Intranasally Administered S100A9 Amyloids Induced Cellular Stress, Amyloid Seeding, and Behavioral Impairment in Aged Mice

Direct targeting of S100A9 with Icariin counteracted acetaminophen‑induced hepatotoxicity

Acetaminophen (APAP) is a widely used antipyretic and analgesic medication, but its overdose can induce acute liver failure with lack of effective therapies. Icariin is a bioactive compound derived from the herb Epimedium that displays hepatoprotective activities. Here, we explored the protective effects and mechanism of icariin on APAP-induced hepatotoxicity. Icariin (25/50 mg/kg) or N-Acetylcysteine (NAC, 300 mg/kg) were orally administered in wild-type C57BL/6 mice for 7 consecutive days before the APAP administration. Icariin attenuated APAP-induced acute liver injury in mice, as measured by alleviated serum enzymes activities and hepatic apoptosis. In vitro, icariin pretreatment significantly inhibited hepatocellular damage and apoptosis by reducing the BAX/Bcl-2 ratio as well as the expression of cleaved-caspase 3 and cleaved-PARP depended on the p53 pathway. Moreover, icariin attenuated APAP-mediated inflammatory response and oxidative stress via the Nrf2 and NF-κB pathways. Importantly, icariin reduced the expression of S100A9, icariin interacts with S100A9 as a direct cellular target, which was supported by molecular dynamics simulation and surface plasmon resonance assay (equilibrium dissociation constant, KD = 1.14 μM). In addition, the genetic deletion and inhibition of S100A9 not only alleviated APAP-induced injury but also reduced the icariin's protective activity in APAP-mediated liver injury. These data indicated that icariin targeted S100A9 to alleviate APAP-induced liver damage via the following signaling pathways NF-κB, p53, and Nrf2.

The Surprising Nonlinear Effects of S100A9 Proteins in the Retina

Age-related macular degeneration (AMD) is a complex disease in which inflammation is implicated as a key factor but the precise molecular mechanisms are poorly understood. AMD lesions contain an excess of the pro-inflammatory S100A9 protein, but its retinal significance was yet unexplored. S100A9 was shown to be intrinsically amyloidogenic in vitro and in vivo. Here, we hypothesized that the retinal effects of S100A9 are related to its supramolecular conformation. ARPE-19 cultures were treated with native dimeric and fibrillar S100A9 preparations, and cell viability was determined. Wild-type rats were treated intravitreally with the S100A9 solutions in the right eye and with the vehicle in the left. Retinal function was assessed longitudinally by electroretinography (ERG), comparing the amplitudes and configurations for each intervention. Native S100A9 had no impact on cellular viability in vitro or on the retinal function in vivo. Despite dispersed intracellular uptake, fibrillar S100A9 did not decrease ARPE-19 cell viability. In contrast, S100A9 fibrils impaired retinal function in vivo following intravitreal injection in rats. Intriguingly, low-dose fibrillar S100A9 induced contrasting in vivo effects, significantly increasing the ERG responses, particularly over 14 days postinjection. The retinal effects of S100A9 were further characterized by glial and microglial cell activation. We provide the first indication for the retinal effects of S100A9, showing that its fibrils inflicted retinal dysfunction and glial activation in vivo, while low dose of the same assemblies resulted in an unpredicted enhancement of the ERG amplitudes. These nonlinear responses highlight the consequences of self-assembly of S100A9 and provide insight into its pathophysiological and possibly physiological roles in the retina.

