Aerobic exercise attenuates LPS-induced cognitive dysfunction by reducing oxidative stress, glial activation, and neuroinflammation

Physical activity has been considered an important non-medication intervention in preserving mnemonic processes during aging. However, how aerobic exercise promotes such benefits for human health remains unclear. In this study, we aimed to explore the neuroprotective and anti-inflammatory effects of aerobic exercise against lipopolysaccharide (LPS)-induced amnesic C57BL/6J mice and BV-2 microglial cell models. In the in vivo experiment, the aerobic exercise training groups were allowed to run on a motorized treadmill 5 days/week for 4 weeks at a speed of 10 rpm/min, with LPS (0.1 mg/kg) intraperitoneally injected once a week for 4 weeks. We found that aerobic exercise ameliorated memory impairment and cognitive deficits among the amnesic mice. Correspondingly, aerobic exercise significantly increased the protein expressions of FNDC5, which activates target neuroprotective markers BDNF and CREB, and antioxidant markers Nrf2/HO-1, leading to inhibiting microglial-mediated neuroinflammation and reduced the expression of BACE-1 in the hippocampus and cerebral cortex of amnesic mice. We estimated that aerobic exercise inhibited neuroinflammation in part through the action of FNDC5/irisin on microglial cells. Therefore, we explored the anti-inflammatory effects of irisin on LPS-stimulated BV-2 microglial cells. In the in vitro experiment, irisin treatment blocked NF-κB/MAPK/IRF3 signaling activation concomitantly with the significantly lowered levels of the LPS-induced iNOS and COX-2 elevations and promotes the Nrf2/HO-1 expression in the LPS-stimulated BV-2 microglial cells. Together, our findings suggest that aerobic exercise can improve the spatial learning ability and cognitive functions of LPS-treated mice by inhibiting microglia-mediated neuroinflammation through its effect on the expression of BDNF/FNDC5/irisin.

Novel multifunctional nanoliposomes inhibit α-synuclein fibrillization, attenuate microglial activation, and silence the expression of SNCA gene

INTRODUCTION

The aim of this study was to compare the effect of five types of PEGlated nanoliposomes (PNLs) on α-synuclein (α-syn) fibrillization, attenuation of microglial activation, and silence of the SNCA gene, which encodes α-syn.

METHODS

To evaluate the inhibition of α-syn fibrillization, we used standard in vitro assay based on Thioflavin T (ThT) fluorescence. Next, to evaluate the attenuation of microglial activation, the concentration of TNF-a and IL-6 was quantified by ELISA assay in BV2 microglia cells treated with 100nM A53T α-syn and PNLs. In order to determine the silencing of the SNCA, real-time PCR and Western blot analysis was used. Finally, the efficacy of PNLs was confirmed in a transgenic mouse model expressing human α-syn.

RESULTS

ThT assay showed both PNL1 and PNL2 significantly inhibited a-syn fibrillization. ELISA test also showed the production of TNF-a and IL-6 was significantly attenuated when microglial cells treated with PNL1 or PNL2. We also found that SNCA gene, at both mRNA and protein levels, was significantly silenced when BV2 microglia cells were treated with PNL1 or PNL2. Importantly, the efficacy of PNL1 and PNL2 was finally confirmed in vivo in a transgenic mouse model.

CONCLUSIONS

In conclusion, the novel multifunctional nanoliposomes tested in our study inhibit α-syn fibrillization, attenuate microglial activation, and silence SNCA gene. Our findings suggest the therapeutic potential of PNL1 and PNL2 for treating synucleinopathies.

The paradoxical role of zinc on microglia

Zinc is an essential trace element for humans, and its homeostasis is essential for the health of the central nervous system. Microglia, the resident immune cells in the central nervous system, play the roles of sustaining, nourishing, and immune surveillance. Microglia are sensitive to microenvironment changes and are easily activated to M1 phenotype to enhance disease progression or the M2 phenotype to improve peripheral nerves injury repair. Zinc is requisite for microglial activation, However, the cytotoxicity outcome of zinc against microglia, the activated microglia phenotype, and activated microglia function are ambiguous. Herein, we have reviewed the neurological function of zinc and microglia, particularly the ambiguous role of zinc on microglia. We also pay attention to the role of zinc homeostasis on microglial function within the central nervous system disease. Finally, we observe the relationship between zinc and microglia, attempting to design new therapeutic measures against major nervous system disorders.

Galectin-3 modulates microglial activation and neuroinflammation in early brain injury after subarachnoid hemorrhage

BACKGROUND

Aneurysmal subarachnoid hemorrhage (SAH) is a devastating acute cerebrovascular event with high mortality and permanent disability rates. Higher galectin-3 levels on days 1-3 have been shown to predict the development of delayed cerebral infarction or adverse outcomes after SAH. Recent single-cell analysis of microglial transcriptomic diversity in SAH revealed that galectin could influence the development and course of neuroinflammation after SAH.

METHODS

This study aimed to investigate the role and mechanism of galectin-3 in SAH and to determine whether galectin-3 inhibition prevents early brain injury by reducing microglia polarization using a mouse model of SAH and oxyhemoglobin-treated activation of mouse BV2 cells in vitro.

RESULTS

We found that the expression of galectin-3 began to increase 12 h after SAH and continued to increase up to 72 h. Importantly, TD139-inhibited galectin-3 expression reduced the release of inflammatory factors in microglial cells. In the experimental SAH model, TD139 treatment alleviated neuroinflammatory damage after SAH and improved defects in neurological functions. Furthermore, we demonstrated that galectin-3 inhibition affected the activation and M1 polarization of microglial cells after SAH. TD139 treatment inhibited the expression of TLR4, p-NF-κB p65, and NF-κB p65 in microglia activated by oxyhemoglobin as well as eliminated the increased expression and phosphorylation of JAK2 and STAT3.

CONCLUSION

These findings suggest that regulating microglia polarization by galectin-3 after SAH to improve neuroinflammation may be a potential therapeutic target.

Specific transcription factors Ascl1 and Lhx6 attenuate diabetic neuropathic pain by modulating spinal neuroinflammation and microglial activation in mice

Gamma-aminobutyric acid (GABA) neuronal system-related transcription factors (TFs) play a critical role in GABA production, and GABA modulates diabetic neuropathic pain (DNP). The present study investigated the therapeutic effects of intrathecal delivery of two TFs achaete-scute homolog 1 (Ascl1) and LIM homeobox protein 6 (Lhx6) in a mouse model of DNP and elucidated their underlying mechanisms. GABA-related specific TFs, including Ascl1, Lhx6, distal-less homeobox 1, distal-less homeobox 5, the Nkx2.1 homeobox gene, and the Nkx2.2 homeobox gene, were investigated under normal and diabetic conditions. Among these, the expression of Ascl1 and Lhx6 was significantly downregulated in mice with diabetes. Therefore, a single intrathecal injection of combined lenti-Ascl1/Lhx6 was performed. Intrathecal delivery of lenti-Ascl1/Lhx6 significantly relieved mechanical allodynia and heat hyperalgesia in mice with DNP. Ascl1/Lhx6 delivery also reduced microglial activation, decreased the levels of pro-inflammatory cytokines including tumor necrosis factor-α and interleukin (IL)-1β, increased the levels of anti-inflammatory cytokines including IL-4, IL-10, and IL-13, and reduced the activation of p38, c-Jun N-terminal kinase, and NF-κB in the spinal cord of mice with DNP, thereby reducing DNP. The results of this study suggest that intrathecal Ascl1/Lhx6 delivery attenuates DNP via upregulating spinal GABA neuronal function and inducing anti-inflammatory effects.

METTL3 Mediates Microglial Activation and Blood-Brain Barrier Permeability in Cerebral Ischemic Stroke by Regulating NLRP3 Inflammasomes Through m6A Methylation Modification

Cerebral ischemic stroke (CIS) is the main cause of disability. METTL3 is implicated in CIS, and we explored its specific mechanism. Middle cerebral artery occlusion (MCAO) rat model and oxygen-glucose deprivation/reperfusion (OGD/R) HAPI cell model were established and treated with LV-METTL3 or DAA, oe-METTL3, miR-335-3p mimics, or DAA, to assess their effects on MCAO rat neurological and motor function, cerebral infarction area, brain water content, microglial activation, blood-brain barrier (BBB) permeability, and NLRP3 inflammasome activation. METTL3, pri-miR-335-3p, mature miR-335-3p, and miR-335-3p mRNA levels were assessed by RT-qPCR; M1/M2 microglial phenotype proportion and M1/M2 microglia ratio, inflammatory factor levels, and m6A modification were assessed. MCAO rats manifested cerebral ischemia injury. METTL3 was under-expressed in CIS. METTL3 overexpression inhibited microglial activation and M1 polarization and BBB permeability in MCAO rats and inhibited OGD/R-induced microglial activation and reduced M1 polarization. METTL3 regulated miR-335-3p expression and inhibited NLRP3 inflammasome activation. m6A methylation inhibition averted METTL3's effects on NLRP3 activation, thus promoting microglial activation in OGD/R-induced cells and METTL3's effects on BBB permeability in MCAO rats. Briefly, METTL3 regulated miR-335-3p expression through RNA m6A methylation and inhibited NLRP3 inflammasome activation, thus repressing microglial activation, BBB permeability, and protecting against CIS.

