The chemokine CXCL16 modulates neurotransmitter release in hippocampal CA1 area

Collagen VI: Role in synaptic transmission and seizure-related excitability

Collagen VI (Col-VI) is an extracellular matrix protein primarily known for its bridging role in connective tissues that has been suggested to play a neuroprotective role. In the present study we report increased mRNA and protein expression of Col-VI in the hippocampus and cortex at a late stage of epileptogenesis in a post-status epilepticus (SE) model of epilepsy and in brain tissue from patients with epilepsy. We further present a novel finding that exposure of mouse hippocampal slices to Col-VI augments paired-pulse facilitation in Schaffer collateral-CA1 excitatory synapses indicating decreased release probability of glutamate. In line with this finding, lack of Col-VI expression in the knock-out mice show paired-pulse depression in these synapses, suggesting increased release probability of glutamate. In addition, we observed dynamic changes in Col-VI blood plasma levels in rats after Kainate-induced SE, and increased levels of Col-VI mRNA and protein in autopsy or postmortem brain of humans suffering from epilepsy. Thus, our data indicate that elevated levels of ColVI following seizures leads to attenuated glutamatergic transmission, ultimately resulting in less overall network excitability. Presumably, increased Col-VI may act as part of endogenous compensatory mechanism against enhanced excitability during epileptogenic processes in the hippocampus, and could be further investigated as a potential functional biomarker of epileptogenesis, and/or a novel target for therapeutic intervention.

Sustained Microglial Activation Promotes Synaptic Loss and Neuronal Dysfunction after Recovery from ZIKV Infection

Zika virus (ZIKV), transmitted by Aedes mosquitoes, has been a global health concern since 2007. It primarily causes fetal microcephaly and neuronal defects through maternal transmission and induces neurological complications in adults. Recent studies report elevated proinflammatory cytokines and persistent neurological alterations post recovery, but the in vivo mechanisms remain unclear. In our study, viral RNA loads in the brains of mice infected with ZIKV peaked at 7 days post infection and returned to baseline by day 21, indicating recovery. RNA sequencing of the cerebral cortex at 7 and 21 days revealed upregulated genes related to neuroinflammation and microglial activation. Histological analyses indicated neuronal cell death and altered neurite morphology owing to severe neuroinflammation. Additionally, sustained microglial activation was associated with increased phospho-Tau levels, constituting a marker of neurodegeneration. These findings highlight how persistent microglial activation leads to neuronal dysfunction post ZIKV recovery, providing insights into the molecular pathogenesis of ZIKV-induced brain abnormalities.

An Ascending Excitatory Circuit from the Dorsal Raphe for Sensory Modulation of Pain

The dorsal raphe nucleus (DRN) is an important nucleus in pain regulation. However, the underlying neural pathway and the function of specific cell types remain unclear. Here, we report a previously unrecognized ascending facilitation pathway, the DRN to the mesoaccumbal dopamine (DA) circuit, for regulating pain. Chronic pain increased the activity of DRN glutamatergic, but not serotonergic, neurons projecting to the ventral tegmental area (VTA) (DRNGlu-VTA) in male mice. The optogenetic activation of DRNGlu-VTA circuit induced a pain-like response in naive male mice, and its inhibition produced an analgesic effect in male mice with neuropathic pain. Furthermore, we discovered that DRN ascending pathway regulated pain through strengthened excitatory transmission onto the VTA DA neurons projecting to the ventral part of nucleus accumbens medial shell (vNAcMed), thereby activated the mesoaccumbal DA neurons. Correspondingly, optogenetic manipulation of this three-node pathway bilaterally regulated pain behaviors. These findings identified a DRN ascending excitatory pathway that is crucial for pain sensory processing, which can potentially be exploited toward targeting pain disorders.

Cellular and molecular evidence that synaptic Schwann cells contribute to aging of mouse neuromuscular junctions

Age-induced degeneration of the neuromuscular junction (NMJ) is associated with motor dysfunction and muscle atrophy. While the impact of aging on the NMJ presynapse and postsynapse is well-documented, little is known about the changes perisynaptic Schwann cells (PSCs), the synaptic glia of the NMJ, undergo during aging. Here, we examined PSCs in young, middle-aged, and old mice in three muscles with different susceptibility to aging. Using light and electron microscopy, we found that PSCs acquire age-associated cellular features either prior to or at the same time as the onset of NMJ degeneration. Notably, we found that aged PSCs fail to completely cap the NMJ even though they are more abundant in old compared with young mice. We also found that aging PSCs form processes that either intrude into the synaptic cleft or guide axonal sprouts to innervate other NMJs. We next profiled the transcriptome of PSCs and other Schwann cells (SCs) to identify mechanisms altered in aged PSCs. This analysis revealed that aged PSCs acquire a transcriptional pattern previously shown to promote phagocytosis that is absent in other SCs. It also showed that aged PSCs upregulate unique pro-inflammatory molecules compared to other aged SCs. Interestingly, neither synaptogenesis genes nor genes that are typically upregulated by repair SCs were induced in aged PSCs or other SCs. These findings provide insights into cellular and molecular mechanisms that could be targeted in PSCs to stave off the deleterious effects of aging on NMJs.

