Interleukin (IL)-10 inhibits IL-6 production in microglia by preventing activation of NF-kappaB

Dysregulated neuronal-microglial cross-talk during aging, stress and inflammation

Communication between neurons and microglia is essential for maintaining homeostasis in the central nervous system (CNS) during both physiological and inflammatory conditions. While microglial activation is necessary and beneficial in response to injury or disease, excessive or prolonged activation can have deleterious effects on brain function and behavior. To prevent inflammation-associated damage, microglia reactivity is actively modulated by neurons in the healthy brain. Age or stress-induced disruption of normal neuronal-microglial communication could lead to an aberrant central immune response when additional stressors are applied. Recent work suggests that both aging and stress shift the CNS microenvironment to a pro-inflammatory state characterized by increased microglial reactivity and a reduction in anti-inflammatory and immunoregulatory factors. This review will discuss how heightened neuroinflammation associated with aging and stress may be compounded by the concomitant loss of neuronally derived factors that control microglial activation, leaving the brain vulnerable to excessive inflammation and neurobehavioral complications upon subsequent immune challenge.

The regulation of the CNS innate immune response is vital for the restoration of tissue homeostasis (repair) after acute brain injury: a brief review

Neurons and glia respond to acute injury by participating in the CNS innate immune response. This involves the recognition and clearance of "not self " pathogens and "altered self " apoptotic cells. Phagocytic receptors (CD14, CD36, TLR-4) clear "not self" pathogens; neurons and glia express "death signals" to initiate apoptosis in T cells.The complement opsonins C1q, C3, and iC3b facilitate the clearance of apoptotic cells by interacting with CR3 and CR4 receptors. Apoptotic cells are also cleared by the scavenger receptors CD14, Prs-R, TREM expressed by glia. Serpins also expressed by glia counter the neurotoxic effects of thrombin and other systemic proteins that gain entry to the CNS following injury. Complement pathway and T cell activation are both regulated by complement regulatory proteins expressed by glia and neurons. CD200 and CD47 are NIRegs expressed by neurons as "don't eat me" signals and they inhibit microglial activity preventing host cell attack. Neural stem cells regulate T cell activation, increase the Treg population, and suppress proinflammatory cytokine expression. Stem cells also interact with the chemoattractants C3a, C5a, SDF-1, and thrombin to promote stem cell migration into damaged tissue to support tissue homeostasis.

PEGylation of interleukin-10 for the mitigation of enhanced pain states

The anti-inflammatory cytokine interleukin-10 (IL-10) shows promise for the treatment of neuropathic pain, but for IL-10 to be clinically useful as a short-term therapeutic its duration needs to be improved. In this study, IL-10 was covalently modified with polyethylene glycol (PEG) with the goal of stabilizing and increasing protein levels in the CSF to improve the efficacy of IL-10 for treating neuropathic pain. Two different PEGylation methods were explored in vitro to identify suitable PEGylated IL-10 products for subsequent in vivo testing. PEGylation of IL-10 by acylation yielded a highly PEGylated product with a 35-fold in vitro biological activity reduction. PEGylation of IL-10 by reductive amination yielded products with a minimal number of PEG molecules attached and in vitro biological activity reductions of approximately 3-fold. In vivo collections of cerebrospinal fluid after intrathecal administration demonstrated that 20 kDa PEG attachment to IL-10 increased the concentration of IL-10 in the cerebrospinal fluid over time. Relative to unmodified IL-10, the 20 kDa PEG-IL-10 product exhibited an increased therapeutic duration and magnitude in an animal model of neuropathic pain. This suggests that PEGylation is a viable strategy for the short-term treatment or, in conjunction with other approaches, the long-term treatment of enhanced pain states.

Role of cytokines as mediators and regulators of microglial activity in inflammatory demyelination of the CNS

As the resident innate immune cells of the central nervous system (CNS), microglia fulfil a critical role in maintaining tissue homeostasis and in directing and eliciting molecular responses to CNS damage. The human disease Multiple Sclerosis and animal models of inflammatory demyelination are characterized by a complex interplay between degenerative and regenerative processes, many of which are regulated and mediated by microglia. Cellular communication between microglia and other neural and immune cells is controlled to a large extent by the activity of cytokines. Here we review the role of cytokines as mediators and regulators of microglial activity in inflammatory demyelination, highlighting their importance in potentiating cell damage, promoting neuroprotection and enhancing cellular repair in a context-dependent manner.

Central interleukin-10 attenuates lipopolysaccharide-induced changes in food intake, energy expenditure and hypothalamic Fos expression

Lipopolysaccharide (LPS) is often used to mimic acute infection and induces hypophagia, the selective partitioning of fat for energy, and fever. Interleukin-10 (IL-10) is an anti-inflammatory cytokine expressed in the brain which attenuates LPS-induced hypophagia; however the potential sites of interaction within the brain have not been investigated. Hypothalamic orexin (ORX) and melanin-concentrating hormone (MCH) regulate energy expenditure and food intake although the regulation of these neuropeptides through the interactions between central IL-10 and the inflammatory consequences of peripheral LPS have not been investigated. The present study in the rat investigated during the dark phase of the light-dark cycle the ability of central IL-10 (250 ng, i.c.v.) to attenuate the changes in food intake, energy substrate partitioning, and central Fos expression within the hypothalamus to peripheral LPS (100 microg/kg, i.p.); Fos expression changes specifically within ORX and MCH neurons were also investigated. Central IL-10 attenuated the peripheral LPS-induced hypophagia, reduction in motor activity, fever and reduction in respiratory exchange ratio. Central IL-10 also attenuated peripheral LPS-induced increases in Fos expression within ORX neurons and decreases in Fos expression within unidentified cells of the caudal arcuate nucleus. In contrast, both IL-10 and LPS injection independently decreased Fos expression within MCH neurons. The present study provides further insight into the interactions within the brain between the anti-inflammatory cytokine IL-10, the inflammatory consequences of LPS, and neuropeptides known to regulate energy expenditure and food intake.

Replication by the Epistasis Project of the interaction between the genes for IL-6 and IL-10 in the risk of Alzheimer's disease

Background

Chronic inflammation is a characteristic of Alzheimer's disease (AD). An interaction associated with the risk of AD has been reported between polymorphisms in the regulatory regions of the genes for the pro-inflammatory cytokine, interleukin-6 (IL-6, gene: IL6), and the anti-inflammatory cytokine, interleukin-10 (IL-10, gene: IL10).

Methods

We examined this interaction in the Epistasis Project, a collaboration of 7 AD research groups, contributing DNA samples from 1,757 cases of AD and 6,295 controls.

Results

We replicated the interaction. For IL6 rs2069837 AA × IL10 rs1800871 CC, the synergy factor (SF) was 1.63 (95% confidence interval: 1.10–2.41, p = 0.01), controlling for centre, age, gender and apolipoprotein E ε4 (APOEε4) genotype. Our results are consistent between North Europe (SF = 1.7, p = 0.03) and North Spain (SF = 2.0, p = 0.09). Further replication may require a meta-analysis. However, association due to linkage disequilibrium with other polymorphisms in the regulatory regions of these genes cannot be excluded.

Conclusion

We suggest that dysregulation of both IL-6 and IL-10 in some elderly people, due in part to genetic variations in the two genes, contributes to the development of AD. Thus, inflammation facilitates the onset of sporadic AD.

