Inflammation mediates varying effects in neurogenesis: relevance to the pathogenesis of brain injury and neurodegenerative disorders

KSRP: a checkpoint for inflammatory cytokine production in astrocytes

Chronic inflammation in the central nervous system (CNS) is a central feature of many neurodegenerative and autoimmune diseases. As an immunologically competent cell, the astrocyte plays an important role in CNS inflammation. It is capable of expressing a number of cytokines such as tumor necrosis factor alpha (TNF-α) and interleukin-1 beta (IL-1β) that promote inflammation directly and through the recruitment of immune cells. Checkpoints are therefore in place to keep tight control over cytokine production. Adenylate/uridylate-rich elements (ARE) in the 3' untranslated region of cytokine mRNAs serve as a major checkpoint by regulating mRNA stability and translational efficiency. Here, we examined the impact of KH-type splicing regulatory protein (KSRP), an RNA binding protein which destabilizes mRNAs via the ARE, on cytokine expression and paracrine phenotypes of primary astrocytes. We identified a network of inflammatory mediators, including TNF-α and IL-1β, whose expression increased 2 to 4-fold at the RNA level in astrocytes isolated from KSRP(-/-) mice compared to littermate controls. Upon activation, KSRP(-/-) astrocytes produced TNF-α and IL-1β at levels that exceeded control cells by 15-fold or more. Conditioned media from KSRP(-/-) astrocytes induced chemotaxis and neuronal cell death in vitro. Surprisingly, we observed a prolongation of half-life in only a subset of mRNA targets and only after selective astrocyte activation. Luciferase reporter studies indicated that KSRP regulates cytokine gene expression at both transcriptional and post-transcriptional levels. Our results outline a critical role for KSRP in regulating pro-inflammatory mediators and have implications for a wide range of CNS inflammatory and autoimmune diseases.

The chemokine receptor cxcr5 regulates the regenerative neurogenesis response in the adult zebrafish brain

Background

Unlike mammals, zebrafish exhibits extensive neural regeneration after injury in adult stages of its lifetime due to the neurogenic activity of the radial glial cells. However, the genes involved in the regenerative neurogenesis response of the zebrafish brain are largely unknown. Thus, understanding the underlying principles of this regeneration capacity of the zebrafish brain is an interesting research realm that may offer vast clinical ramifications.

Results

In this paper, we characterized the expression pattern of cxcr5 and analyzed the function of this gene during adult neurogenesis and regeneration of the zebrafish telencephalon. We found that cxcr5 was upregulated transiently in the RGCs and neurons, and the expression in the immune cells such as leukocytes was negligible during both adult neurogenesis and regeneration. We observed that the transgenic misexpression of cxcr5 in the ventricular cells using dominant negative and full-length variants of the gene resulted in altered proliferation and neurogenesis response of the RGCs. When we knocked down cxcr5 using antisense morpholinos and cerebroventricular microinjection, we observed outcomes similar to the overexpression of the dominant negative cxcr5 variant.

Conclusions

Thus, based on our results, we propose that cxcr5 imposes a proliferative permissiveness to the radial glial cells and is required for differentiation of the RGCs to neurons, highlighting novel roles of cxcr5 in the nervous system of vertebrates. We therefore suggest that cxcr5 is an important cue for ventricular cell proliferation and regenerative neurogenesis in the adult zebrafish telencephalon. Further studies on the role of cxcr5 in mediating neuronal replenishment have the potential to produce clinical ramifications in efforts for regenerative therapeutic applications for human neurological disorders or acute injuries.

The young brain and concussion: imaging as a biomarker for diagnosis and prognosis

Concussion (mild traumatic brain injury (mTBI)) is a significant pediatric public health concern. Despite increased awareness, a comprehensive understanding of the acute and chronic effects of concussion on central nervous system structure and function remains incomplete. Here we review the definition, epidemiology, and sequelae of concussion within the developing brain, during childhood and adolescence, with current data derived from studies of pathophysiology and neuroimaging. These findings may contribute to a better understanding of the neurological consequences of traumatic brain injuries, which in turn, may lead to the development of brain biomarkers to improve identification, management and prognosis of pediatric patients suffering from concussion.

Current challenges for the advancement of neural stem cell biology and transplantation research

Transplantation of neural stem cells (NSC) is hoped to become a promising primary or secondary therapy for the treatment of various neurodegenerative disorders of the central nervous system (CNS), as demonstrated by multiple pre-clinical animal studies in which functional recovery has already been demonstrated. However, for NSC therapy to be successful, the first challenge will be to define a transplantable cell population. In the first part of this review, we will briefly discuss the main features of ex vivo culture and characterisation of NSC. Next, NSC grafting itself may not only result in the regeneration of lost tissue, but more importantly has the potential to improve functional outcome through many bystander mechanisms. In the second part of this review, we will briefly discuss several pre-clinical studies that contributed to a better understanding of the therapeutic potential of NSC grafts in vivo. However, while many pre-clinical animal studies mainly report on the clinical benefit of NSC grafting, little is known about the actual in vivo fate of grafted NSC. Therefore, the third part of this review will focus on non-invasive imaging techniques for monitoring cellular grafts in the brain under in vivo conditions. Finally, as NSC transplantation research has evolved during the past decade, it has become clear that the host micro-environment itself, either in healthy or injured condition, is an important player in defining success of NSC grafting. The final part of this review will focus on the host environmental influence on survival, migration and differentiation of grafted NSC.

Nuclear factor kappa B signaling initiates early differentiation of neural stem cells

Inflammatory mediators, many of which activate the signaling of nuclear factor kappa B (NFκB), have received increasing attention in the field of neurogenesis. NFκB signaling regulates neurite outgrowth and neural plasticity as well as the proliferation/apoptosis and terminal differentiation of neural stem cells (NSCs). Early neurogenesis from NSCs produces identical progeny through symmetric division and committed daughter cells through asymmetric division. Here, we show that NFκB signaling is required for NSC initial differentiation. The canonical IKKβ/IκBα/p65 pathway is activated during the initial stages of neural differentiation induced by treatment with TNFα or withdrawal of epidermal growth factor/basic fibroblast growth factor. NSC-specific inhibition of NFκB in transgenic mice causes an accumulation of Nestin(+) /Sox2(+) /glial fibrillary acidic protein(+) NSCs. Inhibition of NFκB signaling in vitro blocks differentiation and asymmetric division and maintains NSCs in an undifferentiated state. The induction of initial differentiation and asymmetry by NFκB signaling occurs through the inhibition of C/EBPβ expression. Our data reveal a novel function of NFκB signaling in early neurogenesis and provide insight into the molecular mechanisms underlying neurodevelopmental disorders and neurodegenerative diseases.

NFκB signaling regulates embryonic and adult neurogenesis

Both embryonic and adult neurogenesis involves the self-renewal/proliferation, survival, migration and lineage differentiation of neural stem/progenitor cells. Such dynamic process is tightly regulated by intrinsic and extrinsic factors and complex signaling pathways. Misregulated neurogenesis contributes much to a large range of neurodevelopmental defects and neurodegenerative diseases. The signaling of NFκB regulates many genes important in inflammation, immunity, cell survival and neural plasticity. During neurogenesis, NFκB signaling mediates the effect of numerous niche factors such as cytokines, chemokines, growth factors, extracellular matrix molecules, but also crosstalks with other signaling pathways such as Notch, Shh, Wnt/β-catenin. This review summarizes current progress on the NFκB signaling in all aspects of neurogenesis, focusing on the novel role of NFκB signaling in initiating early neural differentiation of neural stem cells and embryonic stem cells.

