Mmp12 encodes a member of the matrix metalloproteinase family of extracellular matrix-degrading enzymes that are involved in tissue remodeling, wound repair, progression of atherosclerosis and tumor invasion. The encoded preproprotein undergoes proteolytic processing to generate a mature, zinc-dependent endopeptidase enzyme. Mice lacking the encoded protein have a diminished capacity to degrade extracellular matrix components, do not develop emphysema in response to long-term exposure to cigarette smoke, and exhibit impaired clearance and increased mortality upon bacterial infection. Mmp12 is located in a cluster of other matrix metalloproteinase genes on chromosome 9. Alternate splicing generates multiple transcript variants encoding distinct isoforms.