Postnatal TLR2 activation impairs learning and memory in adulthood.

Neuroinflammation in the central nervous system is detrimental for learning and memory, as evident form epidemiological studies linking developmental defects and maternal exposure to harmful pathogens. Postnatal infections can also induce neuroinflammatory responses with long-term consequences. These inflammatory responses can lead to motor deficits and/or behavioral disabilities. Toll like receptors (TLRs) are a family of innate immune receptors best known as sensors of microbial-associated molecular patterns, and are the first responders to infection. TLR2 forms heterodimers with either TLR1 or TLR6, is activated in response to gram-positive bacterial infections, and is expressed in the brain during embryonic development. We hypothesized that early postnatal TLR2-mediated neuroinflammation would adversely affect cognitive behavior in the adult. Our data indicate that postnatal TLR2 activation affects learning and memory in adult mice in a heterodimer-dependent manner. TLR2/6 activation improved motor function and fear learning, while TLR2/1 activation impaired spatial learning and enhanced fear learning. Moreover, developmental TLR2 deficiency significantly impairs spatial learning and enhances fear learning, stressing the involvement of the TLR2 pathway in learning and memory. Analysis of the transcriptional effects of TLR2 activation reveals both common and unique transcriptional programs following heterodimer-specific TLR2 activation. These results imply that adult cognitive behavior could be influenced in part, by activation or alterations in the TLR2 pathway at birth.

The homocysteine-inducible endoplasmic reticulum (ER) stress protein Herp counteracts mutant α-synuclein-induced ER stress via the homeostatic regulation of ER-resident calcium release channel proteins.

Endoplasmic reticulum (ER) stress has been implicated as an initiator or contributing factor in neurodegenerative diseases. The mechanisms that lead to ER stress and whereby ER stress contributes to the degenerative cascades remain unclear but their understanding is critical to devising effective therapies. Here we show that knockdown of Herp (Homocysteine-inducible ER stress protein), an ER stress-inducible protein with an ubiquitin-like (UBL) domain, aggravates ER stress-mediated cell death induced by mutant α-synuclein (αSyn) that causes an inherited form of Parkinson's disease (PD). Functionally, Herp plays a role in maintaining ER homeostasis by facilitating proteasome-mediated degradation of ER-resident Ca(2+) release channels. Deletion of the UBL domain or pharmacological inhibition of proteasomes abolishes the Herp-mediated stabilization of ER Ca(2+) homeostasis. Furthermore, knockdown or pharmacological inhibition of ER Ca(2+) release channels ameliorates ER stress, suggesting that impaired homeostatic regulation of Ca(2+) channels promotes a protracted ER stress with the consequent activation of ER stress-associated apoptotic pathways. Interestingly, sustained upregulation of ER stress markers and aberrant accumulation of ER Ca(2+) release channels were detected in transgenic mutant A53T-αSyn mice. Collectively, these data establish a causative link between impaired ER Ca(2+) homeostasis and chronic ER stress in the degenerative cascades induced by mutant αSyn and suggest that Herp is essential for the resolution of ER stress through maintenance of ER Ca(2+) homeostasis. Our findings suggest a therapeutic potential in PD for agents that increase Herp levels or its ER Ca(2+)-stabilizing action.

Electroconvulsive shock ameliorates disease processes and extends survival in huntingtin mutant mice.

