Increased expression of matrix metalloproteinases and matrix degrading activity in vulnerable regions of human atherosclerotic plaques.

Dysregulated extracellular matrix (ECM) metabolism may contribute to vascular remodeling during the development and complication of human atherosclerotic lesions. We in- vestigated the expression of matrix metalloproteinases (MMPs), a family of enzymes that degrade ECM compo- nents in human atherosclerotic plaques (n =30) and in uninvolved arterial specimens (n=11). We studied members of all three MMP classes (interstitial coilagenase, MMP-1; gel- atinases, MMP-2 and MMP-9; and stromelysin, MMP-3) and their endogenous inhibitors (TIMPs 1 and 2) by immu- nocytochemistry, zymography, and immunoprecipitation. Normal arteries stained uniformly for 72-kD gelatinase and TIMPs. In contrast, plaques' shoulders and regions of foam cell accumulation displayed locally increased expression of 92-kD gelatinase, stromelysin, and interstitial collagenase. However, the mere presence of MMP does not establish their catalytic capacity, as the zymogens lack activity, and TIMPs may block activated MMPs. All plaque extracts con- tained activated forms of gelatinases determined zymo- graphically and by degradation of 3H-collagen type IV. To test directly whether atheromata actually contain active ma- trix-degrading enzymes in situ, we devised a method which allows the detection and microscopic localization of MMP enzymatic activity directly in tissue sections. In situ zymog- raphy revealed gelatinolytic and caseinolytic activity in fro- zen sections of atherosclerotic but not of uninvolved arterial tissues. The MMP inhibitors, EDTA and 1,10-phenanthroline, as well as recombinant TIMP-1, reduced these activities which colocalized with regions of increased immunoreactive MMP expression, i.e., the shoulders, core, and microvascula- ture of the plaques. Focal overexpression of activated MMP may promote destabilization and complication of atherosclerotic plaques and provide novel targets for therapeutic in- tervention. (