Involvement of prostaglandin E2 released from leptomeningeal cells in increased expression of transforming growth factor-β in glial cells and cortical neurons during systemic inflammation

Morphofunctional Changes in Brain and Peripheral Blood in Adult and Aged Wistar Rats with AlCl3-Induced Neurodegeneration

BACKGROUND

the general lifespan has been prolonged greatly during the past century, and the incidence of age-associated diseases, including neurodegenerative ones, has increased as well. However, modelling of age-related pathologies is mostly conducted on adult rodents. We studied morphofunctional changes in the brain and peripheral blood of adult Wistar rats in comparison with old Wistar rats to determine age-related physiological changes and differences in adaptive reactions to AlCl3 exposure.

METHODS

the work was performed on adult and old male Wistar rats. The animals consumed a 100 mg/kg solution of AlCl3 each day for 60 days. Morphological changes of neurons and microglia, mRNA expression levels of pro-inflammatory and anti-inflammatory cytokines, microglia activation markers, amyloid-related proteins, and hallmarks of cellular senescence, monocyte, and lymphocyte subpopulations in the peripheral blood were examined.

RESULTS

old rats showed increasing hyperchromic neurons in the hippocampus; activation of microglia; upregulation of pro-inflammatory cytokines and cellular senescence markers; downregulation of anti-inflammatory cytokines; and Hif-1a and a decrease in B-cells and monocyte in peripheral blood.

CONCLUSION

compared to young animals, aged rats respond to aluminum exposure with a severe decline of most cells' function and irreversible neuronal loss. Regarding all reported data, neurodegeneration modelling and investigating of factors capable of accelerating or preventing it should be performed in experimental work on aged animals.

Inflammation Spreading: Negative Spiral Linking Systemic Inflammatory Disorders and Alzheimer's Disease

As a physiological response to injury in the internal body organs, inflammation is responsible for removing dangerous stimuli and initiating healing. However, persistent and exaggerative chronic inflammation causes undesirable negative effects in the organs. Inflammation occurring in the brain and spinal cord is known as neuroinflammation, with microglia acting as the central cellular player. There is increasing evidence suggesting that chronic neuroinflammation is the most relevant pathological feature of Alzheimer’s disease (AD), regulating other pathological features, such as the accumulation of amyloid-β (Aβ) and hyperphosphorylation of Tau. Systemic inflammatory signals caused by systemic disorders are known to strongly influence neuroinflammation as a consequence of microglial activation, inflammatory mediator production, and the recruitment of peripheral immune cells to the brain, resulting in neuronal dysfunction. However, the neuroinflammation-accelerated neuronal dysfunction in AD also influences the functions of peripheral organs. In the present review, we highlight the link between systemic inflammatory disorders and AD, with inflammation serving as the common explosion. We discuss the molecular mechanisms that govern the crosstalk between systemic inflammation and neuroinflammation. In our view, inflammation spreading indicates a negative spiral between systemic diseases and AD. Therefore, “dampening inflammation” through the inhibition of cathepsin (Cat)B or CatS may be a novel therapeutic approach for delaying the onset of and enacting early intervention for AD.

Coniferyl Aldehyde Inhibits the Inflammatory Effects of Leptomeningeal Cells by Suppressing the JAK2 Signaling

Background

The brain is in many ways an immunologically and pharmacologically privileged site because of the blood-brain barrier (BBB). But for chronic peripheral inflammation, inflammatory signals can be transmitted from the peripheral system into the central nervous system (CNS) through multiple channels and result in neuroinflammation. Leptomeningeal cells that form the BBB can trigger one signaling pathway by releasing cytokines to transmit inflammatory signals. Besides, the Janus kinase (JAK) family may have a certain function in the activation of leptomeninges. In the present study, we try to use coniferyl aldehyde (CA), a natural anti-inflammatory phenolic compound, to inhibit this inflammatory process and elucidate the underlying molecular mechanisms.

