MMP13 and atrial fibrillation: Treatment with IL-1β at 1.0 ng/ml significantly upregulated the mRNA expression levels of both IL-1β (Fig. 5a, b), MMP-3 (Fig. 5c, d), and MMP-13 (Fig. 5e, f) by both AF and NP cells (relative expression: OPG 0 μg/ml + IL-1β (vs. control): AF: IL-1β 477.75 ± 289.11; MMP-3 1829.59 ± 661.95; MMP-13 29.53 ± 8.08; NP: IL-1β 83.00 ± 28.94; MMP-3 384.92 ± 154.13; MMP-13 15.08 ± 5.80, p < 0.01, respectively).