Microglial CD40 Research Articles

Innate and adaptive glial cell responses in Alzheimer’s disease

Alzheimer’s disease (AD), which affects around twenty-seven million people globally, is an aging-related neurodegenerative condition characterized by the extracellular deposition of misfolded amyloid-β (Aβ) peptides and the intracellular production of neurofibrillary tangles (NFTs) AD results from the death of certain groups of neurons in the brain while appearing to have no impact on neighboring neurons. It is progressive and incurable. Therefore, the pathophysiology of afflicted populations and the development of intervention measures to stop neuronal cell death have been the main areas of attention for delineating therapeutic options. Proinflammatory cytokines are responsible for the stimulation of inflammatory responses and are mostly generated by activated macrophages in the brain. This review discusses how glial cells and innate and adaptive immune responses have a critical role in AD. It also provides information about microglial activation through the cluster of differentiation 40 (CD40) ligation and CD40L. CD40L ligation of microglial CD40 results in a large increase in tumor necrosis factor-α (TNF-α) production. Cultured cortical neuronal injury is caused when microglia are activated by CD40 ligation in the presence of interferon-γ (IFN-γ). This injury is significantly reduced by blocking the CD40 pathway or neutralising TNF-α. The management of AD would require integrating all available information about the innate and adaptive immune response affecting AD-related neuronal death.

Phyllanthus amarus prevents LPS-mediated BV2 microglial activation via MyD88 and NF-\u03baB signaling pathways

BackgroundPhyllanthus amarus has been shown to attenuate lipopolysaccharide (LPS)-induced peripheral inflammation but similar studies in the central nervous system are scarce. The aim of the present study was to investigate the neuroprotective effects of 80% ethanol extract of P. amarus (EPA) in LPS-activated BV2 microglial cells.MethodsBV2 microglial cells c for 24 h, pre-treated with EPA for 24 h prior to LPS induction for another 24 h. Surface expression of CD11b and CD40 on BV2 cells was analyzed by flow cytometry. ELISA was employed to measure the production of pro-inflammatory mediators i.e. nitric oxide (NO) and tumor necrosis factor (TNF)-α. Western blotting technique was used to determine the expression of inducible nitric oxide synthase (iNOS), myeloid differentiation protein 88 (MYD88), nuclear factor kappa B (NF-κB), caspase-1, and mitogen activated protein kinase (MAPK).ResultsQualitative and quantitative analyses of the EPA using a validated ultra-high pressure liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method indicated the presence of phyllanthin, hypophyllanthin, niranthin, ellagic acid, corilagin, gallic acid, phyltetralin, isolintetralin and geraniin. EPA suppressed the production of NO and TNFα in LPS-activated BV2 microglial cells. Moreover, EPA attenuated the expression of MyD88, NF-κB and MAPK (p-P38, p-JNK and p-ERK1/2). It also inhibited the expression of CD11b and CD40. EPA protected against LPS-induced microglial activation via MyD88 and NF-κB signaling in BV2 microglial cells.ConclusionsEPA demonstrated neuroprotective effects against LPS-induced microglial cells activation through the inhibition of TNFα secretion, iNOS protein expression and subsequent NO production, inhibition of NF-κB and MAPKs mediated by adapter protein MyD88 and inhibition of microglial activation markers CD11b and CD40.

Role of microglial activation and neuroinflammation in neurotoxicity of acrylamide in vivo and in vitro.

