Expression and localization of the iron-siderophore binding protein lipocalin 2 in the normal rat brain and after kainate-induced excitotoxicity

Lipocalin 2 (LCN2) is produced by mammalian hosts to bind bacterial siderophore and sequester free iron as part of an innate immune response, and could also play a role in tissue iron homeostasis, but thus far, little is known about its expression in the CNS. The present study was carried out to study the expression of the lipocalin in the normal rat brain and after neuronal injury induced by kainate (KA). Low levels of LCN2 mRNA and protein expression were detected in most regions of the normal brain except the olfactory bulb, brainstem and cerebellum. KA lesions resulted in damage to the hippocampus, leading to an early increase at three days and a sustained elevation in LCN2 mRNA level of 16-fold, and protein expression at 80-fold in the lesioned tissue compared to controls at 2 weeks post-KA injection. The sustained elevation in mRNA expression was not detected among other lipocalins surveyed using real-time RT-PCR - apoD, PGDS, Rbp4 and LCN5. Single and double immunostaining confirmed that LCN2 is present in astrocytes in the olfactory bulb, brainstem and cerebellum of the normal brain, and reactive astrocytes in the KA-lesioned hippocampus. In conclusion, the present study showed LCN2 to be present in select brain regions, and is upregulated in astrocytes after neuronal injury induced by kainate. We postulate that, as in the periphery, LCN2 may have a role in iron transport or trafficking in the CNS.     

Increased microglial activation and astrogliosis after intranasal administration of kainic acid in C57BL/6 mice

Glutamate excitotoxicity plays a key role in inducing neuronal cell death in many neurological diseases. In mice, intranasal administration of kainic acid (KA), an analogue of the excitotoxin glutamate, results in hippocampal cell death and provides a well-characterized model for studies of human neurodegenerative diseases. In this study, we describe neurodegeneration and gliosis following intranasal administration of KA in C57BL/6 mice. By using Nissl's staining, neurodegeneration was found in area CA3 of hippocampus, and neuronal apoptosis was demonstrated by enhanced FAS(CD95/APO-1) expression detected by immunohistochemistry and Western blotting. Astrogliosis was exhibited by increased glial fibrillary acidic protein (GFAP) expression in the hippocampus and cortex. We also studied the profile of molecular expression on microglia in C57BL/6 mice. One and 3 days after KA administration, CD45, F4/80, CD86, MHCII, iNOS but not CD40 expression was enhanced or induced on microglia. In summary, KA administration results in an early microglial activation and a prolonged astrogliosis in C57BL/6 mice.     

Proteolytic fragments of laminin promote excitotoxic neurodegeneration by up-regulation of the KA1 subunit of the kainate receptor

Degradation of the extracellular matrix (ECM) protein laminin contributes to excitotoxic cell death in the hippocampus, but the mechanism of this effect is unknown. To study this process, we disrupted laminin γ1 (lamγ1) expression in the hippocampus. Lamγ1 knockout (KO) and control mice had similar basal expression of kainate (KA) receptors, but the lamγ1 KO mice were resistant to KA-induced neuronal death. After KA injection, KA1 subunit levels increased in control mice but were unchanged in lamγ1 KO mice. KA1 levels in tissue plasminogen activator (tPA)–KO mice were also unchanged after KA, indicating that both tPA and laminin were necessary for KA1 up-regulation after KA injection. Infusion of plasmin-digested laminin-1 into the hippocampus of lamγ1 or tPA KO mice restored KA1 up-regulation and KA-induced neuronal degeneration. Interfering with KA1 function with a specific anti-KA1 antibody protected against KA-induced neuronal death both in vitro and in vivo. These results demonstrate a novel pathway for neurodegeneration involving proteolysis of the ECM and KA1 KA receptor subunit up-regulation.     

