Expression of TNF and TNF Receptors (p55 and p75) in the Rat Brain after Focal Cerebral Ischemia

Inflammatory cytokines in experimental and human stroke

Inflammation is a hallmark of stroke pathology. The cytokines, tumor necrosis factor (TNF), interleukin (IL)-1, and IL-6, modulate tissue injury in experimental stroke and are therefore potential targets in future stroke therapy. The effect of these cytokines on infarct evolution depends on their availability in the ischemic penumbra in the early phase after stroke onset, corresponding to the therapeutic window (<4.5 hours), which is similar in human and experimental stroke. This review summarizes a large body of literature on the spatiotemporal and cellular production of TNF, IL-1, and IL-6, focusing on the early phase in experimental and human stroke. We also review studies of cytokines in blood and cerebrospinal fluid in stroke. Tumor necrosis factor and IL-1 are upregulated early in peri-infarct microglia. Newer literature suggests that IL-6 is produced by microglia, in addition to neurons. Tumor necrosis factor- and IL-1-producing macrophages infiltrate the infarct and peri-infarct with a delay. This information is discussed in the context of suggestions that neuronal sensitivity to ischemia may be modulated by cytokines. The fact that TNF and IL-1, and suppossedly also IL-6, are produced by microglia within the therapeutic window place these cells centrally in potential future stroke therapy.

A review: inflammatory process in Alzheimer's disease, role of cytokines

Alzheimer's disease (AD) is the most common neurodegenerative disorder to date. Neuropathological hallmarks are β-amyloid (Aβ) plaques and neurofibrillary tangles, but the inflammatory process has a fundamental role in the pathogenesis of AD. Inflammatory components related to AD neuroinflammation include brain cells such as microglia and astrocytes, the complement system, as well as cytokines and chemokines. Cytokines play a key role in inflammatory and anti-inflammatory processes in AD. An important factor in the onset of inflammatory process is the overexpression of interleukin (IL)-1, which produces many reactions in a vicious circle that cause dysfunction and neuronal death. Other important cytokines in neuroinflammation are IL-6 and tumor necrosis factor (TNF)-α. By contrast, other cytokines such as IL-1 receptor antagonist (IL-1ra), IL-4, IL-10, and transforming growth factor (TGF)-β can suppress both proinflammatory cytokine production and their action, subsequently protecting the brain. It has been observed in epidemiological studies that treatment with nonsteroidal anti-inflammatory drugs (NSAIDs) decreases the risk for developing AD. Unfortunately, clinical trials of NSAIDs in AD patients have not been very fruitful. Proinflammatory responses may be countered through polyphenols. Supplementation of these natural compounds may provide a new therapeutic line of approach to this brain disorder.

Tumor necrosis factor-α receptor type 1, not type 2, mediates its acute responses in the kidney

Acute administration of tumor necrosis factor-α (TNF-α) resulted in decreases in renal blood flow (RBF) and glomerular filtration rate (GFR) but induced diuretic and natriuretic responses in mice. To define the receptor subtypes involved in these renal responses, experiments were conducted to assess the responses to human recombinant TNF-α (0.3 ng·min(-1)·g body wt(-1) iv infusion for 75 min) in gene knockout (KO) mice for TNF-α receptor type 1 (TNFαR1 KO, n = 5) or type 2 (TNFαR2 KO, n = 6), and the results were compared with those obtained in corresponding wild-type [WT (C57BL/6), n = 6] mice. Basal levels of RBF (PAH clearance) and GFR (inulin clearance) were similar in TNFαR1 KO, but were lower in TNFαR2 KO, than WT mice. TNF-α infusion in WT mice decreased RBF and GFR but caused a natriuretic response, as reported previously. In TNFαR1 KO mice, TNF-α infusion failed to cause such vasoconstrictor or natriuretic responses; rather, there was an increase in RBF and a decrease in renal vascular resistance. Similar responses were also observed with infusion of murine recombinant TNF-α in TNFαR1 KO mice (n = 5). However, TNF-α infusion in TNFαR2 KO mice caused changes in renal parameters qualitatively similar to those observed in WT mice. Immunohistochemical analysis in kidney slices from WT mice demonstrated that while both receptor types were generally located in the renal vascular and tubular cells, only TNFαR1 was located in vascular smooth muscle cells. There was an increase in TNFαR1 immunoreactivity in TNFαR2 KO mice, and vice versa, compared with WT mice. Collectively, these functional and immunohistological findings in the present study demonstrate that the activation of TNFαR1, not TNFαR2, is mainly involved in mediating the acute renal vasoconstrictor and natriuretic actions of TNF-α.

Curcumin protects nigrostriatal dopaminergic neurons and reduces glial activation in 6-hydroxydopamine hemiparkinsonian mice model

This study investigated the effects of curcumin on nigrostriatal dopaminergic (DA) neurons and glial response in 6-hydroxydopamine (6-OHDA) hemiparkinsonian mice. Following unilateral intrastriatal 6-OHDA injection, mice were daily injected with curcumin for seven days, beginning on the day of lesion. Seven days after 6-OHDA lesioning, sections from the striatum and the substantia nigra pars compacta (SNpc) were collected and immunohistochemically stained for DA neurons and reactive glia. Curcumin decreased 6-OHDA-induced loss of nigral tyrosine hydroxylase-immunoreactive (TH-IR) neurons and striatal TH-IR fibers. The neuroprotection was coincided with a significant attenuation of microglial and astroglial reaction in the SNpc and the striatum. These results suggest that the neuroprotective effects of curcumin in 6-OHDA-lesioned mice may be mediated through its anti-inflammatory properties or direct protection on nigral DA neurons, thereby reducing neuronal injury-induced glial activation.

Effects of irradiation on brain vasculature using an in situ tumor model

PURPOSE

Damage to normal tissue is a limiting factor in clinical radiotherapy (RT). We tested the hypothesis that the presence of tumor alters the response of normal tissues to irradiation using a rat in situ brain tumor model.

METHODS AND MATERIALS

Intravital microscopy was used with a rat cranial window to assess the in situ effect of rat C6 glioma on peritumoral tissue with and without RT. The RT regimen included 40 Gy at 8 Gy/day starting Day 5 after tumor implant. Endpoints included blood-brain barrier permeability, clearance index, leukocyte-endothelial interactions and staining for vascular endothelial growth factor (VEGF) glial fibrillary acidic protein, and apoptosis. To characterize the system response to RT, animal survival and tumor surface area and volume were measured. Sham experiments were performed on similar animals implanted with basement membrane matrix absent of tumor cells.

RESULTS

The presence of tumor alone increases permeability but has little effect on leukocyte-endothelial interactions and astrogliosis. Radiation alone increases tissue permeability, leukocyte-endothelial interactions, and astrogliosis. The highest levels of permeability and cell adhesion were seen in the model that combined tumor and irradiation; however, the presence of tumor appeared to reduce the volume of rolling leukocytes. Unirradiated tumor and peritumoral tissue had poor clearance. Irradiated tumor and peritumoral tissue had a similar clearance index to irradiated and unirradiated sham-implanted animals. Radiation reduces the presence of VEGF in peritumoral normal tissues but did not affect the amount of apoptosis in the normal tissue. Apoptosis was identified in the tumor tissue with and without radiation.

