COL1A1 and atrial fibrillation: Regarding the matrix remodeling capacity of human AF cells, the secretome downregulated the gene expression of MMP-1 (*p < 0.01) and MMP-3 (p = 0.07) (Figures 5A,B) compared to CTS + IL-1β stimulation alone and did not alter COL1A1, elastin, or fibrillin-1 expression (Figures 5C–E).