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

H2S Regulates the Phenotypic Transformation of Astrocytes Following Cerebral Ischemia/Reperfusion via Inhibiting the RhoA/ROCK Pathway

The role of hydrogen sulfide (H2S) on the phenotypic change of astrocytes following cerebral ischemia/reperfusion (I/R) in mice was investigated in present study. We tested the expression of glial fibrillary acidic protein (GFAP), A2 phenotype marker S100a10, and A1 phenotype marker C3 protein and assessed the change of BrdU/GFAP-positive cells, GFAP/C3-positive cells, and GFAP/S100a10-positive cells in mice hippocampal tissues to evaluate the change of astrocyte phenotypes following cerebral I/R. The role of H2S on the phenotypic change of astrocytes following cerebral I/R in mice was investigated by using H2S synthase cystathionine-γ-lyase (CSE) knockout mice (KO). The results revealed that cerebral I/R injury promoted the astrocytes proliferation of both A1 and A2 phenotypes, which were more significant in mice of H2S synthase CSE KO than in mice of wild type (WT). Interestingly, supplement with H2S could inhibit the A1 phenotype proliferation but promote the proliferation of A2 phenotype, suggesting that H2S could regulate the transformation of astrocytes to A2 phenotype following cerebral I/R, which is beneficial for neuronal recovery. Besides, we found that H2S-mediated change of astrocyte phenotype is related to inhibiting the RhoA/ROCK pathway. Furthermore, both H2S and ROCK inhibitor could ameliorate the brain injury of mice at 9 days after cerebral I/R. In conclusion, H2S regulates the phenotypic transformation of astrocytes to A2 phenotype following the cerebral I/R via inhibiting RhoA/ROCK pathway and then exerts the neuroprotective effect against the subacute brain injury.

Molecular mechanisms underlying microglial sensing and phagocytosis in synaptic pruning

ABSTRACT

Microglia are the main non-neuronal cells in the central nervous system that have important roles in brain development and functional connectivity of neural circuits. In brain physiology, highly dynamic microglial processes are facilitated to sense the surrounding environment and stimuli. Once the brain switches its functional states, microglia are recruited to specific sites to exert their immune functions, including the release of cytokines and phagocytosis of cellular debris. The crosstalk of microglia between neurons, neural stem cells, endothelial cells, oligodendrocytes, and astrocytes contributes to their functions in synapse pruning, neurogenesis, vascularization, myelination, and blood-brain barrier permeability. In this review, we highlight the neuron-derived "find-me," "eat-me," and "don't eat-me" molecular signals that drive microglia in response to changes in neuronal activity for synapse refinement during brain development. This review reveals the molecular mechanism of neuron-microglia interaction in synaptic pruning and presents novel ideas for the synaptic pruning of microglia in disease, thereby providing important clues for discovery of target drugs and development of nervous system disease treatment methods targeting synaptic dysfunction.

Effect of total flavonoids of Dracocephalum moldavica L. On neuroinflammation in Alzheimer's disease model amyloid-β (Aβ1-42)-peptide-induced astrocyte activation

One of the main pathological features noted in Alzheimer's disease (AD) is the presence of plagues of aggregated β-amyloid (Aβ1-42)-peptides. Excess deposition of amyloid-β oligomers (AβO) are known to promote neuroinflammation. Sequentially, following neuroinflammation astrocytes become activated with cellular characteristics to initiate activated astrocytes. The purpose of this study was to determine whether total flavonoids derived from Dracocephalum moldavica L. (TFDM) inhibited Aβ1-42-induced damage attributed to activated C8-D1A astrocytes. Western blotting and ELISA were used to determine the expression of glial fibrillary acidic protein (GFAP), and complement C3 to establish the activation status of astrocytes following induction from exposure to Aβ1-42. Data demonstrated that stimulation of C8-D1A astrocytes by treatment with 40 μM Aβ1-42 for 24 hr produced significant elevation in protein expression and protein levels of acidic protein (GFAP) and complement C3 accompanied by increased expression and levels of inflammatory cytokines. Treatment with TFDM or the clinically employed drug donepezil in AD therapy reduced production of inflammatory cytokines, and toxicity initiated following activation of C8-D1A astrocytes following exposure to Aβ1-42. Therefore, TFDM similar to donepezil inhibited inflammatory secretion in reactive astrocytes, suggesting that TFDM may be considered as a potential compound to be utilized in AD therapy.

Neuroinflammation and neurodegeneration following traumatic brain injuries

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

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.

Neurodegenerative Etiology of Aromatic L-Amino Acid Decarboxylase Deficiency: a Novel Concept for Expanding Treatment Strategies

Aromatic l-amino acid decarboxylase deficiency (AADC-DY) is caused by one or more mutations in the DDC gene, resulting in the deficit in catecholamines and serotonin neurotransmitters. The disease has limited therapeutic options with relatively poor clinical outcomes. Accumulated evidence suggests the involvement of neurodegenerative mechanisms in the etiology of AADC-DY. In the absence of neurotransmitters' neuroprotective effects, the accumulation and the chronic presence of several neurotoxic metabolites including 4-dihydroxy-L-phenylalanine, 3-methyldopa, and homocysteine, in the brain of subjects with AADC-DY, promote oxidative stress and reduce the cellular antioxidant and methylation capacities, leading to glial activation and mitochondrial dysfunction, culminating to neuronal injury and death. These pathophysiological processes have the potential to hinder the clinical efficacy of treatments aimed at increasing neurotransmitters' synthesis and or function. This review describes in detail the mechanisms involved in AADC-DY neurodegenerative etiology, highlighting the close similarities with those involved in other neurodegenerative diseases. We then offer novel strategies for the treatment of the disease with the objective to either reduce the level of the metabolites or counteract their prooxidant and neurotoxic effects. These treatment modalities used singly or in combination, early in the course of the disease, will minimize neuronal injury, preserving the functional integrity of neurons, hence improving the clinical outcomes of both conventional and unconventional interventions in AADC-DY. These modalities may not be limited to AADC-DY but also to other metabolic disorders where a specific mutation leads to the accumulation of prooxidant and neurotoxic metabolites.

C3aR in the medial prefrontal cortex modulates the susceptibility to LPS-induced depressive-like behaviors through glutamatergic neuronal excitability

Complement activation and prefrontal cortical dysfunction both contribute to the pathogenesis of major depressive disorder (MDD), but their interplay in MDD is unclear. We here studied the role of complement C3a receptor (C3aR) in the medial prefrontal cortex (mPFC) and its influence on depressive-like behaviors induced by systematic lipopolysaccharides (LPS) administration. C3aR knockout (KO) or intra-mPFC C3aR antagonism confers resilience, whereas C3aR expression in mPFC neurons makes KO mice susceptible to LPS-induced depressive-like behaviors. Importantly, the excitation and inhibition of mPFC neurons have opposing effects on depressive-like behaviors, aligning with increased and decreased excitability by C3aR deletion and activation in cortical neurons. In particular, inhibiting mPFC glutamatergic (mPFCGlu) neurons, the main neuronal subpopulation expresses C3aR, induces depressive-like behaviors in saline-treated WT and KO mice, but not in LPS-treated KO mice. Compared to hypoexcitable mPFCGlu neurons in LPS-treated WT mice, C3aR-null mPFCGlu neurons display hyperexcitability upon LPS treatment, and enhanced excitation of mPFCGlu neurons is anti-depressant, suggesting a protective role of C3aR deficiency in these circumstances. In conclusion, C3aR modulates susceptibility to LPS-induced depressive-like behaviors through mPFCGlu neuronal excitability. This study identifies C3aR as a pivotal intersection of complement activation, mPFC dysfunction, and depression and a promising therapeutic target for MDD.

