Determining the role of IL-4 induced neuroinflammation in microglial activity and amyloid-β using BV2 microglial cells and APP/PS1 transgenic mice

Mesenchymal stem cell therapy for Alzheimer's disease: A novel therapeutic approach for neurodegenerative diseases

Alzheimer's disease (AD) is one of the most progressive and prevalent types of neurodegenerative diseases in the aging population (aged >65 years) and is considered a major factor for dementia, affecting 55 million people worldwide. In the current scenario, drug-based therapies have been employed for the treatment of Alzheimer's disease but are only able to provide symptomatic relief to patients rather than a permanent solution from Alzheimer's. Recent advancements in stem cell research unlock new horizons for developing effective and highly potential therapeutic approaches due to their self-renewal, self-replicating, regenerative, and high differentiation capabilities. Stem cells come in multiple lineages such as embryonic, neural, and induced pluripotent, among others. Among different kinds of stem cells, mesenchymal stem cells are the most investigated for Alzheimer's treatment due to their multipotent nature, low immunogenicity, ability to penetrate the blood-brain barrier, and low risk of tumorigenesis, immune & inflammatory modulation, etc. They have been seen to substantially promote neurogenesis, synaptogenesis by secreting neurotrophic growth factors, as well as in ameliorating the Aβ and tau-mediated toxicity. This review covers the pathophysiology of AD, new medications, and therapies. Further, it will focus on the advancements and benefits of Mesenchymal Stem Cell therapies, their administration methods, clinical trials concerning AD progression, along with their future prospective.

Dissecting the immune response of CD4+ T cells in Alzheimer's disease

The formation of amyloid-β (Aβ) plaques is a neuropathological hallmark of Alzheimer's disease (AD), however, these pathological aggregates can also be found in the brains of cognitively unimpaired elderly population. In that context, individual variations in the Aβ-specific immune response could be key factors that determine the level of Aβ-induced neuroinflammation and thus the propensity to develop AD. CD4+ T cells are the cornerstone of the immune response that coordinate the effector functions of both adaptive and innate immunity. However, despite intensive research efforts, the precise role of these cells during AD pathogenesis is still not fully elucidated. Both pathogenic and beneficial effects have been observed in various animal models of AD, as well as in humans with AD. Although this functional duality of CD4+ T cells in AD can be simply attributed to the vast phenotype heterogeneity of this cell lineage, disease stage-specific effect have also been proposed. Therefore, in this review, we summarized the current understanding of the role of CD4+ T cells in the pathophysiology of AD, from the aspect of their antigen specificity, activation, and phenotype characteristics. Such knowledge is of practical importance as it paves the way for immunomodulation as a therapeutic option for AD treatment, given that currently available therapies have not yielded satisfactory results.

Cordycepin Modulates Microglial M2 Polarization Coupled with Mitochondrial Metabolic Reprogramming by Targeting HKII and PDK2

The microenvironment mediated by the microglia (MG) M1/M2 phenotypic switch plays a decisive role in the neuronal fate and cognitive function of Alzheimer's disease (AD). However, the impact of metabolic reprogramming on microglial polarization and its underlying mechanism remains elusive. This study reveals that cordycepin improved cognitive function and memory in APP/PS1 mice, as well as attenuated neuronal damage by triggering MG-M2 polarization and metabolic reprogramming characterized by increased OXPHOS and glycolysis, rather than directly protecting neurons. Simultaneously, cordycepin partially alleviates mitochondrial damage in microglia induced by inhibitors of OXPHOS and glycolysis, further promoting MG-M2 transformation and increasing neuronal survival. Through confirmation of cordycepin distribution in the microglial mitochondria via mitochondrial isolation followed by HPLC-MS/MS techniques, HKII and PDK2 are further identified as potential targets of cordycepin. By investigating the effects of HKII and PDK2 inhibitors, the mechanism through which cordycepin targeted HKII to elevate ECAR levels in the glycolysis pathway while targeting PDK2 to enhance OCR levels in PDH-mediated OXPHOS pathway, thereby inducing MG-M2 polarization, promoting neuronal survival and exerting an anti-AD role is elucidated.

Extracellular vesicles as carriers for noncoding RNA-based regulation of macrophage/microglia polarization: an emerging candidate regulator for lung and traumatic brain injuries

Macrophage/microglia function as immune defense and homeostatic cells that originate from bone marrow progenitor cells. Macrophage/microglia activation is historically divided into proinflammatory M1 or anti-inflammatory M2 states based on intracellular dynamics and protein production. The polarization of macrophages/microglia involves a pivotal impact in modulating the development of inflammatory disorders, namely lung and traumatic brain injuries. Recent evidence indicates shared signaling pathways in lung and traumatic brain injuries, regulated through non-coding RNAs (ncRNAs) loaded into extracellular vesicles (EVs). This packaging protects ncRNAs from degradation. These vesicles are subcellular components released through a paracellular mechanism, constituting a group of nanoparticles that involve exosomes, microvesicles, and apoptotic bodies. EVs are characterized by a double-layered membrane and are abound with proteins, nucleic acids, and other bioactive compounds. ncRNAs are RNA molecules with functional roles, despite their absence of coding capacity. They actively participate in the regulation of mRNA expression and function through various mechanisms. Recent studies pointed out that selective packaging of ncRNAs into EVs plays a role in modulating distinct facets of macrophage/microglia polarization, under conditions of lung and traumatic brain injuries. This study will explore the latest findings regarding the role of EVs in the progression of lung and traumatic brain injuries, with a specific focus on the involvement of ncRNAs within these vesicles. The conclusion of this review will emphasize the clinical opportunities presented by EV-ncRNAs, underscoring their potential functions as both biomarkers and targets for therapeutic interventions.

Interleukin-4 Modulates Neuroinflammation by Inducing Phenotypic Transformation of Microglia Following Subarachnoid Hemorrhage

Neuroinflammation, a key pathological feature following subarachnoid hemorrhage (SAH), can be therapeutically targeted by inhibiting microglia M1 polarization and promoting phenotypic transformation to M2 microglia. Interleukin-4 (IL-4) is a pleiotropic cytokine known to its regulation of physiological functions of the central nervous system (CNS) and mediate neuroinflammatory processes. However, its specific role in neuroinflammation and microglia responses following SAH remains unexplored. In this investigation, we established both in vivo and in vitro SAH models and employed a comprehensive array of assessments, including ELISA, neurofunctional profiling, immunofluorescence staining, qRT-PCR, determination of phagocytic capacity, and RNA-Seq analyses. The findings demonstrate an elevated expression of IL-4 within cerebrospinal fluid (CSF) subsequent to SAH. Furthermore, exogenous administration of IL-4 ameliorates post-SAH neurofunctional deficits, attenuates cellular apoptosis, fosters M2 microglia phenotype conversion, and mitigates neuroinflammatory responses. The RNA-Seq analysis signifies that IL-4 governs the modulation of neuroinflammation in microglia within an in vitro SAH model through intricate cascades of signaling pathways, encompassing interactions between cytokines and cytokine receptors. These discoveries not only augment comprehension of the neuropathogenesis associated with post-SAH neuroinflammation but also present novel therapeutic targets for the management thereof.

Microbiota Metabolites and Immune Regulation Affect Ischemic Stroke Occurrence, Development, and Prognosis

The gut microbiota are not only related to the development and occurrence of digestive system disease, but also have a bidirectional relationship with nervous system diseases via the microbiota-gut-brain axis. At present, correlations between the gut microbiota and neurological diseases, including stroke, are one of the focuses of investigation and attention in the medical community. Ischemic stroke (IS) is a cerebrovascular disease accompanied by focal neurological deficit or central nervous system injury or death. In this review, we summarize the contemporary latest research on correlations between the gut microbiota and IS. Additionally, we discuss the mechanisms of gut microbiota implicated in IS and related to metabolite production and immune regulation. Moreover, the factors of gut microbiota that affecting IS occurrence, and research implicating the gut microbiota as potential therapeutic targets for IS, are highlighted. Our review highlights the evidential relationships and connections between the gut microbiota and IS pathogenesis and prognosis.

