Amyloid-β peptide-induced extracellular S100A9 depletion is associated with decrease of antimicrobial peptide activity in human THP-1 monocytes

Abstract

BackgroundS100A9 protein (myeloid-related protein MRP14, also referred to as calgranulin B) is a reliable marker of inflammation, an important proinflammatory factor of innate immunity and acts as an additional antimicrobial peptide in the innate immune system. Evidence indicates that S100A9 contributes to Alzheimer’s disease (AD) pathology, although the precise mechanisms are not clear.MethodsWe were interested to study the mechanisms of S100A9 release upon Aβ1-42 stimulation, the potential roles of extracellular S100A9 depletion in Aβ-induced cytotoxicity, and the interaction with innate immune response in THP-1 monocytic cells that have been challenged with mostly Aβ1-42 monomers instead of oligomers. We used protein preparation, Ca2+ influx fluorescence imaging, MTT assay, siRNA knockdown, colony forming units (CFUs) assay and western blotting techniques to perform our study.ResultsAβ1-42 monomers elicited a marked decrease of S100A9 release into the cell culture supernatant in a dose-dependent manner in human THP-1 monocytes. This reduction of S100A9 release was accompanied by an increase of intracellular Ca2+ level. Aβ1-42-mediated decrease of S100A9 release was not associated with Aβ1-42-induced cytotoxicity as measured by MTT reduction assay. This observation was confirmed with the recombinant S100A9, which had little effect on Aβ1-42-induced cytotoxicity. Moreover, depletion of S100A9 with siRNA did not significantly evoke the cell toxicity. On the other hand, Aβ1-42-induced extracellular S100A9 depletion resulted in decreased antimicrobial activity of the culture supernatant after Aβ1-42 stimulation. Immunodepletion of S100A9 with anti-S100A9 also decreased the antimicrobial peptide activity of the vehicle treated culture supernatant. Consistently, the recombinant S100A9 clearly elicited the antimicrobial peptide activity in vitro, confirming the observed antimicrobial activity of S100A9 in the culture supernatant.ConclusionCollectively, our findings suggest that the mostly monomeric form of Aβ1-42 negatively regulates the innate immune system by down-regulating the secretion of S100A9, which is likely a main mediator of antimicrobial activity in the conditioned media of human THP-1 monocytes.

Bridging the Gap Between Fluid Biomarkers for Alzheimer’s Disease, Model Systems, and Patients

“…S100A9 regulates γ-secretase and BACE1 expression and activity ( Kummer et al, 2012 ; Li et al, 2014 ), and S100B and S100A1 regulate APP levels ( Zimmer et al, 2005 ; Anderson et al, 2009 ; Mori et al, 2010 ). S100A7, S100A8, S100A9, and S100B have been found to influence Aβ levels ( Qin et al, 2009 ; Lee et al, 2013 ; Lodeiro et al, 2017 ; Cristovao et al, 2018 ). Moreover, S100B and S100A6 have been found to reduce zinc levels and senile plaque load in preclinical models ( Roltsch et al, 2010 ; Hagmeyer et al, 2017 ; Tian et al, 2019 ).…”

S100A8 and S100A9 in Saliva, Blood and Gingival Crevicular Fluid for Screening Periodontitis

“…Antimicrobial activity of S100A9 also have been reported. The mechanism behind antimicrobial activity is the monomeric form of amyloid beta (Aβ) 1-42 that is negatively regulated by the innate immune system by downregulating the secretion of S100A9 [33]. However, our data showed that only GCF S100A9 level was signi cantly lower in periodontitis patients than in healthy adults.…”

A Candidate Plasma Protein Classifier to Identify Alzheimer's Disease

“…Among the 5 classifier proteins, S100A9 is the only one associated with AD [67][68][69][70][71][72]. S100A9 in the brain was reported to associate with the neuropathological hallmarks of AD and contribute to AD pathology [67][68][69][70][71][72].…”

“…S100A9 in the brain was reported to associate with the neuropathological hallmarks of AD and contribute to AD pathology [67][68][69][70][71][72]. For example, induction of S100A9 was observed in the brain of AD animal model Tg2576 and in human AD brain.…”