A cardiac mitochondrial cAMP signaling pathway regulates calcium accumulation, permeability transition and cell death.

Z Wang,C Brenner,A-M Gomez,D Courilleau,G Vandecasteele,P Rouet,A Varin,V Nicolas,C Caubere,P Mateo,D Liu,R Fischmeister

doi:10.1038/cddis.2016.106

Abstract

Although cardiac cytosolic cyclic 3′,5′-adenosine monophosphate (cAMP) regulates multiple processes, such as beating, contractility, metabolism and apoptosis, little is known yet on the role of this second messenger within cardiac mitochondria. Using cellular and subcellular approaches, we demonstrate here the local expression of several actors of cAMP signaling within cardiac mitochondria, namely a truncated form of soluble AC (sACt) and the exchange protein directly activated by cAMP 1 (Epac1), and show a protective role for sACt against cell death, apoptosis as well as necrosis in primary cardiomyocytes. Upon stimulation with bicarbonate (HCO3−) and Ca2+, sACt produces cAMP, which in turn stimulates oxygen consumption, increases the mitochondrial membrane potential (ΔΨm) and ATP production. cAMP is rate limiting for matrix Ca2+ entry via Epac1 and the mitochondrial calcium uniporter and, as a consequence, prevents mitochondrial permeability transition (MPT). The mitochondrial cAMP effects involve neither protein kinase A, Epac2 nor the mitochondrial Na+/Ca2+ exchanger. In addition, in mitochondria isolated from failing rat hearts, stimulation of the mitochondrial cAMP pathway by HCO3− rescued the sensitization of mitochondria to Ca2+-induced MPT. Thus, our study identifies a link between mitochondrial cAMP, mitochondrial metabolism and cell death in the heart, which is independent of cytosolic cAMP signaling. Our results might have implications for therapeutic prevention of cell death in cardiac pathologies.

Highlights

Using cellular and subcellular approaches, we demonstrate here the local expression of several actors of cAMP signaling within cardiac mitochondria, namely a truncated form of soluble AC and the exchange protein directly activated by cAMP 1 (Epac1), and show a protective role for sACt against cell death, apoptosis as well as necrosis in primary cardiomyocytes
We characterized a functional cAMP pathway within the mitochondria of neonatal and adult cardiomyocytes, which can regulate mitochondrial function and cell death. cAMP is locally produced within the mitochondria by a Ca2+/HCO3−-sensitive sACt and activates Epac[1] to stimulate oxidative metabolism while preventing mitochondrial permeability transition (MPT) by limiting mitochondrial Ca2+ accumulation via mitochondrial Ca2+ uniporter (MCU)
As HCO3− production can be catalyzed by carbonic anhydrase from CO2 and H2O, CO2 being produced by the Krebs cycle and the pyruvate deshydrogenase inside mitochondrial matrix, our data link, for the first time, mitochondrial metabolism, cAMP and cell death in the heart, independently of cytosolic cAMP signaling

Summary

Introduction

Using cellular and subcellular approaches, we demonstrate here the local expression of several actors of cAMP signaling within cardiac mitochondria, namely a truncated form of soluble AC (sACt) and the exchange protein directly activated by cAMP 1 (Epac1), and show a protective role for sACt against cell death, apoptosis as well as necrosis in primary cardiomyocytes. Cyclic 3′,5′-adenosine monophosphate (cAMP) is a major second messenger in many organs, in the heart, where it regulates diverse physiological processes such as Ca2+ homeostasis, beating frequency and myocardial contractility as well as cell death.[16] In the working myocardium, cAMP can activate protein kinase A (PKA) and/or the exchange protein directly activated by cAMP (Epac) to mediate diverse biological effects, including cardiac remodeling and hypertrophy.[17,18,19,20,21,22] In addition to tmACs, cAMP can be generated by soluble adenylyl cyclase (sAC), which is not regulated by heterotrimeric G proteins or forskolin (FSK), but can be activated by bicarbonate (HCO3−) and Ca2+.16,23,24 sAC was found inside mitochondria in the brain and liver and in certain mammalian cell types.[25,26,27,28,29] In the liver and brain, in response to HCO3− and/or Ca2+, mitochondrial cAMP Intrigued by these previous findings, we tested the existence of a cAMP mitochondrial pathway in differentiated adult and neonatal cardiomyocytes and observed that activation of this pathway prevents various cell deaths.

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Results

Conclusion