SENP1 modulates microglia-mediated neuroinflammation toward intermittent hypoxia-induced cognitive decline through the de-SUMOylation of NEMO

Intermittent hypoxia (IH)-induced cognition decline is related to the neuroinflammation in microglia. SUMOylation is associated with multiple human diseases, which can be reversed by sentrin/SUMO-specific proteases 1 (SENP1). Herein, we investigated the role of SENP1 in IH-induced inflammation and cognition decline. BV-2 microglial cells and mice were used for inflammatory response and cognition function evaluation following IH treatment. Biochemical analysis and Morris water maze methods were used to elaborate the mechanism of SENP1 in IH impairment. Molecular results revealed that IH induced the inflammatory response, as evidenced by the up-regulation of NF-κB activation, IL-1β and TNF-α in vitro and in vivo. Moreover, IH decreased the expression of SENP1, and increased the SUMOylation of NEMO, not NF-κB P65. Moreover, SENP1 overexpression inhibited IH-induced inflammatory response and SUMOylation of NEMO. However, the inhibitions were abolished by siRNA-NEMO. In contrast, SENP1 depletion enhanced IH-induced inflammatory response and SUMOylation of NEMO, accompanying with increased latency and reduced dwell time in mice. Overall, the results demonstrated that SENP1 regulated IH-induced neuroinflammation by modulating the SUMOylation of NEMO, thus activating the NF-κB pathway, revealing that targeting SENP1 in microglia may represent a novel therapeutic strategy for IH-induced cognitive decline.     

Inhibition of NADPH oxidase promotes alternative and anti-inflammatory microglial activation during neuroinflammation

Like macrophages, microglia are functionally polarized into different phenotypic activation states, referred as classical and alternative. The balance of the two phenotypes may be critical to ensure proper brain homeostasis, and may be altered in brain pathological states, such as Alzheimer's disease. We investigated the role of NADPH oxidase in microglial activation state using p47(phox) and gp91(phox) -deficient mice as well as apocynin, a NADPH oxidase inhibitor during neuroinflammation induced by an intracerebroventricular injection of LPS or Aβ????. We showed that NADPH oxidase plays a critical role in the modulation of microglial phenotype and subsequent inflammatory response. We demonstrated that inhibition of NADPH oxidase or gene deletion of its functional p47(phox) subunit switched microglial activation from a classical to an alternative state in response to an inflammatory challenge. Moreover, we showed a shift in redox state towards an oxidized milieu and that subpopulations of microglia retain their detrimental phenotype in Alzheimer's disease brains. Microglia can change their activation phenotype depending on NADPH oxidase-dependent redox state of microenvironment. Inhibition of NADPH oxidase represents a promising neuroprotective approach to reduce oxidative stress and modulate microglial phenotype towards an alternative state.     

Minocycline attenuates post‐operative cognitive impairment in aged mice by inhibiting microglia activation

Although it is known that isoflurane exposure or surgery leads to post‐operative cognitive dysfunction in aged rodents, there are few clinical interventions and treatments available to prevent this disorder. Minocycline (MINO) produces neuroprotection from several neurodegenerative diseases and various experimental animal models. Therefore, we set out to investigate the effects of MINO pre‐treatment on isoflurane or surgery induced cognitive impairment in aged mice by assessing the hippocampal‐dependent spatial memory performance using the Morris water maze task. Hippocampal tissues were isolated from mice and evaluated by Western blot analysis, immunofluorescence procedures and protein array system. Our results elucidate that MINO down‐regulated the isoflurane‐induced and surgery‐induced enhancement in the protein levels of pro‐inflammatory cytokine tumour necrosis factor alpha, interleukin (IL)‐1β, interferon‐γ and microglia marker Iba‐1, and up‐regulated protein levels of the anti‐inflammatory cytokine IL‐4 and IL‐10. These findings suggest that pre‐treatment with MINO attenuated isoflurane or surgery induced cognitive impairment by inhibiting the overactivation of microglia in aged mice.     

