Anti-inflammatory effects of noradrenaline on LPS-treated microglial cells: Suppression of NFκB nuclear translocation and subsequent STAT1 phosphorylation

A dopamine D1-like receptor-specific agonist improves the survival of septic mice

In this study, a murine sepsis model was developed using the cecum ligation and puncture (CLP) technique. The expression of the proinflammatory cytokines tumor necrosis factor alpha (TNF-α) and interleukin-1β (IL-1β) in the brain increased 6 h after CLP but decreased 24 h later when elevated endogenous dopamine levels in the brain were sustained. Methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride reduced dopamine levels in the striatum and increased mortality in septic mice. Dopamine D1-like receptors were significantly expressed in the brain, but not in the lungs. Intraperitoneally administered SKF-81297 (SKF), a blood-brain barrier-permeable D1-like receptor agonist, prevented CLP-induced death of septic mice with ameliorated acute lung injury and cognitive dysfunction and suppressed TNF-α and IL-1β expression. The D1-like receptor antagonist SCH-23390 abolished the anti-inflammatory effects of SKF. These data suggest that D1-like receptor-mediated signals in the brain prevent CLP-induced inflammation in both the brain and the periphery.

Locus coeruleus injury modulates ventral midbrain neuroinflammation during DSS-induced colitis

Parkinson's disease (PD) is characterized by a decades-long prodrome, consisting of a collection of non-motor symptoms that emerges prior to the motor manifestation of the disease. Of these non-motor symptoms, gastrointestinal dysfunction and deficits attributed to central norepinephrine (NE) loss, including mood changes and sleep disturbances, are frequent in the PD population and emerge early in the disease. Evidence is mounting that injury and inflammation in the gut and locus coeruleus (LC), respectively, underlie these symptoms, and the injury of these systems is central to the progression of PD. In this study, we generate a novel two-hit mouse model that captures both features, using dextran sulfate sodium (DSS) to induce gut inflammation and N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) to lesion the LC. We first confirmed the specificity of DSP-4 for central NE using neurochemical methods and fluorescence light-sheet microscopy of cleared tissue, and established that DSS-induced outcomes in the periphery, including weight loss, gross indices of gut injury and systemic inflammation, the loss of tight junction proteins in the colonic epithelium, and markers of colonic inflammation, were unaffected with DSP-4 pre-administration. We then measured alterations in neuroimmune gene expression in the ventral midbrain in response to DSS treatment alone as well as the extent to which prior LC injury modified this response. In this two-hit model we observed that DSS-induced colitis activates the expression of key cytokines and chemokines in the ventral midbrain only in the presence of LC injury and the typical DSS-associated neuroimmune is blunted by pre-LC lesioning with DSP-4. In all, this study supports the growing appreciation for the LC as neuroprotective against inflammation-induced brain injury and draws attention to the potential for NEergic interventions to exert disease-modifying effects under conditions where peripheral inflammation may compromise ventral midbrain dopaminergic neurons and increase the risk for development of PD.

Locus coeruleus injury modulates ventral midbrain neuroinflammation during DSS-induced colitis

Parkinson's disease (PD) is characterized by a decades-long prodrome, consisting of a collection of non-motor symptoms that emerges prior to the motor manifestation of the disease. Of these non-motor symptoms, gastrointestinal dysfunction and deficits attributed to central norepinephrine (NE) loss, including mood changes and sleep disturbances, are frequent in the PD population and emerge early in the disease. Evidence is mounting that injury and inflammation in the gut and locus coeruleus (LC), respectively, underlie these symptoms, and the injury of these systems is central to the progression of PD. In this study, we generate a novel two-hit mouse model that captures both features, using dextran sulfate sodium (DSS) to induce gut inflammation and N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) to lesion the LC. We first confirmed the specificity of DSP-4 for central NE using neurochemical methods and fluorescence light-sheet microscopy of cleared tissue, and established that DSS-induced outcomes in the periphery, including weight loss, gross indices of gut injury and systemic inflammation, the loss of tight junction proteins in the colonic epithelium, and markers of colonic inflammation, were unaffected with DSP-4 pre-administration. We then measured alterations in neuroimmune gene expression in the ventral midbrain in response to DSS treatment alone as well as the extent to which prior LC injury modified this response. In this two-hit model we observed that DSS-induced colitis activates the expression of key cytokines and chemokines in the ventral midbrain only in the presence of LC injury and the typical DSS-associated neuroimmune is blunted by pre-LC lesioning with DSP-4. In all, this study supports the growing appreciation for the LC as neuroprotective against inflammation-induced brain injury and draws attention to the potential for NEergic interventions to exert disease-modifying effects under conditions where peripheral inflammation may compromise ventral midbrain dopaminergic neurons and increase the risk for development of PD.

Exploring Parkinson's Disease-Associated Depression: Role of Inflammation on the Noradrenergic and Serotonergic Pathways

Parkinson's disease (PD) is a multifactorial disease, with genetic and environmental factors contributing to the disease onset. Classically, PD is a movement disorder characterized by the loss of dopaminergic neurons in the nigrostriatal pathway and intraneuronal aggregates mainly constituted of the protein α-synuclein. However, PD patients also display non-motor symptoms, including depression, which have been linked to functional abnormalities of non-dopaminergic neurons, including serotonergic and noradrenergic ones. Thus, through this comprehensive literature review, we shed light on the noradrenergic and serotonergic impairment linked to depression in PD, focusing on the putative involvement of inflammatory mechanisms.

Adolescent high fat diet alters the transcriptional response of microglia in the prefrontal cortex in response to stressors in both male and female mice

Both obesity and high fat diets (HFD) have been associated with an increase in inflammatory gene expression within the brain. Microglia play an important role in early cortical development and may be responsive to HFD, particularly during sensitive windows, such as adolescence. We hypothesized that HFD during adolescence would increase proinflammatory gene expression in microglia at baseline and potentiate the microglial stress response. Two stressors were examined, a physiological stressor [lipopolysaccharide (LPS), IP] and a psychological stressor [15 min restraint (RST)]. From 3 to 7 weeks of age, male and female mice were fed standard control diet (SC, 20% energy from fat) or HFD (60% energy from fat). On P49, 1 h before sacrifice, mice were randomly assigned to either stressor exposure or control conditions. Microglia from the frontal cortex were enriched using a Percoll density gradient and isolated via fluorescence-activated cell sorting (FACS), followed by RNA expression analysis of 30 genes (27 target genes, three housekeeping genes) using Fluidigm, a medium throughput qPCR platform. We found that adolescent HFD induced sex-specific transcriptional response in cortical microglia, both at baseline and in response to a stressor. Contrary to our hypothesis, adolescent HFD did not potentiate the transcriptional response to stressors in males, but rather in some cases, resulted in a blunted or absent response to the stressor. This was most apparent in males treated with LPS. However, in females, potentiation of the LPS response was observed for select proinflammatory genes, including Tnfa and Socs3. Further, HFD increased the expression of Itgam, Ikbkb, and Apoe in cortical microglia of both sexes, while adrenergic receptor expression (Adrb1 and Adra2a) was changed in response to stressor exposure with no effect of diet. These data identify classes of genes that are uniquely affected by adolescent exposure to HFD and different stressor modalities in males and females.

