Proinflammatory cytokines in injured rat brain following perinatal asphyxia.
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In contrast to astrogliosis, which is common to injuries of the adult CNS, in the developing brain this process is minimal. Reasons postulated for this include the relative immaturity of the immune system and the consequent insufficient production of cytokines to evoke astrogliosis. To explore this hypothesis, the study was undertaken to detect the presence of some proinflammatory cytokines in the injured rat brain following perinatal asphyxia (ischaemia/hypoxia). The localisation of TNF-alpha, IL-15, IL-17 and IL-17 receptors was visualised by means of immunohistochemistry. In numerous neurones of the rat brain, the IL-17 appeared to be constitutively expressed. In the early period of inflammation the IL-15 was produced mainly by the blood cells penetrating the injured brain but later it was synthesised also by reactive astrocytes surrounding brain cysts and forming dense astrogliosis around necrotic brain regions. The direct effect on astrogliosis of other estimated cytokines seems to be negligible. All the results lead to the conclusion that from all cytokines identified in the injured immature rat brain the IL-15 plays the most important role during inflammatory response and participates in the gliosis of reactive astrocytes.Keywords:
Astrogliosis
Proinflammatory cytokine
Gliosis
Brain damage
Perinatal asphyxia
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In contrast to astrogliosis, which is common to injuries of the adult CNS, in the developing brain this process is minimal. Reasons postulated for this include the relative immaturity of the immune system and the consequent insufficient production of cytokines to evoke astrogliosis. To explore this hypothesis, the study was undertaken to detect the presence of some proinflammatory cytokines in the injured rat brain following perinatal asphyxia (ischaemia/hypoxia). The localisation of TNF-alpha, IL-15, IL-17 and IL-17 receptors was visualised by means of immunohistochemistry. In numerous neurones of the rat brain, the IL-17 appeared to be constitutively expressed. In the early period of inflammation the IL-15 was produced mainly by the blood cells penetrating the injured brain but later it was synthesised also by reactive astrocytes surrounding brain cysts and forming dense astrogliosis around necrotic brain regions. The direct effect on astrogliosis of other estimated cytokines seems to be negligible. All the results lead to the conclusion that from all cytokines identified in the injured immature rat brain the IL-15 plays the most important role during inflammatory response and participates in the gliosis of reactive astrocytes.
Astrogliosis
Proinflammatory cytokine
Gliosis
Brain damage
Perinatal asphyxia
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The cytokine tumor necrosis factor (TNF-alpha) is a pleotrophic polypeptide that plays a significant role in brain immune and inflammatory activities. TNF-alpha is produced in the brain in response to various pathological processes such as infectious agents [e.g., human immunodeficiency virus (HIV) and malaria], ischemia, and trauma. TNF-alpha mRNA is rapidly produced in response to brain ischemia within 1 h, reaches a peak at 6-12 h post ischemia, and subsides 1-2 days later. TNF-alpha mRNA expression corresponds in a temporal fashion to other cytokines such as interleukin (IL)-6, cytokine-induced neutrophil chemoattractant (KC), and IL-1 and precedes the infiltration of inflammatory cells into the injured zone. TNF-alpha is present early in neuronal cells in and around the ischemic tissue (penumbra), yet at later time points, the peptide is found in macrophages in the infarcted tissue. TNF-alpha has been demonstrated to cause expression of proadhesive molecules on the endothelium, which results in leukocyte accumulation, adherence, and migration from capillaries into the brain. Furthermore, TNF-alpha activates glial cells, thereby regulating tissue remodeling, gliosis, and scar formation. Thus, evidence is emerging in support of a role for TNF-alpha in injury induced by infectious, immune, toxic, traumatic, and ischemic stimuli. TNF-alpha promotes inflammation by stimulation of capillary endothelial cell proinflammatory responses and thereby provides leukocyte adhesion and infiltration into the ischemic brain. The evidence generated so far suggests that agents that suppress TNF-alpha's production or actions will reduce leukocyte infiltration into ischemic brain regions and thereby diminish the extent of tissue loss.