Interleukin 4 Reduces Brain Hyperexcitability after Traumatic Injury by Downregulating TNF-α, Upregulating IL-10/TGF-β, and Potential Directing Macrophage/Microglia to the M2 Anti-inflammatory Phenotype

Macrophage/microglia are activated after Traumatic brain injury (TBI), transform to inflammatory phenotype (M1) and trigger neuroinflammation, which provokes epileptogenesis. Interleukin-4 (IL-4) is a well-known drive of macrophage/microglia to the anti-inflammatory phenotype (M2). We tested effect of IL-4 on speed of epileptogenesis, brain expression of inflammatory and anti-inflammatory cytokines, and lesion size in TBI-injured male rats. Rats underwent TBI by Controlled Cortical Impact. Then 100 ng IL-4 was injected into cerebral ventricles. One day after TBI, pentylenetetrazole (PTZ) kindling started and development of generalized seizures was recorded. The lesion size, cell survival rate, TNF-α, TGF-β, IL-10, and Arginase1 (Arg1) was measured in the brain 6 h, 12 h, 24 h, 48 h, and 5 days after TBI. Astrocytes and macrophage/microglia activation/polarization was assessed by GFAP/Arg1 and Iba1/Arg1 immunostaining. TBI-injured rats were kindled by 50% less PTZ injections than control and sham-operated rats. IL-4 did not change kindling rate in sham-operated rats but inhibited acceleration of kindling rate in the TBI-injured rats. IL-4 decreased damage volume and number of destroyed neurons. IL-4 stopped TNF-α whereas upregulated TGF-β, IL-10, and Arg1 expressions. Iba1/Arg1 positive macrophage/microglia was notably increased 48 h after IL-4 administration. IL-4 suppresses TBI-induced acceleration of epileptogenesis in rats by directing TBI neuroinflammation toward an anti-inflammatory tone and inhibition of cell death.

From the Bush to the Brain: Preclinical Stages of Ethnobotanical Anti-Inflammatory and Neuroprotective Drug Discovery-An Australian Example

The Australian rainforest is a rich source of medicinal plants that have evolved in the face of dramatic environmental challenges over a million years due to its prolonged geographical isolation from other continents. The rainforest consists of an inherent richness of plant secondary metabolites that are the most intense in the rainforest. The search for more potent and more bioavailable compounds from other plant sources is ongoing, and our short review will outline the pathways from the discovery of bioactive plants to the structural identification of active compounds, testing for potency, and then neuroprotection in a triculture system, and finally, the validation in an appropriate neuro-inflammatory mouse model, using some examples from our current research. We will focus on neuroinflammation as a potential treatment target for neurodegenerative diseases including multiple sclerosis (MS), Parkinson's (PD), and Alzheimer's disease (AD) for these plant-derived, anti-inflammatory molecules and highlight cytokine suppressive anti-inflammatory drugs (CSAIDs) as a better alternative to conventional nonsteroidal anti-inflammatory drugs (NSAIDs) to treat neuroinflammatory disorders.

Revisiting the intersection of microglial activation and neuroinflammation in Alzheimer's disease from the perspective of ferroptosis

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by chronic neuroinflammation with amyloid beta-protein deposition and hyperphosphorylated tau protein. The typical clinical manifestation of AD is progressive memory impairment, and AD is considered a multifactorial disease with various etiologies (genetic factors, aging, lifestyle, etc.) and complicated pathophysiological processes. Previous research identified that neuroinflammation and typical microglial activation are significant mechanisms underlying AD, resulting in dysfunction of the nervous system and progression of the disease. Ferroptosis is a novel modality involved in this process. As an iron-dependent form of cell death, ferroptosis, characterized by iron accumulation, lipid peroxidation, and irreversible plasma membrane disruption, promotes AD by accelerating neuronal dysfunction and abnormal microglial activation. In this case, disturbances in brain iron homeostasis and neuronal ferroptosis aggravate neuroinflammation and lead to the abnormal activation of microglia. Abnormally activated microglia release various pro-inflammatory factors that aggravate the dysregulation of iron homeostasis and neuroinflammation, forming a vicious cycle. In this review, we first introduce ferroptosis, microglia, AD, and their relationship. Second, we discuss the nonnegligible role of ferroptosis in the abnormal microglial activation involved in the chronic neuroinflammation of AD to provide new ideas for the identification of potential therapeutic targets for AD.

NOX2 inhibition enables retention of the circadian clock in BV2 microglia and primary macrophages

Introduction

Sustained neuroinflammation is a major contributor to the progression of neurodegenerative diseases such as Alzheimer's (AD) and Parkinson's (PD) diseases. Neuroinflammation, like other cellular processes, is affected by the circadian clock. Microglia, the resident immune cells in the brain, act as major contributors to neuroinflammation and are under the influence of the circadian clock. Microglial responses such as activation, recruitment, and cytokine expression are rhythmic in their response to various stimuli. While the link between circadian rhythms and neuroinflammation is clear, significant gaps remain in our understanding of this complex relationship. To gain a greater understanding of this relationship, the interaction between the microglial circadian clock and the enzyme NADPH Oxidase Isoform 2 (NOX2) was studied; NOX2 is essential for the production of reactive oxygen species (ROS) in oxidative stress, an integral characteristic of neuroinflammation.

Methods

BV2 microglia were examined over circadian time, demonstrating oscillations of the clock genes Per2 and Bmal1 and the NOX2 subunits gp91phox and p47phox.

Results

The BV2 microglial clock exerted significant control over NOX2 expression and inhibition of NOX2 enabled the microglia to retain a functional circadian clock while reducing levels of ROS and inflammatory cytokines. These trends were mirrored in mouse bone marrow-derived primary macrophages.

Conclusions

NOX2 plays a crucial role in the interaction between the circadian clock and the activation of microglia/macrophages into their pro-inflammatory state, which has important implications in the control of neuroinflammation.

Interleukin-4 as a therapeutic target

Interleukin-4 (IL-4) is a pleiotropic cytokine mainly known for its role in type 2 immunity. Therapies antagonizing or blocking IL-4 activity have been developed to counteract diseases such as atopic dermatitis and asthma. In contrast, other disorders experimentally benefit from IL-4-related effects and IL-4 recently demonstrated beneficial activity in experimental stroke, spinal cord injury and the animal model of multiple sclerosis. To exploit IL-4-related activity for therapeutic concepts, current experimental efforts include modifying the pathway without inducing type 2 immune response and targeting of the cytokine to specific tissues. Here, we review different activities of IL-4 as well as therapeutic strategies.

Modulatory effects of mesenchymal stem cells on microglia in ischemic stroke

Ischemic stroke accounts for 70-80% of all stroke cases. Immunity plays an important role in the pathophysiology of ischemic stroke. Microglia are the first line of defense in the central nervous system. Microglial functions are largely dependent on their pro-inflammatory (M1-like) or anti-inflammatory (M2-like) phenotype. Modulating neuroinflammation via targeting microglia polarization toward anti-inflammatory phenotype might be a novel treatment for ischemic stroke. Mesenchymal stem cells (MSC) and MSC-derived extracellular vesicles (MSC-EVs) have been demonstrated to modulate microglia activation and phenotype polarization. In this review, we summarize the physiological characteristics and functions of microglia in the healthy brain, the activation and polarization of microglia in stroke brain, the effects of MSC/MSC-EVs on the activation of MSC in vitro and in vivo, and possible underlying mechanisms, providing evidence for a possible novel therapeutics for the treatment of ischemic stroke.

Licochalcone E, a β-Amyloid Aggregation Inhibitor, Regulates Microglial M1/M2 Polarization via Inhibition of CTL1-Mediated Choline Uptake

Alzheimer's disease (AD) is thought to be a series of neuroinflammatory diseases caused by abnormal deposits of amyloid-β (Aβ) and tau protein in the brain as part of its etiology. We focused on Aβ aggregation and M1 and M2 microglial polarity in microglia to search for novel therapeutic agents. It has been reported that the inhibition of choline uptake via choline transporter-like protein 1 (CTL1) in microglia preferentially induces M2 microglial polarity. However, the role of the choline transport system on the regulation of microglial M1/M2 polarity in AD is not fully understood. Licochalcones (Licos) A-E, flavonoids extracted from licorice, have been reported to have immunological anti-inflammatory effects, and Lico A inhibits Aβ aggregation. In this study, we compared the efficacy of five Licos, from Lico A to E, at inhibiting Aβ1-42 aggregation. Among the five Licos, Lico E was selected to investigate the relationship between the inhibition of choline uptake and microglial M1/M2 polarization using the immortalized mouse microglial cell line SIM-A9. We newly found that Lico E inhibited choline uptake and Aβ1-42 aggregation in SIM-A9 cells in a concentration-dependent manner, suggesting that the inhibitory effect of Lico E on choline uptake is mediated by CTL1. The mRNA expression of tumor necrosis factor (TNF-α), a marker of M1 microglia, was increased by Aβ1-42, and its effect was inhibited by choline deprivation and Lico E in a concentration-dependent manner. In contrast, the mRNA expression of arginase-1 (Arg-1), a marker of M2 microglia, was increased by IL-4, and its effect was enhanced by choline deprivation and Lico E. We found that Lico E has an inhibitory effect on Aβ aggregation and promotes polarity from M1 to M2 microglia via inhibition of the CTL1 function in microglia. Thus, Lico E may become a leading compound for a novel treatment of AD.