Role of Lipocalin-2-Chemokine Axis in the Development of Neuropathic Pain following Peripheral Nerve Injury

Lipocalin 2 (LCN2), which is also known as 24p3 and neutrophil gelatinase-associated lipocalin (NGAL), binds small, hydrophobic ligands and interacts with cell surface receptor 24p3R to regulate diverse cellular processes. In the present study, we examined the role of LCN2 in the pathogenesis of neuropathic pain using a mouse model of spared nerve injury (SNI). Lcn2 mRNA levels were significantly increased in the dorsal horn of the spinal cord after SNI, and LCN2 protein was mainly localized in neurons of the dorsal and ventral horns. LCN2 receptor 24p3R was expressed in spinal neurons and microglia after SNI. Lcn2-deficient mice exhibited significantly less mechanical pain hypersensitivity during the early phase after SNI, and an intrathecal injection of recombinant LCN2 protein elicited mechanical pain hypersensitivity in naive animals. Lcn2 deficiency, however, did not affect acute nociceptive pain. Lcn2-deficient mice showed significantly less microglial activation and proalgesic chemokine (CCL2 and CXCL1) production in the spinal cord after SNI than wild-type mice, and recombinant LCN2 protein induced the expression of these chemokines in cultured neurons. Furthermore, the expression of LCN2 and its receptor was detected in neutrophils and macrophages in the sciatic nerve following SNI, suggesting the potential role of peripheral LCN2 in neuropathic pain. Taken together, our results indicate that LCN2 plays a critical role in the development of pain hypersensitivity following peripheral nerve injury and suggest that LCN2 mediates neuropathic pain by inducing chemokine expression and subsequent microglial activation.     

Lipocalin 2-mediated growth suppression is evident in human erythroid and monocyte/macrophage lineage cells

Lipocalin 2 (LCN2), a secreted protein of the lipocalin family, induces apoptosis in some types of cells and inhibits bacterial growth by sequestration of the iron-laden bacterial siderophore. We have recently reported that LCN2 inhibits the production of red blood cells in the mouse. Here we analyzed the role of LCN2 in human hematopoiesis. Expression of LCN2 was observed not only in mature cells such as those of the granulocyte/macrophage and erythroid lineages but also in hematopoietic stem/progenitor cells. We also examined expression of two candidate receptors for LCN2, brain type organic cation transporter (BOCT) and megalin, in various cell types. BOCT showed relatively high levels of expression in erythroid and hematopoietic stem/progenitor cells but lower levels in granulocyte/macrophage and T lymphoid cells. Megalin was expressed at high levels in T lymphoid and erythroid cells but at lower levels in granulocyte/macrophage lineage cells. LCN2 suppressed the growth of erythroid and monocyte/macrophage lineages in vitro, but did not have this effect on cells of other lineages. In addition, immature hematopoietic stem/progenitor cells were not sensitive to LCN2. These results demonstrate a lineage-specific role for LCN2 in human hematopoiesis that is reminiscent of its effects upon mouse hematopoiesis and strongly suggest an important in vivo function of LCN2 in the regulation of human hematopoiesis.     

NOX activation in reactive astrocytes regulates astrocytic LCN2 expression and neurodegeneration

Reactive astrocytes (RA) secrete lipocalin-2 (LCN2) glycoprotein that regulates diverse cellular processes including cell death/survival, inflammation, iron delivery and cell differentiation. Elevated levels of LCN2 are considered as a biomarker of brain injury, however, the underlying regulatory mechanisms of its expression and release are not well understood. In this study, we investigated the role of astrocytic Na⁺/H⁺ exchanger 1 (NHE1) in regulating reactive astrocyte LCN2 secretion and neurodegeneration after stroke. Astrocyte specific deletion of Nhe1 in Gfap-Cre^ER+/−;Nhe1^f/f mice reduced astrogliosis and astrocytic LCN2 and GFAP expression, which was associated with reduced loss of NeuN⁺ and GRP78⁺ neurons in stroke brains. In vitro ischemia in astrocyte cultures triggered a significant increase of secreted LCN2 in astrocytic exosomes, which caused neuronal cell death and neurodegeneration. Inhibition of NHE1 activity during in vitro ischemia with its potent inhibitor HOE642 significantly reduced astrocytic LCN2⁺ exosome secretion. In elucidating the cellular mechanisms, we found that stroke triggered activation of NADPH oxidase (NOX)-NF-κB signaling and ROS-mediated LCN2 expression. Inhibition of astrocytic NHE1 activity attenuated NOX signaling and LCN2-mediated neuronal apoptosis and neurite degeneration. Our findings demonstrate for the first time that RA use NOX signaling to stimulate LCN2 expression and secretion. Blocking astrocytic NHE1 activity is beneficial to reduce LCN2-mediated neurotoxicity after stroke.Subject terms: Cell death in the nervous system, Astrocyte     

