Enhanced IL‐1β production in response to the activation of hippocampal glial cells impairs neurogenesis in aged mice

A variety of mechanisms that contribute to the accumulation of age‐related damage and the resulting brain dysfunction have been identified. Recently, decreased neurogenesis in the hippocampus has been recognized as one of the mechanisms of age‐related brain dysfunction. However, the molecular mechanism of decreased neurogenesis with aging is still unclear. In the present study, we investigated whether aging decreases neurogenesis accompanied by the activation of microglia and astrocytes, which increases the expression of IL‐1β in the hippocampus, and whether in vitro treatment with IL‐1β in neural stem cells directly impairs neurogenesis. Ionized calcium‐binding adaptor molecule 1 (Iba1)‐positive microglia and glial fibrillary acidic protein (GFAP)‐positive astrocytes were increased in the dentate gyrus of the hippocampus of 28‐month‐old mice. Furthermore, the mRNA level of IL‐1β was significantly increased without related histone modifications. Moreover, a significant increase in lysine 9 on histone H3 (H3K9) trimethylation at the promoter of NeuroD (a neural progenitor cell marker) was observed in the hippocampus of aged mice. In vitro treatment with IL‐1β in neural stem cells prepared from whole brain of E14.5 mice significantly increased H3K9 trimethylation at the NeuroD promoter. These findings suggest that aging may decrease hippocampal neurogenesis via epigenetic modifications accompanied by the activation of microglia and astrocytes with the increased expression of IL‐1β in the hippocampus. Synapse 64:721–728, 2010. © 2010 Wiley‐Liss, Inc.     

Tumor necrosis factor‐α potentiates long‐term potentiation in the rat dentate gyrus after acute hypoxia

An inadequate supply of oxygen in the brain may lead to an inflammatory response through neuronal and glial cells that can result in neuronal damage. Tumor necrosis factor‐α (TNF‐α) is a proinflammatory cytokine that is released during acute hypoxia and can have neurotoxic or neuroprotective effects in the brain. Both TNF‐α and interleukin‐1β (IL‐1β) have been shown by a number of research groups to alter synaptic scaling and also to inhibit long‐term potentiation (LTP) in the hippocampus when induced by specific high‐frequency stimulation (HFS) protocols. This study examines the effects of TNF‐α on synaptic transmission and plasticity in hippocampal slices after acute hypoxia using two HFS protocols. Field excitatory postsynaptic potentials were elicited in the medial perforant pathway of the dentate gyrus. Exogenous TNF‐α (5 ng/ml) attenuated LTP induced by theta burst stimulation but had no effect on LTP induced by a more prolonged HFS. Pretreatment with lipopolysaccharide (100 ng/ml) or TNF‐α but not IL‐1β (4 ng/ml) prior to a 30‐min hypoxic insult resulted in a significant enhancement of LTP post hypoxia when induced by the HFS. Anti‐TNF, 3,6′‐dithiothalidomide (a TNF‐α synthesis inhibitor), and SB203580 (a p38 MAPK inhibitor) significantly reduced this effect. These results indicate an important modulatory role for elevated TNF‐α levels on LTP in the hippocampus after an acute hypoxic event. © 2015 Wiley Periodicals, Inc.     

Involvement of cathepsin B in the processing and secretion of interleukin‐1β in chromogranin A‐stimulated microglia

Cathepsin B (CB) is a cysteine lysosomal protease implicated in a number of inflammatory diseases. Although it is now evident that caspase‐1, an essential enzyme for maturation of interleukin‐1β (IL‐1β), can be activated through the inflammasome, there is still evidence suggesting the existence of lysosomal‐proinflammatory caspase pathways. In the present study, a marked induction of pro‐IL‐1β, its processing to the mature form and secretion were observed in the primary cultured microglia prepared from wild‐type mice after stimulation with chromogranin A (CGA). Although pro‐IL‐1β also markedly increased in microglia prepared from CB‐deficient mice, CB‐deficiency abrogated the pro‐IL‐1β processing. CA‐074Me, a specific inhibitor for CB, inhibited the pro‐IL‐1β maturation and its release from microglia. Furthermore, the caspase‐1 activation was also inhibited by CA‐074Me and E‐64d, a broad cysteine protease inhibitor. After treatment with CGA, CB was markedly induced at both protein and mRNA levels. The induced pro‐CB was rapidly processed to its mature form. The immunoreactivity for CB co‐localized with both that for caspase‐1 and the cleaved IL‐1β, in the acidic enlarged lysosomes. Inconsistent with these in vitro observations, the immunoreactivity for the cleaved IL‐1β was markedly observed in microglia of the hippocampus from aged wild‐type but not CB‐deficient mice. These observations strongly suggest that CB plays a key role in the pro‐IL‐1β maturationthrough the caspase‐1 activation in enlarged lysosomes ofCGA‐treated microglia. Therefore, either pharmacological or genetic inhibition of CB may provide therapeutic intervention in inflammation‐associated neurological diseases. © 2009 Wiley‐Liss, Inc.     

