CARP Plays a Key Role in Cellular Growth Under Hypertrophic Stimuli in Neonatal Rat Ventricular Myocytes

Abstract

Cardiac hypertrophy is a growth process characterized by an increase in individual myocyte size and overall cardiac muscle mass. Although such growth can occur through physiological means such as exercise, this study examined molecular components of the pathological process that occurs in response to long-term stress, injury, or disease states. Such hypertrophic stimuli induce unique cardiac muscle growth, increasing the risk of ischemia and congestive heart failure. During the pathological process, the fundamental unit of cardiac muscle-the sarcomere-is disrupted, both as a consequence of changes in gene expression and local sarcomeric proteins. Cardiac-restricted ankyrin repeat protein (CARP) is a crucial protein that functions both in the cardiac sarcomere and at the nuclear transcriptional level. We postulated that due to this dual nature, CARP plays a key role in maintaining the cardiac sarcomere and inducing hypertrophic growth pathways. GATA4 is a transcription factor with known importance during cardiac hypertrophy. Our studies uniquely suggest that CARP and GATA4 interact, and affirm that GATA4 is activated by hypertrophic stimuli. In order to partly delineate the complex process of cardiac hypertrophy, we applied a novel approach by testing cardiomyocytes for changes in CARP levels and GATA4 activation after hypertrophic stimuli over time. Neonatal Rat Ventricular Myocytes (NRVMs) were used in this study, and induced by the stimuli agents of phenylephrine (PE) and fetal bovine serum (FBS). Aggregate results of changes in GATA4 activation over time after both stimuli did not generate a consistent trend over time and did not gain statistically significance. CARP levels over time after such stimuli, however, were documented for the first known time, and generated a relative trend of increasing then decreasing levels over time after both stimuli with relatively more significance after PE stimuli. The functional role of CARP during hypertrophic growth was clearly and significantly demonstrated in this study through immunofluorescence. Results show that hypertrophic cardiomyocyte growth was significantly blunted when NRVMs were co-treated with CARP small-interfering RNA (siRNA), which disrupts CARP function. These data suggest that CARP plays a crucial role in the hypertrophic response in cardiomyocytes, and catalyzes further study.Summer 2013 | Volume 9 |