Abstract Body (Do not enter title and authors here): Introduction
Obesity is a risk factor for atrial fibrillation (AF) and its incidence that has tripled over the past 30 years. Obesity is associated with dramatic changes in atrial structure and electrophysiology through unclear mechanisms. The linoleic acid metabolite 12,13-dihydroxy-9Z-octadecenoic acid (12,13-diHOME) is a signaling lipid released by brown adipose tissue that acts in an endocrine manner on myriad tissues including the heart. 12,13-diHOME enhances cardiac myocyte Ca²⁺ cycling and overall function, though the precise mechanisms are undetermined. This study tested the hypothesis that 12,13-diHOME inhibits the pro-arrhythmic molecule Ca²⁺/calmodulin-dependent kinase II (CaMKII). We propose that obesity-induced loss of 12,13-diHOME promotes CaMKII dysfunction, in vitro ectopy and atrial arrhythmia (AA).
Methods
Adult male and female mice were fed either high fat diet (HFD, 60% kcal from fat) or normal chow (NFD) (21% kcal from fat) for 8-16 weeks. Atrial myocytes were isolated for action potential (AP) measurements using whole-cell patch clamp ±12,13-diHOME (5 μM). To test the effect of 12,13-diHOME on AA inducibility, a second cohort of mice was fed HFD and subjected to weekly tissue nanotransfection for non-viral delivery of either Ephx1/2 (HFD-TNT), enzymes responsible for production of 12,13-diHOME, or empty plasmid (HFD-con). Following treatment, mice underwent intracardiac pacing studies to determine AA inducibility. The ability of 12,13-diHOME to directly interact with and inhibit CaMKII was tested using purified components with in vitro radioassay and microscale thermophoresis.
Results
HFD induced atrial myocyte AP duration prolongation and a higher incidence of spontaneous depolarization compared to NFD, both of which were reversed by 12,13-diHOME (figure). HFD-TNT exhibited decreased phospho-CaMKII compared to HFD-con mice. In parallel, HFD-TNT trended toward reduced inducibility of AA (0/7 mice inducible, 0%) compared to TNT-CON mice (5/7, 58%) (p=0.07). Radioassay revealed that 12,13-diHOME inhibits CaMKII; thermophoresis demonstrated direct binding with K_1/2 = 19 mM.
Conclusion
HFD induces dysregulation in 12,13-diHOME and CaMKII signaling together with defects in atrial myocyte excitability and AA in mice. Non-viral overexpression of 12,13-diHOME shows promise in normalizing CaMKII activity and reducing AA burden. 12,13-diHOME represents a novel avenue for direct regulation of CaMKII signaling and downstream pathology in the heart.