Neuroimmunology of rabies: New insights into an ancient disease

Rabies is an ancient neuroinvasive viral (genus Lyssavirus, family Rhabdoviridae) disease affecting approximately 59,000 people worldwide. The central nervous system (CNS) is targeted, and rabies has a case fatality rate of almost 100% in humans and animals. Rabies is entirely preventable through proper vaccination, and thus, the highest incidence is typically observed in developing countries, mainly in Africa and Asia. However, there are still cases in European countries and the United States. Recently, demographic, increasing income levels, and the coronavirus disease 2019 (COVID-19) pandemic have caused a massive raising in the animal population, enhancing the need for preventive measures (e.g., vaccination, surveillance, and animal control programs), postexposure prophylaxis, and a better understanding of rabies pathophysiology to identify therapeutic targets, since there is no effective treatment after the onset of clinical manifestations. Here, we review the neuroimmune biology and mechanisms of rabies. Its pathogenesis involves a complex and poorly understood modulation of immune and brain functions associated with metabolic, synaptic, and neuronal impairments, resulting in fatal outcomes without significant histopathological lesions in the CNS. In this context, the neuroimmunological and neurochemical aspects of excitatory/inhibitory signaling (e.g., GABA/glutamate crosstalk) are likely related to the clinical manifestations of rabies infection. Uncovering new links between immunopathological mechanisms and neurochemical imbalance will be essential to identify novel potential therapeutic targets to reduce rabies morbidity and mortality.

Minocycline treatment improves cognitive and functional plasticity in a preclinical mouse model of major depressive disorder

Major depressive disorder (MDD) is a chronic, recurring, and potentially life-threatening illness, which affects over 300 million people worldwide. MDD affects not only the emotional and social domains but also cognition. However, the currently available treatments targeting cognitive deficits in MDD are limited. Minocycline, an antibiotic with anti-inflammatory properties recently identified as a potential antidepressant, has been shown to attenuate learning and memory deficits in animal models of cognitive impairment. Here, we explored whether minocycline recovers the deficits in cognition in a mouse model of depression. C57BL6/J adult male mice were exposed to two weeks of chronic unpredictable mild stress to induce a depressive-like phenotype. Immediately afterward, mice received either vehicle or minocycline for three weeks in standard housing conditions. We measured anhedonia as a depressive-like response, and place learning to assess cognitive abilities. We also recorded long-term potentiation (LTP) as an index of hippocampal functional plasticity and ran immunohistochemical assays to assess microglial proportion and morphology. After one week of treatment, cognitive performance in the place learning test was significantly improved by minocycline, as treated mice displayed a higher number of correct responses when learning novel spatial configurations. Accordingly, minocycline-treated mice displayed higher LTP compared to controls. However, after three weeks of treatment, no difference between treated and control animals was found for behavior, neural plasticity, and microglial properties, suggesting that minocycline has a fast but short effect on cognition, without lasting effects on microglia. These findings together support the usefulness of minocycline as a potential treatment for cognitive impairment associated with MDD.

A novel transgenic mouse model expressing primate-specific nuclear choline acetyltransferase: insights into potential cholinergic vulnerability

The acetylcholine (ACh) synthesizing enzyme choline acetyltransferase (ChAT) is an important cholinergic neuronal marker whose levels and/or activity are reduced in physiological and pathological aging. One isoform of ChAT, 82-kDa ChAT, is expressed only in primates and found primarily in nuclei of cholinergic neurons in younger individuals, but this protein becomes mostly cytoplasmic with increasing age and in Alzheimer's disease (AD). Previous studies suggest that 82-kDa ChAT may be involved in regulating gene expression during cellular stress. Since it is not expressed in rodents, we developed a transgenic mouse model that expresses human 82-kDa ChAT under the control of an Nkx2.1 driver. Behavioral and biochemical assays were used to phenotype this novel transgenic model and elucidate the impact of 82-kDa ChAT expression. The 82-kDa ChAT transcript and protein were expressed predominantly in basal forebrain neurons and subcellular distribution of the protein recapitulated the age-related pattern found previously in human necropsy brains. Older 82-kDa ChAT-expressing mice presented with better age-related memory and inflammatory profiles. In summary, we established a novel transgenic mouse expressing 82-kDa ChAT that is valuable for studying the role of this primate-specific cholinergic enzyme in pathologies associated with cholinergic neuron vulnerability and dysfunction.

Microglial diversity along the hippocampal longitudinal axis impacts synaptic plasticity in adult male mice under homeostatic conditions

The hippocampus is a plastic brain area that shows functional segregation along its longitudinal axis, reflected by a higher level of long-term potentiation (LTP) in the CA1 region of the dorsal hippocampus (DH) compared to the ventral hippocampus (VH), but the mechanisms underlying this difference remain elusive. Numerous studies have highlighted the importance of microglia-neuronal communication in modulating synaptic transmission and hippocampal plasticity, although its role in physiological contexts is still largely unknown. We characterized in depth the features of microglia in the two hippocampal poles and investigated their contribution to CA1 plasticity under physiological conditions. We unveiled the influence of microglia in differentially modulating the amplitude of LTP in the DH and VH, showing that minocycline or PLX5622 treatment reduced LTP amplitude in the DH, while increasing it in the VH. This was recapitulated in Cx3cr1 knockout mice, indicating that microglia have a key role in setting the conditions for plasticity processes in a region-specific manner, and that the CX3CL1-CX3CR1 pathway is a key element in determining the basal level of CA1 LTP in the two regions. The observed LTP differences at the two poles were associated with transcriptional changes in the expression of genes encoding for Il-1, Tnf-α, Il-6, and Bdnf, essential players of neuronal plasticity. Furthermore, microglia in the CA1 SR region showed an increase in soma and a more extensive arborization, an increased prevalence of immature lysosomes accompanied by an elevation in mRNA expression of phagocytic markers Mertk and Cd68 and a surge in the expression of microglial outward K⁺ currents in the VH compared to DH, suggesting a distinct basal phenotypic state of microglia across the two hippocampal poles. Overall, we characterized the molecular, morphological, ultrastructural, and functional profile of microglia at the two poles, suggesting that modifications in hippocampal subregions related to different microglial statuses can contribute to dissect the phenotypical aspects of many diseases in which microglia are known to be involved.