Alisol A Exerts Neuroprotective Effects Against HFD-Induced Pathological Brain Aging via the SIRT3-NF-κB/MAPK Pathway

Chronic consumption of a high-fat diet (HFD) has profound effects on brain aging, which is mainly characterized by cognitive decline, inflammatory responses, and neurovascular damage. Alisol A (AA) is a triterpenoid with therapeutic potential for metabolic diseases, but whether it has a neuroprotective effect against brain aging caused by a HFD has not been investigated. Six-month-old male C57BL6/J mice were exposed to a HFD with or without AA treatment for 12 weeks. Behavioral tasks were used to assess the cognitive abilities of the mice. Neuroinflammation and changes in neurovascular structure in the brains were examined. We further assessed the mechanism by which AA exerts neuroprotective effects against HFD-induced pathological brain aging in vitro and in vivo. Behavioral tests showed that cognitive function was improved in AA-treated animals. AA treatment reduced microglia activation and inflammatory cytokine release induced by a HFD. Furthermore, AA treatment increased the number of hippocampal neurons, the density of dendritic spines, and the expression of tight junction proteins. We also demonstrated that AA attenuated microglial activation by targeting the SIRT3-NF-κB/MAPK pathway and ameliorated microglial activation-induced tight junction degeneration in endothelial cells and apoptosis in hippocampal neurons. The results of this study show that AA may be a promising agent for the treatment of HFD-induced brain aging.

Rapamycin Alleviates Neuronal Injury and Modulates Microglial Activation After Cerebral Ischemia

Neurons and microglia are sensitive to cerebral microcirculation and their responses play a crucial part in the pathological processes, while they are also the main target cells of many drugs used to treat brain diseases. Rapamycin exhibits beneficial effects in many diseases; however, whether it can affect neuronal injury or alter the microglial activation after global cerebral ischemia remains unclear. In this study, we performed global cerebral ischemia combined with rapamycin treatment in CX3CR1GFP/+ mice and explored the effects of rapamycin on neuronal deficit and microglial activation. Our results showed that rapamycin reduced neuronal loss, neurodegeneration, and ultrastructural damage after ischemia by histological staining and transmission electron microscopy (TEM). Interestingly, rapamycin suppressed de-ramification and proliferation of microglia and reduced the density of microglia. Immunofluorescence staining indicated that rapamycin skewed microglial polarization toward an anti-inflammatory state. Furthermore, rapamycin as well suppressed the activation of astrocytes. Meanwhile, quantitative real-time polymerase chain reaction (qRT-PCR) analyses revealed a significant reduction of pro-inflammatory factors as well as an elevation of anti-inflammatory factors upon rapamycin treatment. As a result of these effects, behavioral tests showed that rapamycin significantly alleviated the brain injury after stroke. Together, our study suggested that rapamycin attenuated neuronal injury, altered microglial activation state, and provided a more beneficial immune microenvironment for the brain, which could be used as a promising therapeutic approach to treat ischemic cerebrovascular diseases.

Pseudoginsenoside GQ mitigates chronic intermittent hypoxia-induced cognitive damage by modulating microglia polarization

Obstructive sleep apnea (OSA), a state of sleep disruption, is characterized by recurrent apnea, chronic intermittent hypoxia (CIH) and hypercapnia. Previous studies have showed that CIH-induced neuroinflammatory plays a crucial role in cognitive deficits. Pseudoginsenoside GQ (PGQ) is a new oxytetracycline-type saponin formed by the oxidation and cyclization of the 20(S) Rg3 side chain. Rg3 has been found to afford anti-inflammatory effects, while whether PGQ plays a role of anti-neuroinflammatory remains unclear. The purpose of this study was to investigate whether PGQ attenuates CIH-induced neuroinflammatory and cognitive impairment and the possible mechanism it involves. We found that PGQ significantly ameliorated CIH-induced spatial learning deficits, and inhibited microglial activation, pro-inflammatory cytokine release, and neuronal apoptosis in the hippocampus of CIH mice. In addition, PGQ pretreatment promoted microglial M1 to M2 phenotypic transition in IH-induced BV-2 microglial, as well as indirectly inhibited IH-induced neuronal injury via modulation of microglia polarization. Furthermore, we noted that activation of HMGB1/TLR4/NF-κB signaling pathway induced by IH was inhibited by PGQ. Molecular docking results revealed that PGQ could bind to the active sites of HMGB1 and TLR4. Taken together, this work supports that PGQ inhibits M1 microglial polarization via the HMGB1/TLR4/NF-κB signaling pathway, and indirectly exerts neuroprotective effects, suggesting that PGQ may be a potential therapeutic strategy for cognitive impairment accompanied OSA.

Acute exposure of microwave impairs attention process by activating microglial inflammation

BACKGROUND

Attention provides the foundation for cognitions, which was shown to be affected by microwave (MW) radiation. With the ubiquitous of microwaves, public concerns regarding the impact of MW radiation on attention has hence been increased. Our study aims to investigate the potential effect and mechanism of acute microwave exposure on attention.

RESULTS

We identified obvious impairment of attention in mice by the five-choice serial reaction time (5-CSRT) task. Proteomic analysis of the cerebrospinal fluid (CSF) revealed neuroinflammation and microglial activation potentially due to acute MW exposure. Moreover, biochemical analysis further confirmed microglial activation in the prefrontal cortex (PFC) of mice subjected to acute MW exposure. Finally, minocycline, a commercially available anti-inflammatory compound, attenuated neuroinflammation, inhibited the upregulation of N-methyl-D-aspartic acid receptor (NMDAR) including NR2A and NR2B, and also accelerated the attentional recovery after MW exposure.

CONCLUSIONS

We believe that microglial activation and NMDAR upregulation likely contribute to inattention induced by acute MW exposure, and we found that minocycline may be effective in preventing such process.

Connecting the dots: An updated review of the role of autoimmunity in narcolepsy and emerging immunotherapeutic approaches

BACKGROUND

Narcolepsy type 1 (NT1) is a chronic disorder characterized by pathological daytime sleepiness and cataplexy due to the disappearance of orexin immunoreactive neurons in the hypothalamus. Genetic and environmental factors point towards a potential role for inflammation and autoimmunity in the pathogenesis of the disease. This study aims to comprehensively review the latest evidence on the autoinflammatory mechanisms and immunomodulatory treatments aimed at suspected autoimmune pathways in NT1.

METHODS

Recent relevant literature in the field of narcolepsy, its autoimmune hypothesis, and purposed immunomodulatory treatments were reviewed.

RESULTS

Narcolepsy is strongly linked to specific HLA alleles and T-cell receptor polymorphisms. Furthermore, animal studies and autopsies have found infiltration of T cells in the hypothalamus, supporting T cell-mediated immunity. However, the role of autoantibodies has yet to be definitively established. Increased risk of NT1 after H1N1 infection and vaccination supports the autoimmune hypothesis, and the potential role of coronavirus disease 2019 and vaccination in triggering autoimmune neurodegeneration is a recent finding. Alterations in cytokine levels, gut microbiota, and microglial activation indicate a potential role for inflammation in the disease's development. Reports of using immunotherapies in NT1 patients are limited and inconsistent. Early treatment with IVIg, corticosteroids, plasmapheresis, and monoclonal antibodies has seldomly shown some potential benefits in some studies.

CONCLUSION

The current body of literature supports that narcolepsy is an autoimmune disorder most likely caused by T-cell involvement. However, the potential for immunomodulatory treatments to reverse the autoinflammatory process remains understudied. Further clinical controlled trials may provide valuable insights into this area.

PET Imaging to Measure Neuroinflammation In Vivo

This paper provides an overview of the role of neuroinflammation in Alzheimer's disease and other neurodegenerative diseases, highlighting the potential of anti-inflammatory treatments to slow or prevent decline. This research focuses on the use of positron emission tomography (PET) imaging to visualize and quantify molecular brain changes in patients, specifically microglial activation and reactive astrogliosis. We discuss the development and application of several PET radioligands, including first-generation ligands like PK11195 and Ro5-4864, as well as second- and third-generation ligands such as [11C]PBR28, [18F]DPA-714, [18F]GE-180, and [11C]ER176. These ligands target the 18-kDa translocator protein (TSPO), which is overexpressed in activated microglia and upregulated in astrocytes. We also address the limitations of these ligands, such as low brain uptake, poor penetration of the blood-brain barrier, short half-life, and variable kinetic behavior. Furthermore, we demonstrate the impact of genetic polymorphisms on ligand binding.

α-Linolenic Acid Induces Microglial Activation and Extracellular Tau Internalization

Neuroinflammation is the brain condition that occurs due to the hyper-activation of brain's immune cells and microglia, over the stimulation of extracellular aggregated proteins such as amyloid plaques and by extracellular Tau as well. The phenotypic changes of microglia from inflammatory to anti-inflammatory can be triggered by many factors, which also includes dietary fatty acids. The classes of omega-3 fatty acids are the majorly responsible in maintaining the anti-inflammatory phenotype of microglia. The enhanced phagocytic ability of microglia might induce the clearance of extracellular aggregated proteins, such as amyloid beta and Tau. In this study, we emphasized on the effect of α-linolenic acid (ALA) on the activation of microglia and internalization of the extracellular Tau seed in microglia.

The P38MAPK/ATF2 signaling pathway is involved in PND in mice

Accumulating evidence indicates that microglia-mediated neuroinflammation in the hippocampus contributes to the development of perioperative neurocognitive disorder (PND). P38MAPK, a point of convergence for different signaling processes involved in inflammation, can be activated by various stresses. This study aims to investigate the role of the P38MAPK/ATF2 signaling pathway in the development of PND in mice. Aged C57BL/6 mice were subjected to tibial fracture surgery under isoflurane anesthesia to establish a PND animal model. The open field test was used to evaluate the locomotor activity of the mice. Neurocognitive function was assessed with the Morris water maze (MWM) and fear conditioning test (FCT) on postoperative days 1, 3 and 7. The mice exhibited cognitive impairment accompanied by increased expression of proinflammatory factors (IL-1β, TNF-α), proapoptotic molecules (caspase-3, bax) and microglial activation in the hippocampus 1, 3 and 7 days after surgery. Treatment with SB239063 (a P38MAPK inhibitor) decreased the expression of proinflammatory factors, proapoptotic molecules and Iba-1 in the CA1 region of the hippocampus. The number of surviving neurons was significantly increased. Inhibition of the P38MAPK/ATF2 signaling pathway attenuates hippocampal neuroinflammation and neuronal apoptosis in aged mice with PND, thus improving the perioperative cognitive function of the mice.

