Impaired Intracellular Calcium Buffering Contributes to the Arrhythmogenic Substrate in Atrial Myocytes From Patients With Atrial Fibrillation

• DOI: 10.1161/circulationaha.123.066577
• Publication Date: 2024-06-24T09:00:35Z
• Authors: Funsho E. Fakuade; Dominik Hubricht; Vanessa Möller; Izzatullo Sobitov; Aiste Liutkute; Yannic Döring; Fitzwilliam Seibertz; Marcus Gerloff; Julius Ryan D. Pr...; Fereshteh Haghighi; Sören Brandenburg; Khaled Alhussini; Nadezda Ignatyeva; Yara Bonhoff; Stefanie Kestel; Aschraf El-Essawi; Ahmad Fawad Jebran; Marius Großmann; Bernhard C. Danner; Hassina Baraki; Constanze Schmidt; Samuel Sossalla; Ingo Kutschka; Constanze Bening; Christoph Maack; Wolfgang A. Linke; Jordi Heijman; Stephan E. Lehnart; George Kensah; Antje Ebert; Fleur E. Mason; Niels Voigt
• Keywords: Male; 0301 basic medicine; calcium; Induced Pluripotent Stem Cells; ion channels; Action Potentials; Middle Aged; electrophysiology; Mice; 03 medical and health sciences; Original Research Articles; Atrial Fibrillation; Humans; Animals; atrial fibrillation; Myocytes, Cardiac; Calcium; Female; Heart Atria; Calcium Signaling; remodeling; Aged

BACKGROUND:

Alterations in the buffering of intracellular Ca 2+ , for which myofilament proteins play a key role, have been shown to promote cardiac arrhythmia. It is interesting that although studies report atrial myofibrillar degradation in patients with persistent atrial fibrillation (persAF), the intracellular Ca 2+ buffering profile in persAF remains obscure. Therefore, we aimed to investigate the intracellular buffering of Ca 2+ and its potential arrhythmogenic role in persAF.

METHODS:

Transmembrane Ca 2+ fluxes (patch-clamp) and intracellular Ca 2+ signaling (fluo-3-acetoxymethyl ester) were recorded simultaneously in myocytes from right atrial biopsies of sinus rhythm (Ctrl) and patients with persAF, alongside human atrial subtype induced pluripotent stem cell–derived cardiac myocytes (iPSC-CMs). Protein levels were quantified by immunoblotting of human atrial tissue and induced pluripotent stem cell–derived cardiac myocytes. Mouse whole heart and atrial electrophysiology were measured on a Langendorff system.

RESULTS:

Cytosolic Ca 2+ buffering was decreased in atrial myocytes of patients with persAF because of a depleted amount of Ca 2+ buffers. In agreement, protein levels of selected Ca 2+ binding myofilament proteins, including cTnC (cardiac troponin C), a major cytosolic Ca 2+ buffer, were significantly lower in patients with persAF. Small interfering RNA (siRNA)–mediated knockdown of cTnC (si-cTNC) in atrial iPSC-CM phenocopied the reduced cytosolic Ca 2+ buffering observed in persAF. Si-cTnC treated atrial iPSC-CM exhibited a higher predisposition to spontaneous Ca 2+ release events and developed action potential alternans at low stimulation frequencies. Last, indirect reduction of cytosolic Ca 2+ buffering using blebbistatin in an ex vivo mouse whole heart model increased vulnerability to tachypacing-induced atrial arrhythmia, validating the direct mechanistic link between impaired cytosolic Ca 2+ buffering and atrial arrhythmogenesis.

CONCLUSIONS:

Our findings suggest that loss of myofilament proteins, particularly reduced cTnC protein levels, causes diminished cytosolic Ca 2+ buffering in persAF, thereby potentiating the occurrence of spontaneous Ca 2+ release events and atrial fibrillation susceptibility. Strategies targeting intracellular buffering may represent a promising therapeutic lead in persAF management.