NFκB-activated astroglial release of complement C3 compromises neuronal morphology and function associated with Alzheimer's disease

Hippocampal microglial activation induces cognitive impairment and allodynia through neuronal plasticity changes in male mice with neuropathic pain

Clinical evidence indicates that cognitive impairment is a common comorbidity of chronic pain, including neuropathic pain, but the mechanism underlying this comorbidity remains unclear. Neuroinflammation plays a critical role in the development of both neuropathic pain and cognitive impairment. A previous study showed that minocycline, an inhibitor of microglia, ameliorated allodynia and cognitive impairment in partial sciatic nerve ligation (PSNL) mice. Therefore, the current study examined a potential role of brain microglia in allodynia and cognitive impairment in male mice with neuropathic pain due to PSNL. Immunohistochemistry of the microglial markers ionized calcium-binding adapter molecule 1 (Iba1), transmembrane protein 119 (TMEM119), and purinergic receptor P2Y12 (P2RY12) was performed to examine microglial status. Two weeks after PSNL, significant microglial activation was observed in the hippocampus and amygdala, but not in the perirhinal cortex. Inhibition of brain-region-specific microglia with a local microinjection of clodronate liposomes was examined to elucidate the involvement of these microglia in PSNL-induced allodynia and cognitive impairment. Local clodronate liposome microinjection to the hippocampus, but not the amygdala, ameliorated allodynia and cognitive impairment. Other changes in the hippocampus of PSNL mice, e.g., decreased hippocampal dendrite length and intersections number, were prevented by microinjection of clodronate liposomes. The current findings suggest hippocampal microglia are related to cognitive impairment and allodynia through neuronal plasticity changes observed in PSNL mice. Blocking hippocampal microglia-mediated neuroinflammation may be a novel approach for reducing comorbidities such as cognitive impairment associated with neuropathic pain.

Short-term PS-NP exposure in early adulthood induces neuronal damage in middle-aged mice via microglia-mediated neuroinflammation

Nanoplastics (NPs) are ubiquitous environmental pollutants that have garnered considerable attention for their potential adverse health effects. In this study, male C57BL/6 J mice were orally treated with a mixture of 50-nm and 200-nm polystyrene (PS)-NPs for one week followed by measurements of their neurobehavioral performance and neuronal damage 10 months later. Notably, PS-NPs were detected in the brains of the mice by transmission electron microscopy (TEM) and a nanoscale hyperspectral microscope imaging system 10 months after the PS-NP exposure. The mice exposed to short-term PS-NPs exhibited cognitive dysfunction and anxiety-like symptoms, neuronal damage and synapse loss, and an increase in the number of M1-polarized microglia and A1-reactive astrocytes. Interestingly, the inhibition of microglial activation by minocycline significantly mitigated the PS-NP-induced synapse loss and neuron damage. In vitro studies showed that PS-NPs could be readily internalized by three types of neurovascular unit (NVU) cells, including microglia, astrocytes, and brain microvascular endothelial cells, via multiple pathways. RNA-seq analysis confirmed that microglia-mediated neuronal injury was associated with disturbances in synapse and cell death signaling pathways. Collectively, these findings suggest that short-term PS-NP exposure-induced neuroinflammation in early adulthood may not be resolved naturally but may deteriorate under the interaction of microglia and astrocytes, leading to synapse loss, neuron degeneration, and cognitive dysfunction in middle age. The results of the present study provide important insights into the potential neurological impacts of NPs and suggest that targeting microglia to suppress inflammation might be a potential intervention strategy for neurodegeneration induced by NPs.

Neuroimmune regulation of the prefrontal cortex tetrapartite synapse

The prefrontal cortex (PFC) is an essential driver of cognitive, affective, and motivational behavior. There is clear evidence that the neuroimmune system directly influences PFC synapses, in addition to its role as the first line of defense against toxins and pathogens. In this review, we first describe the core structures that form the tetrapartite PFC synapse, focusing on the signaling microdomain created by astrocytic cradling of the synapse as well as the emerging role of the extracellular matrix in synaptic organization and plasticity. Neuroimmune signals (e.g. pro-inflammatory interleukin 1β) can impact the function of each core structure within the tetrapartite synapse, as well as promote intra-synaptic crosstalk, and we will provide an overview of recent advances in this field. Finally, evidence from post mortem human brain tissue and preclinical studies indicate that inflammation may be a key contributor to PFC dysfunction. Therefore, we conclude with a mechanistic discussion of neuroimmune-mediated maladaptive plasticity in neuropsychiatric disorders, with a focus on alcohol use disorder (AUD). Growing recognition of the neuroimmune system's role as a critical regulator of the PFC tetrapartite synapse provides strong support for targeting the neuroimmune system to develop new pharmacotherapeutics.

Downregulation of STAT3 transcription factor reverses synaptotoxic phenotype of reactive astrocytes associated with prion diseases

In neurodegenerative diseases, including prion diseases, astrocytes adopt reactive phenotypes that persist throughout disease progression. While astrocyte reactivity may initially serve as a protective response to prion infection, it transitions into a neurotoxic phenotype that disrupts homeostatic functions and exacerbates disease pathology. The transcription factor Stat3 has been recognized as a master regulator of astrocyte reactivity in neurodegenerative diseases, yet its role in prion disease-associated astrocyte reactive phenotypes remains unexplored. The current study addresses this gap by investigating the effects of Stat3 deletion in reactive astrocytes isolated from prion-infected mice. We demonstrate that Stat3 deletion mitigates the reactive astrocyte phenotype and alleviates their synaptotoxic effects. Stat3-dependent activation of astrocytes was reproduced by co-culturing naïve astrocytes with reactive microglia isolated from prion-infected animals or exposing them to microglia-conditioned media. A cytokine array profiling of 40 molecules revealed partially overlapping inflammatory signatures in reactive microglia and astrocytes, with IL-6 prominently upregulated in both cell types. Notably, IL-6 treatment elevated phosphorylated Stat3 levels in naïve astrocytes and triggered astrocyte reactivity. These findings indicate that the synaptotoxic phenotype of astrocytes in prion diseases can be sustained by reactive microglia and self-reinforced in a cell-autonomous manner. Our work highlights the pivotal role of Stat3 signaling in astrocyte activation and suggests that Stat3 inhibition may suppress the reactive phenotype of astrocytes associated with prion diseases.

Neuroimmune signaling mediates astrocytic nucleocytoplasmic disruptions and stress granule formation associated with TDP-43 pathology

Alterations in transactivating response region DNA-binding protein 43 (TDP-43) are prevalent in amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and other neurological disorders. TDP-43 influences neuronal functions and might also affect glial cells. However, specific intracellular effects of TDP-43 alterations on glial cells and underlying mechanisms are not clear. We report that TDP-43 dysregulation in mouse and human cortical astrocytes causes nucleoporin mislocalization, nuclear envelope remodeling, and changes in nucleocytoplasmic protein transport. These effects are dependent on interleukin-1 (IL-1) receptor activity and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling and are associated with the formation of cytoplasmic stress granules. Stimulation of IL-1 receptors and NF-κB signaling are necessary and sufficient to induce astrocytic stress granules and rapid nucleocytoplasmic changes, which are broadly alleviated by inhibition of the integrated stress response. These findings establish that TDP-43 alterations and neuroimmune factors can induce nucleocytoplasmic changes through NF-κB signaling, revealing mechanistic convergence of proteinopathy and neuroimmune pathways onto glial nucleocytoplasmic disruptions that may occur in diverse neurological conditions.

Refining the interactions between microglia and astrocytes in Alzheimer's disease pathology

Microglia and astrocytes are central to the pathogenesis and progression of Alzheimer's Disease (AD), working both independently and collaboratively to regulate key pathological processes such as β-amyloid protein (Aβ) deposition, tau aggregation, neuroinflammation, and synapse loss. These glial cells interact through complex molecular pathways, including IL-3/IL-3Ra and C3/C3aR, which influence disease progression and cognitive decline. Emerging research suggests that modulating these pathways could offer therapeutic benefits. For instance, recombinant IL-3 administration in mice reduced Aβ plaques and improved cognitive functions, while C3aR inhibition alleviated Aβ and tau pathologies, restored synaptic function, and corrected immune dysregulation. However, the effects of these interactions are context-dependent. Acute C3/C3aR activation enhances microglial Aβ clearance, whereas chronic activation impairs it, highlighting the dual roles of glial signaling in AD. Furthermore, C3/C3aR signaling not only impacts Aβ clearance but also modulates tau pathology and synaptic integrity. Given AD's multifactorial nature, understanding the specific pathological environment is crucial when investigating glial cell contributions. The interplay between microglia and astrocytes can be both neuroprotective and neurotoxic, depending on the disease stage and brain region. This complexity underscores the need for targeted therapies that modulate glial cell activity in a context-specific manner. By elucidating the molecular mechanisms underlying microglia-astrocyte interactions, this research advances our understanding of AD and paves the way for novel therapeutic strategies aimed at mitigating neurodegeneration and cognitive decline in AD and related disorders.

