Article

CD200-CD200R1 interaction contributes to neuroprotective effects of anandamide on experimentally induced inflammation

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Abstract

The endocannabinoid anandamide (AEA) is released by macrophages and microglia on pathological neuroinflammatory conditions such as multiple sclerosis (MS). CD200 is a membrane glycoprotein expressed in neurons that suppresses immune activity via its receptor (CD200R) mainly located in macrophages/microglia. CD200-CD200R interactions contribute to the brain immune privileged status. In this study, we show that AEA protects neurons from microglia-induced neurotoxicity via CD200-CD200R interaction. AEA increases the expression of CD200R1 in LPS/IFN-γ activated microglia through the activation of CB(2) receptors. The neuroprotective effect of AEA disappears when microglial cells derive from CD200R1(-/-) mice. We also show that engagement of CD200R1 by CD200Fc decreased the production of the proinflammatory cytokines IL-1β and IL-6, but increased IL-10 in activated microglia. In the chronic phases of Theiler's virus-induced demyelinating disease (TMEV-IDD) the expression of CD200 and CD200R1 was reduced in the spinal cord. AEA-treated animals up-regulated the expression of CD200 and CD200R1, restoring levels found in sham animals together with increased expression of IL-10 and reduced expression of IL-1β and IL-6. Treated animals also improved their motor behavior. Because AEA up-regulated the expression of CD200R1 in microglia, but failed to enhance CD200 in neurons we suggest that AEA-induced up-regulation of CD200 in TMEV-IDD is likely due to IL-10 as this cytokine increases CD200 in neurons. Our findings provide a new mechanism of action of AEA to limit immune response in the inflamed brain.

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... CD200 is a glycoprotein widely found on the cell membranes of neurons, astrocytes and oligodendrocytes in the CNS (Wright et al., 2001;Barclay et al., 2002;Koning et al., 2009). The target receptor of CD200, CD200R, is only found on macrophages and microglia (Hernangomez et al., 2012). When neuronal CD200 interacts with microglial CD200R, the microglia FIGURE 1 | Bidirectional signaling between microglia (green) and neuron (purple). ...
... will be kept in its inactivated, resting state (Hoek et al., 2000;Biber et al., 2007) thus CD200 signaling plays a critical role in neuronal protection. Defaults in CD200 signaling have been observed in several neuroinflammatory conditions like in multiple sclerosis (MS), Alzheimer's disease, or in the aging brain (Hernangomez et al., 2012;Varnum et al., 2015;Xie et al., 2017). ...
... Autocrine release of CD200 from microglia is also suggested to keep the microglia in an alternative/noninflammatory activation state, involving IL-4 signaling (Yi et al., 2012). The endocannabinoid anandamide (AEA) which can be released by microglia in neuroinflammatory conditions and have an anti-inflammatory effect in stroke (Capettini et al., 2012), is also reported as a mechanism for upregulation of CD200R on microglia (Hernangomez et al., 2012). Additionally, peroxisome proliferator-activated receptor gamma (PPAR-γ), which is a transcription factor controlling the inflammatory response, has been reported to regulate CD200 and CD200R1 gene expression, which could be related to the neuroprotective action of PPARγ agonists (Dentesano et al., 2014). ...
Article
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Microglia are ramified cells that exhibit highly motile processes, which continuously survey the brain parenchyma and react to any insult to the CNS homeostasis. Although microglia have long been recognized as a crucial player in generating and maintaining inflammatory responses in the CNS, now it has become clear, that their function are much more diverse, particularly in the healthy brain. The innate immune response and phagocytosis represent only a little segment of microglia functional repertoire that also includes maintenance of biochemical homeostasis, neuronal circuit maturation during development and experience-dependent remodeling of neuronal circuits in the adult brain. Being equipped by numerous receptors and cell surface molecules microglia can perform bidirectional interactions with other cell types in the CNS. There is accumulating evidence showing that neurons inform microglia about their status and thus are capable of controlling microglial activation and motility while microglia also modulate neuronal activities. This review addresses the topic: how microglia communicate with other cell types in the brain, including fractalkine signaling, secreted soluble factors and extracellular vesicles. We summarize the current state of knowledge of physiological role and function of microglia during brain development and in the mature brain and further highlight microglial contribution to brain pathologies such as Alzheimer's and Parkinson's disease, brain ischemia, traumatic brain injury, brain tumor as well as neuropsychiatric diseases (depression, bipolar disorder, and schizophrenia).
... These changes lead to allodynia and hyperalgesia, which are typical symptoms of neuropathic pain [16][17][18]. CB 2 receptors are expressed in immune cells including microglia, and activation by CB 2 , agonists can reduce pro-inflammatory cytokine production in those cells [19][20][21][22][23][24][25][26]. Previously, we have reported that a CB 2 subtype-selective agonist, ABK5, which is a compound with a distinct structure from the known CB 2 , agonists, has anti-inflammatory effects in T-cells. ...
... Activation of the CB 2 receptor is known to be associated with a decreased production of various pro-inflammatory cytokines such as IL-1β, IL-6, and TNF-α. [26,[29][30][31]. To best characterize anti-inflammatory effects of our compound ABK5-1, we screened for changes in the levels of various cytokines and chemokines after LPS stimulation and LPS stimulation plus ABK5-1 treatment in BV-2 mouse microglia cell line. ...
... Although some studies showed an increase of antiinflammatory cytokines such as IL-4 and IL-10 after activation of CB 2 by various methods [26,29,[34][35][36], we did not observe increase of such cytokines in the current condition. This might be due to the difference between different cell lines and primary microglia and the difference of the stimulation method. ...
Article
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Background and objectives: Neuroinflammation is closely associated with various diseases including neuropathic pain. Microglia are immune cells in the central nervous system which are the main players of immunity and inflammation. Since microglia are activated by nerve injury, and they produce proinflammatory mediators to cause neuropathic pain, targeting activated microglia is considered to be a strategy for treating neuropathic pain. Activation of the cannabinoid CB2 receptor is known to have anti-inflammatory effects in microglia. ABK5-1 is a CB2 subtype selective agonist which inhibits IL-1β and IL-6 production in the microglia cell line BV-2. The purpose of the current study is to further analyze anti-inflammatory effects of ABK5 in terms of different cytokines and the possible pathway involved in the effect in the BV-2 cell line. Methods: A cytokine array was performed to screen the effect of ABK5-1 on forty inflammatory mediators in BV-2 cells. Changes of the inflammatory mediators was further supported by mRNA analysis, and a possible signaling molecule that involved the observation was evaluated by western blot. Results: Stimulating BV-2 cells by lipopolysaccharide increased expression of eleven inflammatory mediators, and ABK5-1 treatment resulted in more than a 50% decrease of sICAM1, IL-6, and RANTES. Real-time PCR results showed a decrease of G-CSF, ICAM1, MCP-1, MIP-1α, and MIP-1β mRNA levels. Western blot analysis showed that ABK5-1 inhibited LPS-induced ERK phosphorylation, which can be a mechanism of ABK5-1-mediated anti-inflammatory effect. Conclusions: Our current results support the possibility that ABK5-1 is an anti-inflammatory drug for microglia.
... Note that whereas in the cerebellum of WT, CD200 expression was mainly found in the neuropil, in transgenic animals, CD200 was also observed in endothelial cells of blood vessels (arrows in C). While CD200R in WT animals was detected just in perivascular macrophages (arrowheads), in GFAP-IL6Tg animals, immunoreaction was also found in microglial cells (arrows in D). Hernangomez et al., 2012). This receptor contains two immunoglobulin superfamily domains, and has a larger cytoplasmic domain that indicates the capacity of CD200R1 to activate an intracellular signaling pathway (Jenmalm et al., 2006;Mihrshahi and Brown, 2010). ...
... In this sense, a study performed in mice after spinal cord injury correlated CD200 expression in CNS resident cells with functional recovery, whereas ablation of CD200 expression specifically in the CNS produced a pro-inflammatory and activated microglia/macrophage profile, impairing recovery (Cohen et al., 2017). Similarly, a viral mouse model of MS (TMEV-IDD, reviewed in Mecha et al., 2013;Procaccini et al., 2015) showed a negative correlation between CD200 expression levels and spinal cord damage, which was reflected in impaired motor function (Hernangomez et al., 2012). Reinforcing these results, a study showed that the administration of an antibody blocking CD200R1 after SCI worsened locomotor performance and exacerbated neuronal loss and demyelination, while intraparenchymal administration of recombinant CD200-His after the same injury induced neuroprotection and long-lasting motor recovery (Lago et al., 2018). ...
... Stimulation of activated microglia with a CD200R agonist results in anti-inflammatory cytokine production, such as IL-10 or IL-4 (Hernangomez et al., 2012;Lyons et al., 2012;2014), whereas suppression of CD200R1 prevents a shift to an anti-inflammatory phenotype of microglia (Yi et al., 2016). Exploration of this effect in microglial cultures revealed that IL-4Ra, a microglial receptor for the anti-inflammatory cytokines IL-4 and IL-13, and CD200R1 share common intracellular signaling pathways, including the phosphorylation of STAT-6 and the upregulation of Foxp3 transcription factor (Yi et al., 2016). ...
Article
Microglia are considered to be the resident macrophages of the CNS and main effector of immune brain function. Due to their essential role in the regulation of neuroinflammatory response, microglia constitute an important target for neurological diseases, such as multiple sclerosis, Alzheimer's or Parkinson's disease. The communication between neurons and microglia contributes to a proper maintenance of homeostasis in the CNS. Research developed in the last decade has demonstrated that this interaction is mediated by “Off-signals” – molecules exerting immune inhibition – and “On signals” – molecules triggering immune activation. Among “Off signals”, molecular pair CD200 and its CD200R receptor, expressed mainly in the membrane of neurons and microglia, respectively, have centered our attention due to its unexplored and powerful immunoregulatory functions. In this review, we will offer an updated global view of the CD200-CD200R role in the microglia-neuron crosstalk during homeostasis and neuroinflammation. Specifically, the effects of CD200-CD200R in the inhibition of pro-inflammatory microglial activation will be explained, and their involvement in other functions such as homeostasis preservation, tissue repair, and brain aging, among others, will be pointed out. In addition, we will depict the effects of CD200-CD200R uncoupling in the etiopathogenesis of autoimmune and neurodegenerative diseases. Finally, we will explore how to translate the scientific evidence of CD200-CD200R interaction into possible clinical therapeutic strategies to tackle neuroinflammatory CNS diseases.
... To investigate the relevance of N-glycosylation in microglia-induced neurotoxicity, we analyzed the effect of CD200-CD200R1 interaction on neuronal death using a neuronal-microglia co-culture system. In all cases, neuronal death was quantitatively assessed by measurement of lactate dehydrogenase (LDH) release into the supernatant after 24 h of co-culture with microglial BV2 cells as previously reported [25]. As shown (Fig. 4), the increased neuronal death by LPS-stimulated microglia was enhanced by the treatment with anti-CD200 antibody. ...