Acrylamide, a soft electrophile, is widely used in the industry and laboratories, and also contaminates certain foods. Neurotoxicity and neurodegenerative effects of acrylamide have been reported in humans and experimental animals, although the underlying mechanism remains obscure. Activation of microglia and neuroinflammation has been demonstrated in various neurodegenerative diseases as well as other pathologies of the brain. The present study aimed to investigate the role of microglial activation and neuroinflammation in acrylamide neurotoxicity. Male 10-week-old Wistar rats were exposed to acrylamide by gavage at 0, 0.2, 2, or 20mg/kg BW, once per day for 5weeks. The results showed that 5-week exposure to acrylamide induced inflammatory responses in the cerebral cortex, evident by upregulated mRNA and protein expression of pro-inflammatory cytokines IL-1β, IL-6, and IL-18. Acrylamide also induced activation of microglia, indicated by increased expression of microglial markers, CD11b and CD40, and increased CD11b/c-positive microglial area and microglial process length. In vitro studies using BV-2 microglial cells confirmed microglial inflammatory response, as evident by time- (0-36h; 50μM) and dose- (0-500μM; 24h) dependent increase in mRNA expression of IL-1β and IL-18, as well as the inflammatory marker iNOS. Furthermore, acrylamide-induced upregulation of pro-inflammatory cytokines was mediated through the NLRP3 inflammasome pathway, as evident by increased expression of NLRP3, caspase 1, and ASC in the rat cerebral cortex, and by the inhibitory effects of NLRP3 inflammasome inhibitor on the acrylamide-induced upregulation of NLRP3, caspase 1, IL-1β, and IL-18 in BV-2 microglia.

Anti-nociceptive Role of CXCL1 in a Murine Model of Peripheral Nerve Injury-induced Neuropathic Pain

Both spinal cord infiltrating CD4+ T lymphocytes and microglial CD40 contribute to the maintenance of neuropathic pain-like behaviors induced by spinal nerve L5 transection (L5Tx), a murine model of neuropathic pain. Here, we sought to investigate the involvement of multiple chemokines in microglial CD40-mediated and CD4+ T lymphocytes-mediated L5Tx-induced sensory hypersensitivity. Spinal cord chemokine expression in CD4 knockout (KO), CD40 KO, and wild type (WT) BALB/c mice was determined at the protein level via multiplex assays and at the RNA level via quantitative real-time PCR. In WT mice, L5Tx induced significant increases in CCL2, CCL3, and CCL5 expression (protein and RNA) up to day 21 post-L5Tx, while CD4 KO mice displayed blunted, predominantly non-significant, responses in these chemokines at protein levels post-L5Tx. L5Tx also induced increased expression of these chemokines in CD40 KO mice; however, the overall protein levels of these chemokines were significantly lower than those in WT mice. Further, L5Tx induced a significant increase in CXCL1 at the protein level and in CXCR2 at RNA level only in CD40 KO mice. Intrathecal administration of CXCL1 in WT mice significantly reduced L5Tx-induced mechanical hypersensitivity. CD40 KO mice also displayed higher levels of Ly6G (neutrophil marker) RNA expression in the lumbar spinal cord post-L5Tx. Altogether, our data suggest that CD4+ T lymphocytes and microglial CD40 mediate their pro-nociceptive effects in part by promoting selected chemokine responses, and more importantly, CXCL1 can play an anti-nociceptive role in peripheral nerve injury-induced neuropathic pain, which is possibly mediated by infiltrating neutrophils.

The role of CD40 in calcitonin gene related protein (CGRP) mediated antiviral effect in glial cells

Abstract LP-BM5 is a murine retrovirus that induces peripheral neuropathy and AIDS like immune deficiency in B6 mice. Upon infection, primary sensory neurons in the spinal cord express elevated levels of calcitonin gene related protein (CGRP). Previously, we showed that CGRP induced reduction of LP-BM5 viral loads in primary mixed glial cells. The purpose of this current study was to investigate possible CGRP downstream targets that may contribute to its antiretroviral response. We hypothesized that CGRP decreases the viral load in glial cells by modifying the CD40 expression; increasing in CD40 signaling may promote production of cytokines and chemokines with antiretroviral properties. Using CD40 knockout mice we showed that CD40 is required for CGRP mediated antiretroviral response in mixed glia. In microglial cell line, CD40 expression was elevated after treatment with CGRP. Similar effect was seen in microglia from spinal cord derived mixed glial cultures. While LP-BM5 increased microglial CD40 expression gradually over time up to 7 days post-infection in primary mixed glia, CGRP caused an early elevation (24 hr post-infection) of microglial CD40 expression in microglia and stayed relatively steady levels 7 days after infection. CGRP also promoted chemokine CXCL1(KC) production in mixed glia. Our data suggest that activation of CD40 mediated signaling may result in increased production of chemokines that may interfere with retroviral replication. Future studies will be directed to specifically delineate CD40 downstream target involved in antiretroviral response in glial cells.

