Role of the innate immune system in the neuropathological consequences induced by adolescent binge drinking

Adolescence is a critical stage of brain maturation in which important plastic and dynamic processes take place in different brain regions, leading to development of the adult brain. Ethanol drinking in adolescence disrupts brain plasticity and causes structural and functional changes in immature brain areas (prefrontal cortex, limbic system) that result in cognitive and behavioral deficits. These changes, along with secretion of sexual and stress‐related hormones in adolescence, may impact self‐control, decision making, and risk‐taking behaviors that contribute to anxiety and initiation of alcohol consumption. New data support the participation of the neuroimmune system in the effects of ethanol on the developing and adult brain. This article reviews the potential pathological bases that underlie the effects of alcohol on the adolescent brain, such as the contribution of genetic background, the perturbation of epigenetic programming, and the influence of the neuroimmune response. Special emphasis is given to the actions of ethanol in the innate immune receptor toll‐like receptor 4 (TLR4), since recent studies have demonstrated that by activating the inflammatory TLR4/NFκB signaling response in glial cells, binge drinking of ethanol triggers the release of cytokines/chemokines and free radicals, which exacerbate the immune response that causes neuroinflammation/neural damage as well as short‐ and long‐term neurophysiological, cognitive, and behavioral dysfunction. Finally, potential treatments that target the neuroimmune response to treat the neuropathological and behavioral consequences of adolescent alcohol abuse are discussed.     

Involvement of TLR4 in the long-term epigenetic changes,rewarding and anxiety effects induced by intermittent ethanol treatment in adolescence

Studies in humans and experimental animals have demonstrated the vulnerability of the adolescent brain to actions of ethanol and the long-term consequences of binge drinking, including the behavioral and cognitive deficits that result from alcohol neurotoxicity, and increased risk to alcohol abuse and dependence. Although the mechanisms that participate in these effects are largely unknown, we have shown that ethanol by activating innate immune receptors, toll-like receptor 4 (TLR4), induces neuroinflammation, impairs myelin proteins and causes cognitive dysfunctions in adolescent mice. Since neuroimmune signaling is also involved in alcohol abuse, the aim of this study was to assess whether ethanol treatment in adolescence promotes the long-term synaptic and molecular events associated with alcohol abuse and addiction. Using wild-type (WT) and TLR4-deficient (TLR4-KO) adolescent mice treated intermittently with ethanol (3 g/kg) for 2 weeks, we showed that binge-like ethanol treatment in adolescent mice promotes short- and long-term alterations in synaptic plasticity and epigenetic changes in the promoter region of bdnf and fosb, which increased their expression in the mPFC of young adult animals. These molecular events were associated with long-term rewarding and anxiogenic-related behavioral effects, along with increased alcohol preference. Our results further showed the participation of neuroimmune system activation and the TLR4 signaling response since deficient mice in TLR4 (TLR4-KO) are protected against molecular and behavioral alterations of ethanol in the adolescent brain. Our results highlight a new role of the neuroimmune function and open up new avenues to develop pharmacological treatments that can normalize the immune signaling responsible for long-term effects in adolescence, including alcohol abuse and related disorders.     

Therapeutic effect of SN50, an inhibitor of nuclear factor-κB, in treatment of TBI in mice

NF-κB upregulation has been demonstrated in neurons and glial cells in response to experimental injury and neuropathological disorders, where it has been related to both neurodegenerative and neuroprotective activities. It has been generally recognized that NF-κB plays important roles in the regulation of apoptosis and inflammation as well as innate and adaptive immunity. However, the regulatory mechanism of NF-κB in apoptosis remained to be determined. The present study sought to first investigate the effect of a NF-κB inhibitor SN50, which inhibits NF-κB nuclear translocation, on cell death and behavioral deficits in our mice traumatic brain injury (TBI) models. Additionally, we tried to elucidate the possible mechanisms of the therapeutic effect of SN50 through NF-κB regulating apoptotic and inflammatory pathway in vivo. Encouragingly, the results showed that pretreatment with SN50 remarkably attenuated TBI-induced cell death (detected by PI labeling), cumulative loss of cells (detected by lesion volume), and motor and cognitive dysfunction (detected by motor test and Morris water maze). To analyze the mechanism of SN50 on cell apoptotic and inflammatory signaling pathway, we thus assessed expression levels of TNF-α, cathepsin B and caspase-3, Bid cleavage and cytochrome c release in SN50-pretreated groups compared with those in saline vehicle groups. The results imply that through NF-κB/TNF-α/cathepsin networks SN50 may contribute to TBI-induced extrinsic and intrinsic apoptosis, and inflammatory pathways, which partly determined the fate of injured cells in our TBI model.     