... Previous studies have demonstrated that the N44 is located at the extracellular region of mouse CD200R1, which is essential for CD200-CD200R1 engagement (Hernangomez et al., 2012). Therefore, it is reasonable to presume that N44Q mutant may impair CD200-CD200R1 interaction, which subsequently led to neuronal injury. ...
... In CNS inflammation, microglia become rapidly activated in response to injury while regulatory immune inhibitory molecules contribute to avoid its detrimental effects [25]. CD200R1 is a membrane glycoprotein, mostly expressed constitutively on cells of the myeloid lineage including microglia [26]. ...
Article
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Background Microglial inflammatory activation is the common feature of the central nervous system (CNS) diseases. Microglia can be activated and particularly polarized toward a dual role in the injured CNS. The CD200 receptor 1 (CD200R1) inhibits inflammatory microglia activation as illustrated by studies. Publications show abnormal activation of microglia secondary to the deficient inhibit of CD200-CD200R interaction. In the present study, we established a neuronal-microglia co-culture system to investigate the association between CD200R1 engagement and classical microglial activation. We analyzed the glycosylation of CD200R1 and the CD200 binding. Secretion of pro-inflammatory cytokines were measured. Results CD200R1 was N-glycosylated at Asparagine 44 (Asn44, N44). Mutation of this site disrupted CD200-CD200R1 interaction and up-regulated the expression of cytokines iNOS, CD86, IL-1β and TNF-α. Conclusion N44 of CD200R1 is a significant binding site for CD200-CD200R1 interaction and play a critical role in the maintenance of microglia. The N-glycosylation of CD200R1 could serve as a therapeutic agent for CNS inflammation. Electronic supplementary material The online version of this article (10.1186/s12950-018-0205-8) contains supplementary material, which is available to authorized users.
... Moreover, microglia in the resting state are continually monitoring neurons' activity and surveilling the brain microenvironment; ramified microglia are often called surveilling or homeostatic microglia [6,7]. Contextually, microglia are kept inhibited in the resting state, partly through their crosstalk with neurons and astrocytes [13,14]. However, this situation changes when a neuron is unhealthy or dysfunctional. ...
... Other protein complexes that facilitate cell-contact mediated microglia-neuron interaction include CD200/CD200R. In the CNS, CD200, a transmembrane glycoprotein, is largely expressed on the surface of neurons and astrocytes, while the expression of the CD200 receptor (CD200R) is confined to microglia [14,35]. It is thought that CD200/ CD200R signaling has a neuroprotective role since, upon microglianeuron interaction, CD200/ CD200R signaling operates to retain microglia in an inhibited resting state. ...
... It is thought that CD200/ CD200R signaling has a neuroprotective role since, upon microglianeuron interaction, CD200/ CD200R signaling operates to retain microglia in an inhibited resting state. The loss of this signaling can lead to microglia activation and the eventual elimination of neuronal synapses [14,35]. Consequently, it is not surprising that defects in CD200/CD200R signaling are involved in a handful of neuronal conditions, such as multiple sclerosis, AD, and neurotrauma [14,35,80]. ...
Article
Full-text available
Microglia are the resident immune cells of the brain and play a crucial role in housekeeping and maintaining homeostasis of the brain microenvironment. Upon injury or disease, microglial cells become activated, at least partly, via signals initiated by injured neurons. Activated microglia, thereby, contribute to both neuroprotection and neuroinflammation. However, sustained microglial activation initiates a chronic neuroinflammatory response which can disturb neuronal health and disrupt communications between neurons and microglia. Thus, microglia-neuron crosstalk is critical in a healthy brain as well as during states of injury or disease. As most studies focus on how neurons and microglia act in isolation during neurotrauma, there is a need to understand the interplay between these cells in brain pathophysiology. This review highlights how neurons and microglia reciprocally communicate under physiological conditions and during brain injury and disease. Furthermore, the modes of microglia-neuron communication are exposed, focusing on cell-contact dependent signaling and communication by the secretion of soluble factors like cytokines and growth factors. In addition, how microglia-neuron interactions could exert either beneficial neurotrophic effects or pathologic proinflammatory responses are discussed. We further explore how aberrations in microglia-neuron crosstalk may be involved in central nervous system (CNS) anomalies, namely: traumatic brain injury (TBI), neurodegeneration, and ischemic stroke. A clear understanding of how the microglia-neuron crosstalk contributes to the pathogenesis of brain pathologies may offer novel therapeutic avenues of brain trauma treatment.
... Other data highlighted the involvement of these factors in oestrogen-related immune signalling in the brain [62,63]. The widely described participation of CD antigens in maintaining the CNS homeostasis also consists of their involvement in other processes, some of these are: priming of microglia [64], antigen presentation, proliferation, apoptosis, cell migration [65][66][67], neuroprotection [68], neurodevelopment [16], BBB stability [69], synaptic plasticity [70], mitochondria functioning [71], insulin action [72] and lipid metabolism [73]. ...
... The use of an anti-CD200R1 blocking antibody showed that the CD200-CD200R interaction played a role in the neuroprotective action of the peroxisome proliferator-activated receptor-gamma agonist called 15-deoxy-Δ 12,14 -prostaglandin J 2 [135]. The CD200-CD200R axis is also engaged in neuroprotective properties of endocannabinoid anandamide (AEA) against LPS or interferon (IFN)-γ activated microglia-induced toxicity [68]. AEA protects neurons from inflammatory damage by upregulating CD200R through the activation of cannabinoid receptor type 2. This phenomenon was supported by data showing that AEA was unable to induce neuroprotection in microglia derived from Cd200r-deficient mice [68]. ...
... The CD200-CD200R axis is also engaged in neuroprotective properties of endocannabinoid anandamide (AEA) against LPS or interferon (IFN)-γ activated microglia-induced toxicity [68]. AEA protects neurons from inflammatory damage by upregulating CD200R through the activation of cannabinoid receptor type 2. This phenomenon was supported by data showing that AEA was unable to induce neuroprotection in microglia derived from Cd200r-deficient mice [68]. ...
Article
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 microglia, resulting in the specific axis that maintains the CNS homeostasis. Disruptions to this balance are suggested as the 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 the controlling of 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.
... pY: Phosphotyrosine. This illustration is based on the findings from [7,22,29,69,85,86]. ...
... The therapeutic potential of CD200 has been explored both in vitro and in vivo. Studies using neuron-microglia co-cultures suggested that CD200-CD200R interaction may be one of the mechanisms by which IL-10 protects neurons from inflammatory damage caused by microglia-induced cytotoxicity, as IL-10 increased the expression of CD200 in neurons [58,84,85]. An up-regulatory effect of IL-4 on CD200 expression has also been reported [43,86]. ...
... Cannabinoids participate in the control of brain immune responses as well as in the protection of the CNS against injury [88][89][90][91][92]. Treatments with the endocannabinoid compound N-arachidonoylethanolamine (AEA) induced the recovery of CD200 and CD200R gene expression that was reduced in the Theiler's murine encephalomyelitis virus induced demyelinating disease (TMEV-IDD) model of MS [85]. This was accompanied by decreased inflammatory mediators and reduced microglial reactivity. ...
Article
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CD200 and its receptor, CD200R, constitutes an endogenous inhibitory signaling, and is being increasingly recognized in studies of various central nervous system (CNS) disorders. Emerging data have demonstrated that neuronal CD200 binds to CD200R to modulate immune responses to pathogenic stimuli. However, on which component of the immune response that CD200-CD200R signaling acts is not well understood. In this review, we focused on cellular expression of the signaling, the effects on immune cell activation, and the function in pathological procedures of neurodegenerative diseases, in both clinical and experimental disease models. Essential functions of CD200-CD200R interaction and the treatment relevance have been elaborated. Immune responses to diseases under the control of CD200-CD200R axis were also discussed in the review.
... Cannabinoid receptor 2 in microglia appears to be involved in a variety of paradigms and diseases involving neuroinflammation, including Alzheimer's disease (AD), Parkinson's disease, multiple sclerosis (MS), as well as stress or addiction (8,31,32). Some studies showed that activation of CB2 receptors prevents the activation of microglia and the release of pro-inflammatory mediators (33)(34)(35). ...
... CD200R is expressed on microglia, whereas CD200 is expressed on neurons, and their interaction plays a crucial role in neuronal protection in inflammationmediated neurodegeneration. Furthermore, CD200R1-CD200 interaction was associated with decreased production of the proinflammatory cytokines IL-1b and IL-6 but increased IL-10 in activated microglia after anandamide treatment (32). Another possible mechanism related to microglia-neuron interaction and CB2r involves the up-regulation of microglial CX3CR1. ...
Article
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Emotional behavior, memory, and learning have been associated with alterations in the immune system in neuropsychiatric and neurodegenerative diseases. In recent years, several studies pointed out the involvement of the cannabinoid receptor 2 (CB2r) in the immune system and the regulation of inflammation. This receptor is widely distributed in different tissues and organs with higher expression in spleen and immune system cells. However, CB2r has also been detected in several brain areas and different brain cell types, such as neurons and glia. These findings suggest that CB2r may closely relate the immune system and the brain circuits regulating inflammation, mood, and cognitive functions. Therefore, we review the studies that may help elucidate the molecular bases of CB2r in regulating inflammation in different brain cells and its role in the pathophysiology of psychiatric and neurodegenerative disorders.
... To obtain all possible combinations of neuron-glia co-cultures (neuron-astrocyte, neuron-microglia and neuron-astrocytemicroglia), primary cortical cell cultures were prepared as stated above. Cells were plated at different ratios as it has been described (Hernangómez et al., 2012;Correa et al., 2013) to find the adequate conditions. The optimal conditions are described in Figure 1A. ...
... In order to establish an in vitro protocol where we could study neuron-glia communication and recapitulate neurodegeneration features such as synaptic loss, we optimized an easy and straightforward murine triple co-culture model with neurons, astrocytes and microglia in all possible combinations (Figures 1A,B). We adapted the protocols for culturing individual murine neurons (Alberdi et al., 2018), astrocytes (Wyssenbach et al., 2016) and microglia (Zabala et al., 2018) to establish the triple co-culture model by identifying the appropriate platting order and ratios for the three cell types and by confirming their survival (Hernangómez et al., 2012;Correa et al., 2013). Plating astrocytes on top of neurons compromised neuronal survival (data not shown). ...