Docosahexaenoic acid attenuates microglial activation and delays early retinal degeneration

Microgliosis is a common phenomenon in neurodegenerative disorders including retinal dystrophies. We performed a detailed characterization of activated microglia in the retinoschisin (Rs1h)-deficient (Rs1h^−/Y) mouse model of inherited retinal degeneration. To visualize and isolate microglia, we crossed Rs1h^−/Y animals with transgenic MacGreen mice, which express green fluorescent protein under the control of the macrophage-specific csf1r promoter. Activated microglia were detected in retinal sections and whole-mounts of early postnatal MacGreen/Rs1h^−/Y mice before the onset of overt neuronal cell death. These activated microglia contained prominent lipid droplets and analysis of the retinal lipid composition showed decreased docosahexaenoic acid (DHA) levels in Rs1h^−/Y retinas. To establish a link between microglia activation, reduced DHA levels, and neurodegeneration, a dietary intervention study was performed. Female Rs1h^−/− mice and their Rs1h^−/Y litter were either subjected to a diet enriched with DHA, or a control chow lacking DHA. Supplementation with DHA enhanced photoreceptor survival and converted activated microglia to a quiescent phenotype. Furthermore, DHA, but not docosapentaenoic acid or adrenic acid reduced pro-inflammatory gene expression, migration, and lipid accumulation of cultured BV-2 microglia. We conclude that retinal DHA levels control the activity of microglia and thereby may affect the progression and extent of retinal degeneration.     

Enhancing fractalkine/CX3CR1 signalling pathway can reduce neuroinflammation by attenuating microglia activation in experimental diabetic retinopathy

The concept of diabetic retinopathy (DR) has been extended from microvascular disease to neurovascular disease in which microglia activation plays a remarkable role. Fractalkine (FKN)/CX3CR1 is reported to regulate microglia activation in central nervous system diseases. To characterize the effect of FKN on microglia activation in DR, we employed streptozotocin‐induced diabetic rats, glyoxal‐treated R28 cells and hypoxia‐treated BV2 cells to mimic diabetic conditions and explored retinal neuronal apoptosis, reactive oxygen species (ROS), as well as the expressions of FKN, Iba‐1, TSPO, NF‐κB, Nrf2 and inflammation‐related cytokines. The results showed that FKN expression declined with diabetes progression and in glyoxal‐treated R28 cells. Compared with normal control, retinal microglia activation and inflammatory factors surged in both diabetic rat retinas and hypoxia‐treated microglia, which was largely dampened by FKN. The NF‐κB and Nrf2 expressions and intracellular ROS were up‐regulated in hypoxia‐treated microglia compared with that in normoxia control, and FKN significantly inhibited NF‐κB activation, activated Nrf2 pathway and decreased intracellular ROS. In conclusion, the results demonstrated that FKN deactivated microglia via inhibiting NF‐κB pathway and activating Nrf2 pathway, thus to reduce the production of inflammation‐related cytokines and ROS, and protect the retina from diabetes insult.     

Adenosine A2A receptors control neuroinflammation and consequent hippocampal neuronal dysfunction

The blockade of adenosine A(2A) receptors (A2AR) affords a robust neuroprotection in different noxious brain conditions. However, the mechanisms underlying this general neuroprotection are unknown. One possible mechanism could be the control of neuroinflammation that is associated with brain damage, especially because A2AR efficiently control peripheral inflammation. Thus, we tested if the intracerebroventricular injection of a selective A2AR antagonist (SCH58261) would attenuate the changes in the hippocampus triggered by intraperitoneal administration of lipopolysaccharide (LPS) that induces neuroinflammation through microglia activation. LPS administration triggers an increase in inflammatory mediators like interleukin-1β that causes biochemical changes (p38 and c-jun N-terminal kinase phosphorylation and caspase 3 activation) contributing to neuronal dysfunction typified by decreased long-term potentiation, a form of synaptic plasticity. Long-term potentiation, measured 30 min after the tetanus, was significantly lower in LPS-treated rats compared with control-treated rats, while SCH58261 attenuated the LPS-induced change. The LPS-induced increases in phosphorylation of c-jun N-terminal kinase and p38 and activation of caspase 3 were also prevented by SCH58261. Significantly, SCH58261 also prevented the LPS-induced recruitment of activated microglial cells and the increase in interleukin-1β concentration in the hippocampus, indicating that A2AR activation is a pivotal step in mediating the neuroinflammation triggered by LPS. These results indicate that A2AR antagonists prevent neuroinflammation and support the hypothesis that this mechanism might contribute for the ability of A2AR antagonists to control different neurodegenerative diseases known to involve neuroinflammation.     

