Accumulation of the pro-inflammatory protein S100A9 has been implicated in neuroinflammatory cascades in neurodegenerative diseases (NDs) such as Alzheimer's disease (AD) and Parkinson's disease (PD). S100A9 co-aggregates with other proteins such as α-synuclein in PD and Aβ in AD, contributing to amyloid plaque formation and neurotoxicity. The amyloidogenic nature of this protein and its role in chronic neuroinflammation suggest that it may play a key role in the pathophysiology of these diseases. Research into molecules targeting S100A9 could be a potential therapeutic strategy to prevent its amyloidogenic self-assembly and to attenuate the neuroinflammatory response in affected brain tissue. This work suggests that bioactive natural molecules, such as those found in the Mediterranean diet, may have the potential to alleviate neuroinflammation associated with the accumulation of proteins such as S100A9 in neurodegenerative diseases. A major component of extra virgin olive oil (EVOO), hydroxytyrosol (HT), with its ability to interact with and modulate S100A9 amyloid self-assembly and expression, offers a compelling approach for the development of novel and effective interventions for the prevention and treatment of ND. The findings highlight the importance of exploring natural compounds, such as HT, as potential therapeutic options for these complex and challenging neurological conditions.

Background Gastrodia elata (GE) has been widely used in clinical practice for many years with the functions of relieving stroke, suppressing liver Yang, dispelling wind and clearing collaterals. Our group's previous experimental studies have proved that GE has therapeutic effect on cerebral ischemia reperfusion injury (CIRI) (Ding et al., 2022). However, the active components of GE in treating CIRI remain unclear and require further research. Purpose The purpose of this paper was to explore the potential effective components of GE improving CIRI based on the “Spectrum-effect” correlation. Zebrafish model was used for verification in vivo experimental. Materials and methods First, the absorption components and metabolites of GE in rat serum were identified using ultra-high performance liquid chromatography-quadrupole time-of-flight tandem mass spectrometry (UHPLC-Q-TOF/MS). Second, pharmacodynamic indexes were determined by ELISA kit method, and the effect-time curve of each pharmacodynamic indexes was established. The potential compounds were screened using the statistical method of grey correlation between pharmacodynamic indicator and component response. Finally, the zebrafish CIRI model was successfully established, and the in vivo effect of the active components of GE was verified intuitively. Results 45 chemical components were detected in GE. A total of 87 active components in serum of GE were identified including 25 prototype components and 62 metabolites. GE can improve CIRI by regulating the levels of interleukin-6 (IL-6), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α), MDA levels and SOD levels. It was found that p‑hydroxy benzaldehyde (PHB), p-hydroxybenzyl alcohol (PHBA) and gastrodin (GA) of GE were the possibly main active components by grey correlation statistics. The in vivo experiments of zebrafish model showed that PHB, PHBA, and GA have the ability to ameliorate cerebral thrombosis by regulation of oxidative stress and apoptosis. Conclusions The potential active components of GE on CIRI were initially excavated using UHPLC-Q-TOF-MS/MS, pharmacodynamics, and in vivo experiments of zebrafish model. It makes up for the disadvantages of separate research on chemical components and pharmacodynamics, and reflects the material basis of pharmacodynamics more objectively. It has provided theoretical basis for further quality evaluation and scientific foundation for rational drug using of GE in clinical.

Alzheimer’s disease (AD) is a multifactorial disease affecting aging population worldwide. Neuroinflammation became a focus of research as one of the major pathologic processes relating to the disease onset and progression. Proinflammatory S100A9 is the central culprit in the amyloid-neuroinflammatory cascade implicated in AD and other neurodegenerative diseases. We studied the effect of S100A9 on microglial BV-2 cell proliferation and migration. The responses of BV-2 cells to S100A9 stimulation were monitored in real-time using live cell microscopy, transcriptome sequencing, immunofluorescence staining, western blot analysis, and ELISA. We observed that a low dose of S100A9 promotes migration and proliferation of BV-2 cells. However, acute inflammatory condition (i.e., high S100A9 doses) causes diminished cell viability; it is uncovered that S100A9 activates TLR-4 and TLR-7 signaling pathways, leading to TNF-α and IL-6 expression, which affect BV-2 cell migration and proliferation in a concentration-dependent manner. Interestingly, the effects of S100A9 are not only inhibited by TNF-α and IL-6 antibodies. The addition of amyloid-β (Aβ) 1–40 peptide resumes the capacities of BV-2 cells to the level of low S100A9 concentrations. Based on these results, we conclude that in contrast to the beneficial effects of low S100A9 dose, high S100A9 concentration leads to impaired mobility and proliferation of immune cells, reflecting neurotoxicity at acute inflammatory conditions. However, the formation of Aβ plaques may be a natural mechanism that rescues cells from the proinflammatory and cytotoxic effects of S100A9, especially considering that inflammation is one of the primary causes of AD.