Article
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Glial cells are essential to understand Alzheimer’s disease (AD) progression, given their role in neuroinflammation and neurodegeneration. There is a need for reliable and easy to manipulate models that allow studying the mechanisms behind neuron and glia communication. Currently available models such as co-cultures require complex methodologies and/or might not be affordable for all laboratories. With this in mind, we aimed to establish a straightforward in vitro setting with neurons and glial cells to study AD. We generated and optimized a 2D triple co-culture model with murine astrocytes, neurons and microglia, based on sequential seeding of each cell type. Immunofluorescence, western blot and ELISA techniques were used to characterize the effects of oligomeric Aβ (oAβ) in this model. We found that, in the triple co-culture, microglia increased the expression of anti-inflammatory marker Arginase I, and reduced pro-inflammatory iNOS and IL-1β, compared with microglia alone. Astrocytes reduced expression of pro-inflammatory A1 markers AMIGO2 and C3, and displayed a ramified morphology resembling physiological conditions. Anti-inflammatory marker TGF-β1 was also increased in the triple co-culture. Lastly, neurons increased post-synaptic markers, and developed more and longer branches than in individual primary cultures. Addition of oAβ in the triple co-culture reduced synaptic markers and increased CD11b in microglia, which are hallmarks of AD. Consequently, we developed a straightforward and reproducible triple co-cultured model, where cells resemble physiological conditions better than in individual primary cultures: microglia are less inflammatory, astrocytes are less reactive and neurons display a more mature morphology. Moreover, we are able to recapitulate Aβ-induced synaptic loss and CD11b increase. This model emerges as a powerful tool to study neurodegeneration and neuroinflammation in the context of AD and other neurodegenerative diseases.
... CB 2 is expressed in microglia, and the level of expression is further enhanced when the microglia are activated [39][40][41]. Both endocannabinoids and exogenous cannabinoid receptor agonists are reported to decrease production of pro-inflammatory cytokines in primary microglia and microglial cell lines [19,34,42,43]. In agreement with these studies, our results also showed inhibitory effects of a CB 2 agonist ABK5-1 on inhibiting production of IL-1β and IL-6, supporting the beneficial effects of CB 2 in inhibition of neuroinflammation. ...
... In addition, microglia are also known to be able to produce antiinflammatory cytokine IL-10 when they undergo alternative activation [44]. Cannabinoid receptor activation by endocannabinoids and some synthetic agonists are also reported to increase IL-10-producing anti-inflammatory microglia (commonly known as M2 microglia) [34,42,43,45,46]. In contrast, CB 2 activation is also reported to promote microglia activation to pro-inflammatory (known as M1 microglia) phases in cancer pain with morphine tolerance [47]. ...
Article
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Activation of the CB2 receptor has been shown to have anti-inflammatory and antinociceptive effects without causing psychoactive effects. Previously, we reported that the compound ethyl 2(2-(N-(2,3-dimethylphenyl) phenylsulfonamido)acetamido)benzoate (ABK5) is a CB2 subtype selective agonist with anti-inflammatory and antinociceptive effects. In the present study, we tested four ABK5 derivatives, ABK5-1, ABK5-2, ABK5-5, and ABK5-6, to analyze the structure of ABK5 to obtain CB2-selective agonists with higher affinity and efficacy. Affinity, subtype selectivity, and G-protein coupling were determined by radioligand binding assays. Selected compounds were then subjected to evaluation of anti-inflammatory effects using two different cell lines, Jurkat (ABK5-1 and 5-2) and BV-2 cells (ABK5-1), which are models of T cells and microglia, respectively. ABK5-1, ABK5-2, and ABK5-6 had comparable CB2 binding affinity with ABK5 (and stimulated G-protein coupling), while only ABK5-1 and ABK5-2 maintained CB2-subtype selectivity. ABK5-5 did not bind CB2 in the detectable range. RT-PCR and ELISA analysis showed that the two compounds also inhibit IL-2 and TNF-α production, and they were more efficacious than ABK5 in inhibiting TNF-α production. CXCL-12 mediated chemotaxis was also evaluated by the transwell migration assay, and both ABK5-1 and ABK5-2 inhibited chemotaxis with a stronger effect observed in ABK5-1. In the microglia cell line BV-2, ABK5-1 inhibited IL-1β and IL-6 production, which suggests this compound has anti-inflammatory effects through targeting multiple immune cells, and may be a candidate for treatment of inflammation.
... Activation of CB 2 enhances production of both IL-4 and IL-10, while decreasing production of nitric oxide and response to chemokines like CCL2, suggesting that activation of this receptor in microglia, promotes phenotype switching to alternative M2-like cells, reducing classical pro-inflammatory responses [74]. An additional mechanism that has been proposed to explain the anti-inflammatory properties of eCBs in neuroinflammation is an AEA and CB 2 -dependent enhancement of the expression of the immune suppressor protein CD200R1 in antigen-stimulated microglia, leading to decreased production of pro-inflammatory cytokines, increased production of IL-10 and increased neuronal survival in an animal model of virus-induced demyelination [75]. AEA supplementation increases the expression of both CD200 and CD200R1 in the brain, decreasing the severity of disease in this model [75]. ...
... An additional mechanism that has been proposed to explain the anti-inflammatory properties of eCBs in neuroinflammation is an AEA and CB 2 -dependent enhancement of the expression of the immune suppressor protein CD200R1 in antigen-stimulated microglia, leading to decreased production of pro-inflammatory cytokines, increased production of IL-10 and increased neuronal survival in an animal model of virus-induced demyelination [75]. AEA supplementation increases the expression of both CD200 and CD200R1 in the brain, decreasing the severity of disease in this model [75]. ...
Article
The endocannabinoid system participates in the regulation of CNS homeostasis and functions, including neurotransmission, cell signaling, inflammation and oxidative stress, as well as neuronal and glial cell proliferation, differentiation, migration and survival. Endocannabinoids are produced by multiple cell types within the CNS and their main receptors, CB1 and CB2, are expressed in both neurons and glia. Signaling through these receptors is implicated in the modulation of neuronal and glial alterations in neuroinflammatory, neurodegenerative and psychiatric conditions, including Alzheimer’s, Parkinson’s and Huntington’s disease, multiple sclerosis, amyotrophic lateral sclerosis, stroke, epilepsy, anxiety and depression. The therapeutic potential of endocannabinoid receptors in neurological disease has been hindered by unwelcome side effects of current drugs used to target them; however, due to their extensive expression within the CNS and their involvement in physiological and pathological process in nervous tissue, they are attractive targets for drug development. The present review highlights the potential applications of the endocannabinoid system for the prevention and treatment of neurologic and psychiatric disorders.
... Treatment with AEA reduced neuron toxicity, downregulated IL-1β and IL-6, and upregulated IL-10 and the CD200 receptor (CD200R), which is known to suppress the microglial inflammatory response and maintain the homeostatic state via interaction with the neuron-derived ligand, CD200 (96). Thus, CD200-CD200R axis enhancement by AEA may underlie its neuroprotective effects, and it may also shift microglial polarization toward the M2 phenotype and/or the homeostatic M0 state (93). In primary microglia activated by infection with Theiler's murine encephalomyelitis virus (TMEV), AEA treatment increased the expression of IL-10 and decreased the expression of the proinflammatory cytokines, IL-12p70 and IL-23. ...
... The latter morphology is thought to be related to classical (M1) activation though microglia have a ramified cell shape with a small soma when in the homeostatic (M0) state. In line with the morphological data, studies showed that eCB administration increased the expression of CD200R in vitro in a mixed neuron/microglia culture (93) and CX3CR1 in a stroke model (113), both of which are thought to be associated with alternative (M2) and homeostatic (M0) states (133). Although it remains uncertain whether the increase in homeostatic microglia is merely an epiphenomenon of terminated neuroinflammation, eCB signaling may directly shift microglial morphology toward not only the neuroprotective (M2) phenotype but also the homeostatic (M0) phenotype, in which microglia are known to have important physiological functions, which include synaptic pruning, synaptic plasticity modulation, and neuronal trophic support (46). ...
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Microglia, the resident immune cells of the central nervous system, mediate brain homeostasis by controlling neuronal proliferation/differentiation and synaptic activity. In response to external signals from neuropathological conditions, homeostatic (M0) microglia can adopt one of two activation states: the classical (M1) activation state, which secretes mediators of the proinflammatory response, and the alternative (M2) activation state, which presumably mediates the resolution of neuroinflammation and tissue repair/remodeling. Since chronic inflammatory activation of microglia is correlated with several neurodegenerative diseases, functional modulation of microglial phenotypes has been considered as a potential therapeutic strategy. The endocannabinoid (eCB) system, composed of cannabinoid receptors and ligands and their metabolic/biosynthetic enzymes, has been shown to activate anti-inflammatory signaling pathways that modulate immune cell functions. Growing evidence has demonstrated that endogenous, synthetic, and plant-derived eCB agonists possess therapeutic effects on several neuropathologies; however, the molecular mechanisms that mediate the anti-inflammatory effects have not yet been identified. Over the last decade, it has been revealed that the eCB system modulates microglial activation and population. In this review, we thoroughly examine recent studies on microglial phenotype modulation by eCB in neuroinflammatory and neurodegenerative disease conditions. We hypothesize that cannabinoid 2 receptor (CB2R) signaling shifts the balance of expression between neuroinflammatory (M1-type) genes, neuroprotective (M2-type) genes, and homeostatic (M0-type) genes toward the latter two gene expressions, by which microglia acquire therapeutic functionality.
... Its ligand, CD200, is mainly expressed by neurons, but also by astroglial cells 24 . Several studies have shown that CD200R1 stimulation inhibits the expression of proinflammatory cytokines and induces the expression of the anti-inflammatory markers IL10 and ARG1 in glial cells treated with pro-inflammatory stimuli [36][37][38][39] . In addition, Yi et al. 39 reported that CD200R1 is necessary for the induction of an anti-inflammatory phenotype by IL4 in microglial cells. ...
Article
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Exposure to pesticides such as rotenone is a risk factor for Parkinson’s disease. Dopaminergic neurons are especially sensitive to the toxicity of compounds that inhibit the mitochondrial respiratory chain such as rotenone and 1-methyl-4-phenylpyridinium (MPP+). However, there is scarce information on their effects on glia. To evaluate whether these neurotoxicants affect the immune response of glia, primary mouse mixed glial and microglial cultures were treated with interleukin (IL) 4 in the absence and presence of MPP+ or rotenone. Using qRTPCR or western blot, we determined the expression of anti-inflammatory markers, the CD200R1 microglial receptor and its ligand CD200, and genes regulating glycolysis and oxidative metabolism. ATP and lactate levels were additionally determined as an index of cell metabolism. Microglial phagocytosis was also evaluated. MPP+ and rotenone clearly abrogated the IL4-induced expression of anti-inflammatory markers in mixed glial cultures. CD200 and CD200R1 expression and microglia phagocytosis were also affected by the neurotoxicants. Changes in the mRNA expression of the molecules regulating glycolysis and oxidative metabolism, as well as in ATP levels and lactate release suggested that metabolic reprogramming in response to MPP+ and rotenone differs between microglial and mixed glial cultures. These findings support the hypothesis that parkinsonian neurotoxicants may impair brain immune response altering glial cell metabolism.
... Astrocytes and microglia can display neuroprotective activities, although many of these are poorly understood [112,113]. For example, healthy neurons express CD200, which interacts with CD200 L to produce survival signals [114]. Both microglia and astrocytes can release trophic factors and provide metabolic support to neurons [115]. ...