Inhibition of Pro-Inflammatory Microglia with Minocycline Improves Cognitive and Sleep-Wake Dysfunction Under Respiratory Stress in a Sporadic Model for Alzheimer's Disease

BACKGROUND

Neuroinflammation in Alzheimer's disease (AD) can occur due to excessive activation of microglia in response to the accumulation of amyloid-β peptide (Aβ). Previously, we demonstrated an increased expression of this peptide in the locus coeruleus (LC) in a sporadic model for AD (streptozotocin, STZ; 2 mg/kg, ICV). We hypothesized that the STZ-AD model exhibits neuroinflammation, and treatment with an inhibitor of microglia (minocycline) can reverse the cognitive, respiratory, sleep, and molecular disorders of this model.

OBJECTIVE

To evaluate the effect of minocycline treatment in STZ model disorders.

METHODS

We treated control and STZ-treated rats for five days with minocycline (30 mg/kg, IP) and evaluated cognitive performance, chemoreflex response to hypercapnia and hypoxia, and total sleep time. Additionally, quantification of Aβ, microglia analyses, and relative expression of cytokines in the LC were performed.

RESULTS

Minocycline treatment improved learning and memory, which was concomitant with a decrease in microglial cell density and re-establishment of morphological changes induced by STZ in the LC region. Minocycline did not reverse the STZ-induced increase in CO2 sensitivity during wakefulness. However, it restored the daytime sleep-wake cycle in STZ-treated animals to the same levels as those observed in control animals. In the LC, levels of A and expression of Il10, Il1b, and Mcp1 mRNA remained unaffected by minocycline, but we found a strong trend of minocycline effect on Tnf- α.

CONCLUSION

Our findings suggest that minocycline effectively reduces microglial recruitment and the inflammatory morphological profile in the LC, while it recovers cognitive performance and restores the sleep-wake pattern impaired by STZ.

Non-Pharmacological Therapeutic Options for the Treatment of Alzheimer's Disease

Alzheimer's disease is a growing global crisis in need of urgent diagnostic and therapeutic strategies. The current treatment strategy mostly involves immunotherapeutic medications that have had little success in halting disease progress. Hypotheses for pathogenesis and development of AD have been expanded to implicate both organ systems as well as cellular reactions. Non-pharmacologic interventions ranging from minimally to deeply invasive have attempted to address these diverse contributors to AD. In this review, we aim to delineate mechanisms underlying such interventions while attempting to provide explanatory links between the observed differences in disease states and postulated metabolic or structural mechanisms of change. The techniques discussed are not an exhaustive list of non-pharmacological interventions against AD but provide a foundation to facilitate a deeper understanding of the area of study.

Microglia-mediated neuroinflammation and neuroplasticity after stroke

Stroke remains a major cause of long-term disability and mortality worldwide. The immune system plays an important role in determining the condition of the brain following stroke. As the resident innate immune cells of the central nervous system, microglia are the primary responders in a defense network covering the entire brain parenchyma, and exert various functions depending on dynamic communications with neurons, astrocytes, and other neighboring cells under both physiological or pathological conditions. Microglia activation and polarization is crucial for brain damage and repair following ischemic stroke, and is considered a double-edged sword for neurological recovery. Microglia can exist in pro-inflammatory states and promote secondary brain damage, but they can also secrete anti-inflammatory cytokines and neurotrophic factors and facilitate recovery following stroke. In this review, we focus on the role and mechanisms of microglia-mediated neuroinflammation and neuroplasticity after ischemia and relevant potential microglia-based interventions for stroke therapy.

Antroquinonol administration in animal preclinical studies for Alzheimer's disease (AD): A new avenue for modifying progression of AD pathophysiology

Despite the rise of Alzheimer's disease (AD) in an ageing population, no cure is currently available for this disorder. This study assessed the role of a natural compound, Antroquinonol, in modifying the progression of AD when administered at the start and/or before appearance of symptoms and when the disease was well established, in a transgenic animal model. Antroquinonol was administered daily for 8 weeks, in 11 week (early stage) and 9 month (late stage) male transgenic mice (3 times Transgenic mice PS1_M146V, APP_Swe, and tau_P301L, 3 ​Tg XAD) and their respective aged controls. Behavioural testing (including Elevated Plus Maze Watermaze, Recognition object testing and Y maze) was performed at the end of the drug administration. In addition AD biomarkers (Amyloid beta 42 (Aβ42), tau and phospho-tau levels), oxidative stress and inflammatory markers, were assessed in tested mice brains after their sacrifice at the end of the treatment. When administered before the start of symptoms at 11 weeks, Antroquinonol treatment at 34 ​mg/kg (D2) and more consistently at 75 ​mg/kg (D3), had a significant effect on reducing systemic inflammatory markers (Interleukin 1, IL-1β and TNF-α) and AD biomarker (Amyloid Beta 42, Aβ42 and tau) levels in the brain. The reduction of behavioural impairment reported for 3TgXAD mice was observed significantly for the D3 drug dose only and for all behavioural tests, when administered at 11 weeks.

Similarly, beneficial effects of Antroquinonol (at higher dose D3) were noted in the transgenic mice in terms of AD biomarkers (tau and phosphorylated-tau), systemic inflammatory (IL-1β), brain anti-inflammatory (Nrf2) and oxidative (3-Nitrotyrosine, 3NT) markers. Improvement of memory impairment was also reported when Antroquinonol (D3) was administered at late stage (9 months).

Since Antroquinonol has been used without adverse effects in previous successful clinical trials, this drug may offer a new avenue of treatment to modify AD development and progression.

The Obese Brain: Mechanisms of Systemic and Local Inflammation, and Interventions to Reverse the Cognitive Deficit

Overweight and obesity are now considered a worldwide pandemic and a growing public health problem with severe economic and social consequences. Adipose tissue is an organ with neuroimmune-endocrine functions, which participates in homeostasis. So, adipocyte hypertrophy and hyperplasia induce a state of chronic inflammation that causes changes in the brain and induce neuroinflammation. Studies with obese animal models and obese patients have shown a relationship between diet and cognitive decline, especially working memory and learning deficiencies. Here we analyze how obesity-related peripheral inflammation can affect central nervous system physiology, generating neuroinflammation. Given that the blood-brain barrier is an interface between the periphery and the central nervous system, its altered physiology in obesity may mediate the consequences on various cognitive processes. Finally, several interventions, and the use of natural compounds and exercise to prevent the adverse effects of obesity in the brain are also discussed.

SK-Channel Activation Alters Peripheral Metabolic Pathways in Mice, but Not Lipopolysaccharide-Induced Fever or Inflammation

Purpose

Previously, we have shown that CyPPA (cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine), a pharmacological small-conductance calcium-activated potassium (SK)–channel positive modulator, antagonizes lipopolysaccharide (LPS)-induced cytokine expression in microglial cells. Here, we aimed to test its therapeutic potential for brain-controlled sickness symptoms, brain inflammatory response during LPS-induced systemic inflammation, and peripheral metabolic pathways in mice.

Methods

Mice were pretreated with CyPPA (15 mg/kg IP) 24 hours before and simultaneously with LPS stimulation (2.5 mg/kg IP), and the sickness response was recorded by a telemetric system for 24 hours. A second cohort of mice were euthanized 2 hours after CyPPA or solvent treatment to assess underlying CyPPA-induced mechanisms. Brain, blood, and liver samples were analyzed for inflammatory mediators or nucleotide concentrations using immunohistochemistry, real-time PCR and Western blot, or HPLC. Moreover, we investigated CyPPA-induced changes of UCP1 expression in brown adipose tissue (BAT)–explant cultures.