S-9-PAHSA Protects Against High-Fat Diet-Induced Diabetes-Associated Cognitive Impairment via Gut Microbiota Regulation

AIM

Diabetes-associated cognitive impairment (DACI) is a common complication of Type 2 diabetes mellitus (T2DM), with its mechanisms and treatments for DACI remaining incompletely clarified. This study investigated the protective efficacy of the novel lipid S-enantiomer of 9-palmitic acid esters of hydroxy stearic acids (S-9-PAHSA, S9P) in a high-fat diet-induced DACI mouse model.

METHODS

Mice were randomly assigned to three groups: normal diet (ND), high-fat diet (HFD), and HFD + 30 mg/kg/day S9P (HFD + S9P). Fasting blood glucose (FBG), intraperitoneal glucose tolerance test (IPGTT), and insulin tolerance test (ITT) were conducted to assess blood glucose homeostasis. Morris Water Maze and Y maze tests evaluated cognitive function, and neuronal status was examined through pathological analysis, Golgi staining, and transmission electron microscopy (TEM). Colonic barrier integrity was assessed using periodic acid-Schiff and Alcian blue staining (AB-PAS) and immunohistochemistry (IHC) staining. Intestinal microbiota composition was analyzed by 16S rDNA sequencing, and serum metabolic characteristics were determined by metabolomics sequencing.

RESULTS

S9P improved glucose homeostasis and alleviated cognitive decline in DACI mice. It also mitigated neuronal damage, dendritic degeneration, and synaptic damage, while restoring colonic barrier integrity and ameliorating gut microbiome imbalances, insulin resistance, and lipid imbalance. Additionally, S9P regulated metabolite profiles and the PI3K/AKT/mTOR signaling pathways, and reduced astrocyte activation and neuroinflammatory responses in the hippocampus of HFD-induced DACI mice.

CONCLUSION

S9P had a protective effect against HFD-induced diabetic cognitive impairment closely related to the modulation of the gut-brain axis, suggesting that S9P has the potential to become a new therapeutic approach for DACI.

A Novel H2S Donor Alleviates Neuroinflammation and Seizures by Inhibiting the C3-C3aR Pathway

Both astrocytes and microglia are activated in the epileptic brain. There is an interaction between them through the complement 3 (C3)-C3a receptor (C3aR) pathway, which plays a detrimental role in seizures. Our self-developed novel H2S donor has been found to have anti-seizure effects. However, its mechanism remains to be explored. In the present study, we showed that the novel H2S donor can inhibit the activation of astrocytes and microglia and their interaction through C3-C3aR signaling, which contributed to alleviating microglial neuroinflammation and seizures. In LPS-treated astrocytes and pilocarpine-induced epileptic mice, the H2S donor reduced C3 production in astrocytes and regulated the expression of inflammatory cytokines IL-1β and IL-10 in microglia. The H2S donor also reduced the EEG amplitude of hippocampal epileptic waves and relieved seizures in epileptic mice. These effects of the H2S donor can be reversed by intranasal C3 treatment and mimicked by a C3aR antagonist. These findings provide a novel mechanism underlying the anti-seizure effects of the H2S donor. Therefore, the H2S donor has the potential to be used as a candidate for antiepileptic drugs.

The complex effects of miR-146a in the pathogenesis of Alzheimer's disease

Alzheimer's disease is a neurodegenerative disorder characterized by cognitive dysfunction and behavioral abnormalities. Neuroinflammatory plaques formed through the extracellular deposition of amyloid-β proteins, as well as neurofibrillary tangles formed by the intracellular deposition of hyperphosphorylated tau proteins, comprise two typical pathological features of Alzheimer's disease. Besides symptomatic treatment, there are no effective therapies for delaying Alzheimer's disease progression. MicroRNAs (miR) are small, non-coding RNAs that negatively regulate gene expression at the transcriptional and translational levels and play important roles in multiple physiological and pathological processes. Indeed, miR-146a, a NF-κB-regulated gene, has been extensively implicated in the development of Alzheimer's disease through several pathways. Research has demonstrated substantial dysregulation of miR-146a both during the initial phases and throughout the progression of this disorder. MiR-146a is believed to reduce amyloid-β deposition and tau protein hyperphosphorylation through the TLR/IRAK1/TRAF6 pathway; however, there is also evidence supporting that it can promote these processes through many other pathways, thus exacerbating the pathological manifestations of Alzheimer's disease. It has been widely reported that miR-146a mediates synaptic dysfunction, mitochondrial dysfunction, and neuronal death by targeting mRNAs encoding synaptic-related proteins, mitochondrial-related proteins, and membrane proteins, as well as other mRNAs. Regarding the impact on glial cells, miR-146a also exhibits differential effects. On one hand, it causes widespread and sustained inflammation through certain pathways, while on the other hand, it can reverse the polarization of astrocytes and microglia, alleviate neuroinflammation, and promote oligodendrocyte progenitor cell differentiation, thus maintaining the normal function of the myelin sheath and exerting a protective effect on neurons. In this review, we provide a comprehensive analysis of the involvement of miR-146a in the pathogenesis of Alzheimer's disease. We aim to elucidate the relationship between miR-146a and the key pathological manifestations of Alzheimer's disease, such as amyloid-β deposition, tau protein hyperphosphorylation, neuronal death, mitochondrial dysfunction, synaptic dysfunction, and glial cell dysfunction, as well as summarize recent relevant studies that have highlighted the potential of miR-146a as a clinical diagnostic marker and therapeutic target for Alzheimer's disease.

Astrocyte-derived complement C3 facilitated microglial phagocytosis of synapses in Staphylococcus aureus-associated neurocognitive deficits

The presence of pathogens is a significant challenge in causing brain infections and tissue damage. There is growing evidence that pathogen infections are commonly associated with cognitive dysfunction and mental health problems, but the underlying mechanisms are not yet fully understood. Here, we found microglia and astrocyte activation, neuronal damage, synapse loss, and cognitive impairment in a Staphylococcus aureus (S. aureus) induced mouse model. An unbiased transcription profile of isolated microglia derived from S. aureus-infected mice identified the involvement of microglial phagosome and regulation of neurogenesis. Our findings indicate that the complement C1q and C3 are upregulated, and astroglial release of C3 activates microglia to phagocytose synapses. Blocking the C3-C3aR axis can improve microglial phagocytosis, thus rescuing synapse loss and cognitive impairment in infected mice. These results indicate that S. aureus induces synapse elimination and cognitive impairment by activating microglia and astrocytes through C3-C3aR signaling. This suggests a mechanism of complement signaling bridged crosstalk between astrocyte and microglia in the S. aureus-associated post-infectious synapse loss and cognitive dysfunction, and provide potential therapeutic targets for managing pathogen-associated brain infections.

CLU alleviates Alzheimer's disease-relevant processes by modulating astrocyte reactivity and microglia-dependent synaptic density

Genetic studies implicate clusterin (CLU) in the pathogenesis of Alzheimer's disease (AD), yet its precise molecular impact remains unclear. Through unbiased proteomic profiling and functional validation in CLU-deficient astrocytes, we identify increased nuclear factor κB (NF-κB)-dependent signaling and complement C3 secretion. Reduction of astrocyte CLU induced microglia-dependent modulation of extracellular apolipoprotein E (APOE) and phosphorylated tau, as well as increased microglial phagocytosis and reduced synapse numbers. By integrating mouse and human cellular models with comprehensive analyses of human plasma and brain tissue, we demonstrate that CLU AD-risk alleles are associated with reduced CLU protein and heightened inflammatory profiles. These findings establish a mechanistic link between AD genetic risk factors, astrocyte reactivity, and microglia-mediated effects on synaptic integrity. Collectively, these results support a model in which CLU upregulation in response to neuropathology is associated with maintenance of cognitive function, while diminished astrocyte CLU levels heighten disease susceptibility.

