Rapid effects of aldosterone in primary cultures of cardiomyocytes – do they suggest the existence of a membrane-bound receptor?

Abstract

Aldosterone acts on its target tissue through a classical mechanism or through the rapid pathway through a putative membrane-bound receptor. Our goal here was to better understand the molecular and biochemical rapid mechanisms responsible for aldosterone-induced cardiomyocyte hypertrophy. We have evaluated the hypertrophic process through the levels of ANP, which was confirmed by the analysis of the superficial area of cardiomyocytes. Aldosterone increased the levels of ANP and the cellular area of the cardiomyocytes; spironolactone reduced the aldosterone-increased ANP level and cellular area of cardiomyocytes. Aldosterone or spironolactone alone did not increase the level of cyclic 3',5'-adenosine monophosphate (cAMP), but aldosterone plus spironolactone led to increased cAMP level; the treatment with aldosterone + spironolactone + BAPTA-AM reduced the levels of cAMP. These data suggest that aldosterone-induced cAMP increase is independent of mineralocorticoid receptor (MR) and dependent on Ca²⁺. Next, we have evaluated the role of A-kinase anchor proteins (AKAP) in the aldosterone-induced hypertrophic response. We have found that St-Ht31 (AKAP inhibitor) reduced the increased level of ANP which was induced by aldosterone; in addition, we have found an increase on protein kinase C (PKC) and extracellular signal-regulated kinase 5 (ERK5) activity when cells were treated with aldosterone alone, spironolactone alone and with a combination of both. Our data suggest that PKC could be responsible for ERK5 aldosterone-induced phosphorylation. Our study suggests that the aldosterone through its rapid effects promotes a hypertrophic response in cardiomyocytes that is controlled by an AKAP, being dependent on ERK5 and PKC, but not on cAMP/cAMP-dependent protein kinase signaling pathways. Lastly, we provide evidence that the targeting of AKAPs could be relevant in patients with aldosterone-induced cardiac hypertrophy and heart failure.

Keywords:

• Aldosterone
• cardiomyocytes
• hypertrophy
• mineralocorticoid receptor
• rapid effects
• spironolactone

Acknowledgements

The authors thank Professor Luís Carlos Crocco Afonso, from the Immunoparasitology Laboratory and Center of Animal Sciences of the Federal University of Ouro Preto (UFOP – Brazil), for granting access to several instruments used in this project, and for his valuable help during the startup of our laboratory at UFOP. de Assis, L.V.M is a fellow of São Paulo Research Foundation (FAPESP − Process 2013/24337-4). Lastly, all the authors thank Pablo Henrique Oliveira de Silva for extensively revising the manuscript.

Declaration of interest

This project was supported by the National Council for Scientific and Technologic Development (CNPq) grant number 474174/2007-7, Minas Gerais Research Foundation (FAPEMIG) grants number APQ-02112-10, APQ 00793-13 and the Federal University of Ouro Preto (UFOP) through the Office of Research and Graduate Studies (PROPP). None of the authors have any actual or potential conflict of interest which could inappropriately influence this work.