Kidney Fibrosis and Matrix Metalloproteinases (MMPs)

Chronic kidney disease (CKD) is a disorder that causes changes in both the structure and function of the kidneys, causing complications such as hypertension, edema, and oliguria. Renal fibrosis is also a common pathological feature of CKD. Matrix metalloproteinases (MMPs) are endopeptidases that degrade extracellular matrix (ECM) proteins. The proteinase domain consists of a zinc ion in the active site, which contributes to its stabilization with another zinc and three calcium structural ions. Many cellular processes are controlled by MMPs, such as cell–cell interactions and various signaling pathways, while they are also involved in degrading substrates on cell surfaces. Tissue inhibitors of metalloproteinases (TIMPs) are key regulators of metalloproteinases, and both are involved in regulating cell turnover, the regulation, and the progression of fibrosis and apoptosis in the tissue. MMPs play a role in renal fibrosis, such as the tubular cell epithelial–mesenchymal transition (TEM), activation of resident fibroblasts, endothelial–mesenchymal transition (EndoMT), and pericyte–myofibroblast transdifferentiation. This review aims to show the mechanisms through which MMPs contribute to renal fibrosis, paying particular attention to MMP-9 and the epithelial–mesenchymal transition.