Transcriptome Profile During Rabies Virus Infection: Identification of Human CXCL16 as a Potential New Viral Target

Rabies virus (RABV), the causative agent for rabies disease is still presenting a major public health concern causing approximately 60,000 deaths annually. This neurotropic virus (genus Lyssavirus, family Rhabdoviridae) induces an acute and almost always fatal form of encephalomyelitis in humans. Despite the lethal consequences associated with clinical symptoms of rabies, RABV limits neuro-inflammation without causing major histopathological lesions in humans. Nevertheless, information about the mechanisms of infection and cellular response in the central nervous system (CNS) remain scarce. Here, we investigated the expression of inflammatory genes involved in immune response to RABV (dog-adapted strain Tha) in mice, the most common animal model used to study rabies. To better elucidate the pathophysiological mechanisms during natural RABV infection, we compared the inflammatory transcriptome profile observed at the late stage of infection in the mouse brain (cortex and brain stem/cerebellum) with the ortholog gene expression in post-mortem brain biopsies of rabid patients. Our data indicate that the inflammatory response associated with rabies is more pronounced in the murine brain compared to the human brain. In contrast to murine transcription profiles, we identified CXC motif chemokine ligand 16 (CXCL16) as the only significant differentially expressed gene in post-mortem brains of rabid patients. This result was confirmed in vitro, in which Tha suppressed interferon alpha (IFN-α)-induced CXCL16 expression in human CNS cell lines but induced CXCL16 expression in IFN-α-stimulated murine astrocytes. We hypothesize that RABV-induced modulation of the CXCL16 pathway in the brain possibly affects neurotransmission, natural killer (NK) and T cell recruitment and activation. Overall, we show species-specific differences in the inflammatory response of the brain, highlighted the importance of understanding the potential limitations of extrapolating data from animal models to humans.

The semantics of microglia activation: neuroinflammation, homeostasis, and stress

Microglia are emerging as critical regulators of neuronal function and behavior in nearly every area of neuroscience. Initial reports focused on classical immune functions of microglia in pathological contexts, however, immunological concepts from these studies have been applied to describe neuro-immune interactions in the absence of disease, injury, or infection. Indeed, terms such as 'microglia activation' or 'neuroinflammation' are used ubiquitously to describe changes in neuro-immune function in disparate contexts; particularly in stress research, where these terms prompt undue comparisons to pathological conditions. This creates a barrier for investigators new to neuro-immunology and ultimately hinders our understanding of stress effects on microglia. As more studies seek to understand the role of microglia in neurobiology and behavior, it is increasingly important to develop standard methods to study and define microglial phenotype and function. In this review, we summarize primary research on the role of microglia in pathological and physiological contexts. Further, we propose a framework to better describe changes in microglia1 phenotype and function in chronic stress. This approach will enable more precise characterization of microglia in different contexts, which should facilitate development of microglia-directed therapeutics in psychiatric and neurological disease.

Gestational exposure to PM2.5 leads to cognitive dysfunction in mice offspring via promoting HMGB1-NLRP3 axis mediated hippocampal inflammation

PM_2.5 is recently identified as a kind of material possessing severe biohazard. It can enter human body and exerts pathological effects on lung, eyes, and the central nervous system (CNS). Maternal exposure to PM_2.5 can affect neural development and cause cognitive decline in offspring, with the underlying mechanisms unclear, however. The inflammasome monitors and responds to biological stressors, with HMGB1-NLRP3 inflammatory axis as an essential pathophysiological player outside the brain. The present work is to investigate its role in cognitive impairment induced by gestational exposure to PM_2.5 in mice offspring. We found that HMGB1-NLRP3 pathway was activated in the hippocampus of mice offspring by gestational exposure to PM_2.5 in a dose-dependent manner, with protein levels of HMGB1, NLRP3, and cleaved caspase-1 as approximately three times as high as those of control. And down-regulating HMGB1 during pregnancy could alleviate the resultant impairment on learning and working memory as well as hippocampal neurons, up-regulate the synapse related proteins of SYP and PSD-95 and correct the increased expression of 5-HT2A to comparable levels to control, as well as inhibiting the activation of microglia and decreasing the expression of HMGB1 and Iba1/HMGB1 double positive cells in the hippocampus of mice offspring. Meanwhile, protein levels of NLRP3, cleaved caspase-1, IL-1β and IL-18, as well as TLR4, phosphorylated NF_-κB, and MAPKs, were almost down-regulated to those of control. Therefore, HMGB1 intervention inhibits the NLRP3 inflammasome mediated hippocampal inflammatory response through TLR4/MAPKs/NF-κB signaling pathway, alleviating PM_2.5-induced cognitive dysfunction. Further in vitro results suggest that PM_2.5 can activate microglia and HMGB1-NLRP3 inflammatory axis. Pretreatment with HMGB1 inhibitor significantly reduced the phosphorylation of MAPKs and NF-κB, and inhibited the inflammatory response mediated by NLRP3 inflammasome similarly to those in vivo. These results suggest that PM_2.5 exposure promotes the inflammatory response in hippocampus mediated by HMGB1-NLRP3 inflammatory axis in microglia, resulting in cognitive dysfunction in offspring, which could be alleviated by simultaneous HMGB1 suppression. These findings provide a theoretical basis for preventing cognitive impairment in offspring caused by environmental pollution during pregnancy.

