Differential cellular expression of tumor necrosis factor-alpha and Type I tumor necrosis factor receptor after transient global forebrain ischemia

Tumor Necrosis Factor (TNF)-α-Stimulated Gene 6 (TSG-6): A Promising Immunomodulatory Target in Acute Neurodegenerative Diseases

Tumor necrosis factor (TNF)-α-stimulated gene 6 (TSG-6), the first soluble chemokine-binding protein to be identified in mammals, inhibits chemotaxis and transendothelial migration of neutrophils and attenuates the inflammatory response of dendritic cells, macrophages, monocytes, and T cells. This immunoregulatory protein is a pivotal mediator of the therapeutic efficacy of mesenchymal stem/stromal cells (MSC) in diverse pathological conditions, including neuroinflammation. However, TSG-6 is also constitutively expressed in some tissues, such as the brain and spinal cord, and is generally upregulated in response to inflammation in monocytes/macrophages, dendritic cells, astrocytes, vascular smooth muscle cells and fibroblasts. Due to its ability to modulate sterile inflammation, TSG-6 exerts protective effects in diverse degenerative and inflammatory diseases, including brain disorders. Emerging evidence provides insights into the potential use of TSG-6 as a peripheral diagnostic and/or prognostic biomarker, especially in the context of ischemic stroke, whereby the pathobiological relevance of this protein has also been demonstrated in patients. Thus, in this review, we will discuss the most recent data on the involvement of TSG-6 in neurodegenerative diseases, particularly focusing on relevant anti-inflammatory and immunomodulatory functions. Furthermore, we will examine evidence suggesting novel therapeutic opportunities that can be afforded by modulating TSG-6-related pathways in neuropathological contexts and, most notably, in stroke.

Vitamin D3 exerts immunomodulatory and memory improving properties in rats with lipopolysaccharide-induced inflammation

INTRODUCTION

Vitamin D is a fat-soluble secosteroid, its primary function being regulation of calcium-phosphate homeostasis and maintenance of bone integrity and mineralization. Recently, pleotropic effects of this vitamin have been recognized, including an immunomodulatory role and involvement in normal brain development and functioning.

Bibliometric analysis of tumor necrosis factor in post-stroke neuroinflammation from 2003 to 2021

Objective

Tumor necrosis factor (TNF), a crucial cytokine, has important research value in post-stroke neuroinflammation (PSN). We analyzed the studies that have been conducted in this area and used bibliometric methods to predict research hotspots and identify trends regarding TNF in PSN.

Methods

Publications were accessed at the Science Citation Index Expanded 1975-2021 (SCI expanded), Web of Science Core Collection (WoSCC), on May 1, 2022. Additionally, software such as CiteSpace and VOSviewer were utilized for bibliometric analyses.

Results

In total, 1391 original articles and reviews on TNF in PSN published from 2003 to 2021 were identified. An upward trend was observed in the number of publications on TNF in PSN. These publications were primarily from 57 countries and 1446 institutions, led by China and the United States with China leading the number of publications (NP) and the US with the number of citations (NC). The League of European Research Universities (LERU) and Journal of Neuroinflammation, respectively were the most prolific branches and journals. Zhang, John H. published the most papers and Finsen, Bente had the most cited papers. One paper by Kettenmann, H. published in 2011 reached the highest level of Global Citation Score (GCS). The keyword co-occurrence and reference co-citation analyses suggest that poststroke therapy and potential mechanistic pathways are important topics related to PSN in recent years. Reference burst detection suggests new burst hotspots after 2015, focusing on pathway modulation and discovery of therapeutic targets, suggesting a substantial development in the study of TNF in PSN research.

Conclusion

The present bibliometric analysis shows a continuous trend of increasing literature related to TNF in PSN, and shows that TNF plays an important role in PSN involves multiple immune mechanisms and may contribute as a potential target for neuroprotective therapeutics after stroke. Prior to 2011, most of the research was focused on discovering the specific role of TNF in PSN, and in recent years studies have mainly targeted the exploration of the signaling pathways. Future research prospects may lie in finding key therapeutic targets in pathway of TNF in PSN.

Upregulation of hemeoxygenase enzymes HO-1 and HO-2 following ischemia-reperfusion injury in connection with experimental cardiac arrest and cardiopulmonary resuscitation: Neuroprotective effects of methylene blue

Oxidative stress plays an important role in neuronal injuries after cardiac arrest. Increased production of carbon monoxide (CO) by the enzyme hemeoxygenase (HO) in the brain is induced by the oxidative stress. HO is present in the CNS in two isoforms, namely the inducible HO-1 and the constitutive HO-2. Elevated levels of serum HO-1 occurs in cardiac arrest patients and upregulation of HO-1 in cardiac arrest is seen in the neurons. However, the role of HO-2 in cardiac arrest is not well known. In this review involvement of HO-1 and HO-2 enzymes in the porcine brain following cardiac arrest and resuscitation is discussed based on our own observations. In addition, neuroprotective role of methylene blue- an antioxidant dye on alterations in HO under in cardiac arrest is also presented. The biochemical findings of HO-1 and HO-2 enzymes using ELISA were further confirmed by immunocytochemical approach to localize selective regional alterations in cardiac arrest. Our observations are the first to show that cardiac arrest followed by successful cardiopulmonary resuscitation results in significant alteration in cerebral concentrations of HO-1 and HO-2 levels indicating a prominent role of CO in brain pathology and methylene blue during CPR followed by induced hypothermia leading to superior neuroprotection after return of spontaneous circulation (ROSC), not reported earlier.

Microglia activated by microbial neuraminidase contributes to ependymal cell death

The administration of microbial neuraminidase into the brain ventricular cavities of rodents represents a model of acute aseptic neuroinflammation. Ependymal cell death and hydrocephalus are unique features of this model. Here we demonstrate that activated microglia participates in ependymal cell death. Co-cultures of pure microglia with ependymal cells (both obtained from rats) were performed, and neuraminidase or lipopolysaccharide were used to activate microglia. Ependymal cell viability was unaltered in the absence of microglia or inflammatory stimulus (neuraminidase or lipopolysaccharide). The constitutive expression by ependymal cells of receptors for cytokines released by activated microglia, such as IL-1β, was demonstrated by qPCR. Besides, neuraminidase induced the overexpression of both receptors in ventricular wall explants. Finally, ependymal viability was evaluated in the presence of functional blocking antibodies against IL-1β and TNFα. In the co-culture setting, an IL-1β blocking antibody prevented ependymal cell death, while TNFα antibody did not. These results suggest that activated microglia are involved in the ependymal damage that occurs after the administration of neuraminidase in the ventricular cavities, and points to IL-1β as possible mediator of such effect. The relevance of these results lies in the fact that brain infections caused by neuraminidase-bearing pathogens are frequently associated to ependymal death and hydrocephalus.

TNF Production and Release from Microglia via Extracellular Vesicles: Impact on Brain Functions

Tumor necrosis factor (TNF) is a pleiotropic cytokine powerfully influencing diverse processes of the central nervous system (CNS) under both physiological and pathological conditions. Here, we analyze current literature describing the molecular processes involved in TNF synthesis and release from microglia, the resident immune cells of the CNS and the main source of this cytokine both in brain development and neurodegenerative diseases. A special attention has been given to the unconventional vesicular pathway of TNF, based on the emerging role of microglia-derived extracellular vesicles (EVs) in the propagation of inflammatory signals and in mediating cell-to-cell communication. Moreover, we describe the contribution of microglial TNF in regulating important CNS functions, including the neuroinflammatory response following brain injury, the neuronal circuit formation and synaptic plasticity, and the processes of myelin damage and repair. Specifically, the available data on the functions mediated by microglial EVs carrying TNF have been scrutinized to gain insights on possible novel therapeutic strategies targeting TNF to foster CNS repair.

