RESUMEN
RATIONALE: Chronic elevation of 3'-5'-cyclic adenosine monophosphate (cAMP) levels has been associated with cardiac remodeling and cardiac hypertrophy. However, enhancement of particular aspects of cAMP/protein kinase A signaling seems to be beneficial for the failing heart. cAMP is a pleiotropic second messenger with the ability to generate multiple functional outcomes in response to different extracellular stimuli with strict fidelity, a feature that relies on the spatial segregation of the cAMP pathway components in signaling microdomains. OBJECTIVE: How individual cAMP microdomains affect cardiac pathophysiology remains largely to be established. The cAMP-degrading enzymes phosphodiesterases (PDEs) play a key role in shaping local changes in cAMP. Here we investigated the effect of specific inhibition of selected PDEs on cardiac myocyte hypertrophic growth. METHODS AND RESULTS: Using pharmacological and genetic manipulation of PDE activity, we found that the rise in cAMP resulting from inhibition of PDE3 and PDE4 induces hypertrophy, whereas increasing cAMP levels via PDE2 inhibition is antihypertrophic. By real-time imaging of cAMP levels in intact myocytes and selective displacement of protein kinase A isoforms, we demonstrate that the antihypertrophic effect of PDE2 inhibition involves the generation of a local pool of cAMP and activation of a protein kinase A type II subset, leading to phosphorylation of the nuclear factor of activated T cells. CONCLUSIONS: Different cAMP pools have opposing effects on cardiac myocyte cell size. PDE2 emerges as a novel key regulator of cardiac hypertrophy in vitro and in vivo, and its inhibition may have therapeutic applications.
Asunto(s)
Cardiomegalia/prevención & control , AMP Cíclico/metabolismo , Fosfodiesterasas de Nucleótidos Cíclicos Tipo 2/metabolismo , Miocitos Cardíacos/enzimología , Sistemas de Mensajero Secundario , Adenoviridae/genética , Animales , Animales Recién Nacidos , Cardiomegalia/enzimología , Cardiomegalia/genética , Cardiomegalia/patología , Células Cultivadas , Proteínas Quinasas Dependientes de AMP Cíclico/metabolismo , Fosfodiesterasas de Nucleótidos Cíclicos Tipo 2/antagonistas & inhibidores , Fosfodiesterasas de Nucleótidos Cíclicos Tipo 2/genética , Modelos Animales de Enfermedad , Vectores Genéticos , Masculino , Microdominios de Membrana/enzimología , Ratones Endogámicos C57BL , Miocitos Cardíacos/efectos de los fármacos , Miocitos Cardíacos/patología , Factores de Transcripción NFATC/genética , Factores de Transcripción NFATC/metabolismo , Inhibidores de Fosfodiesterasa/farmacología , Fosforilación , Interferencia de ARN , Ratas Sprague-Dawley , Ratas Wistar , Sistemas de Mensajero Secundario/efectos de los fármacos , Factores de Tiempo , Transducción Genética , TransfecciónRESUMEN
In the heart compartmentalisation of cAMP/protein kinase A (PKA) signalling is necessary to achieve a specific functional outcome in response to different hormonal stimuli. Chronic exposure to catecholamines is known to be detrimental to the heart and disrupted compartmentalisation of cAMP signalling has been associated to heart disease. However, in most cases it remains unclear whether altered local cAMP signalling is an adaptive response, a consequence of the disease or whether it contributes to the pathogenetic process. We have previously demonstrated that isoforms of PKA expressed in cardiac myocytes, PKA-I and PKA-II, localise to different subcellular compartments and are selectively activated by spatially confined pools of cAMP, resulting in phosphorylation of distinct downstream targets. Here we investigate cAMP signalling in an in vitro model of hypertrophy in primary adult rat ventricular myocytes. By using a real time imaging approach and targeted reporters we find that that sustained exposure to catecholamines can directly affect cAMP/PKA compartmentalisation. This appears to involve a complex mechanism including both changes in the subcellular localisation of individual phosphodiesterase (PDE) isoforms as well as the relocalisation of PKA isoforms. As a result, the preferential coupling of PKA subsets with different PDEs is altered resulting in a significant difference in the level of cAMP the kinase is exposed to, with potential impact on phosphorylation of downstream targets.