MMP9 and cancer: Chen et al. [297] demonstrated that secreted exosomal miR-21 activated the pyruvate dehydrogenase kinase 1 (PDK1)/AKT pathway in HSCs located near HCC (cancer-associated fibroblasts) by directly targeting PTEN and promoted cancer progression by inducing the secretion of angiogenic molecules, such as vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), MMP2, MMP9, and TGF-β by HCC cells.