Abstract 791: Cardiac Dysfunction and Heart Failure are Associated with Decreased Levels of Non-Nuclear Oligomeric Muscle LIM Protein
Prolonged hemodynamic overload results in cardiac hypertrophy and failure with detrimental changes in myocardial gene expression and morphology. It has been suggested that CSRP3 or muscle LIM protein (MLP) is a mechano-sensor in cardiac myocytes, relaying messages from the myofilaments to the nucleus. Therefore, the subcellular location of MLP may have important functional implications in health and disease. Our hypothesis is that MLP becomes mislocalized after prolonged overload resulting in impaired mechanosensing in cardiac myocytes. Using the techniques of biochemical subcellular fractionation and immunocytochemistry, we found MLP exhibits oligomerization in the membrane and cytoskeleton of cultured cardiac rat neonatal myocytes. However, nuclear MLP was always monomeric. MLP translocated to the nucleus and nucleolus in response to 10% cyclic stretch at 1Hz for 48 hours. This translocation was associated with a 3 fold increase in S6 ribosomal protein (p<0.01 n=3 cultures). Adenoviral overexpression of MLP also resulted in a 2 fold increase in S6 protein suggesting that MLP can directly activate ribosomal protein synthesis in the nucleolus. In ventricles from aortic banded and myocardial infarcted rat hearts, nuclear MLP increased by 2 fold (p<0.01 n=7) along with a significant decrease in the non-nuclear oligomeric fraction. The ratio of nuclear to non-nuclear MLP increased 3 fold in both groups (p<0.01 n=7). In failing human hearts there was almost a complete loss of oligomeric MLP. Using a flag-tagged adenoviral MLP, we have shown that the C-terminus is required for oligomerization and that this is a precursor to stretch sensing and subsequent nuclear translocation. In conclusion, heart failure may result from impaired mechanosensing associated with reduced oligomeric MLP in the costamere and cytoskeleton.