Defining novel mechanisms for human arrhythmia

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Abstract Defects in cardiac excitability are the basis for human arrhythmia and sudden cardiac death, a leading cause of mortality in developed countries. Unfortunately, arguably the last major “game-changing” breakthroughs in electrical cardiomyocyte biology and cardiac signaling for human health were the beta- blocker (discovered in the 1950s) and `ACE' inhibitor (in the 1970s). On the other hand, therapeutic agents to treat disorders of cardiac excitation (arrhythmias) are plagued by limited efficacy and even off-target pro- arrhythmia. Despite a wealth of negative clinical data, excitable cell researchers have largely remained focused on the same paradigm - pharmacological therapies targeting cardiac ion channels. We contend that improved therapies will only arise through a more sophisticated, working understanding of interactions between structural proteins (such as ankyrins), electrical proteins (ion channels, pumps & exchangers) and signaling systems (kinases, phosphatases, oxidases). Our studies discovered that ankyrin and spectrin proteins, previously considered static membrane adapters, play dynamic roles in ion channel, transporter, and signaling protein targeting in ventricular cardiomyocytes. Further, we have learned that these proteins serve as critical central membrane nodes to regulate normal signaling in heart. Finally, and most importantly, we have learned that dysfunction in these pathways results in potentially fatal forms of both congenital and acquired ventricular arrhythmia. Our long-term goal is to discover novel integrated mechanisms for regulating cardiovascular cell excitability and signaling. We have used the informative case of ankyrins and spectrins as a tractable starting point, but propose to rapidly extend these studies to new systems with diverse interacting structure-electrical- signaling systems. Our laboratory has taken an active lead in the identification of new cellular pathways for regulation of cellular excitability based on human clinical, tissue, and genetic data. In addition, we have pushed innovation in the field through the use of physiologically-relevant model systems to study the mechanisms underlying electrical signaling in the complex vertebrate cardiomyocyte. This approach has ultimately culminated in an ability to not only diagnose new forms of potentially fatal arrhythmia, but to design effective patient-selective therapies for these diseases. If successful in obtaining funding from the NHLBI Outstanding Investigator Award, we will continue to pursue scientific studies with the potential to create new, cell-specific insights for improved understanding of cardiac excitability with direct relevance for congenital and acquired human disease.