Hypertrophic gene expression induced by chronic stretch of excised mouse heart muscle.

Altered mechanical stress and strain in cardiac myocytes induce modifications in gene expression that affects cardiac remodeling and myocyte contractile function. To study the mechanisms of mechanotransduction in cardiomyocytes, probing alterations in mechanics and gene expression has been an effective strategy. However, previous studies are self-limited due to the general use of isolated neonatal rodent myocytes or intact animals. The main goal of this study was to develop a novel tissue culture chamber system for mouse myocardium that facilitates loading of cardiac tissue, while measuring tissue stress and deformation within a physiological environment. Intact mouse right ventricular papillary muscles were cultured in controlled conditions with superfusate at 95% O2/ 5% CO2, and 34 degrees C, such that cell to extracellular matrix adhesions as well as cell to cell adhesions were undisturbed and both passive and active mechanical properties were maintained without significant changes. The system was able to measure the induction of hypertrophic markers (BNP, ANP) in tissue after 2 hrs and 5 hrs of stretch. ANP induction was highly correlated with the diastolic load of the muscle but not with developed systolic load. Load induced ANP expression was blunted in muscles from muscle-LIM protein knockout mice, in which defective mechanotransduction pathways have been predicted.