NMDA receptor–dependent signaling pathways that underlie amyloid β‐protein disruption of LTP in the hippocampus

Alzheimer's disease (AD), the most common neurodegenerative disease in the elderly population, is characterized by the hippocampal deposition of fibrils formed by amyloid β‐protein (Aβ), a 40‐ to 42‐amino‐acid peptide. The folding of Aβ into neurotoxic oligomeric, protofibrillar, and fibrillar assemblies is believed to mediate the key pathologic event in AD. The hippocampus is especially susceptible in AD and early degenerative symptoms include significant deficits in the performance of hippocampal‐dependent cognitive abilities such as spatial learning and memory. Transgenic mouse models of AD that express C‐terminal segments or mutant variants of amyloid precursor protein, the protein from which Aβ is derived, exhibit age‐dependent spatial memory impairment and attenuated long‐term potentiation (LTP) in the hippocampal CA1 and dentate gyrus (DG) regions. Recent experimental evidence suggests that Aβ disturbs N‐methyl‐D ‐aspartic acid (NMDA) receptor–dependent LTP induction in the CA1 and DG both in vivo and in vitro. Furthermore, these studies suggest that Aβ specifically interferes with several major signaling pathways downstream of the NMDA receptor, including the Ca²⁺‐dependent protein phosphatase calcineurin, Ca²⁺/calmodulin‐dependent protein kinase II (CaMKII), protein phosphatase 1, and cAMP response element–binding protein (CREB). The influence of Aβ on each of these downstream effectors of the NMDA receptor is reviewed in this article. Additionally, other mechanisms of LTP modulation, such as Aβ attenuation of α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) receptor currents, are briefly discussed. © 2009 Wiley‐Liss, Inc.     

Proinflammatory cytokine regulation of cyclic AMP‐phosphodiesterase 4 signaling in microglia in vitro and following CNS injury

Cyclic AMP suppresses immune cell activation and inflammation. The positive feedback loop of proinflammatory cytokine production and immune activation implies that cytokines may not only be regulated by cyclic AMP but also conversely regulate cyclic AMP. This study examined the effects of tumor necrosis factor (TNF)‐α and interleukin (IL)‐1β on cyclic AMP‐phosphodiesterase (PDE) signaling in microglia in vitro and after spinal cord injury (SCI) or traumatic brain injury (TBI). TNF‐α or IL‐1β stimulation produced a profound reduction (>90%) of cyclic AMP within EOC2 microglia from 30 min that then recovered after IL‐1β but remained suppressed with TNF‐α through 24 h. Cyclic AMP was also reduced in TNF‐α‐stimulated primary microglia, albeit to a lesser extent. Accompanying TNF‐α‐induced cyclic AMP reductions, but not IL‐1β, was increased cyclic AMP‐PDE activity. The role of PDE4 activity in cyclic AMP reductions was confirmed by using Rolipram. Examination of pde4 mRNA revealed an immediate, persistent increase in pde4b with TNF‐α; IL‐1β increased all pde4 mRNAs. Immunoblotting for PDE4 showed that both cytokines increased PDE4A1, but only TNF‐α increased PDE4B2. Immunocytochemistry revealed PDE4B nuclear translocation with TNF‐α but not IL‐1β. Acutely after SCI/TBI, where cyclic AMP levels are reduced, PDE4B was localized to activated OX‐42⁺ microglia; PDE4B was absent in OX‐42⁺ cells in uninjured spinal cord/cortex or inactive microglia. Immunoblotting showed PDE4B2 up‐regulation from 24 h to 1 wk post‐SCI, the peak of microglia activation. These studies show that TNF‐α and IL‐1β differentially affect cyclic AMP‐PDE signaling in microglia. Targeting PDE4B2 may be a putative therapeutic direction for reducing microglia activation in CNS injury and neurodegenerative diseases. © 2012 Wiley Periodicals, Inc.     