Interplay of Neuroinflammation and Gut Microbiota Dysbiosis in Alzheimer's Disease Using Diffusion Kurtosis Imaging Biomarker in 3 × Tg-AD Mouse Models

The relationship between alterations in brain microstructure and dysbiosis of gut microbiota in Alzheimer's disease (AD) has garnered increasing attention, although the functional implications of these changes are not yet fully elucidated. This research examines how neuroinflammation, systemic inflammation, and gut microbiota interact in male 3 × Tg-AD and B6129SF1/J wild-type (WT) mice at 6 months-old (6-MO) and 12 months-old (12-MO). Employing a combination of behavioral assessments, diffusion kurtosis imaging (DKI), microbiota profiling, cytokine analysis, short-chain fatty acids (SCFAs), and immunohistochemistry, we explored the progression of AD-related pathology. Significant memory impairments in AD mice at both assessed ages were correlated with altered DKI parameters that suggest neuroinflammation and microstructural damage. We observed elevated levels of pro-inflammatory cytokines, such as IL-1β, IL-6, TNFα, and IFN-γ, in the serum, which were associated with increased activity of microglia and astrocytes in brain regions critical for memory. Although gut microbiota analysis did not reveal significant changes in alpha diversity, it did show notable differences in beta diversity and a diminished Firmicutes/Bacteroidetes (F/B) ratio in AD mice at 12-MO. Furthermore, a reduction in six kinds of SCFAs were identified at two time points of 6-MO and 12-MO, indicating widespread disruption in gut microbial metabolism. These findings underscore a complex bidirectional relationship between systemic inflammation and gut dysbiosis in AD, highlighting the gut-brain axis as a crucial factor in disease progression. This study emphasizes the potential of integrating DKI metrics, microbiota profiling, and SCFA analysis to enhance our understanding of AD pathology and to identify new therapeutic targets.

A Neuroimmune-Oncology Microphysiological Analysis Platform (NEO-MAP) for Evaluating Astrocytic Scar Formation and Microgliosis in Glioblastoma Microenvironment

Glioblastoma multiforme (GBM) is the most aggressive type of brain tumor, characterized by its heterogeneity in cellular components, including reactive astrocytes and microglia. Since neuroimmune responses like astrogliosis and microgliosis gain recognition as vital factors in brain tumor progression, there is a growing need for clinically relevant models that assess the interactions between astrocytes, microglia, and GBM. Here, a NEuroimmune-Oncology Microphysiological Analysis Platform (NEO-MAP) is presented as a "new map" to observe astrocytic scar formation and microgliosis in response to GBM. NEO-MAP based on pathophysiological principles is designed to replicate the GBM-glia interactions, multi-phenotypic microglia activities, scar-forming astrocytes with chondroitin sulfate proteoglycans (CSPGs) in the extracellular matrix, and the biophysical characteristics of the astrocytic scar barrier. The NEO-MAP reveals that inhibiting mTORC2 in GBM promotes the proinflammatory transformation of astrocytes and enhanced astrocytic scar formation. Astrocytes that form scars prompted microglia to change from the M2 to M1 phenotype, enhancing chemotherapy sensitivity. Tissues from GBM patients show a significant correlation between reduced mTORC2 activity and increased astrogliosis, alongside a decrease in M2-polarized microgliosis, aligning with the NEO-MAP findings. Overall, the NEO-MAP is foreseen as a clinically significant tool for exploring tumor-glia interactions, opening avenues for drug development aimed at the tumor microenvironment.

Semaglutide improves cognitive function and neuroinflammation in APP/PS1 transgenic mice by activating AMPK and inhibiting TLR4/NF-κB pathway

BackgroundAlzheimer's disease (AD) causes cognitive function disorder and has become the preeminent cause of dementia. Glucagon-like peptide-1 (GLP-1) receptor agonists, semaglutide, have shown positive effects on promoting the cognitive function. However, research about the mechanism of semaglutide as a therapeutic intervention in AD is sparse.ObjectiveThis study was to investigate the therapeutic efficacy of semaglutide in a transgenic mouse model of AD pathology and explored the detailed mechanism by semaglutide modulated neuroinflammatory processes.MethodsMale amyloid precursor protein/presenilin 1 (APP/PS1) transgenic mice were treated with semaglutide or vehicle for 8 weeks. Morris water maze test was used to assess the therapeutic efficacy of semaglutide on recognition function. Pathology analysis was performed to detect the deposition of amyloid plaques. High-throughput sequencing analysis was applied to specify the mechanism. Microglia and astrocyte activation were assessed with immunofluorescent staining. Inflammation cytokine levels were evaluated with enzyme-linked immunosorbent assay (ELISA). Related proteins and pathway were evaluated with western blot.ResultsSemaglutide treatment attenuated Aβ accumulation and enhanced cognitive function in APP/PS1 transgenic mice. Through transcriptomic profiling, immunohistochemical staining, and ELISA, semaglutide was substantiated to inhibit the overactivation of microglia and astrocytes, as well as to curtail the secretion of inflammatory mediators. Furthermore, semaglutide robustly activated AMP-activated protein kinase (AMPK) and suppressed the toll-like receptor 4 (TLR4)/nuclear factor-kappa B (NF-κB) signaling cascade, thus reducing the Aβ deposition and dampening the inflammatory cascade.ConclusionsThe results demonstrated that semaglutide mitigated neuroinflammation and decelerated the advance of AD in APP/PS1 transgenic mice.

The role of astrocyte metabolic reprogramming in ischemic stroke (Review)

Ischemic stroke, a leading cause of disability and mortality worldwide, is characterized by the sudden loss of blood flow in specific area of the brain. Intravenous thrombolysis with recombinant tissue plasminogen activator is the only approved pharmacological treatment for acute ischemic stroke; however, the aforementioned treatment has significant clinical limitations, thus there is an urgent need for the development of novel mechanisms and therapeutic strategies for ischemic stroke. Astrocytes, abundant and versatile cells in the central nervous system, offer crucial support to neurons nutritionally, structurally and physically. They also contribute to blood‑brain barrier formation and regulate neuronal extracellular ion concentrations. Accumulated evidence has revealed the involvement of astrocytes in the regulation of host neurotransmitter metabolism, immune response and tissue repair, and different metabolic characteristics of astrocytes can contribute to the process and development of ischemic stroke, suggesting that targeted regulation of astrocyte metabolic reprogramming may contribute to the treatment and prognosis of ischemic stroke. In the present review, the current understanding of the multifaceted mechanisms of astrocyte metabolic reprogramming in ischemic stroke, along with its regulatory factors and pathways, as well as the strategies to promote its polarization balance, which hold promise for astrocyte immunometabolism‑targeted therapies in the treatment of ischemic stroke, were summarized.

Design, current states, and challenges of nanomaterials in anti-neuroinflammation: A perspective on Alzheimer's disease

Alzheimer's disease (AD), an age-related neurodegenerative disease, brings huge damage to the society, to the whole family and even to the patient himself. However, until now, the etiological factor of AD is still unknown and there is no effective treatment for it. Massive deposition of amyloid-beta peptide(Aβ) and hyperphosphorylation of Tau proteins are acknowledged pathological features of AD. Recent studies have revealed that neuroinflammation plays a pivotal role in the pathology of AD. With the rise of nanomaterials in the biomedical field, researchers are exploring how the unique properties of these materials can be leveraged to develop effective treatments for AD. This article has summarized the influence of neuroinflammation in AD, the design of nanoplatforms, and the current research status and inadequacy of nanomaterials in improving neuroinflammation in AD.

Microbial Trojan Horses: Virulence Factors as Key Players in Neurodegenerative Diseases

Changes in population demographics indicate that the elderly population will reach 2.1 billion worldwide by 2050. In parallel, there will be an increase in neurodegenerative diseases such as Alzheimer's and Parkinson's. This review explores dysbiosis occurring in these pathologies and how virulence factors contribute to the worsening or development of clinical conditions, and it summarizes existing and potential ways to combat microorganisms related to these diseases. Microbiota imbalances can contribute to the progression of neurodegenerative diseases by increasing intestinal permeability, exchanging information through innervation, and even acting as a Trojan horse affecting immune cells. The microorganisms of the microbiota produce virulence factors to protect themselves from host defenses, many of which contribute to neurodegenerative diseases. These virulence factors are expressed according to the genetic composition of each microorganism, leading to a wide range of factors to be considered. Among the main virulence factors are LPS, urease, curli proteins, amyloidogenic proteins, VacA, and CagA. These factors can also be packed into bacterial outer membrane vesicles, which transport proteins, RNA, and DNA, enabling distal communication that impacts various diseases, including Alzheimer's and Parkinson's.