Oxytocin alleviates cognitive and memory impairments by decreasing hippocampal microglial activation and synaptic defects via OXTR/ERK/STAT3 pathway in a mouse model of sepsis-associated encephalopathy

BACKGROUND

Sepsis-associated encephalopathy (SAE) is a diffuse brain dysfunction, characterized by cognitive and memory impairments closely linked to hippocampal dysfunction. Though it is well-known that SAE is a diffuse brain dysfunction with microglial activation, the pathological mechanisms of SAE are not well established and effective clinical interventions are lacking. Oxytocin (OXT) is reported to have anti-inflammatory and neuroprotective roles. However, the effects of OXT on SAE and the underlying mechanisms are not clear.

METHODS

SAE was induced in adult C57BL/6J male mice by cecal ligation and perforation (CLP) surgery. Exogenous OXT was intranasally applied after surgery. Clinical score, survivor rate, cognitive and memory behaviors, and hippocampal neuronal and non-neuronal functions were evaluated. Cultured microglia challenged with lipopolysaccharide (LPS) were used to investigate the effects of OXT on microglial functions, including inflammatory cytokines release and phagocytosis. The possible intracellular signal pathways involved in the OXT-induced neuroprotection were explored with RNA sequencing.

RESULTS

Hippocampal OXT level decreases, while the expression of OXT receptor (OXTR) increases around 24 h after CLP surgery. Intranasal OXT application at a proper dose increases mouse survival rate, alleviates cognitive and memory dysfunction, and restores hippocampal synaptic function and neuronal activity via OXTR in the SAE model. Intraperitoneal or local administration of the OXTR antagonist L-368,899 in hippocampal CA1 region inhibited the protective effects of OXT. Moreover, during the early stages of sepsis, hippocampal microglia are activated, while OXT application reduces microglial phagocytosis and the release of inflammatory cytokines, thereby exerting a neuroprotective effect. OXT may improve the SAE outcomes via the OXTR-ERK-STAT3 signaling pathway.

CONCLUSION

Our study uncovers the dysfunction of the OXT signal in SAE and shows that intranasal OXT application at a proper dose can alleviate SAE outcomes by reducing microglial overactivation, suggests that OXT may be a promising therapeutic approach in managing SAE patients.

Development of a novel histone deacetylase inhibitor unveils the role of HDAC11 in alleviating depression by inhibition of microglial activation

Histone deacetylases (HDACs) are key epigenetic regulators and classified into four subtypes. Despite the various roles of each HDAC isoform, the lack of selective HDAC inhibitors has limited the elucidation of their roles in biological systems. HDAC11, the sole class-IV HDAC, is highly expressed in the brain, however, the role of HDAC11 in microglia is not fully understood. Based on the modification of MC1568, we developed a novel HDAC inhibitor, 5. Interestingly, 5 suppresses lipopolysaccharide-induced microglial activation by the initiation of autophagy and subsequent inhibition of nitric oxide production. Furthermore, we demonstrated that 5 significantly alleviates depression-like behavior by inhibiting microglial activation in mouse brain. Our discovery reveals that specific pharmacological regulation of HDAC11 induces autophagy and reactive nitrogen species balance in microglia for the first time, which makes HDAC11 a new therapeutic target for depressive disorder.

Acyclic retinoid peretinoin reduces hemorrhage-associated brain injury in vitro and in vivo

Peretinoin is an acyclic retinoid that stimulates retinoic acid receptors (NR1Bs) and produces therapeutic effects on hepatocellular cancer. We have previously shown that NR1B agonists such as Am80 and all trans-retinoic acid suppress pathogenic events in intracerebral hemorrhage. The present study addressed the actions of peretinoin and Am80 against cytotoxicity of a blood protease thrombin on cortico-striatal slice cultures obtained from neonatal rat brains. Application of 100 U/ml thrombin to the slice cultures for 72 h caused cell death in the cortical region and tissue shrinkage in the striatal region. Peretinoin (50 μM) and Am80 (1 μM) counteracted these cytotoxic effects of thrombin, and the effect of peretinoin and Am80 was blocked by LE540, an NR1B antagonist. A broad-spectrum kinase inhibitor K252a (3 μM) attenuated the cytoprotective effect of peretinoin in the cortical region, whereas a specific protein kinase A inhibitor KT5720 (1 μM) attenuated the protective effect of peretinoin in the cortical and the striatal regions. On the other hand, nuclear factor-κB (NF-κB) inhibitors such as pyrrolidine dithiocarbamate (50 μM) and Bay11-7082 (10 μM) prevented thrombin-induced shrinkage of the striatal region. Peretinoin and Am80 as well as Bay11-7082 blocked thrombin-induced nuclear translocation of NF-κB in striatal microglia and loss of striatal neurons. We also found that daily administration of peretinoin reduced histopathological injury and alleviated motor deficits in a mouse model of intracerebral hemorrhage. These results indicate that NR1B agonists including peretinoin may serve as a therapeutic option for hemorrhagic brain injury.

Role of omentin-1 in susceptibility to anxiety and depression like behaviors

Neuro-inflammation and blood-brain barrier (BBB) dysfunction are associated with depression. Evidence shows that adipokines enter the brain from the circulation, which regulates depressive behaviors. Omentin-1 is a newly identified adipocytokine that has anti-inflammatory effects, but little is known about its role in neuro-inflammation and mood-relevant behavior. Our results showed omentin-1 knockout mice (Omentin-1-/-) increased susceptibility to anxiety and depressive-like behaviors, which are associated with abnormalities of cerebral blood flow (CBF) and impaired BBB permeability. Moreover, omentin-1 depletion significantly increased hippocampal pro-inflammatory cytokines (IL-1β, TNFα, IL-6), caused microglial activation, inhibited hippocampus neurogenesis, and resulted in autophagy impairment by dysregulating ATG genes. Omentin-1 deficiency also sensitized mice to the behavioral changes induced by lipopolysaccharide (LPS), suggesting that omentin-1 could rescue neuro-inflammation by acting as an anti-depressant. Our in vitro microglia cell culture data confirmed that recombinant omentin-1 suppresses microglial activation and pro-inflammatory cytokine expression induced by LPS. Our study suggests that omentin-1 can be used as a promising therapeutic agent for the prevention or treatment of depression by providing a barrier-promoting effect and an endogenous anti-inflammatory balance to downregulate the proinflammatory cytokines.

Microglia Sirt6 modulates the transcriptional activity of NRF2 to ameliorate high-fat diet-induced obesity

BACKGROUND

Microglia play a pivotal role in neuroinflammation, while obesity triggers hypothalamic microglia activation and inflammation. Sirt6 is an important regulator of energy metabolism in many peripheral tissues and hypothalamic anorexic neurons. However, the exact mechanism for microglia Sirt6 in controlling high-fat diet-induced obesity remain unknown.

METHODS

Microglia Sirt6 expression levels under various nutritional conditions were measured in the hypothalamus of mice. Also, microglia Sirt6-deficient mice were provided various diets to monitor metabolic changes and hypothalamic inflammatory response. Besides, RNA-seq and Co-IP of microglia with Sirt6 alterations were conducted to further investigate the detailed mechanism by which Sirt6 modulated microglia activity.

RESULTS

We found that Sirt6 was downregulated in hypothalamic microglia in mice given a high-fat diet (HFD). Additionally, knockout of microglia Sirt6 exacerbated high-fat diet-induced hypothalamic microglial activation and inflammation. As a result, mice were more prone to obesity, exhibiting a decrease in energy expenditure, impaired glucose tolerance, insulin and leptin resistance, and increased food intake. In vitro, Sirt6 overexpression in BV2 cells displayed protective effects against oleic acid and palmitic acid treatment-derived inflammatory response. Mechanically, Sirt6 deacetylated and stabilised NRF2 to increase the expression of anti-oxidative genes and defend against reactive oxygen species overload. Pharmacological inhibition of NRF2 eliminated the beneficial modulating effects of Sirt6 on microglial activity.

CONCLUSION

Collectively, our results revealed that microglial Sirt6 was a primary contributor of microglial activation in the central regulation of obesity. Thus, microglial Sirt6 may be an important therapeutic target for obesity.

Immunological perturbations, psychiatric disorders and associated therapeutics: a new era for psychiatry?

The three main theories explaining major mental illness, namely mood disorders, psychoses and dementias, have been partially discredited. Alongside this, there are emerging links between perturbations of the immune system and the onset and phenotypic features of these disorders. This article outlines the alternative pathophysiology and suggests potential treatments which could improve disease burden and avoid the need for psychotropic medication, with their associated side effects and relapse following withdrawal.

Elevated blood and cerebrospinal fluid biomarkers of microglial activation and blood‒brain barrier disruption in anti-NMDA receptor encephalitis

BACKGROUND

Anti-NMDA receptor (NMDAR) encephalitis is an autoimmune disease characterized by complex neuropsychiatric syndrome and cerebrospinal fluid (CSF) NMDAR antibodies. Triggering receptor expressed on myeloid cells 2 (TREM2) has been reported to be associated with inflammation of the central nervous system (CNS). Matrix metalloproteinase-9 (MMP9) and cluster of differentiation (CD44) were measured to evaluate blood‒brain barrier (BBB) permeability in anti-NMDAR encephalitis. The roles of microglial activation and BBB disruption in anti-NMDAR encephalitis are not well known.

FINDINGS

In this work, we detected increased expression levels of CSF sTREM2, CSF and serum CD44, and serum MMP9 in anti-NMDAR encephalitis patients compared with controls. CSF sTREM2 levels were positively related to both CSF CD44 levels (r = 0.702, p < 0.0001) and serum MMP9 levels (r = 0.428, p = 0.021). In addition, CSF sTREM2 levels were related to clinical parameters (modified Rankin Scale scores, r = 0.422, p = 0.023, and Glasgow Coma Scale scores, r = - 0.401, p = 0.031).

