These findings added another route for knee AF, the “autocrine fibroblast circuit”, in which TGF-β induces CCN2 and CCN2 in turn amplifies the TGF-β functions.49 In another cohort of patients, we observed a co-localization of fibroblasts, myofibroblasts and macrophages in AF group indicating a possible cell interaction among these cells. Here, TGFB1 is linked to atrial fibrillation.