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Neuro-inflammation occurs as a sequence of brain injury and is associated with production of cytokines. Cytokines can modulate the function and survival of neurons, microglia and astrocytes. The objective of this study is to examine the effect of TNF on the neurons, microglia and astrocytes in normal brain and stab wound brain injury.Normal BALB/c male mice (N) without any injury were subdivided into NA and NB groups. Another set mouse was subjected to stab wound brain injury (I) and were subdivided into IA and IB. NA and IA groups received intraperitoneal injections of TNF (1 µg/kg body weight/day) for nine days, whereas NB and IB groups received intraperitoneal injections of PBS. Animals were killed on 1st, 2nd, 3rd, 7th, and 9th day. Frozen brain sections through the injury site in IA and IB or corresponding region in NA and NB groups were stained for neurodegeneration, immunostained for astrocytes, microglia and neurons. Western blotting for GFAP and ELISA for BDNF were done from the tissues collected from all groups.The number of degenerating neurons significantly decreased in TNF treated groups. There was a significant increase in the number of astrocytes and microglia in TNF treated groups compared to PBS treated groups. In addition, it was found that TNF stimulated the expression of GFAP and BDNF in NA and IA groups.TNF induces astrogliosis and microgliosis in normal and injured brain and promotes the survival of cortical neurons in stab wound brain injury, may be by upregulating the BDNF level.
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Introduction and objective: Neuro-inflammation occurs as a sequence of brain injury and is associated with production of cytokines. Cytokines can modulate the function and survival of neurons and astrocytes. Although the pro-inflammatory cytokine TNF-α is thought to be one of the major mediators of neuro-inflammation, its role in brain injury remains ill-defined. The objective of this study is to examine the effect of TNF-α on the neurons and astrocytes in normal brain and stab wound brain injury. Methods: Two groups of BALB/c mice were used. The first group (I) was subjected to stab wound brain injury. This group was subdivided into IA and IB groups. The second group of mice (N) was not subjected to injury and subdivided into NA and NB. Groups IA and NA received IP injections of TNF-α every day for five days, whereas groups IB and NB received five IP injections of PBS. Animals were killed 1, 3, 7, and 9 days post treatment. Immunostaining of frozen brain sections for glial fibrillary acidic protein (GFAP) specific for astrocytes, NeuN (specific for neurons) and Fluoro-Jade B (specific for degenerating neurons) were used. Western blotting and ELISA were done from the tissues isolated from the injured sites of group I and non-injured brain (N). Results: In group N (NA and NB) there was no significant change in the number of neurons and there was significant increase in the number of astrocytes (astrogliosis) in TNF-α treated group (NA). In group I there was a gradual increase in the number of both astrocytes and neurons with a significant increase in TNF-α-treated group IA. The number of degenerating neurons significantly decreased in TNF-α -treated group IA. In addition, it was found that TNF-α stimulated the expression of GFAP and BDNF in NA and IA groups. Conclusions: TNF-α induces astrogliosis in normal and injured brain, and promotes the survival of cortical neurons in stab wound brain injury. The upregulation of BDNF by TNF-α may contribute to the neuronal protection.
