IN-SITU LOCALIZATION AND QUANTIFICATION OF MESSENGER-RNA FOR 92-KD TYPE-IV COLLAGENASE AND ITS INHIBITOR IN ANEURYSMAL, OCCLUSIVE, AND NORMAL AORTA

Ninety-two-kilodalton type IV collagenase (MMP-9) is present in aortic aneurysms and may be important to the pathogenesis of this disease. A lteration in expression of MMP-9 or its inhibitor, the tissue inhibito r of metalloproteinase type 1 (TIMP-1), could increase degradation of extracellular matrix and lead to aneurysm formation. The purpose of th is study was (1) to measure tissue levels of MMP-9 and TIMP-1 mRNA in aneurysmal (AAA), atherosclerotic occlusive (AOD), and normal (NL) hum an infrarenal aorta; (2) to test for their expression by cultured AAA and NL vascular smooth muscle cells (VSMCs); and (3) to locate in situ the cells responsible for mRNA production within AAA, AOD, and NL aor tic wall. Total RNA extracted from AAA (n=8), AOD (n=8), and NL (n=7) tissue was subjected to Northern analysis. Signals for MMP-9 and TIMP- 1 were normalized to cy-tubulin. Mean values +/-SEM were compared by A NOVA. NL and AAA VSMCs were cultured, passaged, and grown to confluenc e before RNA extraction and Northern analysis. In situ hybridization w ith digoxigenin-labeled RNA probes localized cells responsible for MMP -9 and TIMP-1 mRNA expression within sections of AAA (n=5), AOD (n=2), and NL (n=2) aorta. MMP-9 mRNA levels were significantly greater in A AA (0.855+/-0.180) than NL (0.046+/-0.23) (P<.02), but differences bet ween AOD (0.406+/-0.196) and AAA or AOD and NL were not significant. D ifferences in TIMP-1 mRNA levels between tissue types were not signifi cant (AAA, 1.17+/-0.123; AOD, 1.79+/-0.351; NL, 0.652+/-0.378). Cultur ed AAA and NL aortic VSMCs constitutively expressed mRNA for TIMP-1 bu t not MMP-9. In situ hybridization of AAA and AOD tissue localized MMP -9 mRNA to adventitial macrophages in areas of neovascularization and TIMP-1 mRNA to adventitial VSMCs. MMP-9 mRNA levels are significantly greater in aneurysmal than normal aorta. Cultured VSMCs constitutively express TIMP-1 but not MMP-9. In the diseased aortic wall, MMP-9 mRNA is found in adventitial macrophages and TIMP-1 mRNA in adventitial VS MCs. Localization of MMP-9 mRNA expression to discrete areas surroundi ng vasa vasorum suggests that the enzyme is responsible for localized matrix alterations associated with neovascularization.