Huntington's disease (HD) is an inherited neurodegenerative disorder caused by expanded polyglutamine repeats in the huntingtin (Htt) protein. Mutant Htt may damage and kill striatal neurons by a mechanism involving reduced production of brain-derived neurotrophic factor (BDNF) and increased oxidative and metabolic stress. Because electroconvulsive shock (ECS) can stimulate the production of BDNF and protect neurons against stress, we determined whether ECS treatment would modify the disease process and provide a therapeutic benefit in a mouse model of HD. ECS (50 mA for 0.2 s) or sham treatment was administered once weekly to male N171-82Q Htt mutant mice beginning at 2 months of age. Endpoints measured included motor function, striatal and cortical pathology, and levels of protein chaperones and BDNF. ECS treatment delayed the onset of motor symptoms and body weight loss and extended the survival of HD mice. Striatal neurodegeneration was attenuated and levels of protein chaperones (Hsp70 and Hsp40) and BDNF were elevated in striatal neurons of ECS-treated compared with sham-treated HD mice. Our findings demonstrate that ECS can increase the resistance of neurons to mutant Htt resulting in improved functional outcome and extended survival. The potential of ECS as an intervention in subjects that inherit the mutant Htt gene merits further consideration.

3,6'-dithiothalidomide improves experimental stroke outcome by suppressing neuroinflammation.

Tumor necrosis factor-α (TNF) plays a prominent role in the brain damage and functional deficits that result from ischemic stroke. It was recently reported that the thalidomide analog 3,6'-dithiothalidomide (3,6'-DT) can selectively inhibit the synthesis of TNF in cultured cells. We therefore tested the therapeutic potential of 3,6'-DT in a mouse model of focal ischemic stroke. Administration of 3,6'-DT immediately prior to a stroke or within 3 hr after the stroke reduced infarct volume, neuronal death, and neurological deficits, whereas thalidomide was effective only when administered prior to stroke. Neuroprotection was accompanied by decreased inflammation; 3,6'-DT-treated mice exhibited reduced expression of TNF, interleukin-1ß, and inducible nitric oxide synthase; reduced numbers of activated microglia/macrophages, astrocytes, and neutrophils; and reduced expression of intercellular adhesion molecule-1 in the ischemic brain tissue. 3,6'-DT treatment attenuated stroke-induced disruption of the blood-brain barrier by a mechanism that appears to involve suppression of matrix metalloproteinase-9 and preservation of occludin. Treatment with 3,6'-DT did not reduce ischemic brain damage in mice lacking TNF receptors, consistent with a critical role for suppression of TNF production and TNF signaling in the therapeutic action of 3,6'-DT. These findings suggest that anti-inflammatory mechanisms underlie the therapeutic actions of 3,6-DT in an animal model of stroke.

Gamma secretase-mediated Notch signaling worsens brain damage and functional outcome in ischemic stroke.

Mice transgenic for antisense Notch and normal mice treated with inhibitors of the Notch-activating enzyme gamma-secretase showed reduced damage to brain cells and improved functional outcome in a model of focal ischemic stroke. Notch endangers neurons by modulating pathways that increase their vulnerability to apoptosis, and by activating microglial cells and stimulating the infiltration of proinflammatory leukocytes. These findings suggest that Notch signaling may be a therapeutic target for treatment of stroke and related neurodegenerative conditions.

Toll-like receptor 3 inhibits memory retention and constrains adult hippocampal neurogenesis.

Toll-like receptors (TLRs) are innate immune receptors that have recently emerged as regulators of neuronal survival and developmental neuroplasticity. Adult TLR3-deficient mice exhibited enhanced hippocampus-dependent working memory in the Morris water maze, novel object recognition, and contextual fear-conditioning tasks. In contrast, TLR3-deficient mice demonstrated impaired amygdala-related behavior and anxiety in the cued fear-conditioning, open field, and elevated plus maze tasks. Further, TLR3-deficient mice exhibited increased hippocampal CA1 and dentate gyrus volumes, increased hippocampal neurogenesis, and elevated levels of the AMPA receptor subunit GluR1 in the CA1 region of the hippocampus. In addition, levels of activated forms of the kinase ERK and the transcription factor CREB were elevated in the hippocampus of TLR3-deficient mice, suggesting that constitutive TLR3 signaling negatively regulates pathways known to play important roles in hippocampal plasticity. Direct activation of TLR3 by intracerebroventricular infusion of a TLR3 ligand impaired working memory, but not reference memory. Our findings reveal previously undescribed roles for TLR3 as a suppressor of hippocampal cellular plasticity and memory retention.