Motor Cortex and Hippocampus Display Decreased Heme Oxygenase Activity 2 Weeks After Ventricular Fibrillation Cardiac Arrest in Rats

Heme oxygenase (HO) and biliverdin reductase (BVR) activities are important for neuronal function and redox homeostasis. Resuscitation from cardiac arrest (CA) frequently results in neuronal injury and delayed neurodegeneration that typically affect vulnerable brain regions, primarily hippocampus (Hc) and motor cortex (mC), but occasionally also striatum and cerebellum. We questioned whether these delayed effects are associated with changes of the HO/BVR system. We therefore analyzed the activities of HO and BVR in the brain regions Hc, mC, striatum and cerebellum of rats subjected to ventricular fibrillation CA (6 min or 8 min) after 2 weeks following resuscitation, or sham operation. From all investigated regions, only Hc and mC showed significantly decreased HO activities, while BVR activity was not affected. In order to find an explanation for the changed HO activity, we analyzed protein abundance and mRNA expression levels of HO-1, the inducible, and HO-2, the constitutively expressed isoform, in the affected regions. In both regions we found a tendency for a decreased immunoreactivity of HO-2 using immunoblots and immunohistochemistry. Additionally, we investigated the histological appearance and the expression of markers indicative for activation of microglia [tumor necrosis factor receptor type I (TNFR1) mRNA and immunoreactivity for ionized calcium-binding adapter molecule 1 (Iba1])], and activation of astrocytes [immunoreactivity for glial fibrillary acidic protein (GFAP)] in Hc and mC. Morphological changes were detected only in Hc displaying loss of neurons in the cornu ammonis 1 (CA1) region, which was most pronounced in the 8 min CA group. In this region also markers indicating inflammation and activation of pro-death pathways (expression of HO-1 and TNFR1 mRNA, as well as Iba1 and GFAP immunoreactivity) were upregulated. Since HO products are relevant for maintaining neuronal function, our data suggest that neurodegenerative processes following CA may be associated with a decreased capacity to convert heme into HO products in particularly vulnerable brain regions.

Inflammation in Neurological Disorders: The Thin Boundary Between Brain and Periphery

Significance: Accumulating evidence suggests that inflammation is a major contributor in the pathogenesis of several highly prevalent, but also rare, neurological diseases. In particular, the neurodegenerative processes of Alzheimer's disease (AD), vascular dementia (VAD), Parkinson's disease (PD), and multiple sclerosis (MS) are fueled by neuroinflammation, which, in turn, is accompanied by a parallel systemic immune dysregulation. This cross-talk between periphery and the brain becomes substantial when the blood-brain barrier loses its integrity, as often occurs in the course of these diseases. It has been hypothesized that the perpetual bidirectional flux of inflammatory mediators is not a mere "static" collateral effect of the neurodegeneration, but represents a proactive phenomenon sparking and driving the neuropathological processes. However, the upstream/downstream relationship between inflammatory events and neurological pathology is still unclear. Recent Advances: Solid recent evidence clearly suggests that metabolic factors, systemic infections, Microbiota dysbiosis, and oxidative stress are implicated, although to a different extent, in the development in brain diseases. Critical Issues: Here, we reviewed the most solid published evidence supporting the implication of the axis systemic inflammation-neuroinflammation-neurodegeneration in the pathogenesis of AD, VAD, PD, and MS, highlighting the possible cause of the putative downstream component of the axis. Future Directions: Reaching a definitive clinical/epidemiological appreciation of the etiopathogenic significance of the connection between peripheral and brain inflammation in neurologic disorders is pivotal since it could open novel therapeutic avenues for these diseases.

Characterization of the TNF and IL-1 systems in human brain and blood after ischemic stroke

Preclinical and clinical proof-of-concept studies have suggested the effectiveness of pharmacological modulation of inflammatory cytokines in ischemic stroke. Experimental evidence shows that targeting tumor necrosis factor (TNF) and interleukin (IL)-1 holds promise, and these cytokines are considered prime targets in the development of new stroke therapies. So far, however, information on the cellular expression of TNF and IL-1 in the human ischemic brain is sparse.We studied 14 cases of human post-mortem ischemic stroke, representing 21 specimens of infarcts aged 1 to > 8 days. We characterized glial and leukocyte reactions in the infarct/peri-infarct (I/PI) and normal-appearing tissue (NAT) and the cellular location of TNF, TNF receptor (TNFR)1 and TNFR2, IL-1α, IL-1β, and IL-1 receptor antagonist (IL-1Ra). The immunohistochemically stained tissue sections received a score reflecting the number of immunoreactive cells and the intensity of the immunoreactivity (IR) in individual cells where 0 = no immunoreactive cells, 1 = many intermediately to strongly immunoreactive cells, and 2 = numerous and intensively immunoreactive cells. Additionally, we measured blood TNF, TNFR, and IL-1 levels in surviving ischemic stroke patients within the first 8 h and again at 72 h after symptom onset and compared levels to healthy controls.We observed IL-1α and IL-1β IR in neurons, glia, and macrophages in all specimens. IL-1Ra IR was found in glia, in addition to macrophages. TNF IR was initially found in neurons located in I/PI and NAT but increased in glia in older infarcts. TNF IR increased in macrophages in all specimens. TNFR1 IR was found in neurons and glia and macrophages, while TNFR2 was expressed only by glia in I/PI and NAT, and by macrophages in I/PI. Our results suggest that TNF and IL-1 are expressed by subsets of cells and that TNFR2 is expressed in areas with increased astrocytic reactivity. In ischemic stroke patients, we demonstrate that plasma TNFR1 and TNFR2 levels increased in the acute phase after symptom onset compared to healthy controls, whereas TNF, IL-1α, IL-1β, and IL-1Ra did not change.Our findings of increased brain cytokines and plasma TNFR1 and TNFR2 support the hypothesis that targeting post-stroke inflammation could be a promising add-on therapy in ischemic stroke patients.

Flow-cytometric microglial sorting coupled with quantitative proteomics identifies moesin as a highly-abundant microglial protein with relevance to Alzheimer's disease

BACKGROUND

Proteomic characterization of microglia provides the most proximate assessment of functionally relevant molecular mechanisms of neuroinflammation. However, microglial proteomics studies have been limited by low cellular yield and contamination by non-microglial proteins using existing enrichment strategies.

METHODS

We coupled magnetic-activated cell sorting (MACS) and fluorescence activated cell sorting (FACS) of microglia with tandem mass tag-mass spectrometry (TMT-MS) to obtain a highly-pure microglial proteome and identified a core set of highly-abundant microglial proteins in adult mouse brain. We interrogated existing human proteomic data for Alzheimer's disease (AD) relevance of highly-abundant microglial proteins and performed immuno-histochemical and in-vitro validation studies.

RESULTS

Quantitative multiplexed proteomics by TMT-MS of CD11b + MACS-enriched (N = 5 mice) and FACS-isolated (N = 5 mice), from adult wild-type mice, identified 1791 proteins. A total of 203 proteins were highly abundant in both datasets, representing a core-set of highly abundant microglial proteins. In addition, we found 953 differentially enriched proteins comparing MACS and FACS-based approaches, indicating significant differences between both strategies. The FACS-isolated microglia proteome was enriched with cytosolic, endoplasmic reticulum, and ribosomal proteins involved in protein metabolism and immune system functions, as well as an abundance of canonical microglial proteins. Conversely, the MACS-enriched microglia proteome was enriched with mitochondrial and synaptic proteins and higher abundance of neuronal, oligodendrocytic and astrocytic proteins. From the 203 consensus microglial proteins with high abundance in both datasets, we confirmed microglial expression of moesin (Msn) in wild-type and 5xFAD mouse brains as well as in human AD brains. Msn expression is nearly exclusively found in microglia that surround Aβ plaques in 5xFAD brains. In in-vitro primary microglial studies, Msn silencing by siRNA decreased Aβ phagocytosis and increased lipopolysaccharide-induced production of the pro-inflammatory cytokine, tumor necrosis factor (TNF). In network analysis of human brain proteomic data, Msn was a hub protein of an inflammatory co-expression module positively associated with AD neuropathological features and cognitive dysfunction.

