MMP13 and atrial fibrillation: However, OPG significantly suppressed the expression of IL-1β by AF and NP cells (Fig. 5a, b), MMP-3 by NP cells (Fig. 5d), and MMP-13 by AF cells (Fig. 5e) upregulated by IL-1β (1.0 ng/mL) stimulation (relative expression: OPG 1.0 μg/mL + IL-1β (vs. OPG 0 μg/mL + IL-1β), AF: IL-1β 0.77 ± 0.29; MMP-13 0.77 ± 0.22; p < 0.01, respectively, NP: IL-1β 0.62 ± 0.19, p < 0.01; MMP-3 0.81 ± 0.26, p < 0.05).