INHIBITORS OF CATHEPSIN B REDUCE PRODUCTION OF BETA‐AMYLOID IN REGULATED SECRETORY VESICLES: A NOVEL CYSTEINE PROTEASE PATHWAY AS BETA‐SECRETASE FOR GENERATING BETA‐AMYLOID OF ALZHEIMER'S DISEASE

Abstract

The regulated secretory pathway of neurons is the major source of extracellular Aß that accumulates in Alzheimer's disease (AD). Beta-secretase is required to generate Aß from its APP precursor. In this study, the major ß-secretase activity in these secretory vesicles was identified as cathepsin B by tandem mass spectrometry. Immunoelectron microscopy demonstrated colocalization of cathepsin B with Aß in regulated secretory vesicles of neuronal chromaffin cells. Cathepsin B showed efficient kinetics for cleaving the wild-type ß-secretase site. Significantly, the selective cathepsin B inhibitor, CA074, blocked the production of Aß40 from endogenous APP in regulated secretory vesicles isolated from neuronal chromaffin cells. Importantly, in primary neuronal chromaffin cell cultures, CA074Me reduced the content of Aß40 in secretory vesicles, demonstrated by decreased secretion of Aß40 via the regulated secretory pathway upon induction by KCl. These results demonstrate a role for cathepsin B in production of Aß, as novel ß-secretase in the regulated secretory pathway of brain neurons, and that inhibitors of cathepsin B may be considered as therapeutic agents to reduce Aß in AD.