Increased levels of proinflammatory cytokines in the aged rat brain attenuate injury‐induced cytokine response after excitotoxic damage

In order to evaluate proinflammatory cytokine levels and their producing cell types in the control aged rat brain and after acute excitotoxic damage, both adult and aged male Wistar rats were injected with N‐methyl‐D ‐aspartate in the striatum. At different survival times between 6 hr and 7 days after lesioning, interleukin‐1 beta (IL‐1β), interleukin‐6 (IL‐6), and tumor necrosis factor alpha (TNF‐α) were analyzed by enzyme‐linked immunosorbent assay and by double immunofluorescence of cryostat sections by using cell‐specific markers. Basal cytokine expression was attributed to astrocytes and was increased in the normal aged brain showing region specificity: TNF‐α and IL‐6 displayed age‐dependent higher levels in the aged cortex, and IL‐1β and IL‐6 in the aged striatum. After excitotoxic striatal damage, notable age‐dependent differences in cytokine induction in the aged vs. the adult were seen. The adult injured striatum exhibited a rapid induction of all cytokines analyzed, but the aged injured striatum showed a weak induction of cytokine expression: IL‐1β showed no injury‐induced changes at any time, TNF‐α presented a late induction at 5 days after lesioning, and IL‐6 was only induced at 6 hr after lesioning. At both ages, in the lesion core, all cytokines were early expressed by neurons and astrocytes, and by microglia/macrophages later on. However, in the adjacent lesion border, cytokines were found in reactive astrocytes. This study highlights the particular inflammatory response of the aged brain and suggests an important role of increased basal levels of proinflammatory cytokines in the reduced ability to induce their expression after damage. © 2009 Wiley‐Liss, Inc.     

CD38 regulation in activated astrocytes: Implications for neuroinflammation and HIV‐1 brain infection

Reactive astrogliosis is a key pathological aspect of neuroinflammatory disorders including human immunodeficiency virus type 1 (HIV‐1)‐associated neurological disease. On the basis of previous data that showedastrocytes activated with interleukin (IL)‐1β induce neuronal injury, we analyzed global gene changes in IL‐1β‐activated human astrocytes by gene microarray. Among the up‐regulated genes, CD38, a 45‐kDa type II single chain transmembrane glycoprotein, was a top candidate, with a 17.24‐fold change that was validated by real‐time polymerase chain reaction. Key functions of CD38 include enzymatic activities and involvement in adhesion and cell signaling. Importantly, CD38⁺CD8⁺ T‐cell expression is a clinical correlate for progression of HIV‐1 infection and biological marker for immune activation. Thus, CD38 expression in HIV‐1 and/or IL‐1β‐stimulated human astrocytes and human brain tissues was analyzed. IL‐1β and HIV‐1 activation of astrocytes enhanced CD38 mRNA levels. Both CD38 immunoreactivity and adenosine 5′‐diphosphate (ADP)‐ribosyl cyclase activity were up‐regulated in IL‐1β‐activated astrocytes. CD38 knockdown using specific siRNAs significantly reduced astrocyte proinflammatory cytokine and chemokine production. However, CD38 mRNA levels were unchanged in IL‐1β knockdown conditions, suggesting that IL‐1β autocrine loop is not implicated in this process. Quantitative immunohistochemical analysis of HIV‐seropositive without encephalitis and HIV‐1 encephalitis brain tissues showed significant up‐regulation of CD38, which colocalized with glial fibrillary acidic protein–positive cells in areas of inflammation. These results suggest an important role of CD38 in the regulation of astrocyte dysfunction during the neuroinflammatory processes involved in neurodegenerative/neuroinflammatory disorders such as HIV‐1 encephalitis. © 2009 Wiley‐Liss, Inc.     

