Mapping cAMP nanodomains in human atrial myocytes and their dysregulation in atrial fibrillation

• Applicant: Dr. Cristina Espinosa Molina, Ph.D.
• Subject Area: Pharmacology ; Cardiology, Angiology
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 429535956

Atrial fibrillation (AF) is the most common sustained arrhythmia in the clinical setting which is associated with significant morbidity and mortality. AF is also associated with severe cellular calcium (Ca2+)-handling abnormalities in atrial myocytes that may contribute to the initiation and maintenance of the arrhythmia. This so called “remodeling” is supposed to involve abnormal phosphorylation of key Ca2+ handling proteins. In addition, previous studies suggest that impaired phosphodiesterase (PDE)-dependent regulation of spatiotemporal distribution of cAMP may contribute to Ca2+-handling abnormalities associated with AF. The cAMP pathway plays a key role in the regulation of cardiac contractility, relaxation, automaticity, metabolism and gene expression. Few years ago it was demonstrated that there is a specificity in the cAMP-signals generated upon activation of different Gs-protein coupled membrane receptors (GsPCR). A characteristic feature of each GsPCR to induce a specific functional response is a tight control of the cAMP signal by specific PDEs. Several groups have been characterizing the role of PDEs in ventricular myocytes from animal models, but only few studies have evaluated the importance of PDEs in human heart and almost none of them are related to the atria. Our recent studies have indicated the expression and functional role of different PDE1, PDE2, PDE3, PDE4 and PDE8 isoforms in the human atria. We also showed the role of PDE4 in Ca2+-handling in human atrial myocytes from healthy patients. Our preliminary data indicate that PDE8B co-localize with the L-type Ca2+-channel in human atrium and it accumulates in this channel in samples from patients with AF contributing to the reduction of ICa,L and the shortening of the action potential duration. Therefore, we will investigate how PDEs control the spatiotemporal response of intracellular cAMP in key relevant Ca2+-handling nanodomains by measuring real time cAMP, ICa,L, spontaneous Ca2+ releases from the sarcoplasmic reticulum, protein expression and localization, using highly sensitive and specifically targeted cAMP biosensors, patch-clamp, confocal Ca2+ imaging, contractility measurements and biochemical experiments. We hypothesize that there are unifying regulatory mechanisms, such as the second messenger cAMP generated by GPCRs activation and its compartmentalized signaling via PDEs, underpinning pathological changes in electrical properties of the atria that can serve as pharmacological targets for atrial fibrillation therapy. The overall goal of this project is to determine the role of PDEs and GsPCR in the chronic AF associated remodelling of cellular Ca2+-handling and atrial arrhythmogenesis. Since abnormalities in intracellular Ca2+-homeostasis are an important hallmark of AF-associated remodeling and contribute to the maintenance of AF, inhibition of specific PDE isoforms or their overexpression could provide a novel therapeutic approach in chronic AF.

• DFG Programme: Research Grants