However, stimulation with IL-1β significantly upregulated the mRNA expression of MMP-3 (Fig. 4c, d) in both AF and NP cells and that of MMP-13 in NP cells (Fig. 4f) (relative expression: RANKL 0 μg/ml + IL-1β (vs. control): AF: MMP-3 43.34 ± 12.95, p < 0.05; NP: MMP-3237.47 ± 42.88, p < 0.01; MMP-13 19.91 ± 4.88, p < 0.05). Here, MMP3 is linked to atrial fibrillation.