Neutrophil Granule Proteins Inhibit Amyloid Beta Aggregation and Neurotoxicity

Abstract

Background: A role for neutrophils in the pathogenesis of Alzheimer’s disease (AD) is emerging. We previously showed that the neutrophil granule proteins cationic antimicrobial protein of 37 kDa (CAP37), cathepsin G (CG), and neutrophil elastase (NE) directly bind the amyloid-beta peptide Aβ1-42, a central player in AD pathogenesis. CAP37, CG, and NE are serine proteases that can cleave Aβ1-42 at different sites and with different catalytic activities. Objective: In this study, we compared the effects of these three proteins on Aβ1-42 fibrillation and neurotoxicity. Methods: Using mass spectrometry and in vitro aggregation assay, we found that NE and CG effi- ciently cleave Aβ1-42. This cleavage correlates well with the inhibition of Aβ1-42 aggregation into fi- brils. In contrast, CAP37 did not efficiently cleave Aβ1-42, but was still able to inhibit its fibrillation, most likely through a quenching effect. Inhibition of Aβ1-42 aggregation by NE and CG neutralized its toxicity measured in cultured neurons. In contrast, inhibition of Aβ1-42 aggregation by CAP37 did not inhibit its neurotoxicity. Results: We found that a peptide derived from CAP37 could mimic the quenching and inhibition of Aβ1-42 aggregation effects of the full-length protein. Additionally, this peptide was able to inhibit the neurotoxicity of the most toxic Aβ1-42 aggregate, an effect that was not found with the full-length CAP37. Conclusion: These results shed light on the mechanisms of action of neutrophil granule proteins with regard to inhibition of Aβ1-42 aggregation and neurotoxicity and open up a possible strategy for the discovery of new disease-modifying drugs for AD.

Identification of Hub Genes and Immune Cell Infiltration Characteristics in Alzheimer’s Disease

“…AD patients also had a greater proportion of cells expressing CCR4 (expressed on Th2 cells) and CCR5 (Th1 cells and dendritic cells). Kasus-Jacobi et al [ 39 ] used mass spectrometry and in vitro aggregation methods to detect the activity of neutrophil elastase (NE) and cathepsin G (CG) against amyloid-beta peptide A β 1-42 and found that the peptide derived from CAP37 mimics the quenching and inhibitory aggregation effects of A β 1-42 full-length protein. In addition, the peptide inhibited the neurotoxicity of the most toxic A β 1-42 aggregates.…”

Selecting Multitarget Peptides for Alzheimer’s Disease

“…We hypothesized that these neutrophil proteins: cathepsin G (CG), neutrophil elastase (NE), and cationic antimicrobial protein of 37 kDa (CAP37) could modulate neurotoxicity in AD by influencing the Aβ-RAGE interaction [ 2 ]. In a follow up study, we found that NE and CG could cleave Aβ 1–42 , and inhibit its aggregation into oligomers and fibrils [ 16 ]. In contrast, CAP37 did not efficiently cleave Aβ 1–42 , but inhibited Aβ 1–42 oligomerization and fibrillation, most likely through direct binding to the unaggregated form [ 16 ].…”

“…In a follow up study, we found that NE and CG could cleave Aβ 1–42 , and inhibit its aggregation into oligomers and fibrils [ 16 ]. In contrast, CAP37 did not efficiently cleave Aβ 1–42 , but inhibited Aβ 1–42 oligomerization and fibrillation, most likely through direct binding to the unaggregated form [ 16 ]. Of the three proteins, CG was found to be the most potent to inhibit the neurotoxicity of Aβ 1–42 , in a cultured neuron cell line [ 16 ].…”

“…In contrast, CAP37 did not efficiently cleave Aβ 1–42 , but inhibited Aβ 1–42 oligomerization and fibrillation, most likely through direct binding to the unaggregated form [ 16 ]. Of the three proteins, CG was found to be the most potent to inhibit the neurotoxicity of Aβ 1–42 , in a cultured neuron cell line [ 16 ]. In a different study, we looked for binding partners of CAP37 on live cells and found that CAP37 directly interacts with the Toll-like receptor 4 (TLR4) and with one of its natural ligands; the S100 calcium-binding protein A9 (S100A9) [ 17 ].…”

“…As previously described, synthetic ~25-mer peptides covering the entire CAP37 sequence have been tested to identify the domain binding to Aβ 1–42 [ 16 ]. Peptide CAP37 120–146 , which is derived from the native sequence of CAP37 located between residues 120 and 146, was the highest binding peptide [ 16 ]. This sequence is shown in Figure 2 .…”