Ankyrin-G Coordinates Intercalated Disc Signaling Platform to Regulate Cardiac Excitability In Vivo
Rationale: Nav1.5 (SCN5A) is the primary cardiac voltage-gated Nav channel. Nav1.5 is critical for cardiac excitability and conduction, and human SCN5A mutations cause sinus node dysfunction, atrial fibrillation, conductional abnormalities, and ventricular arrhythmias. Further, defects in Nav1.5 regulation are linked with malignant arrhythmias associated with human heart failure. Consequently, therapies to target select Nav1.5 properties have remained at the forefront of cardiovascular medicine. However, despite years of investigation, the fundamental pathways governing Nav1.5 membrane targeting, assembly, and regulation are still largely undefined.
Objective: Define the in vivo mechanisms underlying Nav1.5 membrane regulation.
Methods and Results: Here, we define the molecular basis of a Nav channel regulatory platform in heart. Using new cardiac-selective ankyrin-G-/- mice (cKO), we report that ankyrin-G targetsNav1.5 , and its regulatory protein, calcium/calmodulin-dependent kinase II (CaMKII) to the intercalated disc. Mechanistically, βIV-spectrin is requisite for ankyrin-dependent targeting of CaMKIIδ, however βIV-spectrin is not essential for ankyrin-G expression. Ankyrin-G cKO myocytes display decreased Nav1.5 expression/membrane localization, and reduced INa associated with pronounced bradycardia, conduction abnormalities, and ventricular arrhythmia in response to Nav channel antagonists. Moreover, we report that ankyrin-G links Nav channels with broader intercalated disc signaling/structural nodes, as ankyrin-G loss results in reorganization of plakophilin-2 and lethal arrhythmias in response to beta-adrenergic stimulation.
Conclusions: Our findings provide the first in vivo data for the molecular pathway required for intercalated disc Nav1.5 targeting/regulation in heart. Further, these new data identify the basis of an in vivo cellular platform critical for membrane recruitment and regulation of Nav1.5.
- protein trafficking
- sodium channels
- cytoskeletal dynamics
- mouse mutant
- arrhythmia (mechanisms)
- Received August 27, 2014.
- Revision received September 16, 2014.
- Accepted September 19, 2014.