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Although the precise mechanisms determining the neurotoxic or neuroprotective activation phenotypes in microglia remain poorly characterized, metabolic changes in these cells appear critical for these processes. As cellular metabolism can be tightly regulated by changes in intracellular pH, we tested whether pharmacological targeting of the microglial voltage‐gated proton channel 1 (Hv1), an important regulator of intracellular pH, is critical for activated microglial reprogramming. Using a mouse microglial cell line and mouse primary microglia cultures, either alone, or co‐cultured with rat cerebrocortical neurons, we characterized in detail the microglial activation profile in the absence and presence of Hv1 inhibition. We observed that activated microglia neurotoxicity was mainly attributable to the release of tumor necrosis factor alpha, reactive oxygen species, and zinc. Strikingly, pharmacological inhibition of Hv1 largely abrogated inflammatory neurotoxicity not only by reducing the production of cytotoxic mediators but also by promoting neurotrophic molecule production and restraining excessive phagocytic activity. Importantly, the Hv1‐sensitive change from a pro‐inflammatory to a neuroprotective phenotype was associated with metabolic reprogramming, particularly via a boost in NADH availability and a reduction in lactate. Most critically, Hv1 antagonism not only reduced inflammatory neurotoxicity but also promoted microglia‐dependent neuroprotection against a separate excitotoxic injury. Our results strongly suggest that Hv1 blockers may provide an important therapeutic tool against a wide range of inflammatory neurodegenerative disorders. [ABSTRACT FROM AUTHOR]

Neuroinflammation, especially activation of microglia, the key immune cells in the brain, has been proposed to contribute to the pathogenesis of ischemic stroke. However, the dynamics and the potential mediators of microglial activation following ischemic neuronal injury are not well understood. In this study, using oxygen/glucose deprivation and reoxygenation with neuronal and microglial cell cultures as an in vitro model of ischemic neuronal injury, we set out to identify neuronal factors released from injured neurons that are capable of inducing microglial activation. Conditioned media (CM) from hippocampal and cortical neurons exposed to oxygen/glucose deprivation and reoxygenation induced significant activation of microglial cells as well as primary microglia, evidenced by up-regulation of inducible nitric oxide synthase, increased production of nitrite and reactive oxygen species, and increased expression of microglial markers. Mechanistically, neuronal ischemia-responsive protein 94 (Irp94) was a key contributor to microglial activation since significant increase in Irp94 was detected in the neuronal CM following ischemic insult and immunodepletion of Irp94 rendered ischemic neuronal CM ineffective in inducing microglial activation. Ischemic insult-augmented oxidative stress was a major facilitator of neuronal Irp94 release, and pharmacological inhibition of NADPH oxidase significantly reduced the ischemic injury-induced neuronal reactive oxygen species production and Irp94 release. Taken together, these results indicate that neuronal Irp94 may play a pivotal role in the propagation of ischemic neuronal damage. Continued studies may help identify Irp94 and/or related proteins as potential therapeutic targets and/or diagnostic/prognostic biomarkers for managing ischemia-associated brain disorders. [ABSTRACT FROM AUTHOR]

Cerebral hypoxia/ischemia rapidly induces inflammation in the brain, which is characterized by microglial activation and the release of inflammatory cytokines. We have previously demonstrated that miR-181c can directly regulate tumor necrosis factor ( TNF)-α production post-transcriptionally. Here, we determined that hypoxia up-regulated TLR4 expression but down-regulated miR-181c expression in primary microglia. We also demonstrated that miR-181c suppresses TLR4 by directly binding its 3′-untranslated region. In addition, miR-181c inhibited NF-κB activation and the downstream production of proinflammatory mediators, such as TNF-α, IL-1β, and iNOS. Knocking down TLR4 in microglia significantly decreased TLR4 expression and inhibited NF-κB activation and the downstream production of proinflammatory mediators, whereas ectopic TLR4 expression significantly abrogated the suppressed inflammatory response induced by miR-181c. Therefore, our study identified an important role for the miR-181c- TLR4 pathway in hypoxic microglial activation and neuroinflammation. This pathway could represent a potential therapeutic target for cerebral hypoxic diseases associated with microglial activation and the inflammatory response. [ABSTRACT FROM AUTHOR]

Traumatic brain injury (TBI) is a complex injury involving several physiological alterations, potentially leading to neurological impairment. Previous mouse studies using high-density oligonucleotide array analysis have confirmed the upregulation of transforming growth-interacting factor (TGIF) mRNA in TBI. TGIF is a transcriptional corepressor of transforming growth factor beta (TGF-β) signaling which plays a protective role in TBI. However, the functional roles of TGIF in TBI are not well understood. In this study, we used confocal microscopy after immunofluorescence staining to demonstrate the increase of TGIF levels in the activated microglia of the pericontusional cortex of rats with TBI. Intracerebral knockdown of TGIF in the pericontusional cortex significantly downregulated TGIF expression, attenuated microglial activation, reduced the volume of damaged brain tissue, and facilitated recovery of limb motor function. Collectively, our results indicate that TGIF is involved in TBI-induced microglial activation, resulting in secondary brain injury and motor dysfunction. [ABSTRACT FROM AUTHOR]