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The relevance of astrogliosis remains controversial, especially with respect to the beneficial or detrimental influence of reactive astrocytes on CNS recovery. This dichotomy can be resolved if the mediators of astrogliosis are identified. We have measured the levels of transcripts encoding inflammatory cytokines in injury systems in which the presence or absence of astrogliosis could be produced selectively. A stab injury to the adult mouse brain using a piece of nitrocellulose (NC) membrane elicited a prompt and marked increase in levels of transcripts for interleukin (IL)-1α, IL-1β, and tumor necrosis factor (TNF)-α, which are considered to be microglia/macrophage cytokines. The elevations preceded, or occurred concomitantly with, the rise in glial fibrillary acidic protein mRNA, an early manifestation of astrogliosis. In neonatal mice, IL-1 and TNF-α mRNA were elevated to a greater extent by an NC-implant injury, which produced astrogliosis, than after an NC-stab, with minimal astrogliosis. We determined whether endogenous interferon (IFN)-γ could be responsible for the observed increases in IL-1 and TNF-α, because IFN-γ is a potent microglia/macrophage activator, and because its exogenous administration to rodents enhanced astrogliosis after adult or neonatal insults. A lack of requirement for endogenous IFN-γ was demonstrated by three lines of evidence. First, no increase in IFN-γ transcripts could be found at injury. Second, the administration of a neutralizing antibody to IFN-γ did not attenuate astrogliosis. Third, in IFN-γ knockout adult mice, astrogliosis and increases in levels of IL-1α and TNF-α were induced rapidly by injury. The marked elevation of inflammatory cytokines is discussed in the context of astrogliosis and general CNS recovery.
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By Sophia Norman, Neuroscience
Advisor: Matthew Robson
Abstract:
Traumatic brain injury (TBI) affects nearly 2.8 million people in the United States annually, contributing significantly to financial burden, disability, and death. Currently, there is a lack of any FDA approved treatment to alleviate the negative symptoms following TBI. Post injury, an inflammatory response occurs in the central nervous system contributing to the activation of astrocytes and microglia, a process referred to as gliosis. This inflammatory cascade is largely contributed by pro-inflammatory signaling molecules including interleukin-1α (IL-1α) and interleukin-1β (IL-1β). The interleukin-1 receptor associated kinase (IRAK4) is an essential component to the IL-1 signaling pathway and therefore may serve as a potential target to block this signaling. We hypothesize that IRAK4 may be a viable target to block the interleukin-1- mediated changes in astrocytes including the formation of neurotoxic astrocytes seen in neurodegenerative diseases. Blast-induced TBI resulted in an increase in IL-1α, IL-1β, and the glial fibrillary acidic protein (GFAP) expression in mice, indicating the presence of reactive astrocytes. Astrocytes treated with IL-1α in culture showed an increase in gfap mRNA expression, as well as increased serping1 expression, a characteristic gene of proinflammatory astrocytes. Pre-treatment with an IRAK4 inhibitor (AS2444697), blocked IL-1 induced increases in gfap and serping1 expression. Inhibiting IRAK4 demonstrated efficacy in mitigating astrogliosis and the formation of neurotoxic astrocytes, highlighting its potential as a viable therapeutic target for neurodegenerative disorders.
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Abstract Alzheimer's disease (AD) is the most common progressive dementia and is pathologically characterized by brain deposition of amyloid‐β (Aβ) peptide as senile plaques. Inflammatory and immune response pathways are chronically activated in AD patient brains at low levels, and likely play a role in disease progression. Like microglia, activated astrocytes produce numerous acute‐phase reactants and proinflammatory molecules in the AD brain. One such molecule, S100B, is highly expressed by reactive astrocytes in close vicinity of β‐amyloid deposits. We have previously shown that augmented and prolonged activation of astrocytes has a detrimental impact on neuronal survival. Furthermore, we have implicated astrocyte‐derived S100B as a candidate molecule responsible for this deleterious effect. To evaluate a putative relationship between S100B and AD pathogenesis, we crossed transgenic mice overexpressing human S100B (TghuS100B mice) with the Tg2576 mouse model of AD, and examined AD‐like pathology. Brain parenchymal and cerebral vascular β‐amyloid deposits and Aβ levels were increased in bigenic Tg2576‐huS100B mice. These effects were associated with increased cleavage of the β‐C‐terminal fragment of amyloid precursor protein (APP), elevation of the N‐terminal APP cleavage product (soluble APPβ), and activation of β‐site APP cleaving enzyme 1. In addition, double transgenic mice showed augmented reactive astrocytosis and microgliosis, high levels of S100 expression, and increased levels of proinflammatory cytokines as early as 7–9 months of age. These results provide evidence that (over)‐expression of S100B acts to accelerate AD‐like pathology, and suggest that inhibiting astrocytic activation by blocking S100B biosynthesis may be a promising therapeutic strategy to delay AD progression. © 2009 Wiley‐Liss, Inc.