Prenatal Social Stress in the Rat Programmes Neuroendocrine and Behavioural Responses to Stress in the Adult Offspring: Sex‐Specific Effects

Stress exposure during pregnancy can ‘programme’ adult behaviour and hypothalamic‐pituitary‐adrenal (HPA) axis stress responsiveness. In the present study, we utilised an ethologically relevant social stressor to model the type of stress that pregnant women may experience. We investigated the effects of social defeat by a resident lactating rat over 5 days during the last week of pregnancy on the pregnant intruder rat HPA axis, and on HPA responsivity to stress and anxiety‐related behaviour in the adult offspring of the socially‐defeated intruder rats. HPA axis responses after social defeat were attenuated in the pregnant rats compared to virgin females. In the adult offspring, systemic interleukin (IL)‐1β or restraint increased adrenocorticotrophic hormone and corticosterone secretion in male and female control rats; however, in prenatally stressed (PNS) offspring, HPA responses were greatly enhanced and peak hormone responses to IL‐1β were greater in females versus males. Male PNS rats displayed increased anxiety behaviour on the elevated plus maze; however, despite marked changes in anxiety behaviour across the oestrous cycle, there were no differences between female control and PNS rats. Investigation of possible mechanisms showed mineralocorticoid mRNA levels were reduced in the hippocampus of male and female PNS offspring, whereas glucocorticoid receptor mRNA expression was modestly reduced in the CA2 hippocampal subfield in female PNS rats only. Corticotropin‐releasing hormone mRNA and glucocorticoid receptor mRNA expression in the central amygdala was greater in PNS males and females compared to controls. The data obtained in the present study indicate that prenatal social stress differentially programmes anxiety behaviour and HPA axis responses to stress in male and female offspring. Attenuated glucocorticoid feedback mechanisms in the limbic system may underlie HPA axis hyper‐reactivity to stress in PNS offspring.     

Role of ERK map kinase and CRM1 in IL‐1β‐stimulated release of HMGB1 from cortical astrocytes

Reactive astrocytes are traditionally thought to impede brain plasticity after stroke. However, we previously showed that reactive astrocytes may also contribute to stroke recovery, partly via the release of a nuclear protein called high‐mobility group box 1 (HMGB1). Here, we investigate the mechanisms that allow stimulated astrocytes to release HMGB1. Exposure of rat primary astrocytes to IL‐1β for 24 h elicited a dose‐dependent HMGB1 response. Immunostaining and western blots of cell lysates showed increased intracellular levels of HMGB1. Western blots confirmed that IL‐1β induced a release of HMGB1 into astrocyte conditioned media. MAP kinase signaling was involved. Levels of phospho‐ERK were increased by IL‐1β, and the MEK/ERK inhibitor U0126 decreased HMGB1 upregulation in the stimulated astrocytes. Since HMGB1 is a nuclear protein, the role of the nuclear protein exporter, chromosome region maintenance 1 (CRM1), was assessed as a candidate mechanism for linking MAP kinase signaling to HMGB1 release. IL‐1β increased CRM1 expression in concert with a translocation of HMGB1 from nucleus into cytoplasm. Blockade of IL‐1β‐stimulated HMGB1 release with the ERK inhibitor U0126 was accompanied by a downregulation of CRM1. Our findings reveal that IL‐1β stimulates the release of HMGB1 from activated astrocytes via ERK MAP kinase and CRM1 signaling. These data suggest a novel pathway by which inflammatory cytokines may enhance the ability of reactive astrocytes to release prorecovery mediators after stroke. © 2010 Wiley‐Liss, Inc.     

Dopaminergic lesioning impairs adult hippocampal neurogenesis by distinct modification of α‐synuclein

