OBJECTIVE: The cardiac ankyrin repeat protein (CARP), a nuclear transcription co-factor that negatively regulates cardiac gene expression, is increased in human heart failure and in animal models of cardiac hypertrophy. The mechanism by which CARP expression is regulated and the consequences of CARP overexpression on cardiac contractility are unknown. METHODS AND RESULTS: Compared to vehicle treated controls, 4-day treatment of male Wistar rats with the beta-adrenoceptor agonist isoprenaline (2.4 mg/kg per day) induced hypertrophy and significantly increased CARP mRNA and CARP protein levels in left ventricles. The signalling pathways were investigated in more detail in isolated neonatal rat cardiomyocytes. Treatment of cells with isoprenaline (1 micromol/l) caused a significant increase in CARP mRNA and protein by approximately 50%. Combined beta(1)- and beta(2)-adrenoceptor blockade, inhibition of protein kinase A (PKA; Rp-cAMPS, 100 micromol/l), and inhibition of calmodulin-dependent protein kinases (CaMK; KN-62, 10 micromol/l) completely reversed the effects of isoprenaline. To examine the consequences of CARP overexpression on contractile function, an adenovirus encoding human CARP as well as a control virus were constructed. Although the basal force of contraction was not different, contractile response to Ca(2+) and isoprenaline was significantly diminished in engineered heart tissue infected with the recombinant adenovirus that carries the CARP gene (Ad.CARP). CONCLUSIONS: Our study provides the first evidence that overexpression of CARP, which is thought to act as a transcriptional co-repressor, may deteriorate contractile function of the heart tissue. Furthermore, beta-adrenoceptor stimulation and activation of PKA and CaMK have been identified as mechanisms that induce expression of CARP in cardiomyocytes.
