M1 Macrophages cause cardiac arrhythmia in an in vitro hiPSC coculture model of inflammation-induced atrial fibrillation

Atrial fibrillation (AF) has an estimated prevalence of 1.5–2%, making it the most common cardiac arrhythmia. The mechanisms that cause and sustain AF are still not completely understood. An association between AF and systemic as well as local inflammatory processes has been reported, however, the exact mechanisms underlying this association have not been established. While it is understood that tissue resident macrophages can influence cardiac electrophysiology, the effects of activated pro-inflammatory macrophages have not been described yet. This study investigated the pro-arrhythmic effects of activated macrophages (M1) on human induced pluripotent stem cell (hiPSC)-derived atrial cardiomyocytes (aCM), to propose a mechanistic link between inflammation and AF. Two hiPSC lines from healthy individuals were differentiated to aCMs and M1 macrophages. Electrophysiology characteristics of M1 and aCM cocultures were analysed for beat rate irregularity, electrogram amplitude and conduction velocity. M1 cocultures resulted in a significant increase in beat rate irregularity and decrease in electrogram amplitude compared to other conditions tested, including aCMs treated with activated M1 supernatant, which did not produce an increase in irregularity. Conduction analysis further showed significantly lower conduction homogeneity in M1 cocultures. Immunosuppression through glucocorticoids significantly decreased beat irregularity in aCM+M1 cocultures compared to vehicle. RNA sequencing performed in aCMs, revealed downregulation of various ion channels (SCNA5, KCNA5, ATP1A1), as a result of the M1 coculture. Electrophysiology related transcription changes were reversed by glucocorticoid treatment. This study establishes a causal relationship between M1 activation and the development of subsequent atrial arrhythmia, documented as irregularity in spontaneous electrical activation in aCM cocultured with activated macrophages. Further, beat rate irregularity could be alleviated using anti-inflammatory steroidal glucocorticoids. These results strongly support the relevance of the proposed hiPSC-derived coculture model and point at macrophage mediated inflammation as a potential AF mechanism.