Potential anti-nociceptive role of chemokine CXCL1 in peripheral nerve injury-induced neuropathic pain

Abstract Our previous studies have indicated that both microglial CD40 and spinal cord infiltrating CD4+ T cells play critical roles in the maintenance of peripheral nerve injury-induced neuropathic pain using a murine model of neuropathic pain, spinal nerve L5 transection (L5Tx). It is well accepted that chemokines play important role in the development of neuropathic pain. To further understand the role of microglial CD40 and CD4+ T cells in peripheral nerve injury-induced spinal cord chemokine response, we determined the levels of various chemokines in the lumbar spinal cord in CD40 knockout (KO), CD4 KO, and wild type (WT) BALB/c mice post-L5Tx. Using a multiplex assay, a total of eight chemokines CXCL1 (KC), CCL1 (TCA-3), CCL2 (MCP-1), CCL3 (MIP-1 alpha), CCL5 (RANTES), CCL11 (Eotaxin), CCL17 (TARC), and CCL22 (MDC) were examined. In WT mice, but not KO mice, L5Tx induced significant, gradual increases in CCL2, CCL3 and CCL5 up to day 21 post-L5Tx. At RNA level, L5Tx induced less pronounced increases of these chemokines in both types of KO mice compared to WT mice. These reduced chemokine response correlate with our previous observation that both CD40 KO and CD4 KO mice displayed significantly less mechanical hypersensitivity following L5Tx. Interestingly, L5Tx induced a significant increase in CXCL1 only in CD40 KO mice. Intrathecal injection of CXCL1 significantly reduced L5Tx-induced mechanical hypersensitivity in WT mice, indicating a potential protective effect of CXCL1 in neuropathic pain. Altogether, our data suggest chemokines’ roles in the development of neuropathic pain are chemokine type-specific.

Differential effects of stress on microglial cell activation in male and female medial prefrontal cortex

Susceptibility to stress-linked psychological disorders, including post-traumatic stress disorder and depression, differs between men and women. Dysfunction of medial prefrontal cortex (mPFC) has been implicated in many of these disorders. Chronic stress affects mPFC in a sex-dependent manner, differentially remodeling dendritic morphology and disrupting prefrontally mediated behaviors in males and females. Chronic restraint stress induces microglial activation, reflected in altered microglial morphology and immune factor expression, in mPFC in male rats. Unstressed females exhibit increased microglial ramification in several brain regions compared to males, suggesting both heightened basal activation and a potential for sex-dependent effects of stress on microglial activation. Therefore, we assessed microglial density and ramification in the prelimbic region of mPFC, and immune-associated genes in dorsal mPFC in male and female rats following acute or chronic restraint stress. Control rats were left unstressed. On the final day of restraint, brains were collected for either qPCR or visualization of microglia using Iba-1 immunohistochemistry. Microglia in mPFC were classified as ramified, primed, reactive, or amoeboid, and counted stereologically. Expression of microglia-associated genes (MHCII, CD40, IL6, CX3CL1, and CX3CR1) was also assessed using qPCR. Unstressed females showed a greater proportion of primed to ramified microglia relative to males, alongside heightened CX3CL1–CX3CR1 expression. Acute and chronic restraint stress reduced the proportion of primed to ramified microglia and microglial CD40 expression in females, but did not significantly alter microglial activation in males. This sex difference in microglial activation could contribute to the differential effects of stress on mPFC structure and function in males versus females.