CONCLUSIONS

Using FACS coupled with TMT-MS as the method of choice for microglial proteomics, we define a core set of highly-abundant adult microglial proteins. Among these, we validate Msn as highly-abundant in plaque-associated microglia with relevance to human AD.

Tumor necrosis factor receptor 2 is required for ischemic preconditioning-mediated neuroprotection in the hippocampus following a subsequent longer transient cerebral ischemia

Tumor Necrosis Factor-α (TNF-α) is a proinflammatory cytokine implicated in neuronal damage in response to cerebral ischemia. Ischemic preconditioning (IPC) provides neuroprotection against a subsequent severer or longer transient ischemia by ischemic tolerance. Here, we focused on the role of TNF-α in IPC-mediated neuroprotection against neuronal death following a subsequent longer transient cerebral ischemia (TCI). Gerbils used in this study were randomly assigned to eight groups; sham group, TCI operated group, IPC plus (+) sham group, IPC + TCI operated group, sham + etanercept (an inhibitor of TNF-a) group, TCI + etanercept group, IPC + sham + etanercept group, and IPC + TCI + etanercept group. IPC was induced by a 2-min sublethal transient ischemia, which was operated 1 day prior to a longer (5-min) TCI. A significant death of neurons was found in the stratum pyramidale (SP) in the CA1 area (CA1) of the hippocampus 5 days after TCI; however, IPC protected SP neurons from TCI. We found that TNF-α immunoreactivity was significantly increased in CA1 pyramidal neurons in the TCI and IPC + TCI groups compared to the sham group. TNF-R1 expression in CA1 pyramidal neurons of the TCI group was also increased 1 and 2 days after TCI; however, in the IPC + TCI group, TNF-R1 expression was significantly lower than that in the TCI group. On the other hand, we did not detect TNF-R2 immunoreactivity in CA1 pyramidal neurons 1 and 2 days after TCI; meanwhile, in the IPC + TCI group, TNF-R2 expression was significantly increased compared to TNF-R2 expression at 1 and 2 days after TCI. In addition, in this group, TNF-R2 was newly expressed in pericytes, which are important cells in the blood brain barrier, from 1 day after TCI. When we treated etanercept to the IPC + TCI group, IPC-induced neuroprotection was significantly weakened. In brief, this study indicates that IPC confers neuroprotection against TCI by TNF-α signaling through TNF-R2 and suggests that the enhancement of TNF-R2 expression by IPC may be a legitimate strategy for a therapeutic intervention of TCI.

Targeting Tumor Necrosis Factor Alpha for Alzheimer's Disease

Alzheimer's disease (AD) affects an estimated 44 million individuals worldwide, yet no therapeutic intervention is available to stop the progression of the dementia. Neuropathological hallmarks of AD are extracellular deposits of amyloid beta (Aβ) peptides assembled in plaques, intraneuronal accumulation of hyperphosphorylated tau protein forming tangles, and chronic inflammation. A pivotal molecule in inflammation is the pro-inflammatory cytokine TNF-α. Several lines of evidence using genetic and pharmacological manipulations indicate that TNF-α signaling exacerbates both Aβ and tau pathologies in vivo. Interestingly, preventive and intervention anti-inflammatory strategies demonstrated a reduction in brain pathology and an amelioration of cognitive function in rodent models of AD. Phase I and IIa clinical trials suggest that TNF-α inhibitors might slow down cognitive decline and improve daily activities in AD patients. In the present review, we summarize the evidence pointing towards a beneficial role of anti-TNF-α therapies to prevent or slow the progression of AD. We also present possible physical and pharmacological interventions to modulate TNF-α signaling in AD subjects along with their limitations.

Population dynamics of neural progenitor cells during aging in the cerebral cortex

Recent studies indicate that adult neurogenesis occurs in the cerebral cortex of rodents. Neural progenitor cells (NPCs) have been found in the adult cerebral cortex. These cells are expected to be regulated by various stimuli, including environmental enrichment, exercise, learning, and stress. However, it is unclear what stimuli can regulate cortical NPCs. In this study, we examined whether aging has an impact on population dynamics of NPCs in the murine cerebral cortex, using immunohistological staining for NPCs. The density of NPCs was kept from 5- to 12-month-old, dramatically decreased at 17-month-old, and thereafter maintained the same level until 24-month-old. Comparing the densities of NPCs in the cortical areas, such as the cingulate, primary motor, primary somatosensory, and insular cortices, we found that the degrees of decreased densities of NPCs in the cingulate and insular cortices were significantly smaller than those in the primary motor and somatosensory cortices. NPCs in aged cortex produced new neurons by ischemia. These results indicate that in aged mice, NPCs exist and produce new neurons in the cerebral cortex. Additionally, the extent of reduction of the density of NPCs in the cortices with higher cognitive functions may be less than that in the primary motor and somatosensory cortices.

Neuroprotective Effects of Exercise on Brain Edema and Neurological Movement Disorders Following the Cerebral Ischemia and Reperfusion in Rats

Introduction:

Cerebral ischemia and reperfusion causes physiological and biochemical changes in the neuronal cells that will eventually lead to cell damage. Evidence indicates that exercise reduces the ischemia and reperfusion-induced brain damages in animal models of stroke. In the present study, the effect of exercise preconditioning on brain edema and neurological movement disorders following the cerebral ischemia and reperfusion in rats was investigated.

Methods:

Twenty-one adult male wistar rats (weighing 260–300 g) were randomly divided into three groups: sham operated, exercise plus ischemia, and ischemia group (7 rats per group). The rats in exercise group were trained to run on a treadmill 5 days a week for 4 weeks. Transient focal cerebral ischemia and reperfusion were induced by middle cerebral artery occlusion (MCAO) for 60 minutes, followed by reperfusion for 23 hours. After 24 hours ischemia, movement disorders were tested by a special neurological examination. Also, cerebral edema was assessed by determining the brain water content.

Results:

The results showed that pre-ischemic exercise significantly reduced brain edema (P<0.05). In addition, exercise preconditioning decreased the neurological movement disorders caused by brain ischemia and reperfusion (P<0.05).

Conclusion:

Preconditioning by exercise had neuroprotective effects against brain ischemia and reperfusion-induced edema and movement disorders. Thus, it could be considered as a useful strategy for prevention of ischemic injuries, especially in people at risk.

Cognitive dysfunction in Duchenne muscular dystrophy: a possible role for neuromodulatory immune molecules

Duchenne muscular dystrophy (DMD) is an X chromosome-linked disease characterized by progressive physical disability, immobility, and premature death in affected boys. Underlying the devastating symptoms of DMD is the loss of dystrophin, a structural protein that connects the extracellular matrix to the cell cytoskeleton and provides protection against contraction-induced damage in muscle cells, leading to chronic peripheral inflammation. However, dystrophin is also expressed in neurons within specific brain regions, including the hippocampus, a structure associated with learning and memory formation. Linked to this, a subset of boys with DMD exhibit nonprogressing cognitive dysfunction, with deficits in verbal, short-term, and working memory. Furthermore, in the genetically comparable dystrophin-deficient mdx mouse model of DMD, some, but not all, types of learning and memory are deficient, and specific deficits in synaptogenesis and channel clustering at synapses has been noted. Little consideration has been devoted to the cognitive deficits associated with DMD compared with the research conducted into the peripheral effects of dystrophin deficiency. Therefore, this review focuses on what is known about the role of full-length dystrophin (Dp427) in hippocampal neurons. The importance of dystrophin in learning and memory is assessed, and the potential importance that inflammatory mediators, which are chronically elevated in dystrophinopathies, may have on hippocampal function is also evaluated.

