Neutrophil Granule Proteins Inhibit Amyloid Beta Aggregation and Neurotoxicity.

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 Aß1-42, a central player in AD pathogenesis. CAP37, CG, and NE are serine proteases that can cleave Aß1-42 at different sites and with different catalytic activities. OBJECTIVE: In this study, we compared the effects of these three proteins on Aß1-42 fibrillation and neurotoxicity. METHODS: Using mass spectrometry and in vitro aggregation assay, we found that NE and CG efficiently cleave Aß1-42. This cleavage correlates well with the inhibition of Aß1-42 aggregation into fibrils. In contrast, CAP37 did not efficiently cleave Aß1-42, but was still able to inhibit its fibrillation, most likely through a quenching effect. Inhibition of Aß1-42 aggregation by NE and CG neutralized its toxicity measured in cultured neurons. In contrast, inhibition of Aß1-42 aggregation by CAP37 did not inhibit its neurotoxicity. RESULTS: We found that a peptide derived from CAP37 could mimic the quenching and inhibition of Aß1-42 aggregation effects of the full-length protein. Additionally, this peptide was able to inhibit the neurotoxicity of the most toxic Aß1-42 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 Aß1-42 aggregation and neurotoxicity and open up a possible strategy for the discovery of new disease-modifying drugs for AD.

Complement inhibition decreases early fibrogenic events in the lung of septic baboons.

Acute respiratory distress syndrome (ARDS) induced by severe sepsis can trigger persistent inflammation and fibrosis. We have shown that experimental sepsis in baboons recapitulates ARDS progression in humans, including chronic inflammation and long-lasting fibrosis in the lung. Complement activation products may contribute to the fibroproliferative response, suggesting that complement inhibitors are potential therapeutic agents. We have been suggested that treatment of septic baboons with compstatin, a C3 convertase inhibitor protects against ARDS-induced fibroproliferation. Baboons challenged with 10(9) cfu/kg (LD50) live E. coli by intravenous infusion were treated or not with compstatin at the time of challenge or 5 hrs thereafter. Changes in the fibroproliferative response at 24 hrs post-challenge were analysed at both transcript and protein levels. Gene expression analysis showed that sepsis induced fibrotic responses in the lung as early as 24 hrs post-bacterial challenge. Immunochemical and biochemical analysis revealed enhanced collagen synthesis, induction of profibrotic factors and increased cell recruitment and proliferation. Specific inhibition of complement with compstatin down-regulated sepsis-induced fibrosis genes, including transforming growth factor-beta (TGF-ß), connective tissue growth factor (CTGF), tissue inhibitor of metalloproteinase 1 (TIMP1), various collagens and chemokines responsible for fibrocyte recruitment (e.g. chemokine (C-C motif) ligand 2 (CCL2) and 12 (CCL12)). Compstatin decreased the accumulation of myofibroblasts and proliferating cells, reduced the production of fibrosis mediators (TGF-ß, phospho-Smad-2 and CTGF) and inhibited collagen deposition. Our data demonstrate that complement inhibition effectively attenuates collagen deposition and fibrotic responses in the lung after severe sepsis. Inhibiting complement could prove an attractive strategy for preventing sepsis-induced fibrosis of the lung.