Involvement of microglial CD40 in murine retrovirus-induced peripheral neuropathy

B6 mice infected with LP-BM5 develop severe immunodeficiency (termed murine acquired immunodeficiency syndrome (MAIDS)) and peripheral neuropathy. To determine whether microglial CD40 is involved in LP-BM5-induced peripheral neuropathy, B6-CD40 knockout (KO) mice and B6-CD40 KO mice adoptively transferred either total leukocytes or B cells were examined for behavioral sensitivity, tissue viral loads, cytokine responses, and the development of MAIDS. All three CD40 KO groups developed MAIDS, the severity of which was correlated with peripheral cytokine responses. CD40 KO mice displayed significantly reduced mechanical hypersensitivity post-infection compared to wild-type mice regardless of cell transfer. These findings support microglial CD40 involvement in LP-BM5-induced peripheral neuropathy.

Involvement of microglial CD40 in murine retrovirus-induced peripheral neuropathy (P6173)

Abstract The underlying mechanism of HIV-associated peripheral neuropathy is unclear. C57BL/6 (B6) mice infected with LP-BM5 develop severe immunodeficiency (termed as MAIDS) and peripheral neuropathy. It is known that CD154-CD40 interactions between CD4+ T and B cells are required for the manifestation of MAIDS post-LP-BM5 infection (p.i.) and that HIV encephalitis is associated with increased expression of CD40 on microglia. We aimed to determine whether spinal cord microglial CD40 signaling is involved in LP-BM5-induced peripheral neuropathy. B6-CD40 KO mice were adoptively transferred with either total leukocytes or B cells and examined for mechanical sensitivity, tissue viral loads, and cytokine responses along with the development of MAIDS p.i.. CD40 KO mice transferred either cell population developed MAIDS, the severity of which was correlated with peripheral cytokine responses. CD40 KO mice displayed transient and slightly increased mechanical sensitivity p.i. regardless of cell transfer. In all peripheral tissues examined, increased viral RNA was detected in all infected mice without significant group differences. However, in the lumbar spinal cord, infected wild type B6 mice had the highest viral load and cytokine responses among all groups. Neither type of cell transfer enhanced the LP-BM5-induced increase in viral load and cytokine responses in CD40 KO mice. Together, these data support the involvement of microglial CD40 in LP-BM5-induced peripheral neuropathy.

The neural cell adhesion molecule-derived peptide, FGL, attenuates lipopolysaccharide-induced changes in glia in a CD200-dependent manner

Fibroblast growth loop (FGL) is a neural cell adhesion molecule (NCAM)-mimetic peptide that mimics the interaction of NCAM with fibroblast growth factor receptor (FGFR). FGL increases neurite outgrowth and promotes neuronal survival in vitro, and it has also been shown to have neuroprotective effects in vivo. More recent evidence has indicated that FGL has anti-inflammatory effects, decreasing age-related changes in microglial activation and production of inflammatory cytokines. These changes have been associated with an FGL-induced increase in expression of the glycoprotein, CD200, which interacts with its receptor to help maintain microglia in a quiescent state. However whether the FGL-induced anti-inflammatory effects are CD200-dependent has not been examined. The objective of this study was to address this question. Mixed glia were prepared from brain tissue of neonatal wildtype and CD200-deficient mice and preincubated with FGL prior to stimulation with lipopolysaccharide (LPS). Cells were assessed for mRNA expression of markers of microglial activation, CD11b, CD40 and intercellular adhesion molecule 1 (ICAM-1) and also the inflammatory cytokines, interleukin (IL)-1β, IL-6 and tumour necrosis factor (TNF)-α, while supernatant concentrations of these cytokine were also assessed. LPS significantly increased all these parameters and the effect was greater in cells prepared from CD200-deficient mice. Whereas FGL attenuated the LPS-induced changes in cells from wildtype mice, it did not do so in cells from CD200-deficient mice. We conclude that the FGL-induced changes in microglial activation are CD200-dependent and demonstrate that the interaction of astrocytes with microglia is critically important for modulating microglial activation.