IκB kinase/nuclear factor κB-dependent insulin-like growth factor 2 (Igf2) expression regulates synapse formation and spine maturation via Igf2 receptor signaling

Alterations of learning and memory in mice with deregulated neuron-specific nuclear factor κB (NF-κB) activity support the idea that plastic changes of synaptic contacts may depend at least in part on IκB kinase (IKK)/NF-κB-related synapse-to-nucleus signaling. There is, however, little information on the molecular requirements and mechanisms regulating this IKK/NF-κB-dependent synapse development and remodeling. Here, we report that the NF-κB inducing IKK kinase complex is localized at the postsynaptic density (PSD) and activated under basal conditions in the adult mouse brain. Using different models of conditional genetic inactivation of IKK2 function in mouse principal neurons, we show that IKK/NF-κB signaling is critically involved in synapse formation and spine maturation in the adult brain. IKK/NF-κB blockade in the forebrain of mutant animals is associated with reduced levels of mature spines and postsynaptic proteins PSD95, SAP97, GluA1, AMPAR-mediated basal synaptic transmission and a spatial learning impairment. Synaptic deficits can be restored in adult animals within 1 week by IKK/NF-κB reactivation, indicating a highly dynamic IKK/NF-κB-dependent regulation process. We further identified the insulin-like growth factor 2 gene (Igf2) as a novel IKK/NF-κB target. Exogenous Igf2 was able to restore synapse density and promoted spine maturation in IKK/NF-κB signaling-deficient neurons within 24 h. This process depends on Igf2/Igf2R-mediated MEK/ERK activation. Our findings illustrate a fundamental role of IKK/NF-κB-Igf2-Igf2R signaling in synapse formation and maturation in adult mice, thus providing an intriguing link between the molecular actions of IKK/NF-κB in neurons and the memory enhancement factor Igf2.     

Methylmercury chloride exposure aggravates proinflammatory mediators and Notch-1 signaling in CD14+ and CD40+ cells and is associated with imbalance of neuroimmune function in BTBR T+ Itpr3tf/J mice

Autism spectrum disorder (ASD) is a severe neurodevelopmental disorder characterized by deficits in social interaction, communication, and repetitive behaviors. A key role for immune dysfunction has been suggested in ASD. Recent studies have indicated that inflammatory mediators and Notch-1 signaling may contribute to the development of ASD. Methylmercury chloride (MeHgCl) is an environmental pollutant that primarily affects the central nervous system, causing neurological alterations. Its effects on immunological responses have not been fully investigated in ASD. In this study, we examined the influence of MeHgCl exposure on inflammatory mediators and Notch-1 signaling in BTBR T⁺ Itpr3tf/J (BTBR) mice, a model of ASD. We examined the effects of MeHgCl on the IL-6-, GM-CSF-, NF-κB p65-, Notch-1-, and IL-27-producing CD14⁺ and CD40⁺ cells in the spleen. We assessed the effect of MeHgCl on IL-6, GM-CSF, NF-κB p65, Notch-1, and IL-27 mRNA levels in brain tissue. We also measured IL-6, GM-CSF, and NF-κB p65 protein expression levels in brain tissue. MeHgCl exposure of BTBR mice significantly increased IL-6-, GM-CSF-, NF-κB p65-, and Notch-1-, and decreased IL-27-producing CD14⁺, and CD40⁺ cells in the spleen. MeHgCl exposure of BTBR mice upregulated IL-6, GM-CSF, NF-κB p65, and Notch-1, and decreased IL-27 mRNA expression levels in brain tissue. Moreover, MeHgCl resulted in elevated expression of the IL-6, GM-CSF, and NF-κB p65 proteins in brain tissue. Taken together, these results indicate that MeHgCl exposure aggravates proinflammatory mediators and Notch-1 signaling which are associated with imbalance of neuroimmune function in BTBR mice.     