Neuroprotective Efficacy of the Glucocorticoid Receptor Modulator PT150 in the Rotenone Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is the most common neurodegenerative movement disorder worldwide. Current treatments for PD largely center around dopamine replacement therapies and fail to prevent the progression of pathology, underscoring the need for neuroprotective interventions. Approaches that target neuroinflammation, which occurs prior to dopaminergic neuron (DAn) loss in the substantia nigra (SN), represent a promising therapeutic strategy. The glucocorticoid receptor (GR) has been implicated in the neuropathology of PD and modulates numerous neuroinflammatory signaling pathways in the brain. Therefore, we investigated the neuroprotective effects of the novel GR modulator, PT150, in the rotenone mouse model of PD, postulating that inhibition of glial inflammation would protect DAn and reduce accumulation of neurotoxic misfolded ⍺-synuclein protein. C57Bl/6 mice were exposed to 2.5 mg/kg/day rotenone by intraperitoneal injection for 14 days, immediately followed by oral treatment with 30 mg/kg/day or 100 mg/kg/day PT150 in the 14-day post-lesioning incubation period, during which the majority of DAn loss and α-synuclein (α-syn) accumulation occurs. Our results indicate that treatment with PT150 reduced both loss of DAn and microgliosis in the nigrostriatal pathway. Although morphologic features of astrogliosis were not attenuated, PT150 treatment promoted potentially neuroprotective activity in these cells, including increased phagocytosis of hyperphosphorylated α-syn. Ultimately, PT150 treatment reduced the loss of DAn cell bodies in the SN, but not the striatum, and prohibited intra-neuronal accumulation of α-syn. Together, these data indicate that PT150 effectively reduced SN pathology in the rotenone mouse model of PD.

Overexpression of the schizophrenia risk gene C4 in PV cells drives sex-dependent behavioral deficits and circuit dysfunction

Fast-spiking parvalbumin (PV)-positive cells are key players in orchestrating pyramidal neuron activity, and their dysfunction is consistently observed in myriad brain diseases. To understand how immune complement dysregulation - a prevalent locus of brain disease etiology - in PV cells may drive disease pathogenesis, we have developed a transgenic mouse line that permits cell-type specific overexpression of the schizophrenia-associated complement component 4 (C4) gene. We found that overexpression of mouse C4 (mC4) in PV cells causes sex-specific behavioral alterations and concomitant deficits in synaptic connectivity and excitability of PV cells of the prefrontal cortex. Using a computational network, we demonstrated that these microcircuit deficits led to hyperactivity and disrupted neural communication. Finally, pan-neuronal overexpression of mC4 failed to evoke the same deficits in behavior as PV-specific mC4 overexpression, suggesting that C4 perturbations in fast-spiking neurons are more harmful to brain function than pan-neuronal alterations. Together, these results provide a causative link between C4 and the vulnerability of PV cells in brain disease.

Ketamine's mechanism of action with an emphasis on neuroimmune regulation: can the complement system complement ketamine's antidepressant effects?

Over 300 million people worldwide suffer from major depressive disorder (MDD). Unfortunately, only 30-40% of patients with MDD achieve complete remission after conventional monoamine antidepressant therapy. In recent years, ketamine has revolutionized the treatment of MDD, with its rapid antidepressant effects manifesting within a few hours as opposed to weeks with conventional antidepressants. Many research endeavors have sought to identify ketamine's mechanism of action in mood disorders; while many studies have focused on ketamine's role in glutamatergic modulation, several studies have implicated its role in regulating neuroinflammation. The complement system is an important component of the innate immune response vital for synaptic plasticity. The complement system has been implicated in the pathophysiology of depression, and studies have shown increases in complement component 3 (C3) expression in the prefrontal cortex of suicidal individuals with depression. Given the role of the complement system in depression, ketamine and the complement system's abilities to modulate glutamatergic transmission, and our current understanding of ketamine's anti-inflammatory properties, there is reason to suspect a common link between the complement system and ketamine's mechanism of action. This review will summarize ketamine's anti- inflammatory roles in the periphery and central nervous system, with an emphasis on complement system regulation.

Hexahydrocurcumin attenuated demyelination and improved cognitive impairment in chronic cerebral hypoperfusion rats

Age-related white matter lesions (WML) frequently present vascular problems by decreasing cerebral blood supply, resulting in the condition known as chronic cerebral hypoperfusion (CCH). This study aimed to investigate the effect of hexahydrocurcumin (HHC) on the processes of demyelination and remyelination induced by the model of the Bilateral Common Carotid Artery Occlusion (BCCAO) for 29 days to mimic the CCH condition. The pathological appearance of myelin integrity was significantly altered by CCH, as evidenced by Transmission Electron Microscopy (TEM) and Luxol Fast Blue (LFB) staining. In addition, CCH activated A1-astrocytes and reactive-microglia by increasing the expression of Glial fibrillary acidic protein (GFAP), complement 3 (C3d) and pro-inflammatory cytokines. However, S100a10 expression, a marker of neuroprotective astrocytes, was suppressed, as were regenerative factors including (IGF-1) and Transglutaminase 2 (TGM2). Therefore, the maturation step was obstructed as shown by decreases in the levels of myelin basic protein (MBP) and the proteins related with lipid synthesis. Cognitive function was therefore impaired in the CCH model, as evidenced by the Morris water maze test. By contrast, HHC treatment significantly improved myelin integrity, and inhibited A1-astrocytes and reactive-microglial activity. Consequently, pro-inflammatory cytokines and A1-astrocytes were attenuated, and regenerative factors increased assisting myelin maturation and hence improving cognitive performance. In conclusion, HHC improves cognitive function and also the integrity of white matter in CCH rats by reducing demyelination, and pro-inflammatory cytokine production and promoting the process of remyelination.

Astroglial activation: Current concepts and future directions

Astrocytes are abundantly and ubiquitously expressed cell types with diverse functions throughout the central nervous system. Astrocytes show remarkable plasticity and exhibit morphological, molecular, and functional remodeling in response to injury, disease, or infection of the central nervous system, as evident in neurodegenerative diseases. Astroglial mediated inflammation plays a prominent role in the pathogenesis of neurodegenerative diseases. This review focus on the role of astrocytes as essential players in neuroinflammation and discuss their morphological and functional heterogeneity in the normal central nervous system and explore the spatial and temporal variations in astroglial phenotypes observed under different disease conditions. This review discusses the intimate relationship of astrocytes to pathological hallmarks of neurodegenerative diseases. Finally, this review considers the putative therapeutic strategies that can be deployed to modulate the astroglial functions in neurodegenerative diseases. HIGHLIGHTS: Astroglia mediated neuroinflammation plays a key role in the pathogenesis of neurodegenerative diseases. Activated astrocytes exhibit diverse phenotypes in a region-specific manner in brain and interact with β-amyloid, tau, and α-synuclein species as well as with microglia and neuronal circuits. Activated astrocytes are likely to influence the trajectory of disease progression of neurodegenerative diseases, as determined by the stage of disease, individual susceptibility, and state of astroglial priming. Modulation of astroglial activation may be a therapeutic strategy at various stages in the trajectory of neurodegenerative diseases to modify the disease course.

Early life phenobarbital exposure dysregulates the hippocampal transcriptome

Introduction: Phenobarbital (PB) and levetiracetam (LEV) are the first-line therapies for neonates with diagnosed seizures, however, a growing body of evidence shows that these drugs given during critical developmental windows trigger lasting molecular changes in the brain. While the targets and mechanism of action of these drugs are well understood-what is not known is how these drugs alter the transcriptomic landscape, and therefore molecular profile/gene expression during these critical windows of neurodevelopment. PB is associated with a range of neurotoxic effects in developing animals, from cell death to altered synaptic development to lasting behavioral impairment. LEV does not produce these effects. Methods: Here we evaluated the effects of PB and Lev on the hippocampal transcriptome by RNA sequencing. Neonatal rat pups were given a single dose of PB, Lev or vehicle and sacrificed 72 h later-at time at which drug is expected to be cleared. Results: We found PB induces broad changes in the transcriptomic profile (124 differentially expressed transcripts), as compared to relatively small changes in LEV-treated animals (15 transcripts). PB exposure decreased GABAergic and oligodendrocyte markers pvalb and opalin, and increased the marker of activated microglia, cd68 and the astrocyte- associated gene vegfa. These data are consistent with the existing literature showing developmental neurotoxicity associated with PB, but not LEV. Discussion: The widespread change in gene expression after PB, which affected transcripts reflective of multiple cell types, may provide a link between acute drug administration and lasting drug toxicity.