Results

Secretion of proinflammatory cytokines (TNF-α, IL-1β, and IL-6) significantly increased after incubation with P. gingivalis. Moreover, TNF-α, IL-1β, and IL-6 levels were upregulated, and the JAK2 signaling was enhanced in leptomeningeal cells in a conditioned medium from activated macrophages, which leads to the immune response in microglia. However, this inflammatory effect of leptomeningeal cells was reversed by CA administration, accompanied by the decreased immune response in microglia. The western blot assay revealed that JAK2 phosphorylation was suppressed in leptomeningeal cells treated with CA.

Conclusions

This study demonstrates that activated macrophages by P. gingivalis markedly induce the release of proinflammatory cytokines (TNF-α, IL-1β, and IL-6) from leptomeningeal cells, thereby activating the JAK2 signaling pathway and subsequently enhancing immune responses in microglia in the CNS. CA effectively inhibits the inflammatory effect of leptomeningeal cells via suppressing the JAK2 signaling pathway.

Interaction between genetic factors, Porphyromonas gingivalis and microglia to promote Alzheimer's disease

In late-onset Alzheimer disease (AD) pathogenesis, genes, infections and immunity could be significant factors. We have reviewed if the keystone periodontal pathogen Porphyromonas gingivalis may affect genes and microglia (primary immune cells in the brain) to promote AD development. Genes for apolipoprotein, clusterin, CD33, triggering receptor expressed on myeloid cells-2 (TREM-2), tyrosine kinase binding protein (TYR-OBP), and complement receptors can affect microglia. Most of these genes can also be affected by P. gingivalis via its mastering of immune suppression. Besides, P. gingivalis can affect microglia directly in several ways. Taken together, genetic predisposition, P. gingivalis infection and microglia could promote neurodegeneration typical of that reported for AD.

Targeting Microglia and Macrophages: A Potential Treatment Strategy for Multiple Sclerosis

Multiple sclerosis (MS) is a chronic inflammatory neurodegenerative disease of the central nervous system (CNS). The early stage is characterized by relapses and the later stage, by progressive disability. Results from experimental and clinical investigations have demonstrated that microglia and macrophages play a key part in the disease course. These cells actively initiate immune infiltration and the demyelination cascade during the early phase of the disease; however, they promote remyelination and alleviate disease in later stages. This review aims to provide a comprehensive overview of the existing knowledge regarding the neuromodulatory function of macrophages and microglia in the healthy and injured CNS, and it discusses the feasibility of harnessing microglia and macrophage physiology to treat MS. The review encourages further investigations into macrophage-targeted therapy, as well as macrophage-based drug delivery, for realizing efficient treatment strategies for MS.

Diurnal dynamic behavior of microglia in response to infected bacteria through the UDP-P2Y6 receptor system

It has long been believed that microglia morphologically transform into the activated state by retracting their long processes and consuming pathogens when bacteria infect into the brain parenchyma. In the present study, however, we showed for the first time that murine cortical microglia extend their processes towards focally injected Porphyromonas gingivalis. This P. gingivalis-induced microglial process extension was significantly increased during the light (sleeping) phase than the dark (waking) phase. In contrast, focally injected ATP-induced microglial process extension was significantly increased during the dark phase than the light phase. Furthermore, in contrast to the P2Y₁₂ receptor-mediated mechanism of ATP-induced microglial process extension, the P. gingivalis-mediated microglial process extension was mediated by P2Y₆ receptors. The infection of bacteria such as P. gingivalis to the brain parenchyma may induce the secretion of UDP from microglia at the site of infection, which in turn induces the process extension of the neighboring microglia.

Nutrients, Microglia Aging, and Brain Aging

As the life expectancy continues to increase, the cognitive decline associated with Alzheimer's disease (AD) becomes a big major issue in the world. After cellular activation upon systemic inflammation, microglia, the resident immune cells in the brain, start to release proinflammatory mediators to trigger neuroinflammation. We have found that chronic systemic inflammatory challenges induce differential age-dependent microglial responses, which are in line with the impairment of learning and memory, even in middle-aged animals. We thus raise the concept of “microglia aging.” This concept is based on the fact that microglia are the key contributor to the acceleration of cognitive decline, which is the major sign of brain aging. On the other hand, inflammation induces oxidative stress and DNA damage, which leads to the overproduction of reactive oxygen species by the numerous types of cells, including macrophages and microglia. Oxidative stress-damaged cells successively produce larger amounts of inflammatory mediators to promote microglia aging. Nutrients are necessary for maintaining general health, including the health of brain. The intake of antioxidant nutrients reduces both systemic inflammation and neuroinflammation and thus reduces cognitive decline during aging. We herein review our microglia aging concept and discuss systemic inflammation and microglia aging. We propose that a nutritional approach to controlling microglia aging will open a new window for healthy brain aging.

