Astrocyte-Microglia Cross Talk through Complement Activation Modulates Amyloid Pathology in Mouse Models of Alzheimer's Disease

Neuroinflammation: An Oligodendrocentric View

Chronic neuroinflammation, driven by central nervous system (CNS)-resident astrocytes and microglia, as well as infiltration of the peripheral immune system, is an important pathologic mechanism across a range of neurologic diseases. For decades, research focused almost exclusively on how neuroinflammation impacted neuronal function; however, there is accumulating evidence that injury to the oligodendrocyte lineage is an important component for both pathologic and clinical outcomes. While oligodendrocytes are able to undergo an endogenous repair process known as remyelination, this process becomes inefficient and usually fails in the presence of sustained inflammation. The present review focuses on our current knowledge regarding activation of the innate and adaptive immune systems in the chronic demyelinating disease, multiple sclerosis, and provides evidence that sustained neuroinflammation in other neurologic conditions, such as perinatal white matter injury, traumatic brain injury, and viral infections, converges on oligodendrocyte injury. Lastly, the therapeutic potential of targeting the impact of inflammation on the oligodendrocyte lineage in these diseases is discussed.

GABA-dependent microglial elimination of inhibitory synapses underlies neuronal hyperexcitability in epilepsy

Neuronal hyperexcitability is a common pathophysiological feature of many neurological diseases. Neuron-glia interactions underlie this process but the detailed mechanisms remain unclear. Here, we reveal a critical role of microglia-mediated selective elimination of inhibitory synapses in driving neuronal hyperexcitability. In epileptic mice of both sexes, hyperactive inhibitory neurons directly activate surveilling microglia via GABAergic signaling. In response, these activated microglia preferentially phagocytose inhibitory synapses, disrupting the balance between excitatory and inhibitory synaptic transmission and amplifying network excitability. This feedback mechanism depends on both GABA-GABAB receptor-mediated microglial activation and complement C3-C3aR-mediated microglial engulfment of inhibitory synapses, as pharmacological or genetic blockage of both pathways effectively prevents inhibitory synapse loss and ameliorates seizure symptoms in mice. Additionally, putative cell-cell interaction analyses of brain tissues from males and females with temporal lobe epilepsy reveal that inhibitory neurons induce microglial phagocytic states and inhibitory synapse loss. Our findings demonstrate that inhibitory neurons can directly instruct microglial states to control inhibitory synaptic transmission through a feedback mechanism, leading to the development of neuronal hyperexcitability in temporal lobe epilepsy.

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.

The Role of Neuroinflammation and Network Anomalies in Drug-Resistant Epilepsy

Epilepsy affects over 50 million people worldwide. Drug-resistant epilepsy (DRE) accounts for up to a third of these cases, and neuro-inflammation is thought to play a role in such cases. Despite being a long-debated issue in the field of DRE, the mechanisms underlying neuroinflammation have yet to be fully elucidated. The pro-inflammatory microenvironment within the brain tissue of people with DRE has been probed using single-cell multimodal transcriptomics. Evidence suggests that inflammatory cells and pro-inflammatory cytokines in the nervous system can lead to extensive biochemical changes, such as connexin hemichannel excitability and disruption of neurotransmitter homeostasis. The presence of inflammation may give rise to neuronal network abnormalities that suppress endogenous antiepileptic systems. We focus on the role of neuroinflammation and brain network anomalies in DRE from multiple perspectives to identify critical points for clinical application. We hope to provide an insightful overview to advance the quest for better DRE treatments.

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.

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.

The anti-inflammatory drug Montelukast ameliorates cognitive deficits by rescuing the inflammatory levels in young AD animal models

Neuroinflammation precedes the clinical symptoms onset of Alzheimer's disease (AD) by decades. However, the anti-inflammatory drugs were not always effective at all stages of the disease. Here, using the fly and mouse AD models, we evaluated the effects of anti-inflammatory drugs on inflammatory-related factors and the proinflammatory cytokines at different ages of AD animals. We also performed behavioral tests to evaluate the cognitive aspects of AD. Combined with the bioinformatics analysis, we would like to exhibit a better understanding of AD. Based on the previous studies and reanalysis of published database, we found aged AD animals might better represent the inflammatory status of symptomatic AD. Our results showed that mRNA levels of antimicrobial peptides (AMPs) were highly expressed in 10-day-old AD flies, while no significant difference was observed in 40-day-old AD. In aged APP/PS1 mice (22.5 months), inflammatory-related factors NF-κB, IBA1, and the mRNA levels of proinflammatory cytokines Il-1β and Il-6 were not differentially expressed. In contrast, a significant increase was observed in 7.5-month-old APP/PS1 mice. Moreover, the anti-inflammatory drug Montelukast (MON) did not ameliorate the inflammatory and cognitive defects in 22.5-month-old aged mice but showed a rescue effect in 7.5-month-old young APP/PS1 mice. Altogether, our study demonstrates the different inflammatory status might lead to variations of anti-inflammatory drug efficacy, which helps to clarify the importance of considering the pathological stage of the disease when administering treatment.

Neuroimmune crosstalk in chronic neuroinflammation: microglial interactions and immune modulation

Neuroinflammation is a fundamental feature of many chronic neurodegenerative diseases, where it contributes to disease onset, progression, and severity. This persistent inflammatory state arises from the activation of innate and adaptive immune responses within the central nervous system (CNS), orchestrated by a complex interplay of resident immune cells, infiltrating peripheral immune cells, and an array of molecular mediators such as cytokines, chemokines, and extracellular vesicles. Among CNS-resident cells, microglia play a central role, exhibiting a dynamic spectrum of phenotypes ranging from neuroprotective to neurotoxic. In chronic neurodegenerative diseases, sustained microglial activation often leads to the amplification of inflammatory cascades, reinforcing a pathogenic cycle of immune-mediated damage. Intercellular communication within the inflamed CNS is central to the persistence and progression of neuroinflammation. Microglia engage in extensive crosstalk with astrocytes, neurons, oligodendrocytes, and infiltrating immune cells, shaping both local and systemic inflammatory responses. These interactions influence key processes such as synaptic pruning, phagocytosis, blood-brain barrier integrity, and cytokine-mediated signaling. Understanding the mechanisms of cell-cell signaling in this context is critical for identifying therapeutic strategies to modulate the immune response and restore homeostasis. This review explores the key players in CNS neuroinflammation, with a focus on the role of microglia, the molecular pathways underlying intercellular communication, and potential therapeutic approaches to mitigate neuroinflammatory damage in chronic neurodegenerative diseases.

