Cyclic AMP-binding protein Epac1 acts as a metabolic sensor to promote cardiomyocyte lipotoxicity

Marion Laudette,Dorian Bergonnier,Olivier Lairez,Jeanne Mialet-Perez,Jan Borén,Jérémy Fauconnier,Grégoire Cousin,Bertrand Marcheix,Stéphanie Brun,Alexandre Lucas,Florence Tortosa,Loubna Laib,Karina Formoso,Ismahane Belhabib,Cédric Moro,Frank Lezoualc’H,Yannis Sainte-Marie,Camille Bergoglio

doi:10.1038/s41419-021-04113-9

Abstract

Cyclic adenosine monophosphate (cAMP) is a master regulator of mitochondrial metabolism but its precise mechanism of action yet remains unclear. Here, we found that a dietary saturated fatty acid (FA), palmitate increased intracellular cAMP synthesis through the palmitoylation of soluble adenylyl cyclase in cardiomyocytes. cAMP further induced exchange protein directly activated by cyclic AMP 1 (Epac1) activation, which was upregulated in the myocardium of obese patients. Epac1 enhanced the activity of a key enzyme regulating mitochondrial FA uptake, carnitine palmitoyltransferase 1. Consistently, pharmacological or genetic Epac1 inhibition prevented lipid overload, increased FA oxidation (FAO), and protected against mitochondrial dysfunction in cardiomyocytes. In addition, analysis of Epac1 phosphoproteome led us to identify two key mitochondrial enzymes of the the β-oxidation cycle as targets of Epac1, the long-chain FA acyl-CoA dehydrogenase (ACADL) and the 3-ketoacyl-CoA thiolase (3-KAT). Epac1 formed molecular complexes with the Ca2+/calmodulin-dependent protein kinase II (CaMKII), which phosphorylated ACADL and 3-KAT at specific amino acid residues to decrease lipid oxidation. The Epac1-CaMKII axis also interacted with the α subunit of ATP synthase, thereby further impairing mitochondrial energetics. Altogether, these findings indicate that Epac1 disrupts the balance between mitochondrial FA uptake and oxidation leading to lipid accumulation and mitochondrial dysfunction, and ultimately cardiomyocyte death.

Highlights

The heart has a high energy demand and most of the adenosine triphosphate (ATP) produced comes from mitochondrial oxidative phosphorylation, from which fatty acid oxidation (FAO) contributes to 70% of the energy supply [1]
We demonstrate that a saturated fatty acids (FA) palmitate regulates Epac1 activity by stimulating Cyclic adenosine monophosphate (cAMP) production via soluble adenylyl cyclase (sAC) palmitoylation at a highly conserved Cys342 residue
Epac1-calmodulin-dependent protein kinase II (CaMKII) axis interacted with the ATP5A and regulated ATP synthase activity, most likely to impair mitochondrial energetics during lipid overload

Summary

INTRODUCTION

The heart has a high energy demand and most of the ATP produced comes from mitochondrial oxidative phosphorylation, from which fatty acid oxidation (FAO) contributes to 70% of the energy supply [1] In metabolic diseases such as obesity and type 2 diabetes mellitus, accumulation of intramyocardial lipids contributes to cardiac defects termed lipotoxic cardiomyopathy [2]. An imbalance between FA uptake and oxidation results in intracellular accumulation of lipid intermediates thereby causing reactive oxygen species (ROS) generation, mitochondrial dysfunction, and cardiomyocyte death [2] This metabolic alteration contributes to cardiac alteration [4]. Direct activation of Epac with 8which cAMP-Epac signaling induces metabolic inflexibility and CPT-AM had similar effect of palmitate on mitochondrial dysfunction contributes to lipotoxicity in cardiomyocytes. Epac pharmacological inhibitors and palmitate failed to dysregulate the expression level of oxidative

RESULTS

DISCUSSION

MATERIALS AND METHODS

Findings

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