Alzheimer's disease promotion by obesity: induced mechanisms-molecular links and perspectives

The incidence of AD is increasing in parallel with the increase in life expectancy. At the same time the prevalence of metabolic syndrome and obesity is reaching epidemic proportions in western populations. Stress is one of the major inducers of visceral fat and obesity development, underlying accelerated aging processes. Adipose tissue is at present considered as an active endocrine organ, producing important mediators involved in metabolism regulation as well as in inflammatory mechanisms. Insulin and leptin resistance has been related to the dysregulation of energy balance and to the induction of a chronic inflammatory status which have been recognized as important cofactors in cognitive impairment and AD initiation and progression. The aim of this paper is to disclose the correlation between the onset and progression of AD and the stress-induced changes in lifestyle, leading to overnutrition and reduced physical activity, ending with metabolic syndrome and obesity. The involved molecular mechanisms will be briefly discussed, and advisable guide lines for the prevention of AD through lifestyle modifications will be proposed.

Lesional accumulation of CD163+ macrophages/microglia in rat traumatic brain injury

A robust neuroinflammation, contributing to the development of secondary injury, is a common histopathological feature of traumatic brain injury (TBI). Characterization of leukocytic subpopulations contributing to the early infiltration of the damaged tissue might aid in further understanding of lesion development. Reactive macrophages/microglia can exert protective or damaging effects in TBI. CD163 is considered a marker of M2 (alternatively activated) macrophages. Therefore we investigated the accumulation of CD163(+) macrophages/microglia in the brain of TBI rats. TBI was induced in rats using an open skull weight-drop contusion model and the accumulation of CD163(+) cells was analyzed by immunohistochemistry. In normal rat brains, CD163 was expressed by meningeal, choroid plexus and perivascular macrophages. Significant parenchymal CD163(+) cell accumulation was observed two days post TBI and continuously increased in the investigated survival time. The accumulated CD163(+) cells were mainly distributed to the lesional areas and exhibited macrophage phenotypes with amoeboid morphologic characteristics but not activated microglial phenotypes with hypertrophic morphology and thick processes. Double-labeling experiments showed that most CD163(+) cells co-expressed heme oxygenase-1 (HO-1). In addition, in vitro incubating of macrophage RAW264.7 cells or primary peritoneal macrophages with hemoglobin- haptoglobin (Hb-Hp) complex suppressed LPS-induced inflammatory macrophages phenotype and induced CD163 and HO-1 upregulation, indicating that CD163(+) macrophages/microglia in TBI might have anti-inflammatory effects. And further study is necessary to identify functions of these cells in TBI.

CNF1 improves astrocytic ability to support neuronal growth and differentiation in vitro

Modulation of cerebral Rho GTPases activity in mice brain by intracerebral administration of Cytotoxic Necrotizing Factor 1 (CNF1) leads to enhanced neurotransmission and synaptic plasticity and improves learning and memory. To gain more insight into the interactions between CNF1 and neuronal cells, we used primary neuronal and astrocytic cultures from rat embryonic brain to study CNF1 effects on neuronal differentiation, focusing on dendritic tree growth and synapse formation, which are strictly modulated by Rho GTPases. CNF1 profoundly remodeled the cytoskeleton of hippocampal and cortical neurons, which showed philopodia-like, actin-positive projections, thickened and poorly branched dendrites, and a decrease in synapse number. CNF1 removal, however, restored dendritic tree development and synapse formation, suggesting that the toxin can reversibly block neuronal differentiation. On differentiated neurons, CNF1 had a similar effacing effect on synapses. Therefore, a direct interaction with CNF1 is apparently deleterious for neurons. Since astrocytes play a pivotal role in neuronal differentiation and synaptic regulation, we wondered if the beneficial in vivo effect could be mediated by astrocytes. Primary astrocytes from embryonic cortex were treated with CNF1 for 48 hours and used as a substrate for growing hippocampal neurons. Such neurons showed an increased development of neurites, in respect to age-matched controls, with a wider dendritic tree and a richer content in synapses. In CNF1-exposed astrocytes, the production of interleukin 1β, known to reduce dendrite development and complexity in neuronal cultures, was decreased. These results demonstrate that astrocytes, under the influence of CNF1, increase their supporting activity on neuronal growth and differentiation, possibly related to the diminished levels of interleukin 1β. These observations suggest that the enhanced synaptic plasticity and improved learning and memory described in CNF1-injected mice are probably mediated by astrocytes.

Alteration of forebrain neurogenesis after cervical spinal cord injury in the adult rat

Spinal cord injury (SCI) triggers a complex cellular response at the injury site, leading to the formation of a dense scar tissue. Despite this local tissue remodeling, the consequences of SCI at the cellular level in distant rostral sites (i.e., brain), remain unknown. In this study, we asked whether cervical SCI could alter cell dynamics in neurogenic areas of the adult rat forebrain. To this aim, we quantified BrdU incorporation and determined the phenotypes of newly generated cells (neurons, astrocytes, or microglia) during the subchronic and chronic phases of injury. We find that subchronic SCI leads to a reduction of BrdU incorporation and neurogenesis in the olfactory bulb and in the hippocampal dentate gyrus. By contrast, subchronic SCI triggers an increased BrdU incorporation in the dorsal vagal complex of the hindbrain, where most of the newly generated cells are identified as microglia. In chronic condition 90 days after SCI, BrdU incorporation returns to control levels in all regions examined, except in the hippocampus, where SCI produces a long-term reduction of neurogenesis, indicating that this structure is particularly sensitive to SCI. Finally, we observe that SCI triggers an acute inflammatory response in all brain regions examined, as well as a hippocampal-specific decline in BDNF levels. This study provides the first demonstration that forebrain neurogenesis is vulnerable to a distal SCI.

Inflammatory regulators of redirected neural migration in the injured brain

Brain injury following stroke or trauma induces the migration of neuroblasts derived from subventricular zone neural precursor cells (NPCs) towards the damaged tissue, where they then have the potential to contribute to repair. Enhancing the recruitment of new cells thus presents an enticing prospect for the development of new therapeutic approaches to treat brain injury; to this end, an understanding of the factors regulating this process is required. During the neuroinflammatory response to ischemic and traumatic brain injuries, a plethora of pro- and anti-inflammatory cytokines, chemokines and growth factors are released in the damaged tissue, and recent work indicates that a variety of these are able to influence injury-induced migration. In this review, we will discuss the contribution of specific chemokines and growth factors towards stimulating NPC migration in the injured brain.

Macrophage migration inhibitory factor (MIF) promotes cell survival and proliferation of neural stem/progenitor cells

In a previous study, we showed that murine dendritic cells (DCs) can increase the number of neural stem/progenitor cells (NSPCs) in vitro and in vivo. In the present study, we identified macrophage migration inhibitory factor (MIF) as a novel factor that can support the proliferation and/or survival of NSPCs in vitro. MIF is secreted by DCs and NSPCs, and its function in the normal brain remains largely unknown. It was previously shown that in macrophages, MIF binds to a CD74-CD44 complex. In the present study, we observed the expression of MIF receptors in mouse ganglionic-eminence-derived neurospheres using flow cytometry in vitro. We also found CD74 expression in the ganglionic eminence of E14 mouse brains, suggesting that MIF plays a physiological role in vivo. MIF increased the number of primary and secondary neurospheres. By contrast, retrovirally expressed MIF shRNA and MIF inhibitor (ISO-1) suppressed primary and secondary neurosphere formation, as well as cell proliferation. In the neurospheres, MIF knockdown by shRNA increased caspase 3/7 activity, and MIF increased the phosphorylation of Akt, Erk, AMPK and Stat3 (Ser727), as well as expression of Hes3 and Egfr, the products of which are known to support cell survival, proliferation and/or maintenance of NSPCs. MIF also acted as a chemoattractant for NSPCs. These results show that MIF can induce NSPC proliferation and maintenance by multiple signaling pathways acting synergistically, and it may be a potential therapeutic factor, capable of activating NSPC, for the treatment of degenerative brain disorders.