Cellular, synaptic, and network effects of chemokines in the central nervous system and their implications to behavior

Accumulating evidence highlights chemokines as key mediators of the bidirectional crosstalk between neurons and glial cells aimed at preserving brain functioning. The multifaceted role of these immune proteins in the CNS is mirrored by the complexity of the mechanisms underlying its biological function, including biased signaling. Neurons, only in concert with glial cells, are essential players in the modulation of brain homeostatic functions. Yet, attempts to dissect these complex multilevel mechanisms underlying coordination are still lacking. Therefore, the purpose of this review is to summarize the current knowledge about mechanisms underlying chemokine regulation of neuron-glia crosstalk linking molecular, cellular, network, and behavioral levels. Following a brief description of molecular mechanisms by which chemokines interact with their receptors and then summarizing cellular patterns of chemokine expression in the CNS, we next delve into the sequence and mechanisms of chemokine-regulated neuron-glia communication in the context of neuroprotection. We then define the interactions with other neurotransmitters, neuromodulators, and gliotransmitters. Finally, we describe their fine-tuning on the network level and the behavioral relevance of their modulation. We believe that a better understanding of the sequence and nature of events that drive neuro-glial communication holds promise for the development of new treatment strategies that could, in a context- and time-dependent manner, modulate the action of specific chemokines to promote brain repair and reduce the neurological impairment.

The role of meningeal populations of type II innate lymphoid cells in modulating neuroinflammation in neurodegenerative diseases

Recent research into meningeal lymphatics has revealed a never-before appreciated role of type II innate lymphoid cells (ILC2s) in modulating neuroinflammation in the central nervous system (CNS). To date, the role of ILC2-mediated inflammation in the periphery has been well studied. However, the exact distribution of ILC2s in the CNS and therefore their putative role in modulating neuroinflammation in neurodegenerative diseases such as Alzheimer's disease (AD), multiple sclerosis (MS), Parkinson's disease (PD), and major depressive disorder (MDD) remain highly elusive. Here, we review the current evidence of ILC2-mediated modulation of neuroinflammatory cues (i.e., IL-33, IL-25, IL-5, IL-13, IL-10, TNFα, and CXCL16-CXCR6) within the CNS, highlight the distribution of ILC2s in both the periphery and CNS, and discuss some challenges associated with cell type-specific targeting that are important for therapeutics. A comprehensive understanding of the roles of ILC2s in mediating and responding to inflammatory cues may provide valuable insight into potential therapeutic strategies for many dementia-related disorders.

T lymphocytes and preeclampsia: The potential role of T-cell subsets and related MicroRNAs in the pathogenesis of preeclampsia

Innate and adaptive immune systems have a crucial role in initiating and progressing some pregnancy disorders such as preeclampsia (PE), which is one of the pregnancy-specific disorders that could result in neonatal and maternal morbidity and mortality. The dysregulation of the spiral artery and inadequate trophoblast invasion lead to PE symptoms through producing various inflammatory cytokines and anti-angiogenic factors from the placenta. T lymphocytes play a special role in the epithelium and stroma of the human endometrium. CD4+ T helper (Th) cells, Th1/Th2, and Th17/T regulatory (Treg) balance mainly contribute to the establishment of a pregnancy-favorable environment. This review examined the dysregulation of some cytokines produced from T cells, the dysregulation of the transcription factors of Th cells, the expression of chemokine receptors on T cells, as well as the effects of some factors including vitamin D on the activity of T cells, and finally, the dysregulation of various miRNAs related to T cells, which could cause PE.

Selecting antidepressants according to a drug-by-environment interaction: A comparison of fluoxetine and minocycline effects in mice living either in enriched or stressful conditions

Selective serotonin reuptake inhibitors (SSRIs) are the first-line treatment for major depressive disorder. It has been recently proposed that these drugs, by enhancing neural plasticity, amplify the influences of the living conditions on mood. Consequently, SSRI outcome depends on the quality of the environment, improving symptomatology mainly in individuals living in favorable conditions. In adverse conditions, drugs with a different mechanism of action might have higher efficacy. The antibiotic minocycline, with neuroprotective and anti-inflammatory properties, has been recently proposed as a novel potential antidepressant treatment. To explore the drug-by-environment interaction, we compared the effects on depressive-like behavior and neural plasticity of the SSRI fluoxetine and minocycline in enriched and stressful conditions. We first exposed C57BL/6 adult female mice to 14 days of chronic unpredictable mild stress to induce a depressive-like profile. Afterward, mice received vehicle, fluoxetine, or minocycline for 21 days, while exposed to either enriched or stressful conditions. During the first five days, fluoxetine led to an improvement in enrichment but not in stress. By contrast, minocycline led to an improvement in both conditions. After 21 days, all groups showed a significant improvement in enrichment while fluoxetine worsened the depressive like behavior in stress. The effects of the drugs on neural plasticity, measured as long-term potentiation, were also environment-dependent. Overall, we show that the environment affects fluoxetine but not minocycline outcome, indicating that the latter represents a potential alternative to SSRIs to treat depressed patients living in adverse conditions. From a translation perspective, our finding call for considering the drug-by-environment interaction to select the most effective pharmacological treatment.

Prenatal Alcohol Exposure in Rats Diminishes Postnatal Cxcl16 Chemokine Ligand Brain Expression

Maternal ethanol consumption during pregnancy is one of the main causes of Neurodevelopmental disorders (NDD). Prenatal alcohol exposure (PAE) produces several adverse manifestations. Even low or moderate intake has been associated with long-lasting behavioral and cognitive impairment in offspring. In this study we examined the gene expression profile in the rat nucleus accumbens using microarrays, comparing animals exposed prenatally to ethanol and controls. Microarray gene expression showed an overall downward regulatory effect of PAE. Gene cluster analysis reveals that the gene groups most affected are related to transcription regulation, transcription factors and homeobox genes. We focus on the expression of the C-X-C motif chemokine ligand 16 (Cxcl16) which was differentially expressed. There is a significant reduction in the expression of this chemokine throughout the brain under PAE conditions, evidenced here by quantitative polymerase chain reaction qPCR and immunohistochemistry. Chemokines are involved in neuroprotection and implicated in alcohol-induced brain damage and neuroinflammation in the developing central nervous system (CNS), therefore, the significance of the overall decrease in Cxcl16 expression in the brain as a consequence of PAE may reflect a reduced ability in neuroprotection against subsequent conditions, such as excitotoxic damage, inflammatory processes or even hypoxic-ischemic insult.

