Abstract 14468: Atrial Fibrillation-Related Nuclear Calcium Remodeling and Transcriptional Signaling
Introduction: Atrial fibrillation (AF) is the most common clinical arrhythmia, and contributes to cardiovascular morbidity and mortality. AF-related remodeling is mechanistically important but underlying signaling is cryptic. Nucleoplasmic Ca2+ regulates gene expression; the nature and significance of nuclear Ca2+ changes in AF is poorly understood. Here, we studied the effects of AF on atrial cardiomyocyte (ACM) nuclear Ca2+ and related downstream signaling.
Methods and Results: ACMs were isolated from control dogs (CTL, N=13) and dogs kept in AF for 1 week by atrial tachypacing at 600 bpm (AT-P, N=11). Immunostaining was used to detect CaMKII-delta and HDAC4 expression. Nucleoplasmic and cytoplasmic Ca2+ were recorded via confocal imaging in intact atrial cardiomyocytes loaded with Fluo-4 AM. [Ca2+]nuc and [Ca2+ ]cyto were calibrated independently by exposure of permeabilized ACMs to standardized Ca2+ solutions. [Ca2+]nuc was higher than [Ca2+ ]cyto at baseline and increased further in AT-P vs CTL (Figure A). Time to peak and time for 50% relaxation from peak of the Ca2+ transient were not changed by AT-P. A physiological IP3R activator, endothelin (100 nM), increased diastolic [Ca2+]nuc and [Ca2+ ]cyto in both CTL (by 67%, 52%) and AT-P (by 82%, 63%) ACMs (Figure B). Immunochemistry was used to quantify local expression of total (t-) and phosphorylated (p-) CaMKII, as well as HDAC4. AT-P significantly enhanced t-CaMKII expression in cytoplasm, but not in nucleoplasm (Figure C). AT-P increased p-CaMKIIδ expression in both cyto- and nucleoplasm (Figure D), and enhanced the phosphorylation-ratio of CaMKII prominently in the nucleus (Figure E). Nuclear HDAC4 expression was reduced by AT-P (Figures F, G), suggesting HDAC4 export.
Conclusions: AF-related remodeling alters ACM cyto- and nucleoplamic Ca2+ handling to increase nuclear Ca2+ load. Increased [Ca2+]nuc may play an important role in AF-induced gene dysregulation through the CaMKII/HDAC4 pathway.
Author Disclosures: X. Qi: None. F. Xiong: None. L. Villeneuve: None. Y. Sobue: None. S. Ljubojevic: None. D.M. Bers: None. S. Nattel: None.
- © 2016 by American Heart Association, Inc.