Where are MMPs expressed?

There are 28 distinct types of MMPs in vertebrates, in which 23 are expressed in human tissue. They can be expressed in many different types of cells. Classical MMPs (MMP -1, -2, -3, -7, -9, -11) have been identified in endometrium by in situ hybridization and immunohistochemistry. New members of the MMP family (MMP–19 and -26) are in general found in both epithelial cells and in epithelial tumor cells. It has been suggested that MMP-26 could have an important role in ECM remodeling that is associated with angiogenesis and rapid epithelial growth. MMP-14, -15,-16, -17, -24, and -25 in specific are all activated intracellularly and are typically expressed on the cell surface. MMP-12 in specific are expressed mainly in macrophages, and are also found in osteoclasts and hypertrophic chondrocytes. Overall, MMPs are secreted by connective tissue, pro-inflammatory and uteroplacental cells such as endothelial cells, osteoblasts, vascular smooth muscle, macrophages and neutrophils.