The TNFα-Transgenic Rat: Hippocampal Synaptic Integrity, Cognition, Function, and Post-Ischemic Cell Loss

The cytokine, tumor necrosis factor α (TNFα), is a key regulator of neuroinflammation linked to numerous neurodegenerative conditions and diseases. The present study used transgenic rats that overexpress a murine TNFα gene, under the control of its own promoter, to investigate the impact of chronically elevated TNFα on hippocampal synaptic function. Neuronal viability and cognitive recovery in TNFα Tg rats were also determined following an ischemic insult arising from reversible middle cerebral artery occlusion (MCAO). Basal CA3-CA1 synaptic strength, recorded in acute brain slices, was not significantly different between eight-week-old TNFα Tg rats and non-Tg rats. In contrast, slices from TNFα Tg rats showed significantly greater levels of long-term potentiation (LTP) in response to 100 Hz stimulation, suggesting that synaptic networks may be hyperexcitable in the context of elevated TNFα. Cognitive and motor deficits (assessed on the Morris Water Maze and Rotarod task, respectively) were present in TNFα Tg rats in the absence of significant differences in the loss of cortical and hippocampal neurons. TNF overexpression exacerbated MCAO-dependent deficits on the rotarod, but ameliorated cortical neuron loss in response to MCAO.

Role of adenosine A2A receptor in cerebral ischemia reperfusion injury: Signaling to phosphorylated extracellular signal-regulated protein kinase (pERK1/2)

Following brain ischemia reperfusion (IR), the dramatic increase in adenosine activates A2AR to induce further neuronal damage. Noteworthy, A2A antagonists have proven efficacious in halting IR injury, however, the detailed downstream signaling remains elusive. To this end, the present study aimed to investigate the possible involvement of phospho-extracellular signal-regulated kinase (pERK1/2) pathway in mediating protection afforded by the central A2A blockade. Male Wistar rats (250-270 g) subjected to bilateral carotid occlusion for 45 min followed by a 24-h reperfusion period showed increased infarct size corroborating histopathological damage, memory impairment and motor incoordination as well as increased locomotor activity. Those events were mitigated by the unilateral intrahippocampal administration of the selective A2A antagonist SCH58261 via a decrease in pERK1/2 downstream from diacyl glycerol (DAG) signaling. Consequent to pERK1/2 inhibition, reduced hippocampal microglial activation, glial tumor necrosis factor-alpha (TNF-α) and brain-derived neurotropic factor (BDNF) expression, glutamate (Glu), inducible nitric oxide synthase (iNOS) and thiobarbituric acid reactive substances (TBARS) were evident in animals receiving SCH58261. Additionally, the anti-inflammatory cytokine interleukin-10 (IL-10) increased following nuclear factor (erythroid-derived 2)-like 2 (Nrf-2). Taken all together, these events suppressed apoptotic pathways via a reduction in cytochrome c (Cyt. c) as well as caspase-3 supporting a crucial role for pERK1/2 inhibition in consequent reduction of inflammatory and excitotoxic cascades as well as correction of the redox imbalance.

TNF-α/TNFR2 Regulatory Axis Stimulates EphB2-Mediated Neuroregeneration Via Activation of NF-κB

HIV-1 infected individuals are at high risk of developing HIV-associated neurocognitive disorders (HAND) as HIV infection leads to neuronal injury and synaptic loss in the central nervous system (CNS). The neurotoxic effects of HIV-1 are primarily a result of viral replication leading to the production of inflammatory chemokines and cytokines, including TNF-α. Given an important role of TNF-α in regulating synaptic plasticity, we investigated the effects of TNF-α on the development of neuronal processes after mechanical injury, and we showed that TNF-α treatment stimulates the regrowth of neuronal processes. To investigate transcriptional effects of TNF-α on synaptic plasticity, we analyzed both human neurosphere and isolated neuronal cultures for the regulation of genes central to synaptic alterations during learning and memory. TNF-α treatment upregulated Ephrin receptor B2 (EphB2), which is strongly involved in dendritic arborization and synaptic integrity. TNF-α strongly activates the NF-κB pathway, therefore, we propose that TNF-α-induced neurite regrowth occurs primarily through EphB2 signaling via stimulation of NF-κB. EphB2 promoter activity increased with TNF-α treatment and overexpression of NF-κB. Direct binding of NF-κB to the EphB2 promoter occurred in the ChIP assay, and site-directed mutagenesis identified binding sites involved in TNF-α-induced EphB2 activation. TNF-α induction of EphB2 was determined to occur specifically through TNF-α receptor 2 (TNFR2) activation in human primary fetal neurons. Our observations provide a new avenue for the investigation on the impact of TNF-α in the context of HIV-1 neuronal cell damage as well as providing a potential therapeutic target in TNFR2 activation of EphB2.

Exercise preconditioning exhibits neuroprotective effects on hippocampal CA1 neuronal damage after cerebral ischemia

Recent evidence has suggested the neuroprotective effects of physical exercise on cerebral ischemic injury. However, the role of physical exercise in cerebral ischemia-induced hippocampal damage remains controversial. The aim of the present study was to evaluate the effects of pre-ischemia treadmill training on hippocampal CA1 neuronal damage after cerebral ischemia. Male adult rats were randomly divided into control, ischemia and exercise + ischemia groups. In the exercise + ischemia group, rats were subjected to running on a treadmill in a designated time schedule (5 days per week for 4 weeks). Then rats underwent cerebral ischemia induction through occlusion of common carotids followed by reperfusion. At 4 days after cerebral ischemia, rat learning and memory abilities were evaluated using passive avoidance memory test and rat hippocampal neuronal damage was detected using Nissl and TUNEL staining. Pre-ischemic exercise significantly reduced the number of TUNEL-positive cells and necrotic cell death in the hippocampal CA1 region as compared to the ischemia group. Moreover, pre-ischemic exercise significantly prevented ischemia-induced memory dysfunction. Pre-ischemic exercise mighct prevent memory deficits after cerebral ischemia through rescuing hippocampal CA1 neurons from ischemia-induced degeneration.

Brain parenchymal TNF-α and IL-1β induction in experimental pneumococcal meningitis

Triggers of brain inflammation in pneumococcal meningitis are unknown. TNF-α and IL-1β were upregulated (real time PCR and in situ hybridization) in neurons and astrocytes time-dependently and maximally in the hippocampus during murine pneumococcal meningitis. Upregulation of TNF-α and IL-1β mRNA in the brain parenchyma was independent of cerebrospinal fluid leukocytosis, pneumococcal pneumolysin and H2O2, but it was potently induced by pneumococcal cell wall (PCW) fragments. Brain TNF-α mRNA was downregulated by a matrix metalloproteinases inhibitor. PCW fragments were located in the brain parenchyma. In conclusion, PCW fragments and matrix metalloproteinases trigger cytokine induction in the brain parenchyma during pneumococcal meningitis.