Expression and changes of endogenous insulin-like growth factor-1 in neurons and glia in the gerbil hippocampus and dentate gyrus after ischemic insult

In the present study, we focused upon expression and changes of endogenous insulin-like growth factor-1 (IGF-1) in the hippocampus of the Mongolian gerbil after ischemic insult. In sham-operated animals, IGF-1 immunoreactivity was absent from the hippocampus. IGF-1-immunoreactive (IR) neurons were detected at 12 h and 1 day after ischemic insult. In the hippocampal CA1 area, the IGF-IR neurons were non-pyramidal cells (GABAergic neurons). In the hippocampal CA2/3 areas, the IGF-1-IR neurons were pyramidal and non-pyramidal cells, and in the dentate gyrus the IGF-1-IR neurons were hilar neurons. Four days after ischemia-reperfusion, IGF-1 immunoreactivity disappeared from neurons, and significantly increased in astrocytes and microglia. These results suggest that the induction of IGF-1 in the CA1 area during the early stage (12-24 h after ischemic insult) is associated with the relative vulnerabilities of pyramidal glutamatergic neurons and non-pyramidal GABAergic neurons. The later increase (4 days after ischemic insult) of IGF-1 expression and protein content was found to promote the activities of astrocytes and microglia. These increases of IGF-1 in astrocytes and in microglia are associated with mechanisms that compensate for the effects of delayed neuronal death.     

小胶质细胞活化对癫痫发病的影响

目的探讨抑制小胶质细胞活化对癫痫发作的影响及对脑神经元的保护作用。方法将大鼠随机分为4组：生理盐水对照组（NS组）,海人酸致痫组（KA组）,美满霉素预处理＋海人酸组（MC＋KA组）,单纯美满霉素组（MC组）。采用免疫组化法观察各组大鼠造模后脑内Ox-42、c—fos和caspase-3免疫反应性。RT—PCR或Westernblot法检测造模后Apaf-1mRNA含量和caspase-3蛋白表达量。结果在KA致痫后2h大脑皮质及海马部位有明显的小胶质细胞活化、增殖,同时C—los蛋白的表达在致痫组也较对照组显著增强,Mc干预致痫组可明显减弱上述效应。Apaf-1mRNA的含量及caspase-3蛋白含量和免疫反应在造模后24h时间点四组之间无明显差异,在48h和72h时间点,KA组明显高于对照组（P〈0．05）,MC预处理则明显拮抗其高表达（P〈O．05）。结论KA致痫不仅通过提高神经元的兴奋性而且也通过激活小胶质细胞共同导致癫痫发作,二者相互协同作用,可进一步促进神经元凋亡,而MC能通过抑制小胶质细胞活化在癫痫中发挥神经保护作用。     

Lipocalin-2 Protein Deficiency Ameliorates Experimental Autoimmune Encephalomyelitis: THE PATHOGENIC ROLE OF LIPOCALIN-2 IN THE CENTRAL NERVOUS SYSTEM AND PERIPHERAL LYMPHOID TISSUES*

Lipocalin-2 (LCN2) plays an important role in cellular processes as diverse as cell growth, migration/invasion, differentiation, and death/survival. Furthermore, recent studies indicate that LCN2 expression and secretion by glial cells are induced by inflammatory stimuli in the central nervous system. The present study was undertaken to examine the regulation of LCN2 expression in experimental autoimmune encephalomyelitis (EAE) and to determine the role of LCN2 in the disease process. LCN2 expression was found to be strongly increased in spinal cord and secondary lymphoid tissues after EAE induction. In spinal cords astrocytes and microglia were the major cell types expressing LCN2 and its receptor 24p3R, respectively, whereas in spleens, LCN2 and 24p3R were highly expressed in neutrophils and dendritic cells, respectively. Furthermore, disease severity, inflammatory infiltration, demyelination, glial activation, the expression of inflammatory mediators, and the proliferation of MOG-specific T cells were significantly attenuated in Lcn2-deficient mice as compared with wild-type animals. Myelin oligodendrocyte glycoprotein-specific T cells in culture exhibited an increased expression of Il17a, Ifng, Rorc, and Tbet after treatment with recombinant LCN2 protein. Moreover, LCN2-treated glial cells expressed higher levels of proinflammatory cytokines, chemokines, and MMP-9. Adoptive transfer and recombinant LCN2 protein injection experiments suggested that LCN2 expression in spinal cord and peripheral immune organs contributes to EAE development. Taken together, these results imply LCN2 is a critical mediator of autoimmune inflammation and disease development in EAE and suggest that LCN2 be regarded a potential therapeutic target in multiple sclerosis.     

