Isolation and Characterisation of Novel Metalloproteases from Embryonic Mouse Hippocampus

Abstract

Alzheimer’s disease (AD) is a debilitating neurodegenerative condition which is currently being investigated via a wide range of clinical and molecular approaches. β-amyloid forms part of the amyloid precursor protein (APP) and its deposition in dense extracellular plaques is one of the hallmarks of AD (Glenner and Wong 1984; Masters et al. 1985). The processing of APP leading to the production of β-amyloid is being extensively studied both in vivo and in vitro. Since β-amyloid is produced by the proteolytic cleavage of APP (Kang et al. 1987), there is evidence for as yet uncharacterized protease activity at the earliest stages of AD neuropathology (Sisodia et al. 1990; Seubert et al. 1993). The β-amyloid domain is embedded in the plasma membrane and it was initially assumed that membrane damage must precede proteolytic action in order for the full length peptide to be released. Since it was shown that β-amyloid is present within intracellular lysosomal organelles (Benowitz et al. 1989), much work has concentrated on the routes of APP processing, with evidence for the targetting of up to half of the APP produced directly into the lysosomal pathway (Caporaso et al. 1992a, b). However, the cellular location of β-amyloid production and the enzymes which cleave APP in either the “normal” pathway, which results in secreted proteins with C terminal β-amyloid fragments, or an alternative processing pathway, resulting in the complete β-amyloid peptide, have still to be identified.