CONCLUSION

Increased sTREM2 levels in CSF as well as increased CD44 and MMP9 in serum and CSF reflected activation of microglia and disruption of the BBB in anti-NMDAR encephalitis, expanding the understanding of neuroinflammation in this disease. The factors mentioned above may have potential as novel targets for intervention or novel diagnostic biomarkers.

Ameliorative effects of Fingolimod (FTY720) on microglial activation and psychosis-related behavior in short term cuprizone exposed mice

Schizophrenia is a psychiatric disorder that affects around 1% of the population in widespread populations, with severe cases leading to long-term hospitalization and necessitation of lifelong treatment. Recent studies on schizophrenia have highlighted the involvement of inflammatory and immunoregulatory mechanisms with the onset of symptoms, and the usage of anti-inflammatory treatments are being tested against periods of rapid psychosis. In the central nervous system, microglia are the innate immune population which are activated in response to a wide range of physical and psychological stress factors and produce proinflammatory mediators such as cytokines. Microglial activation and neuroinflammation has been associated to numerous psychiatric disorders including schizophrenia, especially during psychotic episodes. Thus, novel treatments which dampen microglial activation may be of great relevance in the treatment of psychiatric disorders. Fingolimod (FTY720) is a drug used as an immunosuppressive treatment to multiple sclerosis. Recent clinical trials have focused on FTY720 as a treatment for the behavioral symptoms in schizophrenia. However, the mechanisms of Fingolimod in treating the symptoms of schizophrenia are not clear. In this study we use a recently developed neuroinflammatory psychosis model in mice: cuprizone short-term exposure, to investigate the effects of FTY720 administration. FTY720 administration was able to completely alleviate methamphetamine hypersensitivity caused by cuprizone exposure. Moreover, administration of FTY720 improved multiple measures of neuroinflammation (microglial activation, cytokine production, and leucocyte infiltration). In conclusion, our results highlight the future use of FTY720 as a direct anti-inflammatory treatment against microglial activation and psychosis.

Characterization of neuroinflammation pattern in anti-LGI1 encephalitis based on TSPO PET and symptom clustering analysis

PURPOSE

TSPO PET with radioligand [18F]DPA-714 is an emerging molecular imaging technique that reflects cerebral inflammation and microglial activation, and it has been recently used in central nervous system diseases. In this study, we aimed to investigate the neuroinflammation pattern of anti-leucine-rich glioma-inactivated 1 (LGI1) protein autoimmune encephalitis (AIE) and to evaluate its possible correlation with clinical phenotypes.

METHODS

Twenty patients with anti-LGI1 encephalitis from the autoimmune encephalitis cohort in Huashan Hospital and ten with other AIE and non-inflammatory diseases that underwent TSPO PET imaging were included in the current study. Increased regional [18F]DPA-714 retention in anti-LGI1 encephalitis was detected on a voxel basis using statistic parametric mapping analysis. Multiple correspondence analysis and hierarchical clustering were conducted for discriminate subgroups in anti-LGI1 encephalitis. Standardized uptake value ratios normalized to the cerebellum (SUVRc) were calculated for semiquantitative analysis of TSPO PET features between different LGI1-AIE subgroups.

RESULTS

Increased regional retention of [18F]DPA-714 was identified in the bilateral hippocampus, caudate nucleus, and frontal cortex in LGI1-AIE patients. Two subgroups of LGI1-AIE patients were distinguished based on the top seven common symptoms. Patients in cluster 1 had a high frequency of facio-brachial dystonic seizures than those in cluster 2 (p = 0.004), whereas patients in cluster 2 had a higher frequency of general tonic-clonic (GTC) seizures than those in cluster 1 (p < 0.001). Supplementary motor area and superior frontal gyrus showed higher [18F]DPA-714 retention in cluster 2 patients compared with those in cluster 1 (p = 0.024; p = 0.04, respectively).

CONCLUSIONS

Anti-LGI1 encephalitis had a distinctive molecular imaging pattern presented by TSPO PET scan. LGI1-AIE patients with higher retention of [18F]DPA-714 in the frontal cortex were more prone to present with GTC seizures. Further studies are required for verifying its value in clinical application.

Dysfunction of the medial prefrontal cortex contributes to BPA-induced depression- and anxiety-like behavior in mice

Bisphenol A (BPA), a well-known environmental endocrine disruptor, has been implicated in anxiety-like behavior. But the neural mechanism remains elusive. Herein, we found that mice exposed to 0.5 mg/kg/day BPA chronically from postnatal days (PND) 21 to PND 80 exhibited depression- and anxiety-like behavior. Further study showed that medial prefrontal cortex (mPFC), was associated with BPA-induced depression- and anxiety-like behavior, as evidenced by decreased c-fos expression in mPFC of BPA-exposed mice. Both the morphology and function of glutamatergic neurons (also called pyramidal neurons) in mPFC of mice were impaired following BPA exposure, characterized by reduced primary branches, weakened calcium signal, and decreased mEPSC frequency. Importantly, optogenetic activation of the pyramidal neurons in mPFC greatly reversed BPA-induced depression- and anxiety-like behavior in mice. Furthermore, we reported that microglial activation in mPFC of mice may also have a role in BPA-induced depression- and anxiety-like behavior. Taken together, the results indicated that mPFC is the brain region that is greatly damaged by BPA exposure and is associated with BPA-induced depression- and anxiety-like behavior. The study thus provides new insights into BPA-induced neurotoxicity and behavioral changes.

Retinoic acid administration normalizes aberrant microglial activation via regulating TREM2 transcription in the PFC of valproic acid induced autism rat

Autism spectrum disorder (ASD) is a complex neurodevelopmental disease with an unclear underlying pathogenesis. Disruption of retinoic acid (RA)-retinoic acid receptor α (RARα) signaling and aberrant microglial activation were reported to be involved in the pathogenesis of ASD. However, the effect of RA-RARα signaling on microglial activation in ASD and the underlying mechanisms are unknown. Herein, we found inhibited RA-RARα signaling and increased microglial activation in valproic acid (VPA)-induced autism rats. Furthermore, we administered RA to VPA rats and found that RA ameliorated autism-like behaviors, inhibited microglial activation and normalized microglial polarization in VPA rats. Additionally, the expression levels of RARα and triggering receptor expressed on myeloid cells 2 (TREM2) were increased in the prefrontal cortex (PFC) of VPA rats given RA. Chromatin immunoprecipitation (ChIP) and dual luciferase reporter assays confirmed that RARα can regulate the transcriptional activity of the TREM2 gene by binding to its promoter. We conclude that RA administration ameliorates autism-like behaviors in VPA rats by inhibiting microglial activation and normalizing microglial polarization through the regulation of TREM2 transcription by RARα.

Deletion of PTEN in microglia ameliorates chronic neuroinflammation following repetitive mTBI

Traumatic brain injury is a leading cause of morbidity and mortality in adults and children in developed nations. Following the primary injury, microglia, the resident innate immune cells of the CNS, initiate several inflammatory signaling cascades and pathophysiological responses that may persist chronically; chronic neuroinflammation following TBI has been closely linked to the development of neurodegeneration and neurological dysfunction. Phosphoinositide 3-kinases (PI3Ks) are a family of lipid kinases that have been shown to regulate several key mechanisms in the inflammatory response to TBI. Increasing evidence has shown that the modulation of the PI3K/AKT signaling pathway has the potential to influence the cellular response to inflammatory stimuli. However, directly targeting PI3K signaling poses several challenges due to its regulatory role in several cell survival pathways. We have previously identified that the phosphatase and tensin homolog deleted on chromosome 10 (PTEN), the major negative regulator of PI3K/AKT signaling, is dysregulated following exposure to repetitive mild traumatic brain injury (r-mTBI). Moreover, this dysregulated PI3K/AKT signaling was correlated with chronic microglial-mediated neuroinflammation. Therefore, we interrogated microglial-specific PTEN as a therapeutic target in TBI by generating a microglial-specific, Tamoxifen inducible conditional PTEN knockout model using a CX3CR1 Cre recombinase mouse line PTEN^fl/fl/CX3CR1^+/CreERT2 (mcg-PTEN^cKO), and exposed them to our 20-hit r-mTBI paradigm. Animals were treated with tamoxifen at 76 days post-last injury, and the effects of microglia PTEN deletion on immune-inflammatory responses were assessed at 90-days post last injury. We observed that the deletion of microglial PTEN ameliorated the proinflammatory response to repetitive brain trauma, not only reducing chronic microglial activation and proinflammatory cytokine production but also rescuing TBI-induced reactive astrogliosis, demonstrating that these effects extended beyond microglia alone. Additionally, we observed that the pharmacological inhibition of PTEN with BpV(HOpic) ameliorated the LPS-induced activation of microglial NFκB signaling in vitro. Together, these data provide support for the role of PTEN as a regulator of chronic neuroinflammation following repetitive mild TBI.

Prenatally VPA exposure is likely to cause autistic-like behavior in the rats offspring via TREM2 down-regulation to affect the microglial activation and synapse alterations

Microglial dysfunction has been reported in the valproic acid (VPA)-induced autism spectrum disorder (ASD) rat models. However, how does prenatal VPA exposure affect microglia remains to be elucidated. The triggering receptor expressed on myeloid cells 2 (TREM2) is revealed to be implicated in a range of microglia functions. However, reports on the association between TREM2 and VPA-induced ASD rat models are scarce. Our results showed that prenatal VPA exposure induced autistic-like behaviors, downregulated the levels of TREM2, up-regulated microglial activation, dysregulated microglial polarization, and altered synapse in offspring. TREM2 overexpression partly ameliorated microglia dysfunction and autistic-like behaviors in prenatal VPA-exposed rats. Our findings demonstrated that prenatally VPA exposure is likely to cause autistic-like behavior in the rat offspring via TREM2 down-regulation to affect the microglial activation, microglial polarization and synaptic pruning of microglia for the first time.