Results

CyPPA treatment did not affect LPS-induced fever, anorexia, adipsia, or expression profiles of inflammatory mediators in the hypothalamus or plasma or microglial reactivity to LPS (CD11b staining and CD68 mRNA expression). However, CyPPA alone induced a rise in core body temperature linked to heat production via altered metabolic pathways like reduced levels of adenosine, increased protein content, and increased UCP1 expression in BAT-explant cultures, but no alteration in ATP/ADP concentrations in the liver. CyPPA treatment was accompanied by altered pathways, including NFκB signaling, in the hypothalamus and cortex, while circulating cytokines remained unaltered.

Conclusion

Overall, while CyPPA has promise as a treatment strategy, in particular according to results from in vitro experiments, we did not reveal anti-inflammatory effects during severe LPS-induced systemic inflammation. Interestingly, we found that CyPPA alters metabolic pathways inducing short hyperthermia, most likely due to increased energy turnover in the liver and heat production in BAT.

Anti-Inflammatory Gene Therapy Improves Spatial Memory Performance in a Mouse Model of Alzheimer's Disease

The immune system plays a critical role in neurodegenerative processes involved in Alzheimer’s disease (AD). In this study, a gene-based immunotherapeutic method examined the effects of anti-inflammatory cellular immune response elements (CIREs) in the amyloid-β protein precursor (AβPP) mouse model. Bi-monthly intramuscular administration, beginning at either 4 or 6 months, and examined at 7.5 through 16 months, with plasmids encoding Interleukin (IL)-10, IL-4, TGF-β polynucleotides, or a combination thereof, into AβPP mice improved spatial memory performance. This work demonstrates an efficient gene therapy strategy to downregulate neuroinflammation, and possibly prevent or delay cognitive decline in AD.

Treadmill Exercise Attenuates Cerebral Ischemia-Reperfusion Injury by Promoting Activation of M2 Microglia via Upregulation of Interleukin-4

Background: Exercise has been proven to be an effective therapy for stroke by reducing the microglia-initiated proinflammatory response. Few studies, however, have focused on the phenotypic changes in microglia cells caused by exercise training. The present study was designed to evaluate the influence of treadmill exercise on microglia polarization and the molecular mechanisms involved. Methods: Male Sprague-Dawley rats were randomly assigned into 3 groups: sham, MCAO and exercise. The middle cerebral artery occlusion (MCAO) and exercise groups received MCAO surgery and the sham group a sham operation. The exercise group also underwent treadmill exercise after the surgery. These groups were studied after 4 and 7 days to evaluate behavioral performance using a modified neurological severity score (mNSS), and infarct conditions using 2,3,5-triphenyl tetrazolium chloride. Quantitative real-time polymerase chain reaction (qRT-PCR) and Luminex was employed to determine the expressions of markers of microglia phenotypes. Western blotting was employed to identify the phosphorylation levels of Janus kinase1 (JAK1) and signal transducer and activator of transcription 6 (STAT6). Immunofluorescence was conducted to identify microglia phenotypes. Results: Treadmill exercise was found to improve neurobehavioral outcomes, mainly motor and balance functions, reduce infarct volumes and significantly increase interleukin-4 (IL-4) expression. In addition, treadmill exercise inhibited M1 microglia and promoted M2 microglia activation as evidenced by decreased M1 and increased M2 markers. Furthermore, an obvious increase in p-JAK1 and p-STAT6 was observed in the exercise group. Conclusions: Treadmill exercise ameliorates cerebral ischemia-reperfusion injury by enhancing IL-4 expression to promote M2 microglia polarization, possibly via the JAK1-STAT6 pathway.

Regulation of microglia polarization via mannose receptor-mediated delivery of siRNA by ligand-functionalized DoGo LNP

The pro-inflammatory polarization of microglia after stroke is one of the major causes of secondary brain injury. Downregulation of the gene involved in canonical inflammatory pathways in glial cells can exert neuroprotective effects via inhibiting the release of pro-inflammatory factors. In this study, we functionalized DoGo lipids with mannose, the ligand of the mannose receptor (MR) that is expressed in microglia, and evaluated the MR-mediated cellular internalization of DoGo lipid nanoparticles (denote M3) carrying siRNA against TLR4 in BV2 cells in vitro. We confirmed that siTLR4/M3 complexes were specifically internalized by BV2 cells in a MR-dependent manner, and the treatment of oxygen glucose deprivation (OGD)-treated BV2 cells with siTLR4/M3 complexes resulted in remarkable silencing of TLR4, and induced downregulated M1 polarization and upregulated M2 polarization markers. Collectively, our data suggest that the M3 lipoplex is a promising microglia-targeting siRNA delivery agent.

Mannose functionalized DoGo lipid nanoparticles (denote M3) can effectively deliver siRNA to microglia via receptor-mediated internalization, knockdown target gene and induce neuroprotective M2 polarization.

Genetic Therapies for Alzheimer's Disease: A Scoping Review

Effective, disease modifying therapies for Alzheimer's disease (AD) remain a quandary, following a panoply of expensive failures in human clinical trials. Given the stagnation in therapeutics, alternative approaches are needed. Recent successes of genetic therapies in other neurodegenerative diseases may highlight the way forward. This scoping review explores suggested targets of genetic therapy in AD, with a focus on vector-based approaches in pre-clinical and clinical trials. Putative targets of genetic therapies tested in pre-clinical trials include amyloid pathway intermediates and enzymes modulation, tau protein downregulation, APOE4 downregulation and APOE2 upregulation, neurotrophin expression (nerve growth factor (NGF) and brain-derived neurotrophic factor), and inflammatory cytokine alteration, among several other approaches. There have been three completed human clinical trials for genetic therapy in AD patients, all of which upregulated NGF in AD patients, showing some mixed evidence of benefit. Several impediments remain to be surpassed before genetic therapies can be successfully applied to AD, including the challenge of delivering monogenic genetic therapies for complex polygenic disorders, risks in the dominant delivery method (intracranial injection), stability of genetic therapies in vivo, poor translatability of pre-clinical AD models, and the expense of genetic therapy production. Genetic therapies represent an exciting opportunity within the world of AD therapeutics, but clinical applications likely remain a long term, rather than short term, possibility.

The role of meningeal populations of type II innate lymphoid cells in modulating neuroinflammation in neurodegenerative diseases

Recent research into meningeal lymphatics has revealed a never-before appreciated role of type II innate lymphoid cells (ILC2s) in modulating neuroinflammation in the central nervous system (CNS). To date, the role of ILC2-mediated inflammation in the periphery has been well studied. However, the exact distribution of ILC2s in the CNS and therefore their putative role in modulating neuroinflammation in neurodegenerative diseases such as Alzheimer's disease (AD), multiple sclerosis (MS), Parkinson's disease (PD), and major depressive disorder (MDD) remain highly elusive. Here, we review the current evidence of ILC2-mediated modulation of neuroinflammatory cues (i.e., IL-33, IL-25, IL-5, IL-13, IL-10, TNFα, and CXCL16-CXCR6) within the CNS, highlight the distribution of ILC2s in both the periphery and CNS, and discuss some challenges associated with cell type-specific targeting that are important for therapeutics. A comprehensive understanding of the roles of ILC2s in mediating and responding to inflammatory cues may provide valuable insight into potential therapeutic strategies for many dementia-related disorders.

Effects of lead exposure on the activation of microglia in mice fed with high-fat diets

Lead (Pb) exposure can cause central nervous system (CNS) damage. The process of Pb neurotoxicity is accompanied by the microglia activation. In addition, microglia activation was observed under the intervention of high-fat diets (HFD). This study was designed to investigate the effect of Pb on the cognitive function of mice with HFD, with focus on the microglia activation in brain. Male C57BL/6J mice, 8 weeks of age, were randomly divided into control, HFD, Pb, and HFD + Pb groups. The results showed that HFD following Pb exposure could exacerbate the learning and memory impairment in mice. Pb exposure could promote microglia activation and increase the expression of M1 microglia marker and decrease the expression of M2 microglia marker in the hippocampus of mice with HFD. Our finding suggested that Pb exposure may aggravate CNS damage by promoting M1 polarization and inhibiting M2 polarization of hippocampal microglia in HFD mice.

