Pro-Inflammatory S100A9 Protein Aggregation Promoted by NCAM1 Peptide Constructs Jonathan Pansieri, † Lucija Ostojic ́ , † Igor A. Iashchishyn, † Mazin Magzoub, ‡ Cecilia Wallin, § Sebastian K.T.S. Wä rmlä nder, § Astrid Grä slund, § Mai Nguyen Ngoc, ∥ Vytautas Smirnovas, ∥ Z ̌ eljko Svedruž ic ́ , ⊥ and Ludmilla A. Morozova-Roche* ,† † Department of Medical Biochemistry and Biophysics, Umeå University, SE-901 87 Umeå, Sweden ‡ New York University Abu Dhabi, Saadiyat Island, Abu Dhabi, United Arab Emirates § Department of Biochemistry and Biophysics, Arrhenius Laboratories, Stockholm University, Stockholm, Sweden ∥ Institute of Biotechnology, Life Sciences Center, Vilnius University, Vilnius, Lithuania ⊥ Department of Biomedical Technology, University of Rijeka, HR 51000, Rijeka, Croatia * S Supporting Information ABSTRACT: Amyloid cascade and neuroinflammation are hallmarks of neurodegenerative diseases, and pro-inflammatory S100A9 protein is central to both of them. Here, we have shown that NCAM1 peptide constructs carrying polycationic sequences derived from Aβ peptide (KKLVFF) and PrP protein (KKRPKP) significantly promote the S100A9 amyloid self-assembly in a concentration-dependent manner by making transient interactions with individual S100A9 molecules, perturbing its native structure and acting as catalysts. Since the individual molecule misfolding is a rate-limiting step in S100A9 amyloid aggregation, the effects of the NCAM1 construct on the native S100A9 are so critical for its amyloid self-assembly. S100A9 rapid self- assembly into large aggregated clumps may prevent its amyloid tissue propagation, and by modulating S100A9 aggregation as a part of the amyloid cascade, the whole process may be effectively tuned. A myloid cascade and neuroinflammation are the most obvious and closely interlinked pathological manifesta- tions of progressive neurodegenerative diseases such as Alzheimer’s (AD) and Parkinson’s (PD). 1−3 If initially neuroinflammation was considered as a response to neuro- degeneration, recent studies suggest that neuroinflammation could be a trigger and a key player in these diseases by creating a pathogenic microenvironment in the brain tissues and further promoting aggregation. Both AD and PD brain tissues are characterized by extensive microglial activation and a significant rise in pro-inflammatory cytokines, all damaging responses, which can sustain inflammation and exacerbate neurodegeneration. 4−7 Understanding the mechanisms under- lying disease pathology opens an avenue to develop therapeutic strategies targeting these processes. Recently, we demonstrated that the highly amyloidogenic protein and pro-inflammatory mediator S100A9 is involved in the amyloid-neuroinflammatory cascade in AD, PD, and traumatic brain injury, bridging the amyloid formation and neuroinflammation into one common underlying pathological process. 8−10 S100A9 is known as a pro-inflammatory molecule or alarmin involved in the inflammatory signaling pathways. A widespread expression of S100A9 was observed in many diseases associated with inflammatory processes, such as AD, 7,10,11 PD, 9 malaria, 12 cerebral ischemia, 13 obesity, 14 and cardiovascular disease, 15 indicating that S100A9 is very abundant under multiple inflammatory conditions. The abundance of S100A9 mRNA was also found in various mammalian aged tissues, including the central nervous system, and a mechanism of the age-associated inflammation sustained by S100A9 was suggested. 16 We have shown that S100A9 in contrast to other pro-inflammatory molecules is very prone to self-assembly into amyloids, which may lead to the loss of its signaling functions and acquired amyloid cytotoxicity, exceed- ing the cytotoxicity of Aβ in AD 10 and α-synuclein in PD. 9 Therefore, the rising S100A9 level sustained during inflamma- tion may lead to its amyloid formation and deposition as we have shown to take place in neurodegenerative diseases, 8−10 in the aging prostate, 17 and also ina cell model for protein amyloid aggregation. 18 Moreover, we have found that the CSF levels of S100A9 match those of Aβ in AD and mild cognitive impairment, 19 further confirming the involvement of S100A9 together with Aβ in the amyloid-neuroinflammatory cascade in AD. Thus, accumulated evidence demonstrates that S100A9 can coaggregate with other polypeptides implicated in the Received: May 17, 2019 Accepted: June 5, 2019 Published: June 5, 2019 Letters pubs.acs.org/acschemicalbiology Cite This: ACS Chem. Biol. XXXX, XXX, XXX-XXX © XXXX American Chemical Society A DOI: 10.1021/acschembio.9b00394 ACS Chem. Biol. XXXX, XXX, XXX−XXX Downloaded by UMEA UNIV at 05:31:11:920 on June 14, 2019 from https://pubs.acs.org/doi/10.1021/acschembio.9b00394.