Inhibition of TANK-binding kinase1 attenuates the astrocyte-mediated neuroinflammatory response through YAP signaling after spinal cord injury

Aims

TANK-binding kinase 1 (TBK1) is involved in regulating the pathological process of a variety of inflammatory diseases in the central nervous system. However, its role and underlying molecular mechanisms in spinal cord injury (SCI) remain largely unknown.

Methods

We employed the TBK1 inhibitor amlexanox (ALX) to address this question. An in vivo clip-compressive SCI model and in vitro lipopolysaccharide (LPS)-induced astrocyte inflammation model were established to examine the effects of TBK1 inhibition on the expression of proinflammatory cytokines.

Results

In this study, we found that TBK1 and TBK1-medicated innate immune pathways, such as TBK1/IRF3 and noncanonical NF-κB signaling, were activated in astrocytes and neurons after SCI. Furthermore, inhibition of TBK1 by ALX alleviated neuroinflammation response, reduced the loss of motor neurons, and improved the functional recovery after SCI. Mechanistically, inhibition of TBK1 activity promoted the activation of the noncanonical NF-κB signaling pathway and inhibited p-IRF3 activity in LPS-induced astrocytes, and the TBK1 activity was required for astrocytic activation through yes-associated protein (YAP) signaling after SCI and in LPS-induced astrocytes inflammation model.

Conclusion

TBK1-medicated innate immune pathway in astrocytes through YAP signaling plays an important role in the pathogenesis of SCI and inhibition of TBK1 may be a potential therapeutic drug for SCI.     

CORRELATION BETWEEN AGE-RELATED CHANGES IN OPEN FIELD BEHAVIOR AND PLAQUE FORMING CELL RESPONSE IN DA FEMALE RATS

We investigated the relationship between immunological and behavioral changes during ageing in Dark Agouti female rats. Results showed that ageing was associated with decreased exploratory behavior and increased emotionality (open field test) and decreased pain perception (writhing assay), but not with altered depression-like behavior (forced swim test). The observed behavioral changes were paralleled with decreased innate immunity in middle-aged and old rats, as revealed by reduced peroxide production of peritoneal macrophages; and decreased specific immunity, measured by the plaque-forming cell response, in old rats in comparison with young rats. Correlation analyses between behavioral and immune parameters demonstrated a significant correlation between the lines crossed in the open field test and the plaque-forming cell response. Taken together, the demonstrated age-dependent association between exploratory behavior and specific immune response suggests a senescent decline of a common neuroimmune regulatory mechanism.­­     

Alcohol-induced sedation and synergistic interactions between alcohol and morphine: A key mechanistic role for Toll-like receptors and MyD88-dependent signaling

Increasing evidence demonstrates induction of proinflammatory Toll-like receptor (TLR) 2 and TLR4 signaling by morphine and, TLR4 signaling by alcohol; thus indicating a common site of drug action and a potential novel innate immune-dependent hypothesis for opioid and alcohol drug interactions. Hence, the current study aimed to assess the role of TLR2, TLR4, MyD88 (as a critical TLR-signaling participant), NF-κB, Interleukin-1β (IL-1β; as a downstream proinflammatory effector molecule) and the μ opioid receptor (MOR; as a classical site for morphine action) in acute alcohol-induced sedation (4.5 g/kg) and alcohol (2.5 g/kg) interaction with morphine (5 mg/kg) by assessing the loss of righting reflex (LORR) as a measure of sedation. Wild-type male Balb/c mice and matched genetically-deficient TLR2, TLR4, and MyD88 strains were utilized, together with pharmacological manipulation of MOR, NF-κB, TLR4 and Interleukin-1β. Alcohol induced significant LORR in wild-type mice; this was halved by MyD88 and TLR4 deficiency, and surprisingly nearly completely eliminated by TLR2 deficiency. In contrast, the interaction between morphine and alcohol was found to be MOR-, NF-κB-, TLR2- and MyD88-dependent, but did not involve TLR4 or Interleukin-1β. Morphine–alcohol interactions caused acute elevations in microglial cell counts and NF-κB-p65 positive cells in the motor cortex in concordance with wild-type and TLR2 deficient mouse behavioral data, implicating neuroimmunopharmacological signaling as a pivotal mechanism in this clinically problematic drug–drug interaction.     

