Cleavage of a beta-amyloid precursor sequence by cathepsin D

Area of Science:

• Neuroscience
• Biochemistry
• Molecular Biology

Background:

• Alzheimer's disease is characterized by senile plaques containing beta-amyloid.
• The specific proteases responsible for cleaving amyloid precursor protein (APP) to release beta-amyloid remain largely unidentified.
• Lysosomal enzymes and the inhibitory effects of lysosomotrophic agents suggest a role for cathepsins in amyloidogenesis.

Purpose of the Study:

• To investigate the identity of proteases involved in the generation of beta-amyloid.
• To explore the potential role of cathepsins in the N-terminal processing of beta-amyloid.

Main Methods:

• Enzymatic digestion of a synthetic 31-residue peptide encompassing the beta-secretase cleavage site of APP.
• Analysis of digestion products to identify cleavage sites.
• Consideration of aminopeptidase activity in conjunction with cathepsin action.

Main Results:

• The synthetic peptide was cleaved at two distinct sites, N-terminal to the beta-amyloid sequence.
• These cleavage sites suggest a mechanism for generating the N-terminus of beta-amyloid.
• Cathepsin D, acting with aminopeptidases, is proposed as a candidate enzyme for this N-terminal processing.

Conclusions:

• Lysosomal or endosomal cathepsin D, in conjunction with aminopeptidases, may be responsible for generating the N-terminus of beta-amyloid in vivo.
• This study provides evidence implicating cathepsins in the pathway of beta-amyloid formation.
• Further research is warranted to confirm the role of specific cathepsins in Alzheimer's disease pathogenesis.