interaction. To saturate phosphorylation of titin, PKA was applied first. Immunofluorescent images were obtained of cardiomyocytes co-stained for alpha-actinin (Z-disc marker) and nitrotyrosine (oxidative stress marker). Baseline RT was lowest in Control (n=11), intermediate in AS (n=11) and highest in HF (n=14). RT of Control fell only after gelsolin (Table⇓). RT of AS and HF fell both after PKA and after gelsolin (Table⇓). The higher the RT prior to gelsolin, the larger the fall in RT after gelsolin (p<0.0001, r=0.40). In Control, AS and HF, cardiomyocytes stained positively for nitrotyrosine in areas in-between Z-discs. In HF, positive nitrotyrosine staining also extended into the Z-discs.
Conclusion: Titin-actin interaction at the Z-disc contributes to RT of human cardiomyocytes. Possibly because of oxidative damage to the Z-disc, the effect of titin-actin interaction on RT is especially prominent in HF cardiomyocytes with elevated RT.