NF-κB and JAK/STAT Signaling Pathways as Crucial Regulators of Neuroinflammation and Astrocyte Modulation in Spinal Cord Injury

Spinal cord injury (SCI) leads to significant functional impairments below the level of the injury, and astrocytes play a crucial role in the pathophysiology of SCI. Astrocytes undergo changes and form a glial scar after SCI, which has traditionally been viewed as a barrier to axonal regeneration and functional recovery. Astrocytes activate intracellular signaling pathways, including nuclear factor κB (NF-κB) and Janus kinase-signal transducers and activators of transcription (JAK/STAT), in response to external stimuli. NF-κB and STAT3 are transcription factors that play a pivotal role in initiating gene expression related to astrogliosis. The JAK/STAT signaling pathway is essential for managing secondary damage and facilitating recovery processes post-SCI: inflammation, glial scar formation, and astrocyte survival. NF-κB activation in astrocytes leads to the production of pro-inflammatory factors by astrocytes. NF-κB and STAT3 signaling pathways are interconnected: NF-κB activation in astrocytes leads to the release of interleukin-6 (IL-6), which interacts with the IL-6 receptor and initiates STAT3 activation. By modulating astrocyte responses, these pathways offer promising avenues for enhancing recovery outcomes, illustrating the crucial need for further investigation into their mechanisms and therapeutic applications in SCI treatment.

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

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

Microglial over-pruning of synapses during development in autism-associated SCN2A-deficient mice and human cerebral organoids

Autism spectrum disorder (ASD) is a major neurodevelopmental disorder affecting 1 in 36 children in the United States. While neurons have been the focus of understanding ASD, an altered neuro-immune response in the brain may be closely associated with ASD, and a neuro-immune interaction could play a role in the disease progression. As the resident immune cells of the brain, microglia regulate brain development and homeostasis via core functions including phagocytosis of synapses. While ASD has been traditionally considered a polygenic disorder, recent large-scale human genetic studies have identified SCN2A deficiency as a leading monogenic cause of ASD and intellectual disability. We generated a Scn2a-deficient mouse model, which displays major behavioral and neuronal phenotypes. However, the role of microglia in this disease model is unknown. Here, we reported that Scn2a-deficient mice have impaired learning and memory, accompanied by reduced synaptic transmission and lower spine density in neurons of the hippocampus. Microglia in Scn2a-deficient mice are partially activated, exerting excessive phagocytic pruning of post-synapses related to the complement C3 cascades during selective developmental stages. The ablation of microglia using PLX3397 partially restores synaptic transmission and spine density. To extend our findings from rodents to human cells, we established a microglia-incorporated human cerebral organoid model carrying an SCN2A protein-truncating mutation identified in children with ASD. We found that human microglia display increased elimination of post-synapse in cerebral organoids carrying the SCN2A mutation. Our study establishes a key role of microglia in multi-species autism-associated models of SCN2A deficiency from mouse to human cells.

Mechanism of scutellarin inhibition of astrocyte activation to type A1 after ischemic stroke

OBJECTIVE

The aim of this study was to investigate the effects of scutellarin on the activation of astrocytes into the A1 type following cerebral ischemia and to explore the underlying mechanism.

METHODS

In vivo, a mouse middle cerebral artery wire embolism model was established to observe the regulation of astrocyte activation to A1 type by scutellarin, and the effects on neurological function and brain infarct volume. In vitro, primary astrocytes were cultured to establish an oxygen-glucose deprivation model, and the mRNA and protein expression of C3, a specific marker of A1-type astrocytes pretreated with scutellarin, were examined. The neurons were cultured in vitro to detect the toxic effects of ischemia-hypoxia-activated A1 astrocyte secretion products on neurons, and to observe whether scutellarin could reduce the neurotoxicity of A1 astrocytes. To validate the signaling pathway-related proteins regulated by scutellarin on C3 expression in astrocytes.

RESULTS

The results showed that scutellarin treatment reduced the volume of cerebral infarcts and attenuated neurological deficits in mice caused by middle cerebral artery embolism. Immunofluorescence and Western blot showed that treatment with scutellarin down-regulated middle cerebral artery embolism and OGD/R up-regulated A1-type astrocyte marker C3. The secretory products of ischemia-hypoxia-activated A1-type astrocytes were toxic to neurons and induced an increase in neuronal apoptosis, and astrocytes treated with scutellarin reduced the toxic effects on neurons. Further study revealed that scutellarin inhibited the activation of NF-κB signaling pathway and thus inhibited the activation of astrocytes to A1 type.

AAV8 vector induced gliosis following neuronal transgene expression

Introduction

Expression of light sensitive ion channels by selected neurons has been achieved by viral mediated transduction with gene constructs, but for this to have therapeutic uses, for instance in treating epilepsy, any adverse effects of viral infection on the cerebral cortex needs to be evaluated. Here, we assessed the impact of adeno-associated virus 8 (AAV8) carrying DNA code for a soma targeting light activated chloride channel/FusionRed (FR) construct under the CKIIa promoter.

Methods

Viral constructs were harvested from transfected HEK293 cells in vitro and purified. To test functionality of the opsin, cultured rodent neurons were transduced and the light response of transduced neurons was assayed using whole-cell patch-clamp recordings. In vivo expression was confirmed by immunofluorescence for FR. Unilateral intracranial injections of the viral construct were made into the mouse neocortex and non-invasive fluorescence imaging of FR expression made over 1-4 weeks post-injection using an IVIS Spectrum system. Sections were also prepared from injected mouse cortex for immunofluorescence staining of FR, alongside glial and neuronal marker proteins.

Results

In vitro, cortical neurons were successfully transduced, showing appropriate physiological responses to light stimulation. Following injections in vivo, transduction was progressively established around a focal injection site over a 4-week period with spread of transduction proportional to the concentration of virus introduced. Elevated GFAP immunoreactivity, a marker for reactive astrocytes, was detected near injection sites associated with, and proportional to, local FR expression. Similarly, we observed reactive microglia around FR expressing cells. However, we found that the numbers of NeuN+ neurons were conserved close to the injection site, indicating that there was little or no neuronal loss. In control mice, injected with saline only, astrocytosis and microgliosis was limited to the immediate vicinity of the injection site. Injections of opsin negative viral constructs resulted in comparable levels of astrocytic reaction as seen with opsin positive constructs.

Discussion

We conclude that introduction of an AAV8 vector transducing expression of a transgene under a neuron specific promotor evokes a mild inflammatory reaction in cortical tissue without causing extensive short-term neuronal loss. The expression of an opsin in addition to a fluorescent protein does not significantly increase neuroinflammation.

Immune receptors and aging brain

Aging brings about a myriad of degenerative processes throughout the body. A decrease in cognitive abilities is one of the hallmark phenotypes of aging, underpinned by neuroinflammation and neurodegeneration occurring in the brain. This review focuses on the role of different immune receptors expressed in cells of the central and peripheral nervous systems. We will discuss how immune receptors in the brain act as sentinels and effectors of the age-dependent shift in ligand composition. Within this 'old-age-ligand soup,' some immune receptors contribute directly to excessive synaptic weakening from within the neuronal compartment, while others amplify the damaging inflammatory environment in the brain. Ultimately, chronic inflammation sets up a positive feedback loop that increases the impact of immune ligand-receptor interactions in the brain, leading to permanent synaptic and neuronal loss.

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.