Modulating poststroke inflammatory mechanisms: Novel aspects of mesenchymal stem cells, extracellular vesicles and microglia

Inflammation plays an important role in the pathological process of ischemic stroke, and systemic inflammation affects patient prognosis. As resident immune cells in the brain, microglia are significantly involved in immune defense and tissue repair under various pathological conditions, including cerebral ischemia. Although the differentiation of M1 and M2 microglia is certainly oversimplified, changing the activation state of microglia appears to be an intriguing therapeutic strategy for cerebral ischemia. Recent evidence indicates that both mesenchymal stem cells (MSCs) and MSC-derived extracellular vesicles (EVs) regulate inflammation and modify tissue repair under preclinical stroke conditions. However, the precise mechanisms of these signaling pathways, especially in the context of the mutual interaction between MSCs or MSC-derived EVs and resident microglia, have not been sufficiently unveiled. Hence, this review summarizes the state-of-the-art knowledge on MSC- and MSC-EV-mediated regulation of microglial activity under ischemic stroke conditions with respect to various signaling pathways, including cytokines, neurotrophic factors, transcription factors, and microRNAs.

M2a Macrophage-Secreted CHI3L1 Promotes Extracellular Matrix Metabolic Imbalances via Activation of IL-13Rα2/MAPK Pathway in Rat Intervertebral Disc Degeneration

The accumulation of macrophages in degenerated discs is a common phenomenon. However, the roles and mechanisms of M2a macrophages in intervertebral disc degeneration (IDD) have not been illuminated. This study investigated the expression of the M2a macrophage marker (CD206) in human and rat intervertebral disc tissues by immunohistochemistry. To explore the roles of M2a macrophages in IDD, nucleus pulposus (NP) cells were co-cultured with M2a macrophages in vitro. To clarify whether the CHI3L1 protein mediates the effect of M2a macrophages on NP cells, siRNA was used to knock down CHI3L1 transcription. To elucidate the underlying mechanisms, NP cells were incubated with recombinant CHI3L1 proteins, then subjected to western blotting analysis of the IL-13Rα2 receptor and MAPK pathway. CD206-positive cells were detected in degenerated human and rat intervertebral disc tissues. Notably, M2a macrophages promoted the expression of catabolism genes (MMP-3 and MMP-9) and suppressed the expression of anabolism genes (aggrecan and collagen II) in NP cells. These effects were abrogated by CHI3L1 knockdown in M2a macrophages. Exposure to recombinant CHI3L1 promoted an extracellular matrix metabolic imbalance in NP cells via the IL-13Rα2 receptor, along with activation of the ERK and JNK MAPK signaling pathways. This study elucidated the roles of M2a macrophages in IDD and identified potential mechanisms for these effects.

Resistance Exercise Decreases Amyloid Load and Modulates Inflammatory Responses in the APP/PS1 Mouse Model for Alzheimer's Disease

Neuroinflammation has been shown to play a crucial role in the development of Alzheimer's disease (AD) and also has an association with amyloid-β (Aβ) plaques, a hallmark of this disease. Physical exercise has emerged as an alternative treatment for pathological impairment in AD. In light of this evidence, together with the fact that the hippocampus is one of the first structures to be affected in AD, we analyzed hippocampal changes in Aβ load, inflammatory responses, and locomotor activity in transgenic APP/PS1 mouse model for AD submitted to a resistance exercise (RE) program. One month after the start of the RE program, the locomotor hyperactivity related to AD behavior was reduced and microglia recruitment was increased, which in turn may have contributed to the decrease in the volume of Aβ plaques. In addition, the RE program restored the levels of IL-1α, IL-4, and IL-6 cytokines to control levels. Our study indicates that RE has beneficial effects on the locomotor behavior, amyloid burden, and inflammation of AD pathology and can therefore be used as a therapy to improve the clinical symptoms and neurophysiological alterations in AD. To the best of our knowledge, this is the first study to use a resistance exercise program in transgenic AD model.

Microglial Polarization: Novel Therapeutic Strategy against Ischemic Stroke

Ischemic stroke, which is the second highest cause of death and the leading cause of disability, represents ~71% of all strokes globally. Some studies have found that the key elements of the pathobiology of stroke is immunity and inflammation. Microglia are the first line of defense in the nervous system. After stroke, the activated microglia become a double-edged sword, with distinct phenotypic changes to the deleterious M1 types and neuroprotective M2 types. Therefore, ways to promote microglial polarization toward M2 phenotype after stroke have become the focus of attention in recent years. In this review, we discuss the process of microglial polarization, summarize the alternation of signaling pathways and epigenetic regulation that control microglial polarization in ischemic stroke, aiming to find the potential mechanisms by which microglia can be transformed into the M2 polarized phenotype.

Lentivirus-Mediated Expression of Human Secreted Amyloid Precursor Protein-Alpha Promotes Long-Term Induction of Neuroprotective Genes and Pathways in a Mouse Model of Alzheimer's Disease

BACKGROUND

Secreted amyloid precursor protein-alpha (sAPPα) can enhance memory and is neurotrophic and neuroprotective across a range of disease-associated insults, including amyloid-β toxicity. In a significant step toward validating sAPPα as a therapeutic for Alzheimer's disease (AD), we demonstrated that long-term overexpression of human sAPPα (for 8 months) in a mouse model of amyloidosis (APP/PS1) could prevent the behavioral and electrophysiological deficits that develop in these mice.

OBJECTIVE

To explore the underlying molecular mechanisms responsible for the significant physiological and behavioral improvements observed in sAPPα-treated APP/PS1 mice.

METHODS

We assessed the long-term effects on the hippocampal transcriptome following continuous lentiviral delivery of sAPPα or empty-vector to male APP/PS1 mice and wild-type controls using Affymetrix Mouse Transcriptome Assays. Data analysis was carried out within the Affymetrix Transcriptome Analysis Console and an integrated analysis of the resulting transcriptomic data was performed with Ingenuity Pathway analysis (IPA).

RESULTS

Mouse transcriptome assays revealed expected AD-associated gene expression changes in empty-vector APP/PS1 mice, providing validation of the assays used for the analysis. By contrast, there were specific sAPPα-associated gene expression profiles which included increases in key neuroprotective genes such as Decorin, betaine-GABA transporter and protocadherin beta-5, subsequently validated by qRT-PCR. An integrated biological pathways analysis highlighted regulation of GABA receptor signaling, cell survival and inflammatory responses. Furthermore, upstream gene regulatory analysis implicated sAPPα activation of Interleukin-4, which can counteract inflammatory changes in AD.

CONCLUSION

This study identified key molecular processes that likely underpin the long-term neuroprotective and therapeutic effects of increasing sAPPα levels in vivo.

Microglia-associated neuroinflammation is a potential therapeutic target for ischemic stroke

Microglia-associated neuroinflammation plays an important role in the pathophysiology of ischemic stroke. Microglial activation and polarization, and the inflammatory response mediated by these cells play important roles in the development, progression and outcome of brain injury after ischemic stroke. Currently, there is no effective strategy for treating ischemic stroke in clinical practice. Therefore, it is clinically important to study the role and regulation of microglia in stroke. In this review, we discuss the involvement of microglia in the neuroinflammatory process in ischemic stroke, with the aim of providing a better understanding of the relationship between ischemic stroke and microglia.

