GSK3B and hypertrophy: Now, many TNF-dependent genes linked to ECM remodeling as well as AF are upregulated with exercise in WT atria compared to sedentary, including Mmp14 (Simmers et al., 2016), Fgf2 (i.e., fibroblast growth factor 2, which activates p38 and induces cardiac hypertrophy as well as fibrosis) (Itoh and Ohta, 2013), Gsk3β (Sugden et al., 2008), and Tln1 (Manso et al., 2013).