Low tissue inhibitor of metalloproteinases 3 and high matrix metalloproteinase 14 levels defines a subpopulation of highly invasive foam-cell macrophages.
OBJECTIVE
An excess of metalloproteinases (MMPs) over tissue inhibitors of metalloproteinases (TIMPs) may favor atherosclerotic plaque rupture. We compared TIMP levels in nonfoamy and foam-cell macrophages (FCM) generated in vivo.


RESULTS
In vivo generated rabbit FCM exhibited 84% reduced TIMP-3 protein compared to nonfoamy macrophages, and immunocytochemistry revealed a TIMP-3 negative subset (28%). Strikingly, only TIMP-3 negative FCM invaded a synthetic basement membrane, and invasion was inhibited by exogenous TIMP-3. TIMP-3 negative FCM also had increased proliferation and apoptosis rates compared to TIMP-3 positive cells, which were retarded by exogenous TIMP-3; this also reduced gelatinolytic activity. TIMP-3 negative FCM were found at the base of advanced rabbit plaques and in the rupture-prone shoulders of human plaques. To explain the actions of low TIMP-3 we observed a 26-fold increase in MT1-MMP (MMP-14) protein in FCM. Adding an MT1-MMP neutralizing antibody reduced foam-cell invasion, apoptosis, and gelatinolytic activity. Furthermore, MT1-MMP overexpressing and TIMP-3 negative FCM were found at the same locations in atherosclerotic plaques.


CONCLUSIONS
These results demonstrate that TIMP-3 is downregulated in a distinct subpopulation of FCM which have increased MMP-14. These cells are highly invasive and have increased proliferation and apoptosis, all properties expected to destabilise atherosclerotic plaques.
Johnson
Jason L
JL
Bristol Heart Institute, University of Bristol, England. jason.l.johnson@bristol.ac.uk
Sala-Newby
Graciela B
GB
Ismail
Yasmin
Y
Aguilera
Concepción M
CM
Newby
Andrew C
AC
D000818:Animals; D017209:Apoptosis; D050197:Atherosclerosis / Q000201:enzymology* / Q000473:pathology; D002465:Cell Movement; D049109:Cell Proliferation; D002478:Cells, Cultured; D015536:Down-Regulation; D005487:Foam Cells / Q000201:enzymology* / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry; D053511:Matrix Metalloproteinase 14 / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D011817:Rabbits; D019717:Tissue Inhibitor of Metalloproteinase-3 / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation
D012333:RNA, Messenger; D019717:Tissue Inhibitor of Metalloproteinase-3; C507086:MMP14 protein, human; D053511:Matrix Metalloproteinase 14