Microglial reprogramming by Hv1 antagonism protects neurons from inflammatory and glutamate toxicity

Although the precise mechanisms determining the neurotoxic or neuroprotective activation phenotypes in microglia remain poorly characterized, metabolic changes in these cells appear critical for these processes. As cellular metabolism can be tightly regulated by changes in intracellular pH, we tested whether pharmacological targeting of the microglial voltage-gated proton channel 1 (Hv1), an important regulator of intracellular pH, is critical for activated microglial reprogramming. Using a mouse microglial cell line and mouse primary microglia cultures, either alone, or co-cultured with rat cerebrocortical neurons, we characterized in detail the microglial activation profile in the absence and presence of Hv1 inhibition. We observed that activated microglia neurotoxicity was mainly attributable to the release of tumor necrosis factor alpha, reactive oxygen species, and zinc. Strikingly, pharmacological inhibition of Hv1 largely abrogated inflammatory neurotoxicity not only by reducing the production of cytotoxic mediators but also by promoting neurotrophic molecule production and restraining excessive phagocytic activity. Importantly, the Hv1-sensitive change from a pro-inflammatory to a neuroprotective phenotype was associated with metabolic reprogramming, particularly via a boost in NADH availability and a reduction in lactate. Most critically, Hv1 antagonism not only reduced inflammatory neurotoxicity but also promoted microglia-dependent neuroprotection against a separate excitotoxic injury. Our results strongly suggest that Hv1 blockers may provide an important therapeutic tool against a wide range of inflammatory neurodegenerative disorders.

Apigenin Attenuates Hippocampal Microglial Activation and Restores Cognitive Function in Methotrexate-Treated Rats: Targeting the miR-15a/ROCK-1/ERK1/2 Pathway

Microglial activation underpins the methotrexate (MTX)-induced neurotoxicity; however, the precise mechanism remains unclear. This study appraised the potential impact of apigenin (Api), a neuroprotective flavonoid, in MTX-induced neurotoxicity in rats in terms of microglial activation through targeting the miR-15a/Rho-associated protein kinase-1 (ROCK-1)/extracellular signal-regulated kinase 1/2 (ERK1/2) pathway. Male Sprague Dawley rats were randomly divided into 4 groups: Normal control (saline i.p. daily and i.v. on days 8 and 15); Api control (20 mg/kg, p.o.) daily for 30 days; MTX-alone (75 mg/kg, i.v.) on days 8 and 15, then four i.p. injections of leucovorin (LCV): 6 mg/kg after 18 h, then three doses (3 mg/kg) every 8 h post-MTX; and Api co-treated (20 mg/kg/day, p.o.) throughout the model for 30 days, with administration of MTX and LCV as in group 3. MTX administration elevated hippocampal ionized calcium-binding adaptor protein-1 (Iba-1) immunostaining, indicating microglial activation. This was accompanied by neuroinflammation, oxidative stress, and enhanced apoptosis manifested by elevated hippocampal interleukin-1β, malondialdehyde, and caspase-3, and decreased reduced glutathione levels. Concurrently, abated miR-15a expression, overexpression of its target ROCK-1, diminished downstream ERK1/2 and cAMP response element-binding protein (CREB) phosphorylation, and decreased hippocampal brain-derived neurotrophic factor (BDNF) levels were observed. Api mitigated the MTX-induced neurotoxicity by reversing the biochemical, histopathological, and behavioral derangements tested by novel object recognition and Morris water maze tests. Conclusively, Api lessens MTX-induced neuroinflammation, oxidative stress, and apoptosis and boosts cognitive function through inhibiting microglial activation via modulating the miR-15a/ROCK-1/ERK1/2/CREB/BDNF pathway. Graphical abstract showing the effects of methotrexate and apigenin co-treatment in MTX-induced neurotoxicity model. On the left, methotrexate (MTX) administration to rats resulted in hippocampal miR-15a downregulation, which triggered an enhanced expression of its target ROCK-1, consequently inhibiting the downstream ERK1/2/CREB/BDNF pathway, instigating a state of microglial activation, neuroinflammation, oxidative stress, and apoptosis. On the other hand, apigenin (Api) co-treatment restored miR-15a, inhibited ROCK-1 expression, and activated the ERK1/2/CREB/BDNF pathway, leading to diminished hippocampal microglial activation, neuroinflammation, and apoptosis, and restoration of the redox balance, along with improvement in memory and cognitive function of the MTX-treated rats.

Chronic kidney disease promotes cerebral microhemorrhage formation

BACKGROUND

Chronic kidney disease (CKD) is increasingly recognized as a stroke risk factor, but its exact relationship with cerebrovascular disease is not well-understood. We investigated the development of cerebral small vessel disease using in vivo and in vitro models of CKD.

METHODS

CKD was produced in aged C57BL/6J mice using an adenine-induced tubulointerstitial nephritis model. We analyzed brain histology using Prussian blue staining to examine formation of cerebral microhemorrhage (CMH), the hemorrhagic component of small vessel disease and the neuropathological substrate of MRI-demonstrable cerebral microbleeds. In cell culture studies, we examined effects of serum from healthy or CKD patients and gut-derived uremic toxins on brain microvascular endothelial barrier.

RESULTS

CKD was induced in aged C57BL/6J mice with significant increases in both serum creatinine and cystatin C levels (p < 0.0001) without elevation of systolic or diastolic blood pressure. CMH was significantly increased and positively correlated with serum creatinine level (Spearman r = 0.37, p < 0.01). Moreover, CKD significantly increased Iba-1-positive immunoreactivity by 51% (p < 0.001), induced a phenotypic switch from resting to activated microglia, and enhanced fibrinogen extravasation across the blood-brain barrier (BBB) by 34% (p < 0.05). On analysis stratified by sex, the increase in CMH number was more pronounced in male mice and this correlated with greater creatinine elevation in male compared with female mice. Microglial depletion with PLX3397 diet significantly decreased CMH formation in CKD mice without affecting serum creatinine levels. Incubation of CKD serum significantly reduced transendothelial electrical resistance (TEER) (p < 0.01) and increased sodium fluorescein permeability (p < 0.05) across the endothelial monolayer. Uremic toxins (i.e., indoxyl sulfate, p-cresyl sulfate, and trimethylamine-N-oxide) in combination with urea and lipopolysaccharide induced a marked drop in TEER compared with the control group (p < 0.0001).

CONCLUSIONS

CKD promotes the development of CMH in aged mice independent of blood pressure but directly proportional to the degree of renal impairment. These effects of CKD are likely mediated in part by microglia and are associated with BBB impairment. The latter is likely related to gut-derived bacteria-dependent toxins classically associated with CKD. Overall, these findings demonstrate an important role of CKD in the development of cerebral small vessel disease.

Disturbance of REM sleep exacerbates microglial activation in APP/PS1 mice

Although both nonrapid eye movement (NREM) sleep loss and rapid eye movement (REM) sleep loss exacerbate Alzheimer's disease (AD) progression, they exert different effects. Microglial activation can be beneficial or detrimental to AD patients under different conditions. However, few studies have investigated which sleep stage is the main regulator of microglial activation or the downstream effects of this activation. We aimed to explore the roles of different sleep phases in microglial activation and to investigate the possible effect of microglial activation on AD pathology. In this study, thirty-six 6-month-old APP/PS1 mice were equally divided into 3 groups: the stress control (SC), total sleep deprivation (TSD), and REM deprivation (RD) groups. All mice underwent a 48-hour intervention before their spatial memory was assessed using a Morris water maze (MWM). Then, microglial morphology, activation- and synapse-related protein expression, and inflammatory cytokine and amyloid β (Aβ) levels in hippocampal tissues were measured. We found that the RD and TSD groups exhibited worse spatial memory in the MWM tests. In addition, the RD and TSD groups showed greater microglial activation, higher inflammatory cytokine levels, lower synapse-related protein expression and more severe Aβ accumulation than the SC group, but there were no significant differences between the RD and TSD groups. This study demonstrates that disturbance of REM sleep may activate microglia in APP/PS1 mice. These activated microglia may promote neuroinflammation and engulf synapses but show a weakened ability to clear plaques.

Integrin Mac1 mediates paraquat and maneb-induced learning and memory impairments in mice through NADPH oxidase-NLRP3 inflammasome axis-dependent microglial activation

INTRODUCTION

The mechanisms of cognitive impairments in Parkinson's disease (PD) remain unknown. Accumulating evidence revealed that brain neuroinflammatory response mediated by microglial cells contributes to cognitive deficits in neuropathological conditions and macrophage antigen complex-1 (Mac1) is a key factor in controlling microglial activation.

OBJECTIVES

To explore whether Mac1-mediated microglial activation participates in cognitive dysfunction in PD using paraquat and maneb-generated mouse PD model.

METHODS

Cognitive performance was measured in wild type and Mac1^-/- mice using Morris water maze test. The role and mechanisms of NADPH oxidase (NOX)-NLRP3 inflammasome axis in Mac1-mediated microglial dysfunction, neuronal damage, synaptic degeneration and phosphorylation (Ser129) of α-synuclein were explored by immunohistochemistry, Western blot and RT-PCR.

RESULTS

Genetic deletion of Mac1 significantly ameliorated learning and memory impairments, neuronal damage, synaptic loss and α-synuclein phosphorylation (Ser129) caused by paraquat and maneb in mice. Subsequently, blocking Mac1 activation was found to mitigate paraquat and maneb-elicited microglial NLRP3 inflammasome activation in both in vivo and in vitro. Interestingly, stimulating activation of NOX by phorbol myristate acetate abolished the inhibitory effects of Mac1 blocking peptide RGD on paraquat and maneb-provoked NLRP3 inflammasome activation, indicating a key role of NOX in Mac1-mediated NLRP3 inflammasome activation. Furthermore, NOX1 and NOX2, two members of NOX family, and downstream PAK1 and MAPK pathways were recognized to be essential for NOX to regulate NLRP3 inflammasome activation. Finally, a NLRP3 inflammasome inhibitor glybenclamide abrogated microglial M1 activation, neurodegeneration and phosphorylation (Ser129) of α-synuclein elicited by paraquat and maneb, which were accompanied by improved cognitive capacity in mice.