Nonmotor symptoms of cognitive and affective nature are present in premotor and motor stages of Parkinson's disease (PD). Neurogenesis, the generation of new neurons, persists throughout the mammalian life span in the hippocampal dentate gyrus. Adult hippocampal neurogenesis may be severely affected in the course of PD, accounting for some of the neuropsychiatric symptoms such as depression and cognitive impairment. Two important PD‐related pathogenic factors have separately been attributed to contribute to both PD and adult hippocampal neurogenesis: dopamine depletion and accumulation of α‐synuclein (α‐syn). In the acute 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine model, altered neurogenesis has been linked merely to a reduced dopamine level. Here, we seek to determine whether a distinct endogenous α‐syn expression pattern is associated, possibly contributing to the hippocampal neurogenic deficit. We observed a persistent reduction of striatal dopamine and a loss of tyrosine hydroxylase‐expressing neurons in the substantia nigra pars compacta in contrast to a complete recovery of tyrosine hydroxylase‐immunoreactive dopaminergic fibers within the striatum. However, dopamine levels in the hippocampus were significantly decreased. Survival of newly generated neurons was significantly reduced and paralleled by an accumulation of truncated, membrane‐associated, insoluble α‐syn within the hippocampus. Specifically, the presence of truncated α‐syn species was accompanied by increased activity of calpain‐1, a calcium‐dependent protease. Our results further substantiate the broad effects of dopamine loss in PD‐susceptible brain nuclei, gradually involved in the PD course. Our findings also indicate a detrimental synergistic interplay between dopamine depletion and posttranslational modification of α‐syn, contributing to impaired hippocampal plasticity in PD. © 2015 Wiley Periodicals, Inc.     

IL‐1β induces hypomyelination in the periventricular white matter through inhibition of oligodendrocyte progenitor cell maturation via FYN/MEK/ERK signaling pathway in septic neonatal rats

Neuroinflammation elicited by microglia plays a key role in periventricular white matter (PWM) damage (PWMD) induced by infectious exposure. This study aimed to determine if microglia‐derived interleukin‐1β (IL‐1β) would induce hypomyelination through suppression of maturation of oligodendrocyte progenitor cells (OPCs) in the developing PWM. Sprague‐Dawley rats (1‐day old) were injected with lipopolysaccharide (LPS) (1 mg/kg) intraperitoneally, following which upregulated expression of IL‐1β and IL‐1 receptor 1 (IL‐1R₁) was observed. This was coupled with enhanced apoptosis and suppressed proliferation of OPCs in the PWM. The number of PDGFR‐α and NG2‐positive OPCs was significantly decreased in the PWM at 24 h and 3 days after injection of LPS, whereas it was increased at 14 days and 28 days. The protein expression of Olig1, Olig2, and Nkx2.2 was significantly reduced, and mRNA expression of Tcf4 and Axin2 was upregulated in the developing PWM after LPS injection. The expression of myelin basic protein (MBP) and 2',3'‐cyclic‐nucleotide 3"‐phosphodiesterase (CNPase) was downregulated in the PWM at 14 days and 28 days after LPS injection; this was linked to reduction of the proportion of myelinated axons and thinner myelin sheath as revealed by electron microscopy. Primary cultured OPCs treated with IL‐1β showed the failure of maturation and proliferation. Furthermore, FYN/MEK/ERK signaling pathway was involved in suppression of maturation of primary OPCs induced by IL‐1β administration. Our results suggest that following LPS injection, microglia are activated and produce IL‐1β in the PWM in the neonatal rats. Excess IL‐1β inhibits the maturation of OPCs via suppression of FYN/MEK/ERK phosphorylation thereby leading to axonal hypomyelination. GLIA 2016;64:583–602     

In vivo expression of proinflammatory cytokines in HIV encephalitis: an analysis of 11 autopsy cases

As the pathogenesis of AIDS dementia complex (ADC), cytokines such as TNF‐α and IL‐1β have been thought to have toxic effects on CNS cells and induce neuronal cell death. However, many of the discussions have been based on the studies done by in vitro experiments. There are only a few reports which demonstrate proinflammatory cytokines directly in vivo in HIV encephalitis (HIVE) brains, and roles of these cytokines with relation to HIV‐1 infection are not yet clarified. In the present study, we examined 11 autopsy cases of HIVE using immunohistochemistry, and explored which cell types expressed these cytokines and whether expression of cytokines was related to viral infection. IL‐1β was detected in the frontal white matter of all 11 cases where microglial nodules were observed to varying degrees, whereas TNF‐α was detected in seven cases. IL‐1β? or TNF‐α‐positive cells were almost restricted to CD68‐positive macrophages/microglia and mild expression of these cytokines by astrocytes was observed in two cases with severe HIVE. IL‐1β was detected in some HIVp24‐positive multinucleated giant cells. However, we could not detect TNF‐α expression in the HIVp24‐positive cells, which indicates that IL‐1β is induced by HIV‐1 infection. In conclusion, a macrophage/microglia lineage is the main cell type to release cytokines in HIVE, and IL‐1β expression by HIV‐1‐infected cells may be one of the important factors for induction of HIVE. In addition, many non‐infected macrophages/microglia as well as some astrocytes express IL‐1β and TNF‐α, which might contribute to pathogenesis of ADC.     