Induction of heme oxygenase-1 in the rat brain by kainic acid-mediated excitotoxicity: the dissociation of mRNA and protein expression in hippocampus.

Heme oxygenase-1 (HO-1) is induced under various stresses. Here we report the induction and localization of HO-1 in the rat brain by intraperitoneal administration of kainic acid (KA). Both mRNA and protein of HO-1 were markedly induced by KA treatment, and each maximal induction was observed 24 h after KA administration. In situ hybridization analysis showed that HO-1 mRNA appeared predominantly in glial cells, and confined neurons were positive in the cerebral cortex, basal ganglia, and hippocampal pyramidal cell layer. Immunohistochemical analysis showed that the positive cells in the cerebral cortex and hippocampus were mainly astrocytes and microglia, whereas neurons in the basal ganglia showed intense immunoreactivity. We also demonstrate the dissociation between HO-1 mRNA and protein level in the hippocampal pyramidal neurons, which is known to be vulnerable against excitotoxicity, and discuss the correlation between this dissociation and the vulnerability of hippocampal pyramidal neurons.     

Altered mRNA editing and expression of ionotropic glutamate receptors after kainic acid exposure in cyclooxygenase-2 deficient mice

Kainic acid (KA) binds to the AMPA/KA receptors and induces seizures that result in inflammation, oxidative damage and neuronal death. We previously showed that cyclooxygenase-2 deficient (COX-2(-/-)) mice are more vulnerable to KA-induced excitotoxicity. Here, we investigated whether the increased susceptibility of COX-2(-/-) mice to KA is associated with altered mRNA expression and editing of glutamate receptors. The expression of AMPA GluR2, GluR3 and KA GluR6 was increased in vehicle-injected COX-2(-/-) mice compared to wild type (WT) mice in hippocampus and cortex, whereas gene expression of NMDA receptors was decreased. KA treatment decreased the expression of AMPA, KA and NMDA receptors in the hippocampus, with a significant effect in COX-2(-/-) mice. Furthermore, we analyzed RNA editing levels and found that the level of GluR3 R/G editing site was selectively increased in the hippocampus and decreased in the cortex in COX-2(-/-) compared with WT mice. After KA, GluR4 R/G editing site, flip form, was increased in the hippocampus of COX-2(-/-) mice. Treatment of WT mice with the COX-2 inhibitor celecoxib for two weeks decreased the expression of AMPA/KA and NMDAR subunits after KA, as observed in COX-2(-/-) mice. After KA exposure, COX-2(-/-) mice showed increased mRNA expression of markers of inflammation and oxidative stress, such as cytokines (TNF-α, IL-1β and IL-6), inducible nitric oxide synthase (iNOS), microglia (CD11b) and astrocyte (GFAP). Thus, COX-2 gene deletion can exacerbate the inflammatory response to KA. We suggest that COX-2 plays a role in attenuating glutamate excitotoxicity by modulating RNA editing of AMPA/KA and mRNA expression of all ionotropic glutamate receptor subunits and, in turn, neuronal excitability. These changes may contribute to the increased vulnerability of COX-2(-/-) mice to KA. The overstimulation of glutamate receptors as a consequence of COX-2 gene deletion suggests a functional coupling between COX-2 and the glutamatergic system.     