CONCLUSIONS

Mac1 was involved in cognitive dysfunction in a mouse PD model through NOX-NLRP3 inflammasome axis-dependent microglial activation, providing a novel mechanistic basis of cognitive decline in PD.

Mesenchymal stem cell-derived extracellular vesicles carrying miR-99b-3p restrain microglial activation and neuropathic pain by stimulating autophagy

Neuropathic pain is a complex condition that seriously affects human quality of life. This study aimed to investigate the therapeutic mechanism of mesenchymal stem cell-derived extracellular vesicles (MSC-EVs) and try to discover new targets for alleviating neuropathic pain. Extracellular vesicles were isolated and identified via ultracentrifugation. BV-2 microglial cells were stimulated with lipopolysaccharide (LPS) in the presence or absence of MSC-EVs. Further, microglial activation and neuroinflammation were evaluated by flow cytometry, RT-qPCR, and ELISA. High-throughput sequencing analysis was performed to reveal the differentially expressed (DE) miRNAs in BV-2 microglia. Autophagy-related regulators were assessed by Western blotting and Immunofluorescence staining. Chronic constriction injury (CCI) model was used to induce neuropathic pain in rats, and the mechanical withdrawal threshold (MWT) was measured. High-throughput sequencing analysis identified 17 DE miRNAs, which were mainly enriched in PI3K-AKT and mTOR signaling pathways. MSC-EVs inhibited the activation of PI3K/AKT/mTOR signaling pathway in LPS-stimulated microglia. Moreover, MSC-EVs treatment enhanced the autophagy level in activated microglia, whereas autophagy inhibitor 3-MA reversed the suppressing effects of MSC-EVs on microglial activation and neuroinflammation. The MSC-EV-mediated transfer of miR-99b-3p was verified to promote microglial autophagy, and miR-99b-3p overexpression suppressed the expression of pro-inflammatory factors in activated microglia. During in vivo studies, intrathecal injection of MSC-EVs significantly up-regulated the expression of miR-99b-3p, and alleviated mechanical allodynia caused by activated microglia in the spinal cord dorsal horn of CCI rats. Moreover, MSC-EVs treatment repaired CCI-induced autophagic impairment by stimulating autophagy in the spinal cord. Collectively, our findings demonstrated that MSC-EVs had an analgesic effect on neuropathic pain via promoting autophagy, and these antinociceptive effects were at least in part caused by MSC-EV-mediated transfer of miR-99b-3p, thereby inhibiting microglial activation and pro-inflammatory cytokines expression.

Sirt1 regulates microglial activation and inflammation following oxygen-glucose deprivation/reoxygenation injury by targeting the Shh/Gli-1 signaling pathway

BACKGROUND

Cerebral ischemic injury leads to over-activation of microglia, which release pro-inflammatory factors that deteriorate neurological function during the acute phase of stroke. Thus, inhibiting microglial over-activation is crucial for reducing ischemic injury. Sirtuin 1 (Sirt1) has been shown to play a critical role in stroke, neurodegenerative diseases and aging. However, the effect of Sirt1 on the regulation of microglial activation following cerebral ischemic injury, as well as the underlying mechanism, remain unknown. Therefore, the purpose of the present study is to mainly investigate the effect of Sirt1 on oxygen-glucose deprivation/reoxygenation (OGD/R)-treated N9 microglia following treatment with the Sirt1 agonists resveratrol and SRT1720 and the Sirt1 antagonist sirtinol.

METHODS

Cell viability, Apoptosis, activation and inflammatory responses of microglia, expressions and activity of Shh signaling pathway proteins were detected by Cell Counting Kit 8, Flow Cytometry, immunocytochemistry, ELISA, and Western blotting, respectively.

RESULTS

The results demonstrated that treatment with resveratrol or SRT1720 could inhibit the activation of microglia and inflammation during OGD/R. Moreover, these treatments also led to the translocation of the GLI family zinc finger-1 (Gli-1) protein from the cytoplasm to the nucleus and upregulated the expression of Sonic hedgehog (Shh), Patched homolog-1 (Ptc-1), smoothened frizzled class receptor and Gli-1. By contrast, the inhibition of Sirt1 using sirtinol had the opposite effect.

CONCLUSION

These findings suggested that Sirt1 may regulate microglial activation and inflammation by targeting the Shh/Gli-1 signaling pathway following OGD/R injury. Schematic representation of Sirt1 regulating the microglial activation and inflammation following oxygen-glucose deprivation/reoxygenation injury via mediation of Shh/Gli-1 signaling pathway.

Abcc8 (sulfonylurea receptor-1) knockout mice exhibit reduced axonal injury, cytotoxic edema and cognitive dysfunction vs. wild-type in a cecal ligation and puncture model of sepsis

Sepsis-associated brain injury (SABI) is characterized by an acute deterioration of mental status resulting in cognitive impairment and acquisition of new and persistent functional limitations in sepsis survivors. Previously, we reported that septic mice had evidence of axonal injury, robust microglial activation, and cytotoxic edema in the cerebral cortex, thalamus, and hippocampus in the absence of blood-brain barrier disruption. A key conceptual advance in the field was identification of sulfonylurea receptor 1 (SUR1), a member of the adenosine triphosphate (ATP)-binding cassette protein superfamily, that associates with the transient receptor potential melastatin 4 (TRPM4) cation channel to play a crucial role in cerebral edema development. Therefore, we hypothesized that knockout (KO) of Abcc8 (Sur1 gene) is associated with a decrease in microglial activation, cerebral edema, and improved neurobehavioral outcomes in a murine cecal ligation and puncture (CLP) model of sepsis. Sepsis was induced in 4-6-week-old Abcc8 KO and wild-type (WT) littermate control male mice by CLP. We used immunohistochemistry to define neuropathology and microglial activation along with parallel studies using magnetic resonance imaging, focusing on cerebral edema on days 1 and 4 after CLP. Abcc8 KO mice exhibited a decrease in axonal injury and cytotoxic edema vs. WT on day 1. Abcc8 KO mice also had decreased microglial activation in the cerebral cortex vs. WT. These findings were associated with improved spatial memory on days 7-8 after CLP. Our study challenges a key concept in sepsis and suggests that brain injury may not occur merely as an extension of systemic inflammation. We advance the field further and demonstrate that deletion of the SUR1 gene ameliorates CNS pathobiology in sepsis including edema, axonal injury, neuroinflammation, and behavioral deficits. Benefits conferred by Abcc8 KO in the murine CLP model warrant studies of pharmacological Abcc8 inhibition as a new potential therapeutic strategy for SABI.

Interlacing the relevance of caspase activation in the onset and progression of Alzheimer's disease

Caspases, a family of cysteine proteases is a renowned regulator of apoptosis. Members of this family are responsible for the proteolytic dismantling of numerous cellular structures. Apart from apoptosis, caspases remarkably contribute to a diverse range of molecular processes. Being the imperative members of several cellular cascades their abnormal activation/deactivation has severe implications and also leads to various diseased conditions. Similar aberrant activation of caspases is one of the several causes of neuropathologies associated with Alzheimer's disease (AD), a form of dementia severely affecting neuropsychiatric and cognitive functions. Emerging studies are providing deeper insights into the mechanisms of caspase action in the progression of AD. Current article is an attempt to review these studies and present the action mechanisms of different mammalian caspases in the advancement of AD associated neuropathologies.

Trifluoro-icaritin ameliorates spared nerve injury-induced neuropathic pain by inhibiting microglial activation through α7nAChR-mediated blockade of BDNF/TrkB/KCC2 signaling in the spinal cord of rats

Neuropathic pain is still a serious and unsolved health problem. Activation of α7 nicotinic acetylcholine receptor (α7nAChR) is known to modulate neuropathic pain by inhibiting microglial activation and BDNF/TrkB/KCC2 signaling. We previously identified that trifluoro-icaritin (ICTF) has an attenuated effect on spared nerve injury (SNI)-induced neuropathic pain, but its potential mechanisms remain unknown. Here, the pain-related behaviors were determined by paw withdrawal threshold (PWT), CatWalk gait analysis, rotarod test, open field test and elevated plus maze test. The expression of pain-related signal molecules was evaluated by Western blot and immunofluorescence staining. The results showed that ICTF (5.0 mg/kg, i.p.) successfully relieved SNI-induced mechanical allodynia and anxiety-like behavior, we subsequently found there existed either positive or negative correlation between mechanical allodynia and gait parameters or rotating speed following ICTF treatment. Moreover, ICTF not only enhanced the expression of spinal α7nAChR, KCC2, CD206 and IL-10, but also decreased the levels of spinal BDNF, TrkB, CD11b, Iba-1, CD40 and IL-1β in SNI rats. Conversely, α7nAChR antagonist α-Bgtx (I.T.) effectively reversed the inhibitory effects of ICTF on SNI rats, resulting in a remarkable improvement of mechanical allodynia, activation of microglia. and suppression of α7nAChR-mediated BDNF/TrkB/KCC2 signaling. Additionally, exogenous BDNF (I.T.) dramatically abrogated both blockade of BDNF/TrkB/KCC2 cascade and alleviation of mechanical allodynia by ICTF treatment. Altogether, the study highlighted that ICTF could relieve SNI-induced neuropathic pain by suppressing microglial activation via α7nAChR-mediated inhibition of BDNF/TrkB/KCC2 signaling in the spinal cord, suggesting that ICTF may be served as a possible painkiller against neuropathic pain.

Huc-MSCs-derived exosomes attenuate neuropathic pain by inhibiting activation of the TLR2/MyD88/NF-κB signaling pathway in the spinal microglia by targeting Rsad2

BACKGROUND

Mesenchymal stem cells (MSCs)-derived exosomes have shown promise as a cell-free therapeutic strategy for neuropathic pain. This study was conducted to explore the potential mechanisms underlying the analgesic effects of MSC-derived exosomes in treating neuropathic pain.