Article
Introduction: Immunotherapies for multiple sclerosis (MS) significantly decrease the risk of new relapses. However, the chronic compartmentalized inflammation and neurodegeneration that define progressive MS are not prevented by these therapies and so significant damage to the brain and spinal cord and resulting disability ensues. Hence, the possibility of combining current immunotherapies with neuroprotective, remyelinating or regenerative therapies should be pursued. Areas Covered: This article sheds light on neuroprotective, remyelination and neurorepair strategies for MS, the numerous mechanisms for therapeutic targeting and the new candidates for combination therapies. We searched PubMed for articles with the terms, ‘neuroprotection’, remyelination’ or ‘regeneration’ and ‘therapies’ or ‘drugs’ and ‘Multiple Sclerosis’. Expert Opinion: An enriched understanding of the neurobiology and molecular changes that are activated by inflammatory CNS damage will provide new opportunities for the identification of neuroprotective, remyelinating and regenerative therapies. Success will depend on the improvement of CNS drug delivery, the identification of new predictive biomarkers, the optimization of clinical trials by assessment of the damage to the visual pathway and the testing of novel therapies in acute optic neuritis.
... The ECS in the brain reinforces food consumption by interacting with the mesolimbic pathways involved in reward mechanisms, where this pathway is activated in the hypothalamus [5]. Further, the neuroprotective and anti-inflammatory roles of the endocannabinoid system predominantly mediated by inhibition of pro-inflammatory cytokines have been documented in various in vitro and in vivo models of neurological disorders [6]. ...
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Cannabis (also known as marijuana) is the most frequently used psychoactive substance globally. Cannabis exerts therapeutic functions for many indications and has vast potential as a health and wellness product. Advances in our understanding of the composition and pharmacological properties of cannabis have revealed interactions between cannabis, an individuals’ circadian rhythms and and their endocannabinoid signaling. Exogenously administered cannabinoids can bidirectionally entrain central and peripheral clocks that comprise circadian rhythms, and malfunctions in the endocannabinoid system are reported to impact neurological processes. Therefore, it is necessary to account for the circadian rhythm when designing clinical trials examining the pharmacological properties of cannabis-based products for health and wellness to limit its potential confounding impact on results. Consideration of the entrainment capabilities of the endocannabinoid system is warranted when designing clinical trials.
... The endocannabinoid agonist, anandamide, increased the expression of microglial CD200R through activation of CB(2) receptor and protected neurons from microglial attack. (Hernangómez et al. 2012). In rodents, dysregulation of CD200-CD200R provides an explanation for increasing inflammation with ageing. ...
Article
Neuroimmune regulators (NIREGs)are an emerging group of CNS proteins and glycoproteins with neuroprotective and anti inflammatory properties.NIREGs reduce the effects of collateral tissue injury associated with activation of the CNS innate immune system in response to pathogens , sterile inflammation and neurodegneration.
... CD200R signalling has been shown to inhibit the activation of mouse and human macrophages induced by IL-17 and IFN-γ in vitro [20]. It has also been demonstrated that CD200-CD200R1 pathways can decrease TLR-signalling to suppress inflammatory macrophages and prevent Gram-negative bacterial infections [21], to restrain macrophage attack on oligodendrocyte precursors [22] and to decrease the expression of IL-1b and IL-6 [23]. ...
Article
Psoriasis is an autoimmune skin disease caused by interactions between keratinocytes and immune cells, such as macrophages. CD200 is expressed on the surface of various cell types, and its receptor, CD200R1, belongs to a family of immunosuppressive receptors that are mainly expressed on myeloid cells. CD200/CD200R1 signalling is associated with the prevention of autoimmune diseases; however, the role of CD200/CD200R1 signalling in the pathogenesis of psoriasis remains unknown. In this study, we detected in vivo effect of the CD200 protein on psoriasis and in vitro effects of CD200 on macrophages and keratinocytes co-cultured with macrophages were also evaluated. Our data showed that the expression of CD200 and CD200R1 was decreased and the expression of macrophage-related pro-inflammatory factors (IL-6, IL-1β, TNF-α) was increased in IMQ-induced psoriasis-like skin of mice. After subcutaneous injection of CD200, the symptoms were alleviated, local expression of CD200R1 was markedly induced, infiltrated CD68+ cells were significantly reduced and the expression levels of IL-6, IL-1β, and TNF-α were strongly downregulated. In in vitro experiments, CD200 suppressed the migration of macrophages, induced CD200R1 expression on the surface of macrophages, and decreased the levels of pro-inflammatory factors. Western blot (WB) data showed that the CD200-CD200R1 reaction controlled the activation of inflammatory macrophages by inhibiting the NF-κB signalling pathway. These results demonstrate that CD200-CD200R1 signalling can reduce IMQ-induced psoriasis-like skin inflammation by inhibiting the activation of macrophages.
... One of the main agents through which neurons affect glial activation is the CD200 glycoprotein, which inhibits microglial priming and holds microglia in a quiescent state (Shrivastava et al., 2012). Indeed, alterations in the distribution of the CD200 or its glial receptor CD200R can lead to overactivation of microglia and neuroinflammation (Hernangómez et al., 2012) that accompany neurodegeneration (Oria et al., 2018). Other neuronal agents that affect the course of neuroinflammation are chemokines, such as CX3CL1, CXCR4 and CCL2 which promotes microglial scavenging (Meucci et al., 2000;Hatori et al., 2002;Paolicelli et al., 2014), regulation of the BBB integrity (Rabinovich-Nikitin et al., 2016) and chemotaxis (Coughlan et al., 2000;Conductier et al., 2010) respectively. ...
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Glia, a non-excitable cell type once considered merely as the connective tissue between neurons, is nowadays acknowledged for its essential contribution to multiple physiological processes including learning, memory formation, excitability, synaptic plasticity, ion homeostasis, and energy metabolism. Moreover, as glia are key players in the brain immune system and provide structural and nutritional support for neurons, they are intimately involved in multiple neurological disorders. Recent advances have demonstrated that glial cells, specifically microglia and astroglia, are involved in several neurodegenerative diseases including Amyotrophic lateral sclerosis (ALS), Epilepsy, Parkinson’s disease (PD), Alzheimer’s disease (AD), and frontotemporal dementia (FTD). While there is compelling evidence for glial modulation of synaptic formation and regulation that affect neuronal signal processing and activity, in this manuscript we will review recent findings on neuronal activity that affect glial function, specifically during neurodegenerative disorders. We will discuss the nature of each glial malfunction, its specificity to each disorder, overall contribution to the disease progression and assess its potential as a future therapeutic target.
... Monocytes in patients with GA express CD200 more than healthy aged individuals, and patients who experience a fast progression of their atrophy have a higher CD200 expression level [40]. The glycoprotein CD200 is a ligand to the CD200 receptor (CD200R), and the CD200-CD200R interaction between peripheral monocytes and retinal microglia is thought to play a role in modulating neuroinflammatory activity [41][42][43][44]. Interestingly, in this study we find that the gene CD200R1, which encodes the CD200 receptor CD200R, is increasingly expressed in patients with GA, which further suggests the involvement of neuroinflammation in GA and possible contribution to this from the systemic circulation. ...
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Background: Peripheral blood mononuclear cells (PBMCs) are implicated in the pathogenesis of age-related macular degeneration (AMD). We here mapped the global gene transcriptome of PBMCs from patients with different clinical subtypes of late AMD. Results: We sampled fresh venous blood from patients with geographic atrophy (GA) secondary to AMD without choroidal neovascularizations (n = 19), patients with neovascular AMD without GA (n = 38), patients with polypoidal choroidal vasculopathy (PCV) (n = 19), and aged control individuals with healthy retinae (n = 20). We isolated PBMCs, extracted RNA, and used microarray to investigate gene expression. Volcano plots identified statistically significant differentially expressed genes (P < 0.05) at a high magnitude (≥30% higher/lower) for GA (62 genes), neovascular AMD (41 genes), and PCV (41 genes). These clinical subtypes differed substantially across gene expression and the following pathways identified in enrichment analyses. In a subgroup analysis, we investigated presence vs. absence of subretinal fibrosis and found 826 differentially expressed genes (≥30% higher/lower, P < 0.05) with relation to mRNA splicing, endothelial migration, and interleukin-1 signaling. Conclusions: We here map the global gene transcriptome of PBMCs related to clinical subtypes of late AMD and find evidence of subtype-specific immunological involvement. Our findings provide a transcriptomic insight into the systemic immunity associated with AMD.
... Neuronal CD200-microglial CD200R interaction was reported to play critical role in determining the neuronal protection in setting of inflammation-mediated neurodegeneration, where this neuronal-microglial crosstalk gets altered. The disturbed equilibrium results in disturbance of immunoregulatory system contributing to microglial activation, chronic neuroinflammation and neuronal damage in various neurological disorders [77,78]. Our current data suggests that both altered surface receptor molecules and continuous release of inflammatory mediators from activated microglia present in co-cultures may be collectively responsible for LPS-induced neuroinflammation and subsequent neurodegeneration. ...
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Background: Systemic inflammation driven neuroinflammation is an event which correlates with pathogenesis of several neurodegenerative diseases. Therefore, targeting peripheral and central inflammation simultaneously could be a promising approach for the management of these diseases. Nowadays, herbal medicines are emerging as potent therapeutics against various brain pathologies. Therefore, in this contemporary study, the neuroprotective activity of Ashwagandha (Withania somnifera) was elucidated against the inflammation associated neurodegeneration and cognitive impairments induced by systemic LPS administration using in vivo rat model system. Methods: To achieve this aim, young adult wistar strain male albino rats were randomized into four groups: (i) Control, (ii) LPS alone, (iii) LPS + ASH-WEX, (iv) ASH-WEX alone. Post regimen, the animals were subjected to Rotarod, Narrow Beam Walking and Novel Object Recognition test to analyze their neuromuscular coordination, working memory and learning functions. The rats were then sacrificed to isolate the brain regions and expression of proteins associated with synaptic plasticity and cell survival was studied using Western blotting and Quantitative real time PCR. Further, neuroprotective potential of ASH-WEX and its active fraction (FIV) against inflammatory neurodegeneration was studied and validated using in vitro model system of microglial conditioned medium-treated neuronal cultures and microglial-neuronal co-cultures. Results: Orally administered ASH-WEX significantly suppressed the cognitive and motor-coordination impairments in rats. On the molecular basis, ASH-WEX supplementation also regulated the expression of various proteins involved in synaptic plasticity and neuronal cell survival. Since microglial-neuronal crosstalk is crucial for maintaining CNS homeostasis, the current study was further extended to ascertain whether LPS-mediated microglial activation caused damage to neurons via direct cell to cell contact or through secretion of inflammatory mediators. ASH-WEX and FIV pretreatment was found to restore neurite outgrowth and protect neurons from apoptotic cell death caused by LPS-induced neuroinflammation in both activated microglial conditioned medium-treated neuronal cultures as well as microglial-neuronal co-cultures. Conclusion: This extensive study using in vivo and in vitro model systems provides first ever pre-clinical evidence that ASH-WEX can be used as a promising natural therapeutic remedial for the prevention of neurodegeneration and cognitive impairments associated with peripheral inflammation and neuroinflammation.