M2 Microglia-derived Exosomes Promote Spinal Cord Injury Recovery in Mice by Alleviating A1 Astrocyte Activation

M2 microglia transplantation has previously demonstrated beneficial effects on spinal cord injury (SCI) by regulating neuroinflammation and enhancing neuronal survival. Exosomes (EXOs), secreted by almost all cell types, embody partial functions and properties of their parent cells. However, the effect of M2 microglia-derived EXOs (M2-EXOs) on SCI recovery and the underlying molecular mechanisms remain unclear. In this study, we isolated M2-EXOs and intravenously introduced them into mice with SCI. Considering the reciprocal communication between microglia and astroglia in both healthy and injured central nervous systems (CNSs), we subsequently focused on the influence of M2-EXOs on astrocyte phenotype regulation. Our findings indicated that M2-EXOs promoted neuron survival and axon preservation, reduced the lesion area, inhibited A1 astrocyte activation, and improved motor function recovery in SCI mice. Moreover, they inhibited the nuclear translocation of p65 and the activation of the NF-κB signalling pathway in A1 astrocytes. Therefore, our research suggests that M2-EXOs mitigate the activation of neurotoxic A1 astrocytes by inhibiting the NF-κB signalling pathway, thereby improving spinal tissue preservation and motor function recovery following SCI. This positions M2-EXOs as a promising therapeutic strategy for SCI.

Gypenoside Pretreatment Alleviates the Cerebral Ischemia Injury via Inhibiting the Microglia-Mediated Neuroinflammation

Neuroinflammation is closely related to prognosis in ischemic stroke. Microglia are the main immune cells in the nervous system. Under physiological conditions, microglia participate in clearance of dead cells, synapse pruning and regulation of neuronal circuits to maintain the overall health of the nervous system. Once ischemic stroke occurs, microglia function in the occurrence and progression of neuroinflammation. Therefore, the regulation of microglia-mediated neuroinflammation is a potential therapeutic strategy for ischemic stroke. The anti-inflammatory activity of gypenosides (GPs) has been confirmed to be related to the activity of microglia in other neurological diseases. However, the role of GPs in neuroinflammation after ischemic stroke has not been studied. In this study, we investigated whether GPs could reduce neuroinflammation by regulating microglia and the underlying mechanism through qRT-PCR and western blot. Results showed that GPs pretreatment mitigated blood-brain barrier (BBB) damage in the mice subjected to middle cerebral artery occlusion (MCAO) and improved motor function. According to the results of immunofluorescence staining, GPs pretreatment alleviated neuroinflammation in MCAO mice by reducing the number of microglia and promoting their phenotypic transformation from M1 to M2. Furthermore, GPs pretreatment reduced the number of astrocytes in the penumbra and inhibited their polarization into the A1 type. We applied oxygen and glucose deprivation (OGD) on BV2 cells to mimic ischemic conditions in vitro and found similar effect as that in vivo. At the molecular level, the STAT-3/HIF1-α and TLR-4/NF-κB/HIF1-α pathways were involved in the anti-inflammatory effects of GPs in vitro and in vivo. Overall, this research indicates that GPs are potential therapeutic agents for ischemic stroke and has important reference significance to further explore the possibility of GPs application in ischemic stroke.

Complement-mediated synapse loss in Alzheimer's disease: mechanisms and involvement of risk factors

The complement system is increasingly recognized as a key player in the synapse loss and cognitive impairments observed in Alzheimer's disease (AD). In particular, the process of complement-dependent synaptic pruning through phagocytosis is over-activated in AD brains, driving detrimental excessive synapse elimination and contributing to synapse loss, which is the strongest neurobiological correlate of cognitive impairments in AD. Herein we review recent advances in characterizing complement-mediated synapse loss in AD, summarize the underlying mechanisms, and discuss the possible involvement of AD risk factors such as aging and various risk genes. We conclude with an overview of key questions that remain to be addressed.

Circular RNA HIPK2 Promotes A1 Astrocyte Activation after Spinal Cord Injury through Autophagy and Endoplasmic Reticulum Stress by Modulating miR-124-3p-Mediated Smad2 Repression

Glial scarring formed by reactive astrocytes after spinal cord injury (SCI) is the primary obstacle to neuronal regeneration within the central nervous system, making them a promising target for SCI treatment. Our previous studies have demonstrated the positive impact of miR-124-3p on neuronal repair, but it remains unclear how miR-124-3p is involved in autophagy or ER stress in astrocyte activation. To answer this question, the expression of A1 astrocyte-related markers at the transcriptional and protein levels after SCI was checked in RNA-sequencing data and verified using quantitative polymerase chain reaction (qPCR) and Western blotting in vitro and in vivo. The potential interactions among circHIPK2, miR-124-3p, and Smad2 were analyzed and confirmed by bioinformatics analyses and a luciferase reporter assay. In the end, the role of miR-124-3p in autophagy, ER stress, and SCI was investigated by using Western blotting to measure key biomarkers (C3, LC3, and Chop) in the absence or presence of corresponding selective inhibitors (siRNA, 4-PBA, TG). As a result, SCI caused the increase of A1 astrocyte markers, in which the upregulated circHIPK2 directly targeted miR-124-3p, and the direct downregulating effect of Smad2 by miR-124-3p was abolished, while Agomir-124 treatment reversed this effect. Injury caused a significant change of markers for ER stress and autophagy through the circHIPK2/miR-124-3p/Smad2 pathway, which might activate the A1 phenotype, and ER stress might promote autophagy in astrocytes. In conclusion, circHIPK2 may play a functional role in sequestering miR-124-3p and facilitating the activation of A1 astrocytes through regulating Smad2-mediated downstream autophagy and ER stress pathways, providing a new perspective on potential targets for functional recovery after SCI.

The Importance of Complement-Mediated Immune Signaling in Alzheimer's Disease Pathogenesis

As an essential component of our innate immune system, the complement system is responsible for our defense against pathogens. The complement cascade has complex roles in the central nervous system (CNS), most of what we know about it stems from its role in brain development. However, in recent years, numerous reports have implicated the classical complement cascade in both brain development and decline. More specifically, complement dysfunction has been implicated in neurodegenerative disorders, such as Alzheimer's disease (AD), which is the most common form of dementia. Synapse loss is one of the main pathological hallmarks of AD and correlates with memory impairment. Throughout the course of AD progression, synapses are tagged with complement proteins and are consequently removed by microglia that express complement receptors. Notably, astrocytes are also capable of secreting signals that induce the expression of complement proteins in the CNS. Both astrocytes and microglia are implicated in neuroinflammation, another hallmark of AD pathogenesis. In this review, we provide an overview of previously known and newly established roles for the complement cascade in the CNS and we explore how complement interactions with microglia, astrocytes, and other risk factors such as TREM2 and ApoE4 modulate the processes of neurodegeneration in both amyloid and tau models of AD.

Proposed mechanisms of tau: relationships to traumatic brain injury, Alzheimer's disease, and epilepsy

Traumatic brain injury (TBI), Alzheimer's disease (AD), and epilepsy share proposed mechanisms of injury, including neuronal excitotoxicity, cascade signaling, and activation of protein biomarkers such as tau. Although tau is typically present intracellularly, in tauopathies, phosphorylated (p-) and hyper-phosphorylated (hp-) tau are released extracellularly, the latter leading to decreased neuronal stability and neurofibrillary tangles (NFTs). Tau cleavage at particular sites increases susceptibility to hyper-phosphorylation, NFT formation, and eventual cell death. The relationship between tau and inflammation, however, is unknown. In this review, we present evidence for an imbalanced endoplasmic reticulum (ER) stress response and inflammatory signaling pathways resulting in atypical p-tau, hp-tau and NFT formation. Further, we propose tau as a biomarker for neuronal injury severity in TBI, AD, and epilepsy. We present a hypothesis of tau phosphorylation as an initial acute neuroprotective response to seizures/TBI. However, if the underlying seizure pathology or TBI recurrence is not effectively treated, and the pathway becomes chronically activated, we propose a "tipping point" hypothesis that identifies a transition of tau phosphorylation from neuroprotective to injurious. We outline the role of amyloid beta (Aβ) as a "last ditch effort" to revert the cell to programmed death signaling, that, when fails, transitions the mechanism from injurious to neurodegenerative. Lastly, we discuss targets along these pathways for therapeutic intervention in AD, TBI, and epilepsy.