Impaired attention in the 3xTgAD mouse model of Alzheimer's disease: rescue by donepezil (Aricept).

Several mouse models of Alzheimer's disease (AD) with abundant ß-amyloid and/or aberrantly phosphorylated tau develop memory impairments. However, multiple non-mnemonic cognitive domains such as attention and executive control are also compromised early in AD individuals. Currently, it is unclear whether mutations in the ß-amyloid precursor protein (APP) and tau are sufficient to cause similar, AD-like attention deficits in mouse models of the disease. To address this question, we tested 3xTgAD mice (which express APPswe, PS1M146V, and tauP301L mutations) and wild-type control mice on a newly developed touchscreen-based 5-choice serial reaction time test of attention and response control. The 3xTgAD mice attended less accurately to short, spatially unpredictable stimuli when the attentional demand of the task was high, and also showed a general tendency to make more perseverative responses than wild-type mice. The attentional impairment of 3xTgAD mice was comparable to that of AD patients in two aspects: first, although 3xTgAD mice initially responded as accurately as wild-type mice, they subsequently failed to sustain their attention over the duration of the task; second, the ability to sustain attention was enhanced by the cholinesterase inhibitor donepezil (Aricept). These findings demonstrate that familial AD mutations not only affect memory, but also cause significant impairments in attention, a cognitive domain supported by the prefrontal cortex and its afferents. Because attention deficits are likely to affect memory encoding and other cognitive abilities, our findings have important consequences for the assessment of disease mechanisms and therapeutics in animal models of AD.

Ceruloplasmin deficiency results in an anxiety phenotype involving deficits in hippocampal iron, serotonin, and BDNF.

Ceruloplasmin (Cp) is a ferroxidase involved in iron metabolism by converting Fe(2+) to Fe(3+), and by regulating cellular iron efflux. In the ceruloplasmin knockout (CpKO) mouse, the deregulation of iron metabolism results in moderate liver and spleen hemosiderosis, but the impact of Cp deficiency on brain neurochemistry and behavior in this animal model is unknown. We found that in contrast to peripheral tissues, iron levels in the hippocampus are significantly reduced in CpKO mice. Although it does not cause any discernable deficits in motor function or learning and memory, Cp deficiency results in heightened anxiety-like behavior in the open field and elevated plus maze tests. This anxiety phenotype is associated with elevated levels of plasma corticosterone. Previous studies provided evidence that anxiety disorders and long-standing stress are associated with reductions in levels of serotonin (5HT) and brain-derived neurotrophic factor (BDNF) in the hippocampus. We found that levels of 5HT and norepinephrine (NE), and the expression of BDNF and its receptor trkB, are significantly reduced in the hippocampus of CpKO mice. Thus, Cp deficiency causes an anxiety phenotype by a mechanism that involves decreased levels of iron, 5HT, NE, and BDNF in the hippocampus.

beta1 integrin maintains integrity of the embryonic neocortical stem cell niche.

During embryogenesis, the neural stem cells (NSC) of the developing cerebral cortex are located in the ventricular zone (VZ) lining the cerebral ventricles. They exhibit apical and basal processes that contact the ventricular surface and the pial basement membrane, respectively. This unique architecture is important for VZ physical integrity and fate determination of NSC daughter cells. In addition, the shorter apical process is critical for interkinetic nuclear migration (INM), which enables VZ cell mitoses at the ventricular surface. Despite their importance, the mechanisms required for NSC adhesion to the ventricle are poorly understood. We have shown previously that one class of candidate adhesion molecules, laminins, are present in the ventricular region and that their integrin receptors are expressed by NSC. However, prior studies only demonstrate a role for their interaction in the attachment of the basal process to the overlying pial basement membrane. Here we use antibody-blocking and genetic experiments to reveal an additional and novel requirement for laminin/integrin interactions in apical process adhesion and NSC regulation. Transient abrogation of integrin binding and signalling using blocking antibodies to specifically target the ventricular region in utero results in abnormal INM and alterations in the orientation of NSC divisions. We found that these defects were also observed in laminin alpha2 deficient mice. More detailed analyses using a multidisciplinary approach to analyse stem cell behaviour by expression of fluorescent transgenes and multiphoton time-lapse imaging revealed that the transient embryonic disruption of laminin/integrin signalling at the VZ surface resulted in apical process detachment from the ventricular surface, dystrophic radial glia fibers, and substantial layering defects in the postnatal neocortex. Collectively, these data reveal novel roles for the laminin/integrin interaction in anchoring embryonic NSCs to the ventricular surface and maintaining the physical integrity of the neocortical niche, with even transient perturbations resulting in long-lasting cortical defects.