Alzheimer's disease may develop from changes in the immune system, cell cycle, and protein processing following alterations in ribosome function

The prevalence of Alzheimer's disease (AD) is increasing as society ages. The details of AD pathogenesis have not been fully elucidated, and a comprehensive gene expression analysis of the process leading up to the onset of AD would be helpful for understanding the mechanism. We performed an RNA sequencing analysis on a cohort of 1227 Japanese blood samples, representing 424 AD patients, 543 individuals with mild cognitive impairment (MCI), and 260 cognitively normal (CN) individuals. A total of 883 and 1169 statistically significant differentially expressed genes (DEGs) were identified between CN and MCI (CN-MCI) and between MCI and AD (MCI-AD), respectively. Pathway analyses using these DEGs, followed by protein-protein interaction network analysis, revealed key roles of ribosomal function in MCI progression, whereas immune responses, cell cycle, and protein processing in endoplasmic reticulum were involved in AD progression. Our findings indicate that the onset of AD might be associated with gene expression changes in the immune system, cell cycle, and protein processing following alterations in the expression of ribosomal protein genes during the MCI stage, although validation using brain tissue samples will be necessary in the future. Given the known effectiveness of delaying MCI progression in preventing AD, the genes related to ribosomal function might emerge as biomarkers for early diagnosis.

Multi-target-directed therapeutic strategies for Alzheimer's disease: controlling amyloid-β aggregation, metal ion homeostasis, and enzyme inhibition

Alzheimer's disease (AD) is the most prevalent neurodegenerative dementia, marked by progressive cognitive decline and memory impairment. Despite advances in therapeutic research, single-target-directed treatments often fall short in addressing the complex, multifactorial nature of AD. This arises from various pathological features, including amyloid-β (Aβ) aggregate deposition, metal ion dysregulation, oxidative stress, impaired neurotransmission, neuroinflammation, mitochondrial dysfunction, and neuronal cell death. This review illustrates their interrelationships, with a particular emphasis on the interplay among Aβ, metal ions, and AD-related enzymes, such as β-site amyloid precursor protein cleaving enzyme 1 (BACE1), matrix metalloproteinase 9 (MMP9), lysyl oxidase-like 2 (LOXL2), acetylcholinesterase (AChE), and monoamine oxidase B (MAOB). We further underscore the potential of therapeutic strategies that simultaneously inhibit Aβ aggregation and address other pathogenic mechanisms. These approaches offer a more comprehensive and effective method for combating AD, overcoming the limitations of conventional therapies.

The immunomodulatory effects of psychedelics in Alzheimer's disease-related dementia

Dementia is an increasing disorder, and Alzheimer's disease (AD) is the cause of 60% of all dementia cases. Despite all efforts, there is no cure for stopping dementia progression. Recent studies reported potential effects of psychedelics on neuroinflammation during AD. Psychedelics by 5HT2AR activation can reduce proinflammatory cytokine levels (TNF-α, IL-6) and inhibit neuroinflammation. In addition to neuroinflammation suppression, psychedelics induce neuroplasticity by increasing Brain-derived neurotrophic factor (BDNF) levels through Sigma-1R stimulation. This review discussed the effects of psychedelics on AD from both neuroinflammatory and neuroplasticity standpoints.

Calcium signaling hypothesis: A non-negligible pathogenesis in Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) presents a significant challenge to global healthcare systems, with an exacerbation by an aging population. Although the plethora of hypotheses are proposed to elucidate the underlying mechanisms of AD, from amyloid-beta (Aβ) accumulation and Tau protein aggregation to neuroinflammation, a comprehensive understanding of its pathogenesis remains elusive. Recent research has highlighted the critical role of calcium (Ca2+) signaling pathway in the progression of AD, indicating a complex interplay between Ca2+ dysregulation and various pathological processes.

AIM OF REVIEW

This review aims to consolidate the current understanding of the role of Ca2+ signaling dysregulation in AD, thus emphasizing its central role amidst various pathological hypotheses. We aim to evaluate the potential of the Ca2+ signaling hypothesis to unify existing theories of AD pathogenesis and explore its implications for developing innovative therapeutic strategies through targeting Ca2+ dysregulation.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The review focuses on three principal concepts. First, the indispensable role of Ca2+ homeostasis in neuronal function and its disruption in AD. Second, the interaction between Ca2+ signaling dysfunction and established AD hypotheses posited that Ca2+ dysregulation is a unifying pathway. Third, the dual role of Ca2+ in neurodegeneration and neuroprotection, highlighting the nuanced effects of Ca2+ levels on AD pathology.

Cognitive disorders: Potential astrocyte-based mechanism

Cognitive disorders are a common clinical manifestation, including a deterioration in the patient's memory ability, attention, executive power, language, and other functions. The contributing factors of cognitive disorders are numerous and diverse in nature, including organic diseases and other mental disorders. Neurodegenerative diseases are a common type of organic disease related to the pathology of neuronal death and disruption of glial cell balance, ultimately accompanied with cognitive impairment. Thus, cognitive disorder frequently serves as an extremely critical indicator of neurodegenerative disorders. Cognitive impairments negatively affect patients' daily lives. However, our understanding of the precise pathogenic pathways of cognitive defects remains incomplete. The most prevalent kind of glial cells in the central nervous system are called astrocytes. They have a unique significance in cerebral function because of their wide range of functions in maintaining homeostasis in the central nervous system, regulating synaptic plasticity, and so on. Dysfunction of astrocytes is intimately linked to cognitive disorders, and we are attempting to understand this phenomenon predominantly from those perspectives: neuroinflammation, astrocytic senescence, connexin, Ca2 + signaling, mitochondrial dysfunction, and the glymphatic system.

Neuroinflammation and neurodegeneration following traumatic brain injuries

Traumatic brain injuries (TBI) commonly occur following head trauma. TBI may result in short- and long-term complications which may lead to neurodegenerative consequences, including cognitive impairment post-TBI. When investigating the neurodegeneration following TBI, studies have highlighted the role reactive astrocytes have in the neuroinflammation and degeneration process. This review showcases a variety of markers that show reactive astrocyte presence under pathological conditions, including glial fibrillary acidic protein (GFAP), Crystallin Alpha-B (CRYA-B), Complement Component 3 (C3) and S100A10. Astrocyte activation may lead to white-matter inflammation, expressed as white-matter hyperintensities. Other white-matter changes in the brain following TBI include increased cortical thickness in the white matter. This review addresses the gaps in the literature regarding post-mortem human studies focussing on reactive astrocytes, alongside the potential uses of these proteins as markers in the future studies that investigate the proportions of astrocytes in the post-TBI brain has been discussed. This research may benefit future studies that focus on the role reactive astrocytes play in the post-TBI brain and may assist clinicians in managing patients who have suffered TBI.

Therapeutic Potential of Mesenchymal Stem Cell-Derived Exosomes in Spinal Cord Injury

Spinal cord injury (SCI) can lead to severe motor and sensory dysfunction, with a high rate of disability and mortality. Due to the complicated pathological process of SCI, there is no effective clinical treatment strategy at present. Although mesenchymal stem cells (MSCs) are effective in the treatment of SCI, their application is limited by factors such as low survival rate, cell dedifferentiation, tumorigenesis, blood-brain barrier, and immune rejection. Fortunately, there is growing evidence that most of the biological and therapeutic effects of MSCs may be mediated by the release of paracrine factors, which are extracellular vesicles called exosomes. Exosomes are small endosomal vesicles with bilaminar membranes that have recently been recognized as key mediators for communication between cells and tissues through the transfer of proteins, lipids, nucleic acids, cytokines, and growth factors. Mesenchymal stem cell-derived exosomes (MSC-exos) play a critical role in SCI repair by promoting angiogenesis and axonal growth, regulating inflammation and immune response, inhibiting apoptosis, and maintaining the integrity of the blood-spinal cord barrier. Furthermore, they can be used to transport genetic material or drugs to target cells, and their relatively small size allows them to permeate the blood-brain barrier. Studies have demonstrated that some exosomal miRNAs derived from MSCs play a significant role in the treatment of SCI. In this review, we summarize recent research advances in MSC-exos and exosomal miRNAs in SCI therapy to better understand this emerging cell-free therapeutic strategy and discuss the advantages and challenges of MSC-exos in future clinical applications.

Astrocyte-neuron communication through the complement C3-C3aR pathway in Parkinson's disease

Neuroinflammation and autoimmunity are pivotal in the pathogenesis of neurodegenerative diseases. Complement activation and involvement of astrocyte-neuron C3/C3aR pathway have been observed, yet the mechanisms influencing α-synuclein (α-syn) pathology and neurodegeneration remain unclear. In this study, elevated levels of complement C3 were detected in the plasma of α-syn PFF-induced mice and the substantia nigra of A53T transgenic mice. Colocalization of complement C3 with astrocytes was also observed. Overexpression of complement C3 exacerbated motor dysfunction, dopaminergic neuron loss, and phosphorylated α-syn expression in mice injected with α-syn preformed fibrils (α-syn PFFs). Conversely, downregulation of complement C3 protected α-syn PFF-induced mice. Molecular investigations revealed that inhibition of Toll-like receptor 2 (TLR2) or NF-κB reduced complement C3 expression in primary astrocytes following α-syn PFF treatment. Astrocyte-neuron communication via the C3/C3aR pathway influenced α-syn PFF-induced neuronal apoptosis and α-syn pathology, potentially through modulation of GSK3β. These findings underscore the critical role of astrocyte-neuron communication via the C3/C3aR pathway in PD pathogenesis, highlighting its potential as a therapeutic target.