Microglial Regulation of Sleep and Wakefulness

Sleep serves a multitude of roles in brain maturation and function. Although the neural networks involved in sleep regulation have been extensively characterized, it is increasingly recognized that neurons are not the sole conductor orchestrating the rhythmic cycle of sleep and wakefulness. In the central nervous system, microglia have emerged as an important player in sleep regulation. Within the last two decades, microglia have gained substantial attention for carrying out numerous nonimmune tasks that are crucial for brain development and function by co-opting similar mechanisms used in their conventional immune functions. Here, we highlight the importance of microglia in sleep regulation with recent findings reporting an arrhythmic sleep/wake cycle in the absence of microglia. Although the underlying mechanisms for such regulation are still being uncovered, it is likely that microglial contributions to the rhythmic control of the sleep/wake cycle come from their influence on synaptic strength and neuronal activity. We review the current literature to provide speculative signaling pathways and suggest key questions for future research. Advancing our knowledge of the mechanistic contribution of microglia to sleep regulation will not only further our insight into this critical biological process but also be instrumental in providing novel therapeutic strategies for sleep disorders.

The anti-inflammatory and anti-oxidative effect of a classical hypnotic bromovalerylurea mediated by the activation of NRF2

The Kelch-like ECH-associated protein 1-nuclear factor erythroid 2-related factor 2 (KEAP1-NRF2) system plays a central role in redox homeostasis and inflammation control. Oxidative stress or electrophilic compounds promote NRF2 stabilization and transcriptional activity by negatively regulating its inhibitor, KEAP1. We have previously reported that bromovalerylurea (BU), originally developed as a hypnotic, exerts anti-inflammatory effects in various inflammatory disease models. However, the molecular mechanism underlying its effect remains uncertain. Herein, we found that by real-time multicolor luciferase assay using stable luciferase red3 (SLR3) and green-emitting emerald luciferase (ELuc), BU potentiates NRF2-dependent transcription in the human hepatoblastoma cell line HepG2 cells, which lasted for more than 60 h. Further analysis revealed that BU promotes NRF2 accumulation and the transcription of its downstream cytoprotective genes in the HepG2 and the murine microglial cell line BV2. Keap1 knockdown did not further enhance NRF2 activity, suggesting that BU upregulates NRF2 by targeting KEAP1. Knockdown of Nfe2l2 in BV2 cells diminished the suppressive effects of BU on the production of pro-inflammatory mediators, like nitric oxide (NO) and its synthase NOS2, indicating the involvement of NRF2 in the anti-inflammatory effects of BU. These data collectively suggest that BU could be repurposed as a novel NRF2 activator to control inflammation and oxidative stress.

Promising neurostimulation routes for targeting the hippocampus to improve episodic memory: A review

This review aims to highlight modern neurostimulation approaches that are effectively activating the hippocampus and enhancing episodic memory performance. The hippocampus is a brain region known to play an essential role in episodic memory processes. However, as it is nestled deep within the brain, it has been a challenging target for traditional neurostimulation approaches, with studies reporting inconsistent memory effects. Recent studies suggest more than half of the electrical current from non-invasive transcranial electrical stimulation (tES) methods may be attenuated by the human scalp, skull, and cerebral spinal fluid. Thus, this review aims to highlight novel neurostimulation approaches that are showing promise as alternative routes for activating hippocampal circuitry. Early evidence suggests temporal interference, closed-loop and individualized protocols, sensory stimulation and peripheral nerve-targeted tES protocols warrant further investigation. These approaches each provide promising routes for activating the hippocampus by a) increasing its functional connectiveness to key brain regions, b) strengthening synaptic plasticity mechanisms, or c) enhancing neural entrainment specifically within and between theta and gamma frequencies in these regions. Importantly, these three functional mechanisms and the hippocampus' structural integrity are negatively impacted throughout the progression of Alzheimer's Disease, with episodic memory deficits likewise evident in early stages. Consequently, depending on further validation of the approaches reviewed here, these techniques could offer significant applied therapeutic value for patients suffering from memory deficits or neurodegenerative diseases including amnestic Mild Cognitive Impairment or Alzheimer's disease.

Administration of serotonin and norepinephrine reuptake inhibitors tends to have less ocular surface damage in a chronic stress-induced rat model of depression than selective serotonin reuptake inhibitors

Depressed patients who medicate with selective serotonin reuptake inhibitors (SSRIs) often report ocular dryness. Epidemiological studies have found that serotonin and norepinephrine reuptake inhibitors (SNRIs) are not risk factors for dry eye in depressed patients. However, the effect of SNRIs on the ocular surface is unknown. A depression rat model was induced by chronic unpredictable mild stress (CUMS), and SNRIs or SSRIs were administered to the rats for 3 or 6 weeks. The levels of norepinephrine (NE) and serotonin in tear fluid were tested by ELISA. The corneal fluorescence and lissamine green staining were used to evaluate ocular surface damage. NE and/or serotonin were administered to human corneal epithelial cells in vitro. RNA sequencing (RNA-seq) analysis was performed to investigate the mRNA expression profiles. Tear NE levels were higher in the SNRIs group, and ocular surface inflammation and apoptosis were significantly reduced compared to the SSRIs group. RNA-Seq indicated that NE significantly activate MAPK signaling pathway. NE can inhibit serotonin-induced activation of the NF-κB signaling pathway through α-1 adrenergic receptors and promotes the proliferation of corneal epithelial cells through activation of the MAPK signaling pathway. SNRIs administration have less ocular surface damage than SSRIs. NE protects human corneal epithelial cells from damage, and reduce inflammation on the ocular surface via activating the MAPK signaling pathway. SNRIs might be used as an appropriate treatment for depression-related DED.

