TGFβ produced by IL-10 redirected astrocytes attenuates microglial activation

Impacts of PI3K/protein kinase B pathway activation in reactive astrocytes: from detrimental effects to protective functions

Astrocytes are the most abundant type of glial cell in the central nervous system. Upon injury and inflammation, astrocytes become reactive and undergo morphological and functional changes. Depending on their phenotypic classification as A1 or A2, reactive astrocytes contribute to both neurotoxic and neuroprotective responses, respectively. However, this binary classification does not fully capture the diversity of astrocyte responses observed across different diseases and injuries. Transcriptomic analysis has revealed that reactive astrocytes have a complex landscape of gene expression profiles, which emphasizes the heterogeneous nature of their reactivity. Astrocytes actively participate in regulating central nervous system inflammation by interacting with microglia and other cell types, releasing cytokines, and influencing the immune response. The phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway is a central player in astrocyte reactivity and impacts various aspects of astrocyte behavior, as evidenced by in silico , in vitro , and in vivo results. In astrocytes, inflammatory cues trigger a cascade of molecular events, where nuclear factor-κB serves as a central mediator of the pro-inflammatory responses. Here, we review the heterogeneity of reactive astrocytes and the molecular mechanisms underlying their activation. We highlight the involvement of various signaling pathways that regulate astrocyte reactivity, including the PI3K/AKT/mammalian target of rapamycin (mTOR), α v β 3 integrin/PI3K/AKT/connexin 43, and Notch/PI3K/AKT pathways. While targeting the inactivation of the PI3K/AKT cellular signaling pathway to control reactive astrocytes and prevent central nervous system damage, evidence suggests that activating this pathway could also yield beneficial outcomes. This dual function of the PI3K/AKT pathway underscores its complexity in astrocyte reactivity and brain function modulation. The review emphasizes the importance of employing astrocyte-exclusive models to understand their functions accurately and these models are essential for clarifying astrocyte behavior. The findings should then be validated using in vivo models to ensure real-life relevance. The review also highlights the significance of PI3K/AKT pathway modulation in preventing central nervous system damage, although further studies are required to fully comprehend its role due to varying factors such as different cell types, astrocyte responses to inflammation, and disease contexts. Specific strategies are clearly necessary to address these variables effectively.

Neuron-glia crosstalk and inflammatory mediators in migraine pathophysiology

Migraine is a complex neurological disorder with neuroinflammation playing a crucial role in its pathogenesis. This review provides an overview of the neuroinflammation mechanisms in migraine, focusing on both cellular and molecular aspects. At the cellular level, we examine the role of glial cells, including astrocytes, microglia, oligodendrocytes in the central nervous system, and Schwann cells and satellite glial cells in the peripheral nervous system. On the molecular level, we explore the signaling pathways, including IL-1β, TNF-α, IL-6, and non-coding RNAs, that mediate cell interactions or independent actions. Some of the molecular signaling pathways mentioned, such as TNF-α and IL-1β, have been investigated as druggable targets. Recent advancements, such as [11C] PBR28-targeted imaging for visualizing astrocyte activation and single-cell sequencing for exploring cellular heterogeneity, represent breakthroughs in understanding the mechanisms of neuroinflammation in migraine. By considering factors for personalized treatments, estrogen and TRPM8 emerge as promising therapeutic targets regarding sexual dimorphism. These advancements may help bridge the gap between preclinical findings and clinical applications, ultimately leading to more precise and personalized options for migraine patients.

Glial Cell Activation and Immune Responses in Glaucoma: A Systematic Review of Human Postmortem Studies of the Retina and Optic Nerve

Although researched extensively the understanding regarding mechanisms underlying glaucoma pathogenesis remains limited. Further, the exact mechanism behind neuronal death remains elusive. The role of neuroinflammation in retinal ganglion cell (RGC) death has been prominently theorised. This review provides a comprehensive summary of neuroinflammatory responses in glaucoma. A systematic search of Medline and Embase for articles published up to 8th March 2023 yielded 32 studies using post-mortem tissues from glaucoma patients. The raw data were extracted from tables and text to calculate the standardized mean differences (SMDs). These studies utilized post-mortem tissues from glaucoma patients, totalling 490 samples, compared with 380 control samples. Among the included studies, 27 reported glial cell activation based on changes to cellular morphology and molecular staining. Molecular changes were predominantly attributed to astrocytes (62.5%) and microglia (15.6%), with some involvement of Muller cells. These glial cell changes included amoeboid microglial cells with increased CD45 or HLA-DR intensity and hypertrophied astrocytes with increased glial fibrillary acidic protein labelling. Further, changes to extracellular matrix proteins like collagen, galectin, and tenascin-C suggested glial cells' influence on structural changes in the optic nerve head. The activation of DAMPs-driven immune response and the classical complement cascade was reported and found to be associated with activated glial cells in glaucomatous tissue. Increased pro-inflammatory markers such as interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) were also linked to glial cells. Glial cell activation was also associated with mitochondrial, vascular, metabolic and antioxidant component disruptions. Association of the activated glial cells with pro-inflammatory responses, dysregulation of homeostatic components and antigen presentation indicates that glial cell responses influence glaucoma progression. However, the exact mechanism triggering these responses and underlying interactions remains unexplored. This necessitates further research using human samples for an increased understanding of the precise role of neuroinflammation in glaucoma progression.

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.

Nimodipine attenuates neuroinflammation and delayed apoptotic neuronal death induced by trimethyltin in the dentate gyrus of mice

L-type voltage-gated calcium channels (L-VGCCs) are thought to be involved in epileptogenesis and acute excitotoxicity. However, little is known about the role of L-VGCCs in neuroinflammation or delayed neuronal death following excitotoxic insult. We examined the effects of repeated treatment with the L-VGCC blocker nimodipine on neuroinflammatory changes and delayed neuronal apoptosis in the dentate gyrus following trimethyltin (TMT)-induced convulsions. Male C57BL/6 N mice were administered TMT (2.6 mg/kg, i.p.), and the expression of the Cav1.2 and Cav1.3 subunits of L-VGCC were evaluated. The expression of both subunits was significantly decreased; however, the astroglial expression of Cav1.3 L-VGCC was significantly induced at 6 and 10 days after TMT treatment. Furthermore, astroglial Cav1.3 L-VGCCs colocalized with both the pro-inflammatory phenotype marker C3 and the anti-inflammatory phenotype marker S100A10 of astrocytes. Nimodipine (5 mg/kg, i.p. × 5 at 12-h intervals) did not significantly affect TMT-induced astroglial activation. However, nimodipine significantly attenuated the pro-inflammatory phenotype changes, while enhancing the anti-inflammatory phenotype changes in astrocytes after TMT treatment. Consistently, nimodipine reduced the levels of pro-inflammatory astrocytes-to-microglia mediators, while increasing the levels of anti-inflammatory astrocytes-to-microglia mediators. These effects were accompanied by an increase in the phosphorylation of extracellular signal-regulated kinase (ERK), supporting our previous finding that p-ERK is a signaling factor that regulates astroglial phenotype changes. In addition, nimodipine significantly attenuated TMT-induced microglial activation and delayed apoptosis of dentate granule neurons. Our results suggest that L-VGCC blockade attenuates neuroinflammation and delayed neurotoxicity following TMT-induced convulsions through the regulation of astroglial phenotypic changes by promoting ERK signaling.

Antidepressant Effects of Ginsenoside Rc on L-Alpha-Aminoadipic Acid-Induced Astrocytic Ablation and Neuroinflammation in Mice

Depression is a prevalent and debilitating mental disorder that affects millions worldwide. Current treatments, such as antidepressants targeting the serotonergic system, have limitations, including delayed onset of action and high rates of treatment resistance, necessitating novel therapeutic strategies. Ginsenoside Rc (G-Rc) has shown potential anti-inflammatory and neuroprotective effects, but its antidepressant properties remain unexplored. This study investigated the antidepressant effects of G-Rc in an L-alpha-aminoadipic acid (L-AAA)-induced mouse model of depression, which mimics the astrocytic pathology and neuroinflammation observed in major depressive disorder. Mice were administered G-Rc, vehicle, or imipramine orally after L-AAA injection into the prefrontal cortex. G-Rc significantly reduced the immobility time in forced swimming and tail suspension tests compared to vehicle treatment, with more pronounced effects than imipramine. It also attenuated the expression of pro-inflammatory cytokines (TNF-α, IL-6, TGF-β, lipocalin-2) and alleviated astrocytic degeneration, as indicated by increased GFAP and decreased IBA-1 levels. Additionally, G-Rc modulated apoptosis-related proteins, decreasing caspase-3 and increasing Bcl-2 levels compared to the L-AAA-treated group. These findings suggest that G-Rc exerts antidepressant effects by regulating neuroinflammation, astrocyte-microglia crosstalk, and apoptotic pathways in the prefrontal cortex, highlighting its potential as a novel therapeutic agent for depression.