The Gut Microbiota, Kynurenine Pathway, and Immune System Interaction in the Development of Brain Cancer

Human gut microbiota contains a large, complex, dynamic microbial community of approximately 10¹⁴ microbes from more than 1,000 microbial species, i.e., equivalent to 4 × 10⁶ genes. Numerous evidence links gut microbiota with human health and diseases. Importantly, gut microbiota is involved in the development and function of the brain through a bidirectional pathway termed as the gut-brain axis. Interaction between gut microbiota and immune responses can modulate the development of neuroinflammation and cancer diseases in the brain. With respect of brain cancer, gut microbiota could modify the levels of antioxidants, amyloid protein and lipopolysaccharides, arginase 1, arginine, cytochrome C, granulocyte-macrophage colony-stimulating factor signaling (GM-CSF), IL-4, IL-6, IL-13, IL-17A, interferon gamma (IFN-γ), reactive oxygen species (ROS), reactive nitrogen species (e.g., nitric oxide and peroxynitrite), short-chain fatty acids (SCFAs), tryptophan, and tumor necrosis factor-β (TGF-β). Through these modifications, gut microbiota can modulate apoptosis, the aryl hydrocarbon receptor (AhR), autophagy, caspases activation, DNA integrity, microglia dysbiosis, mitochondria permeability, T-cell proliferation and functions, the signal transducer and activator of transcription (STAT) pathways, and tumor cell proliferation and metastasis. The outcome of such interventions could be either oncolytic or oncogenic. This review scrutinizes the oncogenic and oncolytic effects of gut microbiota by classifying the modification mechanisms into (i) amino acid deprivation (arginine and tryptophan); (ii) kynurenine pathway; (iii) microglia dysbiosis; and (iv) myeloid-derived suppressor cells (MDSCs). By delineating the complexity of the gut-microbiota-brain-cancer axis, this review aims to help the research on the development of novel therapeutic strategies that may aid the efficient eradication of brain cancers.

Inflammatory factors and amyloid β-induced microglial polarization promote inflammatory crosstalk with astrocytes

The immunological responses are a key pathological factor in Alzheimer's disease (AD). We hypothesized that microglial polarization alters microglia-astrocyte immune interactions in AD. M1 and M2 microglia were isolated from primary rat microglia and were confirmed to secrete pro-inflammatory and anti-inflammatory factors, respectively. Primary rat astrocytes were co-cultured with M1 or M2 microglial medium. M1 microglial medium increased astrocyte production of pro-inflammatory factors (interleukin [IL]-1β, tumor necrosis factor α and IL-6), while M2 microglial medium enhanced astrocyte production of anti-inflammatory factors (IL-4 and IL-10). To analyze the crosstalk between microglia and astrocytes after microglial polarization specifically in AD, we co-cultured astrocytes with medium from microglia treated with amyloid-β (Aβ) alone or in combination with other inflammatory substances. Aβ alone and Aβ combined with lipopolysaccharide/interferon-γ induced pro-inflammatory activity in M1 microglia and astrocytes, whereas IL-4/IL-13 inhibited Aβ-induced pro-inflammatory activity. Nuclear factor κB p65 was upregulated in M1 microglia and pro-inflammatory astrocytes, while Stat6 was upregulated in M2 microglia and anti-inflammatory astrocytes. These results provide direct evidence that microglial polarization governs communication between microglia and astrocytes, and that AD debris alters this crosstalk.

Neuroinflammation in Alzheimer's Disease: Microglia, Molecular Participants and Therapeutic Choices

Alzheimer's disease is the world's most common dementing illness. It is pathologically characterized by β-amyloid accumulation, extracellular senile plaques and intracellular neurofibrillary tangles formation, and neuronal necrosis and apoptosis. Neuroinflammation has been widely recognized as a crucial process that participates in AD pathogenesis. In this review, we briefly summarized the involvement of microglia in the neuroinflammatory process of Alzheimer's disease. Its roles in the AD onset and progression are also discussed. Numerous molecules, including interleukins, tumor necrosis factor alpha, chemokines, inflammasomes, participate in the complex process of AD-related neuroinflammation and they are selectively discussed in this review. In the end of this paper from an inflammation- related perspective, we discussed some potential therapeutic choices.

Interleukin 4 Affects Epilepsy by Regulating Glial Cells: Potential and Possible Mechanism

Epilepsy is a chronic brain dysfunction induced by an abnormal neuronal discharge that is caused by complicated psychopathologies. Recently, accumulating studies have revealed a close relationship between inflammation and epilepsy. Specifically, microglia and astrocytes are important inflammatory cells in the central nervous system (CNS) that have been proven to be related to the pathogenesis and development of epilepsy. Additionally, interleukin 4 (IL-4) is an anti-inflammatory factor that can regulate microglia and astrocytes in many aspects. This review article focuses on the regulatory role of IL-4 in the pathological changes of glial cells related to epilepsy. We additionally propose that IL-4 may play a protective role in epileptogenesis and suggest that IL-4 may be a novel therapeutic target for the treatment of epilepsy.

Neuroprotective modulation of microglia effector functions following priming with interleukin 4 and 13: current limitations in understanding their mode-of-action

In recent years the long-standing theory of microglia's properties for dual polarization towards a pro- or anti-inflammatory phenotype has been deeply challenged. Furthermore, the elucidation of microglia ontogenesis exposed intrinsic differences between microglia and peripheral myeloid cells, thereby further underscoring the need to re-evaluate microglia-specific activation behavior, especially within an inflamed central nervous system (CNS) environment. This review critically summarizes recent literature on the in vitro and in vivo response of murine microglia to the immune-modulatory cytokines interleukin 4 (IL4) and interleukin 13 (IL13), i.e. those driving the so-called anti-inflammatory phenotype. Here we highlight several pivotal factors that may influence experimental outcome and/or interpretation of in vitro and in vivo studies evaluating microglia's phenotypical and functional properties upon IL4/IL13 treatment. Finally, the current therapeutic relevance of IL4/IL13-induced microglia activation in both acute and chronic CNS disorders is discussed.

Evaluating the Effect of Interleukin-4 in the 3xTg Mouse Model of Alzheimer's Disease

Chronic neuroinflammation has long been hypothesized to be involved in Alzheimer's Disease (AD) progression. Previous research suggests that both anti-inflammatory and inflammatory microglia ameliorate amyloid pathology, but the latter worsen tau pathology. In this study, we sought to determine whether induction of arginase-1 positive microglia with the anti-inflammatory cytokine IL-4 modulates pathology in the 3xTg mouse model of AD. Our findings indicate that a single intracranial IL-4 injection positively modulated performance of 3xTg AD mice in a Novel Object Recognition task, and locally increased the levels of arginase-1 positive myeloid cells when assessed one-week post injection. Furthermore, immunohistochemical analysis revealed decreased tau phosphorylation in IL-4 injected animals; however, we were not able to detect significant changes in tau phosphorylation utilizing Western blot. Lastly, IL-4 injection did not appear to cause significant changes in amyloid β load. In conclusion, acute intracranial IL-4 led to some positive benefits in the 3xTg mouse model of AD. Although more work remains, these results support therapeutic strategies aimed at modifying microglial activation states in neurodegenerative diseases.

Heterogeneity of Microglia Phenotypes: Developmental, Functional and Some Therapeutic Considerations

BACKGROUND

Microglia play a pivotal role in maintaining homeostasis in complex brain environment. They first exist as amoeboid microglial cells (AMCs) in the developing brain, but with brain maturation, they transform into ramified microglial cells (RMCs). In pathological conditions, microglia are activated and have been classified into M1 and M2 phenotypes. The roles of AMCs, RMCs and M1/M2 microglia phenotypes especially in pathological conditions have been the focus of many recent studies.

METHODS

Here, we review the early development of the AMCs and RMCs and discuss their specific functions with reference to their anatomic locations, immunochemical coding etc. M1 and M2 microglia phenotypes in different neuropathological conditions are also reviewed.

RESULTS

Activated microglia are engaged in phagocytosis, production of proinflammatory mediators, trophic factors and synaptogenesis etc. Prolonged microglia activation, however, can cause damage to neurons and oligodendrocytes. The M1 and M2 phenotypes featured prominently in pathological conditions are discussed in depth. Experimental evidence suggests that microglia phenotype is being modulated by multiple factors including external and internal stimuli, local demands, epigenetic regulation, and herbal compounds.

CONCLUSION

Prevailing views converge that M2 polarization is neuroprotective. Thus, proper therapeutic designs including the use of anti-inflammatory drugs, herbal agents may be beneficial in suppression of microglial activation, especially M1 phenotype, for amelioration of neuroinflammation in different neuropathological conditions. Finally, recent development of radioligands targeting 18 kDa translocator protein (TSPO) in activated microglia may hold great promises clinically for early detection of brain lesion with the positron emission tomography.