CONCLUSIONS

We developed a novel approach to demonstrate that the presence of the tumor in a rat intracranial model alters the response of normal tissues to irradiation.

Transmembrane tumour necrosis factor is neuroprotective and regulates experimental autoimmune encephalomyelitis via neuronal nuclear factor-kappaB

Tumour necrosis factor mediates chronic inflammatory pathologies including those affecting the central nervous system, but non-selective tumour necrosis factor inhibitors exacerbate multiple sclerosis. In addition, TNF receptor SF1A, which encodes one of the tumour necrosis factor receptors, has recently been identified as a multiple sclerosis susceptibility locus in genome-wide association studies in large patient cohorts. These clinical data have emphasized the need for a better understanding of the beneficial effects of tumour necrosis factor during central nervous system inflammation. In this study, we present evidence that the soluble and transmembrane forms of tumour necrosis factor exert opposing deleterious and beneficial effects, respectively, in a multiple sclerosis model. We compared the effects, in experimental autoimmune encephalomyelitis, of selectively inhibiting soluble tumour necrosis factor, and of both soluble and transmembrane tumour necrosis factor. Blocking the action of soluble tumour necrosis factor, but not of soluble tumour necrosis factor and transmembrane tumour necrosis factor, protected mice against the clinical symptoms of experimental autoimmune encephalomyelitis. Therapeutic benefit was independent of changes in antigen-specific immune responses and focal inflammatory spinal cord lesions, but was associated with reduced overall central nervous system immunoreactivity, increased expression of neuroprotective molecules, and was dependent upon the activity of neuronal nuclear factor-κB, a downstream mediator of neuroprotective tumour necrosis factor/tumour necrosis factor receptor signalling, because mice lacking IκB kinase β in glutamatergic neurons were not protected by soluble tumour necrosis factor blockade. Furthermore, blocking the action of soluble tumour necrosis factor, but not of soluble tumour necrosis factor and transmembrane tumour necrosis factor, protected neurons in astrocyte-neuron co-cultures against glucose deprivation, an in vitro neurodegeneration model relevant for multiple sclerosis, and this was dependent upon contact between the two cell types. Our results show that soluble tumour necrosis factor promotes central nervous system inflammation, while transmembrane tumour necrosis factor is neuroprotective, and suggest that selective inhibition of soluble tumour necrosis factor may provide a new way forward for the treatment of multiple sclerosis and possibly other inflammatory central nervous system disorders.

Anti-inflammatory effects of Polygala tenuifolia root through inhibition of NF-κB activation in lipopolysaccharide-induced BV2 microglial cells

ETHNOPHARMACOLOGICAL RELEVANCE

The root of Polygala tenuifolia Willd is a well-known traditional Oriental medicine and has been prescribed for treatment of dysfunction in memorial systems and various brain inflammatory diseases. The present study was designed to validate the anti-inflammatory effects of the water extract of Polygala tenuifolia root (WEPT).

MATERIALS AND METHODS

The anti-inflammatory properties of WEPT were studied using lipopolysaccharide (LPS)-stimulated murine BV2 microglia model. As inflammatory parameters, the production of nitric oxide (NO), inducible NO synthase (iNOS), cyclooxygenase (COX)-2, prostaglandin E(2) (PGE(2)), tumor necrosis factor (TNF)-α, and interleukin (IL)-1β were evaluated. We also examined the extract's effect on the activity of nuclear factor-kappaB (NF-κB), and toll-like receptor 4 (TLR4) and myeloid differentiation factor 88 (Myd-88) expression.

RESULTS

WEPT suppressed LPS-induced production of NO, PGE(2), and expression of iNOS and COX-2 in a dose-dependent manner, without causing cytotoxicity. It also significantly reduced generation of proinflammatory cytokines, including IL-1β and TNF-α. In addition, WEPT suppressed NF-κB translocation by blockade of IkappaB-α (IκB-α) degradation and inhibited TLR4 and Myd-88 expression in LPS-stimulated BV2 cells.

CONCLUSIONS

These results indicate that the inhibitory effects of WEPT on LPS-stimulated inflammatory mediator production in BV2 microglia are associated with suppression of the NF-κB and toll-like receptor signaling pathways. Therefore, Polygala tenuifolia extracts may be useful in treatment of neurodegenerative diseases by inhibition of inflammatory mediator production in activated microglia.

Prevention of the β-amyloid peptide-induced inflammatory process by inhibition of double-stranded RNA-dependent protein kinase in primary murine mixed co-cultures

Background

Inflammation may be involved in the pathogenesis of Alzheimer's disease (AD). There has been little success with anti-inflammatory drugs in AD, while the promise of anti-inflammatory treatment is more evident in experimental models. A new anti-inflammatory strategy requires a better understanding of molecular mechanisms. Among the plethora of signaling pathways activated by β-amyloid (Aβ) peptides, the nuclear factor-kappa B (NF-κB) pathway could be an interesting target. In virus-infected cells, double-stranded RNA-dependent protein kinase (PKR) controls the NF-κB signaling pathway. It is well-known that PKR is activated in AD. This led us to study the effect of a specific inhibitor of PKR on the Aβ42-induced inflammatory response in primary mixed murine co-cultures, allowing interactions between neurons, astrocytes and microglia.

Methods

Primary mixed murine co-cultures were prepared in three steps: a primary culture of astrocytes and microglia for 14 days, then a primary culture of neurons and astrocytes which were cultured with microglia purified from the first culture. Before exposure to Aβ neurotoxicity (72 h), co-cultures were treated with compound C16, a specific inhibitor of PKR. Levels of tumor necrosis factor-α (TNFα), interleukin (IL)-1β, and IL-6 were assessed by ELISA. Levels of P_T451-PKR and activation of IκB, NF-κB and caspase-3 were assessed by western blotting. Apoptosis was also followed using annexin V-FITC immunostaining kit. Subcellular distribution of P_T451-PKR was assessed by confocal immunofluorescence and morphological structure of cells by scanning electron microscopy. Data were analysed using one-way ANOVA followed by a Newman-Keuls' post hoc test

Results

In these co-cultures, PKR inhibition prevented Aβ42-induced activation of IκB and NF-κB, strongly decreased production and release of tumor necrosis factor (TNFα) and interleukin (IL)-1β, and limited apoptosis.

Conclusion

In spite of the complexity of the innate immune response, PKR inhibition could be an interesting anti-inflammatory strategy in AD.

Lipopolysaccharide signaling in the carotid chemoreceptor pathway of rats with sepsis syndrome

In addition to their role in cardiorespiratory regulation, carotid body (CB) chemoreceptors serve as sensors for inflammatory status and as a protective factor during sepsis. However, lipopolysaccharide-induced sepsis (LPS) reduces CB responsiveness to excitatory or depressant stimuli. We tested whether LPS exerts a direct effect on the carotid chemoreceptor pathway, the CB and its sensory ganglion. We determined that the rat CB and nodose-petrosal-jugular ganglion complex (NPJgc) express TLR4, TNF-α and its receptors (TNF-R1 and TNF-R2). LPS administration (15mg/kg intraperitoneally) evoked MyD88-mechanism pathway activation in CB and NPJgc, with NF-κB p65, p38 MAPK, and ERK activation. Consistently, LPS increased TNF-α and TNF-R2. Double-labeling studies showed that the aforementioned pathway occurs in TH-containing glomus cells and NPJgc neurons, components of the chemosensitive neural pathway. Thus, our results suggest that LPS acting directly through TLR4/MyD88-mechanism pathways increases TNF-α and TNF-R2 expression in the carotid chemoreceptor pathway. These results show a novel afferent pathway to the central nervous system during endotoxemia, and could be relevant in understanding sepsis pathophysiology and therapy.

