MT1X and atrial fibrillation: Gene Ontology (GO) analyses indicated that upregulated genes in the FB3 cell subcluster of AF were related to collagen-containing ECM, ECM structural constituent, and actin filament binding (Fig. 2k and l), whereas downregulated genes including MT2A and MT1X were associated with response to metal ions (Figs. S2f, S2g).