Astrocytes and microglia in multiple sclerosis and neuromyelitis optica

Multiple sclerosis and neuromyelitis optica are autoimmune neurodegenerative diseases primarily targeting myelin sheath and neuroglia. In multiple sclerosis, autoantibodies destroy oligodendrocytes and myelin, which underlies primary neurologic symptoms. Focal damage to myelin triggers reactive astrogliosis and microgliosis, which contribute to and to a large extent define the disease progression. In neuromyelitis optica, autoantibodies against water channel aquaporin 4 (AQP4), which are localized at astrocytic endfeet mediate damage of the glia limitans thus facilitating infiltration of blood-borne molecules and cells that propagate the damage to nerves and neurons. This primary astrocytopathy recruits microglia, which contribute to the neuroinflammatory response. Neuroglial cells therefore are potential targets for cell-specific therapies.

Double negative T cells promote surgery-induced neuroinflammation, microglial engulfment and cognitive dysfunction via the IL-17/CEBPβ/C3 pathway in adult mice

CD3(+) CD4(-) CD8(-) double negative T cells (DNTs) manifest themselves in autoimmune diseases and associated inflammation. In the central nervous system, the increased presence of DNTs is associated with the progression of neurological conditions and brain injury. Active DNTs that produce IL-17 have been regarded as a pro-inflammatory phenotype. The IL-17 signaling pathway mediates neuroinflammatory responses by inducing glial activation and producing inflammatory factors. Neuroinflammation is considered integral to the pathogenesis of perioperative neurocognitive disorders (PNDs), commonly developed after surgery in susceptible patients. We and others have demonstrated a significant role for complement C3 in surgery-induced neuroinflammation and cognitive impairment but the regulatory mechanisms for this remain unexplored. We hypothesized that surgery induces DNT infiltration into the CNS that in turn upregulates complement C3 expression and this causes changes that contribute to cognitive impairment. Using an adult murine abdominal surgery model, we investigated perioperative changes in cognitive performance, quantifying the presence of T cell subsets and phenotype, IL-17 signaling pathway activation, glial cell activation and C3 expression in the brain. Postoperative IL-17 specific inhibitor GSK2981278 administration or preoperatively conditional CEBPβ knock-down by AAV9 viral vector were then applied to evaluate the effect of inhibiting IL-17 signaling pathway on postoperative C3 expression and cognitive performance. The results showed an increased hippocampus infiltration of DNTs with augmented IL-17 production, along with C3 upregulation and cognitive impairment. Both inhibition of IL-17 or knock-down of CEBPβ significantly suppressed C3 expression, synaptic engulfment by microglia and attenuated cognitive impairment. These findings indicate that DNTs promote postoperative neuroinflammation and cognitive impairment via the IL-17/CEBPβ/C3 pathway and targeting this IL-17 axis could be a potential therapeutic strategy to ameliorate postoperative neuroinflammation and cognitive impairment.

C3/C3aR Bridges Spinal Astrocyte-Microglia Crosstalk and Accelerates Neuroinflammation in Morphine-Tolerant Rats

AIMS

Communication within glial cells acts as a pivotal intermediary factor in modulating neuroimmune pathology. Meanwhile, an increasing awareness has emerged regarding the detrimental role of glial cells and neuroinflammation in morphine tolerance (MT). This study investigated the influence of crosstalk between astrocyte and microglia on the evolution of morphine tolerance.

METHODS

Sprague-Dawley rats were intrathecally treated with morphine twice daily for 9 days to establish morphine-tolerant rat model. Tail-flick latency test was performed to identify the analgesic effect of morphine. The role of microglia, astrocyte and C3-C3aR axis in morphine tolerance were elucidated by real-time quantitative polymerase chain reaction, Western blot, and immunofluorescence.

RESULTS

Chronic morphine treatment notably promoted the activation of microglia, upregulated the production of proinflammatory mediators (interleukin-1 alpha (IL-1α), tumor necrosis factor alpha (TNFα), and complement component 1q (C1q)). Simultaneously, it programed astrocytes to a pro-inflammatory phenotype (A1), which mainly expresses complement 3 (C3) and serping1. PLX3397 (a colony-stimulating factor 1 receptor (CSF1R) inhibitor), Compstain (a C3 inhibitor) and SB290157(a C3aR antagonist) could reverse the above pathological process and alleviate morphine tolerance to different extents.

CONCLUSION

Our findings identify C3-C3aR axis as an amplifier of microglia-astrocyte crosstalk, neuroinflammation and a node for therapeutic intervention in morphine tolerance.

Alzheimer's disease and the immune system: A comprehensive overview with a focus on B cells, humoral immunity, and immunotherapy

Alzheimer's disease (AD) is a complex neurodegenerative disorder and the major cause of dementia. Amyloid-β (Aβ) and tau aggregation, mitochondrial dysfunction, and microglial dysregulation are key contributors to AD pathogenesis. Impairments in the blood-brain barrier have unveiled the contribution of the immune system, particularly B cells, in AD pathology. B cells, a crucial component of adaptive immunity, exhibit diverse functions, including antigen presentation and antibody production. While their role in neuroinflammatory disorders has been well-documented, their specific function in AD lacks adequate data. This review examines the dual role of the B cells and humoral immunity in modulating brain inflammation in AD and explores recent advancements in passive and active immunotherapeutic strategies targeting AD pathobiology. We summarize preclinical and clinical studies investigating B cell frequency, altered antibody levels, and their implications in neuroinflammation and immunotherapy. Notably, B cells demonstrate protective and pathological roles in AD, influencing neurodegeneration through antibody-mediated clearance of toxic aggregates and inflammatory activation inflammation. Passive immunotherapies targeting Aβ have shown potential in reducing amyloid plaques, while active immunotherapies are emerging as promising strategies, requiring further validation. Understanding the interplay between B cells, humoral immunity, microglia, and mitochondrial dysfunction is critical to unraveling AD pathogenesis. Their dual nature in disease progression underscores the need for precise therapeutic interventions to optimize immunotherapy outcomes and mitigate neuroinflammation effectively.

Redox regulation, protein S-nitrosylation, and synapse loss in Alzheimer's and related dementias

Redox-mediated posttranslational modification, as exemplified by protein S-nitrosylation, modulates protein activity and function in both health and disease. Here, we review recent findings that show how normal aging, infection/inflammation, trauma, environmental toxins, and diseases associated with protein aggregation can each trigger excessive nitrosative stress, resulting in aberrant protein S-nitrosylation and hence dysfunctional protein networks. These redox reactions contribute to the etiology of multiple neurodegenerative disorders as well as systemic diseases. In the CNS, aberrant S-nitrosylation reactions of single proteins or, in many cases, interconnected networks of proteins lead to dysfunctional pathways affecting endoplasmic reticulum (ER) stress, inflammatory signaling, autophagy/mitophagy, the ubiquitin-proteasome system, transcriptional and enzymatic machinery, and mitochondrial metabolism. Aberrant protein S-nitrosylation and transnitrosylation (transfer of nitric oxide [NO]-related species from one protein to another) trigger protein aggregation, neuronal bioenergetic compromise, and microglial phagocytosis, all of which contribute to the synapse loss that underlies cognitive decline in Alzheimer's disease and related dementias.

Progress of Astrocyte-Neuron Crosstalk in Central Nervous System Diseases

Neurons are the primary cells responsible for information processing in the central nervous system (CNS). However, they are vulnerable to damage and insult in a variety of neurological disorders. As the most abundant glial cells in the brain, astrocytes provide crucial support to neurons and participate in synapse formation, synaptic transmission, neurotransmitter recycling, regulation of metabolic processes, and the maintenance of the blood-brain barrier integrity. Though astrocytes play a significant role in the manifestation of injury and disease, they do not work in isolation. Cellular interactions between astrocytes and neurons are essential for maintaining the homeostasis of the CNS under both physiological and pathological conditions. In this review, we explore the diverse interactions between astrocytes and neurons under physiological conditions, including the exchange of neurotrophic factors, gliotransmitters, and energy substrates, and different CNS diseases such as Alzheimer's disease, Parkinson's disease, stroke, traumatic brain injury, and multiple sclerosis. This review sheds light on the contribution of astrocyte-neuron crosstalk to the progression of neurological diseases to provide potential therapeutic targets for the treatment of neurological diseases.