The inhalation anesthetic isoflurane increases levels of proinflammatory TNF-α, IL-6, and IL-1β

Anesthetics have been reported to promote Alzheimer's disease (AD) neuropathogenesis by inducing β-amyloid protein accumulation and apoptosis. Neuroinflammation is associated with the emergence of AD. We therefore set out to determine the effects of the common anesthetic isoflurane on the levels of tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-1β, the proinflammatory cytokines, in vitro and in vivo, employing Western blot, immunohistochemistry, enzyme-linked immunosorbent assay (ELISA), and reverse transcriptase polymerase chain reaction (RT-PCR). Here, we show that a clinically relevant isoflurane anesthesia increased the protein and messenger ribonucleic acid (mRNA) levels of TNF-α, IL-6, and IL-1β in the brain tissues of mice. The isoflurane anesthesia increased the amounts of TNF-α immunostaining positive cells in the brain tissues of mice, the majority of which were neurons. Furthermore, isoflurane increased TNF-α levels in primary neurons, but not microglia cells, of mice. Finally, isoflurane induced a greater degree of TNF-α increase in the AD transgenic mice than in the wild-type mice. These results suggest that isoflurane may increase the levels of proinflammatory cytokines, which may cause neuroinflammation, leading to promotion of AD neuropathogenesis.

Anti-inflammatory effects of cordycepin via suppression of inflammatory mediators in BV2 microglial cells

Cordyceps militaris, a traditional medicinal mushroom, produces the bioactive compound cordycepin (3'-deoxyadenosine). Although cordycepin has been shown to have pharmacological, immunological stimulating, anti-cancer, and anti-inflammatory activities, its activities and cellular mechanisms during microglial activation have yet to be elucidated. Thus, we evaluated the anti-inflammatory effect of cordycepin on the production of inflammatory mediators in lipopolysaccharide (LPS)-stimulated murine BV2 microglia. We also investigated the effects of cordycepin on LPS-induced nuclear factor-kappaB (NF-κB) activation and on phosphorylation of mitogen-activated protein kinases (MAPKs). After LPS stimulation, nitric oxide (NO), prostaglandin E₂ (PGE₂), and pro-inflammatory cytokine production was detected in BV2 microglia. However, we found that cordycepin significantly inhibited the excessive production of NO, PGE₂, and pro-inflammatory cytokines in a concentration-dependent manner without causing cytotoxicity. In addition, cordycepin suppressed NF-κB translocation by blocking IkappaB-α (IκB-α) degradation and inhibited the phosphorylation of Akt, ERK-1/2, JNK, and p38 kinase. Our results indicate that the inhibitory effect of cordycepin on LPS-stimulated inflammatory mediator production in BV2 microglia is associated with the suppression of the NF-κB, Akt, and MAPK signaling pathways. Therefore, cordycepin may be useful in treating neurodegenerative diseases by inhibiting inflammatory mediator production in activated microglia.

Neuroinflammatory processes in Alzheimer's disease

Generation of neurotoxic amyloid beta peptides and their deposition along with neurofibrillary tangle formation represent key pathological hallmarks in Alzheimer's disease (AD). Recent evidence suggests that inflammation may be a third important component which, once initiated in response to neurodegeneration or dysfunction, may actively contribute to disease progression and chronicity. Various neuroinflammatory mediators including complement activators and inhibitors, chemokines, cytokines, radical oxygen species and inflammatory enzyme systems are expressed and released by microglia, astrocytes and neurons in the AD brain. Degeneration of aminergic brain stem nuclei including the locus ceruleus and the nucleus basalis of Meynert may facilitate the occurrence of inflammation in their projection areas given the antiinflammatory and neuroprotective action of their key transmitters norepinephrine and acetylcholine. While inflammation has been thought to arise secondary to degeneration, recent experiments demonstrated that inflammatory mediators may stimulate amyloid precursor protein processing by various means and therefore can establish a vicious cycle. Despite the fact that some aspects of inflammation may even be protective for bystander neurons, antiinflammatory treatment strategies should therefore be considered. Non-steroidal anti-inflammatory drugs have been shown to reduce the risk and delay the onset to develop AD. While, the precise molecular mechanism underlying this effect is still unknown, a number of possible mechanisms including cyclooxygenase 2 or gamma-secretase inhibition and activation of the peroxisome proliferator activated receptor gamma may alone or, more likely, in concert account for the epidemiologically observed protection.

Functional aspects of redox control during neuroinflammation

Neuroinflammation is a CNS reaction to injury in which some severe pathologies, regardless of their origin, converge. The phenomenon emphasizes crosstalk between neurons and glia and reveals a complex interaction with oxidizing agents through redox sensors localized in enzymes, receptors, and transcription factors. When oxidizing pressures cause reversible molecular changes, such as minimal or transitory proinflammatory cytokine overproduction, redox couples provide a means of translating the presence of reactive oxygen or nitrogen species into useful signals in the cell. Additionally, thiol-based redox sensors convey information about localized changes in redox potential induced by physiologic or pathologic situations. They are susceptible to oxidative changes and become key events during neuroinflammation, altering the course of a signaling response or the behavior of specific transcription factors. When oxidative stress augments the pressure on the intracellular environment, the effective reduction potential of redox pairs diminishes, and cell signaling shifts toward proinflammatory and proapoptotic signals, creating a vicious cycle between oxidative stress and neuroinflammation. In addition, electrophilic compounds derived from the oxidative cascade react with key protein thiols and interfere with redox signaling. This article reviews the relevant functional aspects of redox control during the neuroinflammatory process.

Peripheral administration of fetuin-A attenuates early cerebral ischemic injury in rats

Cerebral ischemia-elicited inflammatory responses are driven by inflammatory mediators produced both by central (e.g., neurons and microglia) and infiltrating peripheral immune cells (e.g., macrophage/monocyte), and contribute to the evolution of tissue injury. A ubiquitous molecule, spermine, is released from injured cells, and counter-regulates release of various proinflammatory cytokines. However, the spermine-mediated anti-inflammatory activities are dependent on the availability of fetuin-A, a liver-derived negative acute-phase protein. Using an animal model of focal cerebral ischemia (i.e., permanent middle cerebral artery occlusion, MCAo), we found that levels of fetuin-A in the ischemic brain tissue were elevated in a time-dependent manner, starting between 2 and 6 h, peaking around 24 to 48 h, and returning to baseline 72 h after MCAo. When administered peripherally, exogenous fetuin-A gained entry across the BBB into the ischemic brain tissue, and dose dependently reduced brain infarct volume at 24 h after MCAo. Meanwhile, fetuin-A effectively attenuated (i) ischemia-induced HMGB1 depletion from the ischemic core; (ii) activation of centrally (e.g., microglia) and peripherally derived immune cells (e.g., macrophage/monocytes); and (iii) TNF production in ischemic brain tissue. Taken together, these experimental data suggest that fetuin-A protects against early cerebral ischemic injury partly by attenuating the brain inflammatory response.