Propofol anesthesia induces proapoptotic tumor necrosis factor-α and pro-nerve growth factor signaling and prosurvival Akt and XIAP expression in neonatal rat brain

Previously we observed that prolonged exposure to propofol anesthesia causes caspase-3- and calpain-mediated neuronal death in the developing brain. The present study examines the effects of propofol anesthesia on the expression of tumor necrosis factor-α (TNFα), pro-nerve growth factor (NGF), and their receptors in the cortex and the thalamus. We also investigated how propofol influences the expression of Akt and X-linked inhibitor of apoptosis (XIAP) expression, proteins that promote prosurvival pathways. Seven-day-old rats (P7) were exposed to propofol anesthesia lasting 2, 4, or 6 hr and killed 0, 4, 16, or 24 hr after anesthesia termination. The relative levels of mRNA and protein expression were estimated by RT-PCR and Western blot analysis, respectively. The treatments caused marked activation of TNFα and its receptor TNFR-1 and pro-NGF and p75(NTR) receptor expression. In parallel with the induction of these prodeath signals, we established that propofol anesthesia promotes increased expression of the prosurvival molecules pAkt and XIAP during the 24-hr postanesthesia period. These results show that different brain structures respond to propofol anesthesia with a time- and duration of exposure-dependent increase in proapoptotic signaling and with concomitant increases in activities of prosurvival proteins. We hypothesized that the fine balance between these opposing processes sustains homeostasis in the immature rat brain and prevents unnecessary damage after exposure to an injurious stimulus. The existence of this highly regulated process provides a time frame for potential therapeutic intervention directed toward suppressing the deleterious component of propofol anesthesia.

Minocycline attenuates brain tissue levels of TNF-α produced by neurons after prolonged hypothermic cardiac arrest in rats

Neuro-cognitive disabilities are a well-recognized complication of hypothermic circulatory arrest. We and others have reported that prolonged cardiac arrest (CA) produces neuronal death and microglial proliferation and activation that are only partially mitigated by hypothermia. Microglia, and possibly other cells, are suggested to elaborate tumor necrosis factor alpha (TNF-α), which can trigger neuronal death cascades and exacerbate edema after CNS insults. Minocycline is neuroprotective in some brain ischemia models in part by blunting the microglial response. We tested the hypothesis that minocycline would attenuate neuroinflammation as reflected by brain tissue levels of TNF-α after hypothermic CA in rats. Rats were subjected to rapid exsanguination, followed by a 6 min normothermic CA. Hypothermia (30 °C) was then induced by an aortic saline flush. After a total of 20 min CA, resuscitation was achieved via cardiopulmonary bypass (CPB). After 5 min reperfusion, minocycline (90 mg kg−1; n = 6) or vehicle (PBS; n = 6) was given. Hypothermia (34 °C) was maintained for 6 h. Rats were sacrificed at 6 or 24 h. TNF-α was quantified (ELISA) in four brain regions (cerebellum, CEREB; cortex, CTX; hippocampus, HIP; striatum, STRI). Naïve rats (n = 6) and rats subjected to the same anesthesia and CPB but no CA served as controls (n = 6). Immunocytochemistry was used to localize TNF-α. Naïve rats and CPB controls had no detectable TNF-α in any brain region. CA markedly increased brain TNF-α. Regional differences were seen, with the highest TNF-α levels in striatum in CA groups (10-fold higher, P < 0.05 vs. all other brain regions). TNF-α was undetectable at 24 h. Minocycline attenuated TNF-α levels in CTX, HIP and STRI (P < 0.05). TNF-α showed unique co-localization with neurons. In conclusion, we report region-dependent early increases in brain TNF-α levels after prolonged hypothermic CA, with maximal increases in striatum. Surprisingly, TNF-α co-localized in neurons and not microglia. Minocycline attenuated TNF-α by approximately 50% but did not totally ablate its production. That minocycline decreased brain TNF-α levels suggests that it may represent a therapeutic adjunct to hypothermia in CA neuroprotection. University of Pittsburgh IACUC 0809278B-3.

TNF-α/NF-κB signaling in the CNS: possible connection to EPHB2

Tumor necrosis factor-alpha, TNF-α, is a cytokine that is a well-known factor in multiple disease conditions and is recognized for its major role in central nervous system signaling. TNF-α signaling is most commonly associated with neurotoxicity, but in some conditions it has been found to be neuroprotective. TNF-α has long been known to induce nuclear factor-kappa B, NF-κB, signaling by, in most cases, translocating the p65 (RelA) DNA binding factor to the nucleus. p65 is a key member of NF-κB, which is well established as a family of transcription factors that regulates many signaling events, including growth and process development, in neuronal cell populations. NF-κB has been shown to affect both the receiving aspect of neuronal signaling events in dendritic development as well as the sending of neuronal signals in axonal development. In both cases, NK-κB functions as a promoter and/or inhibitor of growth, depending on the environmental conditions and signaling cascade. In addition, NF-κB is involved in memory formation or neurogenesis, depending on the region of the brain in which the signaling occurs. The ephrin (Eph) receptor family represents a subfamily of receptor tyrosine kinases, RTKs, which received much attention due to its potential involvement in neuronal cell health and function. There are two subsets of ephrin receptors, Eph A and Eph B, each with distinct functions in cardiovascular and skeletal development and axon guidance and synaptic plasticity. The presence of multiple binding sites for NF-κB within the regulatory region of EphB2 gene and its potential regulation by NF-κB pathway suggests that TNF-α may modulate EphB2 via NF-κB and that this may contribute to the neuroprotective activity of TNF-α.

Proximal cerebral arteries develop myogenic responsiveness in heart failure via tumor necrosis factor-α-dependent activation of sphingosine-1-phosphate signaling

BACKGROUND

Heart failure is associated with neurological deficits, including cognitive dysfunction. However, the molecular mechanisms underlying reduced cerebral blood flow in the early stages of heart failure, particularly when blood pressure is minimally affected, are not known.

METHODS AND RESULTS

Using a myocardial infarction model in mice, we demonstrate a tumor necrosis factor-α (TNFα)-dependent enhancement of posterior cerebral artery tone that reduces cerebral blood flow before any overt changes in brain structure and function. TNFα expression is increased in mouse posterior cerebral artery smooth muscle cells at 6 weeks after myocardial infarction. Coordinately, isolated posterior cerebral arteries display augmented myogenic tone, which can be fully reversed in vitro by the competitive TNFα antagonist etanercept. TNFα mediates its effect via a sphingosine-1-phosphate (S1P)-dependent mechanism, requiring sphingosine kinase 1 and the S1P(2) receptor. In vivo, sphingosine kinase 1 deletion prevents and etanercept (2-week treatment initiated 6 weeks after myocardial infarction) reverses the reduction of cerebral blood flow, without improving cardiac function.

CONCLUSIONS

Cerebral artery vasoconstriction and decreased cerebral blood flow occur early in an animal model of heart failure; these perturbations are reversed by interrupting TNFα/S1P signaling. This signaling pathway may represent a potential therapeutic target to improve cognitive function in heart failure.

Combinations of ketamine and atropine are neuroprotective and reduce neuroinflammation after a toxic status epilepticus in mice

Epileptic seizures and status epilepticus (SE) induced by the poisoning with organophosphorus nerve agents (OP), like soman, are accompanied by neuroinflammation whose role in seizure-related brain damage (SRBD) is not clear. Antagonists of the NMDA glutamate ionotropic receptors are currently among the few compounds able to arrest seizures and provide neuroprotection even during refractory status epilepticus (RSE). Racemic ketamine (KET), in combination with atropine sulfate (AS), was previously shown to counteract seizures and SRBD in soman-poisoned guinea-pigs. In a mouse model of severe soman-induced SE, we assessed the potentials of KET/AS combinations as a treatment for SE/RSE-induced SRBD and neuroinflammation. When starting 30min after soman challenge, a protocol involving six injections of a sub-anesthetic dose of KET (25mg/kg) was evaluated on body weight loss, brain damage, and neuroinflammation whereas during RSE, anesthetic protocols were considered (KET 100mg/kg). After confirming that during RSE, KET injection was to be repeated despite some iatrogenic deaths, we used these proof-of-concept protocols to study the changes in mRNA and related protein contents of some inflammatory cytokines, chemokines and adhesion molecules in cortex and hippocampus 48h post-challenge. In both cases, the KET/AS combinations showed important neuroprotective effects, suppressed neutrophil granulocyte infiltration and partially suppressed glial activation. KET/AS could also reduce the increase in mRNA and related pro-inflammatory proteins provoked by the poisoning. In conclusion, the present study confirms that KET/AS treatment has a strong potential for SE/RSE management following OP poisoning. The mechanisms involved in the reduction of central neuroinflammation remain to be studied.