Low serum IL-10 concentrations and loss of regulatory association between IL-6 and IL-10 in adults with major depression

Elevated circulating pro-inflammatory cytokines are associated with symptoms of depression, and disorders involving chronic inflammation are often co-morbid with major depression. Since healthy immune regulation is accomplished through counter-balancing effects of pro- and anti-inflammatory cytokines, we hypothesized that depressed subjects (compared to controls) would express lower concentrations of the anti-inflammatory/immunoregulatory cytokine interleukin (IL)-10, and a higher IL-6/IL-10 ratio. We also examined the possibility that depressed subjects may exhibit a deficiency in the regulatory loop involving IL-6 induced secretion of IL-10. Therefore, we hypothesized that circulating IL-6 and IL-10 would be positively correlated in controls, while the correlation would be weaker in depressed subjects. Resting state serum cytokine concentrations were quantified in 12 unmedicated depressed subjects, and 11 age, gender, and ethnicity-matched controls. Depressed subjects showed significantly lower IL-10 (p=0.03, Cohen's d=-0.96), non-significantly higher IL-6, and significantly higher IL-6/IL-10 ratios (p=0.05, Cohen's d=0.50). Across all participants, higher scores on the self-rated Inventory of Depressive Symptoms were associated with lower IL-10 (r(21)=-0.57, p=0.005) and non-significantly higher IL-6/IL-10 ratios (r(21)=0.38, p=0.07), but not related to IL-6 concentrations. As hypothesized, IL-6 and IL-10 concentrations were strongly and positively correlated in controls (r(9)=0.81, p=0.003), but were completely dissociated in depressed subjects (r(10)=0.01, p=0.98). These results suggest that lower IL-10 levels, a higher IL-6/IL-10 ratio, and the apparent absence of a counter-balancing, immunoregulatory increase in IL-10 in response to elevated IL-6 concentrations contribute to the pro-inflammatory physiological milieu that is known to be associated with major depression. Therefore, reduced induction/availability of IL-10, that would normally inhibit pro-inflammatory cytokine actions and resolve inflammation, may contribute to the depressogenic as well as the inflammatory disease-promoting effects of chronic, low-level elevations in pro-inflammatory cytokines.

Immune and behavioral consequences of microglial reactivity in the aged brain

Bidirectional communication between the immune system and the brain is essential for mounting the appropriate immunological, physiological, and behavioral responses to immune activation. Aging, however, may impair this important bi-directional interaction. In support of this notion, peripheral infection in the elderly is associated with an increased frequency of behavioral and cognitive complications. Recent findings in animal models of aging and neurodegenerative disease indicate that microglia, innate immune cells of the brain, become primed or reactive. Understanding age- and disease-associated alterations in microglia is important because glia (microglia and astrocytes) play an integral role in propagating inflammatory signals that are initiated in the periphery. In this capacity, brain glia produce inflammatory cytokines that target neuronal substrates and elicit a sickness-behavior syndrome that is normally beneficial to the host organism. Increased reactivity of microglia sets the stage for an exaggerated neuroinflammatory cytokine response following activation of the peripheral innate immune system, which may underlie subsequent long-lasting behavioral and cognitive deficits. In support of this premise, recent findings indicate that stimulation of the peripheral immune system in aged rodents causes exaggerated neuroinflammation that is paralleled by cognitive impairment, prolonged sickness, and depressive-like complications. Therefore, the purpose of this review is to discuss the new evidence that age-associated priming of microglia could play a pathophysiological role in exaggerated behavioral and cognitive sequelae to peripheral infection.

SDF-1alpha up-regulates interleukin-6 through CXCR4, PI3K/Akt, ERK, and NF-kappaB-dependent pathway in microglia

Stromal cell-derived factor-1 (SDF-1), also known as CXCL12, and its receptor CXC chemokine receptor 4 (CXCR4) express in various kinds of cells in central nervous system. The SDF-1/CXCR4 signaling pathway is regulated by diverse biological effects. SDF-1 is up-regulated in the ischemic penumbra following stroke and has been known to be associated with the homing of bone marrow cells to injury. However, the effect of SDF-1alpha/CXCR4 on cytokine production in microglia is mostly unknown. Here, we demonstrated that SDF-1alpha enhanced IL-6 production in both primary cultured microglia and BV-2 microglia. We further investigated the signaling pathway involved in IL-6 production stimulated by SDF-1alpha in microglia. SDF-1alpha increased IL-6 production in both protein and mRNA levels. These effects were attenuated by ERK, phosphatidylinositol 3-kinase (PI3K), NF-kappaB inhibitors, and IkappaB protease inhibitor. Stimulation of microglia with SDF-1alpha also increased Akt and ERK1/2 phosphorylation. In addition, SDF-1alpha treatment also increased IkappaB kinase alpha/beta (IKK alpha/beta) phosphorylation, IkappaBalpha phosphorylation, IkappaBalpha degradation, p65 phosphorylation at Ser(276), translocation of p65 and p50 from cytosol to nucleus and kappaB-luciferase activity. Moreover, SDF-1alpha-mediated increase of kappaB-luciferase activity was inhibited by pre-transfection of DN-p85, DN-Akt or DN-ERK2. Increase of IKK alpha/beta phosphorylation and binding of p65 and p50 to the NF-kappaB element were both antagonized by PI3K and ERK inhibitors. Our results demonstrate a mechanism linking SDF-1alpha and IL-6, and provide additional support for the notion that SDF-1alpha plays a regulatory role in microglia activation.

Peripheral lipopolysaccharide (LPS) challenge promotes microglial hyperactivity in aged mice that is associated with exaggerated induction of both pro-inflammatory IL-1beta and anti-inflammatory IL-10 cytokines

In the elderly, systemic infection is associated with an increased frequency of behavioral and cognitive complications. We have reported that peripheral stimulation of the innate immune system with lipopolysaccharide (LPS) causes an exaggerated neuroinflammatory response and prolonged sickness/depressive-like behaviors in aged BALB/c mice. Therefore, the purpose of this study was to determine the degree to which LPS-induced neuroinflammation was associated with microglia-specific induction of neuroinflammatory mediators. Here, we show that peripheral LPS challenge caused a hyperactive microglial response in the aged brain associated with higher induction of inflammatory IL-1beta and anti-inflammatory IL-10. LPS injection caused a marked induction of mRNA expression of both IL-1beta and IL-10 in the cortex of aged mice compared to adults. In the next set of studies, microglia (CD11b(+)/CD45(low)) were isolated from the brain of adult and aged mice following experimental treatments. An age-dependent increase in major histocompatibility complex (MHC) class II mRNA and protein expression was detected in microglia. Moreover, peripheral LPS injection caused a more pronounced increase in IL-1beta, IL-10, Toll-like receptor (TLR)-2, and indoleamine 2,3-dioxygenase (IDO) mRNA levels in microglia isolated from aged mice than adults. Intracellular cytokine protein detection confirmed that peripheral LPS caused the highest increase in IL-1beta and IL-10 levels in microglia of aged mice. Finally, the most prominent induction of IL-1beta was detected in MHC II(+) microglia from aged mice. Taken together, these findings provide novel evidence that age-associated priming of microglia plays a central role in exaggerated neuroinflammation induced by activation of the peripheral innate immune system.

Cytokines and their relationship to the symptoms and outcome of cancer

Tumours contain immune cells and a network of pro- and anti-inflammatory cytokines, which collaborate in the development and progression of cancer. Cytokine profiles might prove to be prognostic. The systemic effects of pro-inflammatory cytokines are associated with fatigue, depression and cognitive impairment, and can affect quality of life before, during and after treatment. In people with advanced cancer, pro-inflammatory cytokines are additionally associated with anorexia and cachexia, pain, toxicity of treatment and resistance to treatment. However, physical activity might modify cytokine levels and decrease fatigue in patients with cancer, and might also improve their prognosis.

