Identification of a serum gelatinase associated with the occurrence of cerebral aneurysms as pro-matrix metalloproteinase-2.

BACKGROUND AND PURPOSE Subarachnoid hemorrhage from intracranial aneurysm rupture produces a severe form of stroke. Extracellular matrix remodeling is associated with cerebral aneurysms and may play a role in the formation or rupture of these lesions. We previously reported a 3-fold increase in a 72-kDa serum gelatinase in a subgroup of aneurysm patients. The purpose of the present study was to further characterize and identify this gelatinase. METHODS Serum samples were collected from surgical patients with intracranial aneurysms. The following series of experiments was designed to further characterize and identify the predominant serum gelatinase found in the subgroup of patients with increased gelatinase activity. Gelatin zymography was performed on native serum samples and compared with serum that had been pretreated with a known metalloproteinase activator (4-aminophenylmercuric acetate [APMA]). Gelatin zymography was repeated in the presence of a matrix metalloproteinase (MMP) inhibitor (EDTA) and a serine proteinase inhibitor (phenylmethylsulfonyl fluoride [PMSF]). Final identification was made by Western blotting with the use of monoclonal antibodies to MMP-2 and MMP-9. RESULTS A consistent gelatinolytic band (72 kDa) was identified in all serum samples (n = 60). Pretreatment of the serum by APMA (n = 60) lowered the molecular weight of the band to 66 kDa. The band was inhibited by EDTA (n = 10) but not PMSF (n = 10), thus characterizing the circulating 72-kDa gelatinase as an inactive pro-MMP. Western blotting (n=20) identified the 72-kDa band as MMP-2. CONCLUSIONS These findings confirm that the increased gelatinolytic activity observed in vitro in a subset of cerebral aneurysm patients is due to pro-MMP-2.