Exploring neuroglial signaling: diversity of molecules implicated in microglia-to-astrocyte neuroimmune communication

Effective communication between different cell types is essential for brain health, and dysregulation of this process leads to neuropathologies. Brain glial cells, including microglia and astrocytes, orchestrate immune defense and neuroimmune responses under pathological conditions during which interglial communication is indispensable. Our appreciation of the complexity of these processes is rapidly increasing due to recent advances in molecular biology techniques, which have identified numerous phenotypic states of both microglia and astrocytes. This review focuses on microglia-to-astrocyte communication facilitated by secreted neuroimmune modulators. The combinations of interleukin (IL)-1α, tumor necrosis factor (TNF), plus complement component C1q as well as IL-1β plus TNF are already well-established microglia-derived stimuli that induce reactive phenotypes in astrocytes. However, given the large number of inflammatory mediators secreted by microglia and the rapidly increasing number of distinct functional states recognized in astrocytes, it can be hypothesized that many more intercellular signaling molecules exist. This review identifies the following group of cytokines and gliotransmitters that, while not established as interglial mediators yet, are known to be released by microglia and elicit functional responses in astrocytes: IL-10, IL-12, IL-18, transforming growth factor (TGF)-β, interferon (IFN)-γ, C-C motif chemokine ligand (CCL)5, adenosine triphosphate (ATP), l-glutamate, and prostaglandin E2 (PGE2). The review of molecular mechanisms engaged by these mediators reveals complex, partially overlapping signaling pathways implicated in numerous neuropathologies. Additionally, lack of human-specific studies is identified as a significant knowledge gap. Further research on microglia-to-astrocyte communication is warranted, as it could discover novel interglial signaling-targeted therapies for diverse neurological disorders.

IL-10 and Cdc42 modulate astrocyte-mediated microglia activation in methamphetamine-induced neuroinflammation

Methamphetamine (Meth) use is known to induce complex neuroinflammatory responses, particularly involving astrocytes and microglia. Building upon our previous research, which demonstrated that Meth stimulates astrocytes to release tumor necrosis factor (TNF) and glutamate, leading to microglial activation, this study investigates the role of the anti-inflammatory cytokine interleukin-10 (IL-10) in this process. Our findings reveal that the presence of recombinant IL-10 (rIL-10) counteracts Meth-induced excessive glutamate release in astrocyte cultures, which significantly reduces microglial activation. This reduction is associated with the modulation of astrocytic intracellular calcium (Ca2+) dynamics, particularly by restricting the release of Ca2+ from the endoplasmic reticulum to the cytoplasm. Furthermore, we identify the small Rho GTPase Cdc42 as a crucial intermediary in the astrocyte-to-microglia communication pathway under Meth exposure. By employing a transgenic mouse model that overexpresses IL-10 (pMT-10), we also demonstrate in vivo that IL-10 prevents Meth-induced neuroinflammation. These findings not only enhance our understanding of Meth-related neuroinflammatory mechanisms, but also suggest IL-10 and Cdc42 as putative therapeutic targets for treating Meth-induced neuroinflammation.

Astrocyte-TREM2 alleviates brain injury by regulating reactive astrocyte states following ischemic stroke

Triggering receptor expressed on myeloid cells 2 (TREM2) has been shown to confer strong neuroprotective effects in acute ischemic stroke (AIS). However, as the vast majority of research findings to date are based on its functions in microglia, the precise role of TREM2 in astrocytes after AIS is unknown. Here, both loss- and gain-of-function experiments were employed to investigate how astrocytic TREM2 influences the pathogenesis of AIS in vivo and in vitro. Our results demonstrated that cerebral ischemia triggered induction of TREM2 expression on reactive astrocytes following AIS. In addition, astrocyte-specific TREM2 knockout mice exhibited much greater brain injury than TREM2 flox/flox controls following AIS, as evidenced by increased cerebral infarct volume, neuronal apoptosis and neurological deficit, which was associated with an increased expression of pro-inflammatory molecule complement component 3 (C3) on reactive astrocytes and activation of microglia/macrophages but decreased expression of S100 calcium binding protein A10 (S100A10) and arginase1 (Arg1) on reactive astrocytes. Mechanistic analyses revealed that astrocytic TREM2 alleviated brain injury by inhibiting detrimental actions of reactive astrocytes but promoting their neuro- and glioprotective actions via the kruppel-like transcription factor-4-nuclear factor-κB axis. Together, this study provides novel evidence for a critical protective role of astrocyte-derived TREM2 in AIS and highlights a potential therapeutic target for the treatment of AIS.

Myelin oligodendrocyte glycoprotein reactive Th17 cells drive Janus Kinase 1 dependent transcriptional reprogramming in astrocytes and alter cell surface cytokine receptor profiles during experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is an autoimmune demyelinating disease affecting the central nervous system (CNS). T helper (Th) 17 cells are involved in the pathogenesis of MS and its animal model of experimental autoimmune encephalomyelitis (EAE) by infiltrating the CNS and producing effector molecules that engage resident glial cells. Among these glial cells, astrocytes have a central role in coordinating inflammatory processes by responding to cytokines and chemokines released by Th17 cells. In this study, we examined the impact of pathogenic Th17 cells on astrocytes in vitro and in vivo. We identified that Th17 cells reprogram astrocytes by driving transcriptomic changes partly through a Janus Kinase (JAK)1-dependent mechanism, which included increased chemokines, interferon-inducible genes, and cytokine receptors. In vivo, we observed a region-specific heterogeneity in the expression of cell surface cytokine receptors on astrocytes, including those for IFN-γ, IL-1, TNF-α, IL-17, TGFβ, and IL-10. Additionally, these receptors were dynamically regulated during EAE induced by adoptive transfer of myelin-reactive Th17 cells. This study overall provides evidence of Th17 cell reprogramming of astrocytes, which may drive changes in the astrocytic responsiveness to cytokines during autoimmune neuroinflammation.

CSF1R blockade slows progression of cerebral hemorrhage by reducing microglial proliferation and increasing infiltration of CD8 + CD122+ T cells into the brain

Microglia play a pivotal role in the neuroinflammatory response after brain injury, and their proliferation is dependent on colony-stimulating factors. In the present study, we investigated the effect of inhibiting microglia proliferation on neurological damage post intracerebral hemorrhage (ICH) in a mouse model, an aspect that has never been studied before. Using a colony-stimulating factor-1 receptor antagonist (GW2580), we observed that inhibition of microglia proliferation significantly ameliorated neurobehavioral deficits, attenuated cerebral edema, and reduced hematoma volume after ICH. This intervention was associated with a decrease in pro-inflammatory factors in microglia and an increased infiltration of peripheral regulatory CD8 + CD122+ T cells into the injured brain tissue. The CXCR3/CXCL10 axis is the mechanism of brain homing of regulatory CD8 + CD122+ T cells, and the high expression of IL-10 is the hallmark of their synergistic anti-inflammatory effect with microglia. And activated astrocytes around the insult site are a prominent source of CXCL10. Thus, inhibition of microglial proliferation offers a new perspective for clinical translation. The cross-talk between multiple cells involved in the regulation of the inflammatory response highlights the comprehensive nature of neuroimmunomodulation.

Astrocyte-Microglia Crosstalk: A Novel Target for the Treatment of Migraine

Migraine is a pervasive neurologic disease closely related to neurogenic inflammation. The astrocytes and microglia in the central nervous system are vital in inducing neurogenic inflammation in migraine. Recently, it has been found that there may be a crosstalk phenomenon between microglia and astrocytes, which plays a crucial part in the pathology and treatment of Alzheimer's disease and other central nervous system diseases closely related to inflammation, thus becoming a novel hotspot in neuroimmune research. However, the role of the crosstalk between microglia and astrocytes in the pathogenesis and treatment of migraine is yet to be discussed. Based on the preliminary literature reports, we have reviewed relevant evidence of the crosstalk between microglia and astrocytes in the pathogenesis of migraine and summarized the crosstalk pathways, thereby hoping to provide novel ideas for future research and treatment.