Inhibition of sevoflurane postconditioning against cerebral ischemia reperfusion-induced oxidative injury in rats

The volatile anesthetic sevoflurane is capable of inducing preconditioning and postconditioning effects in the brain. In this study, we investigated the effects of sevoflurane postconditioning on antioxidant and immunity indexes in cerebral ischemia reperfusion (CIR) rats. Rats were randomly assigned to five separate experimental groups I–V. In the sham group (I), rats were subjected to the same surgery procedures except for occlusion of the middle cerebral artery and exposed to 1.0 MAC sevoflurane 90 min after surgery for 30 min. IR control rats (group II) were subjected to middle cerebral artery occlusion (MCAO) for 90 min and exposed to O₂ for 30 min at the beginning of reperfusion. Sevoflurane 0.5, 1.0 and 1.5 groups (III, IV, V) were all subjected to MCAO for 90 min, but at the beginning of reperfusion exposed to 0.5 MAC, 1.0 MAC or 1.5 MAC sevoflurane for 30 min, respectively. Results showed that sevoflurane postconditioning can decrease serum tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), nitric oxide (NO), nitric oxide synthase (NOS) and increase serum interleukin-10 (IL-10) levels in cerebral ischemia reperfusion rats. In addition, sevoflurane postconditioning can still decrease blood lipid, malondialdehyde (MDA) levels, infarct volume and increase antioxidant enzymes activities, normal pyramidal neurons density in cerebral ischemia reperfusion rats. It can be concluded that sevoflurane postconditioning may decrease blood and brain oxidative injury and enhance immunity indexes in cerebral ischemia reperfusion rats.

P2X7 receptor activation ameliorates CA3 neuronal damage via a tumor necrosis factor-α-mediated pathway in the rat hippocampus following status epilepticus

BACKGROUND

The release of tumor necrosis factor-α (TNF-α) appears depend on the P2X7 receptor, a purinergic receptor. In the present study, we addressed the question of whether P2X7 receptor-mediated TNF-α regulation is involved in pathogenesis and outcome of status epilepticus (SE).

METHODS

SE was induced by pilocarpine in rats that were intracerebroventricularly infused with saline-, 2',3'-O-(4-benzoylbenzoyl)-adenosine 5'-triphosphate (BzATP), adenosine 5'-triphosphate-2',3'-dialdehyde (OxATP), A-438079, or A-740003 prior to SE induction. Thereafter, we performed Fluoro-Jade B staining and immunohistochemical studies for TNF-α and NF-κB subunit phosphorylations.

RESULTS

Following SE, P2X7 receptor agonist (BzATP) infusion increased TNF-α immunoreactivity in dentate granule cells as compared with that in saline-infused animals. In addition, TNF-α immunoreactivity was readily apparent in the mossy fibers, while TNF-α immunoreactivity in CA1-3 pyramidal cells was unaltered. However, P2X7 receptor antagonist (OxATP-, A-438079, and A-740003) infusion reduced SE-induced TNF-α expression in dentate granule cells. In the CA3 region, BzATP infusion attenuated SE-induced neuronal damage, accompanied by enhancement of p65-Ser276 and p65-Ser311 NF-κB subunit phosphorylations. In contrast, OxATP-, A-438079, and A-740003 infusions increased SE-induced neuronal death. Soluble TNF p55 receptor (sTNFp55R), and cotreatment with BzATP and sTNFp55R infusion also increased SE-induced neuronal damage in CA3 region. However, OxATP-, sTNFp55R or BzATP+sTNFp55R infusions could not exacerbate SE-induced neuronal damages in the dentate gyrus and the CA1 region, as compared to BzATP infusion.

CONCLUSIONS

These findings suggest that TNF-α induction by P2X7 receptor activation may ameliorate SE-induced CA3 neuronal damage via enhancing NF-κB p65-Ser276 and p65-Ser311 phosphorylations.

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.

MicroRNA expression changes in the hippocampi of rats subjected to global ischemia

The hippocampus is particularly vulnerable to ischemia, which is accompanied by substantial alterations in gene expression. Recent studies show that microRNAs extensively mediate post-transcriptional gene expression. However, the regulatory mechanisms in the hippocampus that microRNAs participate in remain unclear. Here, we used microarray analysis to characterize the microRNA expression profile in rat hippocampus and to identify changes in expression after 20 minutes of global ischemia followed by either 30 minutes or 24 hours of reperfusion. In the normal hippocampus, we detected 286 microRNAs, of which the let-7 family accounted for 32%. After ischemia followed by 30 minutes of reperfusion, 23 microRNAs were upregulated and 32 were downregulated; after 24 hours of reperfusion 40 were upregulated and 31 were downregulated. These results suggest that several microRNAs may be involved in regulating the normal physiological activity of the hippocampus and its response to ischemia and reperfusion.

Ischemia-induced neurogenesis of neocortical layer 1 progenitor cells

Adult mammalian neurogenesis occurs in the hippocampus and the olfactory bulb, whereas neocortical adult neurogenesis remains controversial. Several occurrences of neocortical adult neurogenesis in injured neocortex were recently reported, suggesting that neural stem cells (NSCs) or neuronal progenitor cells (NPCs) that can be activated by injury are maintained in the adult brain. However, it is not clear whether or where neocortical NSCs/NPCs exist in the brain. We found NPCs in the neocortical layer 1 of adult rats and observed that their proliferation was highly activated by global forebrain ischemia. Using retrovirus-mediated labeling of layer 1 proliferating cells with membrane-targeted green fluorescent protein, we found that the newly generated neurons were GABAergic and that the neurons were functionally integrated into the neuronal circuitry. Our results suggest that layer 1 NPCs are a source of adult neurogenesis under ischemic conditions.

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.

Cerebral tumor necrosis factor alpha expression and long-term neurocognitive performance after cardiopulmonary bypass in rats

OBJECTIVE

Cerebral inflammatory reaction is discussed as a contributor to adverse cerebral outcome after cardiac surgery with cardiopulmonary bypass. This study was designed to determine the effect of cardiopulmonary bypass on both cerebral expression of tumor necrosis factor alpha and neurocognitive outcome in rats.

METHODS

With institutional review board approval, 50 rats were randomly assigned to one of 3 groups: rats of the cardiopulmonary bypass group were subjected to 75 minutes of normothermic cardiopulmonary bypass. Sham-operated animals underwent identical preparation but were not connected to cardiopulmonary bypass, whereas rats of the control group were neither anesthetized nor cannulated. Ten rats per group survived 4 hours after cardiopulmonary bypass or the sham operation for immediate postoperative determination of tumor necrosis factor alpha-expressing cells (immunohistochemistry) and cerebral tumor necrosis factor alpha mRNA levels (polymerase chain reaction). The remaining animals survived 10 days for neurocognitive assessment by using the modified hole-board test and for analysis of cerebral tumor necrosis factor alpha activation in the late postoperative period.

RESULTS

Expression of tumor necrosis factor alpha mRNA was increased 4 hours after cardiopulmonary bypass and the sham operation, with higher expression in the cardiopulmonary bypass group (chi(2) [2] = 25.08, P < .001). Both experimental groups demonstrated larger numbers of tumor necrosis factor alpha-positive cells in the early and late postoperative periods (F [1] = 13.08, P < or = .001) and an impaired neurocognitive performance on the first postoperative days compared with that seen in the control group (F [2, 24] = 4.26, P = .02).