Dual inhibition of butyrylcholinesterase and p38α mitogen-activated protein kinase: A new approach for the treatment of Alzheimer's disease

The simultaneous targeting of neuroinflammation and cholinergic hypofunction, the key pathological changes in Alzheimer's disease (AD), is not addressed by drugs currently in clinical trials, highlighting a critical therapeutic gap. We propose that dual-acting small molecules that inhibit butyrylcholinesterase (BChE) and mitogen-activated protein kinase p38α (p38α MAPK) represent a novel strategy to combat AD. This hypothesis is supported by cellular and animal studies as well as in silico modelling showing that it is possible to act simultaneously on both enzymes. Amyloid beta (Aβ) plaques trigger a pro-inflammatory microglial response that overactivates p38α MAPK, leading to increased Aβ synthesis, tau hyperphosphorylation, and altered synaptic plasticity. Overactivated microglia exacerbate neuroinflammation and cholinergic degeneration, ultimately leading to cognitive impairment. Structural similarities between the binding sites of BChE and p38α MAPK provide a promising basis for the development of dual inhibitors that could alleviate AD symptoms and address the underlying pathology.

Transcriptome Analysis Reveals Dynamic Microglial-Induced A1 Astrocyte Reactivity via C3/C3aR/NF-κB Signaling After Ischemic Stroke

Microglia and astrocytes are key players in neuroinflammation and ischemic stroke. A1 astrocytes are a subtype of astrocytes that are extremely neurotoxic and quickly kill neurons. Although the detrimental A1 astrocytes are present in many neurodegenerative diseases and are considered to accelerate neurodegeneration, their role in the pathophysiology of ischemic stroke is poorly understood. Here, we combined RNA-seq, molecular and immunological techniques, and behavioral tests to investigate the role of A1 astrocytes in the pathophysiology of ischemic stroke. We found that astrocyte phenotypes change from a beneficial A2 type in the acute phase to a detrimental A1 type in the chronic phase following ischemic stroke. The activated microglial IL1α, TNF, and C1q prompt commitment of A1 astrocytes. Inhibition of A1 astrocytes induction attenuates reactive gliosis and ameliorates morphological and functional defects following ischemic stroke. The crosstalk between astrocytic C3 and microglial C3aR contributes to the formation of A1 astrocytes and morphological and functional defects. In addition, NF-κB is activated following ischemic stroke and governs the formation of A1 astrocytes via direct targeting of inflammatory cytokines and chemokines. Taken together, we discovered that A2 astrocytes and A1 astrocytes are enriched in the acute and chronic phases of ischemic stroke respectively, and that the C3/C3aR/NF-κB signaling leads to A1 astrocytes induction. Therefore, the C3/C3aR/NF-κB signaling is a novel therapeutic target for ischemic stroke treatment.

Brain-immune interactions: implication for cognitive impairments in Alzheimer's disease and autoimmune disorders

Progressive memory loss and cognitive dysfunction, encompassing deficits in learning, memory, problem solving, spatial reasoning, and verbal expression, are characteristics of Alzheimer's disease and related dementia. A wealth of studies has described multiple roles of the immune system in the development or exacerbation of dementia. Individuals with autoimmune disorders can also develop cognitive dysfunction, a phenomenon termed "autoimmune dementia." Together, these findings underscore the pivotal role of the neuroimmune axis in both Alzheimer's disease and related dementia and autoimmune dementia. The dynamic interplay between adaptive and innate immunity, both in and outside the brain, significantly affects the etiology and progression of these conditions. Multidisciplinary research shows that cognitive dysfunction arises from a bidirectional relationship between the nervous and immune systems, though the specific mechanisms that drive cognitive impairments are not fully understood. Intriguingly, this reciprocal regulation occurs at multiple levels, where neuronal signals can modulate immune responses, and immune system-related processes can influence neuronal viability and function. In this review, we consider the implications of autoimmune responses in various autoimmune disorders and Alzheimer's disease and explore their effects on brain function. We also discuss the diverse cellular and molecular crosstalk between the brain and the immune system, as they may shed light on potential triggers of peripheral inflammation, their effect on the integrity of the blood-brain barrier, and brain function. Additionally, we assess challenges and possibilities associated with developing immune-based therapies for the treatment of cognitive decline.

Complement Molecule C3a Exacerbates Early Brain Injury After Subarachnoid Hemorrhage by Inducing Neuroinflammation Through the C3aR-ERK-P2X7-NLRP3 Inflammasome Signaling Axis

An important aspect of the pathophysiology of early brain damage (EBI) after subarachnoid hemorrhage (SAH) is inflammasome-mediated neuroinflammation. It has been demonstrated that C3aR activation exacerbates neuronal damage in a number of neurological disorders. This study aims to explore the role of C3a in activating the NLRP3 inflammasome and exacerbating neuroinflammation after SAH. Preprocessing of RNA-seq transcriptome datasets using bioinformatics analysis, and screening of differentially expressed genes between SAH patients and healthy individuals from the GEO database. Internal carotid artery puncture was performed to establish SAH models in rats and mice. SAH grading, neurological scoring, brain water content, behavioral analysis, and assessments using ELISA, Western blot, immunofluorescence, and immunohistochemistry were conducted. An in vitro model of SAH was induced in BV-2 cells treated with heme (200 μM). The mechanism of C3a in post-SAH neuroinflammation was studied by interfering with and inhibiting C3aR. Results showed that the expression of C3aR was upregulated in the GEO dataset (serum of SAH patients) and identified as a key differential gene in SAH. Further, elevated levels of C3a were found in the cerebrospinal fluid of clinically collected SAH patients. In the cerebral cortex and/or serum of SAH rats, expression of C3a, IL-1β, IL-6, TNF-α, CD11b, and Ki67 were significantly increased, while IL-10 was significantly decreased. Correlation analysis revealed that C3a showed negative correlation with IL-10 and positive correlation with IL-1β, IL-6, TNF-α, CD11b, and Ki67. After stimulation with heme, protein levels of C3a increased in BV-2 cells. Interfering with C3aR significantly reduced LDH release, IL-1β secretion, Caspase1 activation, levels of NLRP3 expression and ASC oligomerization, and ATP release after heme stimulation in BV-2. Subsequently, the addition of inhibitors of ERK1/2 phosphorylation demonstrated that C3a promotes ATP efflux by activating ERK1/2 phosphorylation, thereby activating P2X7. Further addition of JNJ-55308942 (a P2X7R antagonist) revealed that C3a activated the NLRP3 inflammasome via P2X7. Finally, administering SB290157 (a C3aR inhibitor) in vivo effectively alleviated brain edema, reduced mortality, improved Garcia score, ameliorated motor dysfunction, and suppressed inflammation and NLRP3 inflammasome activation in mice after SAH. Overall, C3a exacerbates EBI-associated NLRP3 inflammasome and neuroinflammation via the C3aR-ERK-P2X7 pathway after SAH. Inhibiting C3aR may serve as a one possible treatment approach to alleviate SAH after EBI.

Activation of astrocytic NMDA receptors counteracted Aβ-induced reduction of BDNF and elevation of GFAP and complement 3 in the hippocampal astrocytes

N-methyl-D-aspartate receptors (NMDARs) play a crucial role in mediating Amyloid-β (Aβ) synaptotoxicity. Our previous studies have demonstrated an opposite (neuroprotection and neurotoxicity) effect of activating astrocytic and neuronal NMDARs with higher dose (10 μM) of NMDA, an agonist of NMDARs. By contrast, activating neuronal or astrocyitc NMDARs with lower dose (1 μM) of NMDA both exerts neuroprotective effect in Aβ-induced neurotoxicity. However, the underlying mechanism of activating astrocytic NMDARs with lower dose of NMDA to protect against Aβ neurotoxicity remains unclear. Based on our previous related work, in this study, using a co-cultured cell model of primary hippocampal neurons and astrocytes, we further investigated the possible factors involved in 1 μM of NMDA activating astrocytic NMDARs to oppose Aβ-induced synaptotoxicity. Our results showed that activation of astrocytic NMDARs by 1 μM NMDA rescued Aβ-induced reduction of brain-derived neurotrophic factor (BDNF), and inhibited Aβ-induced increase of GFAP, complement 3 (C3) and activation of NF-κB. Furthermore, blockade of astrocytic GluN2A with TCN201 abrogated the ability of 1 μM NMDA to counteract the effects of Aβ decreasing BDNF, and increasing GFAP, C3 and activation of NF-κB. These findings suggest that activation of astrocytic NMDARs protect against Aβ-induced synaptotoxicity probably through elevating BDNF and suppressing GFAP and C3. Our present research provides valuable insights for elucidating the underlying mechanism of astrocytic NMDARs activation resisting the toxic effects of Aβ.

