Four and half LIM domain-1 protein and its role in passive mechanics and hypertrophic signaling of the heart

Abstract

Altered mechanical stresses and strains in cardiac myocytes can induce modifications in gene expression that can affect cardiac remodeling and myocyte contractile function. Most studies of myocyte mechanotransduction use isolated neonatal rat myocytes. To study the genetics of these pathways it is helpful to be able to probe alterations in gene expression in intact muscle from genetically engineered mice. We have developed a tissue culture system that facilitates straining of cardiac tissue, while measuring its force within a physiological environment. The system was developed to house intact right ventricular papillary muscles, such that cell to extracellular matrix adhesions as well as cell to cell adhesions, which influence cardiac remodeling, were undisturbed. The tissue chamber is isolated from the external environment and provides control of O₂ supply, temperature, and superfusate delivery. Isolated papillary muscles are suspended within the chamber in modified M199 cell culture media, between a micromanipulator attached to a linear voltage displacement transducer and a force transducer. Through this mechanism, the diastolic and systolic mechanics of papillary muscles were studied and hypertrophic markers can be induced in specimens for a period up to 12 hours. By quantifying mRNA levels of hypertrophic markers (BNP, ELK1, ANP) we monitored the development of hypertrophy within normal specimens and within specimens obtained from FHL1 knock out mice that may have dysregulated hypertrophic or biochemical signaling. Our results revealed that the system is capable of maintaining tissue viability, measuring tissue mechanics, and induces hypertrophic markers (ANP, BNP) in specimens in the acute phase of development (2-5 hours). Compared to wild type specimens, specimens deficient in FHL1 were more compliant and had a blunted response to mechanical load induced hypertrophy. We concluded that FHL1 has dual functions in modulating the passive mechanics of myocardial tissue and hypertrophic signaling of the heart