Tumor necrosis factor receptor 1 induces interleukin-6 upregulation through NF-kappaB in a rat neuropathic pain model

Peripheral nerve injury resulting in neuropathic pain induces the upregulation of interleukin (IL)-6 and tumor necrosis factor-alpha, which binds to tumor necrosis factor receptor 1 (TNFR1) and induces NF-kappaB and p38 MAPK activation in the spinal cord and dorsal root ganglia (DRG). We here investigated whether TNFR1 regulates IL-6 expression through NF-kappaB or p38 MAPK activations in the spinal cord and DRG in rats with chronic constriction injury (CCI) of the sciatic nerve. Intrathecal treatment with a TNFR1 antisense oligonucleotide (ASO) significantly inhibited CCI-elevated IKKs phosphorylation, IkB-alpha degradation, the nuclear translocation, phosphorylation, and DNA-binding activity of NF-kappaB, p38 MAPK activation, and IL-6 mRNA and protein expression in the spinal cord and DRG. Interestingly, CCI remarkably elevated IKKalpha and p65 phosphorylations in the spinal cord rather than in the DRG. In addition, NF-kappaB decoy, but not p38 MAPK inhibitor, SB203580 reduced CCI-elevated IL-6 expression in the spinal cord and DRG. Therefore, these data suggest that TNFR1 induces IL-6 upregulation and neuropathic pain through NF-kappaB, but not p38 MAPK activation in the spinal cord and DRG and that the NF-kappaB/IL-6 pathways in the DRG may be less dependent on TNFR1 than the spinal cord pathway.

Luteolin reduces IL-6 production in microglia by inhibiting JNK phosphorylation and activation of AP-1

Luteolin, a flavonoid found in high concentrations in celery and green pepper, has been shown to reduce production of proinflammatory mediators in LPS-stimulated macrophages, fibroblasts, and intestinal epithelial cells. Because excessive production of proinflammatory cytokines by activated brain microglia can cause behavioral pathology and neurodegeneration, we sought to determine whether luteolin also regulates microglial cell production of a prototypic inflammatory cytokine, IL-6. Pretreatment of primary murine microlgia and BV-2 microglial cells with luteolin inhibited LPS-stimulated IL-6 production at both the mRNA and protein levels. To determine how luteolin inhibited IL-6 production in microglia, EMSAs were performed to establish the effects of luteolin on LPS-induced binding of transcription factors to the NF-kappaB and activator protein-1 (AP-1) sites on the IL-6 promoter. Whereas luteolin had no effect on the LPS-induced increase in NF-kappaB DNA binding activity, it markedly reduced AP-1 transcription factor binding activity. Consistent with this finding, luteolin did not inhibit LPS-induced degradation of IkappaB-alpha but inhibited JNK phosphorylation. To determine whether luteolin might have similar effects in vivo, mice were provided drinking water supplemented with luteolin for 21 days and then they were injected i.p. with LPS. Luteolin consumption reduced LPS-induced IL-6 in plasma 4 h after injection. Furthermore, luteolin decreased the induction of IL-6 mRNA by LPS in hippocampus but not in the cortex or cerebellum. Taken together, these data suggest luteolin inhibits LPS-induced IL-6 production in the brain by inhibiting the JNK signaling pathway and activation of AP-1 in microglia. Thus, luteolin may be useful for mitigating neuroinflammation.

The encephalopathy in sepsis

Brain dysfunction is a severe complication of sepsis with an incidence ranging from 9% to 71% that is associated with increased morbidity and mortality. Its diagnosis relies mainly on neurologic examination with clinical manifestations ranging from confusion to coma. An electroencephalogram, somatosensory evoked potentials, and measurement of plasma S-100b protein and neuron-specific enolase can be useful for the detection of brain dysfunction. Brain MRI can identify brain lesions such as cerebral infarction, posterior reversible encephalopathy syndrome, and leukoencephalopathy. The mechanism of sepsis-associated encephalopathy involves inflammatory and non-inflammatory processes that affect endothelial cells, glial cells, and neurons and induce blood-brain barrier breakdown, derangements of intracellular metabolism, and cell death. Specific treatments for sepsis-associated encephalopathy need to be developed. Currently, treatment is mainly the management of sepsis.

From inflammation to sickness and depression: when the immune system subjugates the brain

In response to a peripheral infection, innate immune cells produce pro-inflammatory cytokines that act on the brain to cause sickness behaviour. When activation of the peripheral immune system continues unabated, such as during systemic infections, cancer or autoimmune diseases, the ensuing immune signalling to the brain can lead to an exacerbation of sickness and the development of symptoms of depression in vulnerable individuals. These phenomena might account for the increased prevalence of clinical depression in physically ill people. Inflammation is therefore an important biological event that might increase the risk of major depressive episodes, much like the more traditional psychosocial factors.

Immunosuppression after traumatic or ischemic CNS damage: it is neuroprotective and illuminates the role of microglial cells

Acute traumatic and ischemic events in the central nervous system (CNS) invariably result in activation of microglial cells as local representatives of the immune system. It is still under debate whether activated microglia promote neuronal survival, or whether they exacerbate the original extent of neuronal damage. Protagonists of the view that microglial cells cause secondary damage have proposed that inhibition of microglial activation by immunosuppression is beneficial after acute CNS damage. It is the aim of this review to analyse the effects of immunosuppressants on isolated microglial cells and neurons, and to scrutinize the effects of immunosuppression in different in vivo models of acute CNS trauma or ischemia. It is found that the immunosuppressants cytosine-arabinoside, different steroids, cyclosporin A, FK506, rapamycin, mycophenolate mofetil, and minocycline all have direct inhibitory effects on microglial cells. These effects are mainly exerted by inhibiting microglial proliferation or microglial secretion of neurotoxic substances such as proinflammatory cytokines and nitric oxide. Furthermore, immunosuppression after acute CNS trauma or ischemia results in improved structure preservation and, mostly, in enhanced function. However, all investigated immunosuppressants also have direct effects on neurons, and some immunosuppressants affect other glial cells such as astrocytes. In summary, it is safe to conclude that immunosuppression after acute CNS trauma or ischemia is neuroprotective. Furthermore, circumferential evidence indicates that microglial activation after traumatic or ischemic CNS damage is not beneficial to adjacent neurons in the immediate aftermath of such acute lesions. Further experiments with more specific agents or genetic approaches that specifically inhibit microglial cells are needed in order to fully answer the question of whether microglial activation is "good or bad".

Multiple mechanisms that prevent excessive brain inflammation

Inflammation of the injured brain has a double-edged effect. Inflammation protects the brain from infection, but it aggravates injury. Furthermore, brain inflammation is considered a risk factor for neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases. Emerging evidence supports the activation of negative regulatory mechanisms during this process to prevent prolonged and extensive inflammation. The inflammatory stimulators themselves or products of inflammatory cells may induce the expression of negative feedback regulators, such as suppressor of cytokine signaling (SOCS)-family proteins, antioxidant enzymes, and antiinflammatory cytokines. Furthermore, death of activated microglia (major inflammatory cells in the brain) may regulate brain inflammation. Astrocytes, the most abundant cells in the brain, may also act in preventing microglial overactivation. Therefore, we propose that the extent and duration of brain inflammation is tightly regulated through the cooperation of multiple mechanisms to maximize antipathogenic effects and minimize tissue damage.