The Relationships Among Metal Homeostasis, Mitochondria, and Locus Coeruleus in Psychiatric and Neurodegenerative Disorders: Potential Pathogenetic Mechanism and Therapeutic Implications

While alterations in the locus coeruleus-noradrenergic system are present during early stages of neuropsychiatric disorders, it is unclear what causes these changes and how they contribute to other pathologies in these conditions. Data suggest that the onset of major depressive disorder and schizophrenia is associated with metal dyshomeostasis that causes glial cell mitochondrial dysfunction and hyperactivation in the locus coeruleus. The effect of the overactive locus coeruleus on the hippocampus, amygdala, thalamus, and prefrontal cortex can be responsible for some of the psychiatric symptoms. Although locus coeruleus overactivation may diminish over time, neuroinflammation-induced alterations are presumably ongoing due to continued metal dyshomeostasis and mitochondrial dysfunction. In early Alzheimer's and Parkinson's diseases, metal dyshomeostasis and mitochondrial dysfunction likely induce locus coeruleus hyperactivation, pathological tau or α-synuclein formation, and neurodegeneration, while reduction of glymphatic and cerebrospinal fluid flow might be responsible for β-amyloid aggregation in the olfactory regions before the onset of dementia. It is possible that the overactive noradrenergic system stimulates the apoptosis signaling pathway and pathogenic protein formation, leading to further pathological changes which can occur in the presence or absence of locus coeruleus hypoactivation. Data are presented in this review indicating that although locus coeruleus hyperactivation is involved in pathological changes at prodromal and early stages of these neuropsychiatric disorders, metal dyshomeostasis and mitochondrial dysfunction are critical factors in maintaining ongoing neuropathology throughout the course of these conditions. The proposed mechanistic model includes multiple pharmacological sites that may be targeted for the treatment of neuropsychiatric disorders commonly.

Anti-inflammatory effects of dopamine on microglia and a D1 receptor agonist ameliorates neuroinflammation of the brain in a rat delirium model

Microglia play a central role in neuroinflammatory processes by releasing proinflammatory mediators. This process is tightly regulated along with neuronal activities, and neurotransmitters may link neuronal activities to the microglia. In this study, we showed that primary cultured rat microglia express the dopamine (DA) D1 receptor (D1R) and D4R, but not D2R, D3R, or D5R. In response to a D1R-specific agonist SKF-81297 (SKF), the cultured microglia exhibited increased intracellular cAMP levels. DA and SKF suppressed lipopolysaccharide (LPS)-induced expression of interleukin-1β (IL-1β) and tumor necrosis α (TNFα) in cultured microglia. Microglia in the normal mature rat prefrontal cortex (PFC) were sorted and significant expression of D1R, D2R, and D4R was observed. A delirium model was established by administering LPS intraperitoneally to mature male Wistar rats. The model also displayed sleep-wake disturbances as revealed by electroencephalogram and electromyogram recordings as well as increased expression of IL-1β and TNFα in the PFC. DA levels were increased in the PFC 21 h after LPS administration. Increased cytokine expression was observed in sorted microglia from the PFC of the delirium model; however, TNFα, but not IL-1β expression, was abruptly decreased 21 h after LPS administration in the delirium model, whereas DA levels were increased. A D1R antagonist SCH23390 partially abolished the TNFα expression change. This suggests that endogenous DA may play a role in suppressing neuroinflammation. Administration of the DA precursor L-DOPA or SKF to the delirium model rats inhibited the expression of IL-1β and TNFα. The simultaneous administration of clozapine, a D4R antagonist, strengthened the suppressive effects of L-DOPA. These results suggest that D1R mediates the suppressive effects of LPS-induced neuroinflammation, in which microglia may play an important role. Agonists for D1R may be effective for treating delirium.

Activation of β2-Adrenergic Receptors in Microglia Alleviates Neuropathic Hypersensitivity in Mice

Drugs enhancing the availability of noradrenaline are gaining prominence in the therapy of chronic neuropathic pain. However, underlying mechanisms are not well understood, and research has thus far focused on α2-adrenergic receptors and neuronal excitability. Adrenergic receptors are also expressed on glial cells, but their roles toward antinociception are not well deciphered. This study addresses the contribution of β2-adrenergic receptors (β2-ARs) to the therapeutic modulation of neuropathic pain in mice. We report that selective activation of β2-ARs with Formoterol inhibits pro-inflammatory signaling in microglia ex vivo and nerve injury-induced structural remodeling and functional activation of microglia in vivo. Systemic delivery of Formoterol inhibits behaviors related to neuropathic pain, such as mechanical hypersensitivity, cold allodynia as well as the aversive component of pain, and reverses chronically established neuropathic pain. Using conditional gene targeting for microglia-specific deletion of β2-ARs, we demonstrate that the anti-allodynic effects of Formoterol are primarily mediated by microglia. Although Formoterol also reduces astrogliosis at late stages of neuropathic pain, these functions are unrelated to β2-AR signaling in microglia. Our results underline the value of developing microglial β2-AR agonists for relief from neuropathic pain and clarify mechanistic underpinnings.

Bromovalerylurea modulates GABAA receptor-mediated inhibitory neurotransmission while inducing sleep

Bromovalerylurea (BU), an acyl urea derivative, was originally developed as a hypnotic/sedative. We recently reported that BU at a dose of 50 mg/kg ameliorates sepsis, Parkinson's disease, and traumatic brain injury in Wistar rat models through its anti-inflammatory actions on microglia and macrophages. However, since BU was developed more than 100 years ago, its hypnotic mechanism and characteristics are poorly understood. Herein, we conducted an electroencephalogram (EEG) study and found that BU, when administered at a dose of more than 125 mg/kg but not at a dose of 50 mg/kg in Wistar rats, significantly increased non-rapid eye movement (NREM) sleep duration and dose-dependently decreased rapid eye movement (REM) sleep duration. This characteristic of sleep induced by BU is similar to the effect of compounds such as barbiturate, benzodiazepine, and z-drugs, all of which require γ-aminobutyric acid _A receptors (GABA_AR) for hypnotic/sedative activity. To investigate whether BU could potentiate GABA_Aergic neurotransmission, we conducted a whole-cell patch-clamp recording from pyramidal neurons in rat cortical slices to detect spontaneous GABA_AR-mediated inhibitory postsynaptic currents (IPSCs). We found that BU dose-dependently prolonged IPSCs. Importantly, the prolonged IPSCs were not attenuated by flumazenil, a benzodiazepine receptor antagonist, suggesting that modulation of IPSCs by BU is mediated by different mechanisms from that of benzodiazepine. Taken together, these data elucidate the basic characteristics of the hypnotic effects of BU and suggest that the enhancement of GABA_AR-mediated Cl^- flux may be a possible mechanism that contributes to its hypnotic/sedative activity.

Systemic immune responses after ischemic stroke: From the center to the periphery

Ischemic stroke is a leading cause of disability and death. It imposes a heavy economic burden on individuals, families and society. The mortality rate of ischemic stroke has decreased with the help of thrombolytic drug therapy and intravascular intervention. However, the nerve damage caused by ischemia-reperfusion is long-lasting and followed by multiple organ dysfunction. In this process, the immune responses manifested by systemic inflammatory responses play an important role. It begins with neuroinflammation following ischemic stroke. The large number of inflammatory cells released after activation of immune cells in the lesion area, along with the deactivated neuroendocrine and autonomic nervous systems, link the center with the periphery. With the activation of systemic immunity and the emergence of immunosuppression, peripheral organs become the second “battlefield” of the immune response after ischemic stroke and gradually become dysfunctional and lead to an adverse prognosis. The purpose of this review was to describe the systemic immune responses after ischemic stroke. We hope to provide new ideas for future research and clinical treatments to improve patient outcomes and quality of life.