Quiescence and activation of stem and precursor cell populations in the subependymal zone of the mammalian brain are associated with distinct cellular and extracellular matrix signals.

The subependymal zone (SEZ) of the lateral ventricles is one of the areas of the adult brain where new neurons are continuously generated from neural stem cells (NSCs), via rapidly dividing precursors. This neurogenic niche is a complex cellular and extracellular microenvironment, highly vascularized compared to non-neurogenic periventricular areas, within which NSCs and precursors exhibit distinct behavior. Here, we investigate the possible mechanisms by which extracellular matrix molecules and their receptors might regulate this differential behavior. We show that NSCs and precursors proceed through mitosis in the same domains within the SEZ of adult male mice--albeit with NSCs nearer ependymal cells--and that distance from the ventricle is a stronger limiting factor for neurogenic activity than distance from blood vessels. Furthermore, we show that NSCs and precursors are embedded in a laminin-rich extracellular matrix, to which they can both contribute. Importantly, they express differential levels of extracellular matrix receptors, with NSCs expressing low levels of alpha6beta1 integrin, syndecan-1, and lutheran, and in vivo blocking of beta1 integrin selectively induced the proliferation and ectopic migration of precursors. Finally, when NSCs are activated to reconstitute the niche after depletion of precursors, expression of laminin receptors is upregulated. These results indicate that the distinct behavior of adult NSCs and precursors is not necessarily regulated via exposure to differential extracellular signals, but rather via intrinsic regulation of their interaction with their microenvironment.

Pregabalin suppresses calcium-mediated proteolysis and improves stroke outcome.

Pregabalin, a Ca(2+) channel α(2)δ-subunit antagonist with analgesic and antiepileptic activity, reduced neuronal loss and improved functional outcome in a mouse model of focal ischemic stroke. Pregabalin administration (5-10mg/kg, i.p.) 30-90 min after transient middle cerebral artery occlusion/reperfusion reduced infarct volume, neuronal death in the ischemic penumbra and neurological deficits at 24h post-stroke. Pregabalin significantly decreased the amount of Ca(2+)/calpain-mediated α-spectrin proteolysis in the cerebral cortex measured at 6h post-stroke. Together with the extensive clinical experience with pregabalin for other neurological indications, our findings suggest the potential for a therapeutic benefit of pregabalin in stroke patients.

Neuronal Aquaporin 1 Inhibits Amyloidogenesis by Suppressing the Interaction Between Beta-Secretase and Amyloid Precursor Protein.