Lessons from Microglia Aging for the Link between Inflammatory Bone Disorders and Alzheimer's Disease

Bone is sensitive to overactive immune responses, which initiate the onset of inflammatory bone disorders, such as rheumatoid arthritis and periodontitis, resulting in a significant systemic inflammatory response. On the other hand, neuroinflammation is strongly implicated in Alzheimer's disease (AD), which can be enhanced by systemic inflammation, such as that due to cardiovascular disease and diabetes. There is growing clinical evidence supporting the concept that rheumatoid arthritis and periodontitis are positively linked to AD, suggesting that inflammatory bone disorders are risk factors for this condition. Recent studies have suggested that leptomeningeal cells play an important role in transducing systemic inflammatory signals to brain-resident microglia. More importantly, senescent-type, but not juvenile-type, microglia provoke neuroinflammation in response to systemic inflammation. Because the prevalence of rheumatoid arthritis and periodontitis increases with age, inflammatory bone disorders may be significant sources of covert systemic inflammation among elderly people. The present review article highlights our current understanding of the link between inflammatory bone disorders and AD with a special focus on microglia aging.

The activation of NG2 expressing cells is downstream to microglial reaction and mediated by the transforming growth factor beta 1

In the present study, we investigated the mechanism of activation of NG2 expressing cells. Application of microglial inhibitors not only attenuated morphological changes but also significantly retarded increase in the number of NG2 expressing cells. Intracerebral injection of TGF-β1 led to a profound activation of NG2 glia as well as an earlier accumulation of NG2(+)-microglia, whilst inhibition of TGF-β1 Smad2/3 signalling pathway eventually attenuated their active responses. We conclude that the activation of NG2 expressing cells is an event downstream to microglial reaction and TGF-β1 secreted from microglia might play an important role in modulation of the function of NG2 expressing cells.

Connection between periodontitis and Alzheimer's disease: possible roles of microglia and leptomeningeal cells

Neuroinflammation, inflammation of the brain, is strongly implicated in Alzheimer's disease (AD), which can be enhanced by systemic inflammation. Therefore, the initiation and progression of AD are affected by systemic diseases such as cardiovascular disease and diabetes. This concept suggests a possible link between periodontitis and AD because periodontitis is a peripheral, chronic infection that elicits a significant systemic inflammatory response. There is now growing clinical evidence that chronic periodontitis is closely linked to the initiation and progression of AD. Recent studies have suggested that leptomeningeal cells play an important role in transducing systemic inflammatory signals to the brain-resident microglia, which in turn initiate neuroinflammation. Furthermore, it is apparent that senescent-type microglia respond in an exaggerated manner to systemic inflammation. It is estimated that a high percentage of adults are suffering from periodontitis, and the prevalence of periodontitis increases with age. Therefore, chronic periodontitis can be a significant source of covert systemic inflammation within the general population. The present review article highlights our current understanding of the link between periodontitis and AD.

HHV-7 in adults with drug-resistant epilepsy: a pathological role in hippocampal sclerosis?

BACKGROUND

Human herpesvirus-7 (HHV-7) is a β-herpesvirus associated with febrile seizures. No association between HHV-7 and epilepsy has been confirmed.

OBJECTIVES

The aim of this study was to investigate the presence of HHV-7 protein (KR4) in brain tissue from patients with drug-resistant epilepsy and to determine whether inflammatory molecules are activated in the presence of HHV-7 infection.