Oxidative stress and microglial cells in Parkinson's disease

Significant evidence has now been accumulated that microglial cells play a central role in the degeneration of DA neurons in animal models of PD. The oxidative stress response by microglial cells, most notably the activity of the enzyme NADPH oxidase, appears to play a central role in the pathology of PD. This oxidative stress response occurs in microglia through the activation of the ERK signaling pathway by proinflammatory stimuli, leading to the phosphorylation and translocation of the p47(phox) and p67(phox) cytosolic subunits, the activation of membrane-bound PHOX, and the production of ROS. Therapeutic anti-inflammatories which prevent DA neurodegeneration in PD, including anti-inflammatory cytokines, morphinan compounds, NADPH oxidase inhibitors, NF-κB inhibitors, and β2-AR agonists, all function to inhibit the activation of the PHOX in microglial cells. These observations suggest a central role for the oxidative stress response in microglial cells as a mediator or regulator of DA neurodegeneration in PD.

Microglial activation - tuning and pruning adult neurogenesis

NEW NEURONS ARE CONTINUOUSLY GENERATED IN TWO ADULT BRAIN REGIONS: the subgranular zone of the hippocampus and the subependyma by the lateral ventricles, referred to as the neurogenic niches. During their development from neural stem cells to mature functionally integrated neurons numerous choices are made, such as proliferation or quiescence, cell survival or death, migration or establishment, growth or retraction of processes, synaptic assembly or pruning, or tuning of synaptic transmission. The process is altered by physiological stimuli as well as several brain diseases. Microglia are located within the neurogenic niches and have become interesting candidates for modulating neurogenesis in both the healthy and injured brain. They become activated by foreign antigens or changes in the brain homeostasis and transform this innate immunity into an adaptive immune response by recruiting systemic immune cells. Most studies report an acute decrease in the survival of new neurons following this classically activated microglia reaction. The long-term effects are more complex. In neurodegenerative diseases, microglial activation is more heterogeneous and the transformation from a pro- to an anti-inflammatory cytokine profile and the deactivation of microglia is not well defined. The diversity is reflected by numerous reports describing both beneficial and detrimental effects on neurogenesis, primarily on the proliferation, survival, and cell fate. However, relatively few studies have investigated alterations at later stages of neurogenesis including the functional integration. Though likely, it is not established how a fine-tuned cross-talk between microglia and adult-born neurons would work and how it changes upon microglia activation. This review will therefore launch three hypotheses for how microglia might direct synaptic integration of newborn neurons, currently a fast expanding research field.

A lifespan approach to neuroinflammatory and cognitive disorders: a critical role for glia

Cognitive decline is a common problem of aging. Whereas multiple neural and glial mechanisms may account for these declines, microglial sensitization and/or dystrophy has emerged as a leading culprit in brain aging and dysfunction. However, glial activation is consistently observed in normal brain aging as well, independent of frank neuroinflammation or functional impairment. Such variability suggests the existence of additional vulnerability factors that can impact neuronal-glial interactions and thus overall brain and cognitive health. The goal of this review is to elucidate our working hypothesis that an individual's risk or resilience to neuroinflammatory disorders and poor cognitive aging may critically depend on their early life experience, which can change immune reactivity within the brain for the remainder of the lifespan. For instance, early-life infection in rats can profoundly disrupt memory function in young adulthood, as well as accelerate age-related cognitive decline, both of which are linked to enduring changes in glial function that occur in response to the initial infection. We discuss these findings within the context of the growing literature on the role of immune molecules and neuroimmune crosstalk in normal brain development. We highlight the intrinsic factors (e.g., chemokines, hormones) that regulate microglial development and their colonization of the embryonic and postnatal brain, and the capacity for disruption or "re-programming" of this crucial process by external events (e.g., stress, infection). An impact on glia, which in turn alters neural development, has the capacity to profoundly impact cognitive and mental health function at all stages of life.

Exposure of foetal neural progenitor cells to IL-1β impairs their proliferation and alters their differentiation - a role for maternal inflammation?

During pregnancy, activation of the maternal immune system results in inflammation in the foetal nervous system. The causative agents are pro-inflammatory cytokines like interleukin-1β (IL-1β), produced by the foetus. In this study, we examine the effect of IL-1β on the proliferation and differentiation of neural progenitor cells (NPCs) to better understand its potential effects on the developing brain. We find that the IL-1β receptor (IL-1R1) is expressed in the ventral mesencephalon of the developing brain. Furthermore, IL-1R1 is expressed on Nestin-positive, Sox-2-positive NPCs. IL-1β treatment reduced the numbers of proliferating NPCs, an effect prevented by the IL-1R1 receptor antagonist. LDH and MTT assays, and western blot analysis for cleaved caspase 3 and poly(ADP-ribose) polymerase, confirmed that this was not due to an increase in cell death but rather an induction of differentiation. To further study the effects of IL-1β on cell fate determination, we differentiated NPCs in the presence and absence of IL-1β. Il-1β promoted gliogenesis and inhibited neurogenesis, an effect that required p38-MAPK kinase signalling. In summary, these data show that exposure of NPCs to IL-1β affects their development. This necessitates an examination of the consequences that maternal immune system activation during pregnancy has on the cellular architecture of the developing brain.

Neural stem cells: therapeutic potential for neurodegenerative diseases

INTRODUCTION

Neural stem cells (NSCs) from specific brain areas or developed from progenitors of different sources are of therapeutic potential for neurodegenerative diseases.

SOURCES OF DATA

Treatment strategies involve the (i) transplantation of exogenous NSCs; (ii) pharmacological modulations of endogenous NSCs and (iii) modulation of endogenous NSCs via the transplantation of exogenous NSCs.

AREAS OF AGREEMENT

There is a consensus about the therapeutic potential of transplanted NSCs. The ability of NSCs to home into areas of central nervous system injury allows their delivery by intravenous injection. There is also a general agreement about the neuroprotective mechanisms of NSCs involving a 'bystander effect'.

AREAS OF CONTROVERSY

Individual laboratories may be using phenotypically diverse NSCs, since these cells have been differentiated by a variety of neurotrophins and/or cultured on different ECM proteins, therefore differing in the expression of neuronal markers.

GROWING POINTS

Optimization of the dose, delivery route, timing of administration of NSCs, their interactions with the immune system and combination therapies in conjunction with tissue engineered neural prostheses are under investigation.

AREAS TIMELY FOR DEVELOPING RESEARCH

In-depth understanding of the biological properties of NSCs, including mechanisms of therapy, safety, efficacy and elimination from the organism. These areas are central for further use in cell therapy. CAUTIONARY NOTE: As long as critical safety and efficacy issues are not resolved, we need to be careful in translating NSC therapy from animal models to patients.