Astrocyte and oligodendrocyte pathology in Alzheimer's disease

Astrocytes and oligodendrocytes, once considered passive support cells, are now recognized as active participants in the pathogenesis of Alzheimer's disease. Emerging evidence highlights the critical role that these glial cells play in the pathological features of Alzheimer's, including neuroinflammation, excitotoxicity, synaptic dysfunction, and myelin degeneration, which contribute to neurodegeneration and cognitive decline. Here, we review the current understanding of astrocyte and oligodendrocyte pathology in Alzheimer's disease and highlight research that supports the therapeutic potential of modulating astrocyte and oligodendrocyte functions to treat 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.

Acute exposure of perchlorate on zebrafish larvae: Neurotoxicity during development

OBJECTIVE

This study aimed to assess the acute developmental toxicity of perchlorate exposure and identify its manifestation of neurotoxicity in zebrafish (Danio rerio) model.

METHODS

Zebrafish larvae were exposed to sodium perchlorate at early developmental stages and the phenotypes of various developmental abnormalities were observed and recorded. Neurodevelopmental toxicity has been studied in particular in terms of central nervous system apoptosis, peripheral motor abnormalities, and abnormal autonomic motor behavior. Samples were processed for pathological, transcriptomic, and PCR analyses.

RESULTS

Acute exposure of zebrafish larvae to perchlorate resulted in developmental toxicity in a concentration-dependent manner. Heart rate abnormality (33 %), slow blood flow (37 %), abnormal size of liver (23 %), delayed yolk absorption (70 %), and abnormal body pigmentation (100 %) were observed in the 3.83 mg/mL group. Heart edema (10 %), heart rate abnormality (60 %), slow blood flow (67 %), abnormal size of liver (77 %), delayed yolk absorption (100 %), abnormalities in intestinal morphology (30 %), abnormal body pigmentation (100 %), and shorter body length (47 %) were observed in the 4.03 mg/mL group. Developmental neurotoxicity was characterized by brain apoptosis, damage to the central nervous system (P < 0.01) and peripheral motor neurons (P < 0.0001), and reduced autonomous motor distance (P < 0.01). Transcriptomic analysis revealed that c3a.1, c5, fga, fgb, and fgg were upregulated in the complement and coagulation cascades, and the mRNA levels of c3a.1, dusp1, slc2a6, purba, and klf9 were found upregulated in PCR.

CONCLUSION

Acute perchlorate exposure on zebrafish larvae caused various developmental toxicity in a concentration-dependent manner, notably neurotoxicity. We believed the immunological and inflammatory responses were involved.

Neuroinflammation-A Crucial Factor in the Pathophysiology of Depression-A Comprehensive Review

Depression is a multifactorial psychiatric condition with complex pathophysiology, increasingly linked to neuroinflammatory processes. The present review explores the role of neuroinflammation in depression, focusing on glial cell activation, cytokine signaling, blood-brain barrier dysfunction, and disruptions in neurotransmitter systems. The article highlights how inflammatory mediators influence brain regions implicated in mood regulation, such as the hippocampus, amygdala, and prefrontal cortex. The review further discusses the involvement of the hypothalamic-pituitary-adrenal (HPA) axis, oxidative stress, and the kynurenine pathway, providing mechanistic insights into how chronic inflammation may underlie emotional and cognitive symptoms of depression. The bidirectional relationship between inflammation and depressive symptoms is emphasized, along with the role of peripheral immune responses and systemic stress. By integrating molecular, cellular, and neuroendocrine perspectives, this review supports the growing field of immunopsychiatry and lays the foundation for novel diagnostic biomarkers and anti-inflammatory treatment approaches in depression. Further research in this field holds promise for developing more effective and personalized interventions for individuals suffering from depression.

Radial astroglia cooperate with microglia to clear neuronal cell bodies during zebrafish optic tectum development

The clearance of dead cells by phagocytes is an essential component of neural development in many organisms. Microglia are the main phagocytes in the central nervous system (CNS), but the extent of participation by other glial cells remains unclear, especially under homeostatic conditions. During zebrafish optic tectum (OT) development, we observed radial astroglia forming dynamic, spherical projections from their basal processes. These projections, which we call scyllate heads, coincide with a wave of neuronal cell death in the OT. We show that scyllate heads surround the majority of dying neurons soon after phosphatidylserine exposure. However, unlike traditional phagosomes, scyllate heads persist for many hours and are rarely acidified or internalized. Instead, microglia invade scyllate heads and remove their contents for terminal degradation. Our study reveals an active role for radial astroglia in homeostatic cell clearance and cooperation between microglia and radial astroglia during zebrafish OT development.

Highlights

Optic tectum astroglia form large, dynamic projections called scyllate headsScyllate heads surround the majority of dying neurons during a wave of apoptosisScyllate heads are intermediate containers of dying cells rather than phagosomesMicroglia invade scyllate heads to remove their contents for terminal degradation.

Lysosomal acidification impairment in astrocyte-mediated neuroinflammation

Astrocytes are a major cell type in the central nervous system (CNS) that play a key role in regulating homeostatic functions, responding to injuries, and maintaining the blood-brain barrier. Astrocytes also regulate neuronal functions and survival by modulating myelination and degradation of pathological toxic protein aggregates. Astrocytes have recently been proposed to possess both autophagic activity and active phagocytic capability which largely depend on sufficiently acidified lysosomes for complete degradation of cellular cargos. Defective lysosomal acidification in astrocytes impairs their autophagic and phagocytic functions, resulting in the accumulation of cellular debris, excessive myelin and lipids, and toxic protein aggregates, which ultimately contributes to the propagation of neuroinflammation and neurodegenerative pathology. Restoration of lysosomal acidification in impaired astrocytes represent new neuroprotective strategy and therapeutic direction. In this review, we summarize pathogenic factors, including neuroinflammatory signaling, metabolic stressors, myelin and lipid mediated toxicity, and toxic protein aggregates, that contribute to lysosomal acidification impairment and associated autophagic and phagocytic dysfunction in astrocytes. We discuss the role of lysosomal acidification dysfunction in astrocyte-mediated neuroinflammation primarily in the context of neurodegenerative diseases along with other brain injuries. We then highlight re-acidification of impaired lysosomes as a therapeutic strategy to restore autophagic and phagocytic functions as well as lysosomal degradative capacity in astrocytes. We conclude by providing future perspectives on the role of astrocytes as phagocytes and their crosstalk with other CNS cells to impart neurodegenerative or neuroprotective effects.