Noradrenaline in Alzheimer's Disease: A New Potential Therapeutic Target

A growing body of evidence demonstrates the important role of the noradrenergic system in the pathogenesis of many neurodegenerative processes, especially Alzheimer’s disease, due to its ability to control glial activation and chemokine production resulting in anti-inflammatory and neuroprotective effects. Noradrenaline involvement in this disease was first proposed after finding deficits of noradrenergic neurons in the locus coeruleus from Alzheimer’s disease patients. Based on this, it has been hypothesized that the early loss of noradrenergic projections and the subsequent reduction of noradrenaline brain levels contribute to cognitive dysfunctions and the progression of neurodegeneration. Several studies have focused on analyzing the role of noradrenaline in the development and progression of Alzheimer’s disease. In this review we summarize some of the most relevant data describing the alterations of the noradrenergic system normally occurring in Alzheimer’s disease as well as experimental studies in which noradrenaline concentration was modified in order to further analyze how these alterations affect the behavior and viability of different nervous cells. The combination of the different studies here presented suggests that the maintenance of adequate noradrenaline levels in the central nervous system constitutes a key factor of the endogenous defense systems that help prevent or delay the development of Alzheimer’s disease. For this reason, the use of noradrenaline modulating drugs is proposed as an interesting alternative therapeutic option for Alzheimer’s disease.

Surgical stress quickly affects the numbers of circulating B-cells and neutrophils in murine septic and aseptic models through a β2 adrenergic receptor

Sepsis is a pathology accompanied by increases in myeloid cells and decreases in lymphoid cells in circulation. In a murine sepsis model induced by cecum ligation and puncture (CLP), increasing numbers of neutrophils and decreasing levels of B-cells in circulation are among the earliest changes in the immune system. However, to date, the mechanisms for these changes remain to be elucidated. The study here sought to elucidate mechanisms underlying the changes in the leukocyte levels after CLP and also to determine what, if any, role for an involvement of the sympathetic nervous system (SNS). Here, male C57/BL6 mice were subjected to CLP or sham-CLP (abdominal wall incised, but cecum was not punctured). The changes in the number of circulating leukocytes over time were then investigated using flow cytometry. The results showed that a sham-CLP led to increased polymorphonuclear cells (PMN; most of which are neutrophils) and decreased B-cells in the circulation to an extent similar to that induced by CLP. Effects of adrenergic agonists and antagonists, as well as of adrenalectomy, were also examined in mice that underwent CLP or sham-CLP. Administering adrenaline or a β₂ adrenergic receptor agonist (clenbuterol) to mice 3 h before sacrifice produced almost identical changes to as what was seen 2 h after performing a sham-CLP. In contrast, giving a β₂ adrenergic receptor antagonist ICI118,551 1 h before a CLP or sham-CLP suppressed the expected changes 2 h after the operations. Noradrenaline and an α1 adrenergic receptor agonist phenylephrine did not exert significant effects. Adrenalectomy 24 h before a sham-CLP significantly abolished the expected sham-CLP-induced changes seen earlier. Clenbuterol increased splenocyte expression of Cxcr4 (a chemokine receptor gene); adrenalectomy abolished sham-CLP-induced Cxcr4 expression. A CXCR4 antagonist AMD3100 repressed the sham-CLP-induced changes. From these results, it may be concluded that sepsis-induced activation of the SNS may be one cause for immune dysfunction in sepsis - regardless of the pathogenetic processes.

Microglia and the Aging Brain: Are Geriatric Microglia Linked to Poor Sleep Quality?

Poor sleep quality and disrupted circadian behavior are a normal part of aging and include excessive daytime sleepiness, increased sleep fragmentation, and decreased total sleep time and sleep quality. Although the neuronal decline underlying the cellular mechanism of poor sleep has been extensively investigated, brain function is not fully dependent on neurons. A recent antemortem autographic study and postmortem RNA sequencing and immunohistochemical studies on aged human brain have investigated the relationship between sleep fragmentation and activation of the innate immune cells of the brain, microglia. In the process of aging, there are marked reductions in the number of brain microglial cells, and the depletion of microglial cells disrupts circadian rhythmicity of brain tissue. We also showed, in a previous study, that pharmacological suppression of microglial function induced sleep abnormalities. However, the mechanism underlying the contribution of microglial cells to sleep homeostasis is only beginning to be understood. This review revisits the impact of aging on the microglial population and activation, as well as microglial contribution to sleep maintenance and response to sleep loss. Most importantly, this review will answer questions such as whether there is any link between senescent microglia and age-related poor quality sleep and how this exacerbates neurodegenerative disease.

Chloride intracellular channel protein 2 is secreted and inhibits MMP14 activity, while preventing tumor cell invasion and metastasis

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CLIC2 is highly expressed in benign, less invasive and less metastatic tumors.

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Forced expression of CLIC2 prevents metastasis and invasion in animal tumor models.

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CLIC2 is associated with decreased vascular permeability in tumor masses.

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CLIC2, a secretable soluble protein, can bind to and inhibit MMP14.

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Extracellular CLIC2 can suppress malignant cell invasion.

The abilities to invade surrounding tissues and metastasize to distant organs are the most outstanding features that distinguish malignant from benign tumors. However, the mechanisms preventing the invasion and metastasis of benign tumor cells remain unclear. By using our own rat distant metastasis model, gene expression of cells in primary tumors was compared with that in metastasized tumors. Among many distinct gene expressions, we have focused on chloride intracellular channel protein 2 (CLIC2), an ion channel protein of as-yet unknown function, which was predominantly expressed in the primary tumors. We created CLIC2 overexpressing rat glioma cell line and utilized benign human meningioma cells with naturally high CLIC2 expression. CLIC2 was expressed at higher levels in benign human brain tumors than in their malignant counterparts. Moreover, its high expression was associated with prolonged survival in the rat metastasis and brain tumor models as well as with progression-free survival in patients with brain tumors. CLIC2 was also correlated with the decreased blood vessel permeability likely by increased contents of cell adhesion molecules. We found that CLIC2 was secreted extracellularly, and bound to matrix metalloproteinase (MMP) 14. Furthermore, CLIC2 prevented the localization of MMP14 in the plasma membrane, and inhibited its enzymatic activity. Indeed, overexpressing CLIC2 and recombinant CLIC2 protein effectively suppressed malignant cell invasion, whereas CLIC2 knockdown reversed these effects. Thus, CLIC2 suppress invasion and metastasis of benign tumors at least partly by inhibiting MMP14 activity.