TNF-α affects human cortical neural progenitor cell differentiation through the autocrine secretion of leukemia inhibitory factor

Proinflammatory cytokine tumor necrosis factor-alpha (TNF-α) is a crucial effector of immune responses in the brain that participates in the pathogenesis of several acute and chronic neurodegenerative disorders. Accumulating evidence has suggested that TNF-α negatively regulates embryonic and adult neurogenesis. However, the effect of TNF-α on cell fate decision in human neural progenitor cells (NPCs) has rarely been studied. Our previous studies have shown that recombinant TNF-α enhances astrogliogenesis and inhibits neurogenesis of human NPCs through the STAT3 (signal transducer and activator of transcription 3) pathway. In the current study, we further elucidated the specific mechanism involved in TNF-α-induced astrogliogenesis. We found that TNF-α activated STAT3 at delayed time points (6 h and 24 h), whereas conditioned medium collected from TNF-α-treated NPCs induced an immediate STAT3 activation. These data suggest TNF-α plays an indirect role on STAT3 activation and the subsequent NPC differentiation. Further, we showed that TNF-α induced abundant amounts of the IL-6 family cytokines, including Leukemia inhibitory factor (LIF) and Interleukin 6 (IL-6), in human NPCs. TNF-α-induced STAT3 phosphorylation and astrogliogenesis were abrogated by the addition of neutralizing antibody for LIF, but not for IL-6, revealing a critical role of autocrine secretion of LIF in TNF-α-induced STAT3 activation and astrogliogenesis. This study generates important data elucidating the role of TNF-α in neurogenesis and may provide insight into new therapeutic strategies for brain inflammation.

Posttraumatic hypothermia increases doublecortin expressing neurons in the dentate gyrus after traumatic brain injury in the rat

Previous studies have demonstrated that moderate hypothermia reduces histopathological damage and improves behavioral outcome after experimental traumatic brain injury (TBI). Further investigations have clarified the mechanisms underlying the beneficial effects of hypothermia by showing that cooling reduces multiple cell injury cascades. The purpose of this study was to determine whether hypothermia could also enhance endogenous reparative processes following TBI such as neurogenesis and the replacement of lost neurons. Male Sprague-Dawley rats underwent moderate fluid-percussion brain injury and then were randomized into normothermia (37°C) or hypothermia (33°C) treatment. Animals received injections of 5-bromo-2'-deoxyuridine (BrdU) to detect mitotic cells after brain injury. After 3 or 7 days, animals were perfusion-fixed and processed for immunocytochemistry and confocal analysis. Sections were stained for markers selective for cell proliferation (BrdU), neuroblasts and immature neurons (doublecortin), and mature neurons (NeuN) and then analyzed using non-biased stereology to quantify neurogenesis in the dentate gyrus (DG). At 7 days after TBI, both normothermic and hypothermic TBI animals demonstrated a significant increase in the number of BrdU-immunoreactive cells in the DG as compared to sham-operated controls. At 7 days post-injury, hypothermia animals had a greater number of BrdU (ipsilateral cortex) and doublecortin (ipsilateral and contralateral cortex) immunoreactive cells in the DG as compared to normothermia animals. Because adult neurogenesis following injury may be associated with enhanced functional recovery, these data demonstrate that therapeutic hypothermia sustains the increase in neurogenesis induced by TBI and this may be one of the mechanisms by which hypothermia promotes reparative strategies in the injured nervous system.

Glial reactivity in dogs with visceral leishmaniasis: correlation with T lymphocyte infiltration and with cerebrospinal fluid anti-Leishmania antibody titres

Visceral leishmaniasis is a multisystemic zoonotic disease that can manifest with several symptoms, including neurological disorders. Because glial cells are extensively associated with the immune response within the brain, we evaluated the morphology of astrocytes and microglia of dogs naturally infected with Leishmania chagasi. We used immunohistochemical and lectin-histochemical techniques for morphological analyses and we also examined the glial correlation with lymphocyte infiltration of the brain and with the presence of anti-Leishmania antibodies within the cerebrospinal fluid of the dogs. Although we did not detect a shared morphological pattern in the astrocytes or microglia in the brain tissue, these cells were more intensely labelled in infected dogs than in the control group. The density of microglia was increased in the ependymal/subependymal area, thus demonstrating a strong correlation with the presence of T lymphocytes and with cerebrospinal fluid antibody titres. Thus, our results indicate a pro-inflammatory state in the brains of dogs naturally infected with L. chagasi and strongly suggest that microglia and astrocytes are involved in the pathogenesis of the neurological disorders of visceral leishmaniasis in dogs.

Hemorrhagic progression of a contusion after traumatic brain injury: a review

The magnitude of damage to cerebral tissues following head trauma is determined by the primary injury, caused by the kinetic energy delivered at the time of impact, plus numerous secondary injury responses that almost inevitably worsen the primary injury. When head trauma results in a cerebral contusion, the hemorrhagic lesion often progresses during the first several hours after impact, either expanding or developing new, non-contiguous hemorrhagic lesions, a phenomenon termed hemorrhagic progression of a contusion (HPC). Because a hemorrhagic contusion marks tissues with essentially total unrecoverable loss of function, and because blood is one of the most toxic substances to which the brain can be exposed, HPC is one of the most severe types of secondary injury encountered following traumatic brain injury (TBI). Historically, HPC has been attributed to continued bleeding of microvessels fractured at the time of primary injury. This concept has given rise to the notion that continued bleeding might be due to overt or latent coagulopathy, prompting attempts to normalize coagulation with agents such as recombinant factor VIIa. Recently, a novel mechanism was postulated to account for HPC that involves delayed, progressive microvascular failure initiated by the impact. Here we review the topic of HPC, we examine data relevant to the concept of a coagulopathy, and we detail emerging data elucidating the mechanism of progressive microvascular failure that predisposes to HPC after head trauma.

Mifepristone prevents stress-induced apoptosis in newborn neurons and increases AMPA receptor expression in the dentate gyrus of C57/BL6 mice

Chronic stress produces sustained elevation of corticosteroid levels, which is why it is considered one of the most potent negative regulators of adult hippocampal neurogenesis (AHN). Several mood disorders are accompanied by elevated glucocorticoid levels and have been linked to alterations in AHN, such as major depression (MD). Nevertheless, the mechanism by which acute stress affects the maturation of neural precursors in the dentate gyrus is poorly understood. We analyzed the survival and differentiation of 1 to 8 week-old cells in the dentate gyrus of female C57/BL6 mice following exposure to an acute stressor (the Porsolt or forced swimming test). Furthermore, we evaluated the effects of the glucocorticoid receptor (GR) antagonist mifepristone on the cell death induced by the Porsolt test. Forced swimming induced selective apoptotic cell death in 1 week-old cells, an effect that was abolished by pretreatment with mifepristone. Independent of its antagonism of GR, mifepristone also induced an increase in the percentage of 1 week-old cells that were AMPA⁺. We propose that the induction of AMPA receptor expression in immature cells may mediate the neuroprotective effects of mifepristone, in line with the proposed antidepressant effects of AMPA receptor potentiators.

Melanoma differentiation-associated gene 5 is critical for protection against Theiler's virus-induced demyelinating disease

Infection of dendritic and glial cells with Theiler's murine encephalomyelitis virus (TMEV) induces various cytokines via Toll-like receptor- and melanoma differentiation-associated gene 5 (MDA5)-dependent pathways. However, the involvement and role of MDA5 in cytokine gene activation and the pathogenesis of TMEV-induced demyelinating disease are largely unknown. In this study, we demonstrate that MDA5 plays a critical role in the production of TMEV-induced alpha interferon (IFN-α) during early viral infection and in protection against the development of virus-induced demyelinating disease. Our results indicate that MDA5-deficient 129SvJ mice display significantly higher viral loads and apparent demyelinating lesions in the central nerve system (CNS) accompanied by clinical symptoms compared with wild-type 129SvJ mice. During acute viral infection, MDA5-deficient mice produced elevated levels of chemokines, consistent with increased cellular infiltration, but reduced levels of IFN-α, known to control T cell responses and cellular infiltration. Additional studies with isolated CNS glial cells from these mice suggest that cells from MDA5-deficient mice are severely compromised in the production of IFN-α upon viral infection, which results in increased cellular infiltration and viral loads in the CNS. Despite inadequate stimulation, the overall T cell responses to the viral determinants were significantly elevated in MDA5-deficient mice, reflecting the increased cellular infiltration. Therefore, the lack of MDA5-mediated IFN-α production may facilitate a massive viral load and elevated cellular infiltration in the CNS during early viral infection, leading to the pathogenesis of demyelinating disease.