STUDY DESIGN

We used immunohistochemistry (IHC) to detect HHV-7 protein KR4 in samples from 305 patients with drug-resistant epilepsy. Liquid nitrogen-preserved hippocampal sclerosis (HS) samples from 63 of these patients were available, and we used nested polymerase chain reaction (PCR) to detect HHV-7 DNA. Inflammatory molecules including tumor necrosis factor-alpha (TNF-α), transforming growth factor-beta (TGF-β), interleukin-1 (IL-1) and interleukin-6 (IL-6) were identified by real-time PCR (rt-PCR) and IHC.

RESULTS AND CONCLUSIONS

The study sample included 201 male subjects. The mean age was 23.9, SD 6.2 years (range 15-45). HS was the pathology in 69 samples (23%). The HHV-7 protein was detected in 27 (9%) of the 305 samples and in none of the 42 controls. The factors associated with HHV-7 infection were HS (11/69), glial scar (8/58), arachnoid cyst (2/21), focal cortical dysplasia (2/31) and vascular malformation (4/52). HHV-7 antigen was distributed mainly in the cytoplasm of astrocyte and oligodendrocyte in HS samples. HHV-7 DNA was detected in 20 of the 63 nitrogen preserved HS samples. The expression of TGF-β was up-regulated in samples that were positive for the HHV-7 protein and was mainly detected in neurons. This finding suggests a possible association between HHV-7 positivity, activation of TGF-β and drug-resistant epilepsy, especially HS, but these data need to be replicated.

Macrophage subsets and microglia in multiple sclerosis

Along with microglia and monocyte-derived macrophages, macrophages in the perivascular space, choroid plexus, and meninges are the principal effector cells in neuroinflammatory and neurodegenerative disorders. These phagocytes are highly heterogeneous cells displaying spatial- and temporal-dependent identities in the healthy, injured, and inflamed CNS. In the last decade, researchers have debated on whether phagocytes subtypes and phenotypes are pathogenic or protective in CNS pathologies. In the context of this dichotomy, we summarize and discuss the current knowledge on the spatiotemporal physiology of macrophage subsets and microglia in the healthy and diseased CNS, and elaborate on factors regulating their behavior. In addition, the impact of macrophages present in lymphoid organs on CNS pathologies is defined. The prime focus of this review is on multiple sclerosis (MS), which is characterized by inflammation, demyelination, neurodegeneration, and CNS repair, and in which microglia and macrophages have been extensively scrutinized. On one hand, microglia and macrophages promote neuroinflammatory and neurodegenerative events in MS by releasing inflammatory mediators and stimulating leukocyte activity and infiltration into the CNS. On the other hand, microglia and macrophages assist in CNS repair through the production of neurotrophic factors and clearance of inhibitory myelin debris. Finally, we define how microglia and macrophage physiology can be harnessed for new therapeutics aimed at suppressing neuroinflammatory and cytodegenerative events, as well as promoting CNS repair. We conclude that microglia and macrophages are highly dynamic cells displaying disease stage and location-specific fates in neurological disorders. Changing the physiology of divergent phagocyte subsets at particular disease stages holds promise for future therapeutics for CNS pathologies.

Interactions between glia, the immune system and pain processes during early development

Pain is a serious problem for infants and children and treatment options are limited. Moreover, infants born prematurely or hospitalized for illness likely have concurrent infection that activates the immune system. It is now recognized that the immune system in general and glia in particular influence neurotransmission and that the neural bases of pain are intimately connected to immune function. We know that injuries that induce pain activate immune function and suppressing the immune system alleviates pain. Despite this advance in our understanding, virtually nothing is known of the role that the immune system plays in pain processing in infants and children, even though pain is a serious clinical issue in pediatric medicine. This brief review summarizes the existing data on immune-neural interactions in infants, providing evidence for the immaturity of these interactions.