Correlation between age-related changes in open field behavior and plaque forming cell response in DA female rats

We investigated the relationship between immunological and behavioral changes during ageing in Dark Agouti female rats. Results showed that ageing was associated with decreased exploratory behavior and increased emotionality (open field test) and decreased pain perception (writhing assay), but not with altered depression-like behavior (forced swim test). The observed behavioral changes were paralleled with decreased innate immunity in middle-aged and old rats, as revealed by reduced peroxide production of peritoneal macrophages; and decreased specific immunity, measured by the plaque-forming cell response, in old rats in comparison with young rats. Correlation analyses between behavioral and immune parameters demonstrated a significant correlation between the lines crossed in the open field test and the plaque-forming cell response. Taken together, the demonstrated age-dependent association between exploratory behavior and specific immune response suggests a senescent decline of a common neuroimmune regulatory mechanism.     

Increased peripheral NF-κB pathway activity in women with childhood abuse-related posttraumatic stress disorder

In addition to neuroendocrine changes PTSD pathophysiology may also involve dysfunction of the innate immune inflammatory system. PTSD patients have been found to exhibit increased concentrations of circulating inflammatory markers such as C-reactive protein and interleukin-6, suggesting dysfunction of the innate immune inflammatory system. However, few studies have investigated molecular signaling pathways known to critically regulate inflammation. Additionally, the relationship between inflammatory function and immune cell glucocorticoid sensitivity has not been extensively explored in PTSD. Nuclear factor-κB (NF-κB) pathway activity was examined in peripheral blood mononuclear cells obtained from 12 women with childhood abuse-related PTSD and 24 healthy controls (ages 19-48) using DNA-binding ELISA. Glucocorticoid sensitivity of monocytes in whole blood was measured as the concentration of dexamethasone needed to suppress in vitro lipopolysaccharide-induced tumor necrosis factor-alpha production by 50% (DEX IC₅₀). Women with PTSD displayed increased NF-κB pathway activity compared to controls (t [34] = 2.45, p = 0.02) that was positively correlated with PTSD severity (determined by PTSD symptom severity scale) (r_s = 0.39, p = 0.02). Increased NF-κB pathway activity was associated with increased whole blood monocyte DEX IC₅₀ (i.e. decreased sensitivity of monocytes to glucocorticoids) across all participants (r = 0.66, p < 0.001). These findings suggest that enhanced inflammatory system activity in participants with childhood abuse-related PTSD is observable at the level of NF-κB, and that in general decreased immune cell glucocorticoid sensitivity may contribute to increased NF-κB pathway activity. Enhanced inflammation may contribute to co-morbid somatic disease risk in persons with childhood abuse-related PTSD.     

Daily exercise improves memory,stimulates hippocampal neurogenesis and modulates immune and neuroimmune cytokines in aging rats

