Matrix metalloproteinases in lung biology

Despite much information on their catalytic properties and gene regulation, we actually know very little of what matrix metalloproteinases (MMPs) do i n tissues. The catalytic activity of these enzymes has been implicated to f unction in normal lung biology by participating in branching morphogenesis, homeostasis, and repair, among other events. Overexpression of MMPs, howev er, has also been blamed for much of the tissue destruction associated with lung inflammation and disease. Beyond their role in the turnover and degra dation of extracellular matrix proteins, MMPs also process, activate, and d eactivate a variety of soluble factors, and seldom is it readily apparent b y presence alone if a specific proteinase in an inflammatory setting is con tributing to a reparative or disease process. An important goal of MMP rese arch will be to identify the actual substrates upon which specific enzymes act. This information, in turn, will lead to a clearer understanding of how these extracellular proteinases function in lung development, repair, and disease.