Neuroactive Steroids, Toll-like Receptors, and Neuroimmune Regulation: Insights into Their Impact on Neuropsychiatric Disorders

Pregnane neuroactive steroids, notably allopregnanolone and pregnenolone, exhibit efficacy in mitigating inflammatory signals triggered by toll-like receptor (TLR) activation, thus attenuating the production of inflammatory factors. Clinical studies highlight their therapeutic potential, particularly in conditions like postpartum depression (PPD), where the FDA-approved compound brexanolone, an intravenous formulation of allopregnanolone, effectively suppresses TLR-mediated inflammatory pathways, predicting symptom improvement. Additionally, pregnane neurosteroids exhibit trophic and anti-inflammatory properties, stimulating the production of vital trophic proteins and anti-inflammatory factors. Androstane neuroactive steroids, including estrogens and androgens, along with dehydroepiandrosterone (DHEA), display diverse effects on TLR expression and activation. Notably, androstenediol (ADIOL), an androstane neurosteroid, emerges as a potent anti-inflammatory agent, promising for therapeutic interventions. The dysregulation of immune responses via TLR signaling alongside reduced levels of endogenous neurosteroids significantly contributes to symptom severity across various neuropsychiatric disorders. Neuroactive steroids, such as allopregnanolone, demonstrate efficacy in alleviating symptoms of various neuropsychiatric disorders and modulating neuroimmune responses, offering potential intervention avenues. This review emphasizes the significant therapeutic potential of neuroactive steroids in modulating TLR signaling pathways, particularly in addressing inflammatory processes associated with neuropsychiatric disorders. It advances our understanding of the complex interplay between neuroactive steroids and immune responses, paving the way for personalized treatment strategies tailored to individual needs and providing insights for future research aimed at unraveling the intricacies of neuropsychiatric disorders.

ALS iPSC-derived microglia and motor neurons respond to astrocyte-targeted IL-10 and CCL2 modulation

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the loss of upper and lower motor neurons (MNs). The loss of MNs in ALS leads to muscle weakness and wasting, respiratory failure, and death often within two years of diagnosis. Glial cells in ALS show aberrant expression of pro-inflammatory and neurotoxic proteins associated with activation and have been proposed as ideal therapeutic targets. In this study, we examined astrocyte-targeted treatments to reduce glial activation and neuron pathology using cells differentiated from ALS patient-derived iPSC carrying SOD1 and C9ORF72 mutations. Specifically, we tested the ability of increasing interleukin 10 (IL-10) and reducing C-C motif chemokine ligand 2 (CCL2/MCP-1) signaling targeted to astrocytes to reduce activation phenotypes in both astrocytes and microglia. Overall, we found IL10/CCL2NAb treated astrocytes to support anti-inflammatory phenotypes and reduce neurotoxicity, through different mechanisms in SOD1 and C9ORF72 cultures. We also found altered responses of microglia and motor neurons to astrocytic influences when cells were cultured together rather than in isolation. Together these data support IL-10 and CCL2 as non-mutation-specific therapeutic targets for ALS and highlight the role of glial-mediated pathology in this disease.

Neuroinflammation and Post-Stroke Depression: Focus on the Microglia and Astrocytes

Post-stroke depression (PSD), a frequent and disabling complication of stroke, has a strong impact on almost thirty percent of stroke survivors. The pathogenesis of PSD is not completely clear so far. Neuroinflammation following stroke is one of underlying mechanisms that involves in the pathophysiology of PSD and plays an important function in the development of depression and is regarded as a sign of depression. During the neuroinflammation after ischemic stroke onset, both astrocytes and microglia undergo a series of morphological and functional changes and play pro-inflammatory or anti-inflammatory effect in the pathological process of stroke. Importantly, astrocytes and microglia exert dual roles in the pathological process of PSD due to the phenotypic transformation. We summarize the latest evidence of neuroinflammation involving in PSD in this review, focus on the phenotypic transformation of microglia and astrocytes following ischemic stroke and reveal the dual roles of both microglia and astrocytes in the PSD via modulating the neuroinflammation.

Deplete and repeat: microglial CSF1R inhibition and traumatic brain injury

Traumatic brain injury (TBI) is a public health burden affecting millions of people. Sustained neuroinflammation after TBI is often associated with poor outcome. As a result, increased attention has been placed on the role of immune cells in post-injury recovery. Microglia are highly dynamic after TBI and play a key role in the post-injury neuroinflammatory response. Therefore, microglia represent a malleable post-injury target that could substantially influence long-term outcome after TBI. This review highlights the cell specific role of microglia in TBI pathophysiology. Microglia have been manipulated via genetic deletion, drug inhibition, and pharmacological depletion in various pre-clinical TBI models. Notably, colony stimulating factor 1 (CSF1) and its receptor (CSF1R) have gained much traction in recent years as a pharmacological target on microglia. CSF1R is a transmembrane tyrosine kinase receptor that is essential for microglia proliferation, differentiation, and survival. Small molecule inhibitors targeting CSF1R result in a swift and effective depletion of microglia in rodents. Moreover, discontinuation of the inhibitors is sufficient for microglia repopulation. Attention is placed on summarizing studies that incorporate CSF1R inhibition of microglia. Indeed, microglia depletion affects multiple aspects of TBI pathophysiology, including neuroinflammation, oxidative stress, and functional recovery with measurable influence on astrocytes, peripheral immune cells, and neurons. Taken together, the data highlight an important role for microglia in sustaining neuroinflammation and increasing risk of oxidative stress, which lends to neuronal damage and behavioral deficits chronically after TBI. Ultimately, the insights gained from CSF1R depletion of microglia are critical for understanding the temporospatial role that microglia develop in mediating TBI pathophysiology and recovery.

Understanding immune microenvironment alterations in the brain to improve the diagnosis and treatment of diverse brain diseases

Abnormal inflammatory states in the brain are associated with a variety of brain diseases. The dynamic changes in the number and function of immune cells in cerebrospinal fluid (CSF) are advantageous for the early prediction and diagnosis of immune diseases affecting the brain. The aggregated factors and cells in inflamed CSF may represent candidate targets for therapy. The physiological barriers in the brain, such as the blood‒brain barrier (BBB), establish a stable environment for the distribution of resident immune cells. However, the underlying mechanism by which peripheral immune cells migrate into the brain and their role in maintaining immune homeostasis in CSF are still unclear. To advance our understanding of the causal link between brain diseases and immune cell status, we investigated the characteristics of immune cell changes in CSF and the molecular mechanisms involved in common brain diseases. Furthermore, we summarized the diagnostic and treatment methods for brain diseases in which immune cells and related cytokines in CSF are used as targets. Further investigations of the new immune cell subtypes and their contributions to the development of brain diseases are needed to improve diagnostic specificity and therapy.

Glaucoma: from pathogenic mechanisms to retinal glial cell response to damage

Glaucoma is a neurodegenerative disease of the retina characterized by the irreversible loss of retinal ganglion cells (RGCs) leading to visual loss. Degeneration of RGCs and loss of their axons, as well as damage and remodeling of the lamina cribrosa are the main events in the pathogenesis of glaucoma. Different molecular pathways are involved in RGC death, which are triggered and exacerbated as a consequence of a number of risk factors such as elevated intraocular pressure (IOP), age, ocular biomechanics, or low ocular perfusion pressure. Increased IOP is one of the most important risk factors associated with this pathology and the only one for which treatment is currently available, nevertheless, on many cases the progression of the disease continues, despite IOP control. Thus, the IOP elevation is not the only trigger of glaucomatous damage, showing the evidence that other factors can induce RGCs death in this pathology, would be involved in the advance of glaucomatous neurodegeneration. The underlying mechanisms driving the neurodegenerative process in glaucoma include ischemia/hypoxia, mitochondrial dysfunction, oxidative stress and neuroinflammation. In glaucoma, like as other neurodegenerative disorders, the immune system is involved and immunoregulation is conducted mainly by glial cells, microglia, astrocytes, and Müller cells. The increase in IOP produces the activation of glial cells in the retinal tissue. Chronic activation of glial cells in glaucoma may provoke a proinflammatory state at the retinal level inducing blood retinal barrier disruption and RGCs death. The modulation of the immune response in glaucoma as well as the activation of glial cells constitute an interesting new approach in the treatment of glaucoma.