Cilostazol is anti-inflammatory in BV2 microglial cells by inactivating nuclear factor-kappaB and inhibiting mitogen-activated protein kinases

BACKGROUND AND PURPOSE

Cilostazol is a specific inhibitor of 3'-5'-cyclic adenosine monophosphate (cAMP) phosphodiesterase, which is widely used to treat ischemic symptoms of peripheral vascular disease. Although cilostazol has been shown to exhibit vasodilator properties as well as antiplatelet and anti-inflammatory effects, its cellular mechanism in microglia is unknown. In the present study, we assessed the anti-inflammatory effect of cilostazol on the production of pro-inflammatory mediators in lipopolysaccharide (LPS)-stimulated murine BV2 microglia.

EXPERIMENTAL APPROACH

We examined the effects of cilostazol on LPS-induced nuclear factor-kappaB (NF-kappaB) activation and phosphorylation of mitogen-activated protein kinases (MAPKs).

KEY RESULTS

Cilostazol suppressed production of nitric oxide (NO), prostaglandin E(2) (PGE(2)) and the proinflammatory cytokines, interleukin-1 (IL-1), tumour necrosis factor-alpha, and monocyte chemoattractant protein-1 (MCP-1), in a concentration-dependent manner. Inhibitory effects of cilostazol were not affected by treatment with an adenylate cyclase inhibitor, SQ 22536, indicating that these actions of cilostazol were cAMP-independent. Cilostazol significantly inhibited the DNA binding and transcriptional activity of NF-kappaB. Moreover, cilostazol blocked signalling upstream of NF-kappaB activation by inhibiting extracellular signal-regulated kinases 1 and 2 (ERK1/2) and c-Jun N-terminal kinase (JNK), but without affecting the activity of p38 MAPK.

CONCLUSION AND IMPLICATIONS

Our results demonstrate that suppression of the NF-kappaB, ERK, JNK signalling pathways may inhibit LPS-induced NO and PGE(2) production. Therefore, cilostazol may have therapeutic potential for neurodegenerative diseases by inhibiting pro-inflammatory mediators and cytokine production in activated microglia.

Cerebral cortical gene expression in acutely anemic rats: a microarray analysis

PURPOSE

Hemodilution in perioperative patients has been associated with neurological morbidity and increased mortality by undefined mechanisms. This study assesses whether hemodilutional anemia up-regulated inflammatory cerebral gene expression (microarray) to help define the mechanism.

METHODS

Hemodilution was performed in anesthetized rats by exchanging 50% of the estimated blood volume (30 mL kg(-1)) with pentastarch. Two groups of control animals were utilized, i.e., a non-anesthetized control (Normal Control) and an anesthetized control group (Anesthesia Control). Blood pressure, hemoglobin concentration, and arterial blood gas analysis were performed before and after hemodilution. Cerebral cortex was harvested from isoflurane-anesthetized rats (n = 6) after 6 and 24 hr of recovery and was used to perform complimentary DNA (cDNA) microarray analyses. Pro-inflammatory chemokine and cytokine protein levels were also measured.

RESULTS

Microarray analysis demonstrated up-regulation of 72 and 27 genes (6 and 24 hr, respectively) in anemic cerebral cortex. These genes were involved in a number of biological functions, including (1) inflammatory responses; (2) angiogenesis; (3) vascular homeostasis; (4) cellular biology; and (5) apoptosis. Chemokine ribonucleic acid (RNA) expression (CXCL-1, -10, and -11) was highest in anemic brain tissue (P < 0.0125 for each). Protein measurements demonstrated a significant increase in interleukin-6, tumor necrosis factor alpha, and monocyte chemoattractant protein-1 (P < 0.05 for each).

CONCLUSION

This study utilizes microarray technology to elucidate changes in cerebral cortical gene expression in response to acute hemodilution. These findings demonstrate an increase in pro-inflammatory chemokines (RNA, protein) and cytokines (protein). An improved understanding of the inflammatory response to anemia may help to minimize associated morbidity and mortality.

Heterogeneity of microglia and TNF signaling as determinants for neuronal death or survival

Microglia do not constitute a single, uniform cell population, but rather comprise cells with varied phenotypes, some which are beneficial and others that may require active regulatory control. Thus, gaining a better understanding of the heterogeneity of resident microglia responses will contribute to any interpretation regarding the impact of any such response in the brain. Microglia are the primary source of the pro-inflammatory cytokine, tumor necrosis factor (TNF) that can initiate various effects through the activation of membrane receptors. The TNF p55 receptor contains a death domain and activation normally leads to cellular apoptosis; however, under specific conditions, receptor activation can also lead to the activation of NF-kappaB and contribute to cell survival. These divergent outcomes have been linked to receptor localization with receptor internalization leading to cell death and membrane localization supporting cell survival. A second TNF receptor, TNF p75 receptor, is normally linked to cell growth and survival, however, it can cooperate with the p55 receptor and contribute to cell death. Thus, while an elevation in TNFalpha in the brain is often considered an indicator of microglia activation and neuroinflammation, a number of factors come into play to determine the final outcome. Data are reviewed demonstrating that heterogeneity in morphological response of microglia and the expression of TNFalpha and TNF receptors are critical in identifying and characterizing neurotoxic events as they relate to neuroinflammation, neuronal damage and in stimulating neuroprotection.

Role of tumor necrosis factor-alpha and matrix metalloproteinase-9 in blood-brain barrier disruption after peripheral thermal injury in rats

OBJECT

A relationship has been found between peripheral thermal injury and cerebral complications leading to injury and death. In the present study, the authors examined whether tumor necrosis factor-alpha (TNF-alpha) and matrix metalloproteinase-9 (MMP-9) play a causative role in blood-brain barrier (BBB) disruption after peripheral thermal injury.

METHODS

Thirty-two male Sprague-Dawley rats were subjected to thermal injury. One hour later, 8 rats were injected with TNF-alpha neutralizing antibody, and 8 were injected with doxycycline, an inhibitor of the MMP family proteins; 16 rats did not receive any treatment. Brain tissue samples obtained 7 hours after injury in the treated animals were examined for BBB function by using fluorescein isothiocyanate-dextran and by assessing parenchymal water content. Protein expression of basement membrane components (collagen IV, laminin, and fibronectin) was quantified on Western blot analysis, and MMP-9 protein expression and enzyme activity were determined using Western blot and gelatin zymography. Thermally injured rats that did not receive treatment were killed at 3, 7, or 24 hours after injury and tested for BBB functioning at each time point. Histological analysis for basement membrane proteins was also conducted in untreated rats killed at 7 hours after injury. Results of testing in injured rats were compared with those obtained in a control group of rats that did not undergo thermal injury.

RESULTS

At 7 hours after thermal injury, a significant increase in the fluorescein isothiocyanate-dextran and water content of the brain was found (p < 0.05), but BBB dysfunction was significantly decreased in the rats that received TNF-alpha antibody or doxycycline (p < 0.05). In addition, the components of the basal lamina were significantly decreased at 7 hours after thermal injury (p < 0.01), and there were significant increases in MMP-9 protein expression and enzyme activity (p < 0.05). The basal lamina damage was reversed by inhibition of TNF-alpha and MMP-9, and the increase in MMP-9 protein was reduced in the presence of doxycycline (p < 0.05). The authors found that MMP-9 enzyme activity was significantly increased after thermal injury (p < 0.01) but decreased in the presence of either TNF-alpha antibody or doxycycline (p < 0.01).

