Small extracellular vesicles from epicardial fat of patients with atrial fibrillation facilitate inflammation, fibrosis and re-entry

Background and Aim: Epicardial fat (eFat) has been linked to atrial remodeling and fibrillation (AF). Small extracellular vesicles (sEVs) are heterogeneous membrane vesicles released by all cell types. They can both protect and damage tissues by the delivery of multiple different messengers. Surprisingly, the role of sEVs in the pathogenesis of AF has not been studied. Thus, we aimed to determine whether extracellular vesicles (sEVs) derived from eFat play a role in the pathogenesis of AF.

Methods and Results: We collected eFat specimens from patients with and without chronic or paroxysmal AF undergoing open-heart surgery. Isolated eFat specimens were cut into small pieces and incubated as organ cultures. We isolated sEVs from the medium of the explant by differential ultra-centrifugation and characterized the vesicle size distributions, morphology, specific markers, and molecular cargo. The levels of pro-inflammatory and pro-fibrotic cytokines and miRNA were higher in sEVs from patients with, compared with those without AF (Fig. 1A – Fig. 1K). Immunostaining for macrophage accumulation, fibrosis and apoptosis confirmed the pro-inflammatory and pro-fibrotic properties of eFat sEVs from patients with AF(Fig. 2L – Fig. 2O) . Finally, while eFat sEVs from patients with and without AF induced shorter action potential duration, only eFat sEVs from patients with AF induced sustained re-entry (rotor) in human induced pluripotent stem cell (iPS)-derived cardiomyocytes (Fig. 3Q – Fig. 3U).

Conclusion: We show, for the first time, that sEVs from eFat of patients with AF demonstrate unique pro-inflammatory, pro-fibrotic, and pro-arrhythmic effects. Our findings suggest that eFat sEVs can induce, cellular, molecular and electrophysiological remodeling that subsequently lead to the development of AF.