Inhibition of cathepsin B reduces beta-amyloid production in regulated secretory vesicles of neuronal chromaffin cells: evidence for cathepsin B as a candidate beta-secretase of Alzheimer's disease.
The regulated secretory pathway of neurons is the major source of extracellular A beta that accumulates in Alzheimer's disease (AD). Extracellular A beta secreted from that pathway is generated by beta-secretase processing of amyloid precursor protein (APP). Previously, cysteine protease activity was demonstrated as the major beta-secretase activity in regulated secretory vesicles of neuronal chromaffin cells. In this study, the representative cysteine protease activity in these secretory vesicles was purified and identified as cathepsin B by peptide sequencing. Immunoelectron microscopy demonstrated colocalization of cathepsin B with A beta in these vesicles. The selective cathepsin B inhibitor, CA074, blocked the conversion of endogenous APP to A beta in isolated regulated secretory vesicles. In chromaffin cells, CA074Me (a cell permeable form of CA074) reduced by about 50% the extracellular A beta released by the regulated secretory pathway, but CA074Me had no effect on A beta released by the constitutive pathway. Furthermore, CA074Me inhibited processing of APP into the COOH-terminal beta-secretase-like cleavage product. These results provide evidence for cathepsin B as a candidate beta-secretase in regulated secretory vesicles of neuronal chromaffin cells. These findings implicate cathepsin B as beta-secretase in the regulated secretory pathway of brain neurons, suggesting that inhibitors of cathepsin B may be considered as therapeutic agents to reduce A beta in AD.
Hook
Vivian
V
Department of Pharmacology, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California at San Diego, La Jolla, CA 92093, USA. vhook@ucsd.edu
Toneff
Thomas
T
Bogyo
Matthew
M
Greenbaum
Doron
D
Medzihradszky
Katalin F
KF
Neveu
John
J
Lane
William
W
Hook
Gregory
G
Reisine
Terry
T
D000544:Alzheimer Disease / Q000201:enzymology / Q000378:metabolism*; D000595:Amino Acid Sequence; D053829:Amyloid Precursor Protein Secretases; D016229:Amyloid beta-Peptides / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000378:metabolism; D000818:Animals; D002401:Cathepsin B / Q000037:antagonists & inhibitors* / Q000302:isolation & purification / Q000378:metabolism; D002417:Cattle; D019439:Chromaffin Cells / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D010450:Endopeptidases / Q000378:metabolism*; D008969:Molecular Sequence Data; D009474:Neurons / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D022142:Secretory Vesicles / Q000201:enzymology / Q000378:metabolism*
D016229:Amyloid beta-Peptides; D015853:Cysteine Proteinase Inhibitors; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; D003546:Cysteine Endopeptidases; D002401:Cathepsin B