Impaired LPS-induced signaling in microglia overexpressing the Wiskott-Aldrich syndrome protein N-terminal domain

Wiskott-Aldrich syndrome protein (WASP) plays important roles in TCR signaling, but its roles in signal transduction in innate immune cells have not been well characterized. As microglia are the primary immune effector cells in the brain, WASP may possibly have important roles in microglial activation, such as production of inflammatory and anti-inflammatory cytokines and neurotoxic factors. Here, we established a microglial cell line from WASP dominant-negative transgenic (Tg) mice overexpressing the N-terminal enabled/vasodilator-stimulated phosphoprotein homology 1 (EVH1) domain. WASP Tg microglia were impaired in production of inflammatory cytokines such as tumor necrosis factor-alpha, IL-6 and IL-1beta upon LPS stimulation, whereas anti-inflammatory IL-10 production was significantly enhanced. Also, LPS-induced phosphorylation of nuclear factor kappaB was reduced in WASP Tg microglia. Furthermore, WASP Tg microglia exhibited less cytotoxicity against co-cultured neurons after stimulation by LPS and IFN-gamma, with a concordant decrease in nitric oxide production. These results strongly suggest that WASP may have pivotal roles through the EVH1 domain in the LPS signaling cascade, either directly or indirectly, and modulates inflammatory immune responses in microglia.

Manganese-induced potentiation of in vitro proinflammatory cytokine production by activated microglial cells is associated with persistent activation of p38 MAPK

Previous studies that investigated the role of inflammation in the neurotoxicity of manganese (Mn) found that Mn enhanced the production of inflammogen (lipopolysaccharide; LPS)-induced proinflammatory cytokines such as IL-6 and TNF-alpha. Although we have shown that the enhanced cytokine production occurs via a NF-kappaB-dependent mechanism, the role of upstream kinases in this Mn-induced enhancement has not been explored. As other studies have demonstrated that p38 mitogen activated protein kinase (p38) is necessary for LPS-induced, NF-kappaB-dependent expression of proinflammatory cytokines, we hypothesized that Mn enhancement of LPS-induced production of IL-6 and TNF-alpha may be associated with p38 activation and conducted a series of experiments to address our hypothesis. We found that pre-treatment of microglial cells with a p38-inhibitor (SB203580) prevented Mn+LPS-induced production of IL-6 and TNF-alpha. Moreover, potentiation of IL-6 and TNF-alpha production, which occurred in both concurrent and sequential (3h apart) exposures to Mn and LPS, was inhibited by inhibition of p38. Additionally, Mn exposure enhanced the phosphorylation and activity of p38 and this effect was persistent. Although p38 activity declined over time LPS-exposed cells, it persisted in cells exposed to Mn or Mn+LPS. Thus, the increased production of proinflammatory cytokines by LPS-activated microglia exposed to Mn is associated with increased and persistent activation of p38.

Interleukin-10 protects lipopolysaccharide-induced neurotoxicity in primary midbrain cultures by inhibiting the function of NADPH oxidase

The role of anti-inflammatory cytokines in Parkinson's disease is not completely understood. In this study, using mesencephalic neuron-glia cultures, we report that both pretreatment and post-treatment of rat mesencephalic neuron-glia cultures with interleukin (IL)-10, a natural immune modulator, reduced lipopolysaccharide (LPS)-induced DA neurotoxicity. The main purpose of this study was to elucidate the molecular mechanism underlying IL-10-elicited neuroprotection. IL-10 significantly inhibited LPS-induced production of tumor necrosis factor-alpha, nitric oxide, and extracellular superoxide in microglia cells. In addition, using reconstituted neuron and glia cell cultures, IL-10 was shown to be neuroprotective only in the presence of microglia. More importantly, IL-10 failed to protect DA neurons in cultures from mice lacking NADPH oxidase (PHOX), a key enzyme for extracellular superoxide production in immune cells, suggesting the critical role of PHOX in IL-10 neuroprotection. This conclusion was further supported by the finding that IL-10 inhibited LPS-induced translocation of the cytosolic subunit of NADPH oxidase p47(phox) to the membrane. When the Janus tyrosine kinase (JAK) 1 signaling pathway was blocked, IL-10 failed to attenuate LPS-induced superoxide production, indicating that the JAK1 signaling cascade mediates the inhibitory effect of IL-10. Together, our results suggest that IL-10 inhibits LPS-induced DA neurotoxicity through the inhibition of PHOX activity in a JAK1-dependent mechanism.

Nonparticipation of nuclear factor kappa B (NFkappaB) in the signaling cascade of c-Jun N-terminal kinase (JNK)- and p38 mitogen-activated protein kinase (p38MAPK)-dependent tumor necrosis factor alpha (TNFalpha) induction in lipopolysaccharide (LPS)-stimulated microglia

The molecular mechanism of cytotoxic cytokine tumor necrosis factor alpha (TNFalpha) induction in microglia remains to be clarified. We have previously reported that p38 mitogen-activated protein kinase (p38MAPK) is an important signaling molecule for the induction of TNFalpha in lipopolysaccharide (LPS)-stimulated microglia. Recently, we have shown that c-Jun N-terminal kinase (JNK) is associated with the induction of TNFalpha. Furthermore, using an NFkappaB inhibitor (SN50), we discovered that activation of nuclear factor kappaB (NFkappaB) may also be linked to TNFalpha induction. We therefore examined the relationship between NFkappaB and the two MAPKs (p38MAPK and JNK) in the signaling cascade of TNFalpha induction in LPS-stimulated microglia. NFkappaB inhibitor SN50 decreased the induction of TNFalpha under the suppressed NFkappaB activation. However, SN50 was found to prevent the activation of MKK3/6-p38MAPK and MKK4-JNK pathways. On the other hand, the other NFkappaB inhibitor ammonium pyrrolidine dithiocarbamate (APDC) neither prevented the activation of p38MAPK and JNK nor inhibited TNFalpha induction in LPS-stimulated microglia, although it was confirmed to serve as an NFkappaB inhibitor. These results suggest that both MKK3/6-p38MAPK and MKK4-JNK pathways are important signaling cascades leading to the induction of TNFalpha in LPS-stimulated microglia, but that NFkappaB itself is not required for this induction.

Regulation by GD3 of the proinflammatory response of microglia mediated by interleukin-15

The interleukin (IL)-15-dependent immune responses of murine microglia were strongly affected by low concentrations of the ganglioside GD3. The ganglioside binding to IL-15 inhibited the proinflammatory effects of the cytokine, reducing IL-15-dependent T-cell proliferation as well as mRNA expression for IL-15Ralpha, p65, and NFATc2 in the N13 murine microglial cell line. Treatment of primary murine microglial cultures with GD3 abolished IL-15 production, without affecting cellular viability, but decreased the production of nitric oxide, a direct sensor of inflammation and nuclear factor-kappaB activity. We conclude that low doses of GD3 could inhibit specific proinflammatory mechanisms and modulate the inflammatory environment, leading to a less reactive scene. Microglial cells are one of the main actors in the inflammatory events that follow CNS trauma or an autoimmune disease episode, modulating the internal production of cytokines, growth factors, and other homeostatic molecules that may determine the evolution and outcome of tissue damage. Proinflammatory cytokines have a relevant role in the initial events, and modulation of their activity by gangliosides could cut down their harmful effects and interfere with invasion of the CNS by peripheral immune cells. The antiinflammatory properties of GD3 could be significant in the treatment of pain subsequent to CNS damage.