Dok2 mediates the CD200Fc attenuation of Aβ-induced changes in glia

BackgroundThe interaction between the membrane glycoprotein, CD200 and its cognate receptor CD200 receptor (CD200R), has been shown to play a role in maintaining microglia in a quiescent state. There is evidence of increased activation under resting and stimulated conditions in microglia prepared from CD200-deficient mice compared with wild-type mice, whereas activation of the receptor by CD200 fusion protein (CD200Fc) ameliorates inflammatory changes which are evident in the central nervous system (CNS) of the mouse model of multiple sclerosis (MS), experimental autoimmune encephalomyelitis (EAE) and also in the hippocampus of aged rats. Additionally, an inverse relationship between microglial activation and expression of CD200 has been observed in animals treated with lipopolysaccharide (LPS) or amyloid-β (Aβ).MethodsWe assessed the effect of CD200R activation by CD200Fc on Aβ-induced production of the pro-inflammatory cytokines, interleukin-1β (IL-1β) and tumor necrosis factor-α (TNFα) and the expression of microglial activation markers, CD68 and CD40 in cultured glia. The role played by downstream of tyrosine kinase 2 (Dok2) phosphorylation in mediating the effects of CD200R activation was evaluated by siRNA knockdown of Dok2. To further examine the impact of inflammatory changes on synaptic plasticity, the effect of CD200Fc on Aβ-induced impairment of long-term potentiation (LTP) in the CA1 region of hippocampal slices was also investigated.ResultsWe demonstrate that Aβ-induced increases in IL-1β, TNFα, CD68 and CD40 were inhibited by CD200Fc. The evidence suggests that Dok2 phosphorylation is a key factor in mediating the effect of CD200Fc, since Dok2 knockdown by siRNA abrogated its effects on microglial activation and inflammatory cytokine production. Consistent with evidence that inflammatory changes negatively impact on LTP, we show that the Aβ-induced impairment of LTP was attenuated by CD200Fc.ConclusionsThe findings suggest that activation of CD200R and Dok2 is a valuable strategy for modulating microglial activation and may have therapeutic potential in neurodegenerative conditions.

Differential lumbar spinal cord mononuclear cell responses among wild type, CD4 knockout, and CD40 knockout mice in spinal nerve L5 transection-induced neuropathic pain (54.17)

Abstract We have previously demonstrated that both lumbar spinal cord-infiltrating CD4+ T cells and lumbar spinal cord microglial CD40 contribute to the maintenance of mechanical hypersensitivity in the murine model of neuropathic pain spinal nerve L5 transection (L5Tx). To further delineate the CD4 and CD40-mediated mechanisms involved in the development of L5Tx-induced neuropathic pain behaviors, we examined the lumbar spinal cord mononuclear cells of wild type (WT) BALB/c, BALB/c-CD4 knockout (KO), and BALB/c-CD40 KO mice in time course studies via flow cytometry. In WT mice, L5Tx significantly increased the total numbers of lumbar spinal cord mononuclear cells, microglial cells (CD45loCD11b+), and infiltrating leukocytes (CD45hi) in the ipsilateral side of the spinal cord on both days 3 and 7 post-surgery. Meanwhile, in CD4 KO mice, the only significant elevation in microglial cells was observed on day 7 post-L5Tx, and there were no increases in mononuclear cells and infiltrating leukocytes numbers post-L5Tx. On the other hand, in CD40 KO mice, L5Tx did not induce any of the changes observed in WT mice. Altogether, these data indicate that both CD4 and CD40 play a role in L5Tx-induced leukocyte infiltration into the lumbar spinal cord but have differential contributions to spinal cord microglial activation following peripheral nerve injury.