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.

SIRT2 and ALDH1A1 as critical enzymes for astrocytic GABA production in Alzheimer's disease

BACKGROUND

Alzheimer's Disease (AD) is a neurodegenerative disease with drastically altered astrocytic metabolism. Astrocytic GABA and H2O2 are associated with memory impairment in AD and synthesized through the Monoamine Oxidase B (MAOB)-mediated multi-step degradation of putrescine. However, the enzymes downstream to MAOB in this pathway remain unidentified.

METHODS

Using transcriptomics analysis, we identified two candidate enzymes, Aldehyde Dehydrogenase 1 family member A1 (ALDH1A1) and Sirtuin 2 (SIRT2) for the steps following MAOB in the astrocytic GABA production pathway. We used immunostaining, metabolite analysis and electrophysiology, both in vitro and in vivo, to confirm the participation of these enzymes in astrocytic GABA production. We checked for the presence of SIRT2 in human AD patients as well as the mouse model APP/PS1 and finally, we selectively ablated SIRT2 in the astrocytes of APP/PS1 mice to observe its effects on pathology.

RESULTS

Immunostaining, metabolite analysis, and electrophysiology recapitulated the participation of ALDH1A1 and SIRT2 in GABA production. Inhibition of SIRT2 reduced the production of astrocytic GABA but not H2O2, a key molecule in neurodegeneration. Elevated expression of these enzymes was found in hippocampal astrocytes of AD patients and APP/PS1 mice. Astrocyte-specific gene-silencing of SIRT2 in APP/PS1 mice restored GABA production and partially improved memory function.

CONCLUSIONS

Our study is the first to identify the specific role of SIRT2 in reactive astrogliosis and determine the specific pathway and metabolic step catalyzed by the enzyme. We determine the partial, yet significant role of ALDH1A1 in this process, thereby highlighting 2 new players the astrocytic GABA production pathway. Our findings therefore, offer SIRT2 as a new tool to segregate GABA from H2O2 production, aiding future research in neurodegenerative diseases.

The Rise of Pluripotent Stem Cell-Derived Glia Models of Neuroinflammation

Neuroinflammation is a blanket term that describes the body's complex inflammatory response in the central nervous system (CNS). It encompasses a phenotype shift to a proinflammatory state, the release of cytokines, the recruitment of peripheral immune cells, and a wide variety of other processes. Neuroinflammation has been implicated in nearly every major CNS disease ranging from Alzheimer's disease to brain cancer. Understanding and modeling neuroinflammation is critical for the identification of novel therapeutic targets in the treatment of CNS diseases. Unfortunately, the translation of findings from non-human models has left much to be desired. This review systematically discusses the role of human pluripotent stem cell (hPSC)-derived glia and supporting cells within the CNS, including astrocytes, microglia, oligodendrocyte precursor cells, pericytes, and endothelial cells, to describe the state of the field and hope for future discoveries. hPSC-derived cells offer an expanded potential to study the pathobiology of neuroinflammation and immunomodulatory cascades that impact disease progression. While much progress has been made in the development of models, there is much left to explore in the application of these models to understand the complex inflammatory response in the CNS.

From Homeostasis to Neuroinflammation: Insights into Cellular and Molecular Interactions and Network Dynamics

Neuroinflammation is a complex and multifaceted process that involves dynamic interactions among various cellular and molecular components. This sophisticated interplay supports both environmental adaptability and system resilience in the central nervous system (CNS) but may be disrupted during neuroinflammation. In this article, we first characterize the key players in neuroimmune interactions, including microglia, astrocytes, neurons, immune cells, and essential signaling molecules such as cytokines, neurotransmitters, extracellular matrix (ECM) components, and neurotrophic factors. Under homeostatic conditions, these elements promote cellular cooperation and stability, whereas in neuroinflammatory states, they drive adaptive responses that may become pathological if dysregulated. We examine how neuroimmune interactions, mediated through these cellular actors and signaling pathways, create complex networks that regulate CNS functionality and respond to injury or inflammation. To further elucidate these dynamics, we provide insights using a multilayer network (MLN) approach, highlighting the interconnected nature of neuroimmune interactions under both inflammatory and homeostatic conditions. This perspective aims to enhance our understanding of neuroimmune communication and the mechanisms underlying shifts from homeostasis to neuroinflammation. Applying an MLN approach offers a more integrative view of CNS resilience and adaptability, helping to clarify inflammatory processes and identify novel intervention points within the layered landscape of neuroinflammatory responses.

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.

Therapeutic Potential of Polyphenols in Cellular Reversal of Patho-Mechanisms of Alzheimer's Disease Using In Vitro and In Vivo Models: A Comprehensive Review

Alzheimer's disease (AD) is considered one of the most common neurological conditions associated with memory and cognitive impairment and mainly affects people aged 65 or above. Even with tremendous progress in modern neuroscience, a permanent remedy or cure for this crippling disease is still unattainable. Polyphenols are a group of naturally occurring potent compounds that can modulate the neurodegenerative processes typical of AD. The present comprehensive study has been conducted to find out the preclinical and clinical potential of polyphenols and elucidate their possible mechanisms in managing AD. Additionally, we have reviewed different clinical studies investigating polyphenols as single compounds or cotherapies, including those currently recruiting, completed, terminated, withdrawn, or suspended in AD treatment. Natural polyphenols were systematically screened and identified through electronic databases including Google Scholar, PubMed, and Scopus based on in vitro cell line studies and preclinical data demonstrating their potential for neuroprotection. A total of 63 significant polyphenols were identified. A multimechanistic pathway for polyphenol's mode of action has been proposed in the study. Out of 63, four potent polyphenols have been identified as promising potential candidates, based on their reported clinical efficacy. Polyphenols hold tremendous scope for the development of a future drug molecule as a phytopharmaceutical that may be incorporated as an adjuvant to the therapeutic regime. However, more high-quality studies with novel delivery methods and combinatorial approaches are required to overcome obstacles such as bioavailability and blood-brain barrier crossing to underscore the therapeutic potential of these compounds in AD management.