Suppression of glial activation is involved in the protection of IL-10 on maternal E. coli induced neonatal white matter injury

White matter damage (WMD) is an important cause of disability including cerebral palsy in preterm, low birth-weight infants. Maternal infection is now recognized as one of the risk factors for WMD. Previously we reported that intrauterine inoculation of Escherichia coli to pregnant rats resulted in WMD in offspring and interleukin-10 (IL-10) was protective against this damage. The objective of this study was to elucidate the mechanism involved in the protective effect of IL-10 against neonatal WMD. We found that E. coli treatment in dams resulted in significant apoptosis in periventricular white matter of rat pups on postnatal day 0 (P0). On P8, a remarkable increase in ED-1 immunostaining (indicating either microglial activation or macrophage infiltration) was detected in brains of pups in the E. coli-treated group. Astrogliosis was also noticed in brain white matter of pups in the E. coli-treated group. In addition to the strong activation of microglia and astrocytes, oligodendrocytes (OLs) were significantly reduced in periventricular areas in the brains of pups from the E. coli-treated group. Later, on P15, hypomyelination was also noticed in rat brains from the E. coli-treated group, using myelin basic protein (MBP) immunostaining. Treatment with IL-10 after E. coli inoculation significantly reduced TUNEL staining and caspase-3 activation, and partially restored the impaired immunostaining markers for immature and mature OLs, such as CNPase, O4, adenomatous polyposis coli (APC) and MBP. These results indicate that the protective effect of IL-10 against brain WMD is linked with suppression of microglial activation/macrophage infiltration, as shown by significantly reduced ED-1+ cells in the white matter.

Interleukin-10 inhibits endotoxin-induced pro-inflammatory cytokines in microglial cell cultures

Inflammation contributes to perinatal brain injury and can be induced by hypoxia-ischemia (HI) or exposure to infection (fetal inflammatory response). The anti-inflammatory cytokine interleukin-10 (IL10) has been shown to have neuroprotective effects following HI. To determine whether IL10 can reduce the inflammatory response to lipopolysaccharide (LPS) in microglial cell cultures, primary microglial (MG) and/or HAPI cells (new MG-like cell line) were treated with LPS (50 ng/ml) in the presence or absence of IL10 (20 ng/ml) for 0.5, 1, 4, and 8 h. TNFalpha, MIP-1alpha, and RANTES were assayed by ELISA. Chemokine receptors, CCR5, CXCR3, and CX3CR1 (fractalkine receptor) were assayed by semiquantitative RT-PCR. We found that in MG cell cultures TNFalpha, MIP-1alpha, and RANTES release after 8-h exposure to LPS was significantly higher compared to non-exposed MG cells (P < 0.001). In HAPI cell cultures similar stimulation of mRNA levels was found for TNFalpha, MIP-1alpha, CXCR3, and CX3CR1. IL10 inhibited TNFalpha, MIP-1alpha, and RANTES release of LPS-stimulated MG cells as well as TNFalpha, MIP-1alpha, and CXCR3 mRNA expression by HAPI cells after exposure to LPS (P < 0.05). In contrast to those inhibitory effects, there was no change in fractalkine, and a modest increase in CX3CR1 mRNA levels was found in the presence of IL10. We conclude that the inflammatory response induced in microglial cells by LPS can be markedly reduced by IL10. The increase in fractalkine receptor (CX3CR1) is also potentially protective. Our results suggest that treatment of damaging neuroinflammatory insults such hypoxia-ischemia, with IL10 may be protective for the immature brain.

JP-8 jet fuel exposure induces inflammatory cytokines in rat skin

The Department of Defense (DoD) has identified that one of the main complaints of personnel exposed to JP-8 jet fuel is irritant dermatitis. The purpose of this investigation is to describe the JP-8-induced inflammatory cytokine response in skin. JP-8 jet fuel or acetone control (300 microl) was applied to the denuded skin of rats once a day for 7 days. Skin samples from the exposed area were collected 2 and 24 h after the final exposure. Histological examination of skin biopsies showed neutrophilic inflammatory infiltrate. Reverse transcription-polymerase chain reaction (RT-PCR) was performed utilizing skin total RNA to examine the expression of various inflammatory cytokines. The CXC chemokine GROalpha was significantly upregulated at both time points, whereas GRObeta was only increased 2 h post final exposure. The CC chemokines MCP-1, Mip-1alpha, and eotaxin were induced at both time points, whereas Mip-1beta was induced only 24 h post exposure. Interleukins-1beta and -6 (IL-1beta and IL-6) mRNAs were significantly induced at both time points, while TNFalpha was not significantly different from control. Enzyme-linked immunosorbent assay (ELISA) of skin protein confirmed that MCP-1, TNFalpha, and IL-1beta were modulated as indicated by PCR analysis. However, skin IL-6 protein content was not increased 2 h post exposure, whereas it was significantly upregulated by jet fuel after 24 h. Data from the present study indicate that repeated (7 days) JP-8 exposure induces numerous proinflammatory cytokines in skin. The increased expression of these cytokines and chemokines may lead to increased inflammatory infiltrate in exposed skin, resulting in JP-8-induced irritant dermatitis.

Science review: The brain in sepsis--culprit and victim

On one side, brain dysfunction is a poorly explored complication of sepsis. On the other side, brain dysfunction may actively contribute to the pathogenesis of sepsis. The current review aimed at summarizing the current knowledge about the reciprocal interaction between the immune and central nervous systems during sepsis. The immune-brain cross talk takes part in circumventricular organs that, being free from blood-brain-barrier, interface between brain and bloodstream, in autonomic nuclei including the vagus nerve, and finally through the damaged endothelium. Recent observations have confirmed that sepsis is associated with excessive brain inflammation and neuronal apoptosis which clinical relevance remains to be explored. In parallel, damage within autonomic nervous and neuroendocrine systems may contribute to sepsis induced organ dysfunction.

Role of interleukin-1 in prion disease-associated astrocyte activation

Prion-induced chronic neurodegeneration has a substantial inflammatory component, and the activation of glia cells may play an important role in disease development and progression. However, the functional contribution of cytokines to the development of the gliosis in vivo was never systematically studied. We report here that the expression of interleukin-1beta (IL-1beta), IL-1beta-converting enzyme, and IL-1 receptor type 1 (IL-1RI) is up-regulated in a murine scrapie model. The scrapie-induced gliosis in IL-1RI(-/-) mice was characterized by an attenuated activation of astrocytes in the asymptomatic stage of the disease and a reduced expression of CXCR3 ligands. Furthermore, the accumulation of the misfolded isoform of the prion protein PrP(Sc) was significantly delayed in the IL-1RI(-/-) mice. These observations indicate that IL-1 is a driver of the scrapie-associated astrocytosis and possibly the accompanying amyloid deposition. In addition, scrapie-infected IL-1RI-deficient (IL-1RI(-/-)) mice showed a delayed disease onset and significantly prolonged survival times suggesting that an anti-inflammatory therapeutical approach to suppress astrocyte activation and/or glial IL-1 expression may help to delay disease onset in established prion infections of the central nervous system.