METHODS

Human umbilical cord MSCs (huc-MSCs)-derived exosomes were isolated and identified. BV-2 microglia were stimulated with lipopolysaccharide (LPS) in the presence or absence of exosomes. Differentially expressed proteins were identified by tandem mass tag (TMT)-based proteomic analysis. The analgesic effects of huc-MSCs-derived exosomes were evaluated in a rat model of chronic constriction injury (CCI). The underlying mechanism was investigated by flow cytometry, RT-qPCR, Western blotting, immunofluorescent staining, and small interfering RNA transfection.

RESULTS

In vitro, huc-MSCs-derived exosomes suppressed LPS-induced microglial activation and inhibited activation of the TLR2/MyD88/NF-κB signaling pathway. Based on the proteomic analysis, Rsad2 was identified and confirmed to be down-regulated by huc-MSCs-derived exosomes. Importantly, knockdown of Rsad2 also inhibited microglial activation and restrained activation of the TLR2/MyD88/NF-κB signaling pathway. In vivo, intrathecal injection of exosomes ameliorated CCI-induced mechanical allodynia, down-regulated Rsad2 expression and restrained TLR2/MyD88/NF-κB signaling activation in the spinal microglia.

CONCLUSION

Huc-MSCs-derived exosomes exerted analgesic effects on neuropathic pain by inhibiting activation of the TLR2/MyD88/NF-κB signaling pathway in the spinal microglia. The mechanism underlying these antinociceptive effects involved exosome-mediated interference with Rsad2 expression, thereby inhibiting microglial activation.

Signalling Pathways Involved in Microglial Activation in Alzheimer's Disease and Potential Neuroprotective Role of Phytoconstituents

Alzheimer's disease (AD) is a commonly reported neurodegenerative disorder associated with dementia and cognitive impairment. The pathophysiology of AD comprises Aβ, hyperphosphorylated tau protein formation, abrupt cholinergic cascade, oxidative stress, neuronal apoptosis, and neuroinflammation. Recent findings have established the profound role of immunological dysfunction and microglial activation in the pathogenesis of AD. Microglial activation is a multifactorial cascade encompassing various signalling molecules and pathways such as Nrf2/NLRP3/NF-kB/p38 MAPKs/ GSK-3β. Additionally, deposited Aβ or tau protein triggers microglial activation and accelerates its pathogenesis. Currently, the FDA-approved therapeutic regimens are based on the modulation of the cholinergic system, and recently, one more drug, aducanumab, has been approved by the FDA. On the one hand, these drugs only offer symptomatic relief and not a cure for AD. Additionally, no targeted-based microglial medicines are available for treating and managing AD. On the other hand, various natural products have been explored for the possible anti-Alzheimer effect via targeting microglial activation or different targets of microglial activation. Therefore, the present review focuses on exploring the mechanism and associated signalling related to microglial activation and a detailed description of various natural products that have previously been reported with anti-Alzheimer's effect via mitigation of microglial activation. Additionally, we have discussed the various patents and clinical trials related to managing and treating AD.

D-beta-hydroxybutyrate protects against microglial activation in lipopolysaccharide-treated mice and BV-2 cells

Microglial activation is a key event in neuroinflammation, which, in turn, is a central process in neurological disorders. In this study, we investigated the protective effects of D-beta-hydroxybutyrate (BHB) against microglial activation in lipopolysaccharide (LPS)-treated mice and BV-2 cells. The effects of BHB in mice were assessed using behavioral testing, morphological analysis and immunofluorescence labeling for the microglial marker ionizing calcium-binding adaptor molecule 1 (IBA-1) and the inflammatory cytokine interleukin-6 (IL-6) in the hippocampus. Moreover, we examined the levels of the inflammatory IL-6 and tumor necrosis factor-α (TNF-α), as well as those of the neuroprotective brain-derived neurotrophic factor (BDNF) and transforming growth factor-β (TGF-β) in the brain. In addition, we examined the effects of BHB on IL-6, TNF-α, BDNF, TGF-β, reactive oxygen species (ROS) level and cell viability in LPS-stimulated BV-2 cells. BHB treatments attenuated behavioral abnormalities, reduced the number of IBA-1-positive cells and the intensity of IL-6 fluorescence in the hippocampus, with amelioration of microglia morphological changes in the LPS-treated mice. Furthermore, BHB inhibited IL-6 and TNF-α generation, but promoted BDNF and TGF-β production in the brain of LPS-treated mice. In vitro, BHB inhibited IL-6 and TNF-α generation, increased BDNF and TGF-β production, reduced ROS level, ameliorated morphological changes and elevated cell viability of LPS-stimulated BV-2 cells. Together, our findings suggest that BHB exerts protective effects against microglial activation in vitro and in vivo, thereby reducing neuroinflammation.

Association of Glial Activation and α-Synuclein Pathology in Parkinson's Disease

The accumulation of pathological α-synuclein (α-syn) in the central nervous system and the progressive loss of dopaminergic neurons in the substantia nigra pars compacta are the neuropathological features of Parkinson's disease (PD). Recently, the findings of prion-like transmission of α-syn pathology have expanded our understanding of the region-specific distribution of α-syn in PD patients. Accumulating evidence suggests that α-syn aggregates are released from neurons and endocytosed by glial cells, which contributes to the clearance of α-syn. However, the activation of glial cells by α-syn species produces pro-inflammatory factors that decrease the uptake of α-syn aggregates by glial cells and promote the transmission of α-syn between neurons, which promotes the spread of α-syn pathology. In this article, we provide an overview of current knowledge on the role of glia and α-syn pathology in PD pathogenesis, highlighting the relationships between glial responses and the spread of α-syn pathology.

Adolescent microglia stimulation produces long-lasting protection against chronic stress-induced behavioral abnormalities in adult male mice

Our previous studies had reported that microglia activation one day before stress exposure prevented the behavioral abnormalities induced by chronic stress in adult mice, and a 10-day interval between microglia stimulation and stress exposure can abolish the prophylactic effect of LPS preinjection on the behavioral abnormalities induced by chronic stress, which, however, could be rescued by repeated LPS injection. This suggests that increased stimulation of microglia results in animals developing a strong ability to prevent deleterious stress stimuli. Because microglia in the adolescent brain exhibit flexible immunological plasticity, we hypothesize that a single low-dose LPS injection during adolescence may provide long-lasting protection against behavioral abnormalities induced by chronic stress in adult mice. As expected, our results showed that a single injection of LPS (100 μg/kg) at post-natal day 28 (PND 28) prevented the development of abnormal behaviors and shifted neuroinflammatory responses toward an anti-inflammatory phenotype in adult mice treated with CSDS at their different stages of the age (PND 56, 140, and 252). Moreover, pretreatment with minocycline or PLX3397 to inhibit microglial activation abolished the prophylactic effect of LPS preinjection after PND 28 on behavioral abnormalities and neuroinflammatory responses induced by CSDS in adult mice at their different stages of the age, PND 56, 140, and 252. These results indicate that stimulation of microglia in adolescence may confer long-lasting protection against neuroinflammatory responses and behavioral abnormalities induced by chronic stress in adult mice. This may offer the potential for the development of a "vaccine-like strategy" to prevent mental disorders.

The heterogeneity of microglial activation and its epigenetic and non-coding RNA regulations in the immunopathogenesis of neurodegenerative diseases

Microglia are resident immune cells in the brain and play a central role in the development and surveillance of the nervous system. Extensive gliosis is a common pathological feature of several neurodegenerative diseases, such as Alzheimer's disease (AD), the most common cause of dementia. Microglia can respond to multiple inflammatory insults and later transform into different phenotypes, such as pro- and anti-inflammatory phenotypes, thereby exerting different functions. In recent years, an increasing number of studies based on both traditional bulk sequencing and novel single-cell/nuclear sequencing and multi-omics analysis, have shown that microglial phenotypes are highly heterogeneous and dynamic, depending on the severity and stage of the disease as well as the particular inflammatory milieu. Thus, redirecting microglial activation to beneficial and neuroprotective phenotypes promises to halt the progression of neurodegenerative diseases. To this end, an increasing number of studies have focused on unraveling heterogeneous microglial phenotypes and their underlying molecular mechanisms, including those due to epigenetic and non-coding RNA modulations. In this review, we summarize the epigenetic mechanisms in the form of DNA and histone modifications, as well as the general non-coding RNA regulations that modulate microglial activation during immunopathogenesis of neurodegenerative diseases and discuss promising research approaches in the microglial era.

Glibenclamide attenuates brain edema associated with microglia activation after intracerebral hemorrhage

OBJECTIVE

Glibenclamide, Sulfonylurea receptor 1 antagonist, reduces brain edema after cerebral hemorrhage. However, the effects of glibenclamide on microglial activation and inflammatory cell infiltration after cerebral hemorrhage are unclear. The present study investigated the effect of glibenclamide on microglial activation and inflammatory cell infiltration in a rat cerebral hemorrhage model.

METHODS

A collagenase intracerebral injection model was used to cause cerebral hemorrhage in rats. After injury, glibenclamide was continuously administered at 1.0μL/h for 24hours. We evaluated hematoma volume, brain edema, expression of ABCC8, galectin-3 and CD11b, and anti-Iba-1 antibody staining.

RESULTS

Glibenclamide significantly reduced water content. Meanwhile, glibenclamide significantly reduced expression of galectin-3 and CD11b in the cerebral cortex and putamen on the bleeding side. Immunohistochemical staining confirmed that glibenclamide attenuated activation of microglia around the hematoma.

CONCLUSIONS

Glibenclamide reduced microglial activation and infiltration of inflammatory cells, resulting in amelioration of cerebral edema.

