Abstract 18393: Plakophilin-2, Ankyrin-G and Connexin43 Mutually Interact to Regulate Intercellular Coupling and Sodium Channel Function. Implications to Arrhythmogenic Cardiomyopathies?
Plakophilin-2 (PKP2) is a protein associated with the cardiac desmosome. Mutations in PKP2 have been linked to up to 70% of cases of familial Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC) with an identifiable genotype. We recently demonstrated a physical association of PKP2 with Nav1.5 (the major alpha subunit of the cardiac sodium channel) and connexin43 (Cx43; the major cardiac gap junction protein). Loss of PKP2 expression caused gap junction remodeling, decreased the amplitude and shifted the kinetics of the sodium current, and decreased propagation velocity in ventricular myocytes. It is possible that PKP2 directly partners with both, Cx43 and Nav1.5. A non-opposing alternative is that a separate scaffolding protein associates with the three complexes, within a shared microdomain. In exploring the latter scenario, we focused on ankyrin-G (ankG), a cytoskeletal adaptor protein known to associate with the sodium channel complex. Experiments were conducted in neonatal rat ventricular myocytes. In control, Nav1.5 and ankG co-localized at sites of cell apposition. Loss of PKP2 expression (by shRNA; non-silencing construct as control) caused a reduction in ankG abundance; Nav1.5 protein levels were unchanged, but the protein no longer concentrated at the sites of cell contact. The PKP2-ankG interaction was reciprocal: Loss of ankG expression caused partial redistribution of PKP2, from sites of cell contact to the intracellular space. Furthermore, loss of ankG expression led to a 37±4.8% decrease in the abundance of Cx43 (n=9) and a decrease in electrical coupling (dual patch clamp) from 30.91 ± 2.06 nS in control (n=12) to 21.33 ± 2.20 nS in AnkG-silenced cells (n=16). Overall we show for the first time an inter-dependence of PKP2 with ankG, and a functional interaction of ankG with Cx43. The emerging picture is that of desmosomes, gap junctions and sodium channels not as independent complexes but rather, as a ”functional triad” where changes in one can affect the function and integrity of the other. This ”electromechanical coupling,” occurring at the intercalated disc, may be relevant not only to arrhythmogenesis in a rare inherited disease (ARVC), but also in acquired cardiomyopathies affecting the integrity of the intercalated disc.
- © 2010 by American Heart Association, Inc.