J. Neurochem. (2012) 122, 995-1009. Abstract Up-regulation of proinflammatory cytokines and chemokines in brain ('neuroinflammation') accompanies neurological disease and neurotoxicity. Previously, we documented a striatal neuroinflammatory response to acute administration of a neurotoxic dose of methamphetamine (METH), i.e. one associated with evidence of dopaminergic terminal damage and activation of microglia and astroglia. When we used minocycline to suppress METH-induced neuroinflammation, indices of dopaminergic neurotoxicity were not affected, but suppression of neuroinflammation was incomplete. Here, we administered the classic anti-inflammatory glucocorticoid, corticosterone (CORT), in an attempt to completely suppress METH-related neuroinflammation. METH alone caused large increases in striatal proinflammatory cytokine/chemokine mRNA and subsequent astrocytic hypertrophy, microglial activation, and dopaminergic nerve terminal damage. Pre-treatment of mice with acute CORT failed to prevent neuroinflammatory responses to METH. Surprisingly, when mice were pre-treated with chronic CORT in the drinking water, an enhanced striatal neuroinflammatory response to METH was observed, an effect that was accompanied by enhanced METH-induced astrogliosis and dopaminergic neurotoxicity. Chronic CORT pre-treatment also sensitized frontal cortex and hippocampus to mount a neuroinflammatory response to METH. Because the levels of chronic CORT used are associated with high physiological stress, our data suggest that chronic CORT therapy or sustained physiological stress may sensitize the neuroinflammatory and neurotoxicity responses to METH. [ABSTRACT FROM AUTHOR]

Methamphetamine (METH) damages dopamine (DA) nerve endings by a process that has been linked to microglial activation but the signaling pathways that mediate this response have not yet been delineated. Cardona et al. [Nat. Neurosci. 9 (2006), 917] recently identified the microglial-specific fractalkine receptor (CX3CR1) as an important mediator of MPTP-induced neurodegeneration of DA neurons. Because the CNS damage caused by METH and MPTP is highly selective for the DA neuronal system in mouse models of neurotoxicity, we hypothesized that the CX3CR1 plays a role in METH-induced neurotoxicity and microglial activation. Mice in which the CX3CR1 gene has been deleted and replaced with a cDNA encoding enhanced green fluorescent protein (eGFP) were treated with METH and examined for striatal neurotoxicity. METH depleted DA, caused microglial activation, and increased body temperature in CX3CR1 knockout mice to the same extent and over the same time course seen in wild-type controls. The effects of METH in CX3CR1 knockout mice were not gender-dependent and did not extend beyond the striatum. Striatal microglia expressing eGFP constitutively show morphological changes after METH that are characteristic of activation. This response was restricted to the striatum and contrasted sharply with unresponsive eGFP-microglia in surrounding brain areas that are not damaged by METH. We conclude from these studies that CX3CR1 signaling does not modulate METH neurotoxicity or microglial activation. Furthermore, it appears that striatal-resident microglia respond to METH with an activation cascade and then return to a surveying state without undergoing apoptosis or migration. [ABSTRACT FROM AUTHOR]

The neurotransmitter dopamine (DA) has long been implicated as a participant in the neurotoxicity caused by methamphetamine (METH), yet, its mechanism of action in this regard is not fully understood. Treatment of mice with the tyrosine hydroxylase (TH) inhibitor α-methyl- p-tyrosine (AMPT) lowers striatal cytoplasmic DA content by 55% and completely protects against METH-induced damage to DA nerve terminals. Reserpine, by disrupting vesicle amine storage, depletes striatal DA by more than 95% and accentuates METH-induced neurotoxicity.l-DOPA reverses the protective effect of AMPT against METH and enhances neurotoxicity in animals with intact TH. Inhibition of MAO-A by clorgyline increases pre-synaptic DA content and enhances METH striatal neurotoxicity. In all conditions of altered pre-synaptic DA homeostasis, increases or decreases in METH neurotoxicity paralleled changes in striatal microglial activation. Mice treated with AMPT,l-DOPA, or clorgyline + METH developed hyperthermia to the same extent as animals treated with METH alone, whereas mice treated with reserpine + METH were hypothermic, suggesting that the effects of alterations in cytoplasmic DA on METH neurotoxicity were not strictly mediated by changes in core body temperature. Taken together, the present data reinforce the notion that METH-induced release of DA from the newly synthesized pool of transmitter into the extracellular space plays an essential role in drug-induced striatal neurotoxicity and microglial activation. Subtle alterations in intracellular DA content can lead to significant enhancement of METH neurotoxicity. Our results also suggest that reactants derived from METH-induced oxidation of released DA may serve as neuronal signals that lead to microglial activation early in the neurotoxic process associated with METH. [ABSTRACT FROM AUTHOR]

