Human macrophage metalloelastase (HME) is produced in abdominal aortic aneurysms (AAA) and localized to its matrix substrate

Several elastolytic matrix metalloproteinases(MMPs) have been implicated in the pathogenesis of AAA, a disease characterized by chronic inflammation and believed to result from destruction of medial elastin. The purpose of this study was to determine if HME, a recently discovered MMP with elastolytic activity, might participate in this process. Aortic tissues were obtained from 6 patients with AAA, 5 with atherosclerotic occlusive disease(AOD), and 4 normal organ donors(NA). Aortic extracts were examined by western blot(WB) with affinity-purifled rabbit anti-HME IgG. Formalin-fixed, paraffin-embedded serial sections were examined by immunohistochemistry(IMH) and by in situ hybridization(ISH) using HME-specific digoxigenin-labeled cRNA probes. All three forms of HME (54-, 40-, and 22-kD) were present in extracts of AAA, but not in AOD or NA. IMH demonstrated the presence of HME in AAA, where it was localized to macrophages throughout the thickness of the aortic wall. HME was also found bound to residual elastic fibers in the media of AAA tissues. HME was localized to intimai macrophages in AOD, but it was not detected in cells or matrix of the media in either AOD or NA tissues. Macrophage expression of HME in AAA was confirmed by ISH. These studies demonstrate that, like other elastolytic MMPs, HME is expressed in vivo by macrophages. However, HME is unique in being prominently localized to elastin-rich extracellular matrices, a potential matrix substrate for the enzyme in vivo. These findings indicate that HME may have a more direct role in aortic elastic degradation than other MMPs during the evolution of aneurysmal degeneration.