Differential Lumbar Spinal Cord Responses among Wild Type, CD4 Knockout, and CD40 Knockout Mice in Spinal Nerve L5 Transection-Induced Neuropathic Pain

BackgroundOur previous studies have indicated that both lumbar spinal cord-infiltrating CD4+ T cells and microglial CD40 contribute to the maintenance of mechanical hypersensitivity in a murine model of neuropathic pain spinal nerve L5 transection (L5Tx). To further delineate the CD4 and CD40-mediated mechanisms involved in the development of L5Tx-induced neuropathic pain behaviors, we examined the lumbar spinal cord mononuclear cells of wild type (WT) BALB/c, BALB/c-CD4 knockout (KO), and BALB/c-CD40 KO mice via flow cytometry.ResultsIn WT mice, L5Tx induced significant but transient (at day 3 and/or day 7) increases of the total numbers of mononuclear cells, microglial cells (CD45loCD11b+), and infiltrating leukocytes (CD45hi) in the ipsilateral side of the spinal cord. In CD4 KO mice, significant elevation of microglia was detected only on day 7 post-L5Tx, while no significant increase in infiltrating leukocytes post-L5Tx was observed. CD40 KO mice did not exhibit any of the changes observed in WT mice. Furthermore, neutralizing CD40 antibody treatment indicated an early involvement of CD40 signaling in the development of L5Tx-induced mechanical hypersensitivity.ConclusionsAltogether, data indicate that both CD4 and CD40 play a role in L5Tx-induced leukocyte infiltration into the lumbar spinal cord but have differential contributions to spinal cord microglial activation following peripheral nerve injury.

Involvement of calcitonin gene-related peptide and CCL2 production in CD40-mediated behavioral hypersensitivity in a model of neuropathic pain

The neuropeptide calcitonin gene-related peptide (CGRP) is known to play a pro-nociceptive role after peripheral nerve injury upon its release from primary afferent neurons in preclinical models of neuropathic pain. We previously demonstrated a critical role for spinal cord microglial CD40 in the development of spinal nerve L5 transection (L5Tx)-induced mechanical hypersensitivity. Herein, we investigated whether CGRP is involved in the CD40-mediated behavioral hypersensitivity. First, L5Tx was found to significantly induce CGRP expression in wild-type (WT) mice up to 14 days post-L5Tx. This increase in CGRP expression was reduced in CD40 knockout (KO) mice at day 14 post-L5Tx. Intrathecal injection of the CGRP antagonist CGRP8-37 significantly blocked L5Tx-induced mechanical hypersensitivity. In vitro, CGRP induced glial IL-6 and CCL2 production, and CD40 stimulation added to the effects of CGRP in neonatal glia. Further, there was decreased CCL2 production in CD40 KO mice compared to WT mice 21 days post-L5Tx. However, CGRP8-37 did not significantly affect spinal cord CCL2 production following L5Tx in WT mice. Altogether, these data suggest that CD40 contributes to the maintenance of behavioral hypersensitivity following peripheral nerve injury in part through two distinct pathways, the enhancement of CGRP expression and spinal cord CCL2 production.

Critical role of microglial CD40 in the maintenance of mechanical hypersensitivity in a murine model of neuropathic pain

We recently demonstrated a contributing role of spinal cord infiltrating CD4+ T lymphocytes in the maintenance of mechanical hypersensitivity in a rodent model of neuropathic pain, spinal nerve L5 transection (L5Tx). It has been demonstrated that microglia play a role in the etiology of pain states. We hypothesized that infiltrating CD4+ T lymphocytes communicate with microglia via a CD40-CD154 interaction. Here, we investigated the role of CD40 in the development of mechanical hypersensitivity post-L5Tx. CD40 KO mice displayed significantly decreased mechanical sensitivity compared with WT mice starting from day 5 post-L5Tx. Using bone marrow chimeric mice, we further identified a pro-nociceptive role of CNS microglial CD40 rather than the peripheral leukocytic CD40. Flow cytometric analysis determined a significant increase of CD40+ microglia in the ipsilateral side of lumbar spinal cord post-L5Tx. Further, spinal cord proinflammatory cytokine (IL-1beta, IL-6, IL-12, and TNF-alpha) profiling demonstrated an induction of IL-6 in both WT and CD40 KO mice post-L5Tx prior to the increase of microglial CD40 expression, indicating a CD40-independent induction of IL-6 following L5Tx. These data establish a novel role of microglial CD40 in the maintenance of nerve injury-induced behavioral hypersensitivity, a behavioral sign of neuropathic pain.