IL-4 Switches Microglia/macrophage M1/M2 Polarization and Alleviates Neurological Damage by Modulating the JAK1/STAT6 Pathway Following ICH

Inflammatory damage following ICH is often attributed to microglia/macrophage activation. In many diseases, IL-4 has been proven to switch microglia/macrophages from the pro-inflammatory to the anti-inflammatory subtype. However, the role and underlying mechanism of IL-4 in ICH, especially in neuroprotection, remain unknown. In our study, we constructed a microglia/macrophage polarization model in BV2 cells to verify that the M2 shift of microglia/macrophages was mediated by JAK1/STAT6 after IL-4 treatment and then revealed that in vitro administration of IL-4 decreased M1 markers, pro-inflammatory cytokines and neuroapoptosis markers but significantly increased M2 markers and anti-inflammatory cytokines. Using an ICH model in mice, we observed that IL-4 administration decreased neurological deficits, brain edema and infarct lesions induced by ICH. We verified that IL-4 mediates inflammation by regulating M1/M2 polarization in ICH and explored the underlying mechanism. Furthermore, we discovered that pathway components and apoptosis-related proteins showed consistent trends based on their respective roles, and inferred that the process that TNF-α activates caspase-3 may be the crosstalk that microglia phagocytosis developed into accelerate apoptosis of cells in ICH. In conclusion, our study demonstrates that IL-4 may promote M2 microglia/macrophage polarization partly through the JAK1/STAT6 pathway to alleviate neuroinflammation after ICH.

Ketone production by ketogenic diet and by intermittent fasting has different effects on the gut microbiota and disease progression in an Alzheimer's disease rat model

The benefits of ketone production regimens remain controversial. Here, we hypothesized that the ketone-producing regimens modulated cognitive impairment, glucose metabolism, and inflammation while altering the gut microbiome. The hypothesis and the mechanism were explored in amyloid-β infused rats. Rats that received an amyloid-β(25–35) infusion into the hippocampus had either ketogenic diet (AD-KD), intermittent fasting (AD-IMF), 30 energy percent fat diet (AD-CON), or high carbohydrate (starch) diet (AD-CHO) for 8 weeks. AD-IMF and AD-CHO, but not AD-KD, lowered the hippocampal amyloid-β deposition compared to the AD-CON despite serum ketone concentrations being elevated in both AD-KD and AD-IMF. AD-IMF and AD-CHO, but not AD-KD, improved memory function in passive avoidance, Y maze, and water maze tests compared to the AD-CON. Hippocampal insulin signaling (pAkt→pGSK-3β) was potentiated and pTau was attenuated in AD-IMF and AD-CHO much more than AD-CON. AD-IMF and AD-CON had similar glucose tolerance results during OGTT, but AD-KD and AD-IMF exhibited glucose intolerance. AD-KD exacerbated gut dysbiosis by increasing Proteobacteria, and AD-CHO improved it by elevating Bacteriodetes. In conclusion, ketone production itself might not improve memory function, insulin resistance, neuroinflammation or the gut microbiome when induced by ketone-producing remedies. Intermittent fasting and a high carbohydrate diet containing high starch may be beneficial for people with dementia.

Glial Cells: Role of the Immune Response in Ischemic Stroke

Ischemic stroke, which accounts for 75-80% of all strokes, is the predominant cause of morbidity and mortality worldwide. The post-stroke immune response has recently emerged as a new breakthrough target in the treatment strategy for ischemic stroke. Glial cells, including microglia, astrocytes, and oligodendrocytes, are the primary components of the peri-infarct environment in the central nervous system (CNS) and have been implicated in post-stroke immune regulation. However, increasing evidence suggests that glial cells exert beneficial and detrimental effects during ischemic stroke. Microglia, which survey CNS homeostasis and regulate innate immune responses, are rapidly activated after ischemic stroke. Activated microglia release inflammatory cytokines that induce neuronal tissue injury. By contrast, anti-inflammatory cytokines and neurotrophic factors secreted by alternatively activated microglia are beneficial for recovery after ischemic stroke. Astrocyte activation and reactive gliosis in ischemic stroke contribute to limiting brain injury and re-establishing CNS homeostasis. However, glial scarring hinders neuronal reconnection and extension. Neuroinflammation affects the demyelination and remyelination of oligodendrocytes. Myelin-associated antigens released from oligodendrocytes activate peripheral T cells, thereby resulting in the autoimmune response. Oligodendrocyte precursor cells, which can differentiate into oligodendrocytes, follow an ischemic stroke and may result in functional recovery. Herein, we discuss the mechanisms of post-stroke immune regulation mediated by glial cells and the interaction between glial cells and neurons. In addition, we describe the potential roles of various glial cells at different stages of ischemic stroke and discuss future intervention targets.

Deletion of Chitinase-3-like 1 accelerates stroke development through enhancement of Neuroinflammation by STAT6-dependent M2 microglial inactivation in Chitinase-3-like 1 knockout mice

Chitinase 3-like 1 (Chi3L1) plays a major role in the pathogenesis of inflammatory diseases. We investigated the effect of Chi3L1 knockout on stroke development. Ischemia/reperfusion was induced by middle cerebral artery occlusion (MCAO) in Chi3L1 knockout and wildtype mice. Significantly increased infarct volume and decreased neurological deficit scores at 24 h after ischemia/reperfusion were found in Chi3L1 knockout mice compared to wildtype mice. Moreover, ischemic neuronal cell death was increased in Chi3L1 knockout mice through increased oxidative stress and release of IL-6 and IL-1β but IL-10 and IL-4 were reduced. Furthermore, expression of inflammation-related proteins (iNOS, COX-2, Iba-1, and GFAP) was significantly increased in Chi3L1 knockout mice compared to wildtype. In microglia isolated from MCAO-injured Chi3L1 knockout mice, expression of M1 markers (iNOS, CD86, IL-1β, and IL-6) was increased and M2 markers (Arg1, Mrc1, IL-10, and IL-4Ra) was decreased. In BV-2 cells, knockdown of Chi3L1 increased TNF-α- and INF-γ-induced expression of iNOS, COX-2, and Iba-1, but decreased the expression of Arg1, MRC1, and IL-4 receptor-alpha (IL-4Rα). Expression of IL-4Rα, an important factor of M2 polarization, and its downstream signals p-JAK1, p-JAK3, and p-STAT6, was much reduced in the knockout mice. Additionally, in BV-2 cells, knockdown of Chi3L1 by siRNA Chi3L1 decreased rhTNF-α- and INF-γ-induced expression of IL-4Rα, p-JAK1, p-JAK3, and p-STAT6. Furthermore, treatment with AS1517499 abolished Chi3L1 knockdown-induced reduced IL-4Rα and Arg1 but not CD86 expression. Our results indicate that deletion of Chi3L1 accelerates stroke development through enhancement of neuroinflammation by markedly decreasing STAT6-dependent M2 macrophage polarization.

Gamma Visual Stimulation Induces a Neuroimmune Signaling Profile Distinct from Acute Neuroinflammation

Many neurodegenerative and neurological diseases are rooted in dysfunction of the neuroimmune system; therefore, manipulating this system has strong therapeutic potential. Prior work has shown that exposing mice to flickering lights at 40 Hz drives gamma frequency (∼40 Hz) neural activity and recruits microglia, the primary immune cells of the brain, revealing a novel method to manipulate the neuroimmune system.

Many neurodegenerative and neurological diseases are rooted in dysfunction of the neuroimmune system; therefore, manipulating this system has strong therapeutic potential. Prior work has shown that exposing mice to flickering lights at 40 Hz drives gamma frequency (∼40 Hz) neural activity and recruits microglia, the primary immune cells of the brain, revealing a novel method to manipulate the neuroimmune system. However, the biochemical signaling mechanisms between 40 Hz neural activity and immune recruitment remain unknown. Here, we exposed wild-type male mice to 5–60 min of 40 Hz or control flicker and assessed cytokine and phosphoprotein networks known to play a role in immune function. We found that 40 Hz flicker leads to increases in the expression of cytokines which promote microglial phagocytic states, such as IL-6 and IL-4, and increased expression of microglial chemokines, such as macrophage-colony-stimulating factor and monokine induced by interferon-γ. Interestingly, cytokine effects differed as a function of stimulation frequency, revealing a range of neuroimmune effects of stimulation. To identify possible mechanisms underlying cytokine expression, we quantified the effect of the flicker on intracellular signaling pathways known to regulate cytokine levels. We found that a 40 Hz flicker upregulates phospho-signaling within the nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) and mitogen-activated protein kinase (MAPK) pathways. While cytokine expression increased after 1 h of 40 Hz flicker stimulation, protein phosphorylation in the NF-κB pathway was upregulated within minutes. Importantly, the cytokine expression profile induced by 40 Hz flicker was different from cytokine changes in response to acute neuroinflammation induced by lipopolysaccharides. These results are the first, to our knowledge, to show how visual stimulation rapidly induces critical neuroimmune signaling in healthy animals.