Cerebral Expression of the Neuregulin-1 Gene NRG1 during Induced Spatial Memory Impairment and Its Reversal in Aging Mice

We studied the effects of chronic intranasal administration of amyloidogenic fibrils of the proinflammatory protein S100A9 alone or in combination with glutamate antibodies on the expression of the neuregulin-1 gene (NRG1), a regulator of various physiological processes, in particular, regulation of neurogenesis and apoptosis, in the hippocampus, prefrontal cortex, and cerebellum of aging C57BL/6 mice under conditions of long-term memory disturbances. Under conditions of amnesia induced by S100A9 fibrils, pronounced (>90%) blockade of the expression of the NRG1 gene was found in all cerebral structures. Glutamate antibodies prevented/corrected disturbances in the cerebral expression of the NRG1 gene, thereby maintaining the activity of the NRG1/ErbB molecular signaling system, probably associated with the formation of spatial memory.

Selecting Multitarget Peptides for Alzheimer's Disease

Alzheimer's disease (AD) is a multifactorial disease with a complex pathogenesis. Developing multitarget drugs could be a powerful strategy to impact the progressive loss of cognitive functions in this disease. The purpose of this study is to select a multitarget lead peptide candidate among a series of peptide variants derived from the neutrophil granule protein cathepsin G. We screened eight peptide candidates using the following criteria: (1) Inhibition and reversion of amyloid beta (Aβ) oligomers, quantified using an enzyme-linked immunosorbent assay (ELISA); (2) direct binding of peptide candidates to the human receptor for advanced glycation end-products (RAGE), the Toll-like receptor 4 (TLR4) and the S100 calcium-binding protein A9 (S100A9), quantified by ELISA; (3) protection against Aβ oligomer-induced neuronal cell death, using trypan blue to measure cell death in a murine neuronal cell line; (4) inhibition of TLR4 activation by S100A9, using a human TLR4 reporter cell line. We selected a 27-mer lead peptide that fulfilled these four criteria. This lead peptide is a privileged structure that displays inherent multitarget activity. This peptide is expected to significantly impact cognitive decline in mouse models of Alzheimer's disease, by targeting both neuroinflammation and neurodegeneration.

Effects of Antibodies to Glutamate on Cerebral Expression of the Tnfrsf1A Gene under Conditions of Spatial Amnesia Induced by Proinflammatory Protein S100A9 Fibrils in Aging Mice

Proinflammatory S100A9 protein is a promoter of inflammation-linked neurodegeneration and the Tnfrsf1A gene encodes the TNF receptor 1A that binds TNFα to function as a regulator of inflammation. We studied the effects of chronic intranasal administration of in vitro prepared S100A9 fibrils alone or in combination with anti-glutamate antibodies on the expression of the Tnfrsf1A gene in the hippocampus, prefrontal cortex, and cerebellum of aging C57BL/6 mice under conditions of impaired spatial memory. A differential cerebral pattern of Tnfrsf1A gene activity and its modification by S100A9 fibrillar structures were observed: inhibition of Tnfrsf1A gene expression in the hippocampus and cerebellum and its activation in the prefrontal cortex. Anti-glutamate antibodies normalized the expression of the Tnfrsf1A gene in the prefrontal cortex by affecting the TNF signaling pathway and preventing the development of inflammation.

Co-Aggregation of S100A9 with DOPA and Cyclen-Based Compounds Manifested in Amyloid Fibril Thickening without Altering Rates of Self-Assembly

The amyloid cascade is central for the neurodegeneration disease pathology, including Alzheimer’s and Parkinson’s, and remains the focus of much current research. S100A9 protein drives the amyloid-neuroinflammatory cascade in these diseases. DOPA and cyclen-based compounds were used as amyloid modifiers and inhibitors previously, and DOPA is also used as a precursor of dopamine in Parkinson’s treatment. Here, by using fluorescence titration experiments we showed that five selected ligands: DOPA-D-H-DOPA, DOPA-H-H-DOPA, DOPA-D-H, DOPA-cyclen, and H-E-cyclen, bind to S100A9 with apparent K_d in the sub-micromolar range. Ligand docking and molecular dynamic simulation showed that all compounds bind to S100A9 in more than one binding site and with different ligand mobility and H-bonds involved in each site, which all together is consistent with the apparent binding determined in fluorescence experiments. By using amyloid kinetic analysis, monitored by thioflavin-T fluorescence, and AFM imaging, we found that S100A9 co-aggregation with these compounds does not hinder amyloid formation but leads to morphological changes in the amyloid fibrils, manifested in fibril thickening. Thicker fibrils were not observed upon fibrillation of S100A9 alone and may influence the amyloid tissue propagation and modulate S100A9 amyloid assembly as part of the amyloid-neuroinflammatory cascade in neurodegenerative diseases.