Leptomeningeal cells transduce peripheral macrophages inflammatory signal to microglia in reponse to Porphyromonas gingivalis LPS

We report here that the leptomeningeal cells transduce inflammatory signals from peripheral macrophages to brain-resident microglia in response to Porphyromonas gingivalis (P.g.) LPS. The expression of Toll-like receptor 2 (TLR2), TLR4, TNF-α, and inducible NO synthase was mainly detected in the gingival macrophages of chronic periodontitis patients. In in vitro studies, P.g. LPS induced the secretion of TNF-α and IL-1β from THP-1 human monocyte-like cell line and RAW264.7 mouse macrophages. Surprisingly, the mean mRNA levels of TNF-α and IL-1β in leptomeningeal cells after treatment with the conditioned medium from P.g. LPS-stimulated RAW264.7 macrophages were significantly higher than those after treatment with P.g. LPS alone. Furthermore, the mean mRNA levels of TNF-α and IL-1β in microglia after treatment with the conditioned medium from P.g. LPS-stimulated leptomeningeal cells were significantly higher than those after P.g. LPS alone. These observations suggest that leptomeninges serve as an important route for transducing inflammatory signals from macrophages to microglia by secretion of proinflammatory mediators during chronic periodontitis. Moreover, propolis significantly reduced the P.g. LPS-induced TNF-α and IL-1 β production by leptomeningeal cells through inhibiting the nuclear factor-κB signaling pathway. Together with the inhibitory effect on microglial activation, propolis may be beneficial in preventing neuroinflammation during chronic periodontitis.

Meningeal and choroid plexus cells--novel drug targets for CNS disorders

The meninges and choroid plexus perform many functions in the developing and adult human central nervous system (CNS) and are composed of a number of different cell types. In this article I focus on meningeal and choroid plexus cells as targets for the development of drugs to treat a range of traumatic, ischemic and chronic brain disorders. Meningeal cells are involved in cortical development (and their dysfunction may be involved in cortical dysplasia), fibrotic scar formation after traumatic brain injuries (TBI), brain inflammation following infections, and neurodegenerative disorders such as Multiple Sclerosis (MS) and Alzheimer's disease (AD) and other brain disorders. The choroid plexus regulates the composition of the cerebrospinal fluid (CSF) as well as brain entry of inflammatory cells under basal conditions and after injuries. The meninges and choroid plexus also link peripheral inflammation (occurring in the metabolic syndrome and after infections) to CNS inflammation which may contribute to the development and progression of a range of CNS neurological and psychiatric disorders. They respond to cytokines generated systemically and secrete cytokines and chemokines that have powerful effects on the brain. The meninges may also provide a stem cell niche in the adult brain which could be harnessed for brain repair. Targeting meningeal and choroid plexus cells with therapeutic agents may provide novel therapies for a range of human brain disorders.

The neuroprotective functions of transforming growth factor beta proteins

Transforming growth factor beta (TGF-β) proteins are multifunctional cytokines whose neural functions are increasingly recognized. The machinery of TGF-β signaling, including the serine kinase type transmembrane receptors, is present in the central nervous system. However, the 3 mammalian TGF-β subtypes have distinct distributions in the brain suggesting different neural functions. Evidence of their involvement in the development and plasticity of the nervous system as well as their functions in peripheral organs suggested that they also exhibit neuroprotective functions. Indeed, TGF-β expression is induced following a variety of types of brain tissue injury. The neuroprotective function of TGF-βs is most established following brain ischemia. Damage in experimental animal models of global and focal ischemia was shown to be attenuated by TGF-βs. In addition, support for their neuroprotective actions following trauma, sclerosis multiplex, neurodegenerative diseases, infections, and brain tumors is also accumulating. The review will also describe the potential mechanisms of neuroprotection exerted by TGF-βs including anti-inflammatory, -apoptotic, -excitotoxic actions as well as the promotion of scar formation, angiogenesis, and neuroregeneration. The participation of these mechanisms in the neuroprotective effects of TGF-βs during different brain lesions will also be discussed.