Dual Roles of Microglia in the Basal Ganglia in Parkinson's Disease

With the increasing age of the population, the incidence of Parkinson’s disease (PD) has increased exponentially. The development of novel therapeutic interventions requires an understanding of the involvement of senescent brain cells in the pathogenesis of PD. In this review, we highlight the roles played by microglia in the basal ganglia in the pathophysiological processes of PD. In PD, dopaminergic (DAergic) neuronal degeneration in the substantia nigra pars compacta (SNc) activates the microglia, which then promote DAergic neuronal degeneration by releasing potentially neurotoxic factors, including nitric oxide, cytokines, and reactive oxygen species. On the other hand, microglia are also activated in the basal ganglia outputs (the substantia nigra pars reticulata and the globus pallidus) in response to excess glutamate released from hyperactive subthalamic nuclei-derived synapses. The activated microglia then eliminate the hyperactive glutamatergic synapses. Synapse elimination may be the mechanism underlying the compensation that masks the appearance of PD symptoms despite substantial DAergic neuronal loss. Microglial senescence may correlate with their enhanced neurotoxicity in the SNc and the reduced compensatory actions in the basal ganglia outputs. The dual roles of microglia in different basal ganglia regions make it difficult to develop interventions targeting microglia for PD treatment.

Microglia regulate synaptic development and plasticity

Synapses are fundamental structures of neural circuits that transmit information between neurons. Thus, the process of neural circuit formation via proper synaptic connections shapes the basis of brain functions and animal behavior. Synapses continuously undergo repeated formation and elimination throughout the lifetime of an organism, reflecting the dynamics of neural circuit function. The structural transformation of synapses has been described mainly in relation to neural activity-dependent strengthening and weakening of synaptic functions, that is, functional plasticity of synapses. An increasing number of studies have unveiled the roles of microglia, brain-resident immune cells that survey the brain parenchyma with highly motile processes, in synapse formation and elimination as well as in regulating synaptic function. Over the past 15 years, the molecular mechanisms underlying microglia-dependent regulation of synaptic plasticity have been thoroughly studied, and researchers have reported that the disruption of microglia-dependent regulation causes synaptic dysfunction that leads to brain diseases. In this review, we will broadly introduce studies that report the roles of microglia in synaptic plasticity and the possible underlying molecular mechanisms.

Noradrenaline as a key neurotransmitter in modulating microglial activation in stress response

State of mind can influence susceptibility and progression of diseases and disorders not only in peripheral organs, but also in the central nervous system (CNS). However, the underlying mechanism how state of mind can affect susceptibility to various illnesses in the CNS is not fully understood. Among a number of candidates responsible for stress-induced neuroimmunomodulation, noradrenaline has recently been shown to play crucial roles in the major immune cells of the brain, microglia. In particular, recent studies have demonstrated that noradrenaline may be a key neurotransmitter in modulating microglial cells, thereby determining different cell conditions and responses ranging from resting to activation state depending on host stress level or whether the host is awake or asleep. For instance, microglia under resting conditions may have constructive roles in surveillance, such as debris clearance, synaptic monitoring, pruning, and remodeling. In contrast, once activated, microglia may become less efficient in surveillance activities, and instead implicated in detrimental roles such as cytokine or superoxide release. It is also likely that glial activation, both astrocytes and microglia, are negatively associated with the clearance of brain waste via the glymphatic system. In this review, we discuss the possible underlying mechanism as well as the roles of stress-induced microglial activation.

Significance of vagus nerve function in terms of pathogenesis of psychosocial disorders

The vagus nerve (VN) belongs to the parasympathetic nervous system, which is well known to be involved in the regulation of the functions of organs in the body. The neurotransmitter acetylcholine, released from the cholinergic system including VN, has been known to play an anti-inflammatory role through the efferent pathways in regulating peripheral inflammatory responses profoundly involved in the pathogenesis of diseases. In contrast, anatomically, it connects the central nervous system (CNS) and peripheral organs, including the heart and gastrointestinal (GI) tract. Therefore, it has been recently reported that the VN also plays an important role in the pathogenesis of psychological disorders since it confers varied signals from the GI tract to the CNS, and alteration of microbiota residing in GI definitely influences the condition of neuropsychiatric disorders. Furthermore, the CNS includes microglia, a neuroinflammatory effector in the brain, which is also influenced by the VN to modulate its inflammatory status. Based on significant findings of the VN, the VN stimulation (VNS) has recently drawn attention from many scientific fields. VNS was initially applied to patients with refractory epilepsy, followed by patients with refractory depression. Subsequently, VNS was also attempted to be introduced to other diseases. However, against whichever disease, central or peripheral, detailed underlying mechanisms of VNS involved in neuropsychiatric disorders as well as VNS target molecules in the GI tract and the CNS remains to be studied. In this review, we discuss the mechanisms and predicted responsible factors of VNS in terms of neuropsychiatric disorders.

Shifts of Immune Cell Populations Differ in Response to Different Effectors of Beige Remodeling of Adipose Tissue

White adipose tissue (WAT) is a dynamic tissue, which responds to environmental stimuli and dietary cues by changing its morphology and metabolic capacity. The ability of WAT to undergo a beige remodeling has become an appealing strategy to combat obesity and its comorbidities. Here, by using single-cell RNA sequencing, we provide a comprehensive atlas of the cellular dynamics during beige remodeling. We reveal drastic changes both in the overall cellular composition and transcriptional states of individual cell subtypes between Adrb3- and cold-induced beiging. Moreover, we demonstrate that cold induces a myeloid to lymphoid shift of the immune compartment compared to Adrb3 activation. Further analysis showed that, Adrb3 stimulation leads to activation of the interferon/Stat1 pathways favoring infiltration of myeloid immune cells, while repression of this pathway by cold promotes lymphoid immune cell recruitment. These findings highlight that pharmacological mimetics may not provide the same beneficial effects as physiological stimuli.

Stress and brain immunity: Microglial homeostasis through hypothalamus-pituitary-adrenal gland axis and sympathetic nervous system

Stress has been well documented to bring about various clinical disorders, ranging from neurodegeneration, such as Parkinson’s (PD) and Alzheimer’s diseases (AD), to metabolic disorders including diabetes mellitus. Importantly, microglia, immunocompetent cells in the brain, have been shown to be involved in these clinical disorders. In the recent studies aiming to clarify the microglial responses, microglia are found to be quite responsive to stressful events, such as acute, subchronic, chronic stress, and social defeat stress. However, the mechanisms of these stress response on microglial activation have been not fully understood. In response to stress exposure, both the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system (SNS) are simultaneously activated, with the former inducing glucocorticoids (GCs) and the latter noradrenaline (NA), respectively. However, the effects of these stress-induced GCs and NA have not been consistent. The GCs, conventionally known to act on microglia as immunosuppressant, is also reported to act on it as stimulator. Similarly, the NA has been reported to act on microglia as stimulator or inhibitor depending on environmental conditions. Since any kinds of stress upregulate the HPA axis and SNS, with the levels of upregulation variable depending on the stress type, it is plausible that microglia is closely regulated by these two stress pathways. In this review, we discuss the microglial responses induced by various stresses as well as the possible mechanism by which stress induces microglial activation.

