Abstract 1911: Cardiac Junctophilin-2 Expression Silencing Results in Cellular Hypertrophy and Isoproterenol-Sensitive Derangements in Calcium-Handling
Background: Heart failure and cardiomyopathies represent a significant cause of morbidity and mortality both in the United States and globally. Hypertrophic cardiomyopathy (HCM) is the most common cause of autopsy positive sudden death in the young. Junctophilin-2 (JPH2), encoded by JPH2 (20q12), is necessary for proper intracellular calcium (Ca2+) signaling and maintaining Ca2+ homeostasis within the cardiac cell and has been shown to be down-regulated in rodent models of HCM, DCM, and heart failure. In addition, HCM-associated mutations in JPH2 have been elucidated in humans. We sought to explore the possible association of this down-regulation with the cardiac remodeling and arrhythmic predisposition of HCM.
Methods: JPH2 protein expression was measured in flash frozen human cardiac tissue procured from patients with HCM and was compared with previously healthy traumatic death victims. A small interfering RNA probe targeted to murine JPH2 mRNA (shJPH2) was transiently transfected, or adenovirally transduced, into the HL-1 murine cardiac cell line. Cell morphology, peak transient, resting, and store-Ca2+ levels were assessed using Fura-2 AM Ca2+ dye with caffeine and ionomycin treatment. β-adrenergic stimulation was achieved through isoproterenol treatment.
Results: Patients with HCM demonstrated marked reduction in JPH2 expression regardless of the underlying HCM-causative gene. In addition, in vitro expression silencing of JPH2 i) increased cellular size, ii) suppressed maximal Ca2+ transients with a trend towards increased basal levels, and iii) impaired caffeine-trigger store Ca2+ release that was reversed by ionomycin treatment. Isoproterenol treatment unmasked deranged Ca2+ oscillations precipitated by JPH2 silencing.
Conclusions: Taken together, these results may indicate that reduced expression of JPH2 is an initiating factor in the pathogenic growth and electrophysiologic remodeling during hypertrophic cardiomyopathy. Further, perturbed Ca2+ -signaling and homeostasis may not only initiate these pathologic changes but may also provide an arrhythmogenic substrate for a disease associated with sudden cardiac death.
This research has received full or partial funding support from the American Heart Association, Midwest Affiliate (Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, South Dakota & Wisconsin).