A Free Radical-Generating System Regulates Amyloid Oligomers: Involvement of Cathepsin B

Abstract

Amyloid-␤ (A␤), a major component of senile plaques, is generated via the proteolysis of amyloid-␤ protein precursor (A␤PP). This cleavage also produces A␤PP fragment-derived oligomers which can be highly neurotoxic. A␤PP metabolism/processing is affected by many factors, one of which is oxidative stress (OS). Associated with aging, OS is an important risk factor for Alzheimer's disease. In addition, the protein degradation systems, especially those involving cathepsins, are impaired in aging brains. Moreover, cathepsin B (CTSB) is a cysteine protease with potentially specific roles in A␤PP proteolysis (␤-secretase activity) and A␤ clearance (A␤ degradative activity). The present work examines the effect of OS and the involvement of CTSB in amyloid oligomer formation. The xanthine/xanthine oxidase (X-XOD) free radical generating system induced the partial inhibition of CTSB activity, which was accompanied by an increase in large amyloid oligomers. These were located throughout the cytosol and in endo-lysosomal vesicles. Cells treated with the CTSB inhibitor CA-074Me also showed increased amyloid oligomer levels, whereas those subjected to OS in the presence of the inhibitor showed no such increase. However, CTSB inhibition clearly modulated the A␤PP metabolism/processing induced by X-XOD, as revealed by the increase in intracellular A␤PP and secreted ␣-secretase-cleaved soluble A␤PP. The present results suggest that CTSB participates in the changes of amyloid oligomer induced by mild OS.

27-Hydroxycholesterol Contributes to Lysosomal Membrane Permeabilization-Mediated Pyroptosis in Co-cultured SH-SY5Y Cells and C6 Cells

“…Recent research has demonstrated that APP degraded by lysosomal system (Hein et al, 2017). CTSB is a most abundant cysteine protease with potentially specific roles that cleaves APP and also degrades the Aβ42 peptide (Llorente et al, 2018) in the endo-lysosome system. Lysosomes are ubiquitous organelles that constitute the primary degradative compartments of the cell.…”

Matrix Metalloproteinase 14 Mediates APP Proteolysis and Lysosomal Alterations Induced by Oxidative Stress in Human Neuronal Cells

“…Since APP processing is central to AD pathogenesis, the mechanisms linking OS to APP proteolysis could offer therapeutic targets. Our group previously reported the involvement of OS in APP processing [1], the connection between APP proteolysis and the lysosome system in response to OS [3], and the role of the lysosomal protease CTSB in the accumulation of Aβ oligomers in response to OS [28].…”

“…Expression is shown as the fold change after X-XOD treatment compared to control cells at 24 and 36 h. In bold, p < 0:01. (c) SK-N-MC cells were treated with X-XOD for 24 h and then fractionated by differential centrifugation as described in [28]. Western blotting was performed using anti-APP (22C11), anti-MMP14, anti-LAMP1, anti-Rab7, anti-CTSB, anti-EEA1, and anti-GAPDH antibodies.…”

Pro-Aging Effects of Xanthine Oxidoreductase Products

“…However, the mild oxidative stress generated by X/XO addition causes a reduction in beta-secretase activity and consequently the level of the amyloidogenic protein Aβ [57]. This protective role of the X/XO system is due to a partial inhibition of cathepsin B, which possess a beta-secretase activity [58].…”