... Most of these studies performed in vivo demonstrate that the beneficial effects of FAAH inhibition are possibly mediated by activation of cannabinoid receptors or PPARs. From in vitro studies, several molecular mechanisms mediated by distinct receptors [25,26] and signaling pathways [27][28][29] have been reported. However, the reports on the role of FAAH inhibition on microglial inflammatory response are inconsistent between genetic deficiency and pharmacological blockade [30] and also among the different FAAH inhibitors [31]. ...
Article
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Fatty acid amide hydrolase (FAAH) has been recognized as a therapeutic target for several neurological diseases because its inhibition can exert neuroprotective and anti-inflammatory effects by boosting the endogenous levels of N-acylethanolamines. However, previous studies have shown inconsistent results by pharmacological inhibition and genetic deletion of FAAH in response to inflammation. In this study we used two inhibitors, PF3845 and URB597, together with siRNA knockdown to characterize further the effects of FAAH inhibition in BV2 microglial cells. Treatment with PF3845 suppressed lipopolysaccharide (LPS)-induced prostaglandin E2 (PGE2) production, and down-regulated cyclooxygenase-2 and microsomal PGE synthase. PF3845 reduced the expression of pro-inflammatory cytokines but had no effect on the expression of anti-inflammatory cytokines. The anti-inflammatory effects of URB597 were not as potent as those of PF3845. Knockdown of FAAH also suppressed PGE2 production and pro-inflammatory gene expression. Interestingly, FAAH knockdown enhanced expression of anti-inflammatory molecules in both the absence and presence of LPS treatment. The anti-inflammatory effects of FAAH inhibition and knockdown were not affected by the cannabinoid receptor antagonists or the peroxisome proliferator-activated receptor (PPAR) antagonists. Although inhibition and knockdown of FAAH have potent anti-inflammatory effects and possibly lead to the dynamic change of microglial gene regulation, the underlying mechanisms remain to be elucidated.
... CD200 is a member of the Ig superfamily, which contains 2 extracellular Ig domains and an unknown intracellular segment motif, and is expressed on the surface of B cells and activated T cells [17][18][19][20]. CD200R, the receptor of CD200, was also a member of the Ig superfamily and is mainly expressed in neutrophils, macrophages, and rod cells [21,22]. Previous studies have shown that CD200 is expressed in a variety of cancer cells and shows tumorigenesis effects [23,24]. ...
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BACKGROUND In this study, we assessed the role of CD200 and CD200 receptor (CD200R) in regulating CD4+T cell subsets and assessed the therapeutic efficacy of thermal ablation for liver hepatocellular carcinoma (HCC) in rats. MATERIAL AND METHODS Seventy-eight male C57BL/6 rats were randomly divided into 7 groups: a control group, a model group, a CD200FC group, an anti-CD200R1 mAb group, a thermal ablation group, a thermal ablation+CD200 FC group, and a thermal ablation+anti-CD200R1 mAb group. The levels of CD200, CD200R1, Th1, Th17, and Treg in peripheral blood were detected by flow cytometry. Immunohistochemistry was used to detect CD200, CD200R1, IFN-γ, IL-17, Foxp3 protein expression in tumor tissues. RESULTS The levels of CD200, CD200R1, Th17, and Treg were significantly increased after CD200FC treatment (p<0.05). After treatment with anti-CD200R1 mAb, the levels of CD200, CD200R1, Th17, and Treg decreased and Th1 increased. Compared with the control group, the expression of CD200, CD200R1, IL-17, and Foxp3 in the model group increased significantly, and the expression of IFN-γ decreased significantly (p<0.05). The expression of CD200, CD200R1, IL-17, and Foxp3 was significantly reduced by adding anti-CD200R1 mAb, and the expression of IFN-γ was increased (p<0.05). After the thermal ablation treatment, the proteins continued to decrease and the expression of IFN-γ continued to increase. CONCLUSIONS The CD200/CD200R pathway participates in HCC tumor growth and the expression of CD4+T cell subsets in cancer tissues. Furthermore, thermal ablation treatment inhibited cancer recurrence.
... In addition, some studies have demonstrated that FAAH inhibition induces anti-inflammatory effects [19,20]. There are also some studies suggesting that AEA protects neurons [21]. Therefore, in our study, while the decrease in FAAH may have contributed positively, the increase in MAGL could have alleviated inflammation in schizophrenia patients. ...
Article
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PURPOSE: While the pathogenesis of schizophrenia has yet to be fully clarified, a huge amount of data suggests the involvement of endocannabinoid system and neurotrophic factors in schizophrenia. Nevertheless, only a very limited number of studies have investigated these two systems together. With this disease containing various unknowns, our primary aim was to simultaneously investigate the serum levels of fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) enzymes, which play significant roles in endocannabinoid system mechanisms, and brain-derived neurotrophic factor (BDNF) as a frequently investigated and important neurotrophic factor in patients with psychiatric disorders. METHODS: This study comprised a total of 34 (24 men, 10 women) schizophrenia patients and 35 (26 men, 9 women) healthy control groups, aged between 18 and 65 years. PANNS and Clinical Global Impression Scale Severity of Illness (CGI-SI) were used to measure disease severity. Serum FAAH, MAGL and BDNF levels of the patients and controls were measured by conventional methods. FINDINGS: Compared to the healthy control group, patients with schizophrenia had decreased FAAH activity, increased MAGL activity and lower BDNF levels. No correlation was noted between BDNF serum levels with FAAH or MAGL activities. CONCLUSION: The findings of the present study showed that there were changes in the levels of metabolizing enzymes of the endocannabinoid system in schizophrenia patients, and these changes were accompanied by a decrease in BDNF levels. While this study provided important information, primarily investigating endocannabinoids and the neurotrophic factor in schizophrenia, future research should be conducted on better designed patient groups and investigate additional parameters.
... Possible mechanisms for this effect would be the switch in microglial phenotypes after CB2 receptor activation with a shift in the gene expression balance towards a neuroprotective phenotype that releases neurotrophic factors and a different pattern of pro-and anti-inflammatory cytokines [36,50]. In addition, endocannabinoids potentiate the expression of CX 3 CR1 [51] and CD200R [52] that interact with their corresponding ligands in the cell surface of neurons promoting the establishment of protective neuron-glia interactions. Modulation of CB1 receptors did not affect neuronal survival at any condition, suggesting a preferential role in other functions not necessarily related to degeneration or repair. ...
Article
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Monoacylglycerol lipase inhibition (MAGL) has emerged as an interesting therapeutic target for neurodegenerative disease treatment due to its ability to modulate the endocannabinoid system and to prevent the production of proinflammatory mediators. To obtain a beneficial response, it is necessary to understand how this inhibition affects the neuron–glia crosstalk and neuron viability. In this study, the effect of MAGL inhibition by KML29 was evaluated in two types of rat cortical primary cultures; mixed cultures, including neuron and glial cells, and neuron-enriched cultures. The risk of neuronal death was estimated by longitudinal survival analysis. The spontaneous neuronal risk of death in culture was higher in the absence of glial cells, a process that was enhanced by KML29 addition. In contrast, neuronal survival was not compromised by MAGL inhibition in the presence of glial cells. Blockade of cannabinoid type 2 (CB2) receptors expressed mainly by microglial cells did not affect the spontaneous neuronal death risk but decreased neuronal survival when KML29 was added. Modulation of cannabinoid type 1 (CB1) receptors did not affect neuronal survival. Our results show that neuron–glia interactions are essential for neuronal survival. CB2 receptors play a key role in these protective interactions when neurons are exposed to toxic conditions.
... Previous work has demonstrated that the endocannabinoid system modulates the pro-inflammatory activity of microglia (Askari and Shafiee-Nick, 2019;Correa et al., 2010;Eljaschewitsch et al., 2006;Hernangómez et al., 2012;Ma et al., 2018;Malek et al., 2015;Tanaka et al., 2020). Both CB 2 receptor-selective agonists and nonselective agonists have demonstrated the potential to suppress the LPS-mediated induction of pro-inflammatory markers in immortalized and primary microglia (Askari and Shafiee-Nick, 2019;Ehrhart et al., 2005;Ma et al., 2018Ma et al., , 2015Mecha et al., 2015;Waksman et al., 1999). ...
Article
Microglia are resident immune cells of the brain that survey the microenvironment, provide trophic support to neurons, and clear debris to maintain homeostasis and healthy brain function. Microglia are also drivers of neuroinflammation in several neurodegenerative diseases. Microglia produce endocannabinoids and express both cannabinoid receptor subtypes suggesting that this system is a target to suppress neuroinflammation. We tested whether cannabinoid type 1 (CB1) or type 2 (CB2) receptors could be targeted selectively or in combination to dampen the pro-inflammatory behavior of microglia, and whether this would have functional relevance to decrease secondary neuronal damage. We determined that components of the endocannabinoid system were altered when microglia are treated with lipopolysaccharide and interferon-gamma and shift to a pro-inflammatory phenotype. Furthermore, pro-inflammatory microglia released cytotoxic factors that induced cell death in cultured STHdhQ7/Q7 neurons. Treatment with synthetic cannabinoids that were selective for CB1 receptors (ACEA) or CB2 receptors (HU-308) dampened the release of nitric oxide (NO) and pro-inflammatory cytokines and decreased levels of mRNA for several pro-inflammatory markers. A nonselective agonist (CP 55,940) exhibited similar influence over NO release but to a lesser extent relative to ACEA or HU-308. All three classes of synthetic cannabinoids ultimately reduced the secondary damage to the cultured neurons. The mechanism for the observed neuroprotective effects appeared to be related to cannabinoid-mediated suppression of MAPK signaling in microglia. Taken together, the data indicate that activation of CB1 or CB2 receptors interfered with the pro-inflammatory activity of microglia in a manner that also reduced secondary damage to neurons.
... The interaction between neurons and microglia occurs in a ligand-dependent way, involving many ligand and receptors. Three main signaling pathways (CD200/ CD200R, CX3CL1/CX3CR1 and Cq1-C3/C3R pathways) have been well described [52]. In all cases, neurons express specific ligands that, by binding to their receptors localized on the microglia, act as a pro-survival stimulus and modulate microglia activation, keeping them in a quiescent state [53]. ...
... CBD produces its anxiolytic effects via activation of the 5-HT1A receptor associated with 5-HT, affecting positively the amygdala. Studies show that CBD acts via the modulation of the 5-HT1A receptors [15]. ...