High-yield isolation of murine microglia by mild trypsinization

Microglia can be isolated with high purity but low yield by shaking off loosely adherent cells from mixed glial cultures. Here we describe a new technique for isolating microglia with an average yield close to 2,000,000 microglial cells/mouse pup, more than five times higher than that of the shaking method. Confluent mixed glial cultures are subjected to mild trypsinization (0.05-0.12%) in the presence of 0.2-0.5 mM EDTA and 0.5-0.8 mM Ca2+. This results in the detachment of an intact layer of cells containing virtually all the astrocytes, leaving undisturbed a population of firmly attached cells identified as >98% microglia. These almost pure microglial preparations can be kept in culture for weeks and show proliferation and phagocytosis. Treatment with macrophage colony-stimulating factor and lipopolysaccharide, alone or in the presence of interferon gamma, induces typical microglial responses in terms of proliferation, morphological changes, nuclear factor-kappaB translocation, NO, and tumor necrosis alpha release and phagocytosis. This method allows for the preparation of highly enriched mouse or rat microglial cultures with ease and reproducibility. Because of its high yield, it can be especially convenient when high amounts of microglial protein/mRNA are required or in cases in which the starting material is limited, such as microglial cultures from transgenic animals.

Absence of the cell cycle inhibitor p21Cip1 reduces LPS-induced NO release and activation of the transcription factor NF-?B in mixed glial cultures

We have studied possible differences in glial activation between cells from wild-type and p21Cip1-/- mice. We compared the effect of serum mitogenic stimulation on proliferation rate and on the total number of glial cells after 7 days of culture. No differences between wild-type and p21Cip1-/- glial cells were observed. We also compared the effect of lipopolysaccharide (LPS) from Escherichia coli, an agent widely used to induce glial activation. Nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha) release, and nuclear factor kappa-B (NF-kappaB) activation were evaluated as indicators of glial activation. We observed an attenuation of NO release and NF-kappaB activation in p21Cip1-/- glial cells when compared with glial cells from wild-type mice. In contrast, TNF-alpha release was enhanced in p21Cip1-/- glia. These results suggest that the cell cycle inhibitor p21Cip1 plays a role in the inflammatory response induced by LPS.

Effects of interleukin-10 on neonatal excitotoxic brain lesions in mice

Interleukin-10 markedly reduces production of proinflammatory cytokines by activated microglia or macrophages and downregulates the expression of activating molecules on these cells. In studies performed in adults or in cell cultures, interleukin-10 protected against hypoxic-ischemic neuronal death and against lipopolysaccharide-mediated oligodendrocyte cell death. Furthermore, it was recently shown that interleukin-10 counteracts metabolic and microcirculatory effects of hypoxia-ischemia in the perinatal pig brain. Intracerebral injection of the glutamatergic analogue ibotenate to newborn mice induces cortical plate and white matter lesions mimicking the brain damage associated with cerebral palsy, and pretreatment with proinflammatory cytokines such as interleukin-1-beta or with interleukin-9 significantly exacerbates these lesions. The present study evaluated the influence of interleukin-10 on ibotenate-induced brain lesions in newborn mice under basal conditions or after exposure to cytokines. Intraperitoneal injection of interleukin-10 for 3 days following ibotenate significantly reduced the size of excitotoxic brain lesions. Intraperitoneal injection of neutralizing anti-interleukin-10 antibody for 3 days following ibotenate had no detectable effect and no difference in ibotenate-induced brain lesion size was found between wild type pups and pups deleted for the interleukin-10 gene, suggesting that endogenous interleukin-10 in newborn mice may have limited effects. Co-administration of intracerebral ibotenate and interleukin-10 had no detectable effect, arguing against a direct neuroprotective effect of interleukin-10 on neurons. While pretreatment with intraperitoneal interleukin-10 alone had no detectable effect on excitotoxic brain lesions, interleukin-10 given with interleukin-1-beta pretreatment blunted the toxic effects of interleukin-1-beta. On the other hand, combined pretreatment with IL-9 and anti-IL-10 antibody largely reversed the exacerbating effect of IL-9 on excitotoxic brain lesions. Altogether, these data suggest that, in newborn mice, exogenous interleukin-10 can be neuroprotective when acting in an inflammatory context.

Hypothermia attenuates iNOS, CAT-1, CAT-2, and nitric oxide expression in lungs of endotoxemic rats

Endotoxemia stimulates endogenous nitric oxide formation, induces transcription of arginine transporters, and causes lung injury. Hypothermia inhibits nitric oxide formation and is used as a means of organ preservation. We hypothesized that hypothermia inhibits endotoxin-induced intrapulmonary nitric oxide formation and that this inhibition is associated with attenuated transcription of enzymes that regulate nitric oxide formation, such as inducible nitric oxide synthase (iNOS) and the cationic amino acid transporters 1 (CAT-1) and 2 (CAT-2). Rats were anesthetized and randomized to treatment with hypothermia (18-24 degrees C) or normothermia (36-38 degrees C). Endotoxin was administered intravascularly. Concentrations of iNOS, CAT-1, CAT-2 mRNA, iNOS protein, and nitrosylated proteins were measured in lung tissue homogenates. We found that hypothermia abrogated the endotoxin-induced increase in exhaled nitric oxide and lung tissue nitrotyrosine concentrations. Western blot analyses revealed that hypothermia inhibited iNOS, but not endothelial nitric oxide synthase, protein expression in lung tissues. CAT-1, CAT-2, and iNOS mRNA concentrations were lower in the lungs of hypothermic animals. These findings suggest that hypothermia protects against intrapulmonary nitric oxide overproduction and nitric oxide-mediated lung injury by inhibiting transcription of iNOS, CAT-1, and CAT-2.

Macrophage colony stimulating factor prevents NMDA-induced neuronal death in hippocampal organotypic cultures

Macrophage colony stimulating factor (M-CSF) and its receptor are up-regulated in the brain in Alzheimer's disease (AD), in transgenic mouse models for AD, and experimental models for traumatic and ischemic brain injury. M-CSF induces activation and proliferation of microglial cells and expression of proinflammatory cytokines. We examined the role of M-CSF in excitotoxic neuronal cell death in organotypic hippocampal cultures. NMDA treatment induced neuronal apoptosis and caspase-3 activation in organotypic hippocampal cultures, whereas treatment with M-CSF protected hippocampal neurons from NMDA-induced apoptosis. Caspase-3 activation was inhibited by M-CSF treatment to the same degree as with the caspase inhibitor Z-VAD-FMK. These results suggest that M-CSF has neuroprotective properties through inhibition of caspase-3 that could promote neuronal survival after excitotoxic insult. The role of M-CSF in neurological disease should be reevaluated as a microglial activator with potentially neuroprotective effects.

Periventricular leukomalacia, inflammation and white matter lesions within the developing nervous system

Periventricular leukomalacia (PVL) occurring in premature infants, represents a major precursor for neurological and intellectual impairment, and cerebral palsy in later life. The disorder is characterized by multifocal areas of necrosis found deep in the cortical white matter, which are often symmetrical and occur adjacent to the lateral ventricles. There is no known cure for PVL. Factors predisposing to PVL include birth trauma, asphyxia and respiratory failure, cardiopulmonary defects, premature birth/low birthweight, associated immature cerebrovascular development and lack of appropriate autoregulation of cerebral blood flow in response to hypoxic-ischemic insults. The intrinsic vulnerability of oligodendrocyte precursors is considered as central to the pathogenesis of PVL. These cells are susceptible to a variety of injurious stimuli including free radicals and excitotoxicity induced by hypoxic-ischemic injury (resulting from cerebral hypoperfusion), lack of trophic stimuli, as well as secondary associated events involving microglial and astrocytic activation and the release of pro-inflammatory cytokines TNF-alpha and IL-6. It is yet unclear whether activated astrocytes and microglia act as principal participants in the development of PVL lesions, or whether they are representatives of an incidental pathological response directed towards repair of tissue injury in PVL. Nevertheless, the accumulated evidence points to a pathological contribution of microglia towards damage. The topography of lesions in PVL most likely reflects a combination of the relatively immature cerebrovasculature together with a failure in perfusion and/or hypoxia during the greatest period of vulnerability occurring around mid-to-late gestation. Mechanisms underlying the pathogenesis of PVL have so far been related to prenatal ischemic injury to the brain initiated within the third trimester, which result in global cognitive and developmental delay and motor disturbances. Over the past few years, several epidemiological and experimental studies have implicated intrauterine infection and chorioamnionitis as causative in the pathogenesis of PVL. In particular, recent investigations have shown that inflammatory responses in the fetus and neonate can contribute towards neonatal brain injury and development-related disabilities including cerebral palsy. This review presents current concepts on the pathogenesis of PVL and emphasizes the increasing evidence for an inflammatory pathogenic component to this disorder, either resulting from hypoxic-ischemic injury or from infection. These findings provide the basis for clinical approaches targeted at protecting the premature brain from inflammatory damage, which may prove beneficial for treating PVL, if identified early in pathogenesis.

