Microglia activation mediated by toll-like receptor-4 impairs brain white matter tracts in rats

Microglia activation and white matter injury coexist after repeated episodes of mild brain trauma and ischemic stroke. Axon degeneration and demyelination can activate microglia; however, it is unclear whether early microglia activation can impair the function of white matter tracts and lead to injury. Rat corpus callosum（CC） slices were treated with lipopolysaccharide（LPS） or LPS ＋ Rhodobacter sphaeroides（RS）-LPS that is a toll-like receptor 4（TLR-4） antagonist. Functional changes reflected by the change of axon compound action potentials（CAPs） and the accumulation of β-amyloid precursor protein（β-APP） in CC nerve fibers. Microglia activation was monitored by ionized calcium binding adaptor-1 immunofluorescent stain, based on well-established morphological criteria and paralleled proportional area measurement. Input-output（I/O） curves of CAPs in response to increased stimuli were significantly downshifted in a dose-dependent manner in LPS（0.2, 0.5 and 1.0μg/mL）-treated slices, implying that axons neurophysiological function was undermined. LPS caused significant β-APP accumulation in CC tissues,reflecting the deterioration of fast axon transport. LPS-induced I/O curve downshift and P-APP accumulation were significantly reversed by the pre-treatment or co-incubation with RS-LPS. RS-LPS alone did not change the I/O curve.The degree of malfunction was correlated with microglia activation, as was shown by the measurements of proportional areas. Function of CC nerve fibers was evidently impaired by microglia activation and reversed by a TLP-4 antagonist, suggesting that the TLP-4 pathway lead to microglia activation.

Microglia activation in the offspring of prenatal Poly I:C exposed rats:a PET imaging and immunohistochemistry study

Background The well-known ‘pyrotherapy’ of Julius Wagner-Jauregg might be the beginning of the study on the immunological concepts of schizophrenia. As the primary immune effector cells in the brain, microglia play a pivotal role in neuroinfammatory processes. Maternal viral infection during pregnancy is associated with an increased risk for psychiatric disorders with presumed neurodevelopmental origin, including autism spectrum disorders and schizophrenia. The present study was to quantify microglia activation in vivo in the mature offspring of rats exposed to polyriboinosinic–polyribocytidilicacid （Poly I：C） during pregnancy using ^11C-PK11195 positron emission tomography （PET） and immunohistochemistry.Objective The study aimed to quantify microglia activation in vivo in the prefrontal cortex and hippocampus in mature offspring of prenatal Poly I：C exposed rats.Methods Offspring of Poly I：C-treated dams were the model group, offspring of saline-treated dams were the control group. Behavioural test for two groups was taken by spontaneous activity, prepulse inhibition （PPI） and latent inhibition （LI） test （including active avoidance conditioning task and passive avoidance conditioning task）. Randomly selected successful model rats were assessed by behavioural test in the model group and control group rats. 11C-PK11195 micro-PET/CT and immunohistochemistry were performed on the selected rats to measure microglia activation.Results The treatment group showed hyperlocomotion and defcits in PPI and LI compared with the control group. The treatment group also showed an increased 11C-PK11195 uptake ratio in the prefrontal cortex （t=-3.990, p=0.003） and hippocampus （t=-4.462, p=0.001）. The number of activated microglia cells was signifcantly higher in the treatment group than in the control group （hippocampus： t=8.204, p〈0.001; prefrontal： t=6.995, p〈0.001）. Within the treatment group, there were signifcant correlations between the behavioural parameters and the activation of microglia as measured by PET and immunohistochemistry.Conclusions The present study demonstrated microglia activation in vivo in the prefrontal cortex and hippocampus in mature offspring of prenatal Poly I：C exposed rats. This study suggests that microglia activation may play a possible or potential role in the pathogenesis of schizophrenia.

Houttuynia cordata Thunb rescues retinal ganglion cells through inhibiting microglia activation in a rat model of retinal ischemia-reperfusion