Use of knockout mice to explore CNS effects of adenosine

The initial exploration using pharmacological tools of the role of adenosine receptors in the brain, concluded that adenosine released as such acted on A₁R to inhibit excitability and glutamate release from principal neurons throughout the brain and that adenosine A_2A receptors (A_2AR) were striatal-'specific' receptors controlling dopamine D₂R. This indicted A₁R as potential controllers of neurodegeneration and A_2AR of psychiatric conditions. Global knockout of these two receptors questioned the key role of A₁R and instead identified extra-striatal A_2AR as robust controllers of neurodegeneration. Furthermore, transgenic lines with altered metabolic sources of adenosine revealed a coupling of ATP-derived adenosine to activate A_2AR and a role of A₁R as a hurdle to initiate neurodegeneration. Additionally, cell-selective knockout of A_2AR unveiled the different roles of A_2AR in different cell types (neurons/astrocytes) in different portions of the striatal circuits (dorsal versus lateral) and in different brain areas (hippocampus/striatum). Finally, a new transgenic mouse line with deletion of all adenosine receptors seems to indicate a major allostatic rather than homeostatic role of adenosine and may allow isolating P2R-mediated responses to unravel their role in the brain, a goal close to heart of Geoffrey Burnstock, to whom we affectionately dedicate this review.

Targeting Chemokines and Chemokine Receptors in Multiple Sclerosis and Experimental Autoimmune Encephalomyelitis

Multiple sclerosis (MS) is an immune-mediated and neurodegenerative disorder that results in inflammation and demyelination of the central nervous system (CNS). MS symptoms include walking difficulties, visual weakening, as well as learning and memory impairment, thus affecting the quality of the patient's life. Chemokines and chemokine receptors are expressed on the immune cells as well as the CNS resident cells. Several sets of chemokine receptors and their ligands tend to be pathogenic players in MS, including CCL2, CCL3, CCL4, CCL5, CCL7, CCL8, CCL11, CCL17, CCL19, CCL21, CCL22, CXCL1, CXCL8, CXCL9, CXCL10, CXCL11, and CXCL16. Furthermore, current modulatory drugs that are used in the treatment of MS and its animal model, the experimental autoimmune encephalomyelitis (EAE), affect the expression of several chemokine and chemokine receptors. In this review, we highlight the pathogenic roles of chemokines and their receptors as well as utilizing them as potential therapeutic targets through selective agents, such as specific antibodies and receptor blockers, or indirectly through MS or EAE immunomodulatory drugs.

Neuroimmune Mechanisms in Signaling of Pain During Acute Kidney Injury (AKI)

Acute kidney injury (AKI) is a significant global health concern. The primary causes of AKI include ischemia, sepsis and nephrotoxicity. The unraveled interface between nervous system and immune response with specific focus on pain pathways is generating a huge interest in reference to AKI. The nervous system though static executes functions by nerve fibers throughout the body. Neuronal peptides released by nerves effect the immune response to mediate the hemodynamic system critical to the functioning of kidney. Pain is the outcome of cellular cross talk between nervous and immune systems. The widespread release of neuropeptides, neurotransmitters and immune cells contribute to bidirectional neuroimmune cross talks for pain manifestation. Recently, we have reported pain pathway genes that may pave the way to better understand such processes during AKI. An auxiliary understanding of the functions and communications in these systems will lead to novel approaches in pain management and treatment through the pathological state, specifically during acute kidney injury.

CXCL16/CXCR6 interaction promotes endometrial decidualization via the PI3K/AKT pathway

Decidualization renders the endometrium transiently receptive to an implanting blastocyst although the underlying mechanisms remain incompletely understood. The aim of this study was to determine the role of chemokine CXCL16 and its receptor CXCR6 in the decidualization during pregnancy. Here, the expression of CXCL16 was investigated in endometrial tissues, decidua and placenta in this study. Compared with endometrial tissue, protein expression of CXCL16 was significantly higher in tissues from the fertile control samples, especially in villus. Meanwhile, the primary trophoblast cells and decidual stromal cells (DSCs) secreted more CXCL16 and expressed higher CXCR6 compared to endometrial stromal cells (ESCs) in vitro. Stimulation with the inducer of decidualization (8-bromoadenosine 3',5'-cyclic with medroxyprogesterone acetate, 8-Br-cAMP plus MPA) significantly upregulated the expression of CXCL16 and CXCR6 in ESCs in vitro. After treatment with exogenous recombinant human CXCL16 (rhCXCL16) or trophoblast-secreted CXLC16, decidualised ESCs showed a significant decidual response, mainly characterised by increased prolactin (PRL) secretion. Simultaneously, PI3K/PDK1/AKT/Cyclin D1 pathway in decidualised ESCs were activated by rhCXCL16, and AKT inhibitor GS 690693 abolished the PRL secretion of ESCs that was triggered by rhCXCL16. Finally, the impaired CXCL16/CXCR6 expression could be observed at the maternal-foetal interface from patients who have experienced spontaneous abortion. This study suggests that the CXCL16/CXCR6 axis contributes to the progression of ESC decidualization by activating PI3K/PDK1/AKT/Cyclin D1 pathway. It unveils a new paradigm at the maternal-foetal interface in which CXCL16 is an initiator for the molecular crosstalk that enhances decidualization of ESCs.