It has been shown that Aβ inhibits long-term potentiation (LTP) in the rat hippocampus and this is accompanied by an increase in hippocampal concentration of IL-1β. Aβ also increases microglial activation, which is the likely cell source of IL-1β. Because IL-4 attenuates the effects of IL-1β in hippocampus, and microglial activation is inhibited by minocycline, we assessed the ability of both IL-4 and minocycline to modulate the effects of Aβ on LTP and IL-1β concentration. Following treatment with Aβ, IL-4 or minocycline, rats were assessed for their ability to sustain LTP in perforant path-granule cell synapses. We report that the Aβ-induced inhibition of LTP was associated with increases in expression of MHCII, JNK phosphorylation and IL-1β concentration, and that these changes were attenuated by treatment of rats with IL-4 and minocycline. We also report that Aβ-induced increases in expression of MHCII and IL-1β were similarly attenuated by IL-4 and minocycline in glial cultures prepared from neonatal rats. These data suggest that glial cell activation and the consequent increase in IL-1β concentration mediate the inhibitory effect of Aβ on LTP and indicate that IL-4, by down-regulating glial cell activation, antagonizes the effects of Aβ. [ABSTRACT FROM AUTHOR]

It is well established that inflammatory changes contribute to brain ageing, and an increased concentration of proinflammatory cytokine, interleukin-1β (IL-1β), has been reported in the aged brain associated with a deficit in long-term potentiation (LTP) in rat hippocampus. The precise age at which changes are initiated is unclear. In this study, we investigate parallel changes in markers of inflammation and LTP in 3-, 9- and 15-month-old rats. We report evidence of increased hippocampal concentrations of the proinflammatory cytokines IL-1α, IL-18 and interferon-γ (IFNγ), which are accompanied by deficits in LTP in the older rats. We also show an increase in expression of markers of microglial activation, CD86, CD40 and intercellular adhesion molecules (ICAM). Associated with these changes, we observed a significant impairment of hippocampal LTP in the same rats. The importance of microglial activation in the attenuation of long-term potentiation (LTP) was demonstrated using an inhibitor of microglial activation, minocycline; partial restoration of LTP in 15-month-old rats was observed following administration of minocycline. We propose that signs of neuroinflammation are observed in middle age and that these changes, which are characterized by microglial activation, may be triggered by IL-18. [ABSTRACT FROM AUTHOR]

There is compelling evidence to suggest that inflammation significantly contributes to neurodegenerative changes. Consistent with this is the observation that several neurodegenerative disorders are accompanied by an increase in the concentration of interleukin (IL)-1β. IL-1β has a negative impact on synaptic plasticity and therefore an increased concentration of IL-1β, such as that in the hippocampus of the aged rat, is associated with a deficit in long-term potentiation (LTP). IL-1β is derived mainly from activated microglia but the trigger leading to this activation, specifically in the aged brain, remains to be identified. Here we examined the possiblity that interferon (IFN)γ may stimulate microglial activation and increase IL-1β concentration, thereby inhibiting LTP. The IFNγ concentration was increased in hippocampus prepared from aged, compared with young, rats and inversely correlated with the ability of rats to sustain LTP. Intracerebroventricular injection of IFNγ inhibited LTP, and increased microglial activation was observed in both IFNγ-injected and aged rats. The age-related increase in IFNγ was accompanied by a decrease in the hippocampal concentration of insulin-like growth factor (IGF)-1. The evidence presented suggests that IGF-1 acts to antagonize the IFNγ-induced microglial activation, the accompanying increase in IL-1β concentration and the consequent deficit in LTP. [ABSTRACT FROM AUTHOR]

Cyclooxygenase-2 (COX-2) is a key molecule in the inflammatory pathway in amyotrophic lateral sclerosis (ALS). Cytosolic phospholipase A (cPLA2) is an important enzyme providing substrate for cyclooxygenases. We therefore examined cPLA2 expression in human ALS and mutant Cu/Zn superoxide dismutase (SOD1) transgenic mice and its relation to COX-2. Immunohistochemistry and real-time RT-PCR revealed elevated cPLA2 protein and its mRNA levels in the lumbar spinal cord of mutant SOD1 mice. COX-2 immunoreactivity was increased in lumbar spinal cord sections from both familial ALS (FALS) and sporadic ALS (SALS) as compared to controls, and cPLA2 immunoreactivity was increased in a patient with FALS. Oral administration of the non-selective cyclooxygenase (COX) inhibitor, sulindac, extended the survival (by 10%) of G93A SOD1 mice as compared to littermate controls. Sulindac, as well as the selective COX-2 inhibitors, rofecoxib and celecoxib reduced cPLA2 immunoreactivity in the lumbar spinal cord of G93A transgenic mice. Sulindac treatment preserved motor neurons, and reduced microglial activation and astrocytosis, in the spinal cord of G93A SOD1 transgenic mice. These results suggest that cPLA2 plays an important role in supplying arachidonic acid to the COX-2 driven inflammatory pathway in ALS associated with SOD1 mutations. [ABSTRACT FROM AUTHOR]