SIGNIFICANCE STATEMENT Prior work has shown that exposing mice to lights flickering at 40 Hz induces neural spiking activity at 40 Hz (within the gamma frequency) and recruits microglia, the primary immune cells of the brain. However, the immediate effect of 40 Hz flicker on neuroimmune biochemical signaling was unknown. We found that 40 Hz flicker leads to significant increases in the expression of cytokines, key immune signals known to recruit microglia. Furthermore, we found that 40 Hz flicker rapidly changes the phosphorylation of proteins in the NF-κB and MAPK pathways, both known to regulate cytokine expression. Our findings are the first to delineate a specific rapid immune signaling response following 40 Hz visual stimulation, highlighting both the unique nature and therapeutic potential of this treatment.

NAD+ in Brain Aging and Neurodegenerative Disorders

NAD⁺ is a pivotal metabolite involved in cellular bioenergetics, genomic stability, mitochondrial homeostasis, adaptive stress responses, and cell survival. Multiple NAD⁺-dependent enzymes are involved in synaptic plasticity and neuronal stress resistance. Here, we review emerging findings that reveal key roles for NAD⁺ and related metabolites in the adaptation of neurons to a wide range of physiological stressors and in counteracting processes in neurodegenerative diseases, such as those occurring in Alzheimer's, Parkinson's, and Huntington diseases, and amyotrophic lateral sclerosis. Advances in understanding the molecular and cellular mechanisms of NAD⁺-based neuronal resilience will lead to novel approaches for facilitating healthy brain aging and for the treatment of a range of neurological disorders.

Protective and Regenerative Roles of T Cells in Central Nervous System Disorders

Pathogenic mechanisms of T cells in several central nervous system (CNS) disorders are well-established. However, more recent studies have uncovered compelling beneficial roles of T cells in neurological diseases, ranging from tissue protection to regeneration. These divergent functions arise due to the diversity of T cell subsets, particularly CD4⁺ T cells. Here, we review the beneficial impact of T cell subsets in a range of neuroinflammatory and neurodegenerative diseases including multiple sclerosis, Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, stroke, and CNS trauma. Both T cell-secreted mediators and direct cell contact-dependent mechanisms deliver neuroprotective, neuroregenerative and immunomodulatory signals in these settings. Understanding the molecular details of these beneficial T cell mechanisms will provide novel targets for therapeutic exploitation that can be applied to a range of neurological disorders.

Inflammation within the neurovascular unit: Focus on microglia for stroke injury and recovery

Neuroinflammation underlies the etiology of multiple neurodegenerative diseases and stroke. Our understanding of neuroinflammation has evolved in the last few years and major players have been identified. Microglia, the brain resident macrophages, are considered sentinels at the forefront of the neuroinflammatory response to different brain insults. Interestingly, microglia perform other physiological functions in addition to their role in neuroinflammation. Therefore, an updated approach in which modulation, rather than complete elimination of microglia is necessary. In this review, the emerging roles of microglia and their interaction with different components of the neurovascular unit are discussed. In addition, recent data on sex differences in microglial physiology and in the context of stroke will be presented. Finally, the multiplicity of roles assumed by microglia in the pathophysiology of ischemic stroke, and in the presence of co-morbidities such as hypertension and diabetes are summarized.

Autoimmune-Mediated Retinopathy in CXCR5-Deficient Mice as the Result of Age-Related Macular Degeneration Associated Proteins Accumulation

Previous research has shown that CXCR5^−/− mice develop retinal degeneration (RD) with age, a characteristic related to age macular degeneration (AMD). RD in these mice is not well-understood, and in this study, we sought to characterize further the RD phenotype and to gain mechanistic insights into the function of CXCR5 in the retina. CXCR5^−/− and WT control mice were used. Fundus images demonstrated a significant (p < 0.001) increase of hypo-pigmented spots in the retina of aged CXCR5^−/− mice compared with WT control mice. PAS staining indicated localization of deposits in the sub-retinal pigment epithelia (RPE) layer. AMD-associated proteins Cryab, amyloid beta, and C3d were detected within the RPE/sub-RPE tissues by immunofluorescence (IF). In addition, western blot analysis of COX-2, Arg1, and VEGF-a revealed an increase in the signaling of these molecules within the RPE/choroid complex. Transmission electron microscopy (TEM) indicated a drusen-like structure of sub-RPE deposits with an accumulation of vacuolated cellular debris. Loss of photoreceptors was detected by peanut lectin staining and was corroborated by a reduction in MAP2 signaling. Loss of blood-retinal barrier integrity was demonstrated by a reduction of ZO-1 expression. Inflammatory cells were detected in the sub-RPE space, with an increase in IBA-1 positive microglia cells on the surface of the RPE. Mass spectrometry analysis of CXCR5^−/− mouse RPE/choroid proteins extracts, separated by SDS-page and incubated with autologous serum, identified autoantibodies against AMD-associated proteins: Cryaa, Cryab, and Anxa2. In vitro evaluations in BV-2 cell culture indicated a significant increase in production of Arg-1 (p < 0.001) and COX-2 (p < 0.01) in the presence of anti-CXCR5 antibody when compared with Igg-treated control BV-2 cells stimulated with IL-4 and TNFα/IFNγ, respectively. Anti-CXCR5 antibody treatment without stimulating agents did not affect Arg-1 and COX-2 expression; this suggests that CXCR5 may have a regulatory role in microglia cells activation. These results indicate that with age, CXCR5^−/− mice develop RD characterized by microglia dysfunction, increased production of CXCL13 in the RPE progressive photoreceptor, neuronal loss, and sub-RPE deposition of cellular debris, resulting in the production of immunogenic proteins and autoimmune-mediated RD.

Natural products as a potential modulator of microglial polarization in neurodegenerative diseases

Neurodegenerative diseases (NDs) are characterized by the progressive loss of structure and function of neurons most common in elderly population, mainly including Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS). Neuroinflammation caused by microglia as the resident macrophages of the central nervous system (CNS) plays a contributory role in the onset and progression of NDs. Activated microglia, as in macrophages, to be heterogeneous, can polarize into M1 (pro-inflammatory) and M2 (anti-inflammatory) functional phenotypes. The former elaborate pro-inflammatory mediators promoting neuroinflammation and neuronal damage. In contrast, the latter generate anti-inflammatory mediators and neurotrophins that inhibit neuroinflammation and promote neuronal healing. Consistently, the regulation of microglial polarization from M1 to M2 phenotype appears as an outstanding therapeutic and preventive approach for NDs treatment. Although non-steroidal anti-inflammatory drugs (NSAIDs) currently used to alleviate M1 microglia-associated neuroinflammation responsible for the development of NDs, these drugs have different degrees of adverse effects and limited efficacy. As the advantages of novel structure, multi-target, high efficiency and low toxicity, natural products as the modulators of microglial polarization have attracted considerable concerns in the therapeutic areas of NDs. In this review, we mainly summarized the therapeutic potential of natural products and their various molecular mechanisms for NDs treatment through modulating microglial polarization. The aim of the current review is expected to be useful to develop innovative modulators of microglial polarization from natural products for the amelioration and treatment of NDs.

Mycoplasma contamination affects cell characteristics and decreases the sensitivity of BV2 microglia to LPS stimulation

Mycoplasma is the most common contaminant and greatly affects host cells. The influence of mycoplasma on microglia cells remains unknown. Here, we investigated the influence of mycoplasma contamination on BV2 cells (a microglia cell line). We found that mycoplasma contamination increased the phosphorylation of NF-kB and MAPK signal pathway and induced the activation of BV2 cells. These mycoplasma-contaminated BV2 cells exhibited a transition of cell morphology and slower proliferation, as well as increased gene expression and protein secretion of inflammatory factors. Furthermore, mycoplasma-contaminated BV2 cells had decreased sensitivity to lipopolysaccharide stimulation. These findings suggested that mycoplasma contamination greatly influenced the characteristics and function of microglia cells. It is important to prevent and exclude mycoplasma contamination in our research.