Comparative Transcriptomic Analysis of Cerebral Organoids and Cortical Neuron Cultures Derived from Human Induced Pluripotent Stem Cells

Human induced pluripotent stem cells (iPSCs) can be differentiated along various neuronal lineages to generate two-dimensional neuronal cultures as well as three-dimensional brain organoids. Such iPSC-derived cellular models are being utilized to study the basic biology of human neuronal function and to interrogate the molecular underpinnings of disease biology. The different cellular models generated from iPSCs have varying properties in terms of the diversity and organization of the cells as well as the cellular functions that are present. To understand transcriptomic differences in iPSC-derived monolayer neuronal cultures and three-dimensional brain organoids, we differentiated eight human iPSC lines from healthy control subjects to generate cerebral organoids and cortical neuron monolayer cultures from the same set of iPSC lines. We undertook RNA-seq experiments in these model systems and analyzed the gene expression data to identify genes that are differentially expressed in cerebral organoids and two-dimensional cortical neuron cultures. In cerebral organoids, gene ontology analysis showed enrichment of genes involved in tissue development, response to stimuli, and the interferon-γ pathway, while two-dimensional cortical neuron cultures showed enrichment of genes involved in nervous system development and neurogenesis. We also undertook comparative analysis of these gene expression profiles with transcriptomic data from the human fetal prefrontal cortex (PFC). This analysis showed greater overlap of the fetal PFC transcriptome with cerebral organoid gene expression profiles compared to monolayer cortical neuron culture profiles. Our studies delineate the transcriptomic differences between cortical neuron monolayer cultures and three-dimensional cerebral organoids and can help inform the appropriate use of these model systems to address specific scientific questions.

Development of Predictive Models for Identifying Potential S100A9 Inhibitors Based on Machine Learning Methods

S100A9 is a potential therapeutic target for various disease including prostate cancer, colorectal cancer, and Alzheimer's disease. However, the sparsity of atomic level data, such as protein-protein interaction of S100A9 with RAGE, TLR4/MD2, or CD147 (EMMPRIN) hinders the rational drug design of S100A9 inhibitors. Herein we first report predictive models of S100A9 inhibitory effect by applying machine learning classifiers on 2D-molecular descriptors. The models were optimized through feature selectors as well as classifiers to produce the top eight random forest models with robust predictability and high cost-effectiveness. Notably, optimal feature sets were obtained after the reduction of 2,798 features into dozens of features with the chopping of fingerprint bits. Moreover, the high efficiency of compact feature sets allowed us to further screen a large-scale dataset (over 6,000,000 compounds) within a week. Through a consensus vote of the top models, 46 hits (hit rate = 0.000713%) were identified as potential S100A9 inhibitors. We expect that our models will facilitate the drug discovery process by providing high predictive power as well as cost-reduction ability and give insights into designing novel drugs targeting S100A9.

Pro-Inflammatory S100A9 Protein Aggregation Promoted by NCAM1 Peptide Constructs

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.