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The present study introduces the mechanism by which microglial activation occurs following acute stress.

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The present study suggests that microglial activation may be regulated through the HPA axis and sympathetic nervous system.

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The present study suggests that microglia may be inhibited by glucocorticoids, while activated by noradrenaline under physiological conditions.

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The present study suggests the hypothesis that the HPA axis may interact with sympathetic nervous system to maintain microglial homeostasis.

Stress-induced microglial activation occurs through β-adrenergic receptor: noradrenaline as a key neurotransmitter in microglial activation

Background

The involvement of microglia in neuroinflammatory responses has been extensively demonstrated. Recent animal studies have shown that exposure to either acute or chronic stress induces robust microglial activation in the brain. In the present study, we investigated the underlying mechanism of brain microglial activation by acute stress.

Methods

We first looked at the spatial distribution of the noradrenaline (NA)-synthesizing enzyme, DBH (dopamine β-hydroxylase), in comparison with NA receptors—β1, β2, and β3 adrenergic receptors (β1-AR, β2-AR, and β3-AR)—after which we examined the effects of the β-blocker propranolol and α-blockers prazosin and yohimbine on stress-induced microglial activation. Finally, we compared stress-induced microglial activation between wild-type (WT) mice and double-knockout (DKO) mice lacking β1-AR and β2-AR.

Results

The results demonstrated that (1) microglial activation occurred in most studied brain regions, including the hippocampus (HC), thalamus (TM), and hypothalamus (HT); (2) within these three brain regions, the NA-synthesizing enzyme DBH was densely stained in the neuronal fibers; (3) β1-AR and β2-AR, but not β3-AR, are detected in the whole brain, and β1-AR and β2-AR are co-localized with microglial cells, as observed by laser scanning microscopy; (4) β-blocker treatment inhibited microglial activation in terms of morphology and count through the whole brain; α-blockers did not show such effect; (5) unlike WT mice, DKO mice exhibited substantial inhibition of stress-induced microglial activation in the brain.

Conclusions

We demonstrate that neurons/microglia may interact with NA via β1-AR and β2-AR.

Aggravating effects of treadmill exercises during the early-onset period in a rat traumatic brain injury model: When should rehabilitation exercises be initiated?

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A traumatic brain injury model was prepared in rats by stab wounding.

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Rats were forced to walk slowly on a treadmill once for 10 min at 24 h or 48 h after wounding.

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Exercise, particularly at 24 h, aggravated motor impairment while increasing the expression of proinflammatory factors.

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Exercise for rehabilitation should be initiated after 48 h of severe brain injury onset.

Physical exercise is one of the best interventions for improving traumatic brain injury (TBI) outcomes. However, an argument has been raised regarding the timing at which physical exercise should be initiated. In this study, male Wistar rats were subjected to stab wounding of the right hemisphere to develop a TBI model and were forced to walk once on a treadmill at a 5-m/min pace at 24 h or 48 h after TBI for 10 min. Injured brain tissue was dissected after TBI to evaluate the effects of exercise. Behavioral abnormalities and motor impairment were assessed by various behavioral tests between 2 and 3 weeks after TBI. Exercise did not affect the circulating corticosterone levels and the weight of the adrenal glands. Exercise particularly that at 24 h, worsened the motor impairment of the left forelimbs. Quantitative reverse-transcription polymerase chain reaction showed that exercise at 24 h increased proinflammatory cytokines and chemokines on the third day while suppressing the proinflammatory reactions on the fourth day. Exercise at both time points decreased expression of transforming growth factor (TGF) β1 and its receptor TGFβR1. Exercise at 24 h increased phosphorylation of IκB kinase on the fourth day, which may be correlated with the decreased effects of TGFβ1. Even a low-intensity exercise activity could cause deleterious effects when it is initiated within 48 h after the onset of severe TBI, probably because of the resulting proinflammatory effects. Therefore, rehabilitation exercise programs should be initiated after 48 h of TBI onset.

Phagocytic elimination of synapses by microglia during sleep

Synaptic strength reduces during sleep, but the underlying mechanisms of this process are unclear. This study showed reduction of synaptic proteins in rat prefrontal cortex (PFC) at AM7 or Zeitgeber Time (ZT0), when the light phase or sleeping period for rats started. At this time point, microglia were weakly activated, displaying larger and more granular somata with increased CD11b expression compared with those at ZT12, as revealed by flow cytometry. Expression of opsonins, such as complements or MFG-E8, matrix metalloproteinases, and microglial markers at ZT0 were increased compared with that at ZT12. Microglia at ZT0 phagocytosed synapses, as revealed by immunohistochemical staining. Immunoblotting detected more synapsin I in the isolated microglia at ZT0 than at ZT12. Complement C3- or MFG-E8-bound synapses were the most abundant at ZT0, some of which were phagocytosed by microglia. Systemic administration of synthetic glucocorticoid dexamethasone reduced microglial size, granularity and CD11b expression at ZT0, resembling microglia at ZT12, and increased synaptic proteins and decreased the sleeping period. Noradrenaline (NA) suppressed glutamate-induced phagocytosis in primary cultured microglia. Systemic administration of the brain monoamine-depleting agent reserpine decreased NA content and synapsin I expression in PFC, and increased expression of microglia markers, C3 and MFG-E8, while increasing the sleeping period. A NA precursor l-threo-dihydroxyphenylserine abolished the reserpine-induced changes. These results suggest that microglia may eliminate presumably weak synapses during every sleep phase. The circadian changes in concentrations of circulating glucocorticoids and brain NA might be correlated with the circadian changes of microglial phenotypes and synaptic strength.

Augmented β2-adrenergic signaling dampens the neuroinflammatory response following ischemic stroke and increases stroke size

Background

Ischemic stroke provokes a neuroinflammatory response and simultaneously promotes release of epinephrine and norepinephrine by the sympathetic nervous system. This increased sympathetic outflow can act on β2-adrenergic receptors expressed by immune cells such as brain-resident microglia and monocyte-derived macrophages (MDMs), but the effect on post-stroke neuroinflammation is unknown. Thus, we investigated how changes in β2-adrenergic signaling after stroke onset influence the microglia/MDM stroke response, and the specific importance of microglia/MDM β2-adrenergic receptors to post-stroke neuroinflammation.