Non-canonical Roles of Complement in the CNS: From Synaptic Organizer to Presynaptic Modulator of Glutamate Transmission

The central nervous system (CNS) is not an immune-privileged compartment, but it is intimately intertwined with the immune system. Among the components shared by the two compartments is the complement, a main constituent of innate immunity, which is also produced centrally and controls the development and organization of synaptic connections. Complement is considered a doubled-faced system that, besides controlling the physiological development of the central network, also subserves synaptic engulfment pivotal to the progression of neurodegenerative diseases. Quite interestingly, besides these "canonical" roles, evidence in the last two decades highlighted other "non-canonical" role(s), thereby complementing modulates chemical transmission at central synapsis. It emerged that glutamate is the preferential target of these "non-canonical" complementinduced effects, which include i) the control of the release of glutamate from neurons and astrocytes and ii) the control of the number and the functions of central glutamatergic receptor subtypes (i.e., the NMDA receptors, the AMPA/kainate receptors, and the metabotropic glutamate receptors) in plasma membranes. This review summarizes some of the available results supporting the role of complement as a "modulator" of central glutamate transmission, paying particular attention to those events that occur presynaptically. Taking into consideration the enormous progress in complement pharmacology and the increasing number of therapeutics in clinical trials, deepening our knowledge of these" non-canonical" role(s) could pave the road to new therapeutic approaches for the management of central neurological diseases.

Hearing modulation affects Alzheimer's disease progression linked to brain inflammation: a study in mouse models

BACKGROUND

Recent studies have identified hearing loss (HL) as a primary risk factor for Alzheimer's disease (AD) onset. However, the mechanisms linking HL to AD are not fully understood. This study explored the effects of drug-induced hearing loss (DIHL) on the expression of proteins associated with AD progression in mouse models.

METHODS

DIHL was induced in 5xFAD and Tg2576 mice aged 3 to 3.5 weeks using kanamycin (700 mg/kg, subcutaneous) and furosemide (600 mg/kg, intraperitoneal). The accumulation and expression of beta-amyloid (Aβ), ionized calcium-binding adaptor molecule 1 (Iba1), and glial fibrillary acidic protein (GFAP) were measured through immunohistochemistry and immunoblotting. Additionally, the expression of proteins involved in the mammalian target of rapamycin (mTOR) pathway, including downstream effectors p70 ribosomal S6 kinase (p70S6K) and S6, as well as proinflammatory cytokines, was analyzed.

RESULTS

Compared to control conditions, HL led to a significant increase in the accumulation of Aβ in the hippocampus and cortex. Elevated levels of neuroinflammatory markers, including Iba1 and GFAP, as well as proinflammatory cytokines such as interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-alpha (TNF-α), were observed. Moreover, DIHL enhanced phosphorylation of mTOR, p70S6K, and S6, indicating activation of the mTOR pathway.

CONCLUSIONS

HL significantly increases Aβ accumulation in the brain. Furthermore, HL activates astrocytes and microglia, leading to increased neuroinflammation and thereby accelerating AD progression. These findings strongly suggest that HL contributes autonomously to neuroinflammation, highlighting the potential for early intervention in HL to reduce AD risk.

Mechanisms of hydrocephalus after intraventricular haemorrhage: a review

Intraventricular haemorrhage (IVH) is bleeding within the ventricular system, which in adults is usually mainly secondary to cerebral haemorrhage and subarachnoid haemorrhage. Hydrocephalus is one of the most common complications of intraventricular haemorrhage, which is characterised by an increase in intracranial pressure due to an increased accumulation of cerebrospinal fluid within the ventricular system, and is closely related to the patient's prognosis. Surgical methods such as shunt surgery have been used to treat secondary hydrocephalus in recent years and have been effective in improving the survival and prognosis of patients with hydrocephalus. However, complications such as shunt blockage and intracranial infection are often faced after surgery. Moreover, little is known about the mechanism of hydrocephalus secondary to intraventricular haemorrhage. This review discusses the mechanisms regarding the occurrence of secondary hydrocephalus after intraventricular haemorrhage in adults in terms of blood clot obstruction, altered cerebrospinal fluid dynamics, inflammation, and blood composition.

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.

Primary cortical cell tri-culture to study effects of amyloid-β on microglia function and neuroinflammatory response

BACKGROUND

Microglia play a critical role in neurodegenerative disorders, such as Alzheimer's disease, where alterations in microglial function may result in pathogenic amyloid-β (Aβ) accumulation, chronic neuroinflammation, and deleterious effects on neuronal function. However, studying these complex factors in vivo, where numerous confounding processes exist, is challenging, and until recently, in vitro models have not allowed sustained culture of critical cell types in the same culture.

OBJECTIVE

We employed a rat primary tri-culture (neurons, astrocytes, and microglia) model and compared it to co-culture (neurons and astrocytes) and mono-culture (microglia) to study microglial function (i.e., motility and Aβ clearance) and proteomic response to exogenous Aβ.

METHODS

The cultures were exposed to fluorescently-labeled Aβ (FITC-Aβ) particles for varying durations. Epifluorescence microscopy images were analyzed to quantify the number of FITC-Aβ particles and assess cytomorphological features. Cytokine profiles from conditioned media were obtained. Live-cell imaging was employed to extract microglia motility parameters.

RESULTS

FITC-Aβ particles were more effectively cleared in the tri-culture compared to the co-culture. This was attributed to microglia engulfing FITC-Aβ particles, as confirmed via epifluorescence and confocal microscopy. FITC-Aβ treatment significantly increased microglia size, but had no significant effect on neuronal surface coverage or astrocyte size. Upon FITC-Aβ treatment, there was a significant increase in proinflammatory cytokines in tri-culture, but not in co-culture. Aβ treatment altered microglia motility evident as a swarming-like motion.

CONCLUSIONS

The results suggest that neuron-astrocyte-microglia interactions influence microglia function and highlight the utility of the tri-culture model for studies of neuroinflammation, neurodegeneration, and cell-cell communication.

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.