Longitudinal trajectory of Amyloid‐related hippocampal subfield atrophy in nondemented elderly

Hippocampal atrophy and abnormal β‐Amyloid (Aβ) deposition are established markers of Alzheimer's disease (AD). Nonetheless, longitudinal trajectory of Aβ‐associated hippocampal subfield atrophy prior to dementia remains unclear. We hypothesized that elevated Aβ correlated with longitudinal subfield atrophy selectively in no cognitive impairment (NCI), spreading to other subfields in mild cognitive impairment (MCI). We analyzed data from two independent longitudinal cohorts of nondemented elderly, including global PET‐Aβ in AD‐vulnerable cortical regions and longitudinal subfield volumes quantified with a novel auto‐segmentation method (FreeSurfer v.6.0). Moreover, we investigated associations of Aβ‐related progressive subfield atrophy with memory decline. Across both datasets, we found a converging pattern that higher Aβ correlated with faster CA1 volume decline in NCI. This pattern spread to other hippocampal subfields in MCI group, correlating with memory decline. Our results for the first time suggest a longitudinal focal‐to‐widespread trajectory of Aβ‐associated hippocampal subfield atrophy over disease progression in nondemented elderly.     

Protective effects of peroxisome proliferator‐activated receptors γ coactivator‐1α against neuronal cell death in the hippocampal CA1 subfield after transient global ischemia

Peroxisome proliferator‐activated receptors γ coactivator‐1α (PGC‐1α) may regulate the mitochondrial antioxidant defense system under many neuropathological settings. However, the exact role of PGC‐1α in ischemic brain damage is still under debate. Based on an experimental model of transient global ischemia (TGI), this study evaluated the hypothesis that the activation of PGC‐1α signaling pathway protects hippocampal CA1 neurons against delayed neuronal death after TGI. In Sprague‐Dawley rats, significantly increased content of oxidized proteins in the hippocampal CA1 tissue was observed as early as 30 min after TGI, followed by augmentation of PGC‐1α expression at 1 hr. Expression of uncoupling protein 2 (UCP2) and superoxide dismutases 2 (SOD2) in the hippocampal CA1 neurons was upregulated 4–48 hr after TGI. In addition, knock‐down of PGC‐1α expression by pretreatment with a specific antisense oligodeoxynucleotide in the hippocampal CA1 subfield downregulated the expression of UCP2 and SOD2 with resultant exacerbation of oxidative stress and augmentation of delayed neuronal cell death in the hippocampus after TGI. Overall, our results indicate that PGC‐1α is induced by cerebral ischemia leading to upregulation of UCP2 and SOD2, thereby providing a neuroprotective effect against ischemic brain injury in the hippocampus by ameliorating oxidative stress. © 2009 Wiley‐Liss, Inc.     

Genetic reductions of β‐site amyloid precursor protein‐cleaving enzyme 1 and amyloid‐β ameliorate impairment of conditioned taste aversion memory in 5XFAD Alzheimer’s disease model mice

Although transgenic mouse models of Alzheimer’s disease (AD) recapitulate amyloid‐β (Aβ)‐related pathologies and cognitive impairments, previous studies have mainly evaluated their hippocampus‐dependent memory dysfunctions using behavioral tasks such as the water maze and fear conditioning. However, multiple memory systems become impaired in AD as the disease progresses and it is important to test whether other forms of memory are affected in AD models. This study was designed to use conditioned taste aversion (CTA) and contextual fear conditioning paradigms to compare the phenotypes of hippocampus‐independent and ‐dependent memory functions, respectively, in 5XFAD amyloid precursor protein/presenilin‐1 transgenic mice that harbor five familial AD mutations. Although both types of memory were significantly impaired in 5XFAD mice, the onset of CTA memory deficits (～9 months of age) was delayed compared with that of contextual memory deficits (～6 months of age). Furthermore, 5XFAD mice that were genetically engineered to have reduced levels of β‐site amyloid precursor protein‐cleaving enzyme 1 (BACE1) (BACE1^+/?·5XFAD) exhibited improved CTA memory, which was equivalent to the performance of wild‐type controls. Importantly, elevated levels of cerebral β‐secretase‐cleaved C‐terminal fragment (C99) and Aβ peptides in 5XFAD mice were significantly reduced in BACE1^+/?·5XFAD mice. Furthermore, Aβ deposition in the insular cortex and basolateral amygdala, two brain regions that are critically involved in CTA performance, was also reduced in BACE1^+/?·5XFAD compared with 5XFAD mice. Our findings indicate that the CTA paradigm is useful for evaluating a hippocampus‐independent form of memory defect in AD model mice, which is sensitive to rescue by partial reductions of the β‐secretase BACE1 and consequently of cerebral Aβ.     