Methods

To investigate the effects of β2-adrenergic receptor manipulation on post-stroke neuroinflammation, we administered the β2-adrenergic receptor agonist clenbuterol to mice 3 h after the onset of photothrombotic stroke. We immunostained to quantify microglia/MDM numbers and proliferation and to assess morphology and activation 3 days later. We assessed stroke outcomes by measuring infarct volume and functional motor recovery and analyzed gene expression levels of neuroinflammatory molecules. Finally, we evaluated changes in cytokine expression and microglia/MDM response in brains of mice with selective knockout of the β2-adrenergic receptor from microglia and monocyte-lineage cells.

Results

We report that clenbuterol treatment after stroke onset causes enlarged microglia/MDMs and impairs their proliferation, resulting in reduced numbers of these cells in the peri-infarct cortex by 1.7-fold at 3 days after stroke. These changes in microglia/MDMs were associated with increased infarct volume in clenbuterol-treated animals. In mice that had the β2-adrenergic receptor specifically knocked out of microglia/MDMs, there was no change in morphology or numbers of these cells after stroke. However, knockdown of β2-adrenergic receptors in microglia and MDMs resulted in increased expression of TNFα and IL-10 in peri-infarct tissue, while stimulation of β2-adrenergic receptors with clenbuterol had the opposite effect, suppressing TNFα and IL-10 expression.

Conclusions

We identified β2-adrenergic receptor signaling as an important regulator of the neuroimmune response after ischemic stroke. Increased β2-adrenergic signaling after stroke onset generally suppressed the microglia/MDM response, reducing upregulation of both pro- and anti-inflammatory cytokines, and increasing stroke size. In contrast, diminished β2-adrenergic signaling in microglia/MDMs augmented both pro- and anti-inflammatory cytokine expression after stroke. The β2-adrenergic receptor may therefore present a therapeutic target for improving the post-stroke neuroinflammatory and repair process.

Sustained anti-inflammatory effects of TGF-β1 on microglia/macrophages

Ischemic brain injuries caused release of damage-associated molecular patterns (DAMPs) that activate microglia/macrophages (MG/MPs) by binding to Toll-like receptors. Using middle cerebral artery transiently occluded rats, we confirmed that MG/MPs expressed inducible nitric oxide synthase (iNOS) on 3days after reperfusion (dpr) in ischemic rat brain. iNOS expression almost disappeared on 7dpr when transforming growth factor-β1 (TGF-β1) expression was robustly increased. After transient incubation with TGF-β1 for 24h, rat primary microglial cells were incubated with lipopolysaccharide (LPS) and released NO level was measured. The NO release was persistently suppressed even 72h after removal of TGF-β1. The sustained TGF-β1 effects were not attributable to microglia-derived endogenous TGF-β1, as revealed by TGF-β1 knockdown and in vitro quantification studies. Then, boiled supernatants prepared from ischemic brain tissues showed the similar sustained inhibitory effects on LPS-treated microglial cells that were prevented by the TGF-β1 receptor-selective blocker SB525334. After incubation with TGF-β1 for 24h and its subsequent removal, LPS-induced phosphorylation of IκB kinases (IKKs), IκB degradation, and NFκB nuclear translocation were inhibited in a sustained manner. SB525334 abolished all these effects of TGF-β1. In consistent with the in vitro results, phosphorylated IKK-immunoreactivity was abundant in MG/MPs in ischemic brain lesion on 3dpr, whereas it was almost disappeared on 7dpr. The findings suggest that abundantly produced TGF-β1 in ischemic brain displays sustained anti-inflammatory effects on microglial cells by persistently inhibiting endogenous Toll-like receptor ligand-induced IκB degradation.

Assessing disease-modifying effects of norepinephrine in Down syndrome and Alzheimer's disease

Building upon the knowledge that a number of important brain circuits undergo significant degeneration in Alzheimer's disease, numerous recent studies suggest that the norepinephrine-ergic system in the brainstem undergoes significant alterations early in the course of both Alzheimer's disease and Down syndrome. Massive projections from locus coeruleus neurons to almost the entire brain, extensive innervation of brain capillaries, and widespread distribution of noradrenergic receptors enable the norepinephrine-ergic system to play a crucial role in neural processes, including cognitive function. These anatomical and functional characteristics support the role of the norepinephrine-ergic system as an important target for developing new therapies for cognitive dysfunction. Careful neuropathological examinations using postmortem samples from individuals with Alzheimer's disease have implicated the role of the norepinephrine-ergic system in the etiopathogenesis of Alzheimer's disease. Furthermore, numerous studies have supported the existence of a strong interaction between norepinephrine-ergic and neuroimmune systems. We explore the interaction between the two systems that could play a role in the disease-modifying effects of norepinephrine in Alzheimer's disease and Down syndrome.

Effects of hypnotic bromovalerylurea on microglial BV2 cells

An old sedative and hypnotic bromovalerylurea (BU) has anti-inflammatory effects. BU suppressed nitric oxide (NO) release and proinflammatory cytokine expression by lipopolysaccharide (LPS)-treated BV2 cells, a murine microglial cell line. However, BU did not inhibit LPS-induced nuclear translocation of nuclear factor-κB and subsequent transcription. BU suppressed LPS-induced phosphorylation of signal transducer and activator of transcription 1 (STAT1) and expression of interferon regulatory factor 1 (IRF1). The Janus kinase 1 (JAK1) inhibitor filgotinib suppressed the NO release much more weakly than that of BU, although filgotinib almost completely prevented LPS-induced STAT1 phosphorylation. Knockdown of JAK1, STAT1, or IRF1 did not affect the suppressive effects of BU on LPS-induced NO release by BV2 cells. A combination of BU and filgotinib synergistically suppressed the NO release. The mitochondrial complex I inhibitor rotenone, which did not prevent STAT1 phosphorylation or IRF1 expression, suppressed proinflammatory mediator expression less significantly than BU. BU and rotenone reduced intracellular ATP (iATP) levels to a similar extent. A combination of rotenone and filgotinib suppressed NO release by LPS-treated BV2 cells as strongly as BU. These results suggest that anti-inflammatory actions of BU may be attributable to the synergism of inhibition of JAK1/STAT1-dependent pathways and reduction in iATP level.

Evaluation of inflammation-related signaling events covering phosphorylation and nuclear translocation of proteins based on mass spectrometry data

Peripheral blood mononuclear cells are important players in immune regulation relying on a complex network of signaling pathways. In this study, we evaluated the power of label-free quantitative shotgun proteomics regarding the comprehensive characterization of signaling pathways in such primary cells by studying regulation of protein abundance, post-translational modifications and nuclear translocation events. The effects of inflammatory stimulation and the treatment of stimulated cells with dexamethasone were investigated. Therefore, a previously published dataset accessible via ProteomeXchange consisting of 6901 identified protein groups was re-evaluated. These data enabled us to comprehensively map the c-JUN, ERK5 and NF-κB signaling cascade in a semi-quantitative fashion. Without the application of any enrichment, 3775 highly confident phosphopeptides derived from 1249 proteins including 66 kinases were identified. Efficient subcellular fractionation and subsequent comparative analysis identified previously unrecognized inflammation-associated nuclear translocation events of proteins such as histone-modifying proteins, zinc finger proteins as well as transcription factors. Profound effects of inflammatory stimulation and dexamethasone treatment on histone H3 and ZFP161 localization represent novel findings and were verified by immunofluorescence. In conclusion, we demonstrate that multiple regulatory events resulting from the activity of signaling pathways can be determined out of untargeted shotgun proteomics data.