Age-dependent neuroinflammatory responses and deficits in long-term potentiation in the hippocampus during systemic inflammation

Chronic systemic inflammation induces age-dependent differential phenotypic changes in microglia and astrocytes, yielding an anti-inflammatory cell phenotype in young rats and a proinflammatory cell phenotype in middle-aged rats. These observations prompted further investigation of the functional outcomes of the resultant differential microglial phenotypic changes. The present study examined the effects of age-dependent differential microglial phenotypic changes following chronic systemic inflammation on the formation of the post-tetanic potentiation (PTP) and long-term potentiation (LTP) in the hippocampus. Microglia formed a proinflammatory cell phenotype to express ED1 and interleukin-1β (IL-1β) in the hippocampal CA1 region of middle-aged rats, but not in young rats following the establishment of adjuvant arthritis (AA). Furthermore, AA induced deficits in the formation of LTP in the Schaffer collateral-CA1 synapses of middle-aged rats, but not in young rats. On the other hand, the formation of PTP was impaired in both young and middle-aged AA rats. Minocycline, a known inhibitor of microglial activation, was systemically administered to middle-aged AA rats significantly restoring the mean magnitudes of both PTP and LTP. The mean expression levels of ED1 and IL-1β were significantly suppressed. These observations strongly suggest that chronic systemic inflammation induces deficits in the hippocampal LTP in middle-aged rats through neuroinflammation mainly induced by microglia.

Distribution of mRNAs encoding transforming growth factors-beta1, -2, and -3 in the intact rat brain and after experimentally induced focal ischemia

Transforming growth factors-beta1 (TGF-beta1), -2, and -3 form a small group of related proteins involved in the regulation of proliferation, differentiation, and survival of various cell types. Recently, TGF-betas were also demonstrated to be neuroprotective. In the present study, we investigated their distribution in the rat brain as well as their expression following middle cerebral artery occlusion. Probes were produced for all types of TGF-betas, and in situ hybridization was performed. We demonstrated high TGF-beta1 expression in cerebral cortex, hippocampus, central amygdaloid nucleus, medial preoptic area, hypothalamic paraventricular nucleus, substantia nigra, brainstem reticular formation and motoneurons, and area postrema. In contrast, TGF-beta2 was abundantly expressed in deep cortical layers, dentate gyrus, midline thalamic nuclei, posterior hypothalamic area and mamillary body, superior olive, areas of monoaminergic neurons, spinal trigeminal nucleus, dorsal vagal complex, cerebellum, and choroid plexus, and a high level of TGF-beta3 mRNA was found in cerebral cortex, hippocampus, basal amygdaloid nuclei, lateral septal nucleus, several thalamic nuclei, arcuate and supramamillary nuclei, superior colliculus, superior olive, brainstem reticular formation and motoneurons, area postrema, and inferior olive. Focal brain ischemia induced TGF-betas with markedly different expression patterns. TGF-beta1 was induced in the penumbral region of cortex and striatum, whereas TGF-beta2 and -beta3 were induced in different layers of the ipsilateral cortex. The expression of the subtypes of TGF-betas in different brain regions suggests that they are involved in the regulation of different neurons and bind to different latent TGF-beta binding proteins. Furthermore, they might have subtype-specific functions following ischemic attack.

Acute p38-mediated inhibition of NMDA-induced outward currents in hippocampal CA1 neurons by interleukin-1beta

Interleukin-1beta (IL-1beta) is a potent pro-inflammatory cytokine that is primarily produced by microglia in the brain. IL-1beta inhibits N-methyl-d-aspartate (NMDA)-induced outward currents (I(NMDA-OUT)) through IL-1 type I receptor (IL-1RI) in hippocampal CA1 neurons (Zhang, R., Yamada, J., Hayashi, Y., Wu, Z, Koyama, S., Nakanishi, H., 2008. Inhibition of NMDA-induced outward currents by interleukin-1beta in hippocampal neurons, Biochem. Biophys. Res. Commun. 372, 816-820). Although IL-1RI is associated with mitogen-activated protein kinases, their involvement in the effect of IL-1beta on I(NMDA-OUT) remains unclear. In the present study, we demonstrate that IL-1beta caused activation of p38 mitogen-activated protein kinase and that the p38 inhibitor SB203580 significantly blocked the effect of IL-1beta on I(NMDA-OUT) in hippocampal CA1 neurons. Furthermore, the intracellular perfusion of active recombinant p38alpha significantly decreased the mean amplitude of I(NMDA-OUT). In neurons prepared from inflamed hippocampus, the mean amplitude of I(NMDA-OUT) was significantly reduced. In the inflamed hippocampus, IL-1beta and IL-1RI were expressed mainly in microglia and neurons, respectively. These results suggest that IL-1beta increases the excitability of hippocampal CA1 neurons in the p38-dependent inhibition of I(NMDA-OUT).