Minocycline and fluorocitrate suppress spinal nociceptive signaling in intrathecal IL‐1β–induced thermal hyperalgesic rats

We previously demonstrated that intrathecal IL‐1β caused thermal hyperalgesia in rats. This study was conducted to examine the effects and cellular mechanisms of glial inhibitors on IL‐1β–induced nociception in rats. The effects of minocycline (20 μg), fluorocitrate (1 nmol), and SB203580 (5 μg) on IL‐1β (100 ng) treatment in rats were measured by nociceptive behaviors, western blotting of p38 mitogen‐activated protein kinase (MAPK) and inducible nitric oxide synthase (iNOS) expression, cerebrospinal fluid nitric oxide (NO) levels, and immunohistochemical analyses. The results demonstrated that intrathecal IL‐1β activated microglia and astrocytes, but not neurons, in the dorsal horn of the lumbar spinal cord, as evidenced by morphological changes and increased immunoreactivity, phosphorylated p38 (P‐p38) MAPK, and iNOS expression; the activation of microglia and astrocytes peaked at 30 min and lasted for 6 h. The immunoreactivities of microglia and astrocytes were significantly increased at 30 min (6.6‐ and 2.7‐fold, respectively) and 6 h (3.3‐ and 4.0‐fold, respectively) following IL‐1β injection, as compared with saline controls at 30 min (all P < 0.01). IL‐1β induced P‐p38 MAPK and iNOS expression predominantly in microglia and less in astrocytes. Minocycline, fluorocitrate, or SB203580 pretreatment suppressed this IL‐1β–upregulated P‐p38 MAPK mainly in microglia and iNOS mainly in astrocytes; minocycline exhibited the most potent effect. Minocycline and fluorocitrate pretreatment abrogated IL‐1β–induced NO release and thermal hyperalgesia in rats. In conclusion, minocycline, fluorocitrate, and SB203580 effectively suppressed the IL‐1β–induced central sensitization and hyperalgesia in rats. © 2012 Wiley Periodicals, Inc.     

α‐Synuclein activates innate immunity but suppresses interferon‐γ expression in murine astrocytes

Glial activation and neuroinflammation contribute to pathogenesis of neurodegenerative diseases, linked to neuron loss and dysfunction. α‐Synuclein (α‐syn), as a metabolite of neuron, can induce microglia activation to trigger innate immune response. However, whether α‐syn, as well as its mutants (A53T, A30P, and E46K), induces astrocyte activation and inflammatory response is not fully elucidated. In this study, we used A53T mutant and wild‐type α‐syns to stimulate primary astrocytes in dose‐ and time‐dependent manners (0.5, 2, 8, and 20 μg/ml for 24 hr or 3, 12, 24, and 48 hr at 2 μg/ml), and evaluated activation of several canonical inflammatory pathway components. The results showed that A53T mutant or wild‐type α‐syn significantly upregulated mRNA expression of toll‐like receptor (TLR)2, TLR3, nuclear factor‐κB and interleukin (IL)‐1β, displaying a pattern of positive dose–effect correlation or negative time–effect correlation. Such upregulation was confirmed at protein levels of TLR2 (at 20 μg/ml), TLR3 (at most doses), and IL‐1β (at 3 hr) by western blotting. Blockage of TLR2 other than TLR4 inhibited TLR3 and IL‐1β mRNA expressions. By contrast, interferon (IFN)‐γ was significantly downregulated at mRNA, protein, and protein release levels, especially at high concentrations of α‐syns or early time‐points. These findings indicate that α‐syn was a TLRs‐mediated immunogenic agent (A53T mutant stronger than wild‐type α‐syn). The stimulation patterns suggest that persistent release and accumulation of α‐syn is required for the maintenance of innate immunity activation, and IFN‐γ expression inhibition by α‐syn suggests a novel immune molecule interaction mechanism underlying pathogenesis of neurodegenerative diseases.     

