Abstract 14251: Nuclear Accumulation of Muscle LIM Protein is Regulated by Myocyte Contractility and Correlates With Cardiac Function in the Transition to Heart Failure
Prolonged increases in hemodynamic load lead to a loss of mechanosensing and heart failure because myocytes are unable to adapt to alterations in mechanical stress. We have previously shown that a decreased ratio of cytoplasmic to nuclear Muscle LIM protein (the MLP ratio) is associated with a loss of mechanosensitivity in human heart failure. However, the type and duration of mechanical stress that leads to impaired mechanosensitivity is unknown. In this study, we tested whether passive or active stress/strain was more important in modulating the MLP ratio (a measure of mechanosensitivity) and determined whether this correlated with heart function during the transition to failure. To test this, we exposed cultured neonatal rat myocytes to 48 h of 10% cyclic mechanical stretch at 1 Hz to mimic the passive forces associated with changes in blood pressure and volume. To mimic the forces generated by crossbridge activity during systole, we electrically paced myocytes at 6.8 V (1Hz) for 48 hours. The MLP ratio decreased 50% (p<0.05, n=4 cultures) only in response to electrical pacing, suggesting impaired mechanosensitivity. We then inhibited contractility by treating myocytes with 10μM blebbistatin which resulted in a 3 fold increase in the MLP ratio (n=8 cultures, p<0.05). This indicates that myocyte contractility regulates MLP nuclear shuttling and mechanosensitivity. To examine how mechanosensitivity changes during the transition to heart failure, we examined a guinea pig model of angiotensin II infusion (400ng/kg/min). The hearts were examined at 4, 8 and 12 weeks post-operatively. Using subcellular fractionation we showed that the MLP ratio increased 88% (n=4, P=0.009) during compensated phase at 8 weeks, but decreased significantly during heart failure at 12 weeks (p=0.0003, n=4). Furthermore, the MLP ratio correlated significantly with the E/A ratio (r=0.71, p<0.01 n=12), a clinical measure of diastolic function. This data indicate that impaired cardiac mechanosensitivity resulting in a reduced MLP ratio is regulated predominantly by myofilament crossbridge activity rather than passive strain. Increased mechanical stress within the contracting myofilaments contributes to the loss of mechanosensing during the transition to heart failure.
Author Disclosures: A. Paudyal: None. S. Dewan: None. C. Ikie: None. P.D. de Tombe: None. S.Y. Boateng: None.
- © 2015 by American Heart Association, Inc.