Fractalkine-induced activation of the phosphatidylinositol-3 kinase pathway attentuates microglial activation in vivo and in vitro

Several neurodegenerative disorders are associated with evidence of inflammation, one feature of which is increased activation of microglia, the most likely cellular source of inflammatory cytokines like interleukin-1β. It is now recognized that interaction of microglia with other cells contributes to maintenance of microglia in a quiescent state and the complementary distribution of the chemokine, fractalkine (CX₃CL1) on neurons and its receptor (CX₃CR1) on microglia, suggests that this interaction may play a role in modulating microglial activation. Here we demonstrate that both soluble and membrane-bound fractalkine attenuate lipopolysaccharide-induced microglial activation in vitro. We also show that fractalkine expression is reduced in the brain of aged rats and this is accompanied by an age-related increase in microglial activation. Treatment of aged rats with fractalkine attenuates the age-related increase in microglial activation and the evidence indicates that fractalkine-induced activation of the phosphatidylinositol-3 kinase pathway is required to maintain microglia in a quiescent state both in vivo and in vitro .     

MKP1 reduces neuroinflammation via inhibiting endoplasmic reticulum stress and mitochondrial dysfunction

MAP kinase phosphatase 1 (MKP1) has been identified as an antiapoptotic protein via sustaining mitochondrial function. However, the role of MKP1 in neuroinflammation has not been fully understood. The aim of this study is to figure out the influence of MKP1 in lipopolysaccharide (LPS)-treated microglia BV-2 cells and investigate whether MKP1 reduces BV-2 cell death via modulating endoplasmic reticulum (ER) stress and mitochondrial dysfunction. The results of this study demonstrated that MKP1 was rapidly downregulated after exposure to LPS. However, the transfection of MKP1 adenovirus could reverse cell viability and attenuate LPS-mediated BV-2 cell apoptosis. Mechanistically, MKP1 overexpression alleviated ER stress and corrected LPS-induced calcium overloading. Besides, MKP1 adenovirus transfection also reversed mitochondrial bioenergetics, maintained mitochondrial membrane potential, and blocked mitochondria-initiated apoptosis signals. Furthermore, we found that MKP1 overexpression is associated with inactivation of mitogen-activated protein kinase–c-Jun N-terminal kinase (MAPK–JNK) pathway. Interestingly, the activation of MAPK–JNK pathway could abolish the protective effects of MKP1 on BV-2 cells survival and mitochondrial function in the presence of LPS. Altogether, our results identified MKP1 as a primary defender of neuroinflammation via modulating ER stress and mitochondrial function in a manner dependent on MAPK–JNK pathway. These findings may open a new window for the treatment of neuroinflammation in the clinical setting.     

Gut bacterial isoamylamine promotes age-related cognitive dysfunction by promoting microglial cell death

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Absent in melanoma 2 mediates aging-related cognitive dysfunction by acting on complement-dependent microglial phagocytosis

Pattern separation (PS) dysfunction is a type of cognitive impairment that presents early during the aging process, and this deficit has been attributed to structural and functional alterations in the dentate gyrus (DG) of the hippocampus. Absent in melanoma 2 (AIM2) is an essential component of the inflammasome. However, whether AIM2 plays a role in aging-associated cognitive dysfunction remains unclear. Here, we found that PS function was impaired in aging mice and was accompanied by marked synaptic loss and increased expression of AIM2 in the DG. Subsequently, we used an AIM2 overexpression virus and mice with AIM2 deletion to investigate the role of AIM2 in regulating PS function and synaptic plasticity and the mechanisms involved. Our study revealed that AIM2 regulates microglial activation during synaptic pruning in the DG region via the complement pathway, leading to impaired synaptic plasticity and PS function in aging mice. These results suggest a critical role for AIM2 in regulating synaptic plasticity and PS function and provide a new direction for ameliorating aging-associated cognitive dysfunction.     