The exploration of neuroinflammatory mechanism by which CRHR2 deficiency induced anxiety disorder

Inflammation stimulates the hypothalamic-pituitary adrenal (HPA) axis and triggers glial neuroinflammatory phenotypes, which reduces monoamine neurotransmitters by activating indoleamine 2,3-dioxygenase enzyme. These changes can induce psychiatric diseases, including anxiety. Corticotropin releasing hormone receptor 2 (CRHR2) in the HPA axis is involved in the etiology of anxiety. Omega(n)-3 polyunsaturated fatty acids (PUFAs) can attenuate anxiety through anti-inflammation and HPA axis modulation. However, the underlying molecular mechanism by CRHR2 modulates anxiety and its correlation with neuroinflammation remain unclear. Here, we first constructed a crhr2 zebrafish mutant line, and evaluated anxiety-like behaviors, gene expression associated with the HPA axis, neuroinflammatory response, neurotransmitters, and PUFAs profile in crhr2+/+ and crhr2-/- zebrafish. The crhr2 deficiency decreased cortisol levels and up-regulated crhr1 and down-regulated crhb, crhbp, ucn3l and proopiomelanocortin a (pomc a) in zebrafish. Interestingly, a significant increase in the neuroinflammatory markers, translocator protein (TSPO) and the activation of microglia M1 phenotype (CD11b) were found in crhr2-/- zebrafish. As a consequence, the expression of granulocyte-macrophage colony-stimulating factor, pro-inflammatory cytokines vascular endothelial growth factor, and astrocyte A1 phenotype c3 were up-regulated. While microglia anti-inflammatory phenotype (CD206), central anti-inflammatory cytokine interleukin-4, arginase-1, and transforming growth factor-β were downregulated. In parallel, crhr2-deficient zebrafish showed an upregulation of vdac1 protein, a TSPO ligand, and its downstream caspase-3. Furthermore, 5-HT/5-HIAA ratio was decreased and n-3 PUFAs deficiency was identified in crhr2-/- zebrafish. In conclusion, anxiety-like behavior displayed by crhr2-deficient zebrafish may be caused by the HPA axis dysfunction and enhanced neuroinflammation, which resulted in n-3 PUFAs and monoamine neurotransmitter reductions.

Toward identifying key mechanisms of progression in multiple sclerosis

A major therapeutic goal in the treatment of multiple sclerosis (MS) is to prevent the accumulation of disability over an often decades-long disease course. Disability progression can result from acute relapses as well as from CNS intrinsic parenchymal disintegration without de novo CNS lesion formation. Research focus has shifted to progression not associated with acute inflammation, as it is not sufficiently controlled by currently available treatments. This review outlines how recent advances in the understanding of the pathogenesis of progressive MS have been facilitated by the development of more precise, less static pathogenetic concepts of progressive MS, as well as by new techniques for the analysis of region-specific proteomic and transcriptomic signatures in the human CNS. We highlight key drivers of MS disease progression and potential targets in its treatment.

Secretory products of DPSC mitigate inflammatory effects in microglial cells by targeting MAPK pathway

Activated microglial cells in the central nervous system (CNS) are the main contributors to neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease. Inhibiting their activation will help in reducing inflammation and oxidative stress during pathogenesis, potentially limiting the progression of the diseases. The immunomodulation properties of dental pulp-derived stem cells (DPSC) make it a promising therapy for neurodegenerative disorders. This study aims to determine whether secretory factors of DPSC (DPSC℗) inhibit inflammation and proliferation of microglial cells and define the molecular mechanisms. Our quantitative RT-PCR analysis showed that the DPSC℗ reduced the markers of the inflammation and induced anti-inflammatory molecules in microglial cells. DPSC ℗ reduced the intracellular and mitochondrial reactive oxygen species (ROS) production and mitochondrial membrane potential in microglial cells. In addition, DPSC ℗ decreased the cellular bioenergetics parameters related to oxygen consumption rate (OCAR) and extracellular acidification rate (ECAR). We found that DPSC℗ inhibited microglial cell proliferation by activating a checkpoint molecule, Chk1 leading an arrest at the G1 phase of the cell cycle. To define the mechanism, we performed the western blot analysis and observed that the MAPK P38 pathway was inhibited by DPSC℗. Furthermore, a System biology analysis revealed that the BDNF and GDNF, secretory factors of DPSC, blocked at the phosphorylation site (Tyr 182) of the P38 molecule resulting in the inhibition of downstream signaling of inflammation. These data suggest that the DPSC℗ may be a potential therapeutic agent for neurodegenerative diseases.

Microglia in Central Control of Metabolism

Beyond their role as brain immune cells, microglia act as metabolic sensors in response to changes in nutrient availability, thus playing a role in energy homeostasis. This review highlights the evidence and challenges of studying the role of microglia in metabolism regulation.

Modulating the polarization phenotype of microglia - A valuable strategy for central nervous system diseases

Central nervous system (CNS) diseases have become one of the leading causes of death in the global population. The pathogenesis of CNS diseases is complicated, so it is important to find the patterns of the disease to improve the treatment strategy. Microglia are considered to be a double-edged sword, playing both harmful and beneficial roles in CNS diseases. Therefore, it is crucial to understand the progression of the disease and the changes in the polar phenotype of microglia to provide guidance in the treatment of CNS diseases. Microglia activation may evolve into different phenotypes: M1 and M2 types. We focused on the roles that M1 and M2 microglia play in regulating intercellular dialogues, pathological reactions and specific diseases in CNS diseases. Importantly, we summarized the strategies used to modulate the polarization phenotype of microglia, including traditional pharmacological modulation, biological therapies, and physical strategies. This review will contribute to the development of potential strategies to modulate microglia polarization phenotypes and provide new alternative therapies for CNS diseases.

Perspective from single-cell sequencing: Is inflammation in acute ischemic stroke beneficial or detrimental?

BACKGROUND

Acute ischemic stroke (AIS) is a common cerebrovascular event associated with high incidence, disability, and poor prognosis. Studies have shown that various cell types, including microglia, astrocytes, oligodendrocytes, neurons, and neutrophils, play complex roles in the early stages of AIS and significantly affect its prognosis. Thus, a comprehensive understanding of the mechanisms of action of these cells will be beneficial for improving stroke prognosis. With the rapid development of single-cell sequencing technology, researchers have explored the pathophysiological mechanisms underlying AIS at the single-cell level.

METHOD

We systematically summarize the latest research on single-cell sequencing in AIS.

RESULT

In this review, we summarize the phenotypes and functions of microglia, astrocytes, oligodendrocytes, neurons, neutrophils, monocytes, and lymphocytes, as well as their respective subtypes, at different time points following AIS. In particular, we focused on the crosstalk between microglia and astrocytes, oligodendrocytes, and neurons. Our findings reveal diverse and sometimes opposing roles within the same cell type, with the possibility of interconversion between different subclusters.

CONCLUSION

This review offers a pioneering exploration of the functions of various glial cells and cell subclusters after AIS, shedding light on their regulatory mechanisms that facilitate the transformation of detrimental cell subclusters towards those that are beneficial for improving the prognosis of AIS. This approach has the potential to advance the discovery of new specific targets and the development of drugs, thus representing a significant breakthrough in addressing the challenges in AIS treatment.

Investigating the Potential Mechanisms and Therapeutic Targets of Inflammatory Cytokines in Post-stroke Depression

Post-stroke depression (PSD) affects approximately one-third of stroke survivors, severely impacting general recovery and quality of life. Despite extensive studies, the exact mechanisms underlying PSD remain elusive. However, emerging evidence implicates proinflammatory cytokines, including interleukin-1β, interleukin-6, tumor necrosis factor-alpha, and interleukin-18, play critical roles in PSD development. These cytokines contribute to PSD through various mechanisms, including hypothalamic-pituitary-adrenal (HPA) axis dysfunction, neurotransmitter alterations, neurotrophic factor changes, gut microbiota imbalances, and genetic predispositions. This review is aimed at exploring the role of cytokines in stroke and PSD while identifying their potential as specific therapeutic targets for managing PSD. A more profound understanding of the mechanisms regulating inflammatory cytokine expression and anti-inflammatory cytokines like interleukin-10 in PSD may facilitate the development of innovative interventions to improve outcomes for stroke survivors experiencing depression.

Emerging Roles of Microglia in Blood-Brain Barrier Integrity in Aging and Neurodegeneration

The blood-brain barrier (BBB) is a highly selective interface between the blood and the brain parenchyma. It plays an essential role in maintaining a specialized environment for central nervous system function and homeostasis. The BBB disrupts with age, which contributes to the development of many age-related disorders due to central and peripheral toxic factors or BBB dysfunction. Microglia, the resident innate immune cells of the brain, have recently been explored for their ability to directly and indirectly regulate the integrity of the BBB. This review will focus on the current understanding of the molecular mechanisms utilized by microglia to regulate BBB integrity and how this becomes disrupted in aging and age-associated diseases. We will also discuss the rationale for considering microglia as a therapeutic target to prevent or slow down neurodegeneration.

