Role of TRPC3 in the heart

The cation channel protein TRPC3 is expressed in cardiac myocytes and has recently been implicated in the pathogenesis of cardiac remodelling and hypertrophy-associated cardiomyopathy. TRPC proteins form a variety of heteromeric pore structures that serve distinct cellular Ca2+ signalling mechanisms. The molecular composition of cardiac TRPC channel complexes as well as their exact role in cardiac (patho)physiology has so far not been elucidated. TRPC3 may represent a multifunctional player in cardiac physiology as well as in various scenarios of cardiac remodelling. The aims of this project are to identify and characterize TRPC3-dependent cardiac membrane conductances and to delineate their impact on cardiac excitability, action potential morphology as well as cellular Ca2+ handling. Moreover, we plan to investigate the role of regulatory subunits and signalling partners of cardiac TRPC3 channels and to explore plasticity of TRPC3 complex composition in response to stimuli that initiate cardiac remodelling. The experimental approach will utilize available transgenic- and knock-out mice as well as different murine cardiac cell models along with classical electrophysiological and biochemical methods complemented by high resolution cellular imaging techniques and genetic manipulation to knock-down TRPC protein expression and/or functions using si/shRNA and dominant negative strategies. The expected results are considered to pave the way towards exploiting cardiac TRPC channel complexes as therapeutic targets.

The work of this project identified novel pathophysiological principles, which are pivotal for acute and long-term modulation of cardiac contractility and excitability. These mechanisms are critically involved in maladaptive, ageing-associated remodeling of the myocardium and their understanding provides the basis for development of novel therapeutic strategies. Central goal of this project was to gain understanding of the cardiac role of a member of the TRPC (transient receptor potential canonical) family of ion channels, the TRPC3 isoform. This cation channel protein is predominantly expressed in heart and brain, and has been recognized as a determinant of transcriptional control and remodeling processes. With our work we identify TRPC3 as a key player in cardiac pathophysiology and, thus, as an attractive target for therapeutic interventions, specifically for prevention of cardiac remodeling and arrhythmogenesis. We were able to demonstrate several novel molecular and pathophysiologic functions of this cardiac ion channel. One key finding of our work is the 2+ interaction of TRPC3 with the phosphatase calcineurin, which is a key enzyme in Ca - dependent control of gene transcription. We provided evidence for a functional TRPC3 containing signaling nanodomain in the heart and proposed a novel concept of cardiac Ca2+ transcription coupling. Besides Ca2+-dependent control of genetranscription we focused attention on the role of TRPC3 as a determinant of cardiac excitability and arrhytmogenesis. The use of a novel pharmacological tool, a selective and direct activator of TRPC3, we demonstrated for the first time that enhanced activity of cardiac TRPC3 is associated with a gain in contractility as well as promotion of arrhythmogenesis. Of particular significance for better understanding of cardiac pathophysiology is our finding of a functional coupling between TRPC3 and the cardiac Na+/ Ca2+ exchanger NCX1. Importantly, we uncovered a dynamic interaction between cardiac TRPC3 and NCX1 and were able to demonstrate that altered/reduced coupling between these molecules is associated with arrhythmogenesis. Our work suggests modulation of cellular localization of Ca2+-handling proteins as a promising basis of new therapeutic approaches. Specifically, our findings may be exploited in terms of prevention of maladaptive remodeling in the heart including hypertrophy and remodeling- associated arrhythmias.