Effects and mechanisms of APP and its cleavage product Aβ in the comorbidity of sarcopenia and Alzheimer's disease

Sarcopenia and AD are both classic degenerative diseases, and there is growing epidemiological evidence of their comorbidity with aging; however, the mechanisms underlying the biology of their commonality have not yet been thoroughly investigated. APP is a membrane protein that is expressed in tissues and is expressed not only in the nervous system but also in the NMJ and muscle. Deposition of its proteolytic cleavage product, Aβ, has been described as a central component of AD pathogenesis. Recent studies have shown that excessive accumulation and aberrant expression of APP in muscle lead to pathological muscle lesions, but the pathogenic mechanism by which APP and its proteolytic cleavage products act in skeletal muscle is less well understood. By summarizing and analyzing the literature concerning the role, pathogenicity and pathological mechanisms of APP and its cleavage products in the nervous system and muscles, we aimed to explore the intrinsic pathological mechanisms of myocerebral comorbidities and to provide new perspectives and theoretical foundations for the prevention and treatment of AD and sarcopenia comorbidities.

Sulfatide deficiency-induced astrogliosis and myelin lipid dyshomeostasis are independent of Trem2-mediated microglial activation

Disrupted lipid homeostasis and neuroinflammation often co-exist in neurodegenerative disorders including Alzheimer's disease (AD). However, the intrinsic connection and causal relationship between these deficits remain elusive. Our previous studies show that the loss of sulfatide (ST), a class of myelin-enriched lipids, causes AD-like neuroinflammatory responses, cognitive impairment, bladder enlargement, as well as lipid dyshomeostasis. To better understand the relationship between neuroinflammation and lipid disruption induced by ST deficiency, we established a ST-deficient mouse model with constitutive Trem2 knockout and studied the impact of Trem2 in regulating ST deficiency-induced microglia-mediated neuroinflammation, astrocyte activation and lipid disruption. Our study demonstrates that Trem2 regulates ST deficiency-induced microglia-mediated neuroinflammatory pathways and astrogliosis at the transcriptomic level, but not astrocyte activation at the protein level, suggesting that Trem2 is indispensable for ST deficiency-induced microglia-mediated neuroinflammation but not astrogliosis. Meanwhile, ST loss-induced lipidome disruption and free water retention were consistently observed in the absence of Trem2 . Collectively, these results emphasize the essential role of Trem2 in mediating lipid loss-associated microglia-mediated neuroinflammation, but not both astrogliosis and myelin lipid disruption. Moreover, we demonstrated that attenuating neuroinflammation has a limited impact on brain ST loss-induced lipidome alteration or AD-like peripheral disorders. Our findings suggest that preserving lipidome and astrocyte balance may be crucial in decelerating the progression of AD.

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.

Neurodegeneration and demyelination in multiple sclerosis

Progressive multiple sclerosis (PMS) is an immune-initiated neurodegenerative condition that lacks effective therapies. Although peripheral immune infiltration is a hallmark of relapsing-remitting MS (RRMS), PMS is associated with chronic, tissue-restricted inflammation and disease-associated reactive glial states. The effector functions of disease-associated microglia, astrocytes, and oligodendrocyte lineage cells are beginning to be defined, and recent studies have made significant progress in uncovering their pathologic implications. In this review, we discuss the immune-glia interactions that underlie demyelination, failed remyelination, and neurodegeneration with a focus on PMS. We highlight the common and divergent immune mechanisms by which glial cells acquire disease-associated phenotypes. Finally, we discuss recent advances that have revealed promising novel therapeutic targets for the treatment of PMS and other neurodegenerative diseases.

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.

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.

Air Pollution as an Environmental Risk Factor for Alzheimer's Disease and Related Dementias

Alzheimer's disease and related dementias are a leading cause of morbidity in our aging populations. Although influenced by genetic factors, fewer than 5% of Alzheimer's disease and related dementia cases are due solely to genetic causes. There is growing scientific consensus that these dementias arise from complex gene by environment interactions. The 2020 Lancet Commission on dementia prevention, intervention, and care identified 12 modifiable risk factors of dementia, including lifestyle, educational background, comorbidities, and environmental exposures to environmental contaminants. In this review, we summarize the current understanding and data gaps regarding the role(s) of environmental pollutants in the etiology of Alzheimer's disease and related dementias with a focus on air pollution. In addition to summarizing findings from epidemiological and experimental animal studies that link airborne exposures to environmental contaminants to increased risk and/or severity of Alzheimer's disease and related dementias, we discuss currently hypothesized mechanism(s) underlying these associations, including peripheral inflammation, neuroinflammation and epigenetic changes. Key data gaps in this rapidly expanding investigative field and approaches for addressing these gaps are also addressed.

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.

Immunoglobulin G and Complement as Major Players in the Neurodegeneration of Multiple Sclerosis

Multiple Sclerosis (MS) is an inflammatory, demyelinating, and neurodegenerative disease of the central nervous system (CNS) and is termed as one of the most common causes of neurological disability in young adults. Axonal loss and neuronal cell damage are the primary causes of disease progression and disability. Yet, little is known about the mechanism of neurodegeneration in the disease, a limitation that impairs the development of more effective treatments for progressive MS. MS is characterized by the presence of oligoclonal bands and raised levels of immunoglobulins in the CNS. The role of complement in the demyelinating process has been detected in both experimental animal models of MS and within the CNS of affected MS patients. Furthermore, both IgG antibodies and complement activation can be detected in the demyelinating plaques and cortical gray matter lesions. We propose here that both immunoglobulins and complement play an active role in the neurodegenerative process of MS. We hypothesize that the increased CNS IgG antibodies form IgG aggregates and bind complement C1q with high affinity, activating the classical complement pathway. This results in neuronal cell damage, which leads to neurodegeneration and demyelination in MS.

Microglia mediate memory dysfunction via excitatory synaptic elimination in a fracture surgery mouse model

Cognitive impairment is a common issue among human patients undergoing surgery, yet the neural mechanism causing this impairment remains unidentified. Surgical procedures often lead to glial cell activation and neuronal hypoexcitability, both of which are known to contribute to postoperative cognitive dysfunction (POCD). However, the role of neuron-glia crosstalk in the pathology of POCD is still unclear. Through integrated transcriptomics and proteomics analyses, we found that the complement cascades and microglial phagocytotic signaling pathways are activated in a mouse model of POCD. Following surgery, there is a significant increase in the presence of complement C3, but not C1q, in conjunction with presynaptic elements. This triggers a reduction in excitatory synapses, a decline in excitatory synaptic transmission, and subsequent memory deficits in the mouse model. By genetically knockout out C3ar1 or inhibiting p-STAT3 signaling, we successfully prevented neuronal hypoexcitability and alleviated cognitive impairment in the mouse model. Therefore, targeting the C3aR and downstream p-STAT3 signaling pathways could serve as potential therapeutic approaches for mitigating POCD.