AIM:To determine whether Houttuynia cordata Thunb(HCT)can increase the survival of the retinal ganglion cells(RGCs)and inhibit microglia activation following retinal ischemia-reperfusion(RIR)injury.METHODS:Rat model of RIR was induced by transient elevation of the intraocular pressure(IOP).HCT was orally administered for 2 d before the performance of retinal RIR model and once a day for the next 14 d.After 14 d of RIR injury,the rats were sacrificed for further analysis.Survival RGCs were stained with haematoxylin and eosin(H&E).Apoptosis of RGCs was detected by TUNEL staining.Retinal function was examined by flash-electroretinography(F-ERG).Retinal microglia were labeled using Iba-1,one specific marker for microglia.The m RNA expression levels of inducible nitric oxide synthase(i NOS),tumor necrosis factor alpha(TNF-α),and interleukin 1 beta(IL-1β)were assessed by quantitative real time reverse transcription polymerase chain reaction(q RT-PCR).RESULTS:Systemic HCT treatment significantly reduced RGCs death by H&E staining and exhibited an anti-apoptotic effect as assessed by TUNEL staining at day 14 after RIR injury.HCT greatly improved the retinal function as examined by F-ERG.The number of activated microglia significantly increased after RIR injury,which was significantly attenuated by HCT treatment.Besides,RIR injury induced a strong upregulation of pro-inflammatory genes TNF-α,i NOS and IL-1βm RNAs at day 14 post injury,which was suppressed by HCT.CONCLUSION:Neuroprotective effects of HCT encourage the survival of RGCs through inhibiting microglia activation due to RIR injury.Together these results support the use of HCT as promising therapy for the ischemic events of the retina diseases.

Mesenchymal stem cell-derived exosomes regulate microglia phenotypes:a promising treatment for acute central nervous system injury

There is growing evidence that long-term central nervous system(CNS)inflammation exacerbates secondary deterioration of brain structures and functions and is one of the major determinants of disease outcome and progression.In acute CNS injury,brain microglia are among the first cells to respond and play a critical role in neural repair and regeneration.However,microglial activation can also impede CNS repair and amplify tissue damage,and phenotypic transformation may be responsible for this dual role.Mesenchymal stem cell(MSC)-derived exosomes(Exos)are promising therapeutic agents for the treatment of acute CNS injuries due to their immunomodulatory and regenerative properties.MSC-Exos are nanoscale membrane vesicles that are actively released by cells and are used clinically as circulating biomarkers for disease diagnosis and prognosis.MSC-Exos can be neuroprotective in several acute CNS models,including for stroke and traumatic brain injury,showing great clinical potential.This review summarized the classification of acute CNS injury disorders and discussed the prominent role of microglial activation in acute CNS inflammation and the specific role of MSC-Exos in regulating pro-inflammatory microglia in neuroinflammatory repair following acute CNS injury.Finally,this review explored the potential mechanisms and factors associated with MSCExos in modulating the phenotypic balance of microglia,focusing on the interplay between CNS inflammation,the brain,and injury aspects,with an emphasis on potential strategies and therapeutic interventions for improving functional recovery from early CNS inflammation caused by acute CNS injury.

Microglia activation-induced mesencephalic dopaminergic neurodegeneration -- an in vitro model for Parkinson＇s disease

Uncontrolled and chronic microglia activation has been implicated in the process of dopaminergic neuron degeneration in sporadic Parkinson＇s disease （PD）. Elevated proinflammatory mediators, presumably from activated microglia （e.g., cytokines, PGE2, nitric oxide, and superoxide radical）, have been observed in PD patients and are accompanied by dopaminergic neuronal loss. Preclinical studies have demonstrated the deleterious effects of proinflammatory mediators in various in vivo and in vitro models of PD. The use of in vitro studies provides a unique tool to investigate the interaction between neurons and microglia and is especially valuable when considering the role of activated microglia in neuronal death. Here we summarize findings highlighting the potential mechanisms of microglia- mediated neurodegeneration in PD.

Rutin pretreatment promotes microglial M1 to M2 phenotype polarization

Microglial cells are important resident innate immune components in the central nervous system that are often activated during neuroinflammation.Activated microglia can display one of two phenotypes,M1 or M2,which each play distinct roles in neuroinflammation.Rutin,a dietary flavonoid,exhibits protective effects against neuroinflammation.However,whether rutin is able to influence the M1/M2 polarization of microglia remains unclear.In this study,in vitro BV-2 cell models of neuroinflammation were established using 100 ng/mL lipopolysaccharide to investigate the effects of 1-hour rutin pretreatment on microglial polarization.The results revealed that rutin pretreatment reduced the expression of the proinflammatory cytokines tumor necrosis factor-α,interleukin-1β,and interleukin-6 and increased the secretion of interleukin-10.Rutin pretreatment also downregulated the expression of the M1 microglial markers CD86 and inducible nitric oxide synthase and upregulated the expression of the M2 microglial markers arginase 1 and CD206.Rutin pretreatment inhibited the expression of Toll-like receptor 4 and myeloid differentiation factor 88 and blocked the phosphorylation of I kappa B kinase and nuclear factor-kappa B.These results showed that rutin pretreatment may promote the phenotypic switch of microglia M1 to M2 by inhibiting the Toll-like receptor 4/nuclear factor-kappa B signaling pathway to alleviate lipopolysaccharide-induced neuroinflammation.