Air pollution and brain damage

Exposure to complex mixtures of air pollutants produces inflammation in the upper and lower respiratory tract. Because the nasal cavity is a common portal of entry, respiratory and olfactory epithelia are vulnerable targets for toxicological damage. This study has evaluated, by light and electron microscopy and immunohistochemical expression of nuclear factor-kappa beta (NF-kappaB) and inducible nitric oxide synthase (iNOS), the olfactory and respiratory nasal mucosae, olfactory bulb, and cortical and subcortical structures from 32 healthy mongrel canine residents in Southwest Metropolitan Mexico City (SWMMC), a highly polluted urban region. Findings were compared to those in 8 dogs from Tlaxcala, a less polluted, control city. In SWMMC dogs, expression of nuclear neuronal NF-kappaB and iNOS in cortical endothelial cells occurred at ages 2 and 4 weeks; subsequent damage included alterations of the blood-brain barrier (BBB), degenerating cortical neurons, apoptotic glial white matter cells, deposition of apolipoprotein E (apoE)-positive lipid droplets in smooth muscle cells and pericytes, nonneuritic plaques, and neurofibrillary tangles. Persistent pulmonary inflammation and deteriorating olfactory and respiratory barriers may play a role in the neuropathology observed in the brains of these highly exposed canines. Neurodegenerative disorders such as Alzheimer's may begin early in life with air pollutants playing a crucial role.

Inhibition of microglial CD40 expression by pituitary adenylate cyclase-activating polypeptide is mediated by interleukin-10

Microglia are intrinsic mediators of the central nervous system (CNS) immune response induced by a variety of insults. Activated microglia express costimulatory molecules CD40 and B7 that are important equally for T-cell activation and further activation of microglia. In this study, we sought to investigate the regulation of costimulatory molecule expression on primary microglia and microglial cell line, BV-2, by pituitary adenylyl cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP), potent anti-inflammatory neuropeptides. The neuropeptides inhibited CD40 and B7-2 mRNA expression in activated microglia. PACAP decreased surface expression of CD40 and B7-2 on activated microglia. The inclusion of an anti-IL-10 antibody completely abrogated PACAP inhibition of lipopolysaccharide (LPS)-induced CD40 expression, suggesting that PACAP inhibition is at least in part mediated by IL-10. Indeed, PACAP enhanced LPS-induced IL-10 mRNA and protein levels in microglia. These data indicate that PACAP, through an increase in IL-10 protein, can down-regulate important costimulatory molecule expression on microglia, thereby possibly affecting CNS immunity.

Nuclear factor-kappa B-independent regulation of lipopolysaccharide-mediated interleukin-6 biosynthesis

The possible involvement of nuclear factor (NF)-kappa B in mediating the regulation of interleukin (IL)-6 biosynthesis in response to E. coli-derived lipopolysaccharide-endotoxin (LPS) was investigated in vitro. In alveolar epithelial cells, irreversible inhibition of the proteasome complex by carbobenzoxy-L-leucyl-L-leucyl-L-leucinal (MG-132; 1-50 muM) did not affect LPS-mediated IL-6 secretion. Whereas the selective inhibition of the NF-kappa B pathway by the action of caffeic acid phenyl ethyl ester (CAPE; 1-100 microM) attenuated LPS-dependent IL-6 production at 100 muM, sulfasalazine (SSA; 0.1--10 mM), a potent and irreversible inhibitor of NF-kappa B, did not inhibit LPS-dependent IL-6 secretion. Incorporation of a selectively permeant inhibitor of NF-kappa B, SN-50 (1-20 microM), a peptide which contains the nuclear localization sequence (NLS) for the p50 NF-kappa B subunit and the amino-terminal sequence of Kaposi fibroblast growth factor to promote cell permeability, did not reduce LPS-mediated release of IL-6. These data indicate a NF-kappa B-independent pathway mediating LPS-dependent regulation of IL-6 biosynthesis in the airway epithelium.

Intra-tumoral interleukin-6 down-regulation system and genetic mutations of tumor suppressor genes in colorectal carcinoma

BACKGROUND

The interleukin (IL)-1-IL-6 network, the most potent cascade of pro-inflammatory cytokines, plays an autocrine role in tumor growth. The IL-1-IL-6 network is down-regulated by a phased cytokine inhibitor IL-1 receptor antagonist (ra) and an anti-inflammatory cytokine IL-10. The current study evaluated this down-regulation system in colorectal carcinoma and its relation to the genetic alteration of tumor suppressor genes.

METHODS

Seventy-four specimens of primary colorectal carcinoma and normal mucosa were collected to measure tissue concentrations of cytokines. Polymerase chain reaction amplification was performed to investigate the loss of heterozygosity of the microsatellite markers on chromosomes 17p and 18q.

RESULTS

The IL-1ra/IL-6 ratio in the carcinoma specimens was lower than ratios in adenomas and normal mucosae and decreased with disease progression. The IL-1ra/IL-6 ratio in early cancers tended to be lower than that in adenomas and normal mucosae. However, the tissue concentrations of IL-1beta and IL-10 were not associated with any clinicopathologic parameters. The tissue IL-1ra concentration correlated with that of IL-6 only in adenomas and early cancers. Immunohistochemically, IL-1ra and IL-6 were localized in the tumor cytoplasm. A reduced tissue IL-1ra/IL-6 ratio in the carcinomas correlated with poor prognosis and was associated with the loss of heterozygosity of the microsatellite markers on chromosomes 18q.

CONCLUSIONS

There is an IL-6-IL-1ra network system in colorectal tumors, but this system deteriorates with carcinogenesis and tumor growth. The deterioration of this network system was associated with the allelic loss of a portion of chromosome 18q, reflecting the genetic alteration of tumor suppressor genes.

Regulation of microglial expression of integrins by poly(ADP-ribose) polymerase-1

Excitotoxic brain lesions initially result in the primary destruction of brain parenchyma, after which microglial cells migrate towards the sites of injury. At these sites, the cells produce large quantities of oxygen radicals and cause secondary damage that accounts for most of the loss of brain function. Here we show that this microglial migration is strongly controlled in living brain tissue by expression of the integrin CD11a, regulated by the nuclear enzyme poly(ADP-ribose) polymerase-1 (PARP-1) through the formation of a nuclear PARP-NF-kappaB-protein complex. Downregulation of PARP or CD11a by transfection with antisense DNA abrogated microglial migration almost completely and prevented neurons from secondary damage.