Astrocyte-secreted C3 signaling impairs neuronal development and cognition in autoimmune diseases

Neuromyelitis optica (NMO) arises from primary astrocytopathy induced by autoantibodies targeting the astroglial protein aquaporin 4 (AQP4), leading to severe neurological sequelae such as vision loss, motor deficits, and cognitive decline. Mounting evidence has shown that dysregulated activation of complement components contributes to NMO pathogenesis. Complement C3 deficiency has been shown to protect against hippocampal neurodegeneration and cognitive decline in neurodegenerative disorders (e.g., Alzheimer's disease, AD) and autoimmune diseases (e.g., multiple sclerosis, MS). However, whether inhibiting the C3 signaling can ameliorate cognitive dysfunctions in NMO remains unclear. In this study, we found that the levels of C3a, a split product of C3, significantly correlate with cognitive impairment in our patient cohort. In response to the stimulation of AQP4 autoantibodies, astrocytes were activated to secrete complement C3, which inhibited the development of cultured neuronal dendritic arborization. NMO mouse models exhibited reduced adult hippocampal newborn neuronal dendritic and spine development, as well as impaired learning and memory functions, which could be rescued by decreasing C3 levels in astrocytes. Mechanistically, we found that C3a engaged with C3aR to impair neuronal development by dampening β-catenin signalling. Additionally, inhibition of the C3-C3aR-GSK3β/β-catenin cascade restored neuronal development and ameliorated cognitive impairments. Collectively, our results suggest a pivotal role of the activation of the C3-C3aR network in neuronal development and cognition through mediating astrocyte and adult-born neuron communication, which represents a potential therapeutic target for autoimmune-related cognitive impairment diseases.

Inflammatory aspects of Alzheimer's disease

Alzheimer´s disease (AD) stands out as the most common chronic neurodegenerative disorder. AD is characterized by progressive cognitive decline and memory loss, with neurodegeneration as its primary pathological feature. The role of neuroinflammation in the disease course has become a focus of intense research. While microglia, the brain's resident macrophages, have been pivotal to study central immune inflammation, recent evidence underscores the contributions of other cellular entities to the neuroinflammatory process. In this article, we review the inflammatory role of microglia and astrocytes, focusing on their interactions with AD's core pathologies, amyloid beta deposition, and tau tangle formation. Additionally, we also discuss how different modes of regulated cell death in AD may impact the chronic neuroinflammatory environment. This review aims to highlight the evolving landscape of neuroinflammatory research in AD and underscores the importance of considering multiple cellular contributors when developing new therapeutic strategies.

Microbiota-Derived Extracellular Vesicle as Emerging Actors in Host Interactions

The human microbiota is an intricate micro-ecosystem comprising a diverse range of dynamic microbial populations mainly consisting of bacteria, whose interactions with hosts strongly affect several physiological and pathological processes. The gut microbiota is being increasingly recognized as a critical player in maintaining homeostasis, contributing to the main functions of the intestine and distal organs such as the brain. However, gut dysbiosis, characterized by composition and function alterations of microbiota with intestinal barrier dysfunction has been linked to the development and progression of several pathologies, including intestinal inflammatory diseases, systemic autoimmune diseases, such as rheumatic arthritis, and neurodegenerative diseases, such as Alzheimer's disease. Moreover, oral microbiota research has gained significant interest in recent years due to its potential impact on overall health. Emerging evidence on the role of microbiota-host interactions in health and disease has triggered a marked interest on the functional role of bacterial extracellular vesicles (BEVs) as mediators of inter-kingdom communication. Accumulating evidence reveals that BEVs mediate host interactions by transporting and delivering into host cells effector molecules that modulate host signaling pathways and cell processes, influencing health and disease. This review discusses the critical role of BEVs from the gut, lung, skin and oral cavity in the epithelium, immune system, and CNS interactions.

Aged-Related Changes in Microglia and Neurodegenerative Diseases: Exploring the Connection

Microglial cells exhibit properties akin to macrophages, thereby enabling them to support and protect the central nervous system environment. Aging induces alterations in microglial polarization, resulting in a shift toward a neurotoxic phenotype characterized by increased expression of pro-inflammatory markers. Dysregulation of microglial cells' regulatory pathways and interactions with neurons contribute to chronic activation and neurodegeneration. A better understanding of the involvement of microglia in neurodegenerative diseases such as Alzheimer's and Parkinson's is a critical topic for studying the role of inflammatory responses in disease progression. Furthermore, the metabolic changes in aged microglia, including the downregulation of oxidative phosphorylation, are discussed in this review. Understanding these mechanisms is crucial for developing better preventive and therapeutic strategies.

Complement C3aR signaling: Immune and metabolic modulation and its impact on Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most common cause of dementia among the elderly population. Despite its widespread prevalence, our comprehension of the intricate mechanisms governing the pathogenesis of the disease remains incomplete, posing a challenge for the development of efficient therapies. Pathologically characterized by the presence of amyloid β plaques and neurofibrillary tau tangles, AD is also accompanied by the hyperactivation of glial cells and the immune system. The complement cascade, the evolutionarily conserved innate immune pathway, has emerged as a significant contributor to AD. This review focuses on one of the complement components, the C3a receptor (C3aR), covering its structure, ligand-receptor interaction, intracellular signaling and its functional consequences. Drawing insights from cellular and AD mouse model studies, we present the multifaceted role of complement C3aR signaling in AD and attempt to convey to the readers that C3aR acts as a crucial immune and metabolic modulator to influence AD pathogenesis. Building on this framework, the objective of this review is to inform future research endeavors and facilitate the development of therapeutic strategies for this challenging condition.