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The endocannabinoid system (ECS) is a neuromodulator system with a crucial role in CNS and the reaction to endogenous and exogenous compounds and inflammation. Cannabidiol (CBD) is a basic part of the ECS which is the overwhelming causative and/or protective factor of major depressive disease (MDD). CBD interacts with brain-derived neurotropic factor (BDNF) that responds to inflammation, dysregulations of the hypothalamic-pituitary-adrenal (HPA) axis, and many more imbalances in MDD patients for which the ECS is a vital part to analyze, diagnose, and reflect the treatment. The ECS and MDD appear to have strong connections and interactions, so interest in ECS and CBD use in MDD patients is developing as a rescue resort.
... Endocannabinoid ligands in both the early and late phases of gliosis have been tested in rodent models (Schmidt et al., 2012) and the effects have been associated with prevention of neurodegenerative symptoms in disorders such as Huntington's Disease (Ullrich et al., 2007;Palazuelos et al., 2009). Specifically, endocannabinoids have a direct effect on the interactions between microglial CD200 and CD200R via anandamide that enhances CD200R expression and increases IL-10 levels to have a neuroprotective effect (Hernangomez et al., 2012). In reciprocal communication, microglia may transmit AEA through EVs to stimulate CB1 receptors, leading to the suppression GABA inhibitory transmission that may lead to neuron vulnerability, if prolonged (Gabrielli et al., 2015). ...
Article
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The aging brain seems to be characterized by neuronal loss leading to cognitive decline and progressively worsening symptoms related to neurodegeneration. Also, pro-inflammatory states, if prolonged, may increase neuronal vulnerability via excessive activation of microglia and their pro-inflammatory by-products, which is seen as individuals increase in age. Consequently, microglial activity is tightly regulated by neuron-microglia communications. The endocannabinoid system (ECS) is emerging as a regulator of microglia and the neuronal-microglia communication system. Recently, it has been demonstrated that cannabinoid 1 (CB1) receptor signaling on GABAergic interneurons plays a crucial role in regulating microglial activity. Interestingly, if endocannabinoid signaling on GABAergic neurons are disturbed, the phenotypes mimic central nervous system insult models by activating microglia and leading to accelerated brain aging. Investigating the endocannabinoid receptors, ligands, and genetic deletions yields the potential to understand the communication system and mechanism by which the ECS regulates glial cells and aspects of aging. While there remains much to discover with the ECS, the information gathered and identified already could lead to the development of cell-specific therapeutic interventions that help in reducing the effects of age-related pro-inflammatory states and neurodegeneration.
... These findings are consistent with many other studies carried out on primary cells and several immortalized cell lines. When microglia are experimentally activated in a reactive state, CB 2 activation could inhibit the release of pro-inflammatory and cytotoxic factors interfering with their switching to a neurotoxic phenotype [102][103][104][105][106]. ...
Article
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Chronic inflammation in Alzheimer’s disease (AD) has been recently identified as a major contributor to disease pathogenesis. Once activated, microglial cells, which are brain-resident immune cells, exert several key actions, including phagocytosis, chemotaxis, and the release of pro- or anti-inflammatory mediators, which could have opposite effects on brain homeostasis, depending on the stage of disease and the particular phenotype of microglial cells. The endocannabinoids (eCBs) are pleiotropic bioactive lipids increasingly recognized for their essential roles in regulating microglial activity both under normal and AD-driven pathological conditions. Here, we review the current literature regarding the involvement of this signalling system in modulating microglial phenotypes and activity in the context of homeostasis and AD-related neurodegeneration.
... In addition, a beneficial role for CD200-CD200R1 signalling has been described in rodent models of brain ischemia using CD200Fc [69,88] or recombinant CD200 [85]. Several in vitro and in vivo studies showed that the CD200R1 agonist exerts its effect by suppressing the proinflammatory microglial activation [15,24,25,33,47,51,79]. In addition, Varnum et al. [75] demonstrated that a CD200R1 agonist stimulated the production of neurotrophic factors in primary microglial cell cultures. ...
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Background It is suggested that neuroinflammation, in which activated microglial cells play a relevant role, contributes to the development of Parkinson’s disease (PD). Consequently, the modulation of microglial activation is a potential therapeutic target to be taken into account to act against the dopaminergic neurodegeneration occurring in this neurological disorder. Several soluble and membrane-associated inhibitory mechanisms contribute to maintaining microglial cells in a quiescent/surveillant phenotype in physiological conditions. However, the presence of activated microglial cells in the brain in PD patients suggests that these mechanisms have been somehow overloaded. We focused our interest on one of the membrane-associated mechanisms, the CD200-CD200R1 ligand-receptor pair. Methods The acute MPTP experimental mouse model of PD was used to study the temporal pattern of mRNA expression of CD200 and CD200R1 in the context of MPTP-induced dopaminergic neurodegeneration and neuroinflammation. Dopaminergic damage was assessed by tyrosine hydroxylase (TH) immunoreactivity, and neuroinflammation was evaluated by the mRNA expression of inflammatory markers and IBA1 and GFAP immunohistochemistry. The effect of the modulation of the CD200-CD200R1 system on MPTP-induced damage was determined by using a CD200R1 agonist or CD200 KO mice. Results MPTP administration resulted in a progressive decrease in TH-positive fibres in the striatum and TH-positive neurons in the substantia nigra pars compacta, which were accompanied by transient astrogliosis, microgliosis and expression of pro- and anti-inflammatory markers. CD200 mRNA levels rapidly decreased in the ventral midbrain after MPTP treatment, while a transient decrease of CD200R1 mRNA expression was repeatedly observed in this brain area at earlier and later phases. By contrast, a transient increase in CD200R1 expression was observed in striatum. The administration of a CD200R1 agonist resulted in the inhibition of MPTP-induced dopaminergic neurodegeneration, while microglial cells showed signs of earlier activation in CD200-deficient mice. Conclusions Collectively, these findings provide evidence for a correlation between CD200-CD200R1 alterations, glial activation and neuronal loss. CD200R1 stimulation reduces MPTP-induced loss of dopaminergic neurons, and CD200 deficiency results in earlier microglial activation, suggesting that the potentiation of CD200R1 signalling is a possible approach to controlling neuroinflammation and neuronal death in PD.
... The neuroprotective effect of AEA against microglial neurotoxicity was mediated by a mechanism between neurons (with reference to membrane glycoproteins) and microglia/macrophages that involves CD200 ligand-receptor interaction [227]. ...
Article
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Neurodegenerative diseases are an increasing cause of global morbidity and mortality. They occur in the central nervous system (CNS) and lead to functional and mental impairment due to loss of neurons. Recent evidence highlights the link between neurodegenerative and inflammatory diseases of the CNS. These are typically associated with several neurological disorders. These diseases have fundamental differences regarding their underlying physiology and clinical manifestations, although there are aspects that overlap. The endocannabinoid system (ECS) is comprised of receptors (type-1 (CB1R) and type-2 (CB2R) cannabinoid-receptors, as well as transient receptor potential vanilloid 1 (TRPV1)), endogenous ligands and enzymes that synthesize and degrade endocannabinoids (ECBs). Recent studies revealed the involvement of the ECS in different pathological aspects of these neurodegenerative disorders. The present review will explore the roles of cannabinoid receptors (CBRs) and pharmacological agents that modulate CBRs or ECS activity with reference to Alzheimer’s Disease (AD), Parkinson’s Disease (PD), Huntington’s Disease (HD) and multiple sclerosis (MS).
... Indeed, CB2R activation in a paclitaxel model of chemotherapyinduced neuropathy leads to decreased IL-6, BDNF, P2X4, and TNFα receptor expression, and increased release of the antiinflammatory cytokine IL-10 (Burgos et al., 2012;Wu et al., 2019). This cannabinoid-induced release of IL-10 by microglia is a phenomenon shared with other areas of the CNS (Correa et al., 2010;Hernangómez et al., 2012). Additionally, activation of CB2R by exercise-induced AEA release reduces levels of TNFα and IL-1β in the spinal cord of mice with carrageenaninduced pain hypersensitivity (dos Santos et al., 2019). ...
Article
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Chronic pain is a complex sensory, cognitive, and emotional experience that imposes a great personal, psychological, and socioeconomic burden on patients. An estimated 1.5 billion people worldwide are afflicted with chronic pain, which is often difficult to treat and may be resistant to the potent pain-relieving effects of opioid analgesics. Attention has therefore focused on advancing new pain therapies directed at the cannabinoid system because of its key role in pain modulation. Endocannabinoids and exogenous cannabinoids exert their actions primarily through G i/o -protein coupled cannabinoid CB1 and CB2 receptors expressed throughout the nervous system. CB1 receptors are found at key nodes along the pain pathway and their activity gates both the sensory and affective components of pain. CB2 receptors are typically expressed at low levels on microglia, astrocytes, and peripheral immune cells. In chronic pain states, there is a marked increase in CB2 expression which modulates the activity of these central and peripheral immune cells with important consequences for the surrounding pain circuitry. Growing evidence indicate that interventions targeting CB1 or CB2 receptors improve pain outcomes in a variety of preclinical pain models. In this mini-review, we will highlight recent advances in understanding how cannabinoids modulate microglia function and its implications for cannabinoid-mediated analgesia, focusing on microglia-neuron interactions within the spinal nociceptive circuitry.
... Additionally, AEA upregulated CD200 and IL-10 but downregulated pro-inflammatory cytokines IL-1β and IL-6 in a mixed culture of neurons and reactive microglia activated by LPS and IFNγ [87]. The CD200-CD200R axis enhanced by AEA is believed to shift microglial cells from an M1 to M2 phenotype, which provides neuroprotection [88]. Furthermore, CB1 agonist WIN55,212-2 induces astrocytes to release purines, which reduce tremors in an animal model of essential tremors [24]. ...
Article
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Chronic inflammation is considered to be a silent killer because it is the underlying cause of a wide range of clinical disorders, from cardiovascular to neurological diseases, and from cancer to obesity. In addition, there are over 80 different types of debilitating autoimmune diseases for which there are no cure. Currently, the drugs that are available to suppress chronic inflammation are either ineffective or overtly suppress the inflammation, thereby causing increased susceptibility to infections and cancer. Thus, the development of a new class of drugs that can suppress chronic inflammation is imperative. Cannabinoids are a group of compounds produced in the body (endocannabinoids) or found in cannabis (phytocannabinoids) that act through cannabinoid receptors and various other receptors expressed widely in the brain and immune system. In the last decade, cannabinoids have been well established experimentally to mediate anti-inflammatory properties. Research has shown that they suppress inflammation through multiple pathways, including apoptosis and inducing immunosuppressive T regulatory cells (Tregs) and myeloid-derived suppressor cells (MDSCs). Interestingly, cannabinoids also mediate epigenetic alterations in genes that regulate inflammation. In the current review, we highlight how the epigenetic modulations caused by cannabinoids lead to the suppression of inflammation and help identify novel pathways that can be used to target autoimmune diseases.