LncRNA-UCA1 inhibits the astrocyte activation in the temporal lobe epilepsy via regulating the JAK/STAT signaling pathway

This article aimed to reveal the mechanism of long noncoding RNA (lncRNA) urothelial cancer-associated 1 (UCA1) regulated astrocyte activation in temporal lobe epilepsy (TLE) rats via mediating the activation of the JAK/STAT signaling pathway. A model of TLE was established based on rats via kainic acid (KA) injection. All rats were divided into the Sham group (without any treatments), KA group, normal control (NC; injection with empty vector) + KA group, and UCA1 + KA group. The Morris water maze was used to test the learning and memory ability of rats, and the expression of UCA1 in the hippocampus was determined by quantitative real time polymerase chain reaction (qRT-PCR). Surviving neurons were counted by Nissl staining, and expression levels of glial cells glial fibrillary acidic protein (GFAP), p-JAK1, and p-STAT3 and glutamate/aspartate transporter (GLAST) were analyzed by immunofluorescence and Western blot analysis. A rat model of TLE was established by intraperitoneal injection of KA. qRT-PCR and fluorescence analyses showed that UCA1 inhibited astrocyte activation in the hippocampus of epileptic rats. Meanwhile, the Morris water maze analysis indicated that UCA1 improved the learning and memory in epilepsy rats. Moreover, the Nissl staining showed that UCA1 might have a protective effect on neuronal injury induced by KA injection. Furthermore, the immunofluorescence and Western blot analysis revealed that the overexpression of UCA1 inhibited KA-induced abnormal elevation of GLAST, astrocyte activation of the JAK/STAT signaling pathway, as well as hippocampus of epilepsy rats. UCA1 inhibited hippocampal astrocyte activation and JAK/STAT/GLAST expression in TLE rats and improved the adverse reactions caused by epilepsy.     

Systemic Administration of Lipopolysaccharide Induces Cyclooxygenase-2 Immunoreactivity in Endothelium and Increases Microglia in the Mouse Hippocampus

In this study, we observed the effects of lipopolysaccharide (LPS) on neurodegeneration and immune response in the hippocampus. LPS is a gram-negative bacterial cell surface proteoglycan and known as a bacterial endotoxin. For this, we investigated the optimal concentration of LPS influencing the ICR mouse hippocampus to measure the LPS receptor, e.g., toll-like receptor 4 (TLR4), expression in mouse hippocampal homogenates. TLR4 expression was significantly and prominently increased in the hippocampal homogenates of the LPS (1 mg/kg)-treated group. Next, we examined pro-inflammatory response in the hippocampus using cyclooxygenase-2 (COX-2, a marker for inflammatory response) immunohistochemistry after LPS treatment. COX-2 immunoreactivity was significantly increased in the endothelium of blood vessels in the hippocampus 6 h after LPS treatment, judging from double immunofluorescence study with platelet-derived endothelial cell adhesion molecule-1 (PECAM-1, a marker for endothelial cells): it decreased 12 h and disappeared 24 h after LPS treatment. In addition, the ionized calcium-binding adapter molecule 1 (Iba-1)-immunoreactive (⁺) microglia were morphologically activated in the mouse hippocampus after LPS treatment. At 24 h after LPS treatment, Iba-1⁺ microglia of activated forms were abundant in the hippocampus. However, NeuN (a neuron-specific soluble nuclear antigen)⁺ neurons were not significantly changed in the hippocampus after LPS treatment. Fluoro-jade B (a marker for neuronal degeneration)⁺ cells were not detected in the hippocampus at any time after LPS treatment. In addition, there were no significant differences in permeability of blood–brain barriers at any time points after LPS treatment. In brief, our results indicate that intraperitoneal administration of 1 mg/kg LPS effectively induces LPS receptor (TLR4) expression in the hippocampus, and the treatment increases corticosterone levels, inflammation in the blood vessels, and microglial activation in the hippocampus without any neuronal damage.     