The role of NLRP3-CASP1 in inflammasome-mediated neuroinflammation and autophagy dysfunction in manganese-induced,hippocampal-dependent impairment of learning and memory ability

Central nervous system (CNS) inflammation and autophagy dysfunction are known to be involved in the pathology of neurodegenerative diseases. Manganese (Mn), a neurotoxic metal, has the potential to induce microglia-mediated neuroinflammation as well as autophagy dysfunction. NLRP3 (NLR family, pyrin domain containing 3)- CASP1 (caspase 1) inflammasome-mediated neuroinflammation in microglia has specific relevance to neurological diseases. However, the mechanism driving these phenomena remains poorly understood. We demonstrate that Mn activates the NLRP3-CASP1 inflammasome pathway in the hippocampus of mice and BV2 cells by triggering autophagy-lysosomal dysfunction. The autophagy-lysosomal dysfunction is induced by lysosomal damage caused by excessive Mn accumulation, damaging the structure and normal function of these organelles. Additionally, we show that the release of lysosomal CTSB (cathepsin B) plays an important role in Mn-induced NLRP3-CASP1 inflammasome activation, and that the increased autophagosomes in the cytoplasm are not the main cause of NLRP3-CASP1 inflammasome activation. The accumulation of proinflammatory cytokines, such as IL1B (interleukin 1 β) and IL18 (interleukin 18), as well as the dysfunctional autophagy pathway may damage hippocampal neuronal cells, thus leading to hippocampal-dependent impairment in learning and memory, which is associated with the pathogenesis of Alzheimer disease (AD).     

Dl‐3‐n‐butylphthalide attenuates acute inflammatory activation in rats with spinal cord injury by inhibiting microglial TLR4/NF‐κB signalling

In this study, we examined the neuroprotective effects and anti‐inflammatory properties of Dl‐3‐n‐butylphthalide (NBP) in Sprague‐Dawley (SD) rats following traumatic spinal cord injury (SCI) as well as microglia activation and inflammatory response both in vivo and in vitro. Our results showed that NBP improved the locomotor recovery of SD rats after SCI an significantly diminished the lesion cavity area of the spinal cord, apoptotic activity in neurons, and the number of TUNEL‐positive cells at 7 days post‐injury. NBP inhibited activation of microglia, diminished the release of inflammatory mediators, and reduced the upregulation of microglial TLR4/NF‐κB expression at 1 day post‐injury. In a co‐culture system with BV‐2 cells and PC12 cells, NBP significantly reduced the cytotoxicity of BV‐2 cells following lipopolysaccharide (LPS) stimulation. In addition, NBP reduced the activation of BV‐2 cells, diminished the release of inflammatory mediators, and inhibited microglial TLR4/NF‐κB expression in BV‐2 cells. Our findings demonstrate that NBP may have neuroprotective and anti‐inflammatory properties in the treatment of SCI by inhibiting the activation of microglia via TLR4/NF‐κB signalling.     

Role of age and neuroinflammation in the mechanism of cognitive deficits in sickle cell disease