γ‐Secretase binding sites in aged and Alzheimer's disease human cerebrum: the choroid plexus as a putative origin of CSF Aβ

Deposition of β ‐amyloid (Aβ) peptides, cleavage products of β‐amyloid precursor protein (APP) by β‐secretase‐1 (BACE1) and γ‐secretase, is a neuropathological hallmark of Alzheimer's disease (AD). γ‐Secretase inhibition is a therapeutical anti‐Aβ approach, although changes in the enzyme's activity in AD brain are unclear. Cerebrospinal fluid (CSF) Aβ peptides are thought to derive from brain parenchyma and thus may serve as biomarkers for assessing cerebral amyloidosis and anti‐Aβ efficacy. The present study compared active γ‐secretase binding sites with Aβ deposition in aged and AD human cerebrum, and explored the possibility of Aβ production and secretion by the choroid plexus (CP). The specific binding density of [³H]‐L‐685,458, a radiolabeled high‐affinity γ‐secretase inhibitor, in the temporal neocortex and hippocampal formation was similar for AD and control cases with similar ages and post‐mortem delays. The CP in post‐mortem samples exhibited exceptionally high [³H]‐L‐685,458 binding density, with the estimated maximal binding sites (Bmax) reduced in the AD relative to control groups. Surgically resected human CP exhibited APP, BACE1 and presenilin‐1 immunoreactivity, and β‐site APP cleavage enzymatic activity. In primary culture, human CP cells also expressed these amyloidogenic proteins and released Aβ40 and Aβ42 into the medium. Overall, our results suggest that γ‐secretase activity appears unaltered in the cerebrum in AD and is not correlated with regional amyloid plaque pathology. The CP appears to be a previously unrecognised non‐neuronal contributor to CSF Aβ, probably at reduced levels in AD.     

Resveratrol prevents CA1 neurons against ischemic injury by parallel modulation of both GSK‐3β and CREB through PI3‐K/Akt pathways

Accumulating evidence indicates that resveratrol potently protects against cerebral ischemia damage due to its oxygen free radicals scavenging and antioxidant properties. However, cellular mechanisms that may underlie the neuroprotective effects of resveratrol in brain ischemia are not fully understood yet. This study aimed to investigate the potential association between the neuroprotective effect of resveratrol and the apoptosis/survival signaling pathways, in particular the glycogen synthase kinase 3 (GSK‐3β) and cAMP response element‐binding protein (CREB) through phosphatidylinositol 3‐kinase (PI3‐K)‐dependent pathway. An experimental model of global cerebral ischemia was induced in rats by the four‐vessel occlusion method for 10 min and followed by different periods of reperfusion. Nissl staining indicated extensive neuronal death at 7 days after ischemia/reperfusion. Administration of resveratrol by i.p. injections (30 mg/kg) for 7 days before ischemia significantly attenuated neuronal death. Both GSK‐3β and CREB appear to play a critical role in resveratrol neuroprotection through the PI3‐K/Akt pathway, as resveratrol pretreatment increased the phosphorylation of Akt, GSK‐3β and CREB in 1 h in the CA1 hippocampus after ischemia/reperfusion. Furthermore, administration of LY294002, an inhibitor of PI3‐K, compromised the neuroprotective effect of resveratrol and decreased the level of p‐Akt, p‐GSK‐3β and p‐CREB after ischemic injury. Taken together, the results suggest that resveratrol protects against delayed neuronal death in the hippocampal CA1 by maintaining the pro‐survival states of Akt, GSK‐3β and CREB pathways. These data suggest that the neuroprotective effect of resveratrol may be mediated through activation of the PI3‐K/Akt signaling pathway, subsequently downregulating expression of GSK‐3β and CREB, thereby leading to prevention of neuronal death after brain ischemia in rats.