Inherited Variant in MRC2 Causes Cardiac Fibroblast Dysfunction and Increases Atrial Fibrillation Susceptibility

Programmed electrical stimulation (PES) was performed to determine AF susceptibility in E990G-het mice and wild-type (WT) controls. ACFs were isolated from these mice and cultured, and their migration, and collagen deposition were quantified. Finally, transcriptomic profiling by RNA sequencing and secretomic/proteomic profiling by mass spectrometry were performed on ACFs and whole atrial tissue.

Results. E990G-het mice exhibited increased susceptibility to pacing-induced AF and had decreased atrioventricular effective refractory periods compared to WT controls. ACFs isolated from E990G-het mice deposited greater amounts of acid-soluble collagen in 2D cultures as quantified by Sirius red staining compared with WT controls.

Transcriptomic, secretomic, and proteomic profiling of cultured ACFs and whole-atrial tissue suggest that some fibrotic regulators are differentially expressed or secreted, including decreased ACF expression of matrix metalloproteinase 13 (MMP-13), which degrades collagen types I, II, and III; decreased ACF expression, ACF secretion, and atrial tissue levels of matrix metalloproteinase 12 (MMP-12), which degrades collagen types I, III, IV, elastin, and fibronectin; and increased tissue levels of cellular communication network factor 2/connective tissue growth factor (CCN2/CTGF), a profibrotic regulator.

Conclusions. MRC2 E990G-het mice exhibit increased AF susceptibility, altered collagen deposition by ACFs, and differentially regulated fibrotic genes and proteins. Together, these findings suggest that excessive collagen deposition and reduced MMP-mediated collagen removal generate a substrate for the development of AF in the presence of a loss-of-function variant in MRC2.