Ramelteon attenuates hippocampal neuronal loss and memory impairment following kainate-induced seizures

Evidence suggests that the neuroprotective effects of melatonin involve both receptor-dependent and -independent actions. However, little is known about the effects of melatonin receptor activation on the kainate (KA) neurotoxicity. This study examined the effects of repeated post-KA treatment with ramelteon, a selective agonist of melatonin receptors, on neuronal loss, cognitive impairment, and depression-like behaviors following KA-induced seizures. The expression of melatonin receptors decreased in neurons, whereas it was induced in astrocytes 3 and 7 days after seizures elicited by KA (0.12 μg/μL) in the hippocampus of mice. Ramelteon (3 or 10 mg/kg, i.p.) and melatonin (10 mg/kg, i.p.) mitigated KA-induced oxidative stress and impairment of glutathione homeostasis and promoted the nuclear translocation and DNA binding activity of Nrf2 in the hippocampus after KA treatment. Ramelteon and melatonin also attenuated microglial activation but did not significantly affect astroglial activation induced by KA, despite the astroglial induction of melatonin receptors after KA treatment. However, ramelteon attenuated KA-induced proinflammatory phenotypic changes in astrocytes. Considering the reciprocal regulation of astroglial and microglial activation, these results suggest ramelteon inhibits microglial activation by regulating astrocyte phenotypic changes. These effects were accompanied by the attenuation of the nuclear translocation and DNA binding activity of nuclear factor κB (NFκB) induced by KA. Consequently, ramelteon attenuated the KA-induced hippocampal neuronal loss, memory impairment, and depression-like behaviors; the effects were comparable to those of melatonin. These results suggest that ramelteon-mediated activation of melatonin receptors provides neuroprotection against KA-induced neurotoxicity in the mouse hippocampus by activating Nrf2 signaling to attenuate oxidative stress and restore glutathione homeostasis and by inhibiting NFκB signaling to attenuate neuroinflammatory changes.

Conditional knockout of AIM2 in microglia ameliorates synaptic plasticity and spatial memory deficits in a mouse model of Alzheimer's disease

AIMS

Synaptic dysfunction is a hallmark pathology of Alzheimer's disease (AD) and is strongly associated with cognitive impairment. Abnormal phagocytosis by the microglia is one of the main causes of synapse loss in AD. Previous studies have shown that the absence of melanoma 2 (AIM2) inflammasome activity is increased in the hippocampus of APP/PS1 mice, but the role of AIM2 in AD remains unclear.

METHODS

Injection of Aβ1-42 into the bilateral hippocampal CA1 was used to mimic an AD mouse model (AD mice). C57BL/6 mice injected with AIM2 overexpression lentivirus and conditional knockout of microglial AIM2 mice were used to confirm the function of AIM2 in AD. Cognitive functions were assessed with novel object recognition and Morris water maze tests. The protein and mRNA expression levels were evaluated by western blotting, immunofluorescence staining, and qRT-PCR. Synaptic structure and function were detected by Golgi staining and electrophysiology.

RESULTS

The expression level of AIM2 was increased in AD mice, and overexpression of AIM2 induced synaptic and cognitive impairments in C57BL/6 mice, similar to AD mice. Elevated expression levels of AIM2 occurred in microglia in AD mice. Conditional knockout of microglial AIM2 rescued cognitive and synaptic dysfunction in AD mice. Excessive microglial phagocytosis activity of synapses was decreased after knockout of microglial AIM2, which was associated with inhibiting complement activation.

CONCLUSION

Our results demonstrated that microglial AIM2 plays a critical role in regulating synaptic plasticity and memory deficits associated with AD, providing a new direction for developing novel preventative and therapeutic interventions for this disease.

Neuroprotective Effects of N-methyl-(2S, 4R)-trans-4-hydroxy-L-proline (NMP) against Amyloid-β-Induced Alzheimer's Disease Mouse Model

Alzheimer's disease (AD), is a progressive neurodegenerative disorder that involves the deposition of β-amyloid plaques and the clinical symptoms of confusion, memory loss, and cognitive dysfunction. Despite enormous progress in the field, no curative treatment is available. Therefore, the current study was designed to determine the neuroprotective effects of N-methyl-(2S, 4R)-Trans-4-hydroxy-L-proline (NMP) obtained from Sideroxylon obtusifolium, a Brazilian folk medicine with anti-inflammatory and anti-oxidative properties. Here, for the first time, we explored the neuroprotective role of NMP in the Aβ1-42-injected mouse model of AD. After acclimatization, a single intracerebroventricular injection of Aβ1-42 (5 µL/5 min/mouse) in C57BL/6N mice induced significant amyloidogenesis, reactive gliosis, oxidative stress, neuroinflammation, and synaptic and memory deficits. However, an intraperitoneal injection of NMP at a dose of (50 mg/kg/day) for three consecutive weeks remarkably decreased beta secretase1 (BACE-1) and Aβ, activated the astrocyte and microglia expression level as well as downstream inflammatory mediators such as pNF-ĸB, TNF-α, and IL-1β. NPM also strongly attenuated oxidative stress, as evaluated by the expression level of NRF2/HO-1, and synaptic failure, by improving the level of both the presynaptic (SNAP-25 and SYN) and postsynaptic (PSD-95 and SNAP-23) regions of the synapses in the cortexes and hippocampi of the Aβ1-42-injected mice, contributing to cognitive improvement in AD and improving the behavioral deficits displayed in the Morris water maze and Y-maze. Overall, our data suggest that NMP provides potent multifactorial effects, including the inhibition of amyloid plaques, oxidative stress, neuroinflammation, and cognitive deficits.

A neuron-immune circuit regulates neurodegeneration in the hindbrain and spinal cord of Arf1-ablated mice

Neuroimmune connections have been revealed to play a central role in neurodegenerative diseases (NDs). However, the mechanisms that link the central nervous system (CNS) and peripheral immune cells are still mostly unknown. We recently found that specific ablation of the Arf1 gene in hindbrain and spinal cord neurons promoted NDs through activating the NLRP3 inflammasome in microglia via peroxided lipids and adenosine triphosphate (ATP) releasing. Here, we demonstrate that IL-1β with elevated chemokines in the neuronal Arf1-ablated mouse hindbrain and spinal cord recruited and activated γδ T cells in meninges. The activated γδ T cells then secreted IFN-γ that entered into parenchyma to activate the microglia-A1 astrocyte-C3-neuronal C3aR neurotoxic pathway. Remarkably, the neurodegenerative phenotypes of the neuronal Arf1-ablated mice were strongly ameliorated by IFN-γ or C3 knockout. Finally, we show that the Arf1-reduction-induced neuroimmune-IFN-γ-gliosis pathway exists in human NDs, particularly in amyotrophic lateral sclerosis and multiple sclerosis. Together, our results uncover a previously unknown mechanism that links the CNS and peripheral immune cells to promote neurodegeneration.

Regulatory T cells: A suppressor arm in post-stroke immune homeostasis

The activation of the immune system and the onset of pro- and anti-inflammatory responses play crucial roles in the pathophysiological processes of ischaemic stroke (IS). CD4+ regulatory T (Treg) cells is the main immunosuppressive cell population that is studied in the context of peripheral tolerance, autoimmunity, and the development of chronic inflammatory diseases. In recent years, more studies have focused on immune modulation after IS, and Treg cells have been demonstrated to be essential in the remission of inflammation, nerve regeneration, and behavioural recovery. However, the exact effects of Treg cells in the context of IS remain controversial, with some studies suggesting a negative correlation with stroke outcomes. In this review, we aim to provide a comprehensive overview of the current understanding of Treg cell involvement in post-stroke homeostasis. We summarized the literature focusing on the temporal changes in Treg cell populations after IS, the mechanisms of Treg cell-mediated immunomodulation in the brain, and the potential of Treg cell-based therapies for treatment. The purposes of the current article are to address the importance of Treg cells and inspire more studies to help physicians, as well as scientists, understand the whole map of immune responses during IS.