... One of the inhibitory mechanisms to control the microglial in ammatory response is CD200/CD200R1 interaction. CD200 is a surface glycoprotein generally expressed by neurons, whereas CD200R1, the receptor of CD200R, is chie y located in microglia [3]. In the retina, microglia migration is promoted by the combination of CD200R and CD200, while preventing M1 phenotype activation of resident microglia [4]. ...
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Objective Based on recent reports, peroxisome proliferator-activated receptor-γ (PPAR-γ) could promote microglial M2 polarization to inhibit inflammation. However, the specific molecular mechanisms instigate the anti-inflammatory ability of PPAR-γ in microglia have not been expounded. In the present study, we explored the molecular mechanisms of the anti-inflammatory effects of PPAR-γ in hypoxia-stimulated rat microglial cells. Methods shRNA expressing lentivirus was used to knock down PPAR-γ and CD200 genes. The hypoxia-induced polarization markers release (M1: iNOS, IL-1β, IL-6 and TNF-α; M2: Arg-1, YM1, IL-4 and IL-10) was assessed by RT-PCR, while PPAR-γ-related signals (PPAR-γ, PPAR-γ in cytoplasm or nucleus, CD200 and CD200Rs) were monitored by western blot and RT-PCR. Results Hypoxia enhanced PPAR-γ and CD200 expressions in microglial cells. In addition, PPAR-γ agonist 15d-PGJ2 elevated CD200 and CD200R1 expressions, while sh-PPAR-γ (PPAR-γ knock-down) had just the opposite effect. Following hypoxia, expressions of M1 markers increased significantly, while those of M2 markers decreased, and the above effects were attenuated by 15d-PGJ2. Conversely, knocking down PPAR-γ or CD200 inhibited the polarization of microglial cells to M2 phenotype. Conclusion Results demonstrated that PPAR-γ performed an anti-inflammatory function in hypoxia-stimulated microglial cells by promoting their polarization to M2 phenotype via CD200-CD200R1 pathway.
... Conversely, the administration of recombinant CD200-His reverses the effect (19). CD200R1 is also associated with microglia priming (20), antigen presentation (18), and cytokine production (21). Activation of CD200R1 slows down microglial migration and phagocytosis (22), whereas microglia isolated from CD200 deficient mouse model shows augmented phagocytosis and lysosomal activity (23). ...
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CD200R1 is an inhibitory surface receptor expressed in microglia and blood macrophages. Microglial CD200R1 is known to control neuroinflammation by keeping the microglia in resting state and therefore, tight regulation of its expression is important. CCAAT/enhancer binding protein β (CEBPβ) is the known regulator of CD200R1 transcription. In the present study our specific intention was to find a possible posttranscriptional regulatory mechanism of CD200R1 expression. Here we investigated a novel regulatory mechanism of CD200R1 expression following exposure to an environmental stressor, arsenic, combining in silico analysis, in vitro, and in vivo experiments, as well as validation in human samples. The in silico analysis and in vitro studies with primary neonatal microglia and BV2 microglia revealed that arsenic demethylates the promoter of a microRNA, miR-129-5p, thereby increasing its expression, which subsequently represses CD200R1 by binding to its 3´- untranslated region and shuttling the CD200R1 mRNA to the cytoplasmic-processing body in mouse microglia. The role of miR-129-5p was further validated in BALB/c mouse by stereotaxically injecting anti-miR-129. We found that anti-miR-129 reversed the expression of CD200R1, as well as levels of inflammatory molecules IL-6 and TNF-α. Experiments with a CD200R1 siRNA-induced loss-of-function mouse model confirmed a miR-129-5p→CD200R1→IL-6/TNF-α signaling axis. These main findings were replicated in a human cell line and validated in human samples. Taken together, our study revealed miR-129-5p as a novel post-transcriptional regulator of CD200R1 expression with potential implications in neuroinflammation and related complications.
... 2021, 11, 1098 4 of 15 superfamily of cell surface proteins [72], which is mainly expressed by neurons [73], and interacts with a receptor, OX2R (CD200R), found mainly in microglia in the CNS [74,75]. Previous studies have indicated that OX2R activation reduces the activity of myeloid cells such as microglia and macrophages [76,77]. The interaction of OX2 with its receptor acts to suppress inflammatory responses [76,[78][79][80]. ...
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Microglia are the first line of defense at the level of the central nervous system (CNS). Phenotypic change in microglia can be regulated by various factors, including the orexin system. Neuroinflammation is an inflammatory process mediated by cytokines, by the lack of interaction of specific receptors such as the OX2-OX2R complex, caused by systemic tissue damage or, more often, associated with direct damage to the CNS. Chronic activation of microglia could lead to long-term neurodegenerative diseases. This review aims to explore how tocopherol (vitamin E) and the orexin system may play a role in the prevention and treatment of microglia inflammation and, consequently, in neurodegenerative diseases thanks to its antioxidant properties. The results of animal and in vitro studies provide evidence to support the use of tocopherol for a reduction in microglia inflammation as well as a greater activation of the orexinergic system. Although there is much in vivo and in vitro evidence of vitamin E antioxidant and protective abilities, there are still conflicting results for its use as a treatment for neurodegenerative diseases that speculate that vitamin E, under certain conditions or genetic predispositions, can be pro-oxidant and harmful.
... Studies have reported the dysregulation of CD200R1 expression in neurodegenerative diseases including PD. For instance, viral model of multiple sclerosis showed reduced CD200R1 expression in the spinal cord at the later chronic-phase [20]. Walker et al. demonstrated that the mRNA expression of CD200R1 was signi cantly reduced in hippocampal and infratemporal gyrus samples from patients with Alzheimer's disease (AD) [21]. ...
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Background: Kynurenine pathway metabolites and endocannabinoids both exert potent regulatory effects on the immune system, but the relationship between these molecules is unknown. The role of these immunobiological mediators in emotionality and personality traits is not previously characterized. Methods: Interleukin-6 (IL-6), 2-arachidonoylglycerol (2-AG) and picolinic acid (PIC) were measured in the plasma of physically healthy individuals who had history of mood, anxiety, and personality disorders (n = 96) or who had no history of any psychiatric disorder (n = 56) by DSM-5 Criteria. Dimensional assessments of personality were performed using the Eysenck Personality Questionnaire (EPQ) and the Tridimensional Personality Questionnaire (TPQ). Results: Plasma IL-6 levels were significantly associated with plasma 2-AG levels and plasma PIC levels across all subjects. PIC levels were also negatively associated with 2-AG levels across all subjects, independent of IL-6 levels. In our analysis of the biological determinants of personality factors, we identified significant associations between IL-6 and novelty seeking assessment, and between PIC and neuroticism assessment. Conclusions: These data provide evidence of a biological link between metabolites of the kynurenine pathway, the endocannabinoid system and IL-6 and suggest that these factors may influence personality traits.
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Aging is a complex biological process that increases the risk of age-related cognitive degenerative diseases such as dementia, including Alzheimer’s disease (AD), Lewy Body Dementia (LBD), and mild cognitive impairment (MCI). Even non-pathological aging of the brain can involve chronic oxidative and inflammatory stress, which disrupts the communication and balance between the brain and the immune system. There has been an increasingly strong connection found between chronic neuroinflammation and impaired memory, especially in AD. While microglia and astrocytes, the resident immune cells of the central nervous system (CNS), exerting beneficial effects during the acute inflammatory phase, during chronic neuroinflammation they can become more detrimental. Central cholinergic circuits are involved in maintaining normal cognitive function and regulating signaling within the entire cerebral cortex. While neuronal-glial cholinergic signaling is anti-inflammatory and anti-oxidative, central cholinergic neuronal degeneration is implicated in impaired learning, memory sleep regulation, and attention. Although there is evidence of cholinergic involvement in memory, fewer studies have linked the cholinergic anti-inflammatory and anti-oxidant pathways to memory processes during development, normal aging, and disease states. This review will summarize the current knowledge of cholinergic effects on microglia and astroglia, and their role in both anti-inflammatory and anti-oxidant mechanisms, concerning normal aging and chronic neuroinflammation.
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Background and Purpose CD200 (cluster of differentiation 200), a highly glycosylated protein primarily expressed on neurons in the central nervous system, binds with its receptor CD200R to form an endogenous inhibitory signal against immune responses. However, little is known about the effect of neuronal CD200 signaling in cerebral ischemia. The aim of this study was to investigate how neuronal CD200 signaling impacts poststroke inflammation and the ischemic injury. Methods CD200 tma1 lf/fl :Thy1CreER mice were treated with tamoxifen to induce conditional gene knockout (ICKO) of neuronal CD200. The mice were subjected to a 60-minute transient middle cerebral artery occlusion. Stroke outcomes, apoptotic cell death, immune cell infiltration, microglia activation, and other inflammatory profiles were evaluated at 3 and 7 days after stroke. Results Infarct volumes were significantly larger, and behavioral deficits more severe in ICKO versus control mice at 3 days after middle cerebral artery occlusion. Terminal deoxynucleotidyl transferase dUTP nick end labeling assay also revealed a significant increase in apoptotic neuronal death in CD200 ICKO mice. An enhancement in lymphocytic infiltration and microglial proinflammatory responses were revealed by flow cytometry at 3 and 7 days after stroke in ICKO mice, accompanied by an increased microglial phagocytosis activity. Plasma proinflammatory cytokine (TNFα [tumor necrosis factor alpha] and IL [interleukin]-1β) levels significantly increased at 3 days, and IL-1β/IL-6 levels increased at 7 days in ICKO versus control animals. ICKO led to significantly lower baseline level of CD200 both in brain and plasma. Conclusions Neuronal CD200 inhibits proinflammatory responses and is protective against stroke injury.
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Increasing evidence suggests that SARS-CoV-2, the virus responsible for the COVID-19 pandemic, is associated with increased risk of developing neurological or psychiatric conditions such as depression, anxiety or dementia. While the precise mechanism underlying this association is unknown, aberrant activation of toll-like receptor (TLR)3, a viral recognizing pattern recognition receptor, may play a key role. Synthetic cannabinoids and enhancing cannabinoid tone via inhibition of fatty acid amide hydrolase (FAAH) has been demonstrated to modulate TLR3-induced neuroimmune responses and associated sickness behaviour. However, the role of individual FAAH substrates, and the receptor mechanisms mediating these effects, are unknown. The present study examined the effects of intracerebral or systemic administration of the FAAH substrates N-oleoylethanolamide (OEA), N-palmitoylethanolamide (PEA) or the anandamide (AEA) analogue meth-AEA on hyperthermia and hypothalamic inflammatory gene expression following administration of the TLR3 agonist, and viral mimetic, poly I:C. The data demonstrate that meth-AEA does not alter TLR3-induced hyperthermia or hypothalamic inflammatory gene expression. In comparison, OEA and PEA attenuated the TLR3-induced hyperthermia, although only OEA attenuated the expression of hyperthermia-related genes (IL-1β, iNOS, COX2 and m-PGES) in the hypothalamus. OEA, but not PEA, attenuated TLR3-induced increases in the expression of all IRF- and NFκB-related genes examined in the hypothalamus, but not in the spleen. Antagonism of PPARα prevented the OEA-induced attenuation of IRF- and NFκB-related genes in the hypothalamus following TLR3 activation but did not significantly alter temperature. PPARα agonism did not alter TLR3-induced hyperthermia or hypothalamic inflammatory gene expression. These data indicate that OEA may be the primary FAAH substrate that modulates TLR3-induced neuroinflammation and hyperthermia, effects partially mediated by PPARα.