The accumulation of amyloid-ß (Aß) is a characteristic event in the pathogenesis of Alzheimer's disease (AD). Aquaporin 1 (AQP1) is a membrane water channel protein belonging to the AQP family. AQP1 levels are elevated in the cerebral cortex during the early stages of AD, but the role of AQP1 in AD pathogenesis is unclear. We first determined the expression and distribution of AQP1 in brain tissue samples of AD patients and two AD mouse models (3xTg-AD and 5xFAD). AQP1 accumulation was observed in vulnerable neurons in the cerebral cortex of AD patients, and in neurons affected by the Aß or tau pathology in the 3xTg-AD and 5xFAD mice. AQP1 levels increased in neurons as aging progressed in the AD mouse models. Stress stimuli increased AQP1 in primary cortical neurons. In response to cellular stress, AQP1 appeared to translocate to endocytic compartments of ß- and γ-secretase activities. Ectopic expression of AQP1 in human neuroblastoma cells overexpressing amyloid precussir protein (APP) with the Swedish mutations reduced ß-secretase (BACE1)-mediated cleavage of APP and reduced Aß production without altering the nonamyloidogenic pathway. Conversely, knockdown of AQP1 enhanced BACE1 activity and Aß production. Immunoprecipitation experiments showed that AQP1 decreased the association of BACE1 with APP. Analysis of a human database showed that the amount of Aß decreases as the expression of AQP1 increases. These results suggest that the upregulation of AQP1 is an adaptive response of neurons to stress that reduces Aß production by inhibiting the binding between BACE1 and APP.

Plumbagin promotes the generation of astrocytes from rat spinal cord neural progenitors via activation of the transcription factor Stat3.

Plumbagin (5-hydroxy-2-methyl-1,4 naphthoquinone) is a naturally occurring low molecular weight lipophilic phytochemical derived from roots of plants of the Plumbago genus. Plumbagin has been reported to have several clinically relevant biological activities in non-neural cells, including anti-atherosclerotic, anticoagulant, anticarcinogenic, antitumor, and bactericidal effects. In a recent screen of a panel of botanical pesticides, we identified plumbagin as having neuroprotective activity. In this study, we determined if plumbagin could modify the developmental fate of rat E14.5 embryonic neural progenitor cells (NPC). Plumbagin exhibited no cytotoxicity when applied to cultured NPC at concentrations below 1 µM. At a concentration of 0.1 µM, plumbagin significantly enhanced the proliferation of NPC as indicated by a 17% increase in the percentage of cells incorporating bromo-deoxyuridine. Plumbagin at a concentration of 0.1 pM (but not 0.1 µM), stimulated the production of astrocytes as indicated by increased GFAP expression. Plumbagin selectively induced the proliferation and differentiation of glial progenitor cells without affecting the proliferation or differentiation of neuron-restricted progenitors. Plumbagin (0.1 pM) rapidly activated the transcription factor signal transducer and activator of transcription 3 (Stat3) in NPC, and a Stat3 inhibitor peptide prevented both plumbagin-induced astrocyte formation and proliferation. These findings demonstrate the ability of a low molecular weight naturally occurring phytochemical to control the fate of glial progenitor cells by a mechanism involving the Stat3 signaling pathway.

TLR2 activation inhibits embryonic neural progenitor cell proliferation.

Toll-like receptors (TLRs) play essential roles in innate immunity, and increasing evidence indicates that these receptors are expressed in neurons, astrocytes, and microglia in the brain, where they mediate responses to infection, stress, and injury. To address the possibility that TLR2 heterodimer activation could affect progenitor cells in the developing brain, we analyzed the expression of TLR2 throughout mouse cortical development, and assessed the role of TLR2 heterodimer activation in neuronal progenitor cell (NPC) proliferation. TLR2 mRNA and protein was expressed in the cortex in embryonic and early postnatal stages of development, and in cultured cortical NPC. While NPC from TLR2-deficient and wild type embryos had the same proliferative capacity, TLR2 activation by the synthetic bacterial lipopeptides Pam(3)CSK(4) and FSL1, or low molecular weight hyaluronan, an endogenous ligand for TLR2, inhibited neurosphere formation in vitro. Intracerebral in utero administration of TLR2 ligands resulted in ventricular dysgenesis characterized by increased ventricle size, reduced proliferative area around the ventricles, increased cell density, an increase in phospho-histone 3 cells, and a decrease in BrdU(+) cells in the sub-ventricular zone. Our findings indicate that loss of TLR2 does not result in defects in cerebral development. However, TLR2 is expressed and functional in the developing telencephalon from early embryonic stages and infectious agent-related activation of TLR2 inhibits NPC proliferation. TLR2-mediated inhibition of NPC proliferation may therefore be a mechanism by which infection, ischemia, and inflammation adversely affect brain development.