Adeno-associated virus (AAV) 9-mediated gene delivery of Nurr1 and Foxa2 ameliorates symptoms and pathologies of Alzheimer disease model mice by suppressing neuro-inflammation and glial pathology

There is a compelling need to develop disease-modifying therapies for Alzheimer's disease (AD), the most common neuro-degenerative disorder. Together with recent progress in vector development for efficiently targeting the central nervous system, gene therapy has been suggested as a potential therapeutic modality to overcome the limited delivery of conventional types of drugs to and within the damaged brain. In addition, given increasing evidence of the strong link between glia and AD pathophysiology, therapeutic targets have been moving toward those addressing glial cell pathology. Nurr1 and Foxa2 are transcription/epigenetic regulators that have been reported to cooperatively regulate inflammatory and neurotrophic response in glial cells. In this study, we tested the therapeutic potential of Nurr1 and Foxa2 gene delivery to treat AD symptoms and pathologies. A series of functional, histologic, and transcriptome analyses revealed that the combined expression of Nurr1 and Foxa2 substantially ameliorated AD-associated amyloid β and Tau proteinopathy, cell senescence, synaptic loss, and neuro-inflammation in multiple in vitro and in vivo AD models. Intra-cranial delivery of Nurr1 and Foxa2 genes using adeno-associated virus (AAV) serotype 9 improved the memory and cognitive function of AD model mice. The therapeutic benefits of gene delivery were attained mainly by correcting pathologic glial function. These findings collectively indicate that AAV9-mediated Nurr1 and Foxa2 gene transfer could be an effective disease-modifying therapy for AD.

Assessing Cannabidiol as a Therapeutic Agent for Preventing and Alleviating Alzheimer's Disease Neurodegeneration

Alzheimer's disease (AD) is a leading neurodegenerative condition causing cognitive and memory decline. With small-molecule drugs targeting Aβ proving ineffective, alternative targets are urgently needed. Neuroinflammation, which is central to AD's pathology, results in synaptic and neuronal damage, highlighting the importance of addressing inflammation and conserving neuronal integrity. Cannabidiol (CBD), derived from cannabis, is noted for its neuroprotective and anti-inflammatory properties, having shown efficacy in neuropathic pain management for epilepsy. To investigate the therapeutic efficacy of CBD in AD and to elucidate its underlying mechanisms, we aimed to contribute valuable insights for incorporating AD prevention recommendations into future CBD nutritional guidelines. Aβ1-42 was employed for in vivo or in vitro model establishment, CBD treatment was utilized to assess the therapeutic efficacy of CBD, and RNA-seq analysis was conducted to elucidate the underlying therapeutic mechanism. CBD mitigates Aβ-induced cognitive deficits by modulating microglial activity, promoting neurotrophic factor release, and regulating inflammatory genes. The administration of CBD demonstrated a protective effect against Aβ toxicity both in vitro and in vivo, along with an amelioration of cognitive impairment in mice. These findings support the potential inclusion of CBD in future nutritional guidelines for Alzheimer's disease prevention.

Irisin reduces amyloid-β by inducing the release of neprilysin from astrocytes following downregulation of ERK-STAT3 signaling

A pathological hallmark of Alzheimer's disease (AD) is the deposition of amyloid-β (Aβ) protein in the brain. Physical exercise has been shown to reduce Aβ burden in various AD mouse models, but the underlying mechanisms have not been elucidated. Irisin, an exercise-induced hormone, is the secreted form of fibronectin type-III-domain-containing 5 (FNDC5). Here, using a three-dimensional (3D) cell culture model of AD, we show that irisin significantly reduces Aβ pathology by increasing astrocytic release of the Aβ-degrading enzyme neprilysin (NEP). This is mediated by downregulation of ERK-STAT3 signaling. Finally, we show that integrin αV/β5 acts as the irisin receptor on astrocytes required for irisin-induced release of astrocytic NEP, leading to clearance of Aβ. Our findings reveal for the first time a cellular and molecular mechanism by which exercise-induced irisin attenuates Aβ pathology, suggesting a new target pathway for therapies aimed at the prevention and treatment of AD.

Mice deficient in complement C3 are protected against recognition memory deficits and astrogliosis induced by status epilepticus

Introduction

Status epilepticus (SE) can significantly increase the risk of temporal lobe epilepsy (TLE) and cognitive comorbidities. A potential candidate mechanism underlying memory defects in epilepsy may be the immune complement system. The complement cascade, part of the innate immune system, modulates inflammatory and phagocytosis signaling, and has been shown to contribute to learning and memory dysfunctions in neurodegenerative disorders. We previously reported that complement C3 is elevated in brain biopsies from human drug-resistant epilepsy and in experimental rodent models. We also found that SE-induced increases in hippocampal C3 levels paralleled the development of hippocampal-dependent spatial learning and memory deficits in rats. Thus, we hypothesized that SE-induced C3 activation contributes to this pathophysiology in a mouse model of SE and acquired TLE.

Methods

In this study C3 knockout (KO) and wild type (WT) mice were subjected to one hour of pilocarpine-induced SE or sham conditions (control; C). Following a latent period of two weeks, recognition memory was assessed utilizing the novel object recognition (NOR) test. Western blotting was utilized to determine the protein levels of C3 in hippocampal lysates. In addition, we assessed the protein levels and distribution of the astrocyte marker glial fibrillary acidic protein (GFAP).

Results

In the NOR test, control WT + C or C3 KO + C mice spent significantly more time exploring the novel object compared to the familiar object. In contrast, WT+SE mice did not show preference for either object, indicating a memory defect. This deficit was prevented in C3 KO + SE mice, which performed similarly to controls. In addition, we found that SE triggered significant increases in the protein levels of GFAP in hippocampi of WT mice but not in C3 KO mice.

Discussion

These findings suggest that ablation of C3 prevents SE-induced recognition memory deficits and that a C3-astrocyte interplay may play a role. Therefore, it is possible that enhanced C3 signaling contributes to SE-associated cognitive decline during epileptogenesis and may serve as a potential therapeutic target for treating cognitive comorbidities in acquired TLE.

Neuroinflammation: An astrocyte perspective

Astrocytes are abundant glial cells in the central nervous system (CNS) that play active roles in health and disease. Recent technologies have uncovered the functional heterogeneity of astrocytes and their extensive interactions with other cell types in the CNS. In this Review, we highlight the intricate interactions between astrocytes, other CNS-resident cells, and CNS-infiltrating cells as well as their potential therapeutic value in the context of inflammation and neurodegeneration.

JAK-STAT signaling in inflammation and stress-related diseases: implications for therapeutic interventions

The Janus kinase-signal transducer and transcription activator pathway (JAK-STAT) serves as a cornerstone in cellular signaling, regulating physiological and pathological processes such as inflammation and stress. Dysregulation in this pathway can lead to severe immunodeficiencies and malignancies, and its role extends to neurotransduction and pro-inflammatory signaling mechanisms. Although JAK inhibitors (Jakinibs) have successfully treated immunological and inflammatory disorders, their application has generally been limited to diseases with similar pathogenic features. Despite the modest expression of JAK-STAT in the CNS, it is crucial for functions in the cortex, hippocampus, and cerebellum, making it relevant in conditions like Parkinson's disease and other neuroinflammatory disorders. Furthermore, the influence of the pathway on serotonin receptors and phospholipase C has implications for stress and mood disorders. This review expands the understanding of JAK-STAT, moving beyond traditional immunological contexts to explore its role in stress-related disorders and CNS function. Recent findings, such as the effectiveness of Jakinibs in chronic conditions such as rheumatoid arthritis, expand their therapeutic applicability. Advances in isoform-specific inhibitors, including filgotinib and upadacitinib, promise greater specificity with fewer off-target effects. Combination therapies, involving Jakinibs and monoclonal antibodies, aiming to enhance therapeutic specificity and efficacy also give great hope. Overall, this review bridges the gap between basic science and clinical application, elucidating the complex influence of the JAK-STAT pathway on human health and guiding future interventions.