Alzheimer's disease (AD) is the main cause of dementia, affecting the increasingly aging population. Growing evidence indicates that neuro-inflammation plays crucial roles, e.g., the association between AD risk genes with innate immune functions. In this study, we demonstrate that moderate concentrations of pro-inflammatory cytokine S100A9 regulate immune response of BV2 microglial cells, i.e., the phagocytic capacity, reflected by elevated number of 1 μm diameter Dsred-stained latex beads in the cytoplasm. In contrast, at high S100A9 concentrations, both the viability and phagocytic capacity of BV2 cells drop substantially. Furthermore, it is uncovered that S100A9 affects phagocytosis of microglia via NF-κB signaling pathways. Application of related target-specific drugs, i.e., IKK and TLR4 inhibitors, effectively suppresses BV2 cells' immune responses. These results suggest that pro-inflammatory S100A9 activates microglial phagocytosis, and possibly contributes to the clearance of amyloidogenic species at the early stage of AD.

The transition of amyloidogenic species into ordered structures (i.e., prefibrillar oligomers, protofibrils, mature fibrils, and amyloidogenic aggregates) is closely associated with many neurodegenerative disease pathologies. It is increasingly appreciated that the liquid-solid interface contributes to peptide aggregation under physiological conditions. However, much remains to be explored on the molecular mechanism of surface-directed amyloid formation. We herein demonstrate that physical environmental conditions (i.e., negatively charged surface) affect amyloid formation. Nontoxic amyloid aggregates quickly develop into intertwisting fibrils on a negatively charged mica surface. These fibrillar structures show significant cytotoxicity on both neuroblastoma cell-lines (SH-SY5Y) and primary neural stem cells. Our results suggest an alternative amyloid development pathway, following which Aβ peptides form large amyloidogenic aggregates upon stimulation, and later transit into neurotoxic fibrillar structures while being trapped and aligned by a negatively charged surface. Conceivably, the interplay between chemical and physical environmental conditions plays important roles in the development of neurodegenerative diseases.

Inflammation is the primary pathological feature of neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease. Proinflammatory molecules (e.g., S100A9) play important roles during the progression of the diseases by regulating behavior and fate of multiple cell types in the nervous system. Our earlier studies reveal that S100A9 is toxic to neurons, and its interaction with Aβ peptides leads to the formation of large nontoxic amyloidogenic aggregates, suggesting a protective role of coaggregation with Aβ amyloids. We herein demonstrate that S100A9 interacts with neural stem cells (NSCs) and causes NSC differentiation. In the brain of transgenic AD mouse models, we found large quantities of proinflammatory S100A9, which colocalizes with the differentiated NSCs. NSC sphere formation, which is a representative character of NSC stemness, is also substantially inhibited by S100A9. These results suggest that S100A9 is a representative marker for the inflammatory conditions in AD, and it promotes NSC differentiation. Intriguingly, in contrast to the death of both stem and differentiated NSCs caused by high S100A9 doses, S100A9 at a moderate concentration is toxic only to the early differentiated NSCs but not the stem cells. We therefore postulate that, at the early stage of AD, the expression of S100A9 leads to NSC differentiation, which remedies the neuron damage. The application of drugs, which help maintain NSC stemness (e.g., the platelet-derived growth factor, PDGF), may help overcome the acute inflammatory conditions and improve the efficacy of NSC transplantation therapy.

[This corrects the article DOI: 10.1371/journal.pone.0212648.].

Senile plaques are well-known hallmarks of Alzheimer’s Diseases (AD). However, drugs targeting tangles of the protein tau and plaques of β-amyloid have no significant effect on disease progression, and the studies on the underlying mechanism of AD remain in high demand. Growing evidence supports the protective role of senile plaques in local inflammation driven by S100A9. We herein demonstrate that oleic acid (OA) micelles interact with hen egg white lysozyme (HEWL) and promote its amyloid formation. Consequently, SH-SY5Y cell line and mouse neural stem cells are rescued from OA toxicity by co-aggregation of OA and HEWL. Using atomic force microscopy in combination with fluorescence microscopy, we revealed that HEWL forms round-shaped aggregates in the presence of OA micelles instead of protofibrils of HEWL alone. These HEWL amyloids act as a sink for toxic OA micelles and their co-aggregate form large clumps, suggesting a protective function in amyloid and OA cytotoxicity.