Prosaposin Overexpression following Kainic Acid-Induced Neurotoxicity

Because excessive glutamate release is believed to play a pivotal role in numerous neuropathological disorders, such as ischemia or seizure, we aimed to investigate whether intrinsic prosaposin (PS), a neuroprotective factor when supplied exogenously in vivo or in vitro, is up-regulated after the excitotoxicity induced by kainic acid (KA), a glutamate analog. In the present study, PS immunoreactivity and its mRNA expression in the hippocampal and cortical neurons showed significant increases on day 3 after KA injection, and high PS levels were maintained even after 3 weeks. The increase in PS, but not saposins, detected by immunoblot analysis suggests that the increase in PS-like immunoreactivity after KA injection was not due to an increase in saposins as lysosomal enzymes after neuronal damage, but rather to an increase in PS as a neurotrophic factor to improve neuronal survival. Furthermore, several neurons with slender nuclei inside/outside of the pyramidal layer showed more intense PS mRNA expression than other pyramidal neurons. Based on the results from double immunostaining using anti-PS and anti-GABA antibodies, these neurons were shown to be GABAergic interneurons in the extra- and intra-pyramidal layers. In the cerebral cortex, several large neurons in the V layer showed very intense PS mRNA expression 3 days after KA injection. The choroid plexus showed intense PS mRNA expression even in the normal rat, and the intensity increased significantly after KA injection. The present study indicates that inhibitory interneurons as well as stimulated hippocampal pyramidal and cortical neurons synthesize PS for neuronal survival, and the choroid plexus is highly activated to synthesize PS, which may prevent neurons from excitotoxic neuronal damage. To the best of our knowledge, this is the first study that demonstrates axonal transport and increased production of neurotrophic factor PS after KA injection.     

Erratum to: Corticosterone Induces Dysregulation of Iron Metabolism in Hippocampal Neurons In Vitro

Iron is required for neuronal function but in excess generates neurodegeneration. Although the iron homeostasis machinery in neurons has been described extensively, little is known about the influence of corticosterone on the iron homeostasis in neurons. In this study, we characterized the response of hippocampal neurons to a model of progressive corticosterone condition. We found that increasing extracellular corticosterone-induced iron accumulation killed a large proportion of neurons. Iron concentrations were significantly increased in the corticosterone-treated cells. In the hippocampal neurons, corticosterone decreased expression of ferritin and increased expression of transferrin receptor1 (TfR1), iron regulatory protein1 (IRP1), and divalent metal transporter 1. Corticosterone-induced elevation of IRP1 expression can cause increase of TfR1 and decrease of ferritin expression, which further leads to iron accumulation in hippocampal neurons and subsequently increases the oxidative damage of the neurons; it is indicated that corticosterone might be an important reason for iron deposition-caused neurodegenerative diseases.     

Corticosterone Induces Dysregulation of Iron Metabolism in Hippocampal Neurons In Vitro

Iron is required for neuronal function but in excess generates neurodegeneration. Although the iron homeostasis machinery in neurons has been described extensively, little is known about the influence of corticosterone on the iron homeostasis in neurons. In this study, we characterized the response of hippocampal neurons to a model of progressive corticosterone condition. We found that increasing extracellular corticosterone-induced iron accumulation killed a large proportion of neurons. Iron concentrations were significantly increased in the corticosterone-treated cells. In the hippocampal neurons, corticosterone decreased expression of ferritin and increased expression of transferrin receptor1 (TfR1), iron regulatory protein1 (IRP1), and divalent metal transporter 1. Corticosterone-induced elevation of IRP1 expression can cause increase of TfR1 and decrease of ferritin expression, which further leads to iron accumulation in hippocampal neurons and subsequently increases the oxidative damage of the neurons; it is indicated that corticosterone might be an important reason for iron deposition-caused neurodegenerative diseases.     

TRP 对KA 诱导的AD 模型大鼠学习记忆的影响及其作用机制

目的:观察雷公藤甲素(Triptolide,TRP)对海人藻酸(Kainic acid,KA)海马内注射后大鼠学习记忆的影响及其作用机制。方法:采用Morris水迷宫筛选空间学习记忆能力正常的SD雄性大鼠90只(200～220g)。将实验动物分成3组:右侧海马注射生理盐水后生理盐水灌胃对照组(NS+NS)、右侧海马注射海人藻酸后生理盐水灌胃干预组(KA+NS)、右侧海马注射海人藻酸后雷公藤甲素灌胃干预组(KA+TRP)。动物存活1天,3天,5天,7天,14天,每个时间点6只,处死前分别于各相应时间点用Morris水迷宫检测各组动物空间位置记忆能力;免疫组织化学方法结合图像分析技术检测海马CA1区神经元COX-2的表达。结果:与NS组(NS+NS)比较,KA组(KA+NS)大鼠逃避潜伏期延长(P<0.05),跨越原平台次数减少(P<0.05);海马CA1区的神经元COX-2表达升高(P<0.05);TRP组(TRP+KA)与KA组比较,大鼠的平均逃避潜伏期从第5天起缩短(P<0.05),跨越原平台次数增多(P<0.05),海马CA1区神经元COX-2表达在5天,7天时下调(P<0.05)。结论:KA海马内注射,可以导致大鼠学习记忆功能障碍及上调海马CA1区神经元COX-2表达;雷公藤甲素干预治疗,能够改善动物的学习和记忆能力,能抑制KA诱导的海马CAl区神经元COX-2的表达。     