Combined effects of hematopoietic progenitor cell mobilization from bone marrow by granulocyte colony stimulating factor and AMD3100 and chemotaxis into the brain using stromal cell-derived factor-1α in an Alzheimer's disease mouse model

Transplantation of bone marrow-derived stem cells (BMSCs) has been suggested as a potential therapeutic approach to prevent neurodegenerative diseases, but it remains problematic due to issues of engraftment, potential toxicities, and other factors. An alternative strategy is pharmacological-induced recruitment of endogenous BMSCs into an injured site by systemic administration of growth factors or chemokines. Therefore, the aim of this study was to examine the effects of therapy involving granulocyte colony stimulating factor (G-CSF)/AMD3100 (CXCR4 antagonist) and stromal cell-derived factor-1α (SDF-1α) on endogenous BM-derived hematopoietic progenitor cell (BM-HPC) recruitment into the brain of an Alzheimer's disease (AD) mouse model. To mobilize BM-HPCs, G-CSF was injected intraperitoneally and boosted by AMD3100. Simultaneously, these mice received an intracerebral injection with SDF-1α to induce migration of mobilized BM-HPCs into brain. We found that the memory deficit in the AD mice was significantly improved by these treatments, but amyloid β deposition was unchanged. Interestingly, microglial activation was increased with alternative activation of microglia to a neuroprotective phenotype. Furthermore, by generating an amyloid precursor protein/presenilin 1-green fluorescent protein (GFP) chimeric mouse, we ascertained that the GFP positive microglia identified in the brain were BM-derived. Additionally, increased hippocampal neurogenesis and improved memory was observed in mice receiving combined G-CSF/AMD3100 and SDF-1α, but not in controls or animals receiving each treatment alone. These results suggest that SDF-1α is an effective adjuvant in inducing migration into brain of the endogenous BM-HPCs, mobilized by G-CSF/AMD3100, and that the two can act synergistically to produce a therapeutic effect. This approach warrants further investigation as a potential therapeutic option for the treatment of AD patients in the future.

Animal modelling of traumatic brain injury in preclinical drug development: where do we go from here?

Traumatic brain injury (TBI) is the leading cause of death and disability in young adults. Survivors of TBI frequently suffer from long-term personality changes and deficits in cognitive and motor performance, urgently calling for novel pharmacological treatment options. To date, all clinical trials evaluating neuroprotective compounds have failed in demonstrating clinical efficacy in cohorts of severely injured TBI patients. The purpose of the present review is to describe the utility of animal models of TBI for preclinical evaluation of pharmacological compounds. No single animal model can adequately mimic all aspects of human TBI owing to the heterogeneity of clinical TBI. To successfully develop compounds for clinical TBI, a thorough evaluation in several TBI models and injury severities is crucial. Additionally, brain pharmacokinetics and the time window must be carefully evaluated. Although the search for a single-compound, 'silver bullet' therapy is ongoing, a combination of drugs targeting various aspects of neuroprotection, neuroinflammation and regeneration may be needed. In summary, finding drugs and prove clinical efficacy in TBI is a major challenge ahead for the research community and the drug industry. For a successful translation of basic science knowledge to the clinic to occur we believe that a further refinement of animal models and functional outcome methods is important. In the clinical setting, improved patient classification, more homogenous patient cohorts in clinical trials, standardized treatment strategies, improved central nervous system drug delivery systems and monitoring of target drug levels and drug effects is warranted.

New striatal neurons in a mouse model of progressive striatal degeneration are generated in both the subventricular zone and the striatal parenchyma

Acute striatal lesions increase proliferation in the subventricular zone (SVZ) and induce migration of SVZ neuroblasts to the striatum. However, the potential of these cells to replace acutely degenerated neurons is controversial. The possible contribution of parenchymal progenitors to striatal lesion-induced neurogenesis has been poorly explored. Here, we present a detailed investigation of neurogenesis in the striatum of a mouse model showing slow progressive neurodegeneration of striatal neurons, the Creb1^Camkcre4Crem^−/− mutant mice (CBCM). By using BrdU time course analyses, intraventricular injections of a cell tracker and 3D reconstructions we showed that neurodegeneration in CBCM mice stimulates the migration of SVZ neuroblasts to the striatum without altering SVZ proliferation. SVZ-neuroblasts migrate as chains through the callosal striatal border and then enter within the striatal parenchyma as individual cells. In addition, a population of clustered neuroblasts showing high turnover rates were observed in the mutant striatum that had not migrated from the SVZ. Clustered neuroblasts might originate within the striatum itself because they are specifically associated with parenchymal proliferating cells showing features of intermediate neuronal progenitors such as clustering, expression of EGF receptor and multiple glial (SOX2, SOX9, BLBP) and neuronal (Dlx, Sp8, and to some extent DCX) markers. Newborn striatal neurons had a short lifespan and did not replace projection neurons nor expressed sets of transcription factors involved in their specification. The differentiation failure of endogenous neuroblasts likely occurred cell autonomously because transplanted wild type embryonic precursors correctly differentiated into striatal projection neurons. Thus, we propose that under progressive degeneration, neither SVZ derived nor intra-striatal generated neurons have the potential to differentiate into striatal projection neurons.

Inflammation, mitochondria, and the inhibition of adult neurogenesis

The process of neurogenesis continues throughout life, with thousands of new neurons generated every day in the mammalian brain. Impairment of hippocampal neurogenesis has been suggested to be involved in neurodegenerative conditions, including the cognitive decline associated with aging, Alzheimer's disease, Parkinson's disease, and ionizing radiation. These neurodegenerative conditions are all characterized by proinflammatory changes and increased numbers of activated microglia. Activated microglia produce a variety of proinflammatory factors, including interleukin-6, tumor necrosis factor-α, reactive oxygen species, and nitric oxide, all of which are antineurogenic. These same factors have also been shown to suppress mitochondrial function, but the role of mitochondria in neurogenesis remains barely investigated. This brief review summarizes the findings of several studies that support a role for mitochondrial impairment as part of the mechanism of the reduction of neurogenesis associated with inflammation.

Neurogenic potential of the vestibular nuclei and behavioural recovery time course in the adult cat are governed by the nature of the vestibular damage

Functional and reactive neurogenesis and astrogenesis are observed in deafferented vestibular nuclei after unilateral vestibular nerve section in adult cats. The newborn cells survive up to one month and contribute actively to the successful recovery of posturo-locomotor functions. This study investigates whether the nature of vestibular deafferentation has an incidence on the neurogenic potential of the vestibular nuclei, and on the time course of behavioural recovery. Three animal models that mimic different vestibular pathologies were used: unilateral and permanent suppression of vestibular input by unilateral vestibular neurectomy (UVN), or by unilateral labyrinthectomy (UL, the mechanical destruction of peripheral vestibular receptors), or unilateral and reversible blockade of vestibular nerve input using tetrodotoxin (TTX). Neurogenesis and astrogenesis were revealed in the vestibular nuclei using bromodeoxyuridine (BrdU) as a newborn cell marker, while glial fibrillary acidic protein (GFAP) and glutamate decarboxylase 67 (GAD67) were used to identify astrocytes and GABAergic neurons, respectively. Spontaneous nystagmus and posturo-locomotor tests (static and dynamic balance performance) were carried out to quantify the behavioural recovery process. Results showed that the nature of vestibular loss determined the cellular plastic events occurring in the vestibular nuclei and affected the time course of behavioural recovery. Interestingly, the deafferented vestibular nuclei express neurogenic potential after acute and total vestibular loss only (UVN), while non-structural plastic processes are involved when the vestibular deafferentation is less drastic (UL, TTX). This is the first experimental evidence that the vestibular complex in the brainstem can become neurogenic under specific injury. These new data are of interest for understanding the factors favouring the expression of functional neurogenesis in adult mammals in a brain repair perspective, and are of clinical relevance in vestibular pathology.