Microglia: sculptors of neuropathic pain?

Neuropathic pain presents a huge societal and individual burden. The limited efficacy of current analgesics, diagnostic markers and clinical trial outcome measures arises from an incomplete understanding of the underlying mechanisms. A large and growing body of evidence has established the important role of microglia in the onset and possible maintenance of neuropathic pain, and these cells may represent an important target for future therapy. Microglial research has further revealed their important role in structural remodelling of the nervous system. In this review, we aim to explore the evidence for microglia in sculpting nervous system structure and function, as well as their important role in neuropathic pain, and finally integrate these studies to synthesize a new model for microglia in somatosensory circuit remodelling, composed of six key and inter-related mechanisms. Summarizing the mechanisms through which microglia modulate nervous system structure and function helps to frame a better understanding of neuropathic pain, and provide a clear roadmap for future research.

The Role of Selected Chemokines and Their Receptors in the Development of Gliomas

Among heterogeneous primary tumors of the central nervous system (CNS), gliomas are the most frequent type, with glioblastoma multiforme (GBM) characterized with the worst prognosis. In their development, certain chemokine/receptor axes play important roles and promote proliferation, survival, metastasis, and neoangiogenesis. However, little is known about the significance of atypical receptors for chemokines (ACKRs) in these tumors. The objective of the study was to present the role of chemokines and their conventional and atypical receptors in CNS tumors. Therefore, we performed a thorough search for literature concerning our investigation via the PubMed database. We describe biological functions of chemokines/chemokine receptors from various groups and their significance in carcinogenesis, cancer-related inflammation, neo-angiogenesis, tumor growth, and metastasis. Furthermore, we discuss the role of chemokines in glioma development, with particular regard to their function in the transition from low-grade to high-grade tumors and angiogenic switch. We also depict various chemokine/receptor axes, such as CXCL8-CXCR1/2, CXCL12-CXCR4, CXCL16-CXCR6, CX3CL1-CX3CR1, CCL2-CCR2, and CCL5-CCR5 of special importance in gliomas, as well as atypical chemokine receptors ACKR1-4, CCRL2, and PITPMN3. Additionally, the diagnostic significance and usefulness of the measurement of some chemokines and their receptors in the blood and cerebrospinal fluid (CSF) of glioma patients is also presented.

The role of CXC chemokine ligand 16 in physiological and pathological pregnancies

The survival and development of a semi-allogeneic fetus during pregnancy require the involvement of a series of cytokines and immune cells. Chemokines are a type of special cytokine those were originally described as having a role in leukocyte trafficking. CXC chemokine ligand (CXCL) 16 is a member of the chemokine family, and CXC chemokine receptor (CXCR) 6 is its sole receptor. Emerging evidence has shown that CXCL16/CXCR6 is expressed at the maternal-fetal interface, by cell types that include trophoblast cells, decidual stroma cells, and decidual immune cells (eg, monocytes, γδT cells, and natural killer T (NKT) cells). The regulation of expression of CXCL16 is quite complex, and this process involves a multitude of factors. CXCL16 exerts a critical role in the establishment of a successful pregnancy through a series of molecular interactions at the maternal-fetal interface. However, an abnormal expression of CXCL16 is associated with certain pathological states associated with pregnancy, including recurrent miscarriage, pre-eclampsia, and gestational diabetes mellitus (GDM). In the present review, the expression and pleiotropic roles of CXCL16 under conditions of physiological and pathological pregnancy are systematically discussed.

The Potential Role of Dysfunctions in Neuron-Microglia Communication in the Pathogenesis of Brain Disorders

The bidirectional communication between neurons and microglia is fundamental for the proper functioning of the central nervous system (CNS). Chemokines and clusters of differentiation (CD) along with their receptors represent ligand-receptor signalling that is uniquely important for neuron - microglia communication. Among these molecules, CX3CL1 (fractalkine) and CD200 (OX-2 membrane glycoprotein) come to the fore because of their cell-type-specific localization. They are principally expressed by neurons when their receptors, CX3CR1 and CD200R, respectively, are predominantly present on the microglia, resulting in the specific axis which maintains the CNS homeostasis. Disruptions to this balance are suggested as contributors or even the basis for many neurological diseases. In this review, we discuss the roles of CX3CL1, CD200 and their receptors in both physiological and pathological processes within the CNS. We want to underline the critical involvement of these molecules in controlling neuron - microglia communication, noting that dysfunctions in their interactions constitute a key factor in severe neurological diseases, such as schizophrenia, depression and neurodegeneration-based conditions.

Inhibiting the LPS-induced enhancement of mEPSC frequency in superficial dorsal horn neurons may serve as an electrophysiological model for alleviating pain

Pain is a major primary health care problem. Emerging studies show that inhibition of spinal microglial activation reduces pain. However, the precise mechanisms by which microglial activation contributes to nociceptive synaptic transmission remain unclear. In this study, we measured spontaneous synaptic activity of miniature excitatory postsynaptic currents (mEPSCs) in rat spinal cord superficial dorsal horn (SDH, laminae I and II) neurons. Lipopolysaccharide (LPS) and adenosine triphosphate (ATP) increased the frequency, but not amplitude, of mEPSCs in SDH neurons. Microglial inhibitors minocycline and paeonol, as well as an astrocyte inhibitor, a P2Y1 receptor (P2Y1R) antagonist, and a metabotropic glutamate receptor 5 (mGluR5) antagonist, all prevented LPS-induced enhancement of mEPSC frequency. In mouse behavioral testing, minocycline and paeonol effectively reduced acetic acid-induced writhing and LPS-induced hyperalgesia. These results indicate that LPS-activated microglia release ATP, which stimulates astrocyte P2Y1Rs to release glutamate, triggering presynaptic mGluR5 receptors and increasing presynaptic glutamate release, leading to an increase in mEPSC frequency and enhancement of nociceptive transmission in SDH neurons. We propose that these effects can serve as a new electrophysiological model for evaluating pain. Moreover, we predict that pharmacologic agents capable of inhibiting the LPS-induced enhancement of mEPSC frequency in SDH neurons will have analgesic effects.