CONCLUSIONS

The dual, inhibitory activity of both TNF-alpha and MMP-9 in brain injury suggests that a TNF-alpha and MMP-9 cascade may play a key role in BBB disruption. These results offer a better understanding of the pathophysiology of burn injuries, which may open new avenues for burn treatment beyond the level of current therapies.

Vessel microport technique for applications in cerebrovascular research

Cerebrovascular research suffers from a lack of reliable methods with which to deliver exogenous substances effectively into the central nervous system (CNS) of small experimental animals. Here we describe a novel vessel microport surgical technique for a variety of cerebrovascular applications that is reproducible and well tolerated in mice. The procedure is based on the insertion of a vessel microport into the external carotid artery for substance delivery into the CNS via the internal carotid artery. The method results in selective substance delivery into the ipsilateral hemisphere. Other novel aspects of this surgical technique include the ability to perform multiple injections, study of conscious mice well removed from surgery, and lack of occlusion of the common or internal carotid artery that allows carotid flow to be maintained. The feasibility of this technique has been validated by infusion of HIV Tat protein to induce permeability of the blood-brain barrier and by implantation of tumor cells to establish a brain metastasis model. Thus, the described vessel microport technique can be employed in a variety of cerebrovascular research applications.

Radiation-induced astrogliosis and blood-brain barrier damage can be abrogated using anti-TNF treatment

PURPOSE

In this article, we investigate the role of tumor necrosis factor-alpha (TNF) in the initiation of acute damage to the blood-brain barrier (BBB) and brain tissue following radiotherapy (RT) for CNS tumors.

METHODS AND MATERIALS

Intravital microscopy and a closed cranial window technique were used to measure quantitatively BBB permeability to FITC-dextran 4.4-kDa molecules, leukocyte adhesion (Rhodamine-6G) and vessel diameters before and after 20-Gy cranial radiation with and without treatment with anti-TNF. Immunohistochemistry was used to quantify astrogliosis post-RT and immunofluorescence was used to visualize protein expression of TNF and ICAM-1 post-RT. Recombinant TNF (rTNF) was used to elucidate the role of TNF in leukocyte adhesion and vessel diameter.

RESULTS

Mice treated with anti-TNF showed significantly lower permeability and leukocyte adhesion at 24 and 48 h post-RT vs. RT-only animals. We observed a significant decrease in arteriole diameters at 48 h post-RT that was inhibited in TNF-treated animals. We also saw a significant increase in activated astrocytes following RT that was significantly lower in the anti-TNF-treated group. In addition, immunofluorescence showed protein expression of TNF and ICAM-1 in the cerebral cortex that was inhibited with anti-TNF treatment. Finally, administration of rTNF induced a decrease in arteriole diameter and a significant increase in leukocyte adhesion in venules and arterioles.

CONCLUSIONS

TNF plays a significant role in acute changes in BBB permeability, leukocyte adhesion, arteriole diameter, and astrocyte activation following cranial radiation. Treatment with anti-TNF protects the brain's microvascular network from the acute damage following RT.

Erythropoietin does not attenuate cytokine production and inflammation in microglia--implications for the neuroprotective effect of erythropoietin in neurological diseases

Erythropoietin is a hematopoietic cytokine which is also produced in the brain under hypoxia. Since this pathology is associated with glial cell activation and release of cytotoxic molecules, we investigated the expression of EPO receptors (EPO-R) and effects of erythropoietin on microglial cell functions in vitro using RT-PCR, Western immunoblotting, nitric oxide measurement, tumor necrosis factor-alpha-(TNF-alpha)-ELISA and gel shift assay analyses. Furthermore, we examined if erythropoietin could modulate proliferation of microglia. As shown by reverse transcription-polymerase chain reaction and immunocytochemistry, rat microglial cells and the murine microglia cell line BV-2 express the EPO-R. However, EPO showed no effect on the release of the proinflammatory mediators' nitric oxide and TNF-alpha. Moreover, EPO was not able to reduce the LPS (lipopolysaccharide) stimulated translocation of the proinflammatory transcription factor NF-kappaB into the nucleus of murine microglia, but induced (3)H-thymidine incorporation into DNA of microglial cells. These results show that microglia are target cells for erythropoietin which possesses mitogenic, but not anti-inflammatory effects on microglia. Therefore, the well-documented neuroprotective effects of erythropoietin could not be ascribed to an anti-inflammatory effect on microglia.

Soluble TNF receptors are associated with Aβ metabolism and conversion to dementia in subjects with mild cognitive impairment

OBJECTIVE

There is evidence supporting that tumor necrosis factor receptor (TNFR)-signaling can induce production of beta-amyloid (Aβ) in the brain. Moreover, amyloid-induced toxicity has been shown to be dependent on TNFR-signaling. However, it is still unclear whether TNFRs are involved in the early stages of dementia.

METHODS

We analyzed soluble TNFR1 and TNFR2 levels in plasma and cerebrospinal fluid (CSF) at baseline in 137 patients with mild cognitive impairment (MCI) and 30 age-matched controls. The MCI patients were followed for 4-6 years with an incidence of Alzheimer's disease (AD) or vascular dementia (VaD) of 15% per year.

RESULTS

The patients with MCI who subsequently developed these forms of dementias had higher levels of sTNFR1 and sTNFR2 in both CSF and plasma already at baseline when compared to age-matched controls (p<0.05). In the CSF of MCI subjects and controls the levels of both sTNFR1 and sTNFR2 correlated strongly with β-site APP-cleaving enzyme 1 (BACE1) activity (r(s)=0.53-0.68, p<0.01) and Aβ 40 levels (r(s)=0.59-0.71, p<0.001). Similarly, both sTNFRs were associated with Aβ 40 (r(s)=0.39-0.46, p<0.05) in plasma. Finally, the levels of both sTNFRs correlated with the axonal damage marker tau in the CSF of MCI subjects and controls (r(s)=0.57-0.83, p<0.001).

CONCLUSION

TNFR-signaling might be involved in the early pathogenesis of AD and VaD, and could be associated with beta-amyloid metabolism.

Neuroprotection in glaucoma: drug-based approaches

In recent years the focus of glaucoma research has shifted toward neuroprotection, as the traditional strategies of lowering intraocular pressure have been shown to be unable to prevent progressive vision loss in some glaucoma patients. As a result various neuroprotective drug-based approaches have been shown capable of reducing the death of retinal ganglion cells, which is the hallmark of glaucomatous optic neuropathy. There has been increasing evidence that glaucomatous neurodegeneration is analogous to other neurodegenerative diseases in the central nervous system, with recent work from our group elucidating a strong link between basic cellular processes in glaucoma and Alzheimer's disease. Additionally, there is a growing trend for using existing neuroprotective strategies in central nervous system diseases for the treatment of glaucoma. In fact, a trial treating patients with primary open-angle glaucoma with memantine, a drug approved for the treatment of Alzheimer's disease, has recently been completed. Results of this trial are not yet available. In this review, we will examine currently advocated neuroprotective drug-based strategies in the potential management of glaucoma.