CD4+ T cell-associated cytokines induce a chronic pro-inflammatory phenotype in induced pluripotent stem cell-derived midbrain astrocytes

Astrocytes are mediators of homeostasis but contribute to neuroinflammation in Parkinson's disease (PD). Mounting evidence suggests involvement of peripheral immune cells in PD pathogenesis. Therefore, this study aimed to determine the potential role of peripheral immune secreted cytokines in modulating midbrain astrocyte reactivity. Human iPSC-derived midbrain astrocytes were exposed to 5% and 10% CD4+ T cell conditioned media (CD4CM) for 24 h, 72 h, and 7 days to assess chronic exposure. Additionally, astrocytes were exposed to the Th17 cell cytokine, IL-17A (10 ng/mL), alone and in combination with TNF-α (0.3 ng/mL) to assess potential synergistic effects of both cytokines at 24 h, 72 h, and 7 days. CD4CM induced acute and chronic alterations in midbrain astrocytes. Increased NFκB translocation to the nucleus, increased expression of the pro-inflammatory genes, IL-1β, CXCL10 at 24 h, C3, LCN2, IL-6 at 24 and 48 h, as well as an increase in their release of pro-inflammatory cytokines IL-6 and CXCL10 at both these time points were observed. A synergistic response to the combination of IL-17A and TNF-α on increasing inflammatory gene expression and cytokine release occurred. IL-17A and TNF-α increased intensity of S100β at 24 h, decreased nuclear area and increased circularity of astrocytes at 72 h. A synergistic effect on γH2AX intensity at 72 h and an increase in LDH release at 7 days was observed. Our results demonstrate that IL-17A and TNF-α act synergistically, enhancing midbrain astrocyte reactivity to a similar degree as CD4CM. This highlights the importance of the peripheral immune secreted cytokines in increasing the reactivity status of midbrain astrocytes, implicating their role in PD.

Edaravone Dexborneol provides neuroprotective effect by inhibiting neurotoxic activation of astrocytes through inhibiting NF-κB signaling in cortical ischemia

Edaravone Dexborneol (EDB), comprised of edaravone and (+)- bornel, has been demonstrated to have synergistic effects of antioxidant and anti-inflammatory, which makes it to be applied for stroke as a protectant. However, the underlying mechanism of neuroprotection of EDB has not been fully elucidated. Increasing evidence has shown that neurotoxic A1 astrocytes were closely related to neuronal death after cerebral ischemia. However, whether EDB could provide neuroprotection by modulating the activation of astrocytes has not yet been elucidated. The present study aimed to explore whether EDB afforded neuroprotection by modulating A1 polarization of astrocytes and the down-stream signaling after cerebral ischemia. We first validated the neuroprotective effects of EDB in mice suffering focal cerebral ischemia via evaluating behavioral test, infarct volumes and neuronal survival. As for the down-stream signaling, our data further showed that EDB alleviated neuronal death by suppressing activation of neurotoxic A1 astrocytes via inhibition of NF-κB signaling pathway in vitro. Additionally, administration of EDB reduced the number of A1 reactive astrocytes in mice of focal cerebral ischemia. The above findings demonstrated that EDB provided neuroprotective effect by inhibiting neurotoxic activation of A1 astrocytes in animal model of cerebral ischemia, which indicated that EDB-mediated phenotypic regulation of astrocytes is a potential research direction to promote neurological recovery in central nervous system (CNS) diseases.

Botch improves cognitive impairment after cerebral ischemia associated with microglia-induced A1-type astrocyte activation

Vascular cognitive impairment (VCI) is a clinical syndrome that arises from cerebrovascular issues and associated risk factors, resulting in difficulties in at least one area of cognitive function. VCI has emerged as the second most prevalent type of dementia following Alzheimer's disease, yet there is no effective clinical treatment. Botch, an endogenous Notch1 antagonist, demonstrates neuroprotective effects by inhibiting neuroinflammatory responses mediated through the Notch pathway. While its role in stroke-induced neuroinflammation is well-established, its involvement in VCI remains largely unexplored. This study investigates the role and potential mechanisms of Botch in a rat model of cognitive impairment caused by bilateral common carotid artery occlusion (BCCAO). Firstly, we observed that Botch levels were down-regulated in BCCAO rats, which correlated with increased release of inflammatory cytokines and neuronal damage. Microglia in BCCAO rats released interleukin-1α (IL-1α), tumor necrosis factor-α (TNF-α), and complement component 1q (C1q), leading to the activation of neurotoxic C3+ A1 reactive astrocytes. Then, the down-regulation of Botch exacerbated microglia-mediated inflammation, activated C3+ A1 astrocytes, worsened neuronal damage, and led to a decline in cognitive function. Conversely, the re-expression of Botch alleviated C3+ astrocyte activation, inhibited neuronal damage, and improved mental function. In conclusion, Botch plays a crucial role in inhibiting neuroinflammation induced by type A1 reactive astrocytes. It achieves this by blocking the activation of microglia triggered by the Notch pathway. Ultimately, it inhibits neuronal damage to play a neuroprotective role. These findings suggest that Botch may represent a novel potential target for treating VCI.

Prevention and Treatment Strategies for Alzheimer's Disease: Focusing on Microglia and Astrocytes in Neuroinflammation

Alzheimer's disease (AD) is a fatal neurodegenerative disease characterized by its insidious onset and progressive development, making it the most common form of dementia. Despite its prevalence, the exact causes and mechanisms responsible for AD remain unclear. Recent studies have highlighted that inflammation in the central nervous system (CNS) plays a crucial role in both the initiation and progression of AD. Neuroinflammation, an immune response within the CNS triggered by glial cells in response to various stimuli, such as nerve injury, infection, toxins, or autoimmune reactions, has emerged as a significant factor alongside amyloid deposition and neurofibrillary tangles (NFTs) commonly associated with AD. This article aims to provide an overview of the most recent research regarding the involvement of neuroinflammation in AD, with a particular focus on elucidating the specific mechanisms involving microglia and astrocytes. By exploring these intricate processes, a new theoretical framework can be established to further probe the impact of neuroinflammation on the development and progression of AD. Through a deeper understanding of these underlying mechanisms, potential targets for therapeutic interventions and novel treatment strategies can be identified in the ongoing battle against AD.

The Dual Role of Amyloid Beta-Peptide in Oxidative Stress and Inflammation: Unveiling Their Connections in Alzheimer's Disease Etiopathology

Alzheimer's disease (AD) is a progressive neurodegenerative disease, and it is currently the seventh leading cause of death worldwide. It is characterized by the extracellular aggregation of the amyloid β-peptide (Aβ) into oligomers and fibrils that cause synaptotoxicity and neuronal death. Aβ exhibits a dual role in promoting oxidative stress and inflammation. This review aims to unravel the intricate connection between these processes and their contribution to AD progression. The review delves into oxidative stress in AD, focusing on the involvement of metals, mitochondrial dysfunction, and biomolecule oxidation. The distinct yet overlapping concept of nitro-oxidative stress is also discussed, detailing the roles of nitric oxide, mitochondrial perturbations, and their cumulative impact on Aβ production and neurotoxicity. Inflammation is examined through astroglia and microglia function, elucidating their response to Aβ and their contribution to oxidative stress within the AD brain. The blood-brain barrier and oligodendrocytes are also considered in the context of AD pathophysiology. We also review current diagnostic methodologies and emerging therapeutic strategies aimed at mitigating oxidative stress and inflammation, thereby offering potential treatments for halting or slowing AD progression. This comprehensive synthesis underscores the pivotal role of Aβ in bridging oxidative stress and inflammation, advancing our understanding of AD and informing future research and treatment paradigms.

JNK inhibitor and ferroptosis modulator as possible therapeutic modalities in Alzheimer disease (AD)

Alzheimer disease (AD) is among the most prevalent neurodegenerative diseases globally, marked by cognitive and behavioral disruptions. Ferroptosis is a form of controlled cell death characterized by intracellular iron accumulation associated with lipid peroxide formation, which subsequently promotes AD initiation and progression. We hypothesized that targeting the ferroptosis pathway may help in AD management. Therefore, our study aimed to evaluate the potential neuroprotective effect of the antifungal Ciclopirox olamine (CPX-O) that acts through iron chelation. We employed CPX-O separately or in combination with the JNK inhibitor (SP600125) in a mice model of AlCl3-induced AD. Animals underwent examination for behavioral, biochemical, histological, and immunohistochemical findings. Our results revealed that AlCl3 was associated with disruptions in learning and memory parameters, neuronal degeneration in the hippocampus, increased immunoreactivity of amyloid-β and tau proteins, a significant rise in iron, nitric oxide (NO), malondialdehyde (MDA), JNK, and P53 levels, along with the significant decrease in glutathione peroxidase activity. Interestingly, the administration of CPX-O alone or in combination with SP600125 in the AlCl3-induced AD model caused an improvement in the previously described examination findings. Therefore, CPX-O may be a promising candidate for AD treatment, and future clinical trials will be required to confirm these preclinical findings.