Inhibition of endotoxin-induced macrophage chemokine production by vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide in vitro and in vivo

Inflammatory chemokines recruit various populations of immune cells that initiate and maintain the inflammatory response against foreign Ags. Although such a response is necessary for the elimination of the Ag, the inflammation has to be eventually resolved in a healthy organism. Neuropeptides such as vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP), released after antigenic stimulation, contribute to the termination of an inflammatory response primarily by inhibiting the production of proinflammatory cytokines. Here we investigated the effects of VIP and PACAP on chemokine production. We report that VIP and PACAP inhibit the expression of the macrophage-derived CXC chemokines macrophage inflammatory protein-2 and KC (IL-8), and of the CC chemokines MIP-1alpha, MIP-1beta, monocyte chemoattractant protein 1, and RANTES in vivo and in vitro. The inhibition of chemokine gene expression correlates with an inhibitory effect of VIP/PACAP on NF-kappaB binding and transactivating activity. The VIP/PACAP inhibition of both chemokine production and of NF-kappaB binding and transactivating activity is mediated through the specific VIP receptor VPAC1, and involves both cAMP-dependent and -independent intracellular pathways. In an in vivo model of acute peritonitis, the inhibition of chemokine production by VIP/PACAP leads to a significant reduction in the recruitment of polymorphonuclear cells, macrophages, and lymphocytes into the peritoneal cavity. These findings support the proposed role of VIP and PACAP as key endogenous anti-inflammatory agents and describe a novel mechanism, i.e., the inhibition of the production of macrophage-derived chemokines.

Microglia in neurodegeneration: molecular aspects

Inflammatory events in the CNS are associated with injuries as well as with well-known chronic degenerative diseases, such as Multiple Sclerosis, Parkinson's, or Alzheimer's disease. Compared to inflammation in peripheral tissues, inflammation in brain appears to follow distinct pathways and time-courses, which likely has to do with a relatively strong immunosuppression in that organ. For this reason, it is of great importance to get insights into the molecular mechanism governing immune reactions in brain tissue. This task is hard to achieve in vivo, but can be approached by studying the major cell type responsible for brain inflammation, the microglia, in culture. Since these cells are the only professional antigen-presenting cells resident in brain parenchyma, molecular mechanisms of antigen presentation are being discussed first. After covering the expression and regulation of anti- and proinflammatory cytokines, induction and regulation of two key enzymes and their products-COX-2 and iNOS-are summarized. Possibly, pivotal molecular targets for drug therapies of brain disorders will be discovered in intracellular signaling pathways leading to activation of transcription factors. Finally, the impact of growth factors, of neurotrophins in particular, is highlighted. It is concluded that the presently available data on the molecular level is far from being statisfying, but that only from better insights into molecular events will we obtain the information required for more specific therapies.

Inflammatory repertoire of Alzheimer's disease and nondemented elderly microglia in vitro

We have previously developed and characterized isolated microglia and astrocyte cultures from rapid (<4 h) brain autopsies of Alzheimer's disease (AD) and nondemented elderly control (ND) patients. In the present study, we evaluate the inflammatory repertoire of AD and ND microglia cultured from white matter (corpus callosum) and gray matter (superior frontal gyrus) with respect to three major proinflammatory cytokines, three chemokines, a classical pathway complement component, a scavenger cell growth factor, and a reactive nitrogen intermediate. Significant, dose-dependent increases in the production of pro-interleukin-1beta (pro-IL-1beta), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), monocyte chemoattractant protein-1 (MCP-1), macrophage inflammatory peptide-1alpha (MIP-1alpha), IL-8, and macrophage colony-stimulating factor (M-CSF) were observed after exposure to pre-aggregated amyloid beta peptide (1-42) (Abeta1-42). Across constitutive and Abeta-stimulated conditions, secretion of complement component C1q, a reactive nitrogen intermediate, and M-CSF was significantly higher in AD compared with ND microglia. Taken together with previous in situ hybridization findings, these results demonstrate unequivocally that elderly human microglia provide a brain endogenous source for a wide range of inflammatory mediators.

From theory to therapy: implications from an in vitro model of ramified microglia

Microglia are the principal immune cells in the central nervous system (CNS), characterized by a highly specific morphology and unusual antigenic phenotype. An increasing number of studies have focused on the role of microglia in the pathogenesis of neurodegenerative diseases. To elucidate the function of microglial cells under several neuropathological conditions, we have studied and established a cell culture model that allows us to cultivate microglial cells in their inactive, resting (ramified) phenotype. In the first part of this work, we describe the interaction of microglia cells with their epithelial (astrocytic) microenvironment. The second part reviews experiments with microglia cell cultures to elucidate underlying signalling pathways and summarizes recent advances of our knowledge in microglial molecular pathways that may ultimately lead to neurodegeneration.

Human immunodeficiency virus type 1 Tat protein decreases cyclic AMP synthesis in rat microglia cultures

We have studied the modulation of cyclic AMP (cAMP) accumulation by the human immunodeficiency virus type 1 (HIV 1) protein Tat in microglia and astrocyte cultures obtained from neonatal rat brain. Pretreatment of microglia with recombinant Tat resulted in a dose- and time-dependent decrease of cAMP accumulation induced by subsequent exposure to isoproterenol (1 microM). The inhibitory action of 100 ng/mL Tat approached 50% after 4 h of preincubation and reached a maximum of 70% after 24 h. The Tat-induced time- and dose-dependent decrease of cAMP accumulation was observed also when microglial cultures were stimulated with the adenylyl cyclase activator forskolin (100 microM). In both cases, Tat inhibitory action was 70% reverted by a specific monoclonal anti-Tat antibody, but was not prevented either by the phosphodiesterase inhibitor 3-isobutyl-1-methyl-xantine (100 microM) or by a 16-h pretreatment of microglial cultures with the Gi protein inhibitor pertussis toxin (10 ng/mL). All these results suggested that the viral protein acts at a step of the cAMP transduction pathway other than receptors, G proteins and phosphodiesterases. The target of Tat appeared to be adenylyl cyclase, whose activity was markedly reduced (up to 60%) in membranes prepared from Tat-treated microglial cells, both in basal conditions and after stimulation with isoproterenol and forskolin. The inability of the competitive inhibitor of nitric oxide synthase N(G)-monometyl- L-arginine (20 and 200 microM) to revert Tat action on forskolin-induced cAMP accumulation, and of two potent nitric oxide donors, PAPA and DETA (0.1-2 m M), to alter forskolin-induced cAMP accumulation, excluded an involvement of nitric oxide in Tat-induced adenylyl cyclase inhibition. On the contrary, two inhibitors of nuclear factor kappaB activation, N-tosyl-( L)-phenylalanine chloromethyl ketone (10 microM) and SN50 (25 microM), markedly prevented the reduction of forskolin-evoked cAMP accumulation by Tat, suggesting a possible role for this nuclear transcriptional factor in the regulation of adenylyl cyclase by Tat in microglia. This assumption was strengthened by the ability of lipopolysaccharide (100 ng/mL, 4 h) to mimic the inhibitory effect of the viral protein. Conversely, astrocyte cAMP accumulation was unaffected by the viral protein, as tested at various concentrations and time points. Finally, Tat inhibition of microglial adenylyl cyclase was not due to non-specific cytotoxicity. As cAMP has been reported to exert a neuroprotective role in several in vivo and in vitro models of brain pathologies, and microglia is believed to mediate Tat-induced neurotoxicity, these results suggest that the ability of Tat to inhibit cAMP synthesis in microglia may contribute to neuronal degeneration and cell death associated with HIV infection.