Introduction: A recent study identified a rare variant in the MRC2 gene in individuals with familial reentrant supraventricular tachycardia, a Wolff-Parkinson-White (WPW) ECG pattern, and structurally normal hearts. WPW syndrome is associated with atrial fibrillation (AF), and MRC2 was recently proposed as a protective gene for AF. Hypothesis/Aim: We aimed to assess the hypothesis that the E990G-heterozygous (het) loss-of-function variant in MRC2 increases AF susceptibility and aberrant atrial cardiofibroblast (ACF) function in mice. Methods: 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 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 (n=15) exhibited increased susceptibility to pacing-induced AF (60% vs. 20%, P =0.030) compared with WT controls (n=15) and had decreased atrioventricular effective refractory periods (mean ± SEM: 44.6 ms ± 1.8 vs. 56.7 ± 1.8, P <0.001) . ACFs isolated from E990G-het mice (n=5) deposited greater amounts of acid-soluble collagen in 2D cultures (median ± IQR: 15.5 µg/3000 ACFs ± 1.3 vs. 10.7 ± 2.6, P =0.009) compared with WT controls (n=5). Transcriptomic (n=4 WT ACF lines + 5 het; 8 WT atrial tissue + 7 het), secretomic (n=4 WT ACF lines + 4 het), and proteomic (n=4 WT atrial tissue + 4 het) profiling of cultured ACFs and whole-atrial tissue revealed differential expression of several fibrotic regulators in E990G-het versus WT mice, including decreased ACF expression of matrix metalloproteinase 13 (MMP-13, P =0.012), which degrades collagen types I, II, and III; decreased ACF expression ( P =0.002) and secretion ( P =0.041) 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, P =0.004), a profibrotic regulator. Conclusions: MRC2 E990G-het mice exhibit increased AF susceptibility, altered ACF collagen deposition, and differentially regulated fibrotic genes and proteins. Together, these findings suggest that the E990G loss-of-function MRC2 variant leads to an AF-prone substrate characterized by excess collagen deposition and reduced MMP-mediated collagen removal.
Ho et al. (Fri,) studied this question.