This study aims to determine whether sickle cell mice could recapitulate features of cognitive and neurobehavioral impairment observed in sickle cell patients and whether neuroinflammation could be a potential therapeutic target as in other non-sickle cell disease-related cognitive dysfunction. Cognitive (learning and memory) and behavioral (anxiety) deficits in 13- and later 6-month-old male Townes humanized sickle cell (SS) and matched control (AA) mice were evaluated using novel object recognition (NOR) and fear conditioning tests. Immunohistochemistry was performed to quantify peripheral immune cell (CD45⁺) and activated microglia (Iba1⁺) as markers of neuroinflammation in the dentate and peri-dentate gyrus areas. We evaluated cell fate by measuring 5''-bromodeoxyuridine and doublecortin fluorescence and phenotyped proliferating cells using either glial fibrillary acid protein (GFAP⁺), neuronal nuclei (NeuN⁺), CD45⁺, and Iba1⁺. In addition, Golgi-Cox staining was used to assess markers of neuroplasticity (dendritic spine density and morphology and density of dendrite arbors) on cortical and hippocampal pyramidal neurons. Compared to matched AA controls, 13-month-old SS mice showed significant evidence of cognitive and behavioral deficit on NOR and fear conditioning tests. Also, SS mice had significantly higher density of CD45⁺ and activated microglia cells (i.e. more evidence of neuroinflammation) in the dentate and peri-dentate gyrus area. Additionally, SS mice had significantly lower dendritic spine density, but a higher proportion of immature dendritic spines. Treatment of 13-month-old SS mice with minocycline resulted in improvement of cognitive and behavioral deficit compared to matched vehicle-treated SS mice. Also, treated SS mice had significantly fewer CD45⁺ and activated microglia cells (i.e. less evidence of neuroinflammation) in the dentate and peri-dentate gyrus, as well as a significant improvement in markers of neuroplasticity.Impact statementThis study provides crucial information that could be helpful in the development of new or repurposing of existing therapies for the treatment of cognitive deficit in individuals with sickle cell disease (SCD). Its impact is in demonstrating for the first time that neuroinflammation and along with abnormal neuroplasticity are among the underlying mechanism of cognitive and behavioral deficits in SCD and that drugs such as minocycline which targets these pathophysiological mechanisms could be repurposed for the treatment of this life altering complication of SCD.     

两种诊断方法对术后认知功能障碍评估分析

目的：探讨更有利于术后认知功能障碍早期诊断的评估方法。方法：选择青年患者（18-45岁）60例,ASAⅠ～Ⅱ级,在全凭静脉麻醉或椎管内麻醉下行手术;青年健康志愿者30例为对照组,术前一天（T1）,术后3天（T2）行认知功能6项测定。所得结果分别采用1个标准差法（SD）和Z计分法对术后认知功能进行评定。P＆lt;0.05差异有统计学意义。结果：术后3天,依据SD法诊断认知功能受损25/90例（27.8%）,术后认知功能障碍2/90例（2.2%）,Z计分法认知受损18/90（20%）例,认知障碍3/90例（3.3%）,两种诊断方法之间差异无统计学意义（P＆gt;0.05）。经K系数检验,SD法与Z计分法诊断吻合度无统计学意义（kappa=0.000,P＆gt;0.05）。结论：两种评估方法同时进行评估,可以弥补相互不足,较大程度地避免了术后认知功能受损假阴性的诊断,更有利于术后认知功能障碍的早期发现。     

A comparison of the high-affinity peripheral benzodiazepine receptor ligands DAA1106 and (R)-PK11195 in rat models of neuroinflammation: implications for PET imaging of microglial activation

Activated microglia are an important feature of many neurological diseases and can be imaged in vivo using 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide (PK11195), a ligand that binds the peripheral benzodiazepine receptor (PBR). N-(2,5-dimethoxybenzyl)-N-(5-fluoro-2-phenoxyphenyl) acetamide (DAA1106) is a new PBR-specific ligand that has been reported to bind to PBR with higher affinity compared with PK11195. We hypothesized that this high-affinity binding of DAA1106 to PBR will enable better delineation of microglia in vivo using positron emission tomography. [(3)H]DAA1106 showed higher binding affinity compared with [(3)H](R)-PK11195 in brain tissue derived from normal rats and the rats injected intrastriatally with 6-hydroxydopamine or lipopolysaccharide at the site of the lesion. Immunohistochemistry combined with autoradiography in brain tissues as well as correlation analyses showed that increased [(3)H]DAA1106 binding corresponded mainly to activated microglia. Finally, ex vivo autoradiography and positron emission tomography imaging in vivo showed greater retention of [(11)C]DAA1106 compared with [(11)C](R)-PK11195 in animals injected with either lipopolysaccaride or 6-hydroxydopamine at the site of lesion. These results indicate that DAA1106 binds with higher affinity to microglia in rat models of neuroinflammation when compared with PK11195, suggesting that [(11)C]DAA1106 may represent a significant improvement over [(11)C](R)-PK11195 for in vivo imaging of activated microglia in human neuroinflammatory disorders.