Systemic inflammation impairs respiratory chemoreflexes and plasticity

Many lung and central nervous system disorders require robust and appropriate physiological responses to assure adequate breathing. Factors undermining the efficacy of ventilatory control will diminish the ability to compensate for pathology, threatening life itself. Although most of these same disorders are associated with systemic and/or neuroinflammation, and inflammation affects neural function, we are only beginning to understand interactions between inflammation and any aspect of ventilatory control (e.g. sensory receptors, rhythm generation, chemoreflexes, plasticity). Here we review available evidence, and present limited new data suggesting that systemic (or neural) inflammation impairs two key elements of ventilatory control: chemoreflexes and respiratory motor (versus sensory) plasticity. Achieving an understanding of mechanisms whereby inflammation undermines ventilatory control is fundamental since inflammation may diminish the capacity for natural, compensatory responses during pathological states, and the ability to harness respiratory plasticity as a therapeutic strategy in the treatment of devastating breathing disorders, such as during cervical spinal injury or motor neuron disease.

Astrocytes are important mediators of Aβ-induced neurotoxicity and tau phosphorylation in primary culture

Alzheimer's disease (AD) is pathologically characterised by the age-dependent deposition of β-amyloid (Aβ) in senile plaques, intraneuronal accumulation of tau as neurofibrillary tangles, synaptic dysfunction and neuronal death. Neuroinflammation, typified by the accumulation of activated microglia and reactive astrocytes, is believed to modulate the development and/or progression of AD. We have used primary rat neuronal, astrocytic and mixed cortical cultures to investigate the contribution of astrocyte-mediated inflammatory responses during Aβ-induced neuronal loss. We report that the presence of small numbers of astrocytes exacerbate Aβ-induced neuronal death, caspase-3 activation and the production of caspase-3-cleaved tau. Furthermore, we show that astrocytes are essential for the Aβ-induced tau phosphorylation observed in primary neurons. The release of soluble inflammatory factor(s) from astrocytes accompanies these events, and inhibition of astrocyte activation with the anti-inflammatory agent, minocycline, reduces astrocytic inflammatory responses and the associated neuronal loss. Aβ-induced increases in caspase-3 activation and the production of caspase-3-truncated tau species in neurons were reduced when the astrocytic response was attenuated with minocycline. Taken together, these results show that astrocytes are important mediators of the neurotoxic events downstream of elevated Aβ in models of AD, and suggest that mechanisms underlying pro-inflammatory cytokine release might be an important target for therapy.

Adult neurogenesis is regulated by endogenous factors produced during neurodegeneration

Adult neurogenesis is the process of generating new neurons that become integrated into existing circuits after fetal and early postnatal development has ceased. In most mammalian species, adult neurogenesis only appears to occur in the olfactory bulb and the hippocampus, where neural stem/progenitor cells (NPCs) exist to create new neurons. In adult neurogenesis, microenviromental change is thought to provide a specific modulation for maintaining the multi-potent state of these NPCs. Neurodegeneration is driven by the activation of resident microglia, astrocytes, and infiltrating peripheral macrophages, which release a plethora of cytokines, chemokines, neurotransmitters, and reactive oxygen species. These endogenous factors cause further bystander damage to neurons and produces both detrimental and favorable conditions for neurogenesis. Interestingly, these endogenous factors also affect the proliferation, migration, differentiation, and survival of the NPCs, as well as regulate the incorporation of newly formed neurons into the brain circuitry. The unique profile of the endogenous factors released can vary the degree of neuroregeneration after neurodegeneration. This current review summarizes recent knowledge in the emerging field that is showing that adult neurogenesis is regulated by endogenous factors produced during neurodegeneration.

S100B protein stimulates microglia migration via RAGE-dependent up-regulation of chemokine expression and release

The Ca(2+)-binding protein of the EF-hand type, S100B, is abundantly expressed in and secreted by astrocytes, and release of S100B from damaged astrocytes occurs during the course of acute and chronic brain disorders. Thus, the concept has emerged that S100B might act an unconventional cytokine or a damage-associated molecular pattern protein playing a role in the pathophysiology of neurodegenerative disorders and inflammatory brain diseases. S100B proinflammatory effects require relatively high concentrations of the protein, whereas at physiological concentrations S100B exerts trophic effects on neurons. Most if not all of the extracellular (trophic and toxic) effects of S100B in the brain are mediated by the engagement of RAGE (receptor for advanced glycation end products). We show here that high S100B stimulates murine microglia migration in Boyden chambers via RAGE-dependent activation of Src kinase, Ras, PI3K, MEK/ERK1/2, RhoA/ROCK, Rac1/JNK/AP-1, Rac1/NF-κB, and, to a lesser extent, p38 MAPK. Recruitment of the adaptor protein, diaphanous-1, a member of the formin protein family, is also required for S100B/RAGE-induced migration of microglia. The S100B/RAGE-dependent activation of diaphanous-1/Rac1/JNK/AP-1, Ras/Rac1/NF-κB and Src/Ras/PI3K/RhoA/diaphanous-1 results in the up-regulation of expression of the chemokines, CCL3, CCL5, and CXCL12, whose release and activity are required for S100B to stimulate microglia migration. Lastly, RAGE engagement by S100B in microglia results in up-regulation of the chemokine receptors, CCR1 and CCR5. These results suggests that S100B might participate in the pathophysiology of brain inflammatory disorders via RAGE-dependent regulation of several inflammation-related events including activation and migration of microglia.

A new role for interferon gamma in neural stem/precursor cell dysregulation

Background

The identification of factors that compromise neurogenesis is aimed at improving stem cell-based approaches in the field of regenerative medicine. Interferon gamma (IFNγ) is a main pro-inflammatory cytokine and up-regulated during several neurological diseases. IFNγ is generally thought to beneficially enhance neurogenesis from fetal or adult neural stem/precursor cells (NSPCs).

Results

We now provide direct evidence to the contrary that IFNγ induces a dysfunctional stage in a substantial portion of NSPC-derived progeny in vitro characterized by simultaneous expression of glial fibrillary acid protein (GFAP) and neuronal markers, an abnormal gene expression and a functional phenotype neither typical for neurons nor for mature astrocytes. Dysfunctional development of NSPCs under the influence of IFNγ was finally demonstrated by applying the microelectrode array technology. IFNγ exposure of NSPCs during an initial 7-day proliferation period prevented the subsequent adequate differentiation and formation of functional neuronal networks.

Conclusions

Our results show that immunocytochemical analyses of NSPC-derived progeny are not necessarily indicating the correct cellular phenotype specifically under inflammatory conditions and that simultaneous expression of neuronal and glial markers rather point to cellular dysregulation. We hypothesize that inhibiting the impact of IFNγ on NSPCs during neurological diseases might contribute to effective neurogenesis and regeneration.

