Treatment of NP (but not AF) cells from degenerate and non-degenerate IVDs with IL-1 resulted in significant increases in gene expression of MMP-13 (an MMP with high affinity for type II collagen), a finding not previously reported in disc cells, although it has been shown in articular chondrocytes [16,47,48]. This evidence concerns the gene IL1B and atrial fibrillation.