Neurosteroid [3α,5α]-3-hydroxy-pregnan-20-one enhances IL-10 production via endosomal TRIF-dependent TLR4 signaling pathway

Background

Previous studies demonstrated the inhibitory effect of allopregnanolone (3α,5α-THP) on the activation of inflammatory toll-like receptor 4 (TLR4) signals in RAW264.7 macrophages and the brains of selectively bred alcohol-preferring (P) rats. In the current study, we investigated the impact of 3α,5α-THP on the levels of IL-10 and activation of the TRIF-dependent endosomal TLR4 pathway.

Methods

The amygdala and nucleus accumbens (NAc) of P rats, which exhibit innately activated TLR4 pathways as well as RAW264.7 cells, were used. Enzyme-linked immunosorbent assays (ELISA) and immunoblotting assays were used to ascertain the effects of 3α,5α-THP on the TRIF-dependent endosomal TLR4 pathway and endosomes were isolated to examine translocation of TLR4 and TRIF. Additionally, we investigated the effects of 3α,5α-THP and 3α,5α-THDOC (0.1, 0.3, and 1.0 µM) on the levels of IL-10 in RAW264.7 macrophages. Finally, we examined whether inhibiting TRIF (using TRIF siRNA) in RAW264.7 cells altered the levels of IL-10.

Results

3α,5α-THP administration facilitated activation of the endosomal TRIF-dependent TLR4 pathway in males, but not female P rats. 3α,5α-THP increased IL-10 levels (+13.2 ± 6.5%) and BDNF levels (+21.1 ± 11.5%) in the male amygdala. These effects were associated with increases in pTRAM (+86.4 ± 28.4%), SP1 (+122.2 ± 74.9%), and PI(3)K-p110δ (+61.6 ± 21.6%), and a reduction of TIRAP (-13.7 ± 6.0%), indicating the activation of the endosomal TRIF-dependent TLR4 signaling pathway. Comparable effects were observed in NAc of these animals. Furthermore, 3α,5α-THP enhanced the accumulation of TLR4 (+43.9 ± 11.3%) and TRIF (+64.8 ± 32.8%) in endosomes, with no significant effect on TLR3 accumulation. Additionally, 3α,5α-THP facilitated the transition from early endosomes to late endosomes (increasing Rab7 levels: +35.8 ± 18.4%). In RAW264.7 cells, imiquimod (30 µg/mL) reduced IL-10 while 3α,5α-THP and 3α,5α-THDOC (0.1, 0.3, and 1.0 µM) restored IL-10 levels. To determine the role of the TRIF-dependent TLR4 signaling pathway in IL-10 production, the downregulation of TRIF (-62.9 ± 28.2%) in RAW264.7 cells led to a reduction in IL-10 levels (-42.3 ± 8.4%). TRIF (-62.9 ± 28.2%) in RAW264.7 cells led to a reduction in IL-10 levels (-42.3 ± 8.4%) and 3α,5α-THP (1.0 µM) no longer restored the reduced IL-10 levels.

Conclusion

The results demonstrate 3α,5α-THP enhancement of the endosomal TLR4-TRIF anti-inflammatory signals and elevations of IL-10 in male P rat brain that were not detected in female P rat brain. These effects hold significant implications for controlling inflammatory responses in both the brain and peripheral immune cells.

Macrophage polarization in spinal cord injury repair and the possible role of microRNAs: A review

The prevention, treatment, and rehabilitation of spinal cord injury (SCI) have always posed significant medical challenges. After mechanical injury, disturbances in microcirculation, edema formation, and the generation of free radicals lead to additional damage, impeding effective repair processes and potentially exacerbating further dysfunction. In this context, inflammatory responses, especially the activation of macrophages, play a pivotal role. Different phenotypes of macrophages have distinct effects on inflammation. Activation of classical macrophage cells (M1) promotes inflammation, while activation of alternative macrophage cells (M2) inhibits inflammation. The polarization of macrophages is crucial for disease healing. A non-coding RNA, known as microRNA (miRNA), governs the polarization of macrophages, thereby reducing inflammation following SCI and facilitating functional recovery. This study elucidates the inflammatory response to SCI, focusing on the infiltration of immune cells, specifically macrophages. It examines their phenotype and provides an explanation of their polarization mechanisms. Finally, this paper introduces several well-known miRNAs that contribute to macrophage polarization following SCI, including miR-155, miR-130a, and miR-27 for M1 polarization, as well as miR-22, miR-146a, miR-21, miR-124, miR-223, miR-93, miR-132, and miR-34a for M2 polarization. The emphasis is placed on their potential therapeutic role in SCI by modulating macrophage polarization, as well as the present developments and obstacles of miRNA clinical therapy.

Microglia trigger the structural plasticity of GABAergic neurons in the hippocampal CA1 region of a lipopolysaccharide-induced neuroinflammation model

It is well-established that microglia-mediated neuroinflammatory response involves numerous neuropsychiatric and neurodegenerative diseases. While the role of microglia in excitatory synaptic transmission has been widely investigated, the impact of innate immunity on the structural plasticity of GABAergic inhibitory synapses is not well understood. To investigate this, we established an inflammation model using lipopolysaccharide (LPS) and observed a prolonged microglial response in the hippocampal CA1 region of mice, which was associated with cognitive deficits in the open field test, Y-maze test, and novel object recognition test. Furthermore, we found an increased abundance of GABAergic interneurons and GABAergic synapse formation in the hippocampal CA1 region. The cognitive impairment caused by LPS injection could be reversed by blocking GABA receptor activity with (-)-Bicuculline methiodide. These findings suggest that the upregulation of GABAergic synapses induced by LPS-mediated microglial activation leads to cognitive dysfunction. Additionally, the depletion of microglia by PLX3397 resulted in a decrease in GABAergic interneurons and GABAergic inhibitory synapses, which blocked the cognitive decline induced by LPS. In conclusion, our findings indicate that excessive reinforcement of GABAergic inhibitory synapse formation via microglial activation contributes to LPS-induced cognitive impairment.

Mesenchymal Stem Cells Combined With Electroacupuncture Treatment Regulate the Subpopulation of Macrophages and Astrocytes to Facilitate Axonal Regeneration in Transected Spinal Cord

OBJECTIVE

Herein, we investigated whether mesenchymal stem cells (MSCs) transplantation combined with electroacupuncture (EA) treatment could decrease the proportion of proinflammatory microglia/macrophages and neurotoxic A1 reactive astrocytes and inhibit glial scar formation to enhance axonal regeneration after spinal cord injury (SCI).

METHODS

Adult rats were divided into 5 groups after complete transection of the spinal cord at the T10 level: a control group, a nonacupoint EA (NA-EA) group, an EA group, an MSC group, and an MSCs+EA group. Immunofluorescence labeling, quantitative real-time polymerase chain reaction, enzyme-linked immunosorbent assay, and Western blots were performed.

RESULTS

The results showed that MSCs+EA treatment reduced the proportion of proinflammatory M1 subtype microglia/macrophages, but increased the differentiation of anti-inflammatory M2 phenotype cells, thereby suppressing the mRNA and protein expression of proinflammatory cytokines (tumor necrosis factor-α and IL-1β) and increasing the expression of an anti-inflammatory cytokine (interleukin [IL]-10) on days 7 and 14 after SCI. The changes in expression correlated with the attenuated neurotoxic A1 reactive astrocytes and glial scar, which in turn facilitated the axonal regeneration of the injured spinal cord. In vitro, the proinflammatory cytokines increased the level of proliferation of astrocytes and increased the expression levels of C3, glial fibrillary acidic protein, and chondroitin sulfate proteoglycan. These effects were blocked by administering inhibitors of ErbB1 and signal transducer and activator of transcription 3 (STAT3) (AG1478 and AG490) and IL-10.

CONCLUSION

These findings showed that MSCs+EA treatment synergistically regulated the microglia/macrophage subpopulation to reduce inflammation, the formation of neurotoxic A1 astrocytes, and glial scars. This was achieved by downregulating the ErbB1-STAT3 signal pathway, thereby providing a favorable microenvironment conducive to axonal regeneration after SCI.