Inflammation and prevention of epileptogenesis

CNS injuries such as trauma, stroke, viral infection, febrile seizures, status epilepticus occurring either in infancy or during a lifetime are considered common risk factors for developing epilepsy. Long term CNS inflammation develops rapidly after these events, suggesting that a pro-inflammatory state in the brain might play a role in the development of the epileptic process. This hypothesis is corroborated by two main lines of evidence: (1) the upregulation of pro-inflammatory signals during epileptogenesis in brain areas of seizure onset/generalization; (2) pharmacological targeting of specific pro-inflammatory pathways after status epilepticus or in kindling shows antiepileptogenic effects. The mechanisms by which pro-inflammatory molecules might favor the establishment of chronic neuronal network hyperexcitability involve both rapid, non-transcriptional effects on glutamate and GABA receptors, and transcriptional activation of genes involved in synaptic plasticity. This emerging evidence predicts that pharmacological interventions targeting brain inflammation might provide a key to new antiepileptic drug design.

Differential regulation of proliferation and differentiation in neural precursor cells by the Jak pathway

Neuronal precursor cells (NPCs) are temporally regulated and have the ability to proliferate and differentiate into mature neurons, oligodendrocytes, and astrocytes in the presence of growth factors (GFs). In the present study, the role of the Jak pathway in brain development was investigated in NPCs derived from neurosphere cultures using Jak2 and Jak3 small interfering RNAs and specific inhibitors. Jak2 inhibition profoundly decreased NPC proliferation, preventing further differentiation into neurons and glial cells. However, Jak3 inhibition induced neuronal differentiation accompanied by neurite growth. This phenomenon was due to the Jak3 inhibition-mediated induction of neurogenin (Ngn)2 and NeuroD in NPCs. Jak3 inhibition induced NPCs to differentiate into scattered neurons and increased the expression of Tuj1, microtubule associated protein 2 (MAP2), Olig2, and neuroglial protein (NG)2, but decreased glial fibrillary acidic protein (GFAP) expression, with predominant neurogenesis/polydendrogenesis compared with astrogliogenesis. Therefore, Jak2 may be important for NPC proliferation and maintenance, whereas knocking-down of Jak3 signaling is essential for NPC differentiation into neurons and oligodendrocytes but does not lead to astrocyte differentiation. These results suggest that NPC proliferation and differentiation are differentially regulated by the Jak pathway.

Human immunodeficiency virus type 1 Tat modulates proliferation and differentiation of human neural precursor cells: implication in NeuroAIDS

Human immunodeficiency virus type 1 (HIV-1) and viral proteins affect neuronal survival and neuron-glial cell interactions, which culminate in neurological disorders. HIV-1 infects regions of neurogenesis in human adult and pediatric brain. However, little is known about the effect of HIV-1 or viral proteins on the properties of human neural precursor cells (hNPCs), particularly neurogenesis, hence a detailed investigation on these lines is warranted. Human neural precursor cells were cultured in presence and absence of HIV-1B transactivating protein Tat to investigate if HIV-1 viral protein alters the properties of human neural precursor cells. Cellular and molecular approaches were adopted to study the effect of HIV-1B transactivating protein Tat on proliferation and differentiation potential of human fetal brain-derived NPCs. Cell proliferation assays such as BrdU and Ki67 staining and pathway-specific cDNA and protein arrays were used in the study. Data reveal that HIV-1B Tat protein severely affects proliferation of hNPCs, as evident by lower incorporation of BrdU and Ki67 staining as well as neurosphere assay. HIV-1 Tat substantially attenuated neurogenesis, as evident by the smaller numbers of Tuj-1- and doublecortin-positive cells differentiated from hNPCs, without affecting their viability. These data suggest that HIV-1 Tat alters the properties of human neural precursor cells via attenuation of the cell cycle regulatory unit cyclin D1 and the mitogen-activated protein kinase (MAPK) pathway, particularly extracellular signal-related kinase 1/2 (ERK1/2). The study provides new insights into cellular and molecular mechanisms that may modulate human neural precursor cell properties in HIV/AIDS (acquired immunodeficiency syndrome) individuals. Validation with autopsy brain samples is necessary to further substantiate these important observations.

Cymbopogon citratus as source of new and safe anti-inflammatory drugs: bio-guided assay using lipopolysaccharide-stimulated macrophages

ETHNOPHARMACOLOGICAL RELEVANCE

Aqueous extracts of Cymbopogon citratus (Cy) leaves are used in traditional medicine for the treatment of inflammatory conditions, however, little is known about their mechanism of action.

AIM OF THE STUDY

The aim of this study is to explore the anti-inflammatory properties of Cymbopogon citratus leaves and their polyphenol-rich fractions (PFs), as well its mechanism of action in murine macrophages.

MATERIALS AND METHODS

A lipid- and essential oil-free infusion of Cy leaves was prepared (Cy extract) and fractionated by column chromatography. Anti-inflammatory properties of Cy extract (1.115 mg/ml) and its PFs, namely phenolic acids (530 μg/ml), flavonoids (97.5 μg/ml) and tannins (78 μg/ml), were investigated using lipopolysaccharide (LPS)-stimulated Raw 264.7 macrophages as in vitro model. As inflammatory parameters, nitric oxide (NO) production was evaluated by Griess reaction, as well as effects on cyclooxygenase-2 (COX-2), inducible NO synthase (iNOS) expression and on intracellular signaling pathways activation, which were analyzed by Western blot using specific antibodies.

RESULTS

Cy extract inhibited iNOS expression, NO production and various LPS-induced pathways like p38 mitogen-activated protein kinase (MAPK), c-jun NH(2)-terminal kinase (JNK) 1/2 and the transcription nuclear factor (NF)-κB. The extracellular signal-regulated kinase (ERK) 1/2 and the phosphatidylinositol-3-kinase (PI3K)/Akt activation were not affected by Cy extract. Both phenolic acid- and tannin-rich fractions significantly inhibited NF-κB activation, iNOS expression and NO production but none of the PFs modulated MAPKs or PI3K/Akt activation. Neither Cy extract nor PFs affected LPS-induced COX-2 expression but LPS-induced PGE(2) production is inhibited by Cy extract and by phenolic acid-rich fraction.

CONCLUSIONS

Our data provide evidence that support the usage of Cymbopogon citratus leaves extract in traditional medicine, and suggest that Cy, in particular its polyphenolic compounds, could constitute a natural source of a new and safe anti-inflammatory drug.

Evaluating the role of Toll-like receptors in diseases of the central nervous system

A key part of the innate immune system is a network of pattern recognition receptors (PRRs) and their associated intracellular signalling pathways. Toll-like receptors (TLRs) are one such group of PRRs that detect pathogen associated molecular patterns (PAMPs). Activation of the TLRs with their respective agonists results in the activation of intracellular signalling pathways leading to the expression of proinflammatory mediators and anti-microbial effector molecules. Activation of the innate immune system through TLRs also triggers the adaptive immune response, resulting in a comprehensive immune program to eradicate invading pathogens. It is now known that immune surveillance and inflammatory responses occur in the central nervous system (CNS). Furthermore it is becoming increasingly clear that TLRs have a role in such CNS responses and are also implicated in the pathogenesis of a number of conditions in the CNS, such as Alzheimer's, stroke and multiple sclerosis. This is likely due to the generation of endogenous TLR agonists in these conditions which amplifies a detrimental neurotoxic inflammatory response. However TLRs in some situations can be neuroprotective, if triggered in a favourable context. This review aims to examine the recent literature on TLRs in the CNS thus demonstrating their importance in a range of infectious and non-infectious diseases of the brain.

Effect of human neural precursor cell transplantation on endogenous neurogenesis after focal cerebral ischemia in the rat

Little is known about the relationship between neuronal cell transplantation and endogenous neurogenesis after experimental stroke. We found previously that transplantation of neuronal precursors derived from BG01 human embryonic stem cells reduced infarct volume and improved behavioral outcome after distal middle cerebral artery occlusion (MCAO) in rats. In this study, transplantation was performed 14 days after distal MCAO and doublecortin (Dcx)-expressing cells in the subventricular zone (SVZ) and subgranular zone of dentate gyrus (SGZ) were counted 60 days post-transplant. Transplantation increased neurogenesis (Dcx expression) in ipsilateral SVZ, but not in contralateral SVZ or either SGZ, in both young adult (3-month-old) and aged (24-month-old) rats. These findings suggest that cell-based therapy for stroke may be associated with changes in endogenous adaptive processes, including neurogenesis.