Induction of IL-6 in mixed glial cultures – potential role of CGRP in CD40-dependent neuropathic pain (91.8)

Abstract We have previously demonstrated a critical role of spinal cord microglial CD40 in the development of spinal nerve L5 transection (L5Tx)-induced neuropathic pain. Cross-talk between pro-inflammatory mediators and pro-nociceptive factors is believed to play an essential role in the development of neuropathic pain. Here, we investigated the effects of the pro-nociceptive factors calcitonin gene-related peptide (CGRP) and CX3CL1 with/without CD40 on the production of several pro-inflammatory mediators by glial cells in vitro. Anti-CD40 induced low levels of nitric oxide, a known pro-nociceptive factor, while CX3CL1 enhanced CXCL10 production by mixed glia. Interestingly, while anti-CD40 and CX3CL1 had little effect on IL-6 production, CGRP induced a significant secretion of IL-6 by glia that is unaffected by CD40 co-stimulation. In vivo data indicated that spinal cord IL-6 was increased by day 1 and spinal cord microglial CD40 expression was increased in an IL-6 dependent fashion by day 3 post-L5Tx. Together, these data lead us to hypothesize that CGRP released from primary sensory nerve terminals following L5Tx induces spinal cord glial IL-6 production, which in turn enhances microglial CD40 expression, thus facilitating the development of neuropathic pain. Future studies with microglial-enriched and depleted populations will be used to further delineate this pathway. Support of this study: 1K01DA023503-01A1 (Cao), NIDA.

Noradrenaline reuptake inhibitors limit neuroinflammation in rat cortex following a systemic inflammatory challenge: implications for depression and neurodegeneration

Evidence suggests that noradrenaline has a tonic anti-inflammatory action in the central nervous system (CNS) via its ability to suppress microglial and astrocytic activation, and inhibit production of inflammatory mediators. Consequently it is suggested that noradrenaline may play an endogenous neuroprotective role in CNS disorders where inflammatory events contribute to pathology. Here we demonstrate that acute treatment of rats with the noradrenaline reuptake inhibitors (NRIs) desipramine and atomoxetine elicited anti-inflammatory actions in rat cortex following a systemic challenge with bacterial lipopolysaccharide (LPS). This was characterized by a reduction in cortical gene expression of the pro-inflammatory cytokines interleukin-1beta (IL-1beta) and tumour necrosis factor-alpha (TNF-alpha), the enzyme inducible nitric oxide synthase (iNOS), and the microglial activation markers CD11b and CD40. These anti-inflammatory actions of NRIs were associated with reduced activation of nuclear factor-kappa B (NF-kappaB); a transcription factor that is considered the major regulator of inflammation in the CNS. To determine whether NRI administration directly altered glial expression of these inflammatory markers, primary cortical glial cells were exposed in vitro to the NRIs desipramine or atomoxetine. In vitro treatment with NRIs largely failed to alter mRNA expression of IL-1beta, TNF-alpha, iNOS, CD11b and CD40, following stimulation with LPS. Similarly, LPS-induced TNF-alpha and IL-1beta protein production from glial cells was unaffected by NRI treatment. In contrast, in vitro exposure of cultured glial cells to noradrenaline suppressed IL-1beta, TNF-alpha, iNOS and CD40 expression. These results suggest that in vivo administration of NRIs limit inflammatory events in the brain, probably by increasing noradrenaline availability. Overall, this study has yielded significant insights into the ability of noradrenaline-augmentation strategies to limit neuroinflammation.