Chemokines: Key Molecules that Orchestrate Communication among Neurons, Microglia and Astrocytes to Preserve Brain Function

In the CNS, chemokines and chemokine receptors are involved in pleiotropic physiological and pathological activities. Several evidences demonstrated that chemokine signaling in the CNS plays key homeostatic roles and, being expressed on neurons, glia and endothelial cells, chemokines mediate the bidirectional cross-talk among parenchymal cells. An efficient communication between neurons and glia is crucial to establish and maintain a healthy brain environment which ensures normal functionality. Glial cells behave as active sensors of environmental changes induced by neuronal activity or detrimental insults, supporting and exerting neuroprotective activities. In this review we summarize the evidence that chemokines (CXCL12, CX3CL1, CXCL16 and CCL2) modulate neuroprotective processes upon different noxious stimuli and participate to orchestrate neurons-microglia-astrocytes action to preserve and limit brain damage. This article is part of a Special Issue entitled: Honoring Ricardo Miledi - outstanding neuroscientist of XX-XXI centuries.

The serum level of soluble CXCL16 is increased in preeclampsia and associated with hepatic/renal damage

OBJECTIVE

To compare the serum level of the chemokine, CXCL 16, in preeclamptic and healthy pregnant patients.

METHODS

This prospective case control study was conducted between January and December 2018 in a tertiary level hospital. The study group was formed of 70 pregnant women diagnosed with preeclampsia, and the control group was formed of 70 healthy pregnant women matched to the study group in respect of age, gestational week and body mass index (BMI). The study group was separated into two subgroups of mild preeclampsia (n = 35) and severe preeclampsia (n = 35). The groups were compared in terms of demographic and clinical parameters and the levels of serum CXCL 16.

RESULTS

No statistically significant difference was determined between the study and control groups in respect of maternal age, gravida, parity, BMI, and gestational age at sampling. Neonatal birth weight was significantly lower in the study group than in the control group. Mean serum alanine aminotransferase (ALT), aspartate amino transferase (AST) and creatinine levels of the study group were significantly higher than those of the control group (p < .05 for all). There was a statistically significant difference between the study and control groups regarding the mean platelet count. Compared to the control group, the severe and mild preeclampsia groups had a significantly higher serum level of CXCL 16. The serum level of CXCL 16 was significantly higher in patients with severe preeclampsia than in patients with mild preeclampsia (2.94 ± 3.89 pg mL^-1 vs. 1.08 ± 1.87 pg mL^-1, p = .14). Correlation analysis revealed a significant positive correlation of serum CXCL 16 level with serum ALT level (r = 0.320, p ≤ .001) and serum AST level (r = 0.373, p ≤ .001) and serum creatinine level (r = 0.279, p = .01) in both groups. High values indicated presence of preeclampsia, with a diagnostic cut-off point of 0.225, sensitivity of 75.7% and specificity of 72.9% for CXCL 16 (area under curve: 0.820, p < .001 CI: 0.753-0.888).

CONCLUSIONS

This is the first study in literature to show a significantly higher level of CXCL 16 in patients with severe preeclampsia compared to those with mild preeclampsia. The study can also be considered of value in respect of showing that CXCL 16 could play a role in the etiopathogenesis of preeclampsia and the emergence of renal-hepatic damage. Blocking the CXCL 16/CXCR six axis in preeclampsia treatment could lay the ground for the development of new drugs which could be used in the treatment of preeclampsia.

Innate Immune Signaling and Alcohol Use Disorders

Innate immune signaling is an important feature in the pathology of alcohol use disorders. Alcohol abuse causes persistent innate immune activation in the brain. This is seen in postmortem human alcoholic brain specimens, as well as in primate and rodent models of alcohol consumption. Further, in vitro models of alcohol exposure in neurons and glia also demonstrate innate immune activation. The activation of the innate immune system seems to be important in the development of alcohol use pathology, as anti-immune therapies reduce pathology and ethanol self-administration in rodent models. Further, innate immune activation has been identified in each of the stages of addiction: binge/intoxication, withdrawal/negative affect, and preoccupation/craving. This suggests that innate immune activation may play a role both in the development and maintenance of alcoholic pathology. In this chapter, we discuss the known contributions of innate immune signaling in the pathology of alcohol use disorders, and present potential therapeutic interventions that may be beneficial for alcohol use disorders.