Sensitization and tolerization to brain antigens in stroke

Despite encounter of novel brain antigens by the systemic immune system following stroke, autoimmune responses to these antigens do not seem to occur. In rats, a systemic inflammatory response at the time of stroke, however, provokes changes that increase the likelihood of developing detrimental autoimmunity. These findings may help to explain why infections in the post-stroke period are associated with worse outcome. In addition, data suggest that the immune response can be manipulated in an antigen specific fashion to improve stroke outcome. Together these data argue that the nature of the post-ischemic immune response influences neurological recovery from stroke.

Tumor necrosis factor p55 and p75 receptors are involved in chemical-induced apoptosis of dentate granule neurons

Localized tumor necrosis factor-alpha (TNFalpha) elevation has diverse effects in brain injury often attributed to signaling via TNFp55 or TNFp75 receptors. Both dentate granule cells and CA pyramidal cells express TNF receptors (TNFR) at low levels in a punctate pattern. Using a model to induce selective death of dentate granule cells (trimethyltin; 2 mg/kg, i.p.), neuronal apoptosis [terminal deoxynucleotidyl transferase-mediated dUTP-biotin in situ end labeling, active caspase 3 (AC3)] was accompanied by amoeboid microglia and elevated TNFalpha mRNA levels. TNFp55R (55 kDa type-1 TNFR) and TNFp75R (75 kDa type-2 TNFR) immunoreactivity in AC3(+) neurons displayed a pattern suggestive of receptor internalization and a temporal sequence of expression of TNFp55R followed by TNFp75R associated with the progression of apoptosis. A distinct ramified microglia response occurred around CA1 neurons and healthy dentate neurons that displayed an increase in the normal punctate pattern of TNFRs. Neuronal damage was decreased with i.c.v. injection of TNFalpha antibody and in TNFp55R-/-p75R-/- mice that showed higher constitutive mRNA levels for interleukin (IL-1alpha), macrophage inflammatory protein 1-alpha (MIP-1alpha), TNFalpha, transforming growth factor beta1, Fas, and TNFRSF6-assoicated via death domain (FADD). TNFp75R-/- mice showed exacerbated injury and elevated mRNA levels for IL-1alpha, MIP-1alpha, and TNFalpha. In TNFp55R-/- mice, constitutive mRNA levels for TNFalpha, IL-6, caspase 8, FADD, and Fas-associated phosphatase were higher; IL-1alpha, MIP-1alpha, and transforming growth factor beta1 lower. The mice displayed exacerbated neuronal death, delayed microglia response, increased FADD and TNFp75R mRNA levels, and co-expression of TNFp75R in AC3(+) neurons. The data demonstrate TNFR-mediated apoptotic death of dentate granule neurons utilizing both TNFRs and suggest a TNFp75R-mediated apoptosis in the absence of normal TNFp55R activity.

Bim(L) displacing Bcl-x(L) promotes Bax translocation during TNFalpha-induced apoptosis

Bcl-2 family proteins are implicated as essential regulators in tumor necrosis factor-alpha (TNFalpha)-induced apoptosis. Bim(L), a BH3-only member of Bcl-2 family, can directly or indirectly activate the proapoptotic Bax and the subsequent mitochondrial apoptotic pathway. However, the molecular mechanism of Bim(L) activating Bax activation during TNFalpha-induced apoptosis is not fully understood. In this study, the role of Bim(L) in Bax activation during TNFalpha-induced apoptosis was investigated in differentiated PC12 and MCF7 cells, with real-time single-cell analysis. The experimental results show that Bax translocated to mitochondria and cytochrome c (Cyt c) released from mitochondria after TNFalpha treatment. Furthermore, SP600125 (specific inhibitor of JNK) could inhibit the Cyt c release from mitochondria. Co-immunoprecipitation results show that, the interaction between Bcl-x(L) and Bax decreased after TNFalpha treatment, while that between Bcl-x(L) and Bim(L) increased. Bax did not co-immunoprecipitate with Bim(L) before or after the TNFalpha treatment. In addition, the increased interaction between Bim(L) and Bcl-x(L) was dynamically monitored by using fluorescence resonance energy transfer (FRET) technique. Most importantly, there was no evidence of Bim(L) redistribution to mitochondria until cell apoptosis. By comprehensively analyzing these data, it is concluded that Bim(L) displaces Bcl-x(L) in the mitochondria and promotes Bax translocation during TNFalpha-induced apoptosis.

CXCR3 mediates region-specific antiviral T cell trafficking within the central nervous system during West Nile virus encephalitis

Regional differences in inflammation during viral infections of the CNS suggest viruses differentially induce patterns of chemoattractant expression, depending on their cellular targets. Previous studies have shown that expression of the chemokine CXCL10 by West Nile virus (WNV)-infected neurons is essential for the recruitment of CD8 T cells for the purpose of viral clearance within the CNS. In the current study we used mice deficient for the CXCL10 receptor, CXCR3, to evaluate its role in leukocyte-mediated viral clearance of WNV infection within various CNS compartments. WNV-infected CXCR3-deficient mice exhibited significantly enhanced mortality compared with wild-type controls. Immunologic and virologic analyses revealed that CXCR3 was dispensable for control of viral infection in the periphery and in most CNS compartments but, surprisingly, was required for CD8 T cell-mediated antiviral responses specifically within the cerebellum. WNV-specific, CXCR3-expressing T cells preferentially migrated into the cerebellum, and WNV-infected cerebellar granule cell neurons expressed higher levels of CXCL10 compared with similarly infected cortical neurons. These results indicate that WNV differentially induces CXCL10 within neuronal populations and suggest a novel model for nonredundancy in chemokine-mediated inflammation among CNS compartments.

Distinct spatial and temporal activation of caspase pathways in neurons and glial cells after excitotoxic damage to the immature rat brain

Although cleaved caspase-3 is known to be involved in apoptotic cell death mechanisms in neurons, it can also be involved in a nonapoptotic role in astrocytes after postnatal excitotoxic injury. Here we evaluate participation of upstream pathways activating caspase-3 in neurons and glial cells, by studying the intrinsic pathway via caspase-9, the extrinsic pathway via caspase-8, and activation of the p53-dependent pathway. N-methyl-D-aspartate (NMDA) was injected intracortically in 9-day-old postnatal rats, which were sacrificed at several survival times between 4 hr postlesion (pl) and 7 days pl. We analyzed temporal and spatial expression of caspase-8, caspase-9, and p53 and correlation with neuronal and glial markers and caspase-3 activation. Caspase-9 was significantly activated at 10 hpl, strongly correlating with caspase-3. It was present mainly in damaged cortical and hippocampal neurons but was also seen in astrocytes and oligodendrocytes in layer VI and corpus callosum (cc). Caspase-8 showed a diminished correlation with caspase-3. It was present in cortical neurons at 10-72 hpl, showing layer specificity, and also in astroglial and microglial nuclei, mainly in layer VI and cc. p53 Expression increased at 10-72 hpl but did not correlate with caspase-3. p53 Was seen in neurons of the degenerating cortex and in some astrocytes and microglial cells of layer VI and cc. In conclusion, after neonatal excitotoxicity, mainly the mitochondrial intrinsic pathway mediates neuronal caspase-3 and cell death. In astrocytes, caspase-3 is not widely correlated with caspase-8, caspase-9, or p53, except in layer VI-cc astrocytes, where activation of upstream cascades occurs.