Role of ginsenoside Rb1 in attenuating depression-like symptoms through astrocytic and microglial complement C3 pathway

Ginsenoside Rb1, known as gypenoside III, exerts antidepressant-like effects in previous studies. It has also been indicated that ginsenoside Rb1 regulated neuroinflammation via inhibiting NF-κB signaling. According to the evidence that astrocytes can regulate microglia and neuroinflammation by secreting complement C3, the present study aimed to demonstrate the molecular mechanisms underlying ginsenoside Rb1-induced antidepressant-like effects from the astrocytic and microglial complement C3 pathway. The complement C3 mediated mechanism of ginsenoside Rb1 was investigated in mice exposed to chronic restraint stress (CRS). The results showed that ginsenoside Rb1 reversed the depressive-like behaviors in CRS. Treatment with ginsenoside Rb1 reduced both the number of astrocytes and microglia. In addition, ginsenoside Rb1 suppressed TLR4/NF-κB/C3 signaling in the astrocytes of the hippocampus. Furthermore, ginsenoside Rb1 attenuated the contents of synaptic protein including synaptophysin and PSD95 in microglia, suggesting the inhibition of microglia-mediated synaptic elimination caused by CRS. Importantly, ginsenoside Rb1 also maintained the dendritic spines in mice. In conclusion, our results demonstrate that ginsenoside Rb1 produces the antidepressant-like effects by inhibiting astrocyte TLR4/NF-κB/C3 signaling to covert microglia from a pro-inflammatory phenotype (amoeboid) towards an anti-inflammatory phenotype (ramified), which inhibit the synaptic pruning in the hippocampus.

In vivo neural regeneration via AAV-NeuroD1 gene delivery to astrocytes in neonatal hypoxic-ischemic brain injury

BACKGROUND

Neonatal hypoxic-ischemic brain injury (HIBI) is a significant contributor to neonatal mortality and long-term neurodevelopmental disability, characterized by massive neuronal loss and reactive astrogliosis. Current therapeutic approaches for neonatal HIBI have been limited to general supportive therapy because of the lack of methods to compensate for irreversible neuronal loss. This study aimed to establish a feasible regenerative therapy for neonatal HIBI utilizing in vivo direct neuronal reprogramming technology.

METHODS

Neonatal HIBI was induced in ICR mice at postnatal day 7 by permanent right common carotid artery occlusion and exposure to hypoxia with 8% oxygen and 92% nitrogen for 90 min. Three days after the injury, NeuroD1 was delivered to reactive astrocytes of the injury site using the astrocyte-tropic adeno-associated viral (AAV) vector AAVShH19. AAVShH19 was engineered with the Cre-FLEX system for long-term tracking of infected cells.

RESULTS

AAVShH19-mediated ectopic NeuroD1 expression effectively converted astrocytes into GABAergic neurons, and the converted cells exhibited electrophysiological properties and synaptic transmitters. Additionally, we found that NeuroD1-mediated in vivo direct neuronal reprogramming protected injured host neurons and altered the host environment, i.e., decreased the numbers of activated microglia, reactive astrocytes, and toxic A1-type astrocytes, and decreased the expression of pro-inflammatory factors. Furthermore, NeuroD1-treated mice exhibited significantly improved motor functions.

CONCLUSIONS

This study demonstrates that NeuroD1-mediated in vivo direct neuronal reprogramming technology through AAV gene delivery can be a novel regenerative therapy for neonatal HIBI.

Glial cells in the mammalian olfactory bulb

The mammalian olfactory bulb (OB), an essential part of the olfactory system, plays a critical role in odor detection and neural processing. Historically, research has predominantly focused on the neuronal components of the OB, often overlooking the vital contributions of glial cells. Recent advancements, however, underscore the significant roles that glial cells play within this intricate neural structure. This review discus the diverse functions and dynamics of glial cells in the mammalian OB, mainly focused on astrocytes, microglia, oligodendrocytes, olfactory ensheathing cells, and radial glia cells. Each type of glial contributes uniquely to the OB's functionality, influencing everything from synaptic modulation and neuronal survival to immune defense and axonal guidance. The review features their roles in maintaining neural health, their involvement in neurodegenerative diseases, and their potential in therapeutic applications for neuroregeneration. By providing a comprehensive overview of glial cell types, their mechanisms, and interactions within the OB, this article aims to enhance our understanding of the olfactory system's complexity and the pivotal roles glial cells play in both health and disease.

Bibliometric analysis of neuroinflammation and Alzheimer's disease

Background

Alzheimer's disease (AD) is the predominant cause of dementia on a global scale, significantly impacting the health of the elderly population. The pathogenesis of AD is closely linked to neuroinflammation. The present study employs a bibliometric analysis to examine research pertaining to neuroinflammation and AD within the last decade, with the objective of providing a comprehensive overview of the current research profile, hotspots and trends.

Methods

This research conducted a comprehensive review of publications within the Science Citation Index Expanded of the Web of Science Core Collection Database spanning the years 2014 to 2024. Bibliometric analyses were performed using VOSviewer (version 1.6.19) and CiteSpace (version 6.3.R1) software to visualize data on countries, institutions, authors, journals, keywords, and references.

Results

A total of 3,833 publications on neuroinflammation and AD were included from January 2014 to January 2024. Publications were mainly from the United States and China. Zetterberg, Henrik emerged as the author with the highest publication output, while Edison, Paul was identified as the most cited author. The most productive journal was Journal of Alzheimers Disease, and the most co-cited was Journal of Neuroinflammation. Research hotspot focused on microglia, mouse models, oxidative stress, and amyloid-beta through keyword analysis. Additionally, keywords such as blood-brain barrier and tau protein exhibited prolonged citation bursts from 2022 to 2024.

Conclusion

This study provides a comprehensive review of the last 10 years of research on neuroinflammation and AD, including the number and impact of research findings, research hotspots, and future trends. The quantity of publications in this field is increasing, mainly in the United States and China, and there is a need to further strengthen close cooperation with different countries and institutions worldwide. Presently, research hotspots are primarily concentrated on microglia, with a focus on inhibiting their pro-inflammatory responses and promoting their anti-inflammatory functions as a potential direction for future investigations.

The complement system in neurodegenerative and inflammatory diseases of the central nervous system

Neurodegenerative and neuroinflammatory diseases, including Alzheimer's disease, Parkinson's disease, and multiple sclerosis, affect millions of people globally. As aging is a major risk factor for neurodegenerative diseases, the continuous increase in the elderly population across Western societies is also associated with a rising prevalence of these debilitating conditions. The complement system, a crucial component of the innate immune response, has gained increasing attention for its multifaceted involvement in the normal development of the central nervous system (CNS) and the brain but also as a pathogenic driver in several neuroinflammatory disease states. Although complement is generally understood as a liver-derived and blood or interstitial fluid operative system protecting against bloodborne pathogens or threats, recent research, particularly on the role of complement in the healthy and diseased CNS, has demonstrated the importance of locally produced and activated complement components. Here, we provide a succinct overview over the known beneficial and pathological roles of complement in the CNS with focus on local sources of complement, including a discussion on the potential importance of the recently discovered intracellularly active complement system for CNS biology and on infection-triggered neurodegeneration.