Dietary restriction mitigates cocaine-induced alterations of olfactory bulb cellular plasticity and gene expression, and behavior.

Because the olfactory system plays a major role in food consumption, and because 'food addiction' and associated morbidities have reached epidemic proportions, we tested the hypothesis that dietary energy restriction can modify adverse effects of cocaine on behavior and olfactory cellular and molecular plasticity. Mice maintained on an alternate day fasting (ADF) diet exhibited increased baseline locomotion and increased cocaine-sensitized locomotion during cocaine conditioning, despite no change in cocaine conditioned place preference, compared with mice fed ad libitum. Levels of dopamine and its metabolites in the olfactory bulb (OB) were suppressed in mice on the ADF diet compared with mice on the control diet, independent of acute or chronic cocaine treatment. The expression of several enzymes involved in dopamine metabolism including tyrosine hydroxylase, monoamine oxidases A and B, and catechol-O-methyltransferase were significantly reduced in OBs of mice on the ADF diet. Both acute and chronic administration of cocaine suppressed the production of new OB cells, and this effect of cocaine was attenuated in mice on the ADF diet. Cocaine administration to mice on the control diet resulted in up-regulation of OB genes involved in mitochondrial energy metabolism, synaptic plasticity, cellular stress responses, and calcium- and cAMP-mediated signaling, whereas multiple olfactory receptor genes were down-regulated by cocaine treatment. ADF abolished many of the effects of cocaine on OB gene expression. Our findings reveal that dietary energy intake modifies the neural substrates underlying some of the behavioral and physiological responses to repeated cocaine treatment, and also suggest novel roles for the olfactory system in addiction. The data further suggest that modification of dietary energy intake could provide a novel potential approach to addiction treatments.

Plumbagin, a novel Nrf2/ARE activator, protects against cerebral ischemia.

Many phytochemicals function as noxious agents that protect plants against insects and other damaging organisms. However, at subtoxic doses, the same phytochemicals may activate adaptive cellular stress response pathways that can protect cells against a variety of adverse conditions. We screened a panel of botanical pesticides using cultured human and rodent neuronal cell models, and identified plumbagin as a novel potent activator of the nuclear factor E2-related factor 2 (Nrf2)/antioxidant response element (ARE) pathway. In vitro, plumbagin increases nuclear localization and transcriptional activity of Nrf2, and induces the expression of the Nrf2/ARE-dependent genes, such as heme oxygenase 1 in human neuroblastoma cells. Plumbagin specifically activates the Nrf2/ARE pathway in primary mixed cultures from ARE-human placental alkaline phosphatase reporter mice. Exposure of neuroblastoma cells and primary cortical neurons to plumbagin provides protection against subsequent oxidative and metabolic insults. The neuroprotective effects of plumbagin are abolished by RNA interference-mediated knockdown of Nrf2 expression. In vivo, administration of plumbagin significantly reduces the amount of brain damage and ameliorates-associated neurological deficits in a mouse model of focal ischemic stroke. Our findings establish precedence for the identification and characterization of neuroprotective phytochemicals based upon their ability to activate adaptive cellular stress response pathways.

Neural progenitor cells grown on hydrogel surfaces respond to the product of the transgene of encapsulated genetically engineered fibroblasts.

Engineered tissue strategies for central nervous system (CNS) repair have the potential for localizing treatment using a wide variety of cells or growth factors. However, these strategies are often limited by their ability to address only one aspect of the injury. Here we report the development of a novel alginate construct that acts as a multifunctional tissue scaffold for CNS repair, and as a localized growth factor delivery vehicle. We show that the surface of this alginate construct acts as an optimal growth environment for neural progenitor cell (NPC) attachment, survival, migration, and differentiation. Importantly, we show that tailor-made alginate constructs containing brain-derived neurotrophic factor or neurotrophin-3 differentially direct lineage fates of NPCs and may therefore be useful in treating a wide variety of injuries. It is this potential for directed differentiation of a scaffold prior to implantation at the injury site that we explore here.