We tested whether daily exercise modulates immune and neuroimmune cytokines, hippocampus-dependent behavior and hippocampal neurogenesis in aging male F344 rats (18mo upon arrival). Twelve weeks after conditioned running or control group assignment, the rats were trained and tested in a rapid water maze followed by an inhibitory avoidance task. The rats were BrdU-injected beginning 12 days after behavioral testing and killed 3 weeks later to quantify cytokines and neurogenesis. Daily exercise increased neurogenesis and improved immediate and 24 h water maze discrimination index (DI) scores and 24 h inhibitory avoidance retention latencies. Daily exercise decreased cortical VEGF, hippocampal IL-1β and serum MCP-1, GRO-KC and leptin levels but increased hippocampal GRO-KC and IL-18 concentrations. Serum leptin concentration correlated negatively with new neuron number and both DI scores while hippocampal IL-1β concentration correlated negatively with memory scores in both tasks. Cortical VEGF, serum GRO-KC and serum MCP-1 levels correlated negatively with immediate DI score and we found novel positive correlations between hippocampal IL-18 and GRO-KC levels and new neuron number. Pathway analyses revealed distinct serum, hippocampal and cortical compartment cytokine relationships. Our results suggest that daily exercise potentially improves cognition in aging rats by modulating hippocampal neurogenesis and immune and neuroimmune cytokine signaling. Our correlational data begin to provide a framework for systematically manipulating these immune and neuroimmune signaling molecules to test their effects on cognition and neurogenesis across lifespan in future experiments.     

Modulation of glutamatergic synaptic transmission in the bed nucleus of the stria terminalis

Glutamate, catecholamine and neuropeptide signaling within the bed nucleus of the stria terminalis (BNST) have all been identified as key participants in anxiety-like behaviors and behaviors related to withdrawal from exposure to substances of abuse. The BNST is thought to serve as a key relay between limbic cognitive centers and reward, stress and anxiety nuclei. Human studies and animal models have demonstrated that stressors and drugs of abuse can result in long term behavioral modifications that can culminate in psychological diseases such as addiction and post-traumatic stress disorder. The ability of catecholamines and neuropeptides to influence synaptic glutamatergic transmission (stemming from cognitive centers) within the BNST may have profound consequences over these behaviors. In this review we highlight studies examining synaptic plasticity and modulation of excitatory transmission within the BNST, emphasizing how such modulation may result in alterations in anxiety and reward related behavior.     

Nuclear factor κ B expression in patients with sporadic amyotrophic lateral sclerosis and hereditary amyotrophic lateral sclerosis with optineurin mutations

Nuclear factor κ B (NF-κB) is involved in the pathogenesis of a number of neurodegenerative disorders with neuroinflammation. In order to clarify the role of NF-κB in ALS, immunohistochemical studies with an antibody that recognizes the p65 subunit of NF-κB were performed on the spinal anterior horn of 4 patients with sporadic ALS (sALS), 1 patient with optineurin-mutated ALS (OPTN-ALS), and 3 normal controls (NC). In patients with sALS or OPTN-ALS, the expression pattern of NF-κB was altered when compared to that of NC; NF-κB immunoreactivity tended to be absent from neuronal nucleus and was increased in microglia. The down-regulation of NF-κB in neuronal nucleus might contribute to a loss of neuroprotection, or neurons with nuclear NF-κB might be lost immediately after its activation. The microglial induction of NF-κB might contribute to neuroinflammation. In conclusion, NF-κB signaling pathway could have a key role in the pathomechanism of ALS.     

Dysregulation of the NF-κB pathway as a potential inducer of bipolar disorder

A century of investigations enhanced our understanding of bipolar disorder although it remains a complex multifactorial disorder with a mostly unknown pathophysiology and etiology. The role of the immune system in this disorder is one of the most controversial topics in genetic psychiatry. Though inflammation has been consistently reported in bipolar patients, it remains unclear how the immunologic process influences the disorder. One of the core components of the immune system is the NF-κB pathway, which plays an essential role in the development of innate and adaptive immunity. Remarkably, the NF-κB pathway received only little attention in bipolar studies, as opposed to studies of related psychiatric disorders where immune dysregulation has been proposed to explain the neurodegeneration in patient conditions. If immune dysregulation can also explains the neurodegeneration in bipolar disorder, it will underscore the role of the immune system in the chronicity and pathophysiology of the disorder and may promote personalized therapeutic strategies. This is the first review to summarize the current knowledge of the pathophysiological functions of NF-κB in bipolar disorder.