Ldl-stimulated microglial activation exacerbates ischemic white matter damage

The role of microglia in triggering the blood-brain barrier (BBB) impairment and white matter damage after chronic cerebral hypoperfusion is unclear. Here we demonstrated that the vessel-adjacent microglia were specifically activated by the leakage of plasma low-density lipoprotein (LDL), which led to BBB breakdown and ischemic demyelination. Interestingly, we found that LDL stimulation enhanced microglial phagocytosis, causing excessive engulfment of myelin debris and resulting in an overwhelming lipid burden in microglia. Surprisingly, these lipid-laden microglia exhibited a suppressed profile of inflammatory response and compromised pro-regenerative properties. Microglia-specific knockdown of LDLR or systematic medication lowering circulating LDL-C showed protective effects against ischemic demyelination. Overall, our findings demonstrated that LDL-stimulated vessel-adjacent microglia possess a disease-specific molecular signature, characterized by suppressed regenerative properties, which is associated with the propagation of demyelination during ischemic white matter damage.

A TrkB and TrkC partial agonist restores deficits in synaptic function and promotes activity-dependent synaptic and microglial transcriptomic changes in a late-stage Alzheimer's mouse model

INTRODUCTION

Tropomyosin related kinase B (TrkB) and C (TrkC) receptor signaling promotes synaptic plasticity and interacts with pathways affected by amyloid beta (Aβ) toxicity. Upregulating TrkB/C signaling could reduce Alzheimer's disease (AD)-related degenerative signaling, memory loss, and synaptic dysfunction.

METHODS

PTX-BD10-2 (BD10-2), a small molecule TrkB/C receptor partial agonist, was orally administered to aged London/Swedish-APP mutant mice (APPL/S) and wild-type controls. Effects on memory and hippocampal long-term potentiation (LTP) were assessed using electrophysiology, behavioral studies, immunoblotting, immunofluorescence staining, and RNA sequencing.

RESULTS

In APPL/S mice, BD10-2 treatment improved memory and LTP deficits. This was accompanied by normalized phosphorylation of protein kinase B (Akt), calcium-calmodulin-dependent kinase II (CaMKII), and AMPA-type glutamate receptors containing the subunit GluA1; enhanced activity-dependent recruitment of synaptic proteins; and increased excitatory synapse number. BD10-2 also had potentially favorable effects on LTP-dependent complement pathway and synaptic gene transcription.

DISCUSSION

BD10-2 prevented APPL/S/Aβ-associated memory and LTP deficits, reduced abnormalities in synapse-related signaling and activity-dependent transcription of synaptic genes, and bolstered transcriptional changes associated with microglial immune response.

HIGHLIGHTS

Small molecule modulation of tropomyosin related kinase B (TrkB) and C (TrkC) restores long-term potentiation (LTP) and behavior in an Alzheimer's disease (AD) model. Modulation of TrkB and TrkC regulates synaptic activity-dependent transcription. TrkB and TrkC receptors are candidate targets for translational therapeutics. Electrophysiology combined with transcriptomics elucidates synaptic restoration. LTP identifies neuron and microglia AD-relevant human-mouse co-expression modules.

Alzheimer's disease early screening and staged detection with plasma proteome using machine learning and convolutional neural network

Alzheimer's disease (AD) stands as the prevalent progressive neurodegenerative disease, precipitating cognitive impairment and even memory loss. Amyloid biomarkers have been extensively used in the diagnosis of AD. However, amyloid proteins offer limited information about the disease process and accurate diagnosis depends on the presence of a substantial accumulation of amyloid deposition which significantly impedes the early screening of AD. In this study, we have combined plasma proteomics with an ensemble learning model (CatBoost) to develop a cost-effective and non-invasive diagnostic method for AD. A longitudinal panel has been identified that can serve as reliable biomarkers across the entire progression of AD. Simultaneously, we have developed a neural network algorithm that utilizes plasma proteins to detect stages of Alzheimer's disease. Based on the developed longitudinal panel, the CatBoost model achieved an area under the operating curve of at least 0.90 in distinguishing mild cognitive impairment from cognitively normal. The neural network model was utilized for the detection of three stages of AD, and the results demonstrated that the neural network model exhibited an accuracy as high as 0.83, surpassing that of the traditional machine learning model.

Associations of amyloid-β oligomers and plaques with neuropathology in the App NL-G-F mouse

Amyloid-β pathology and neurofibrillary tangles lead to glial activation and neurodegeneration in Alzheimer's disease. In this study, we investigated the relationships between the levels of amyloid-β oligomers, amyloid-β plaques, glial activation and markers related to neurodegeneration in the App NL-G-F triple mutation mouse line and in a knock-in line homozygous for the common human amyloid precursor protein (App hu mouse). The relationships between neuropathological features were characterized with immunohistochemistry and imaging mass cytometry. Markers assessing human amyloid-β proteins, microglial and astrocytic activation and neuronal and synaptic densities were used in mice between 2.5 and 12 months of age. We found that amyloid-β oligomers were abundant in the brains of App hu mice in the absence of classical amyloid-β plaques. These brains showed morphological changes consistent with astrocyte activation but no evidence of microglial activation or synaptic or neuronal pathology. In contrast, both high levels of amyloid-β oligomers and numerous plaques accumulated in App NL-G-F mice in association with substantial astrocytic and microglial activation. The increase in amyloid-β oligomers over time was more strongly correlated with astrocytic than with microglia activation. Spatial analyses suggested that activated microglia were more closely associated with amyloid-β oligomers than with amyloid-β plaques in App NL-G-F mice, which also showed age-dependent decreases in neuronal and synaptic density markers. A comparative study of the two models highlighted the dependence of glial and neuronal pathology on the nature and aggregation state of the amyloid-β peptide. Astrocyte activation and neuronal pathology appeared to be more strongly associated with amyloid-β oligomers than with amyloid-β plaques, although amyloid-β plaques were associated with microglia activation.