Phenolic antioxidants attenuate hippocampal neuronal cell damage against kainic acid induced excitotoxicity

Increasing evidence supports the role of excitotoxicity in neuronal cell injury. Thus, it is extremely important to explore methods to retard or reverse excitotoxic neuronal injury. In this regard, certain dietary compounds are beginning to receive increased attention, in particular those involving phytochemicals found in medicinal plants in alleviating neuronal injury. In the present study, we examined whether medicinal plant extracts protect neurons against excitotoxic lesions induced by kainic acid (KA) in female Swiss albino mice. Mice were anesthetized with ketamine and xylazine (200 mg and 2 mg/kg body wt. respectively) and KA (0.25 microg in a volume of 0.5 microl) was administered to mice by intra hippocampal injections. The results showed an impairment of the hippocampus region of brain after KA injection. The lipid peroxidation and protein carbonyl content were significantly (P < 0.05) increased in comparison to controls. Glutathione peroxidase (GPx) activity (EC 1.11.1.9) and reduced glutathione (GSH) content declined after appearance of excitotoxic lesions. As GPx and GSH represent a major pathway in the cell for metabolizing hydrogen peroxide (H2O2), their depletion would be expected to allow H2O2 to accumulate to toxic levels. Dried ethanolic plant extracts of Withania somnifera (WS), Convolvulus pleuricauas (CP) and Aloe vera (AV) dissolved in distilled water were tested for their total antioxidant activity. The diet was prepared in terms of total antioxidant activity of plant extracts. The iron (Fe3+) reducing activity of plant extracts was also tested and it was found that WS and AV were potent reductants of Fe3+ at pH 5 5. CP had lower Fe3+ reducing activity in comparison to WS and AV. Plant extracts given singly and in combination 3 weeks prior to KA injections resulted in a decrease in neurotoxicity. Measures of lipid peroxidation and protein carbonyl declined. GPx activity and GSH content were elevated in hippocampus supplemented with WS and combination of WS + CP + AV. However, when CP and AV were given alone, the changes in the GPx activity and GSH content were not significant. Although the major factors involved in these properties of phytochemicals remain to be specified, the finding of this study has suggested that phytochemicals present in plant extracts mitigate the effects of excitotoxicity and oxidative damage in hippocampus and this might be accomplished by their antioxidative properties.     

Microglial Toll-like receptor 2 contributes to kainic acid-induced glial activation and hippocampal neuronal cell death

Recent studies indicate that Toll-like receptors (TLRs), originally identified as infectious agent receptors, also mediate sterile inflammatory responses during tissue damage. In this study, we investigated the role of TLR2 in excitotoxic hippocampal cell death using TLR2 knock-out (KO) mice. TLR2 expression was up-regulated in microglia in the ipsilateral hippocampus of kainic acid (KA)-injected mice. KA-mediated hippocampal cell death was significantly reduced in TLR2 KO mice compared with wild-type (WT) mice. Similarly, KA-induced glial activation and proinflammatory gene expression in the hippocampus were compromised in TLR2 KO mice. In addition, neurons in organotypic hippocampal slice cultures (OHSCs) from TLR2 KO mouse brains were less susceptible to KA excitotoxicity than WT OHSCs. This protection is partly attributed to decreased expression of proinflammatory genes, such as TNF-α and IL-1β in TLR2 KO mice OHSCs. These data demonstrate conclusively that TLR2 signaling in microglia contributes to KA-mediated innate immune responses and hippocampal excitotoxicity.