Increased CXCL13 and CXCR5 in Anterior Cingulate Cortex Contributes to Neuropathic Pain-Related Conditioned Place Aversion

Pain consists of sensory-discriminative and emotional-affective components. The anterior cingulate cortex (ACC) is a critical brain area in mediating the affective pain. However, the molecular mechanisms involved remain largely unknown. Our recent study indicated that C-X-C motif chemokine 13 (CXCL13) and its sole receptor CXCR5 are involved in sensory sensitization in the spinal cord after spinal nerve ligation (SNL). Whether CXCL13/CXCR5 signaling in the ACC contributes to the pathogenesis of pain-related aversion remains unknown. Here, we showed that SNL increased the CXCL13 level and CXCR5 expression in the ACC after SNL. Knockdown of CXCR5 by microinjection of Cxcr5 shRNA into the ACC did not affect SNL-induced mechanical allodynia but effectively alleviated neuropathic pain-related place avoidance behavior. Furthermore, electrophysiological recording from layer II-III neurons in the ACC showed that SNL increased the frequency and amplitude of spontaneous excitatory postsynaptic currents (sEPSCs), decreased the EPSC paired-pulse ratio, and increased the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor/N-methyl-D-aspartate receptor ratio, indicating enhanced glutamatergic synaptic transmission. Finally, superfusion of CXCL13 onto ACC slices increased the frequency and amplitude of spontaneous EPSCs. Pre-injection of Cxcr5 shRNA into the ACC reduced the increase in glutamatergic synaptic transmission induced by SNL. Collectively, these results suggest that CXCL13/CXCR5 signaling in the ACC is involved in neuropathic pain-related aversion via synaptic potentiation.

CXCL16/CXCR6 Axis Drives Microglia/Macrophages Phenotype in Physiological Conditions and Plays a Crucial Role in Glioma

Microglia are patrolling cells that sense changes in the brain microenvironment and respond acquiring distinct phenotypes that can be either beneficial or detrimental for brain homeostasis. Anti-inflammatory microglia release soluble factors that might promote brain repair; however, in glioma, anti-inflammatory microglia dampen immune response and promote a brain microenvironment that foster tumor growth and invasion. The chemokine CXCL16 is expressed in the brain, where it is neuroprotective against brain ischemia, and it has been found to be over-expressed in glioblastoma (GBM). Considering that CXCL16 specific receptor CXCR6 is diffusely expressed in the brain including in microglia cells, we wanted to investigate the role of CXCL16 in the modulation of microglia cell activity and phenotype, and in the progression of glioma. Here we report that CXCL16 drives microglia polarization toward an anti-inflammatory phenotype, also restraining microglia polarization toward an inflammatory phenotype upon LPS and IFNγ stimulation. In the context of glioma, we demonstrate that CXCL16 released by tumor cells is determinant in promoting glioma associated microglia/macrophages (GAMs) modulation toward an anti-inflammatory/pro-tumor phenotype, and that cxcr6ko mice, orthotopically implanted into the brain with GL261 glioma cells,survive longer compared to wild-type mice. We also describe that CXCL16/CXCR6 signaling acts directly on mouse glioma cells, as well as human primary GBM cells, promoting tumor cell growth, migration and invasion. All together these data suggest that CXCL16 signaling could represent a good target to modulate microglia phenotype in order to restrain inflammation or to limit glioma progression.

A microglia-cytokine axis to modulate synaptic connectivity and function

Microglia have recently been recognized as key regulators of synapse development, function, and plasticity. Critical to progressing the field is the identification of molecular underpinnings necessary for microglia to carry out these important functions within neural circuits. Here, we focus a review specifically on roles for microglial cytokine signaling within developing and mature neural circuits. We review exciting new studies demonstrating essential roles for microglial cytokine signaling in axon outgrowth, synaptogenesis and synapse maturation during development, as well as synaptic transmission and plasticity in adulthood. Together, these studies identify microglia and cytokines as critical modulators of neural circuits within the healthy brain, with implications for a broad range of neurological disorders with disruptions in synaptic structure and function.

The Modulatory Properties of Chronic Antidepressant Drugs Treatment on the Brain Chemokine - Chemokine Receptor Network: A Molecular Study in an Animal Model of Depression

An increasing number of studies indicate that the chemokine system may be the third major communication system of the brain. Therefore, the role of the chemokine system in the development of brain disorders, including depression, has been recently proposed. However, little is known about the impact of the administration of various antidepressant drugs on the brain chemokine - chemokine receptor axis. In the present study, we used an animal model of depression based on the prenatal stress procedure. We determined whether chronic treatment with tianeptine, venlafaxine, or fluoxetine influenced the evoked by prenatal stress procedure changes in the mRNA and protein levels of the homeostatic chemokines, CXCL12 (SDF-1α), CX3CL1 (fractalkine) and their receptors, in the hippocampus and frontal cortex. Moreover, the impact of mentioned antidepressants on the TGF-β, a molecular pathway related to fractalkine receptor (CX3CR1), was explored. We found that prenatal stress caused anxiety and depressive-like disturbances in adult offspring rats, which were normalized by chronic antidepressant treatment. Furthermore, we showed the stress-evoked CXCL12 upregulation while CXCR4 downregulation in hippocampus and frontal cortex. CXCR7 expression was enhanced in frontal cortex but not hippocampus. Furthermore, the levels of CX3CL1 and CX3CR1 were diminished by prenatal stress in the both examined brain areas. The mentioned changes were normalized with various potency by chronic administration of tested antidepressants. All drugs in hippocampus, while tianeptine and venlafaxine in frontal cortex normalized the CXCL12 level in prenatally stressed offspring. Moreover, in hippocampus only fluoxetine enhanced CXCR4 level, while fluoxetine and tianeptine diminished CXCR7 level in frontal cortex. Additionally, the diminished by prenatal stress levels of CX3CL1 and CX3CR1 in the both examined brain areas were normalized by chronic tianeptine and partially fluoxetine administration. Tianeptine modulate also brain TGF-β signaling in the prenatal stress-induced animal model of depression. Our results provide new evidence that not only prenatal stress-induced behavioral disturbances but also changes of CXCL12 and their receptor and at less extend in CX3CL1-CX3CR1 expression may be normalized by chronic antidepressant drug treatment. In particular, the effect on the CXCL12 and their CXCR4 and CXCR7 receptors requires additional studies to elucidate the possible biological consequences.