Clathrin assembly protein AP180 and CALM differentially control axogenesis and dendrite outgrowth in embryonic hippocampal neurons.

Emerging data suggest that, much like epithelial cells, the polarized growth of neurons requires both the secretory and endocytic pathways. The clathrin assembly proteins AP180 and CALM (clathrin assembly lymphoid myeloid protein) are known to be involved in clathrin-mediated endocytosis, but their roles in mammalian neurons and, in particular, in developmental processes before synaptogenesis are unknown. Here we provide evidence that AP180 and CALM play critical roles in establishing the polarity and controlling the growth of axons and dendrites in embryonic hippocampal neurons. Knockdown of AP180 primarily impairs axonal development, whereas reducing CALM levels results in dendritic dystrophy. Conversely, neurons that overexpress AP180 or CALM generate multiple axons. Ultrastructural analysis shows that CALM affiliates with a wider range of intracellular trafficking organelles than does AP180. Functional analysis shows that endocytosis is reduced in both AP180-deficient and CALM-deficient neurons. Additionally, CALM-deficient neurons show disrupted secretory transport. Our data demonstrate previously unknown functions for AP180 and CALM in intracellular trafficking that are essential in the growth of neurons.

Toll-like receptor 3 is a negative regulator of embryonic neural progenitor cell proliferation.

Toll-like receptors (TLRs) play important roles in innate immunity. Several TLR family members have recently been shown to be expressed by neurons and glial cells in the adult brain, and may mediate responses of these cells to injury and infection. To address the possibility that TLRs play a functional role in development of the nervous system, we analyzed the expression of TLRs during different stages of mouse brain development and assessed the role of TLRs in cell proliferation. TLR3 protein is present in brain cells in early embryonic stages of development, and in cultured neural stem/progenitor cells (NPC). NPC from TLR3-deficient embryos formed greater numbers of neurospheres compared with neurospheres from wild-type embryos. Numbers of proliferating cells, as assessed by phospho histone H3 and proliferating cell nuclear antigen labeling, were also increased in the developing cortex of TLR3-deficient mice compared with wild-type mice in vivo. Treatment of cultured embryonic cortical neurospheres with a TLR3 ligand (polyIC) significantly reduced proliferating (BrdU-labeled) cells and neurosphere formation in wild type but not TLR3(-/-)-derived NPCs. Our findings reveal a novel role for TLR3 in the negative regulation of NPC proliferation in the developing brain.

Patterns of laminins and integrins in the embryonic ventricular zone of the CNS.

The extracellular matrix (ECM) provides both a physical framework and a microenvironment that supplies instructive signals from the earliest stages of multicellular development. As a first step toward understanding the role of the ECM in regulating the behavior of neural stem cells (NSCs), here we show the localization of laminins, a heterotrimeric family of ECM molecules expressed in many different stem cell microenvironments, and their corresponding receptors in the embryonic murine ventricular zone (VZ) within which the NSCs undergo symmetrical and asymmetrical divisions required for cortical development. In addition to the presence of laminins containing both the alpha2 and alpha4 chains, we find distinct patterns of ECM receptor expression in the VZ and in the overlying cortex. Neural stem cells derived from the VZ express high levels of the integrin laminin receptor alpha6beta1. At developmental stages at which NSCs undergo asymmetrical divisions, integrin beta1 was unevenly distributed in some mitotic pairs at the ventricular wall. These results suggest a significant role in the regulation of NSC fate for laminin/integrin signaling within the microenvironment of the VZ and provide a framework for future molecular and cellular analyses of the role of the ECM in neural development.