Prenatal inflammation impairs adult neurogenesis and memory related behavior through persistent hippocampal TGFβ1 downregulation

Prenatal exposure to inflammatory stimuli is known to influence adult brain function. In addition, adult hippocampal neurogenesis is impaired by a local pro-inflammatory microenvironment. On this basis, we hypothesized that a pro-inflammatory insult during gestation would have negative effects on adult neurogenesis in the offspring. Pregnant Wistar rats received subcutaneous injections of lipopolysaccharide (LPS; 0.5mg/kg) or saline every other day from gestational day 14 to 20. The adult offspring prenatally treated with LPS showed a decrease in the proliferating cells and the newborn neurons of the dentate gyrus. Furthermore, prenatal LPS treatment impaired performance in the neurogenesis-dependent novel object recognition test. Maternal care was impaired by prenatal LPS administration but did not contribute to the effects of prenatal LPS on adult neurogenesis. Persistent microglial activation and downregulated expression of transforming growth factor beta-1 (TGFβ(1)) occurred specifically in the adult hippocampus of animals treated prenatally with LPS. Importantly, chronic hippocampal TGFβ(1) overexpression restored neurogenesis as well as recognition memory performance to control levels. These findings demonstrate that prenatal inflammation triggered by LPS impairs adult neurogenesis and recognition memory. Furthermore, we provide a model of reduced adult neurogenesis with long-lasting defined alterations in the neurogenic niche. Finally, we show that the expression of a single cytokine (TGFβ(1)) in the hippocampus can restore adult neurogenesis and its related behavior, highlighting the role of TGFβ(1) in these processes.

Neuroimmune pharmacology from a neuroscience perspective

The focus of this commentary is to describe how neuroscience, immunology, and pharmacology intersect and how interdisciplinary research involving these areas has expanded knowledge in the area of neuroscience, in particular. Examples are presented to illustrate that the brain can react to the peripheral immune system and possesses immune function and that resident immune molecules play a role in normal brain physiology. In addition, evidence is presented that the brain immune system plays an important role in mediating neurodegenerative diseases, the aging process, and neurodevelopment and synaptic plasticity. The identification of these mechanisms has been facilitated by pharmacological studies and has opened new possibilities for pharmacotherapeutic approaches to the treatment of brain disorders. The emerging field of neuroimmune pharmacology exemplifies this interdisciplinary approach and has facilitated the study of basic cellular and molecular events and disease states and opens avenues for novel therapies.

Immune system modulates the function of adult neural stem cells

New neurons are continuously produced in most, if not all, mammals. This Neurogenesis occurs only in discrete regions of the adult brain: the subventricular zone (SVZ) and the subgranular zone (SGZ). In these areas, there are neural stem cells (NSCs), multipotent and selfrenewing, which are regulated by a number of molecules and signaling pathways that control their cell fate choices, survival and proliferation rates. It was believed that growth and morphogenic factors were the unique mediators that controlled NSCs in vivo. Recently, chemokines and cytokines have been identified as important regulators of NSCs functions. Some of the most studied immunological effectors are leukemia inhibitory factor (LIF), ciliary neurotrophic factor (CNTF), interferon-gamma (IFN-γ), insulin-like growth factor-1 (IGF-1), tumor necrosis factor alpha (TNF-α), and the chemokines MCP-1 and SDF-1. These substances exert a considerable regulation on proliferation, cell-fate choices, migration and survival of NSCs. Hence, the immune system is emerging as an important regulator of neurogenic niches in the adult brain, but further studies are necessary to fully establish the biological meaning of these neural effects.

APP intracellular domain impairs adult neurogenesis in transgenic mice by inducing neuroinflammation

BACKGROUND

A devastating aspect of Alzheimer's disease (AD) is the progressive deterioration of memory due to neuronal loss. Amyloid precursor protein (APP) occupies a central position in AD and APP-derived amyloid-beta (Abeta) peptides are thought to play a pivotal role in disease pathogenesis. Nonetheless, it is becoming clear that AD etiology is highly complex and that factors other than Abeta also contribute to AD pathogenesis. APP intracellular domain (AICD) is generated together with Abeta and we recently showed that AICD transgenic mice recapitulate pathological features of AD such as tau hyperphosphorylation, memory deficits and neurodegeneration without increasing the Abeta levels. Since impaired adult neurogenesis is shown to augment memory deficits in AD mouse models, here we examined the status of adult neurogenesis in AICD transgenic mice.

METHODOLOGY/PRINCIPAL FINDING

We previously generated transgenic mice co-expressing 59-residue long AICD fragment and its binding partner Fe65. Hippocampal progenitor cell proliferation was determined by BrdU incorporation at 1.5, 3 and 12 months of age. Only male transgenic and their respective wilt type littermate control mice were used. We find age-dependent decrease in BrdU incorporation and doublecortin-positive cells in the dentate gyrus of AICD transgenic mice suggesting impaired adult neurogenesis. This deficit resulted from decreased proliferation and survival, whereas neuronal differentiation remained unaffected. Importantly, this impairment was independent of Abeta since APP-KO mice expressing AICD also exhibit reduced neurogenesis. The defects in adult neurogenesis are prevented by long-term treatment with the non-steroidal anti-inflammatory agents ibuprofen or naproxen suggesting that neuroinflammation is critically involved in impaired adult neurogenesis in AICD transgenic mice.

CONCLUSION/SIGNIFICANCE

Since adult neurogenesis is crucial for spatial memory, which is particularly vulnerable in AD, these findings suggest that AICD can exacerbate memory defects in AD by impairing adult neurogenesis. Our findings further establish that AICD, in addition to Abeta, contributes to AD pathology and that neuroinflammation plays a much broader role in AD pathogenesis than previously thought.

Stem cell quiescence in the hippocampal neurogenic niche is associated with elevated transforming growth factor-beta signaling in an animal model of Huntington disease

Cellular proliferation, differentiation, integration, and survival within the adult neural stem cell niche are altered under pathological conditions, but the molecular cues regulating the biology of this niche are mostly unknown. We examined the hippocampal neural stem cell niche in a transgenic rat model of Huntington disease. In this model, progressive cognitive deficits develop at the age of 9 months, suggesting possible hippocampal dysfunction. We found a disease-associated progressive decline in hippocampal progenitor cell proliferation accompanied by an expansion of the pool of 5-bromo-2-deoxyuridine label-retaining Sox-2-positive quiescent stem cells in the transgenic animals. Increments in quiescent stem cells occurred at the expense of cAMP-responsive element-binding protein-mediated neuronal differentiation and survival. Because elevated levels of transforming growth factor-beta1 (TGF-beta1) impair neural progenitor proliferation, we investigated hippocampal TGF-beta signaling and determined that TGF-beta1 induces the neural progenitors to exit the cell cycle. Although phospho-Smad2, an effector of TGF-beta signaling, is normally absent in subgranular stem cells, it accumulated progressively in Sox2/glial fibrillary acidic protein-expressing cells of the subgranular zone in the transgenic rats. These results indicate that alterations in neurogenesis in transgenic Huntington disease rats occur in successive phases that are associated with increasing TGF-beta signaling. Thus, TGF-beta1 signaling seems to be a crucial modulator of neurogenesis in Huntington disease and may represent a target for future therapy.