MMP9 and atrial fibrillation: Downregulation of Cav-1 in AF revealed in this study may be, at least partially, a cause for reduced MMPs function in AF; this is evidenced by our finding that Cav-1 was able to reverse the downregulation of expression of MMP-1, MMP-2 and MMP-9 induced by TGF-β1 in HAFs.