Transforming Growth Factor β1 Ameliorates Microglial Activation in Perioperative Neurocognitive Disorders

Perioperative neurocognitive disorder (PND) is a common complication of surgery and anesthesia, especially among older patients. Microglial activation plays a crucial role in the occurrence and development of PND and transforming growth factor beta 1 (TGF-β1) can regulate microglial homeostasis. In the present study, abdominal surgery was performed on 12-14 months-old C57BL/6 mice to establish a PND model. The expression of TGF-β1, TGF-β receptor 1, TGF-β receptor 2, and phosphor-smad2/smad3 (psmad2/smad3) was assessed after anesthesia and surgery. Additionally, we examined changes in microglial activation, morphology, and polarization, as well as neuroinflammation and dendritic spine density in the hippocampus. Behavioral tests, including the Morris water maze and open field tests, were used to examine cognitive function, exploratory locomotion, and emotions. We observed decreased TGF-β1 expression after surgery and anesthesia. Intranasally administered exogenous TGF-β1 increased psmad2/smad3 colocalization with microglia positive for ionized calcium-binding adaptor molecule 1. TGF-β1 treatment attenuated microglial activation, reduced microglial phagocytosis, and reduced surgery- and anesthesia-induced changes in microglial morphology. Compared with the surgery group, TGF-β1 treatment decreased M1 microglial polarization and increased M2 microglial polarization. Additionally, surgery- and anesthesia-induced increase in interleukin 1 beta and tumor necrosis factor-alpha levels was ameliorated by TGF-β1 treatment at postoperative day 3. TGF-β1 also ameliorated cognitive function after surgery and anesthesia as well as rescue dendritic spine loss. In conclusion, surgery and anesthesia induced decrease in TGF-β1 levels in older mice, which may contribute to PND development; however, TGF-β1 ameliorated microglial activation and cognitive dysfunction in PND mice.

Astroglial Connexin 43-Mediated Gap Junctions and Hemichannels: Potential Antidepressant Mechanisms and the Link to Neuroinflammation

Major depression disorder (MDD) is a neuropsychiatric disorder associated with a high suicide rate and a higher disability rate than any other disease. Evidence suggests that the pathological mechanism of MDD is related to astrocyte dysfunction. Depression is mainly associated with the expression of connexin 43 (Cx43) and the function of Cx43-mediated gap junctions and hemichannels in astrocytes. Moreover, neuroinflammation has been a hotspot in research on the pathology of depression, and Cx43-mediated functions are thought to be involved in neuroinflammation-related depression. However, the specific mechanism of Cx43-mediated functions in neuroinflammation-related depression pathology remains unclear. Therefore, this review summarizes and discusses Cx43 expression, the role of gap junction intercellular communication, and its relationship with neuroinflammation in depression. This review also focuses on the effects of antidepressant drugs (e.g., monoamine antidepressants, psychotropic drugs, and N-methyl-D-aspartate receptor antagonists) on Cx43-mediated function and provides evidence for Cx43 as a novel target for the treatment of MDD. The pathogenesis of MDD is related to astrocyte dysfunction, with reduced Cx43 expression, GJ dysfunction, decreased GJIC and reduced BDNF expression in the depressed brain. The effect of Cx43 on neuroinflammation-related depression involving inflammatory cytokines, glutamate excitotoxicity, and HPA axis dysregulation. Antidepressant drugs targeting Cx43 can effectively relieve depressive symptoms.

The role of glial autophagy in Alzheimer's disease

Although Alzheimer's disease is the most pervasive neurodegenerative disorder, the mechanism underlying its development is still not precisely understood. Available data indicate that pathophysiology of this disease may involve impaired autophagy in glial cells. The dysfunction is manifested as reduced ability of astrocytes and microglia to clear abnormal protein aggregates. Consequently, excessive accumulation of amyloid beta plaques and neurofibrillary tangles activates microglia and astrocytes leading to decreased number of mature myelinated oligodendrocytes and death of neurons. These pathologic effects of autophagy dysfunction can be rescued by pharmacological activation of autophagy. Therefore, a deeper understanding of the molecular mechanisms involved in autophagy dysfunction in glial cells in Alzheimer's disease may lead to the development of new therapeutic strategies. However, such strategies need to take into consideration differences in regulation of autophagy in different types of neuroglia.

Sepsis-associated encephalopathy: From pathophysiology to clinical management

Sepsis-associated encephalopathy, which presents as delirium and coma, is a significant complication of sepsis characterized by acute brain dysfunction. The presence of inflammatory pathological changes in the brain of sepsis patients and animal models has been recognized since the 1920 s, initially attributed to the entry of microbial toxins into the brain. In the early 2000 s, attention shifted towards the impact of oxidative stress, the cholinergic system, and cytokines on brain function following sepsis onset. More recently, sepsis-associated encephalopathy has been defined as a diffuse brain dysfunction not directly caused by pathogenic infection of the brain. Currently, there is no evidence-based standard for diagnosing sepsis-associated encephalopathy, and clinical management is primarily focused on symptomatic and supportive measures. This review aims to explore the pathophysiology of sepsis-associated encephalopathy and establish the connection between pathophysiological mechanisms and clinical characteristics. We hope that this work will spark the interest of researchers from various fields and contribute to the advancement of sepsis-associated encephalopathy research.

Neuroprotective astroglial response to neural damage and its relevance to affective disorders

Astrocytes not only support neuronal function with essential roles in synaptic neurotransmission, action potential propagation, metabolic support, or neuroplastic and developmental adaptations. They also respond to damage or dysfunction in surrounding neurons and oligodendrocytes by releasing neurotrophic factors and other molecules that increase the survival of the supported cells or contribute to mechanisms of structural and molecular restoration. The neuroprotective responsiveness of astrocytes is based on their ability to sense signals of degeneration, metabolic jeopardy and structural damage, and on their aptitude to locally deliver specific molecules to remedy threats to the molecular and structural features of their cellular partners. To the extent that neuronal and other glial cell disturbances are known to occur in affective disorders, astrocyte responsiveness to those disturbances may help to better understand the roles astrocytes play in affective disorders. The astrocytic sensing apparatus supporting those responses involves receptors for neurotransmitters, purines, cell adhesion molecules and growth factors. Astrocytes also share with the immune system the capacity of responding to cytokines released upon neuronal damage. In addition, in responses to specific signals astrocytes release unique factors such as clusterin or humanin that have been shown to exert potent neuroprotective effects. Astrocytes integrate the signals above to further deliver structural lipids, removing toxic metabolites, stabilizing the osmotic environment, normalizing neurotransmitters, providing anti-oxidant protection, facilitating synaptogenesis and acting as barriers to contain varied deleterious signals, some of which have been described in brain regions relevant to affective disorders and related animal models. Since various of the injurious signals that activate astrocytes have been implicated in different aspects of the etiopathology of affective disorders, particularly in relation to the diagnosis of depression, potentiating the corresponding astrocyte neuroprotective responses may provide additional opportunities to improve or complement available pharmacological and behavioral therapies for affective disorders.

Role of Crosstalk between Glial Cells and Immune Cells in Blood-Brain Barrier Damage and Protection after Acute Ischemic Stroke

Blood-brain barrier (BBB) damage is the main pathological basis for acute ischemic stroke (AIS)-induced cerebral vasogenic edema and hemorrhagic transformation (HT). Glial cells, including microglia, astrocytes, and oligodendrocyte precursor cells (OPCs)/oligodendrocytes (OLs) play critical roles in BBB damage and protection. Recent evidence indicates that immune cells also have an important role in BBB damage, vasogenic edema and HT. Therefore, regulating the crosstalk between glial cells and immune cells would hold the promise to alleviate AIS-induced BBB damage. In this review, we first introduce the roles of glia cells, pericytes, and crosstalk between glial cells in the damage and protection of BBB after AIS, emphasizing the polarization, inflammatory response and crosstalk between microglia, astrocytes, and other glia cells. We then describe the role of glial cell-derived exosomes in the damage and protection of BBB after AIS. Next, we specifically discuss the crosstalk between glial cells and immune cells after AIS. Finally, we propose that glial cells could be a potential target for alleviating BBB damage after AIS and we discuss some molecular targets and potential strategies to alleviate BBB damage by regulating glial cells after AIS.

Microglia in neurodegenerative diseases: mechanism and potential therapeutic targets

Microglia activation is observed in various neurodegenerative diseases. Recent advances in single-cell technologies have revealed that these reactive microglia were with high spatial and temporal heterogeneity. Some identified microglia in specific states correlate with pathological hallmarks and are associated with specific functions. Microglia both exert protective function by phagocytosing and clearing pathological protein aggregates and play detrimental roles due to excessive uptake of protein aggregates, which would lead to microglial phagocytic ability impairment, neuroinflammation, and eventually neurodegeneration. In addition, peripheral immune cells infiltration shapes microglia into a pro-inflammatory phenotype and accelerates disease progression. Microglia also act as a mobile vehicle to propagate protein aggregates. Extracellular vesicles released from microglia and autophagy impairment in microglia all contribute to pathological progression and neurodegeneration. Thus, enhancing microglial phagocytosis, reducing microglial-mediated neuroinflammation, inhibiting microglial exosome synthesis and secretion, and promoting microglial conversion into a protective phenotype are considered to be promising strategies for the therapy of neurodegenerative diseases. Here we comprehensively review the biology of microglia and the roles of microglia in neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, multiple system atrophy, amyotrophic lateral sclerosis, frontotemporal dementia, progressive supranuclear palsy, corticobasal degeneration, dementia with Lewy bodies and Huntington's disease. We also summarize the possible microglia-targeted interventions and treatments against neurodegenerative diseases with preclinical and clinical evidence in cell experiments, animal studies, and clinical trials.