Physical interactions between activated microglia and injured axons:do all contacts lead to phagocytosis?

Axonal injury is a pathological hallmark of both head injury and inflammatory-mediated neurological disorders,including multiple sclerosis（Schirmer et al.,2013）.Such axonal disruptions and/or disconnections typically result in proximal axonal segments that remain in continuity with the neuronal somawhile losing contact with their distal targets.

Protective Effect of an Anthocyanin on Alzheimer’s Disease

Alzheimer’s, characterized by β-amyloid accumulation and tau hyperphosphorylation, is linked to inflammation, oxidative stress, and microglial activation, suggesting potential protective strategies. Studies have shown that natural polyphenolic anthocyanin components found in berries, such as cyanidin, can inhibit amyloid filament formation and modulate Alzheimer’s disease are polyphenolic flavonoids, which are responsible for red, purple, and blue colors in various fruits, such as red cabbage and most berries. Here, we reviewed the protective effects of anthocyanins. It has anti-inflammatory and antioxidant properties, reduces NF-κB, and affects inflammatory signaling pathways. They also improve cognitive function, making them a potential protective strategy against AD.

In depth understanding of retinitis pigmentosa pathogenesis through optical coherence tomography angiography analysis:a narrative review

Retinitis pigmentosa(RP)is the most recognized inherited retinal disorder involving progressive photoreceptors degeneration which eventually causes blindness.However,the pathogenesis of RP is still unclear,making it difficult to establish satisfying treatments.Evidence have been found to support the theory that vascular dysfunction is associated with the progression of RP.Optical coherence tomography angiography(OCTA)is a newly developed technology that enables visualization as well as quantitative assessment of retinal and choroidal vasculature noninvasively.Advances in OCTA have opened a window for indepth understanding of RP pathogenesis.Here,we propose a hypothesis of RP pathogenesis based on the current OCTA findings in RP,which includes four stages and two important key factors,vascular dysfunction and microglia activation.Further,we discuss the future animal experiments needed and how advanced OCTA technology can help to further verity the hypothesis.The final goal is to explore potential treatment options with enhanced understanding of RP pathogenesis.

Inhibiting the kynurenine pathway in spinal cord injury: multiple therapeutic potentials?

Chronic induction of the kynurenine pathway（KP） contributes to neuroinflammation by producing the excitotoxin quinolinic acid（QUIN）. This has led to significant interest in the development of inhibitors of this pathway, particularly in the context of neurodegenerative disease. However, acute spinal cord injury（SCI） also results in deleterious increases in QUIN, as secondary inflammatory processes mediated largely by infiltrating macrophages, become predominant. QUIN mediates significant neurotoxicity primarily by excitotoxic stimulation of the N-methyl-D-aspartate receptor, but other mechanisms of QUIN toxicity are known. More recent focus has assessed the contribution that neuroinflammation and modulations in the KP make in mood and psychiatric disorders with recent studies linking inflammation and modulations in the KP, to impaired cognitive performance and depressed mood in SCI patients. We hypothesize that these findings suggest that in SCI, inhibition of QUIN production and other metabolites, may have multiple therapeutic modalities and further studies investigating this are warranted. However, for central nervous system-based conditions, achieving good blood-brain-barrier permeability continues to be a limitation of current KP inhibitors.

Promise of metformin for preventing age-related cognitive dysfunction

The expanded lifespan of people,while a positive advance,has also amplified the prevalence of age-related disorders,which include mild cognitive impairment,dementia,and Alzheimer's disease.Therefore,competent therapies that could improve the healthspan of people have great significance.Some of the dietary and pharmacological approaches that augment the lifespan could also preserve improved cognitive function in old age.Metformin,a drug widely used for treating diabetes,is one such candidate that could alleviate age-related cognitive dysfunction.However,the possible use of metformin to alleviate age-related cognitive dysfunction has met with conflicting results in human and animal studies.While most clinical studies have suggested the promise of metformin to maintain better cognitive function and reduce the risk for developing dementia and Alzheimer's disease in aged diabetic people,its efficacy in the nondiabetic population is still unclear.Moreover,a previous animal model study implied that metformin could adversely affect cognitive function in the aged.However,a recent animal study using multiple behavioral tests has reported that metformin treatment in late middle age improved cognitive function in old age.The study also revealed that cognitionenhancing effects of metformin in aged animals were associated with the activation of the energy regulator adenosine monophosphate-activated protein kinase,diminished neuroinflammation,inhibition of the mammalian target of rapamycin signaling,and augmented autophagy in the hippocampus.The proficiency of metformin to facilitate these favorable modifications in the aged hippocampus likely underlies its positive effect on cognitive function.Nonetheless,additional studies probing the outcomes of different doses and durations of metformin treatment at specific windows in the middle and old age across sex in nondiabetic and non-obese prototypes are required to substantiate the promise of metformin to maintain better cognitive function in old age.