CONCLUSIONS

Cerebral tumor necrosis factor alpha activation in both experimental groups during the early postoperative period was accompanied by transient neurocognitive impairment. Therefore cardiopulmonary bypass alone demonstrated no effect on cerebral inflammation and neurocognitive outcome.

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.

Activation of caspase-8 by tumour necrosis factor receptor 1 is necessary for caspase-3 activation and apoptosis in oxygen-glucose deprived cultured cortical cells

TNF-alpha has been reported to be relevant in stroke-induced neuronal death. However the precise function of TNF-alpha in brain ischemia remains controversial since there are data supporting either a detrimental or a protective effect. Here we show that TNF-alpha is released after oxygen-glucose deprivation (OGD) of cortical cultures and is a major contributor to the apoptotic death observed without affecting the OGD-mediated necrotic cell death. In this paradigm, apoptosis depends on TNF-alpha-induced activation of caspase-8 and -3 without affecting the activation of caspase-9. By using knock-out mice for TNF-alpha receptor 1, we show that the activation of both caspase-3 and -8 by TNF-alpha is mediated by TNF-alpha receptor 1. The pro-apoptotic role of TNF-alpha in OGD is restricted to neurons and microglia, since astrocytes do not express either TNF-alpha or TNF-alpha receptor 1. Altogether, these results show that apoptosis of cortical neurons after OGD is mediated by TNF-alpha/TNF-alpha receptor 1.

Focal cerebral ischemia in the TNFalpha-transgenic rat

BACKGROUND

To determine if chronic elevation of the inflammatory cytokine, tumor necrosis factor-alpha (TNFalpha), will affect infarct volume or cortical perfusion after focal cerebral ischemia.

METHODS

Transgenic (TNFalpha-Tg) rats overexpressing the murine TNFalpha gene in brain were prepared by injection of mouse DNA into rat oocytes. Brain levels of TNFalpha mRNA and protein were measured and compared between TNFalpha-Tg and non-transgenic (non-Tg) littermates. Mean infarct volume was calculated 24 hours or 7 days after one hour of reversible middle cerebral artery occlusion (MCAO). Cortical perfusion was monitored by laser-Doppler flowmetry (LDF) during MCAO. Cortical vascular density was quantified by stereology. Post-ischemic cell death was assessed by immunohistochemistry and regional measurement of caspase-3 activity or DNA fragmentation. Unpaired t tests or analysis of variance with post hoc tests were used for comparison of group means.

RESULTS

In TNFalpha-Tg rat brain, the aggregate mouse and rat TNFalpha mRNA level was fourfold higher than in non-Tg littermates and the corresponding TNFalpha protein level was increased fivefold (p

CONCLUSION

Chronic elevation of TNFalpha protein in brain increases susceptibility to ischemic injury but has no effect on vascular density. TNFalpha-Tg animals are more susceptible to apoptotic cell death after MCAO than are non-Tg animals. We conclude that the TNFalpha-Tg rat is a valuable new tool for the study of cytokine-mediated ischemic brain injury.

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Key Words Collapse

MESH Headings

• Animals
• Apoptosis/genetics
• Apoptosis/immunology
• Brain/immunology
• Brain/pathology
• Brain/physiopathology
• Brain Infarction/immunology
• Brain Infarction/pathology
• Brain Infarction/physiopathology
• Brain Ischemia/immunology
• Brain Ischemia/physiopathology
• Caspase 3/metabolism
• Cerebral Arteries/immunology
• Cerebral Arteries/pathology
• Cerebral Arteries/physiopathology
• Disease Models, Animal
• Encephalitis/immunology
• Encephalitis/pathology
• Encephalitis/physiopathology
• Female
• Infarction, Middle Cerebral Artery/immunology
• Infarction, Middle Cerebral Artery/physiopathology
• Male
• Microcirculation/genetics
• Microcirculation/immunology
• Neurons/immunology
• Neurons/pathology
• RNA, Messenger/metabolism
• Rats
• Rats, Sprague-Dawley
• Rats, Transgenic
• Regional Blood Flow/genetics
• Regional Blood Flow/immunology
• Tumor Necrosis Factor-alpha/genetics
• Tumor Necrosis Factor-alpha/immunology
• Up-Regulation/genetics
• Up-Regulation/immunology

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Grants

• R01 NS039588 NINDS NIH HHS
• R01 NS047395 NINDS NIH HHS

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Affiliation(s)

L Creed Pettigrew Sanders-Brown Center on Aging, University of Kentucky, Lexington, Kentucky, USA Department of Neurology, University of Kentucky, Lexington, Kentucky, USA Veterans Administration (VA) Medical Center, Lexington, Kentucky, USA
Mark S Kindy Department of Neuroscience, Medical University of South Carolina, Charleston, South Carolina, USA Ralph H. Johnson VA Medical Center, Charleston, South Carolina, USA
Stephen Scheff Sanders-Brown Center on Aging, University of Kentucky, Lexington, Kentucky, USA
Joe E Springer Department of Physical Medicine & Rehabilitation, University of Kentucky, Lexington, Kentucky, USA
Richard J Kryscio Department of Statistics and School of Public Health, University of Kentucky, Lexington, Kentucky, USA
Yizhao Li Jinan Great Wall Hospital, Jinan, Shandong, PR China
David S Grass Xenogen Biosciences, Cranbury, New Jersey, USA

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Collaborators Collapse

Interleukin-1beta and tumor necrosis factor-alpha are expressed by different subsets of microglia and macrophages after ischemic stroke in mice

BACKGROUND

Interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) are expressed by microglia and infiltrating macrophages following ischemic stroke. Whereas IL-1beta is primarily neurotoxic in ischemic stroke, TNF-alpha may have neurotoxic and/or neuroprotective effects. We investigated whether IL-1beta and TNF-alpha are synthesized by overlapping or segregated populations of cells after ischemic stroke in mice.

METHODS

We used flow cytometry and immunohistochemistry to examine cellular co-expression of IL-1beta and TNF-alpha at 6, 12 and 24 hours after permanent middle cerebral artery occlusion in mice, validating the results by the use of bone marrow chimeric mice.

RESULTS

We found that IL-1beta and TNF-alpha were expressed in largely segregated populations of CD11b+CD45dim microglia and CD11b+CD45high macrophages, with cells expressing both cytokines only rarely. The number of Gr1+ granulocytes producing IL-1beta or TNF-alpha was very low, and we observed no IL-1beta- or TNF-alpha-expressing T cells or astrocytes.

CONCLUSION

Taken together, the results show that IL-1beta and TNF-alpha are produced by largely segregated populations of microglia and macrophages after ischemic stroke in mice. Our findings provide evidence of a functional diversity among different subsets of microglia and macrophages that is potentially relevant to future design of anti-inflammatory therapies in 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.

Soluble epoxide hydrolase: regulation by estrogen and role in the inflammatory response to cerebral ischemia

The protection from ischemic brain injury enjoyed by females is linked to the female sex hormone 17beta-estradiol. We tested the hypothesis that neuroprotection by estradiol entails the prevention of ischemia-induced inflammatory response, through suppression of the P450 eicosanoids-metabolizing enzyme soluble epoxide hydrolase (sEH). Ovariectomized female rats with and without estradiol replacement underwent 2-hour middle cerebral artery occlusion (MCAO). SEH expression was determined using Western blot, and inflammatory cytokine mRNA levels were measured at 6, 24 and 48 hours after MCAO. Cytokine mRNA was also measured in sEH-knockout mice, and in rats treated with sEH inhibitors. Estradiol reduced basal and post-ischemic sEH expression. MCAO strongly induced mRNA levels of tumor necrosis factor-alpha, interleukin 6, and interleukin 1beta, which was attenuated in sEH-knockouts, but not by sEH inhibitors. Estradiol replacement exhibited a bimodal effect on cytokine mRNA, with increased early and reduced delayed expression. While estradiol suppresses cerebral sEH expression, and sEH suppression diminishes inflammation after MCAO, our findings suggest that the effect of estrogen on inflammation is complex, and only partially explained by sEH suppression.