SIGNIFICANCE

Relevant functional events such as phosphorylation and nuclear translocation of proteins were extracted from high-resolution mass spectrometry data and provided additional biological information contained in shotgun proteomics data.

The hypnotic bromovalerylurea ameliorates 6-hydroxydopamine-induced dopaminergic neuron loss while suppressing expression of interferon regulatory factors by microglia

The low molecular weight organic compound bromovalerylurea (BU) has long been used as a hypnotic/sedative. In the present study, we found that BU suppressed mRNA expression of proinflammatory factors and nitric oxide release in lipopolysaccharide (LPS)-treated rat primary microglial cell cultures. BU prevented neuronal degeneration in LPS-treated neuron-microglia cocultures. The anti-inflammatory effects of BU were as strong as those of a synthetic glucocorticoid, dexamethasone. A rat hemi-Parkinsonian model was prepared by injecting 6-hydroxydopamine into the right striatum. BU was orally administered to these rats for 7 days, which ameliorated the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and alleviated motor deficits. BU suppressed the expression of mRNAs for interferon regulatory factors (IRFs) 1, 7 and 8 in the right (lesioned) ventral midbrain as well as those for proinflammatory mediators. BU increased mRNA expression of various neuroprotective factors, including platelet-derived growth factor and hepatocyte growth factor, but it did not increase expression of alternative activation (M2) markers. In microglial culture, BU suppressed the LPS-induced increase in expression of IRFs 1 and 8, and it reduced LPS-induced phosphorylation of JAK1 and STATs 1 and 3. Knockdown of IRFs 1 and 8 suppressed LPS-induced NO release by microglial cells. These results suggest that suppression of microglial IRF expression by BU prevents neuronal cell death in the injured brain region, where microglial activation occurs. Because many Parkinsonian patients suffer from sleep disorders, BU administration before sleep may effectively ameliorate neurological symptoms and alleviate sleep dysfunction.

Retinoic acid receptor agonist Am80 inhibits CXCL2 production from microglial BV-2 cells via attenuation of NF-κB signaling

Accumulating lines of evidence suggest that retinoic acid receptor agonists such as Am80 exerts anti-inflammatory actions in the central nervous system, although detailed mechanisms of the action remain largely unknown. Our previous findings suggest that Am80 provides therapeutic effect on intracerebral hemorrhage in mice via suppression of expression of chemokine (C-X-C motif) ligand 2 (CXCL2). Here we investigated the mechanisms of inhibitory action of Am80 on expression of CXCL2 and other pro-inflammatory factors in microglial BV-2 cells. Pretreatment with Am80 markedly suppressed lipopolysaccharide (LPS)-induced expression of CXCL2 mRNA and release of CXCL2 protein. Am80 had no effect on LPS-induced activation of p38 mitogen-activated protein kinase and extracellular signal-regulated kinase. On the other hand, Am80 prevented LPS-induced nuclear translocation of p65 subunit of NF-κB complex. In addition, total expression levels of p65 and IκBα proteins, as well as of mRNAs encoding p65 and IκBα, were lowered by Am80. Dependence of CXCL2 expression on NF-κB was confirmed by the effect of an NF-κB inhibitor caffeic acid phenethyl ester that abolished LPS-induced CXCL2 expression. Caffeic acid phenethyl ester also abolished LPS-induced expression of inducible nitric oxide synthase, interleukin-1β and tumor necrosis factor α, which may be relevant to the inhibitory effect of Am80 on expression of these pro-inflammatory factors. We additionally found that Am80 attenuated LPS-induced up-regulation of CD14, a co-receptor for Toll-like receptor 4 (TLR4). These results suggest that inhibitory effect on TLR4 signaling mediated by NF-κB pathway underlies the anti-inflammatory action of retinoic acid receptor agonists in microglia.

Causes, consequences, and cures for neuroinflammation mediated via the locus coeruleus: noradrenergic signaling system

Aside from its roles in as a classical neurotransmitter involved in regulation of behavior, noradrenaline (NA) has other functions in the CNS. This includes restricting the development of neuroinflammatory activation, providing neurotrophic support to neurons, and providing neuroprotection against oxidative stress. In recent years, it has become evident that disruption of physiological NA levels or signaling is a contributing factor to a variety of neurological diseases and conditions including Alzheimer's disease (AD) and Multiple Sclerosis. The basis for dysregulation in these diseases is, in many cases, due to damage occurring to noradrenergic neurons present in the locus coeruleus (LC), the major source of NA in the CNS. LC damage is present in AD, multiple sclerosis, and a large number of other diseases and conditions. Studies using animal models have shown that experimentally induced lesion of LC neurons exacerbates neuropathology while treatments to compensate for NA depletion, or to reduce LC neuronal damage, provide benefit. In this review, we will summarize the anti-inflammatory and neuroprotective actions of NA, summarize examples of how LC damage worsens disease, and discuss several approaches taken to treat or prevent reductions in NA levels and LC neuronal damage. Further understanding of these events will be of value for the development of treatments for AD, multiple sclerosis, and other diseases and conditions having a neuroinflammatory component. The classical neurotransmitter noradrenaline (NA) has critical roles in modulating behaviors including those involved in sleep, anxiety, and depression. However, NA can also elicit anti-inflammatory responses in glial cells, can increase neuronal viability by inducing neurotrophic factor expression, and can reduce neuronal damage due to oxidative stress by scavenging free radicals. NA is primarily produced by tyrosine hydroxylase (TH) expressing neurons in the locus coeruleus (LC), a relatively small brainstem nucleus near the IVth ventricle which sends projections throughout the brain and spinal cord. It has been known for close to 50 years that LC neurons are lost during normal aging, and that loss is exacerbated in neurological diseases including Parkinson's disease and Alzheimer's disease. LC neuronal damage and glial activation has now been documented in a variety of other neurological conditions and diseases, however, the causes of LC damage and cell loss remain largely unknown. A number of approaches have been developed to address the loss of NA and increased inflammation associated with LC damage, and several methods are being explored to directly minimize the extent of LC neuronal cell loss or function. In this review, we will summarize some of the consequences of LC loss, consider several factors that likely contribute to that loss, and discuss various ways that have been used to increase NA or to reduce LC damage. This article is part of the 60th Anniversary special issue.