Tryptophan Metabolism in Alzheimer's Disease with the Involvement of Microglia and Astrocyte Crosstalk and Gut-Brain Axis

Alzheimer's disease (AD) is an age-dependent neurodegenerative disease characterized by extracellular Amyloid Aβ peptide (Aβ) deposition and intracellular Tau protein aggregation. Glia, especially microglia and astrocytes are core participants during the progression of AD and these cells are the mediators of Aβ clearance and degradation. The microbiota-gut-brain axis (MGBA) is a complex interactive network between the gut and brain involved in neurodegeneration. MGBA affects the function of glia in the central nervous system (CNS), and microbial metabolites regulate the communication between astrocytes and microglia; however, whether such communication is part of AD pathophysiology remains unknown. One of the potential links in bilateral gut-brain communication is tryptophan (Trp) metabolism. The microbiota-originated Trp and its metabolites enter the CNS to control microglial activation, and the activated microglia subsequently affect astrocyte functions. The present review highlights the role of MGBA in AD pathology, especially the roles of Trp per se and its metabolism as a part of the gut microbiota and brain communications. We (i) discuss the roles of Trp derivatives in microglia-astrocyte crosstalk from a bioinformatics perspective, (ii) describe the role of glia polarization in the microglia-astrocyte crosstalk and AD pathology, and (iii) summarize the potential of Trp metabolism as a therapeutic target. Finally, we review the role of Trp in AD from the perspective of the gut-brain axis and microglia, as well as astrocyte crosstalk, to inspire the discovery of novel AD therapeutics.

The role of the gut microbiome in the regulation of astrocytes in Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder and is the most common cause of dementia. AD is characterized pathologically by proteinaceous aggregates composed of amyloid beta (Aβ) and tau as well as progressive neurodegeneration. Concurrently with the buildup of protein aggregates, a strong neuroinflammatory response, in the form of reactive astrocytosis and microgliosis, occurs in the AD brain. It has recently been shown that the gut microbiome (GMB), composed of trillions of bacteria in the human intestine, can regulate both reactive astrocytosis and microgliosis in the context of both amyloidosis and tauopathy. Many studies have implicated microglia in these processes. However, growing evidence suggests that interactions between the GMB and astrocytes have a much larger role than previously thought. In this review, we summarize evidence regarding the gut microbiome in the control of reactive astrocytosis in AD.

Myeloid ectopic viral integration site 2 accelerates the progression of Alzheimer's disease

Amyloid plaques, a major pathological hallmark of Alzheimer's disease (AD), are caused by an imbalance between the amyloidogenic and non-amyloidogenic pathways of amyloid precursor protein (APP). BACE1 cleavage of APP is the rate-limiting step for amyloid-β production and plaque formation in AD. Although the alteration of BACE1 expression in AD has been investigated, the underlying mechanisms remain unknown. In this study, we determined MEIS2 was notably elevated in AD models and AD patients. Alterations in the expression of MEIS2 can modulate the levels of BACE1. MEIS2 downregulation improved the learning and memory retention of AD mice and decreased the number of amyloid plaques. MEIS2 binds to the BACE1 promoter, positively regulates BACE1 expression, and accelerates APP amyloid degradation in vitro. Therefore, our findings suggest that MEIS2 might be a critical transcription factor in AD, since it regulates BACE1 expression and accelerates BACE1-mediated APP amyloidogenic cleavage. MEIS2 is a promising early intervention target for AD treatment.

Progression of mesenchymal stem cell regulation on imbalanced microenvironment after spinal cord injury

Spinal cord injury (SCI) results in significant neural damage and inhibition of axonal regeneration due to an imbalanced microenvironment. Extensive evidence supports the efficacy of mesenchymal stem cell (MSC) transplantation as a therapeutic approach for SCI. This review aims to present an overview of MSC regulation on the imbalanced microenvironment following SCI, specifically focusing on inflammation, neurotrophy and axonal regeneration. The application, limitations and future prospects of MSC transplantation are discussed as well. Generally, a comprehensive perspective is provided for the clinical translation of MSC transplantation for SCI.

LPAR6 Participates in Neuropathic Pain by Mediating Astrocyte Cells via ROCK2/NF-κB Signal Pathway

Neuropathic pain (NPP) is a common type of chronic pain. Glial cells, including astrocytes (AS), are believed to play an important role in the progression of NPP. AS cells can be divided into various types based on their expression profiles, among which A1 and A2 types have clear functions. A1-type AS cells are neurotoxic, while A2-type AS cells exert neuroprotective functions. Some types of lysophosphatidic acid receptors (LPAR) have been shown to play a role in NPP. However, it remains unclear how AS cells and LPAR6 affect the occurrence and progression of NPP. In this study, we established a mouse model of chronic constriction injury (CCI) to simulate NPP. It was found that the expression of LPAR6 in AS cells of the spinal dorsal horn was increased in the CCI model, and the thresholds of mechanical and thermal pain were elevated after knocking out LPAR6, indicating that LPAR6 and AS cells participated in the occurrence of NPP. The experiment involved culturing primary AS cells and knocking down LPAR6 by Lentivirus. The results showed that the NF-κB signal pathway was activated and the number of A1-type AS cells increased in the CCI model. However, LPAR6 knockdown inhibited the NF-κB signal pathway and A1-type AS cells. The results of the mRNA sequencing and immunoprecipitation test indicate an interaction between LPAR6 and ROCK2. Inhibiting ROCK2 by Y-27632 increased mechanical and thermal pain thresholds and alleviated NPP at the molecular level. The study presents evidence that LPAR6 activates the NF-κB pathway through ROCK2 and contributes to the progression of NPP by increasing A1-type AS and decreasing A2-type AS. This suggests that LPAR6 could be a potential therapeutic target for alleviating NPP. Clinical applications that are successful can offer new therapeutic options, enhance the quality of life for patients, and potentially uncover new mechanisms for pain modulation.

Diverse signaling mechanisms and heterogeneity of astrocyte reactivity in Alzheimer's disease

Alzheimer's disease (AD) affects various brain cell types, including astrocytes, which are the most abundant cell types in the central nervous system (CNS). Astrocytes not only provide homeostatic support to neurons but also actively regulate synaptic signaling and functions and become reactive in response to CNS insults through diverse signaling pathways including the JAK/STAT, NF-κB, and GPCR-elicited pathways. The advent of new technology for transcriptomic profiling at the single-cell level has led to increasing recognition of the highly versatile nature of reactive astrocytes and the context-dependent specificity of astrocyte reactivity. In AD, reactive astrocytes have long been observed in senile plaques and have recently been suggested to play a role in AD pathogenesis and progression. However, the precise contributions of reactive astrocytes to AD remain elusive, and targeting this complex cell population for AD treatment poses significant challenges. In this review, we summarize the current understanding of astrocyte reactivity and its role in AD, with a particular focus on the signaling pathways that promote astrocyte reactivity and the heterogeneity of reactive astrocytes. Furthermore, we explore potential implications for the development of therapeutics for AD. Our objective is to shed light on the complex involvement of astrocytes in AD and offer insights into potential therapeutic targets and strategies for treating and managing this devastating neurodegenerative disorder.

Complement 3a induces the synapse loss via C3aR in mitochondria-dependent NLRP3 activating mechanisms during the development and progression of Alzheimer's disease

As a central molecule in complement system (CS), complement (C) 3 is upregulated in the patients and animal models of Alzheimer's disease (AD). C3 will metabolize to iC3b and C3a. iC3b is responsible for clearing β-amyloid protein (Aβ). In this scenario, C3 exerts neuroprotective effects against the disease via iC3b. However, C3a will inhibit microglia to clear the Aβ, leading to the deposition of Aβ and impair the functions of synapses. To their effects on AD, activation of C3a and C3a receptor (C3aR) will impair the mitochondria, leading to the release of reactive oxygen species (ROS), which activates the NOD-like receptor thermal protein domain associated protein 3 (NLRP3) inflammasomes. The overloading of NLRP3 inflammasomes activate microglia, leading to the formation of inflammatory environment. The inflammatory environment will facilitate the deposition of Aβ and abnormal synapse pruning, which results in the progression of AD. Therefore, the current review will decipher the mechanisms of C3a inducing the synapse loss via C3aR in mitochondria-dependent NLRP3 activating mechanisms, which facilitates the understanding the AD.