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.

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.

TNFalpha and TNF receptor 1 expression in the mixed neuronal-glial cultures of hippocampal dentate gyrus exposed to glutamate or trimethyltin

We examined the expression and cellular localization of tumor necrosis factor alpha (TNFalpha) and its type 1 receptor (TNFR1) in mixed neuronal-glial cultures of rat hippocampal dentate gyrus exposed to glutamate (GLU) or trimethyltin (TMT). Our previous studies demonstrated that both pathogenic factors evoked neuronal apoptosis, however, TMT was more potent and caused cell death in almost 90% of neurons. Observed neurodegeneration was accompanied by morphological changes of microglia. In the current study, using RT-PCR and Western blotting analysis, we found that GLU and TMT induced increase in TNFalpha mRNA and protein levels. The induction of transcription was stronger following GLU treatment, however the protein production was much more intensive after TMT exposure. Double fluorescent labeling for TNFalpha, TNFR1 and cellular markers revealed cytokine expression in microglia and some neurons. On the other hand, majority of neuronal cells displayed TNFR1 immunoreactivity, in control and in treated cultures. Moreover, TMT led to a strong increase in TNFR1 expression in astrocytes, which displayed remarkable, granular staining for the cytokine receptor. Western blotting for TNFR1 revealed enhanced protein expression only in cultures treated with TMT. This is the first report demonstrating the changes of expression of TNFalpha and TNFR1 in hippocampal dentate gyrus cultures treated with GLU or TMT. Our results indicate that TNFalpha may be involved in the mechanism of neurotoxic effects evoked by both pathogenic factors and suggest that astrocytes via TNFR1 may enhance TMT-induced injury.

(Peri)vascular production and action of pro-inflammatory cytokines in brain pathology

In response to tissue injury or infection, the peripheral tissue macrophage induces an inflammatory response through the release of IL-1β (interleukin-1β) and TNFα (tumour necrosis factor α). These cytokines stimulate macrophages and endothelial cells to express chemokines and adhesion molecules that attract leucocytes into the peripheral site of injury or infection. The aims of the present review are to (i) discuss the relevance of brain (peri)vascular cells and compartments to bacterial meningitis, HIV-1-associated dementia, multiple sclerosis, ischaemic and traumatic brain injury, and Alzheimer's disease, and (ii) to provide an overview of the production and action of pro-inflammatory cytokines by (peri)vascular cells in these pathologies of the CNS (central nervous system). The brain (peri)vascular compartments are highly relevant to pathologies affecting the CNS, as infections are almost exclusively blood-borne. Insults disrupt blood and energy flow to neurons, and active brain-to-blood transport mechanisms, which are the bottleneck in the clearance of unwanted molecules from the brain. Perivascular macrophages are the most reactive cell type and produce IL-1β and TNFα after infection or injury to the CNS. The main cellular target for IL-1β and TNFα produced in the brain (peri)vascular compartment is the endothelium, where these cytokines induce the expression of adhesion molecules and promote leucocyte infiltration. Whether this and other effects of IL-1 and TNF in the brain (peri)vascular compartments are detrimental or beneficial in neuropathology remains to be shown and requires a clear understanding of the role of these cytokines in both damaging and repair processes in the CNS.

Pathophysiology of Acute Ischaemic Stroke: An Analysis of Common Signalling Mechanisms and Identification of New Molecular Targets

Stroke continues to be a major cause of death and disability. The currently available therapies have proven to be highly unsatisfactory (except thrombolysis) and attempts are being made to identify and characterize signalling proteins which could be exploited to design novel therapeutic modalities. The pathophysiology of stroke is a complex process. Delaying interventions from the first hours to days or even weeks following blood vessel occlusion may lead to worsening or impairment of recovery in later stages. The objective of this review is to critically evaluate the major mechanisms underlying stroke pathophysiology, especially the role of cell signalling in excitotoxicity, inflammation, apoptosis, neuroprotection and angiogenesis, and highlight potential novel targets for drug discovery.

Microglia in cerebral ischemia: molecular actions and interactions

The precise role of microglia in stroke and cerebral ischemia has been the subject of debate for a number of years. Microglia are capable of synthesizing numerous soluble and membrane-bound biomolecules, some known to be neuroprotective, some neurotoxic, whereas others have less definitive bioactivities. The molecular mechanisms through which microglia activate these molecules have thus become an important area of ischemia research. Here we provide a survey review that summarizes the key actions of microglial factors in cerebral ischemia including complement proteins, chemokines, pro-inflammatory cytokines, neurotrophic factors, hormones, and proteinases, as well several important messenger molecules that play a part in how these factors respond to extracellular signals during ischemic injuries. We also provide some new perspectives on how microglial intracellular signaling may contribute to the seemingly contradictory roles of several microglial effector molecules.

Exercise preconditioning upregulates cerebral integrins and enhances cerebrovascular integrity in ischemic rats

We hypothesized that exercise preconditioning strengthens brain microvascular integrity against ischemia/reperfusion injury through the tumor necrosis factor (TNF)-integrin signaling pathway. Adult male Sprague Dawley rats (n = 24) were studied in: (1) exercise (the animals run on a treadmill 30 min each day) for 3 weeks, (2) non-exercise. Six animals from each group (n = 12) were subjected to stroke, the remaining animals served as controls (n = 6 x 2). Brain infarction and edema were determined by Nissl staining. Cerebral integrin expression was detected by immunochemistry and stereological methods. In addition, we used flow cytometry to address the causal role of TNF-alpha in inducing the expression of integrins in the human umbilical vein endothelial cells under TNF-alpha or vascular endothelial growth factor (VEGF) pretreatment. Exercise reduces brain infarction and brain edema in stroke. Expressions of integrin subunit alpha(1), alpha(6), beta(1), and beta(4) were increased after exercise. Exercise preconditioning reversed stroke-reduced integrin expression. An in vitro study revealed a causal link between the gradual upregulation of TNF-alpha (rather than VEGF) and cellular expression of integrins. These results demonstrated an increase in cerebral expression of integrins and a decrease in brain injury from stroke after exercise preconditioning. The study suggests that upregulation of integrins during exercise enhances neurovascular integrity after stroke. The changes in integrins might be altered by TNF-alpha.

Expression of tumor necrosis factor alpha and neuronal apoptosis in the developing rat brain after neonatal stroke

Increased expression of tumor necrosis factor alpha (TNFalpha) has been shown in adult stroke models. However, its expression and relationship with neuronal apoptosis in neonatal rats with transient middle cerebral artery occlusion (MCAO) have not been clearly elucidated. We studied the expression and distribution of TNFalpha and neuronal apoptosis in a postnatal Day 10 rat MCAO model using reverse transcriptase-polymerase chain reaction (RT-PCR), Western blot, immunohistochemistry, fluorescence double-labeling, and terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) analyses. We found TNFalpha mRNA expression increased at 2h and was maintained at high levels until 24h after reperfusion. TNFalpha protein expression was significantly increased from 4 to 8h (p < 0.01) lasting through 24h (p < 0.05) after reperfusion compared to the sham controls. TNFalpha immunoreactive cells were colocalized to neurons in both the core and the penumbra areas of the ischemic cortex. However, apoptotic cells were mainly distributed in the penumbra area and colocalized to neurons as well as to TNFalpha immunoreactive cells in the ischemic cortex. Our findings suggest that TNFalpha expression increases after neonatal stroke and is associated with neuronal apoptosis after transient focal cerebral ischemia.