S100 Proteins in Alzheimer's Disease

S100 proteins are calcium-binding proteins that regulate several processes associated with Alzheimer's disease (AD) but whose contribution and direct involvement in disease pathophysiology remains to be fully established. Due to neuroinflammation in AD patients, the levels of several S100 proteins are increased in the brain and some S100s play roles related to the processing of the amyloid precursor protein, regulation of amyloid beta peptide (Aβ) levels and Tau phosphorylation. S100 proteins are found associated with protein inclusions, either within plaques or as isolated S100-positive puncta, which suggests an active role in the formation of amyloid aggregates. Indeed, interactions between S100 proteins and aggregating Aβ indicate regulatory roles over the aggregation process, which may either delay or aggravate aggregation, depending on disease stage and relative S100 and Aβ levels. Additionally, S100s are also known to influence AD-related signaling pathways and levels of other cytokines. Recent evidence also suggests that metal-ligation by S100 proteins influences trace metal homeostasis in the brain, particularly of zinc, which is also a major deregulated process in AD. Altogether, this evidence strongly suggests a role of S100 proteins as key players in several AD-linked physiopathological processes, which we discuss in this review.

Proinflammatory and amyloidogenic S100A9 induced by traumatic brain injury in mouse model

Traumatic brain injury (TBI) represents a significant risk factor for development of neurodegenerative diseases such as Alzheimer's and Parkinson's. The S100A9-driven amyloid-neuroinflammatory cascade occurring during primary and secondary TBI events can serve as a mechanistic link between TBI and Alzheimer's as demonstrated recently in the human brain tissues. Here by using immunohistochemistry in the controlled cortical impact TBI mouse model we have found pro-inflammatory S100A9 in the brain tissues of all mice on the first and third post-TBI days, while 70% of mice did not show any S100A9 presence on seventh post-TBI day similar to controls. This indicates that defensive mechanisms effectively cleared S100A9 in these mouse brain tissues during post-TBI recovery. By using sequential immunohistochemistry we have shown that S100A9 was produced by both neuronal and microglial cells. However, Aβ peptide deposits characteristic for Alzheimer's disease were not detected in any post-TBI animals. On the first and third post-TBI days S100A9 was found to aggregate intracellularly into amyloid oligomers, similar to what was previously observed in human TBI tissues. Complementary, by using Rayleigh scatting, intrinsic fluorescence and atomic force microscopy we demonstrated that in vitro S100A9 self-assembles into amyloid oligomers within minutes. Its amyloid aggregation is highly dependent on changes of environmental conditions such as variation of calcium levels, pH, temperature and reduction/oxidation, which might be relevant to perturbation of cellular and tissues homeostasis under TBI. Present results demonstrate that S100A9 induction mechanisms in TBI are similar in mice and humans, emphasizing that S100A9 is an important marker of brain injury and therefore can be a potential therapeutic target.

S100A9-Driven Amyloid-Neuroinflammatory Cascade in Traumatic Brain Injury as a Precursor State for Alzheimer's Disease

Pro-inflammatory and amyloidogenic S100A9 protein is an important contributor to Alzheimer's disease (AD) pathology. Traumatic brain injury (TBI) is viewed as a precursor state for AD. Here we have shown that S100A9-driven amyloid-neuroinflammatory cascade was initiated in TBI and may serve as a mechanistic link between TBI and AD. By analyzing the TBI and AD human brain tissues, we demonstrated that in post-TBI tissues S100A9, produced by neurons and microglia, becomes drastically abundant compared to Aβ and contributes to both precursor-plaque formation and intracellular amyloid oligomerization. Conditions implicated in TBI, such as elevated S100A9 concentration, acidification and fever, provide strong positive feedback for S100A9 nucleation-dependent amyloid formation and delay in its proteinase clearance. Consequently, both intracellular and extracellular S100A9 oligomerization correlated with TBI secondary neuronal loss. Common morphology of TBI and AD plaques indicated their similar initiation around multiple aggregation centers. Importantly, in AD and TBI we found S100A9 plaques without Aβ. S100A9 and Aβ plaque pathology was significantly advanced in AD cases with TBI history at earlier age, signifying TBI as a risk factor. These new findings highlight the detrimental consequences of prolonged post-TBI neuroinflammation, which can sustain S100A9-driven amyloid-neurodegenerative cascade as a specific mechanism leading to AD development.