In contrast, there was no change in expression of Timp1 and Timp2 in PAI-1 knockout kidneys compared to wildtype kidneys suggesting Timp1 and Timp2 may play a significant role in the initial phase of cardiac matrix remodeling in aged PAI-1 knockout mice via controlling MMP activities and matrix degradation; vii) MMP23, a 44 kDa metalloproteinase, may be involved in matrix remodeling under pathological conditions and the level of MMP23 is significantly elevated in idiopathic pulmonary fibrosis (IPF) [58], [59]. Here, MMP23B is linked to idiopathic pulmonary fibrosis.