Parthenolide ameliorates neurological deficits and neuroinflammation in mice with traumatic brain injury by suppressing STAT3/NF-κB and inflammasome activation

BACKGROUND

Traumatic brain injury (TBI) triggers a set of complex inflammation that results in secondary injury. Parthenolide (PTN) is a sesquiterpene lactone extracted from the herb Tanacetum parthenium (Feverfew) and has potent anti-inflammatory, anti-apoptosis and anti-oxidative stress effects in the central nervous system (CNS)-related diseases. This study focuses on investigating the potential neuroprotective effect of PTN on TBI and the related mechanism.

METHODS

Bv2 microglia, primary microglia were stimulated by LPS, and HT22 neuron cells were stimulated by OGD/R, and they were treated with different doses of PTN. The expression profiles of pro-inflammatory cytokines, proteins, oxidative stress mediators, STAT3/NF-κB pathway, inflammasomes were detected. Forty male/female C57BL/6 mice were randomly divided into the sham, PTN, TBI, and TBI + PTN groups (10 mice per group). A mouse TBI model was set up with a controlled cortical impact (CCI) device. The modified nerve severity score (mNSS) was implemented to check short-term neurological impairment in mice, and the mice's memory and learning were assessed by the Morris water maze test. The water content in the mice's brains was measured by the dry-wet method. Hematoxylin-eosin (H&E) staining, Nissl staining and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assay were applied for neuronal apoptosis.

RESULTS

PTN dramatically alleviated LPS-induced inflammation in microglia, and OGD-mediated neuronal apoptosis and oxidative stress. In addition, PTN repressed LPS- or OGD-modulated STAT3/NF-κB and NLR family pyrin domain containing 1 (NLRP1), NLRP3, NLR family CARD domain containing 4 (NLRC4) inflammasomes activation. Administering the STAT3 inhibitor Stattic or NF-κB inhibitor Bay 11-7082 attenuated PTN-mediated effects. In vivo, PTN treatment relieved neural function deficits, brain edema and neuron apoptosis and improved the memory and learning function of TBI mice. Additionally, PTN impeded microglial activation and reduced the production of pro-inflammatory cytokines in brain lesions of TBI mice. Furthermore, PTN hindered STAT3/NF-κB and inflammasome activation.

CONCLUSION

PTN can curb microglial activation and neuron apoptosis by dampening the STAT3/NF-κB pathway, thus exerting neuroprotective effects in TBI mice.

Ascorbic acid along with ciprofloxacin regulates S. aureus induced microglial inflammatory responses and oxidative stress through TLR-2 and glucocorticoid receptor modulation

Microglial inflammatory responses play a central role in the pathogenesis of S. aureus induced brain infections. Upon activation, microglia produces free radicals (ROS/RNS) and disrupts the cellular antioxidant defense to combat invading microorganisms. Despite conventional antibiotic or steroid therapy, microglial over-activation could not be controlled. So, an attempt had been taken by using a natural antioxidant ascorbic acid along with ciprofloxacin to regulate microglial over-activation by involving TLR-2 and glucocorticoid receptor (GR) in an in-vitro cell culture-based study. Combinatorial treatment during TLR-2 neutralization effectively reduced the bacterial burden at 60 min compared to the GR blocking condition (p < 0.05). Moreover, the infection-induced H₂O₂, O₂^.-, and NO release in microglial cell culture was diminished possibly by enhancing SOD and catalase activities in the same condition (p < 0.05). The arginase activity was markedly increased after TLR-2 blocking in the combinatorial group compared to single treatments (p < 0.05). Experimental results indicated that combinatorial treatment may act through up-regulating GR expression by augmenting endogenous corticosterone levels. However, better bacterial clearance could further suppress the TLR-2 mediated pro-inflammatory NF-κB signaling. From Western blot analysis, it was concluded that ciprofloxacin-ascorbic acid combination in presence of anti-TLR-2 antibody exhibited 81.25% inhibition of TLR-2 expression while the inhibition for GR was 3.57% with respect to the infected group. Therefore, during TLR-2 blockade ascorbic acid combination might be responsible for the restoration of redox balance in microglia via modulating TLR-2/GR interaction. The combination treatment could play a major role in the neuroendocrine-immune regulation of S. aureus induced microglial activation.

Microglia in depression: an overview of microglia in the pathogenesis and treatment of depression

Major depressive disorder is a highly debilitating psychiatric disorder involving the dysfunction of different cell types in the brain. Microglia are the predominant resident immune cells in the brain and exhibit a critical role in depression. Recent studies have suggested that depression can be regarded as a microglial disease. Microglia regulate inflammation, synaptic plasticity, and the formation of neural networks, all of which affect depression. In this review, we highlighted the role of microglia in the pathology of depression. First, we described microglial activation in animal models and clinically depressed patients. Second, we emphasized the possible mechanisms by which microglia recognize depression-associated stress and regulate conditions. Third, we described how antidepressants (clinical medicines and natural products) affect microglial activation. Thus, this review aimed to objectively analyze the role of microglia in depression and focus on potential antidepressants. These data suggested that regulation of microglial actions might be a novel therapeutic strategy to counteract the adverse effects of devastating mental disorders.

Microglia-induced autophagic death of neurons via IL-6/STAT3/miR-30d signaling following hypoxia/ischemia

BACKGROUND

There is a relationship between autophagy and the occurrence, maintenance, and progression of several neurodegenerative diseases. The activation of microglia after ischemia contributes to neuronal injury via proinflammatory cytokines and neurotoxic elements. The purpose of this study was to evaluate the function of autophagy in the microglia-mediated death of neuronal cells.

METHODS AND RESULTS

Microglial activation by oxygen/glucose deprivation induced both apoptosis and autophagy in neuron-like PC12 cells. Microglia-derived interleukin (IL)-6 induced PC12 cell apoptosis in vitro; however, this effect was inhibited by the autophagy inhibitor chloroquine. Further analysis demonstrated that miR-30d in PC12 cells suppressed microglia-induced PC12 apoptosis and autophagy by directly targeting autophagy protein 5. Moreover, microglia-derived IL-6 activated signal transducer and activator of transcription 3 (STAT3), which can then directly repress miR-30d genes via a conserved STAT3-binding site in its promoter, thereby promoting PC12 cell autophagy and apoptosis.

CONCLUSIONS

Our study identified IL-6-dependent autophagy-related signaling between microglia and neurons, which contributed to neuronal apoptosis. Importantly, we also provided potential therapeutic targets for ischemic treatment via the interruption of proinflammatory signaling.

The association of enlarged perivascular space with microglia-related inflammation and Alzheimer's pathology in cognitively normal elderly

BACKGROUND

Glymphatic dysfunction may contribute to the accumulation of Alzheimer's disease (AD) pathologies. Conversely, AD pathologic change might also cause neuroinflammation and aggravate glymphatic dysfunction, forming a loop that accelerates AD progression. In vivo validations are needed to confirm their relationships.

METHODS

In this study, we included 144 cognitively normal participants with AD pathological biomarker data (baseline CSF Aβ_1-42, T-Tau, P-Tau₁₈₁; plasma P-Tau₁₈₁ at baseline and at least one follow-up) from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database. Each subject had completed structural MRI scans. Among them, 117 subjects have available neuroinflammatory biomarker (soluble triggering receptor expressed on myeloid cells 2 (sTREM2), and 123 subjects have completed two times [18F]-florbetapir PET. The enlarged PVS (EPVS) visual rating scores in basal ganglia (BG) and centrum semiovale (CS) were assessed on T1-weighted images to reflect glymphatic dysfunction. Intracranial volume and white matter hyperintensities (WMH) volume were also calculated for further analysis. We performed stepwise linear regression models and mediation analyses to estimate the association between EPVS severity, sTREM2, and AD biomarkers.

RESULTS

CS-EPVS degree was associated with CSF sTREM2, annual change of plasma P-tau₁₈₁ and total WMH volume, whereas BG-EPVS severity was associated with age, gender and intracranial volume. The sTREM2 mediated the association between CSF P-tau₁₈₁ and CS-EPVS.

CONCLUSION

Impaired glymphatic dysfunction could contribute to the accumulation of pathological tau protein. The association between tauopathy and glymphatic dysfunction was mediated by the microglia inflammatory process. These findings may provide evidence for novel treatment strategies of anti-neuroinflammation therapy in the early stage.

Microglial cell response in α7 nicotinic acetylcholine receptor-deficient mice after systemic infection with Escherichia coli

Background

Development of neurodegeneration in older people has been associated with microglial cell activation triggered by systemic infection. We hypothesize that α7 nicotinic acetylcholine receptor (α7nAChR) plays an important role in regulation of this process.

Methods

8- to 10-week-old male wild-type (WT) and α7nAChR knock-out (α7nAChR^−/−) mice were intraperitoneally inoculated with live Escherichia (E.) coli or saline. After inoculation, all mice were treated with ceftriaxone (an antimicrobial drug) at 12 and 24 h and killed at 2 or 3 days. The microglial response was characterized by immunohistochemical staining with an ionized calcium-binding adaptor molecule 1 (Iba-1) antibody and flow cytometry. To quantify inflammatory response, mRNA expression of pro- and anti-inflammatory mediators was measured in brain and spleen.

Results

We observed no differences in Iba-1 positive cell number or morphology and flow cytometry (CD11b, CD45 and CD14) of microglial cells between WT and α7nAChR^−/− mice after systemic infection. Infected α7nAChR^−/− mice showed significantly higher mRNA expression in brain for tumor necrosis factor alpha (TNF-α) at day 2 and 3, interleukin 6 (IL-6) at day 2 and monocyte chemotactic protein 1 (MCP-1) and suppressor of cytokine signaling 1 (SOCS1) at day 3, there was significantly lower mRNA expression in brain for mitogen-activated protein kinase 1 (MAPK1) at day 2 and 3, high-mobility group 1 (HMGB-1) and CD11b at day 2, and deubiquitinase protein A20 (A20) at day 3 compared to infected WT mice.

Interpretation

Loss of function of α7nAChR during systemic infection led to an increased expression of TNF-α and IL-6 in brain after systemic infection with E. coli, but not to distinct differences in microglial cell number or morphological activation of microglia.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02452-8.