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

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

Mild Oxidative Stress Induced by Sodium Arsenite Reduces Lipocalin-2 Expression Levels in Cortical Glial Cells

Astrocytes and microglia, the most abundant glial cells in the central nervous system, are involved in maintaining homeostasis in the brain microenvironment and in the progression of various neurological disorders. Lipocalin-2 (LCN2) is a small secretory protein that can be transcriptionally upregulated via nuclear factor kappa B (NF-κB) signaling. It is synthesized and secreted by glial cells, resulting in either the restoration of damaged neural tissues or the induction of neuronal apoptosis in a context-dependent manner. It has recently been reported that when glial cells are under lipopolysaccharide-induced inflammatory stress, either reduced production or accelerated degradation of LCN2 can alleviate neurotoxicity. However, the regulatory mechanisms of LCN2 in glial cells are not yet fully understood. In this study, we used primary astroglial-enriched cells which produce LCN2 and found that the production of LCN2 could be reduced by sodium arsenite treatment. Surprisingly, the reduced LCN2 production was not due to the suppression of NF-κB signaling. Mild oxidative stress induced by sodium arsenite treatment activated antioxidant responses and downregulated Lcn2 expression without reducing the viability of astroglial-enriched cells. Intriguingly, reduced LCN2 production could not be achieved by simple activation of the nuclear factor erythroid-2-related factor 2 (Nrf2)-Kelch-like ECH-associated protein 1 (Keap1) pathway in astroglial-enriched cells. Thus, it appears that mild oxidative stress, occurring in an Nrf2-independent manner, is required for the downregulation of Lcn2 expression. Taken together, our findings provide new insights into the regulatory mechanisms of LCN2 and suggest that mild oxidative stress may alter LCN2 homeostasis, even under neuroinflammatory conditions.

Neuroinflammation: The central enabler of postoperative cognitive dysfunction

The proportion of advanced age patients undergoing surgical procedures is on the rise owing to advancements in surgical and anesthesia technologies as well as an overall aging population. As a complication of anesthesia and surgery, older patients frequently suffer from postoperative cognitive dysfunction (POCD), which may persist for weeks, months or even longer. POCD is a complex pathological process involving multiple pathogenic factors, and its mechanism is yet unclear. Potential theories include inflammation, deposition of pathogenic proteins, imbalance of neurotransmitters, and chronic stress. The identification, prevention, and treatment of POCD are still in the exploratory stages owing to the absence of standardized diagnostic criteria. Undoubtedly, comprehending the development of POCD remains crucial in overcoming the illness. Neuroinflammation is the leading hypothesis and a crucial component of the pathological network of POCD and may have complex interactions with other mechanisms. In this review, we discuss the possible ways in which surgery and anesthesia cause neuroinflammation and investigate the connection between neuroinflammation and the development of POCD. Understanding these mechanisms may likely ensure that future treatment options of POCD are more effective.

Microglia mediated neuroinflammation in neurodegenerative diseases: A review on the cell signaling pathways involved in microglial activation

Microglia, the immune sentinels of the central nervous system (CNS), have emerged to be the central players in many neurological and neurodegenerative diseases. Recent studies on large genome databases and omics studies in fact provide support to the idea that microglial cells could be the drivers of these diseases. Microglial cells have the capacity to undergo morphological and phenotypic transformations depending on its microenvironment. From the homeostatic ramified state, they can shift their phenotypes between the two extremes, known as the proinflammatory M1 and anti-inflammatory M2 phenotype, with intermediate transitional states, characterized by different transcriptional signature and release of inflammatory mediators. The temporal regulation of the release of the inflammatory factors are critical for damage control and steering the microglia back towards homeostatic conditions. A dysregulation in these can lead to excessive tissue damage and neuronal death. Therefore, targeting the cell signaling pathways that are the underpinnings of microglial modulations are considered to be an important avenue for treatment of various neurodegenerative diseases. In this review we have discussed various signaling pathways that trigger microglial activation from its ramified state and highlight the mechanisms of microglia-mediated neuroinflammation that are associated with various neurodegenerative diseases. Most of the cellular factors that drive microglia towards a proinflammatory phenotype are components of the immune system signaling pathways and cell proliferation, along with certain ion channels. The anti-inflammatory phenotype is mainly elicited by purinoceptors, metabolic receptors and other receptors that primarily suppress the production proinflammatory mediators.

Clinical trials of new drugs for Alzheimer disease: a 2020-2023 update

Alzheimer's disease (AD) is the leading cause of dementia, presenting a significant unmet medical need worldwide. The pathogenesis of AD involves various pathophysiological events, including the accumulation of amyloid and tau, neuro-inflammation, and neuronal injury. Clinical trials focusing on new drugs for AD were documented in 2020, but subsequent developments have emerged since then. Notably, the US-FDA has approved Aducanumab and Lecanemab, both antibodies targeting amyloid, marking the end of a nearly two-decade period without new AD drugs. In this comprehensive report, we review all trials listed in clinicaltrials.gov, elucidating their underlying mechanisms and study designs. Ongoing clinical trials are investigating numerous promising new drugs for AD. The main trends in these trials involve pathophysiology-based, disease-modifying therapies and the recruitment of participants in earlier stages of the disease. These trends underscore the significance of conducting fundamental research on pathophysiology, prevention, and intervention prior to the occurrence of brain damage caused by AD.

Lipocalin-2: a therapeutic target to overcome neurodegenerative diseases by regulating reactive astrogliosis

Glial cell activation precedes neuronal cell death during brain aging and the progression of neurodegenerative diseases. Under neuroinflammatory stress conditions, lipocalin-2 (LCN2), also known as neutrophil gelatinase-associated lipocalin or 24p3, is produced and secreted by activated microglia and reactive astrocytes. Lcn2 expression levels are known to be increased in various cells, including reactive astrocytes, through the activation of the NF-κB signaling pathway. In the central nervous system, as LCN2 exerts neurotoxicity when secreted from reactive astrocytes, many researchers have attempted to identify various strategies to inhibit LCN2 production, secretion, and function to minimize neuroinflammation and neuronal cell death. These strategies include regulation at the transcriptional, posttranscriptional, and posttranslational levels, as well as blocking its functions using neutralizing antibodies or antagonists of its receptor. The suppression of NF-κB signaling is a strategy to inhibit LCN2 production, but it may also affect other cellular activities, raising questions about its effectiveness and feasibility. Recently, LCN2 was found to be a target of the autophagy‒lysosome pathway. Therefore, autophagy activation may be a promising therapeutic strategy to reduce the levels of secreted LCN2 and overcome neurodegenerative diseases. In this review, we focused on research progress on astrocyte-derived LCN2 in the central nervous system.

Beyond the amyloid cascade: An update of Alzheimer's disease pathophysiology

Alzheimer's disease (AD) is a multi-etiology disease. The biological system of AD is associated with multidomain genetic, molecular, cellular, and network brain dysfunctions, interacting with central and peripheral immunity. These dysfunctions have been primarily conceptualized according to the assumption that amyloid deposition in the brain, whether from a stochastic or a genetic accident, is the upstream pathological change. However, the arborescence of AD pathological changes suggests that a single amyloid pathway might be too restrictive or inconsistent with a cascading effect. In this review, we discuss the recent human studies of late-onset AD pathophysiology in an attempt to establish a general updated view focusing on the early stages. Several factors highlight heterogenous multi-cellular pathological changes in AD, which seem to work in a self-amplifying manner with amyloid and tau pathologies. Neuroinflammation has an increasing importance as a major pathological driver, and perhaps as a convergent biological basis of aging, genetic, lifestyle and environmental risk factors.

