The role of atrial mitochondrial Calciumhandling in arrhythmogenesis in patients with atrial fibrillation.

• Applicant: Professor Dr. Wolfgang Niels Voigt
• Subject Area: Pharmacology ; Cardiology, Angiology
• Term: from 2016 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 315254108

Atrial fibrillation (AF) is the most common sustained arrhythmia in the clinical setting and 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. Ca2+, the main mediator of the excitation-contraction coupling process in cardiac myocytes, is also a key regulator of mitochondrial functions such as ATP-synthesis, reactive oxygene species (ROS)-induced signaling and programmed cell death (apoptosis). Whether impaired mitochondrial Ca2+ handling and resulting dysregulation of mitochondrial functions contribute to AF initiation and/or maintenance is largely unknown. Most of our knowledge about mechanisms by which mitochondrial dysfunction promote arrhythmia comes from experiments in ventricle. Whether similar mechanisms may play a role in AF patients is unclear and is the subject of this application.We propose to investigate the structure and function of mitochondria and related mitochondrial Ca2+ handling in atria from patients with sinus rhythm and persistent (chronic) AF (cAF) and identify mechanisms by which mitochondrial dysfunction may contribute to atrial arrhythmogenesis. As an initial step we will use electron microscopy and confocal imaging techniques for a detailed structural analysis of mitochondrial size, shape and distribution in atria from patients with sinus rhythm and cAF. Then we will exploit molecular biology techniques to investigate structural interaction between sarcoplasmic reticulum (SR), the main Ca2+ storage organelle, and mitochondria as well as expression differences in key mitochondrial Ca2+-handling proteins between sinus rhythm and cAF. To directly measure mitochondrial Ca2+ concentration we established adenoviral infection of human atrial myocytes with Mitycam, a Ca2+ sensitive marker protein, which is selectively expressed in mitochondria. We will employ simultaneous recordings of membrane currents, along with cytosolic and mitochondrial Ca2+ concentration in response to different stimuli to investigate functional interactions between mitochondria and SR. Complementary experiments will assess mitochondrial function by measuring mitochondrial membrane potential, NADH/FAD concentration and mitochondrial ROS in intact human atrial cardiomyocytes. Finally, we will determine the contribution of mitochondrial dysfunction to cellular arrhythmogenic pathomechanisms such as action potential shortening, alternans, and delayed afterdepolarizations by using different pharmacological modulators of mitochondrial function.Combined the proposed experiments will provide structural and functional insights into the function of atrial mitochondria in general and their dysfunction in patients with cAF in particular. Ultimately, the insights from this work will establish mitochondrial dysfunction as a novel therapeutic target for treatment of AF.

• DFG Programme: Research Grants