Age-dependent responses of glial cells and leptomeninges during systemic inflammation

Systemic inflammation causes the age-dependent differential glial responses, but little is known about how age influences the barrier function of leptomeninges during systemic inflammation. This study was conducted to elucidate the relationship between the glial responses and the levels of tight junction proteins, occludin and ZO-1, in adjuvant arthritis (AA) rats. In young AA rats, microglia and astrocytes localized to the proximity of the leptomeninges expressed interleukin (IL)-10 and transforming growth factor (TGF)-beta1. The level of occludin significantly increased. In middle-aged AA rats, however, glial cells expressed IL-1beta and prostaglandin E(2) (PGE(2))-synthesizing enzymes. Furthermore, occludin and ZO-1 significantly decreased, resulting in the increased permeability of leptomeninges. In the cultured leptomeningeal cells, IL-1beta and PGE(2) caused a marked loss of occludin and ZO-1, respectively. Pretreatment with IL-10 and TGF-beta1 significantly antagonized their effects. These findings establish that age strongly influences the barrier functions of the leptomeninges through the age-dependent differential glial responses during systemic inflammation.

The contribution of animal fat oxidation products to colon carcinogenesis, through modulation of TGF-beta1 signaling

It is now unanimously accepted that neoplastic cells tend to become less susceptible to the growth regulatory effects of transforming growth factor-beta1 (TGF-beta1), mainly because of reduced expression and/or activity of TGF-beta1-specific receptors, as reported for many human cancers including colon cancer. Consequently, a sustained increase of TGF-beta1 in the intestinal mucosa, like that caused by inflammatory processes and/or high dietary intake of animal fat, might become crucial for the progression of a neoplastic clone. In fact, this proapoptotic and prodifferentiating cytokine could eliminate neoplastic cells still susceptible to TGF-beta1's antiproliferative action (TGF-beta1 receptor-positive cells), indirectly favoring the expansion of TGF-beta1 resistant ones (TGF-beta1 receptors deficient or negative cells). The actual concentration of TGF-beta1 in the colonic mucosa undergoing neoplastic transformation is still debated, and the phase of the relevant carcinogenetic process in which a reduced susceptibility to this antiproliferative molecule first occurs has not been precisely established yet. However, no doubt that TGF-beta1 level and activity may be upregulated in cells of the macrophage lineage by animal fat oxidation products, such as oxysterols and aldehydes, as reviewed here. But phagocytes as well as fibroblasts constitutively express TGF-beta1 and are accumulating in tumor-associated stroma. Thus, upregulation of this cytokine system within colonic tumor-associated stroma by excess dietary intake of cholesterol and n-6 polyunsaturated fatty acids appears as a primary mechanism of cancer progression at least in neoplastic lesions of the digestive tract.

Role of TGF-beta and PGE2 in T cell responses during Plasmodium yoelii infection

During an acute blood-stage malaria infection, T cell responses to malaria and other bystander antigens are inhibited. Plasmodium infection induces strong cytokine responses that facilitate parasite clearance but may interfere with T cell functions, as some of the soluble immune mediators induced are also general inhibitors of T cell responses. Using a malaria mouse model, we have analyzed the cytokines produced by dendritic cells in response to P. yoelii infection that have potential T cell inhibitory activity. We found that during acute infection DC migrate to the spleen and secrete TGF-beta, prostaglandin E2 (PGE2) and IL-10. We have analyzed the role of these general T cell inhibitors in a particular T cell response of evident importance in malaria infections: the CD8+ T cells generated against the liver-stage of the disease. During blood-stage infection, inhibition of the activity of TGF-beta and PGE2 restores the CD8+ T cell responses generated by sporozoites, increasing protection against re-infection. Our findings suggest that the strong cytokine response induced by blood-stage P. yoelii infection affects host T cell responses, inhibiting protective CD8+ T cells against the liver-stage of the disease.