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P3 peptide
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Abstract Background Older-age individuals are at the highest risk for disability from a traumatic brain injury (TBI). Astrocytes are the most numerous glia in the brain, necessary for brain function, yet there is little known about unique responses of astrocytes in the aged-brain following TBI. Methods Our approach examined astrocytes in young adult, 4-month-old, versus aged, 18-month-old mice, at 1, 3, and 7 days post-TBI. We selected these time points to span the critical period in the transition from acute injury to presumably irreversible tissue damage and disability. Two approaches were used to define the astrocyte contribution to TBI by age interaction: 1) tissue histology and morphological phenotyping, and 2) transcriptomics on enriched astrocytes from the injured brain. Results Aging was found to have a profound effect on the TBI-induced loss of homeostatic astrocyte function needed for maintaining water transport and edema – namely, aquaporin-4. The loss of homoeostatic responses was coupled with a progressive exacerbation of astrogliosis in the aged brain as a function of time after injury. Moreover, clasmatodendrosis, an underrecognized astrogliopathy, was found to be significantly increased in the aged brain, but not in the young brain. As a function of TBI, we observed a transitory refraction in the number of these astrocytes, which rebounded by 7 days post-injury in the aged brain. The transcriptomics found disproportionate changes in genes attributed to reactive astrocytes, inflammatory response, complement pathway, and synaptic support in aged mice following TBI compared to young mice. Additionally, our data highlight that TBI did not evoke a clear alignment with previously defined “A1/A2” dichotomy of reactive astrogliosis. Conclusions Overall, our findings point toward a progressive phenotype of aged astrocytes following TBI that we hypothesize to be maladaptive, shedding new insights into potentially modifiable astrocyte-specific mechanisms that may underlie increased fragility of the aged brain to trauma.
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Aquaporin 4
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Hypoxic-ischemic encephalopathy (HIE) mainly affects preterm and term newborns, leading to a high risk of brain damage. Coexisting infection/inflammation and birth asphyxia are key factors associated with intracerebral increase of proinflammatory cytokines linked to HIE. Microglia are key mediators of inflammation during perinatal brain injury, characterized by their phenotypic plasticity, which may facilitate their participation in both the progression and resolution of injury-induced inflammation. The purpose of this study was to investigate the temporal expression of genes associated with pro- and anti-inflammatory cytokines as well as the nucleotide-binding domain, leucine-rich repeat protein (NLRP-3) inflammasome from microglia cells. For this purpose, we used our established neonatal rat model of inflammation-sensitized hypoxic-ischemic (HI) brain injury in seven-day-old rats. We assessed gene expression profiles of 11 cytokines and for NLRP-3 using real-time PCR from sorted CD11b/c microglia of brain samples at different time points (3.5 h after LPS injection and 0, 5, 24, 48, and 72 hours post HI) following different treatments: vehicle, E. coli lipopolysaccharide (LPS), vehicle/HI, and LPS/HI. Our results showed that microglia are early key mediators of the inflammatory response and exacerbate the inflammatory response following HI, polarizing into a predominant proinflammatory M1 phenotype in the early hours post HI. The brains only exposed to HI showed a delay in the expression of proinflammatory cytokines. We also demonstrated that NLRP-3 plays a role in the inflammatory resolution with a high expression after HI insult. The combination of both, a preinfection/inflammation condition and hypoxia-ischemia, resulted in a higher proinflammatory cytokine storm, highlighting the significant contribution of acute inflammation sensitizing prior to a hypoxic insult on the severity of perinatal brain damage.
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Astrogliosis
Gliosis
Leptomeninges
Grey matter
Neuroglia
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