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Decades after identifying cannabinoids and their beneficial effects on Parkinson's disease (PD), many gaps are still missing. Although, CB2-dependent actions have been shown as underlying positive effects of cannabinoid treatment, in recent years, another receptor of cannabinoids, CB1, emerged as a valuable player in cannabinoid-induced neuroprotection. Remarkably, the effects of CB1 are mainly related to immune cells in the CNS, microglia, and astrocytes. However, oxidative stress, α-syn accumulation, and immune disbalance are essential aspects of both neurons and glial cells. Therefore, in this study, we investigated the effects of the CB1 on both α-syn and rotenone-treated SH-SY5Y and C8-D1A cells. ACEA and AM-251 were used as CB1 agonists and antagonists. Cell viability, IL-1β, IL-6, TNF-α levels, and CD200 expressions were determined in culture mediums. Our results demonstrated that preformed fibril form (pFF) of α-syn did not cause any significant change in SH-SY5Y cells compared to C8-D1A cells. Rotenone significantly increased the expression of IL-1β, IL-6, and TNF-α levels in both cells. pFF α-syn and rotenone treatment caused a decrease in CD200 expression. Surprisingly both ACEA and AM-251 alleviated rotenone-induced increase in cytokine levels in both cell lines. Although ACEA prevented pFF α-syn induced increase in cytokine levels and decrease in CD200 expression in C8-D1A cells, AM-251 failed to affect CD200 expression levels. Additionally, ACEA + AM-251 abolished the protective effects of both ACEA and AM-251 against rotenone and α-syn insults in both cell lines. The current study suggests that cannabinoid receptor agonism alleviates rotenone and α-syn-dependent inflammation in neurons and astrocytes.
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Chapter
CD200 is a membrane protein of the immunoglobulin superfamily of cell-surface proteins and functions as a protective barrier for key cells, such as neurons and oligodendrocytes. It lacks signal-transduction properties, and its sole defined function is to engage the CD200 receptor (CD200R), which is expressed by different classes of inflammatory cells including microglia. Interaction of CD200 and CD200R downregulates activation of these inflammatory cells. Downregulation of CD200 in elderly or diseased human brains has been demonstrated; when recreated in animal models, loss of CD200 results in enhanced inflammation due to loss of this critical control mechanism. Chronic inflammation is a significant feature of Alzheimer's disease pathology, with activated microglia being associated with pathological structures (plaques and tangles). In this article we will discuss how CD200 may have a major role in inflammation control and thus may have a pivotal role in preserving brain structures from inflammatory damage. Enhancing this cellular antiinflammatory system as a therapeutic strategy has not been extensively explored.
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Objective To study how the CD200‐CD200R1 signaling pathway modulates poststroke inflammation and advances our knowledge of immune responses to ischemia insults in stroke. Methods Focal middle cerebral artery occlusion (MCAO) was induced in mice for 90 min, and mice were sacrificed at 1, 3, and 7 days of reperfusion. CD200, CD200R1, iNOS, and Arg‐1 expression in ischemic brains was assessed by Western blotting (WB), and immunohistochemical (IHC) staining was performed to examine the expression of CD200 on neurons and CD200R1 on infiltrating lymphocytes. The severity of neurobehavioral deficits was evaluated by neurological deficit scores (NDS) and infarction volume estimated by TTC staining. To study the relationship between CD200/CD200R1 expression and the diversity of the neuroinflammatory response in stroke, CD200Fc (CD200R1 agonist) was subcutaneously injected at onset, at 1 day and 2 days after MCAO operation, and the brains were collected for detection at 3 days after MCAO/R (reperfusion). Results CD200 expression on neurons increased at 1 day and then decreased at 3 days after MCAO/R, and the expression of CD200R1 on lymphocytes showed an opposite temporal pattern as tested by IHC. The WB results showed that CD200/CD200R1 variance exhibited a similar pattern of IHC results, and the level of iNOS peaked at 1 day and then decreased gradually, but Arg‐1 increased with time after MCAO/R in ischemic brains. After CD200Fc injection, CD200R1 expression significantly increased, and CD200Fc promoted Arg‐1 but inhibited iNOS expression. The infarct volume and NDS of the group treated with CD200Fc were significantly smaller than those of the IgG2a‐treated group. Conclusions The CD200‐CD200R1 signaling pathway regulates neuroinflammation after stroke. Stimulation of CD200R1 by CD200Fc promotes the anti‐inflammatory response and alleviates ischemic injury.
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Theiler murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD) is a mouse model of chronic-progressive multiple sclerosis (MS) characterized by Th1-mediated CNS demyelination and spastic hindlimb paralysis. Existing MS therapies reduce relapse rates in 30% of relapsing-remitting MS patients, but are ineffective in chronic-progressive disease, and their effects on disability progression are unclear. Experimental studies demonstrate cannabinoids are useful for symptomatic treatment of spasticity and tremor in chronic-relapsing experimental autoimmune encephalomyelitis. Cannabinoids, however, have reported immunosuppressive properties. We show that the cannabinoid receptor agonist, R+WIN55,212, ameliorates progression of clinical disease symptoms in mice with preexisting TMEV-IDD. Amelioration of clinical disease is associated with downregulation of both virus and myelin epitope-specific Th1 effector functions (delayed-type hypersensitivity and IFN-gamma production) and the inhibition of CNS mRNA expression coding for the proinflammatory cytokines, TNF-alpha, IL1-beta, and IL-6. Clinical trials investigating the therapeutic potential of cannabinoids for the symptomatic treatment of MS are ongoing, and this study demonstrates that they may also have potent immunoregulatory properties.
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CD200 (OX2) is a broadly distributed cell surface glycoprotein that interacts with a structurally related receptor (CD200R) expressed on rodent myeloid cells and is involved in regulation of macrophage function. We report the first characterization of human CD200R (hCD200R) and define its binding characteristics to hCD200. We also report the identification of a closely related gene to hCD200R, designated hCD200RLa, and four mouse CD200R-related genes (termed mCD200RLa-d). CD200, CD200R, and CD200R-related genes were closely linked in humans and mice, suggesting that these genes arose by gene duplication. The distributions of the receptor genes were determined by quantitative RT-PCR, and protein expression was confirmed by a set of novel mAbs. The distribution of mouse and human CD200R was similar, with strongest labeling of macrophages and neutrophils, but also other leukocytes, including monocytes, mast cells, and T lymphocytes. Two mCD200 receptor-like family members, designated mCD200RLa and mCD200RLb, were shown to pair with the activatory adaptor protein, DAP12, suggesting that these receptors would transmit strong activating signals in contrast to the apparent inhibitory signal delivered by triggering the CD200R. Despite substantial sequence homology with mCD200R, mCD200RLa and mCD200RLb did not bind mCD200, and presently have unknown ligands. The CD200 receptor gene family resembles the signal regulatory proteins and killer Ig-related receptors in having receptor family members with potential activatory and inhibitory functions that may play important roles in immune regulation and balance. Because manipulation of the CD200-CD200R interaction affects the outcome of rodent disease models, targeting of this pathway may have therapeutic utility.
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Chronic progression of two T cell-mediated central nervous system (CNS) demyelinating models of multiple sclerosis, relapsing EAE (R-EAE) and Theiler's murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD) is dependent on the activation of T cells to endogenous myelin epitopes (epitope spreading). Using transfer of carboxyfluorescein succinyl ester (CFSE)-labeled T-cell receptor (TCR)-transgenic T cells and mixed bone marrow chimeras, we show that activation of naive proteolipid protein (PLP)139-151-specific T cells in SJL mice undergoing PLP178-191-induced R-EAE or TMEV-IDD occurs directly in the CNS and not in the cervical lymph nodes or other peripheral lymphoid organs. Examination of the antigen-presentation capacity of antigen-presenting cell (APC) populations purified from the CNS of mice with PLP178-191-induced R-EAE shows that only F4/80-CD11c+CD45hi dendritic cells (DCs) efficiently present endogenous antigen to activate naive PLP139-151-specific T cells in vitro. In contrast, DCs as well as F4/80+CD45hi macrophages and F4/80+CD45lo microglia activate a PLP139-151-specific helper T cell line. The data suggest that naive T cells enter the inflamed CNS and are activated by local APCs, possibly DCs, to initiate epitope spreading.
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Theiler's virus infection of the CNS induces an immune-mediated demyelinating disease in susceptible mouse strains and serves as a relevant infection model for human multiple sclerosis (MS). Cannabinoids may act as immunosuppressive compounds that have shown therapeutic potential in chronic inflammatory disorders. Using the Theiler's murine encephalomyelitis virus model, we report here that treatment with the synthetic cannabinoids WIN 55,212-2, ACEA, and JWH-015 during established disease significantly improved the neurological deficits in a long-lasting way. At a histological level, cannabinoids reduced microglial activation, abrogated major histocompatibility complex class II antigen expression, and decreased the number of CD4+ infiltrating T cells in the spinal cord. Both recovery of motor function and diminution of inflammation paralleled extensive remyelination. Overall, the data presented may have potential therapeutic implications in demyelinating pathologies such as MS; in particular, the possible involvement of cannabinoid receptor CB2 would enable nonpsychoactive therapy suitable for long-term use.
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CD200 is a membrane glycoprotein that suppresses immune activity via its receptor, CD200R. CD200-CD200R interactions have recently been considered to contribute to the "immune privileged" status of the central nervous system (CNS). The mechanisms by which these interactions take place are not well understood in part because there is limited detailed information on the distribution of CD200 and CD200R in the CNS. Here, we used immunohistochemistry to characterize the distinct anatomical and cellular distribution of these molecules in multiple sclerosis (MS) lesions and controls. CD200 was robustly expressed in gray matter areas including the cerebral cortex, hippocampus, striatum, cerebellum, and spinal cord, where neurons appeared immunopositive. CD200 expression was also detected in oligodendrocytes, but not in astrocytes or microglia. In CNS samples from MS patients, CD200 expression was additionally observed on reactive astrocytes in chronic active plaque centers, despite our previous finding of an overall decrease ofCD200 expression in MS lesions. In contrast to CD200, the immunolocalization pattern of CD200R was very distinct, showing high expression on perivascular macrophages in both gray and white matter. Using flow cytometry, we also found that human primary microglia express low levels of CD200R. These data suggest that CD200-mediated immune suppression may occur not only via neuron-microglia interactions, but also via glia-glia interactions, especially in inflammatory conditions in which an immune-suppressive environment needs to be restored; this may occur as a result of increased CD200 expression on reactive astrocytes.
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