Abstract 9: Cardiac BIN1 Improves Dyad Organization and Calcium Transient in Cardiomyocytes

Abstract

BIN1 (bridging integrator 1) is a membrane scaffolding protein that forms microfolds at t-tubules and organizes dyad microdomains essential for a normal calcium transient. Reduction of cBIN1 has emerged as a new hallmark in heart failure and is associated with impaired calcium transient and increased risk of arrhythmias. We hypothesized that gene transfer of cardiac BIN1 (cBIN1) in vivo can improve calcium transients in disease models. We introduced V5-tagged cBIN1 or GFP through AAV9-mediated expression in adult mice. Confocal imaging of isolated cardiomyocytes was used to assess organization of dyad microdomain. Calcium transients in response to acute administration of isoproterenol (ISO) was measured as functional readout of excitation-contraction (EC) coupling. Here we report that cBIN1 significantly enhanced both basal and ISO-induced increase in calcium transient compared to cells expressing GFP. Immunofluorescent labeling revealed that cBIN1 expression increased both LTCC and RyR at t-tubule. In addition, in a mouse model of ischemic cardiomyopathy, permanent LAD ligation resulted in a marked reduction in ISO-induced increment in calcium transient, indicating blunted beta-adrenergic responsiveness and impaired regulation of EC coupling machinery. In comparison, an ISO-induced increment in calcium transient was largely maintained in cBIN1-expressing cells. These results demonstrate that cBIN1 increases calcium transients by upregulating and organizing dyad proteins at t-tubule microfolds. More importantly, cBIN1 rescues diminished beta-adrenergic responsiveness in ischemic cardiomyopathy and improves EC coupling of viable cardiomyocytes. This work suggests that cBIN1 provides a therapeutic opportunity to improve cardiac function in ischemic cardiomyopathy and heart failure.