Mmp12 Knockout mouse models

Mmp12 is the mouse ortholog of human MMP12 and encodes macrophage metalloelastase, a secreted zinc endopeptidase produced almost exclusively by macrophages, with a propeptide cysteine switch, a catalytic domain, and a hemopexin-like domain that undergoes autolytic removal, and with unusually potent activity against elastin as well as fibronectin, laminin, and type IV collagen. Its causal role in emphysema is well established, since Mmp12 nulls resist cigarette smoke induced airspace enlargement and show reduced macrophage recruitment, and the enzyme also contributes to aneurysm formation and to generation of matrikine chemoattractants. Beyond the extracellular compartment it accumulates intracellularly in macrophages where it participates in bacterial killing, a function that secretion-focused assays miss. Conditional deletion with Lyz2-Cre or Cx3cr1-CreER confirms the myeloid source, catalytically dead knockins separate proteolysis from scaffolding, and humanization supports selective inhibitor programs. Compensation by Mmp2, Mmp9, and neutrophil elastase means combined alleles are often needed for full elastolytic loss.

Whole body loss of Mmp12 gives the clearest readout when the question is whether the gene is required at all. Follow up tissue work can still move to a conditional allele if lethality or compensation appears.