Role of cytokines and reactive oxygen species in brain aging

Aging is a complex process that produces profound effects on the brain. Although a number of external factors can promote the initiation and progression of brain aging, peripheral and central changes in the immune cells with time, also play an important role. Immunosenescence, which is an age-associated decline in immune function and Inflammaging, a low-grade inflammatory state in the aging brain contribute to an elevation in cytokine and reactive oxygen species production. In this review, we focus on the pro-inflammatory state that is established in the brain as a consequence of these two phenomena and the resulting detrimental changes in brain structure, function and repair that lead to a decline in central and neuroendocrine function.

A cutting-edge strategy for spinal cord injury treatment: resident cellular transdifferentiation

Spinal cord injury causes varying degrees of motor and sensory function loss. However, there are no effective treatments for spinal cord repair following an injury. Moreover, significant preclinical advances in bioengineering and regenerative medicine have not yet been translated into effective clinical therapies. The spinal cord's poor regenerative capacity makes repairing damaged and lost neurons a critical treatment step. Reprogramming-based neuronal transdifferentiation has recently shown great potential in repair and plasticity, as it can convert mature somatic cells into functional neurons for spinal cord injury repair in vitro and in vivo, effectively halting the progression of spinal cord injury and promoting functional improvement. However, the mechanisms of the neuronal transdifferentiation and the induced neuronal subtypes are not yet well understood. This review analyzes the mechanisms of resident cellular transdifferentiation based on a review of the relevant recent literature, describes different molecular approaches to obtain different neuronal subtypes, discusses the current challenges and improvement methods, and provides new ideas for exploring therapeutic approaches for spinal cord injury.

Morphofunctional Changes in Brain and Peripheral Blood in Adult and Aged Wistar Rats with AlCl3-Induced Neurodegeneration

BACKGROUND

the general lifespan has been prolonged greatly during the past century, and the incidence of age-associated diseases, including neurodegenerative ones, has increased as well. However, modelling of age-related pathologies is mostly conducted on adult rodents. We studied morphofunctional changes in the brain and peripheral blood of adult Wistar rats in comparison with old Wistar rats to determine age-related physiological changes and differences in adaptive reactions to AlCl3 exposure.

METHODS

the work was performed on adult and old male Wistar rats. The animals consumed a 100 mg/kg solution of AlCl3 each day for 60 days. Morphological changes of neurons and microglia, mRNA expression levels of pro-inflammatory and anti-inflammatory cytokines, microglia activation markers, amyloid-related proteins, and hallmarks of cellular senescence, monocyte, and lymphocyte subpopulations in the peripheral blood were examined.

RESULTS

old rats showed increasing hyperchromic neurons in the hippocampus; activation of microglia; upregulation of pro-inflammatory cytokines and cellular senescence markers; downregulation of anti-inflammatory cytokines; and Hif-1a and a decrease in B-cells and monocyte in peripheral blood.

CONCLUSION

compared to young animals, aged rats respond to aluminum exposure with a severe decline of most cells' function and irreversible neuronal loss. Regarding all reported data, neurodegeneration modelling and investigating of factors capable of accelerating or preventing it should be performed in experimental work on aged animals.

Crosstalk of Highly Purified Microglia and Astrocytes in the Frame of Toll-like Receptor (TLR)2/1 Activation

The major immune cells of the central nervous systems (CNS) are microglia and astrocytes, subsets of the glial cell population. The crosstalk between glia via soluble signaling molecules plays an indispensable role for neuropathologies, brain development as well as homeostasis. However, the investigation of the microglia-astrocyte crosstalk has been hampered due to the lack of suitable glial isolation methods. In this study, we investigated for the first time the crosstalk between highly purified Toll-like receptor (TLR)2-knock out (TLR2-KO) and wild-type (WT) microglia and astrocytes. We examined the crosstalk of TLR2-KO microglia and astrocytes in the presence of WT supernatants of the respective other glial cell type. Interestingly, we observed a significant TNF release by TLR2-KO astrocytes, which were activated with Pam3CSK4-stimulated WT microglial supernatants, strongly indicating a crosstalk between microglia and astrocytes after TLR2/1 activation. Furthermore, transcriptome analysis using RNA-seq revealed a wide range of significant up- and down-regulated genes such as Cd300, Tnfrsf9 or Lcn2, which might be involved in the molecular conversation between microglia and astrocytes. Finally, co-culturing microglia and astrocytes confirmed the prior results by demonstrating a significant TNF release by WT microglia co-cultured with TLR2-KO astrocytes. Our findings suggest a molecular TLR2/1-dependent conversation between highly pure activated microglia and astrocytes via signaling molecules. Furthermore, we demonstrate the first crosstalk experiments using ∼100% pure microglia and astrocyte mono-/co-cultures derived from mice with different genotypes highlighting the urgent need of efficient glial isolation protocols, which particularly holds true for astrocytes.

High concentrations of fructose cause brain damage in mice

Excessive fructose consumption is associated with the incidence of obesity and systemic inflammation, resulting in increased oxidative damage and failure to the function of brain structures. Thus, we hypothesized that fructose consumption will significantly increase inflammation, oxidative damage, and mitochondrial dysfunction in the mouse brain and, consequently, memory damage. The effects of different fructose concentrations on inflammatory and biochemical parameters in the mouse brain were evaluated. Male Swiss mice were randomized into four groups: control, with exclusive water intake, 5%, 10%, and 20% fructose group. The 10% and 20% fructose groups showed an increase in epididymal fat, in addition to higher food consumption. Inflammatory markers were increased in epididymal fat and in some brain structures. In the evaluation of oxidative damage, it was possible to observe significant increases in the hypothalamus, prefrontal cortex, and hippocampus. In the epididymal fat and in the prefrontal cortex, there was a decrease in the activity of the mitochondrial respiratory chain complexes and an increase in the striatum. Furthermore, short memory was impaired in the 10% and 20% groups but not long memory. In conclusion, excess fructose consumption can cause fat accumulation, inflammation, oxidative damage, and mitochondrial dysfunction, which can damage brain structures and consequently memory.

Analysis of Why Alzheimer's Dementia Never Spontaneously Reverses, Suggests the Basis for Curative Treatment

A paradox regarding Alzheimer's dementia (AD) and mild cognitive impairment (MCI) is thats spontaneous cure of AD has never been reported, whereas spontaneous cure for MCI occurs fequently. This article analyzes what accounts for this difference. It holds that it is not merely because, for any condition, a stage is reached beyond which it cannot be reversed, since even widely metastatic cancer would be curable were there effective chemotherapy and rheumatoid arthritis became controllable when immune-suppressant treatment was introduced; thus, so could AD be reversible via effective therapy. The analysis presented leads to an explanation of the paradox that is in four categories: (1) levels of transforming growth factor-β are significantly reduced after the transition from MCI to AD; (2) levels of Wnt/β-catenin are significantly reduced after the transition; (3) there is altered epidermal-mesenchymal transition (EMT) in neurons after the transition; (4) there may be risk factors that are either newly operative or pre-existing but worsened at the time of transition, that are particular to individual patients. It is suggested that addressing and ameliorating all of those four categories might cure AD. Medications to address and ameliorate each of the four categories are described.

Neuroprotective effects of interleukin 10 in spinal cord injury

Spinal cord injury (SCI) starts with a mechanical and/or bio-chemical insult, followed by a secondary phase, leading progressively to severe collapse of the nerve tissue. Compared to the peripheral nervous system, injured spinal cord is characterized by weak axonal regeneration, which leaves most patients impaired or paralyzed throughout lifetime. Therefore, confining, alleviating, or reducing the expansion of secondary injuries and promoting functional connections between rostral and caudal regions of lesion are the main goals of SCI therapy. Interleukin 10 (IL-10), as a pivotal anti-inflammatory and immunomodulatory cytokine, exerts a wide spectrum of positive effects in the treatment of SCI. The mechanisms underlying therapeutic effects mainly include anti-oxidative stress, limiting excessive inflammation, anti-apoptosis, antinociceptive effects, etc. Furthermore, IL-10 displays synergistic effects when combined with cell transplantation or neurotrophic factor, enhancing treatment outcomes. This review lists pleiotropic mechanisms underlying IL-10-mediated neuroprotection after SCI, which may offer fresh perspectives for clinical translation.

