Macrophage elastase kills bacteria within murine macrophages

Abstract

Macrophages are aptly positioned to function as the primary line of defence against invading pathogens in many organs, including the lung and peritoneum. Their ability to phagocytose and clear microorganisms has been well documented1 , 2. Macrophages possess several substances with which they can kill bacteria, including reactive oxygen species, nitric oxide, and antimicrobial proteins3 -9 . We proposed that macrophage-derived proteinases may contribute to the antimicrobial properties of macrophages. Macrophage elastase (also known as matrix metalloproteinase 12 or MMP12) is an enzyme predominantly expressed in mature tissue macrophages 10 and is implicated in several disease processes, including emphysema11. Physiological functions for MMP12 have not been described. Here we show that Mmp12 −/− mice exhibit impaired bacterial clearance and increased mortality when challenged with both Gram-negative and Gram-positive bacteria at macrophage-rich portals of entry, such as the peritoneum and lung. Intracellular stores of MMP12 are mobilized to macrophage phagolysosomes after the ingestion of bacterial pathogens. Once inside phagolysosomes, MMP12 adheres to bacterial cell walls where it disrupts cellular membranes resulting in bacterial death. The antimicrobial properties of MMP12 do not reside within its catalytic domain, but rather within the carboxy-terminal domain. This domain contains a unique four amino acid sequence on an exposed β loop of the protein that is required for the observed antimicrobial activity. The present study represents, to our knowledge, the first report of direct antimicrobial activity by a matrix metallopeptidase, and describes a new antimicrobial peptide that is sequentially and structurally unique in nature.To determine whether MMP12 has a role in host defence against bacteria, we subjected Mmp12 −/− mice and wild-type littermates to intraperitoneal (i.p.) injection of either Staphylococcus aureus or Escherichia coli. In each case, there was a significant survival advantage for wild-type mice as compared to Mmp12 −/− mice over a 3-day period (Fig. 1a-c, g). Lower titres of i.p. S. aureus injection (1 ×10 7 colony-forming units (c.f.u.)), which did not result in mortality in wild-type mice, still proved >50% lethal in Mmp12 −/− mice. Soon afterCorrespondence and requests for materials should be addressed to A.M.H. (houghtonm@dom.pitt.edu). * These authors contributed equally to this work.Author Information Reprints and permissions information is available at www.nature.com/reprints. Author Contributions A.M.H. performed in vivo and in vitro studies, contributed to data interpretation and mechanistic advance, prepared the manuscript and figures, and performed all revisions. W.O.H. performed in vivo and in vitro studies and contributed to study design, data analysis, and mechanistic advance. C.S.R. performed CTD processing studies. F.X.G.-R. constructed the three-dimensional homology model of MMP12 CTD. S.D.S. generated Mmp12 −/− mice and all recombinant proteins, was responsible fo...

ExperimentalPneumocystislung infection promotes M2a alveolar macrophage-derived MMP12 production

“…Recent studies have reported that MMP12 expressed in macrophage phagolysosomes has potent antimicrobial activity (12). Moreover, data presented in Fig.…”

“…Our data suggested that the level of Mmp12 expression correlated with the level of P. murina clearance from the lungs, thus bringing into question whether MMP12 possessed the ability to directly inhibit the growth of P. murina. Indeed, a 20-amino acid sequence in the carboxy-terminal domain of MMP12 has been shown to be a potent growth inhibitor of multiple Gram-positive and Gram-negative bacteria (12). The proenzyme form of MMP12 is secreted and subsequently activated in the phagolysosome of macrophages (12).…”

Matrix metalloproteinases in COPD

“…Additionally, HOUGHTON et al [65] have shown that MMP-12 has an important role in killing of bacteria within murine macrophages; MMP-12-/-mice showed impaired bacterial clearance and increased mortality with Gram-positive and Gram-negative experimental infections. Interestingly, this effect is not mediated by the catalytic domain of the enzyme but rather by the carboxy terminal domain.…”

Antibodies protect against intracellular bacteria by Fc receptor-mediated lysosomal targeting

“…Host cell proteases, such as the MΦ elastase, can exhibit bactericidal activity against Gram-positive and Gram-negative bacteria (14). To address whether FcR signaling ultimately induces activation and mobilization of host proteases to the LCV, we pretreated the host cells with cell-permeable protease inhibitors before infecting them with opsonized Lpn.…”