Apigenin and luteolin modulate microglial activation via inhibition of STAT1-induced CD40 expression

BackgroundIt is well known that most neurodegenerative diseases are associated with microglia-mediated inflammation. Our previous research demonstrates that the CD40 signaling is critically involved in microglia-related immune responses in the brain. For example, it is well known that the activation of the signal transducer and activator of transcription (STAT) signaling pathway plays a central role in interferon-gamma (IFN-γ)-induced microglial CD40 expression. We and others have previously reported that microglial CD40 expression is significantly induced by IFN-γ and amyloid-β (Aβ) peptide. Recent studies have shown that certain flavonoids possess anti-inflammatory and neuroprotective properties distinct from their well-known anti-oxidant effects. In particular, flavonoids, apigenin and luteolin have been found to be effective CD40 immunomodulators.MethodsCultured microglia, both N9 and primary derived lines, were treated with flavonoids in the presence of IFN-γ and/or CD40 ligation to assess any anti-inflammatory effects and/or mechanisms. CD40 expression on microglia was analyzed by fluorescence activated cell sorting (FACS). Anti-inflammatory effects and mechanisms were confirmed by ELISA for interlekin-6 (IL-6) and TNF-α, lactate dehydrogenase (LDH) assay, and STAT1 Western blotting.ResultsApigenin and luteolin concentration-dependently suppressed IFN-γ-induced CD40 expression. Apigenin and luteolin also suppressed microglial TNF-α and IL-6 production stimulated by IFN-gamma challenge in the presence of CD40 ligation. In addition, apigenin and luteolin markedly inhibited IFN-γ-induced phosphorylation of STAT1 with little impact on cell survival.ConclusionOur findings provide further support for apigenin and luteolin's anti-inflammatory effects and suggest that these flavonoids may have neuroprotective/disease-modifying properties in various neurodegenerative disorders, including Alzheimer's disease (AD).

Peripherally Administered Human Umbilical Cord Blood Cells Reduce Parenchymal and Vascularβ-Amyloid Deposits in Alzheimer Mice

Modulation of immune/inflammatory responses by diverse strategies including amyloid-beta (Abeta) immunization, nonsteroidal anti-inflammatory drugs, and manipulation of microglial activation states has been shown to reduce Alzheimer's disease (AD)-like pathology and cognitive deficits in AD transgenic mouse models. Human umbilical cord blood cells (HUCBCs) have unique immunomodulatory potential. We wished to test whether these cells might alter AD-like pathology after infusion into the PSAPP mouse model of AD. Here, we report a marked reduction in Abeta levels/beta-amyloid plaques and associated astrocytosis following multiple low-dose infusions of HUCBCs. HUCBC infusions also reduced cerebral vascular Abeta deposits in the Tg2576 AD mouse model. Interestingly, these effects were associated with suppression of the CD40-CD40L interaction, as evidenced by decreased circulating and brain soluble CD40L (sCD40L), elevated systemic immunoglobulin M (IgM) levels, attenuated CD40L-induced inflammatory responses, and reduced surface expression of CD40 on microglia. Importantly, deficiency in CD40 abolishes the effect of HUCBCs on elevated plasma Abeta levels. Moreover, microglia isolated from HUCBC-infused PSAPP mice demonstrated increased phagocytosis of Abeta. Furthermore, sera from HUCBC-infused PSAPP mice significantly increased microglial phagocytosis of the Abeta1-42 peptide while inhibiting interferon-gammainduced microglial CD40 expression. Increased microglial phagocytic activity in this scenario was inhibited by addition of recombinant CD40L protein. These data suggest that HUCBC infusion mitigates AD-like pathology by disrupting CD40L activity.

Critical role of microglial CD40 in neuropathic pain

Critical role of microglial CD40 in neuropathic pain