Inflammation in the pathogenesis of depression: a disorder of neuroimmune origin

There are several hypotheses concerning the underlying pathophysiological mechanisms of major depression, which centre largely around adaptive changes in neuronal transmission and plasticity, neurogenesis, and circuit and regional connectivity. The immune and endocrine systems are commonly implicated in driving these changes. An intricate interaction of stress hormones, innate immune cells and the actions of soluble mediators of immunity within the nervous system is described as being associated with the symptoms of depression. Bridging endocrine and immune processes to neurotransmission and signalling within key cortical and limbic brain circuits are critical to understanding depression as a disorder of neuroimmune origins. Emergent areas of research include a growing recognition of the adaptive immune system, advances in neuroimaging techniques and mechanistic insights gained from transgenic animals. Elucidation of glial-neuronal interactions is providing additional avenues into promising areas of research, the development of clinically relevant disease models and the discovery of novel therapies. This narrative review focuses on molecular and cellular mechanisms that are influenced by inflammation and stress. The aim of this review is to provide an overview of our current understanding of depression as a disorder of neuroimmune origin, focusing on neuroendocrine and neuroimmune dysregulation in depression pathophysiology. Advances in current understanding lie in pursuit of relevant biomarkers, as the potential of biomarker signatures to improve clinical outcomes is yet to be fully realised. Further investigations to expand biomarker panels including integration with neuroimaging, utilising individual symptoms to stratify patients into more homogenous subpopulations and targeting the immune system for new treatment approaches will help to address current unmet clinical need.

Mechanism of M2 macrophages modulating astrocyte polarization through the TGF-β/PI3K/Akt pathway

Recent studies have revealed that activated astrocytes (AS) are divided into two distinct types, termed A1 and A2. A2 astrocytes are neuroprotective and promote tissue repair and regeneration following spinal cord injury. Whereas, the specific mechanism for the formation of the A2 phenotype remains unclear. This study focused on the PI3K/Akt pathway and examined whether TGF-β secreted by M2 macrophages could mediate A2 polarization by activating this pathway. In this study, we revealed that both M2 macrophages and their conditioned medium (M2-CM) could facilitate the secretion of IL-10, IL-13 and TGF-β from AS, and this effect was significantly reversed after the administration of SB431542 (a TGF-β receptor inhibitor) or LY294002 (a PI3K inhibitor). Moreover, immunofluorescence results demonstrated that TGF-β secreted by M2 macrophages could facilitate the expression of A2 biomarker S100A10 in AS; combined with the results of western blot, it was found that this effect was closely related to the activation of PI3K/Akt pathway in AS. In conclusion, TGF-β secreted by M2 macrophages may induce the conversion of AS to the A2 phenotype through the activation of the PI3K/Akt pathway.

Microglia and the Blood-Brain Barrier: An External Player in Acute and Chronic Neuroinflammatory Conditions

Microglia are the resident immune cells of the central nervous system that guarantee immune surveillance and exert also a modulating role on neuronal synaptic development and function. Upon injury, microglia get activated and modify their morphology acquiring an ameboid phenotype and pro- or anti-inflammatory features. The active role of microglia in blood-brain barrier (BBB) function and their interaction with different cellular components of the BBB-endothelial cells, astrocytes and pericytes-are described. Here, we report the specific crosstalk of microglia with all the BBB cell types focusing in particular on the involvement of microglia in the modulation of BBB function in neuroinflammatory conditions that occur in conjunction with an acute event, such as a stroke, or in a slow neurodegenerative disease, such as Alzheimer's disease. The potential of microglia to exert a dual role, either protective or detrimental, depending on disease stages and environmental conditioning factors is also discussed.

Plasma concentrations of anti-inflammatory cytokine TGF-β are associated with hippocampal structure related to explicit memory performance in older adults

Human cognitive abilities, and particularly hippocampus-dependent memory performance typically decline with increasing age. Immunosenescence, the age-related disintegration of the immune system, is increasingly coming into the focus of research as a considerable factor contributing to cognitive decline. In the present study, we investigated potential associations between plasma levels of pro- and anti-inflammatory cytokines and learning and memory performance as well as hippocampal anatomy in young and older adults. Plasma concentrations of the inflammation marker CRP as well as the pro-inflammatory cytokines IL-6 and TNF-α and the anti-inflammatory cytokine TGF-β₁ were measured in 142 healthy adults (57 young, 24.47 ± 4.48 years; 85 older, 63.66 ± 7.32 years) who performed tests of explicit memory (Verbal Learning and Memory Test, VLMT; Wechsler Memory Scale, Logical Memory, WMS) with an additional delayed recall test after 24 h. Hippocampal volumetry and hippocampal subfield segmentation were performed using FreeSurfer, based on T1-weighted and high-resolution T2-weighted MR images. When investigating the relationship between memory performance, hippocampal structure, and plasma cytokine levels, we found that TGF-β₁ concentrations were positively correlated with the volumes of the hippocampal CA4-dentate gyrus region in older adults. These volumes were in turn positively associated with better performance in the WMS, particularly in the delayed memory test. Our results support the notion that endogenous anti-inflammatory mechanisms may act as protective factors in neurocognitive aging.

Scutellarin Acts via MAPKs Pathway to Promote M2 Polarization of Microglial Cells

Scutellarin, an herbal agent, is known to possess anti-oxidant and anti-inflammatory properties. In activated microglia, it has been reported that this is achieved through acting on the MAPKs, a key pathway that regulates microglia activation. This study sought to determine if scutellarin would affect the commonly described microglia phenotypes, namely, M1 and M2, thought to contribute to pro- and anti-inflammatory roles, respectively. This is in consideration of its potential effect on the polarization of microglia phenotypes that are featured prominently in cerebral ischemia. For this purpose, we have used an experimentally induced cerebral ischemia rat model and LPS-stimulated BV-2 cell model. Thus, by Western blot and immunofluorescence, we show here a noticeable increase in expression of M2 microglia markers, namely, CD206, Arg1, YM1/2, IL-4 and IL-10 in activated microglia both in vivo and in vitro. Besides, we have confirmed that Scutellarin upregulated expression of Arg1, IL-10 and IL-4 in medium supernatants of BV-2 microglia. Remarkably, scutellarin treatment markedly augmented the increased expression of the respective markers in activated microglia. It is therefore suggested scutellarin can exert the polarization of activated microglia from M1 to M2 phenotype. Because M1 microglia are commonly known to be proinflammatory, while M2 microglia are anti-inflammatory and neuroprotective effect, it stands to reason therefore that with the increase of M2 microglia which became predominant by scutellarin, the local inflammatory response is ameliorated. More importantly, we have found that scutellarin promotes the M2 polarization through inhibiting the JNK and p38 signaling pathways, and concomitantly augmenting the ERK1/2 signaling pathway. This lends its strong support from observations in LPS activated BV-2 microglia treated with p38 and JNK inhibitors in which expression of M2 markers was increased; on the other hand, in cells subjected to ERK1/2 inhibitor treatment, the expression was suppressed. In light of the above, MAPKs pathway is deemed to be a potential therapeutic target of scutellarin in mitigating microglia mediated neuroinflammation in activated microglia.

Neuropathology of New-Onset Refractory Status Epilepticus (NORSE)

New-Onset Refractory Status Epilepticus (NORSE), including its subtype with a preceding febrile illness known as FIRES (Febrile Infection-Related Epilepsy Syndrome), is one of the most severe forms of status epilepticus. Despite an extensive workup (clinical evaluation, EEG, imaging, biological tests), the majority of NORSE cases remain unexplained (i.e., "cryptogenic NORSE"). Understanding the pathophysiological mechanisms underlying cryptogenic NORSE and the related long-term consequences is crucial to improve patient management and preventing secondary neuronal injury and drug-resistant post-NORSE epilepsy. Previously, neuropathological evaluations conducted on biopsies or autopsies have been found helpful for identifying the etiologies of some cases that were previously of unknown cause. Here, we summarize the findings of studies reporting neuropathology findings in patients with NORSE, including FIRES. We identified 64 cryptogenic cases and 66 neuropathology tissue samples, including 37 biopsies, 18 autopsies, and seven epilepsy surgeries (the type of tissue sample was not detailed for 4 cases). We describe the main neuropathology findings and place a particular emphasis on cases for which neuropathology findings helped establish a diagnosis or elucidate the pathophysiology of cryptogenic NORSE, or on described cases in which neuropathology findings supported the selection of specific treatments for patients with NORSE.