Propane-2-sulfonic acid octadec-9-enyl-amide,a novel PPARα/γ dual agonist,protects against ischaemiainduced brain damage in mice by inhibiting inflammatory responses

OBJECTIVE Propane-2-sulfonic acid octadec-9-enyl-amide(N15),an analogue of oleoylethanolamide(OEA),is a novel PPARα/γdual agonist.Our previous studies verified the positive effects of OEA on the acute and delayed stages of cerebral ischaemia.However,it is not clear whether N15 is effective against ischaemic cerebral injury.In the present study,male Kunming mice were subjected to middle cerebral artery occlusion(MCAO).METHODS To evaluate its preventive effects,N15(50,100 or 200 mg·kg-1,ip)was administered for3 d before ischaemia.To evaluate its therapeutic effects,N15(200 mg·kg-1,ip)was administered 1 h before reperfusion or 0,1,2 or 4 h after reperfusion.Neurological deficit scores,infarct volume and the degree of brain oedema were determined at 24 h after reperfusion.Blood brain barrier(BBB)disruption was evaluated by Evans blue(EB)leakage at 6 h after reperfusion.The activation/inflammatory responses of microglia were detected using immunohistochemistry and Western blotting.RESULTS N15 pretreatment improved neurological dysfunction,reduced infarct volume and alleviated brain oedema in a dose-dependent manner;the most effective dose was 200 mg·kg-1.The therapeutic time window was within 2 h after reperfusion.Moreover,N15was more potent in the treatment of cerebral ischaemia injury than OEA.N15 treatment preserved the BBB integrity and suppressed the activation of microglia.N15 inhibited inflammatory cytokine expression not only in MCAO mice but also in lipopolysaccharide(LPS)-stimulated BV-2microglial cells.Moreover,N15 decreased the phosphorylation levels of NF-κBp65,STAT3,and ERK1/2 both in vivo and in vitro.CONCLUSION Our findings demonstrated that N15 exerts neuroprotective effects and was more potent than OEA.Additionally,the neuroprotective effects of N15 on cerebral ischaemia may be attributed to its anti-inflammatory properties,at least in part,by enhancing PPARα/γdual signalling and inhibiting the activation of the NF-κB,STAT3,and ERK1/2 signalling pathways.These findings suggest that N15 may be a potential therapeutic choice for the prevention and treatment of ischaemic stroke.

Substantial subpial cortical demyelination in progressive multiple sclerosis: have we underestimated the extent of cortical pathology?

Aim: Multiple sclerosis (MS) is an inflammatory demyelinating and neurodegenerative disease. Much of the complex symptomatology relates to pathology outside the classic white matter plaque, whereby lesions of the cortical grey matter, which are difficult to resolve by conventional clinical imaging, are in part predictive of outcome. We investigated the extent of grey matter pathology in whole coronal macrosections to reassess the contribution of cortical pathology to total demyelinating lesion area in progressive MS. Methods: Twenty-two cases of progressive MS were prepared as whole bi-hemispheric macrosections for histology, immunostaining and quantitative analysis of lesion number and relative area, leptomeningeal inflammation and microglial/macrophage activation. Results: Cortical grey matter demyelination was seen in all cases, which was more extensive than in white and deep grey matter (hippocampus, thalamus and basal ganglia) and accounted for 0.8%-60.2% of the entire measurable cortical ribbon. The pattern of cortical grey matter demyelination was predominantly subpial (mean 90.9%, range 60%-100%, of total cortical grey matter lesion area) and cases with the largest areas of subpial cortical lesions had more and larger deep grey matter lesions, greater numbers of activated microglia/macrophages, both in lesions as well as in normal cortical grey matter, together with elevated leptomeningeal inflammation and lymphoid-like ;structures. White matter lesion area was unchanged when compared with the progressive MS cases with little subpial cortical demyelination. Conclusion: Analysis of whole coronal macrosections reveals cortical demyelination is more extensive than reported by conventional histological methods. Cases of progressive MS with substantial subpial cortical demyelination that is independent of underlying white matter lesion area support the implications that these lesions may in-part arise through different pathogenetic mechanisms. Biomarkers and/or imaging correlates of this subpial pathology are required if we are to fully comprehend the clinical disease process.