Slit modulates cerebrovascular inflammation and mediates neuroprotection against global cerebral ischemia

Cerebrovascular inflammation contributes to secondary brain injury following ischemia. Recent in vitro studies of cell migration and molecular guidance mechanisms have indicated that the Slit family of secreted proteins can exert repellant effects on leukocyte recruitment in response to chemoattractants. Utilizing intravital microscopy, we addressed the role of Slit in modulating leukocyte dynamics in the mouse cortical venular microcirculation in vivo following TNFalpha application or global cerebral ischemia. We also studied whether Slit affected neuronal survival in the mouse global ischemia model as well as in mixed neuronal-glial cultures subjected to oxygen-glucose deprivation. We found that systemically administered Slit significantly attenuated cerebral microvessel leukocyte-endothelial adherence occurring 4 h after TNFalpha and 24 h after global cerebral ischemia. Administration of RoboN, the soluble receptor for Slit, exacerbated the acute chemotactic response to TNFalpha. These findings are indicative of a tonic repellant effect of endogenous Slit in brain under acute proinflammatory conditions. Three days of continuous systemic administration of Slit following global ischemia significantly attenuated the delayed neuronal death of hippocampal CA1 pyramidal cells. Moreover, Slit abrogated neuronal death in mixed neuronal-glial cultures exposed to oxygen-glucose deprivation. The ability of Slit to reduce the recruitment of immune cells to ischemic brain and to provide cytoprotective effects suggests that this protein may serve as a novel anti-inflammatory and neuroprotective target for stroke therapy.

Tumor necrosis factor and stroke: role of the blood-brain barrier

The progression and outcome of stroke is affected by the intricate relationship between the blood-brain barrier (BBB) and tumor necrosis factor alpha (TNFalpha). TNFalpha crosses the intact BBB by a receptor-mediated transport system that is upregulated by CNS trauma and inflammation. In this review, we discuss intracellular trafficking and transcytosis of TNFalpha, regulation of TNFalpha transport after stroke, and the effects of TNFalpha on stroke preconditioning. TNFalpha can activate cytoprotective pathways by pretreatment or persistent exposure to low doses. This explains the paradoxical observation that transport of this proinflammatory cytokine improves the survival and function of hypoxic cells and of mice with stroke. The dual effects of TNFalpha may be related to differential regulation of TNFalpha trafficking downstream to TNFR1 and TNFR2 receptors. As we better understand how peripheral TNFalpha affects its own transport and modulates neuroregeneration, we may be in a better position to pharmacologically manipulate its regulatory transport system to treat stroke.

Minocycline protects the blood-brain barrier and reduces edema following intracerebral hemorrhage in the rat

Intracerebral hemorrhage (ICH) results from rupture of a blood vessel in the brain. After ICH, the blood-brain barrier (BBB) surrounding the hematoma is disrupted, leading to cerebral edema. In both animals and humans, edema coincides with inflammation, which is characterized by production of pro-inflammatory cytokines, activation of resident brain microglia and migration of peripheral immune cells into the brain. Accordingly, inflammation is an attractive target for reducing edema following ICH. In the present study, BBB damage was assessed by quantifying intact microvessels surrounding the hematoma, monitoring extravasation of IgG and measuring brain water content 3 days after ICH induced by collagenase injection into the rat striatum. In the injured brain, the water content increased in both ipsilateral and contralateral hemispheres compared with the normal brain. Quantitative real-time RT-PCR revealed an up-regulation of inflammatory genes associated with BBB damage; IL1beta, TNFalpha and most notably, MMP-12. Immunostaining showed MMP-12 in damaged microvessels and their subsequent loss from tissue surrounding the hematoma. MMP-12 was also observed for the first time in neurons. Dual-antibody labeling demonstrated that neutrophils were the predominant source of TNFalpha protein. Intraperitoneal injection of the tetracycline derivative, minocycline, beginning 6 h after ICH ameliorated the damage by reducing microvessel loss, extravasation of plasma proteins and edema; decreasing TNFalpha and MMP-12 expression; and reducing the numbers of TNFalpha-positive cells and neutrophils in the brain. Thus, minocycline, administered at a clinically relevant time, appears to target the inflammatory processes involved in edema development after ICH.

Up-regulation of p55 TNF alpha-receptor in dorsal root ganglia neurons following lumbar facet joint injury in rats

The rat L5/6 facet joint is multisegmentally innervated from the L1 to L6 dorsal root ganglia (DRG). Tumor necrosis factor (TNF) is a known mediator of inflammation. It has been reported that satellite cells are activated, produce TNF and surround DRG neurons innervating L5/6 facet joints after facet injury. In the current study, changes in TNF receptor (p55) expression in DRG neurons innervating the L5/6 facet joint following facet joint injury were investigated in rats using a retrograde neurotransport method followed by immunohistochemistry. Twenty rats were used for this study. Two crystals of Fluorogold (FG; neurotracer) were applied into the L5/6 facet joint. Seven days after surgery, the dorsal portion of the capsule was cut in the injured group (injured group n = 10). No injury was performed in the non-injured group (n = 10). Fourteen days after the first application of FG, bilateral DRGs from T13 to L6 levels were resected and sectioned. They were subsequently processed for p55 immunohistochemistry. The number of FG labeled neurons and number of FG labeled p55-immunoreactive (IR) neurons were counted. FG labeled DRG neurons innervating the L5/6 facet joint were distributed from ipsilateral L1 to L6 levels. Of FG labeled neurons, the ratio of DRG neurons immunoreactive for p55 in the injured group (50%) was significantly higher than that in the non-injured group (13%). The ratio of p55-IR neurons of FG labeled DRG neurons was significantly higher in total L1 and L2 DRGs than that in total L3, 4, 5 and 6 DRGs in the injured group (L1 and 2 DRG, 67%; L3, 4, 5 and 6 DRG, 37%, percentages of the total number of p55-IR neurons at L1 and L2 level or L3-6 level/the total number of FG-labeled neurons at L1 and L2 level or L3-6 level). These data suggest that up-regulation of p55 in DRG neurons may be involved in the sensory transmission from facet joint injury. Regulation of p55 in DRG neurons innervating the facet joint was different between upper DRG innervated via the paravertebral sympathetic trunks and lower DRG innervated via other direct routes.

Lymphocytes: potential mediators of postischemic injury and neuroprotection

Antigen-nonspecific inflammation appears to contribute to postischemic brain injury. Because there is a breach in the integrity of the blood-brain barrier after stroke, the immune system encounters novel central nervous system (CNS) antigens that allow for the development of a CNS antigen-specific autoimmune response. The nature of the immune response generated on antigen encounter is determined by the microenvironment at the site of antigen encounter. For instance, a systemic inflammatory response, such as that which would accompany an infection, could alter the microenvironment in such a way as to promote the initiation of deleterious autoimmunity. If patients who develop an infection in the immediate poststroke period are predisposed toward a CNS autoimmune response, it might help to explain why infection after stroke is associated with increased disability. We present data to support this hypothesis and to show that the breach in the blood-brain barrier can also be capitalized on to modulate the immune response to create a neuroprotective environment after stroke.