TAK1 Improves Cognitive Function via Suppressing RIPK1-Driven Neuronal Apoptosis and Necroptosis in Rats with Chronic Hypertension

Chronic hypertension is a major risk factor for cognitive impairment, which can promote neuroinflammation and neuronal loss in the central nervous system. Transforming growth factor β-activated kinase 1 (TAK1) is a key molecular component in determining cell fate and can be activated by inflammatory cytokines. This study aimed to investigate the role of TAK1 in mediating neuronal survival in the cerebral cortex and hippocampus under chronic hypertensive conditions. To that end, we used stroke-prone renovascular hypertension rats (RHRSP) as chronic hypertension models. Adeno-associated virus (AAV) designed to overexpress or knock down TAK1 expression were injected into the lateral ventricles of rats and the subsequent effects on cognitive function and neuronal survival under chronic hypertensive conditions were assessed. We found that, TAK1 knockdown in RHRSP markedly increased neuronal apoptosis and necroptosis and induced cognitive impairment, which could be reversed by Nec-1s, an inhibitor of receptor interacting protein kinase 1 (RIPK1). In contrast, overexpression of TAK1 in RHRSP significantly suppressed neuronal apoptosis and necroptosis and improved cognitive function. Further knockdown of TAK1 in sham-operated rats received similar phenotype with RHRSP. The results have been verified in vitro. In this study, we provide in vivo and in vitro evidence that TAK1 improves cognitive function by suppressing RIPK1-driven neuronal apoptosis and necroptosis in rats with chronic hypertension.

Microglial over-pruning of synapses during development in autism-associated SCN2A-deficient mice and human cerebral organoids

Autism spectrum disorder (ASD) is a major neurodevelopmental disorder affecting 1 in 36 children in the United States. While neurons have been the focus to understand ASD, an altered neuro-immune response in the brain may be closely associated with ASD, and a neuro-immune interaction could play a role in the disease progression. As the resident immune cells of the brain, microglia regulate brain development and homeostasis via core functions including phagocytosis of synapses. While ASD has been traditionally considered a polygenic disorder, recent large-scale human genetic studies have identified SCN2A deficiency as a leading monogenic cause of ASD and intellectual disability. We generated a Scn2a-deficient mouse model, which displays major behavioral and neuronal phenotypes. However, the role of microglia in this disease model is unknown. Here, we reported that Scn2a-deficient mice have impaired learning and memory, accompanied by reduced synaptic transmission and lower spine density in neurons of the hippocampus. Microglia in Scn2a-deficient mice are partially activated, exerting excessive phagocytic pruning of post-synapses related to the complement C3 cascades during selective developmental stages. The ablation of microglia using PLX3397 partially restores synaptic transmission and spine density. To extend our findings from rodents to human cells, we established a microglial-incorporated human cerebral organoid model carrying an SCN2A protein-truncating mutation identified in children with ASD. We found that human microglia display increased elimination of post-synapse in cerebral organoids carrying the SCN2A mutation. Our study establishes a key role of microglia in multi-species autism-associated models of SCN2A deficiency from mouse to human cells.

PI3K-AKT activation resculpts integrin signaling to drive filamentous tau-induced proinflammatory astrogliosis

BACKGROUND

Microtubule-binding protein tau is a misfolding-prone protein associated with tauopathies. As tau undergoes cell-to-cell transmission, extracellular tau aggregates convert astrocytes into a pro-inflammatory state via integrin activation, causing them to release unknown neurotoxic factors.

RESULTS

Here, we combine transcriptomics with isotope labeling-based quantitative mass spectrometry analysis of mouse primary astrocyte secretome to establish PI3K-AKT as a critical differentiator between pathogenic and physiological integrin activation; simultaneous activation of PI3K-AKT and focal adhesion kinase (FAK) in tau fibril-treated astrocytes changes the output of integrin signaling, causing pro-inflammatory gene upregulation, trans-Golgi network restructuring, and altered secretory flow. Furthermore, NCAM1, as a proximal signaling component in tau-stimulated integrin and PI3K-AKT activation, facilitates the secretion of complement C3 as a main neurotoxic factor. Significantly, tau fibrils-associated astrogliosis and C3 secretion can be mitigated by FAK or PI3K inhibitors.

CONCLUSIONS

These findings reveal an unexpected function for PI3K-AKT in tauopathy-associated reactive astrogliosis, which may be a promising target for anti-inflammation-based Alzheimer's therapy.

Hydrocortisone Mitigates Alzheimer's-Related Cognitive Decline through Modulating Oxidative Stress and Neuroinflammation

Alzheimer's disease (AD), an age-related degenerative disorder, is characterized by β-amyloid deposition, abnormal phosphorylation of tau proteins, synaptic dysfunction, neuroinflammation, and oxidative stress. Despite extensive research, there are no medications or therapeutic interventions to completely treat and reverse AD. Herein, we explore the potential of hydrocortisone (HC), a natural and endogenous glucocorticoid known to have potent anti-inflammatory properties, in an Aβ1-42-induced AD mouse model. Our investigation highlights the beneficial effects of HC administration on cognitive impairment, synaptic function enhancement, and neuronal protection in Aβ1-42-induced AD mice. Notably, HC treatment effectively suppresses the hyperactivation of microglia and astrocytes, leading to a reduction in proinflammatory factors and alleviation of neuroinflammation. Furthermore, HC intervention demonstrates the capacity to mitigate the generation of ROS and oxidative stress. These compelling findings underscore the potential therapeutic application of HC in AD and present promising opportunities for its utilization in AD prevention and treatment. The implications drawn from our findings indicate that hydrocortisone holds promise as a viable candidate for adjunctive use with other anti-AD drugs for the clinical management of patients presenting with moderate to severe AD.

Hepatic soluble epoxide hydrolase activity regulates cerebral Aβ metabolism and the pathogenesis of Alzheimer's disease in mice

Alzheimer's disease (AD) is caused by a complex interaction between genetic and environmental factors. However, how the role of peripheral organ changes in response to environmental stimuli during aging in AD pathogenesis remains unknown. Hepatic soluble epoxide hydrolase (sEH) activity increases with age. Hepatic sEH manipulation bidirectionally attenuates brain amyloid-β (Aβ) burden, tauopathy, and cognitive deficits in AD mouse models. Moreover, hepatic sEH manipulation bidirectionally regulates the plasma level of 14,15-epoxyeicosatrienoic acid (-EET), which rapidly crosses the blood-brain barrier and modulates brain Aβ metabolism through multiple pathways. A balance between the brain levels of 14,15-EET and Aβ is essential for preventing Aβ deposition. In AD models, 14,15-EET infusion mimicked the neuroprotective effects of hepatic sEH ablation at biological and behavioral levels. These results highlight the liver's key role in AD pathology, and targeting the liver-brain axis in response to environmental stimuli may constitute a promising therapeutic approach for AD prevention.

Neuroprotection of low-molecular-weight galactan obtained from Cantharellus cibarius Fr. against Alzheimer's disease

The large molecular weight of polysaccharides limits their absorption and utilization by organisms, affecting their biological activities. In this study, we purified α-1,6-galactan from Cantharellus cibarius Fr. (chanterelle) and reduced its molecular weight from approximately 20 kDa to 5 kDa (named CCP) to increase its solubility and absorption. In APP/PS1 mice, CCP improved both spatial and non-spatial memory loss in Alzheimer's disease (AD) mice, as confirmed by the Morris water maze, step-down, step-through, and novel object recognition tests, and dampened the deposition of amyloid-β plaques, as assessed by immunohistochemical analysis. Proteomic analysis suggested that the neuroprotective effects of CCP are related to anti-neuroinflammation. Immunofluorescence analysis and western blotting confirmed that CCP attenuated AD-like symptoms partly by inhibiting neuroinflammation, which was related to the blocking of complement component 3. Our study provides theoretical support and experimental evidence for the future application of chanterelle-extracted polysaccharides in AD treatment, promoting the modern development of traditional medicines originating from natural polysaccharides.