Divergent roles for tumor necrosis factor-alpha in the brain

Proinflammatory cytokines and chemokines have been implicated in the pathogenesis of several neurological and neurodegenerative disorders. Prominent among such factors is the pleiotropic cytokine, tumor necrosis factor (TNF)-alpha. Under normal physiological conditions, TNF-alpha orchestrates a diverse array of functions involved in immune surveillance and defense, cellular homeostasis, and protection against certain neurological insults. However, paradoxical effects of this cytokine have been observed. TNF-alpha is elicited in the brain following injury (ischemia, trauma), infection (HIV, meningitis), neurodegeneration (Alzheimer's, Parkinson's), and chemically induced neurotoxicity. The multifarious identity for this cytokine appears to be influenced by several mechanisms. Among the most prominent are the regulation of TNFalpha-induced NF-kappaB activation by adapter proteins such as TRADD and TRAF, and second, the heterogeneity of microglia and their distribution pattern across brain regions. Here, we review the differential role of TNF-alpha in response to brain injury, with emphasis on neurodegeneration, and discuss the possible mechanisms for such diverse and region-specific effects.

Neurobiological mechanisms for the regulation of mammalian sleep-wake behavior: reinterpretation of historical evidence and inclusion of contemporary cellular and molecular evidence

At its most basic level, the function of mammalian sleep can be described as a restorative process of the brain and body; recently, however, progressive research has revealed a host of vital functions to which sleep is essential. Although many excellent reviews on sleep behavior have been published, none have incorporated contemporary studies examining the molecular mechanisms that govern the various stages of sleep. Utilizing a holistic approach, this review is focused on the basic mechanisms involved in the transition from wakefulness, initiation of sleep and the subsequent generation of slow-wave sleep and rapid eye movement (REM) sleep. Additionally, using recent molecular studies and experimental evidence that provides a direct link to sleep as a behavior, we have developed a new model, the cellular-molecular-network model, explaining the mechanisms responsible for regulating REM sleep. By analyzing the fundamental neurobiological mechanisms responsible for the generation and maintenance of sleep-wake behavior in mammals, we intend to provide a broader understanding of our present knowledge in the field of sleep research.

Genomic and proteomic microglial profiling: pathways for neuroprotective inflammatory responses following nerve fragment clearance and activation

Microglia, a primary immune effector cell of the central nervous system (CNS) affects homeostatic, neuroprotective, regenerative and degenerative outcomes in health and disease. Despite these broad neuroimmune activities linked to specific environmental cues, a precise cellular genetic profile for microglia in the context of disease and repair has not been elucidated. To this end we used nucleic acid microarrays, proteomics, immunochemical and histochemical tests to profile microglia in neuroprotective immune responses. Optic and sciatic nerve (ON and SN) fragments were used to stimulate microglia in order to reflect immune consequences of nervous system injury. Lipopolysaccharide and latex beads-induced microglial activation served as positive controls. Cytosolic and secreted proteins were profiled by surface enhanced laser desorption ionization-time of flight (SELDI-TOF) ProteinChip, 1D and 2D difference gel electrophoresis. Proteins were identified by peptide sequencing with tandem mass spectrometry, ELISA and western blot tests. Temporal expression of pro-inflammatory cytokines, antioxidants, neurotrophins, and lysosomal enzyme expression provided, for the first time, a unique profile of secreted microglia proteins with neuroregulatory functions. Most importantly, this molecular and biochemical signature supports a broad range of microglial functions for debris clearance and promotion of neural repair after injury.

Microglia and macrophages express tumor necrosis factor receptor p75 following middle cerebral artery occlusion in mice

The proinflammatory and potential neurotoxic cytokine tumor necrosis factor (TNF) is produced by activated CNS resident microglia and infiltrating blood-borne macrophages in infarct and peri-infarct areas following induction of focal cerebral ischemia. Here, we investigated the expression of the TNF receptors, TNF-p55R and TNF-p75R, from 1 to 10 days following permanent occlusion of the middle cerebral artery in mice. Using quantitative polymerase chain reaction (PCR), we observed that the relative level of TNF-p55R mRNA was significantly increased at 1-2 days and TNF-p75R mRNA was significantly increased at 1-10 days following arterial occlusion, reaching peak values at 5 days, when microglial-macrophage CD11b mRNA expression was also increased. In comparison, the relative level of TNF mRNA was significantly increased from 1 to 5 days, with peak levels 1 day after arterial occlusion. In situ hybridization revealed mRNA expression of both receptors in predominantly microglial- and macrophage-like cells in the peri-infarct and subsequently in the infarct, and being most marked from 1 to 5 days. Using green fluorescent protein-bone marrow chimeric mice, we confirmed that TNF-p75R was expressed in resident microglia and blood-borne macrophages located in the peri-infarct and infarct 1 and 5 days after arterial occlusion, which was supported by Western blotting. The data show that increased expression of the TNF-p75 receptor following induction of focal cerebral ischemia in mice can be attributed to expression in activated microglial cells and blood-borne macrophages.

Interleukin-1β but not tumor necrosis factor-α potentiates neuronal damage by quinolinic acid: Protection by an adenosine A2A receptor antagonist

Quinolinic acid is an agonist at glutamate receptors sensitive to N-methyl-D-aspartate (NMDA). It has been implicated in neural dysfunction associated with infections, trauma, and ischemia, although its neurotoxic potency is relatively low. This study was designed to examine the effects of a combination of quinolinic acid and the proinflammatory cytokines interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha). Compounds were administered to the hippocampus of anesthetized male rats, animals being allowed to recover for 7 days before histological analysis of the hippocampus for neuronal damage estimated by counting of intact, healthy neurons. A low dose of quinolinic acid or IL-1beta produced no damage by itself, but the two together induced a significant loss of pyramidal neurons in the hippocampus. Higher doses produced almost total loss of pyramidal cells. Intrahippocampal TNF-alpha produced no effect alone but significantly reduced the neuronal loss produced by quinolinic acid. The adenosine A(2A) receptor antagonist ZM241385 reduced neuronal loss produced by the combinations of quinolinic acid and IL-1beta. The results suggest that simultaneous quinolinic acid and IL-1beta, both being induced by cerebral infection or injury, are synergistic in the production of neuronal damage and could together contribute substantially to traumatic, infective, or ischemic cerebral damage. Antagonism of adenosine A(2A) receptors protects neurons against the combination of quinolinic acid and IL-1beta.

Decreased focal inflammatory response by G-CSF may improve stroke outcome after transient middle cerebral artery occlusion in rats

Recent studies have shown that administration of granulocyte colony-stimulating factor (G-CSF) is neuroprotective. However, the precise mechanisms of the neuroprotective effect of G-CSF are not entirely known. We carried out 90-min transient middle cerebral occlusion (tMCAO) of rats. The rats were injected with vehicle or G-CSF (50 mug/kg) immediately after reperfusion and sacrificed 8, 24, or 72 hr later. 2,3,5-Triphenyltetrazolium chloride (TTC) staining was carried out using brain sections of 72 hr, and immunohistochemistry was carried out with those of 8, 24, and 72 hr. TTC-staining showed a significant reduction of infarct volume in the G-CSF-treated group (**P < 0.01). Immunohistochemistry showed a significant decrease of the number of cells expressing tumor necrosis factor-alpha (TNF-alpha) at 8-72 hr, transforming growth factor-beta (TGF-beta) and inducible nitric oxide synthase (iNOS) at 24 and 72 hr after tMCAO in the peri-ischemic area (*P < 0.05 each). Our data suggest that the suppression of inflammatory cytokines and iNOS expression may be one mechanism of neuroprotection by G-CSF.