Opposing roles for CXCR3 signaling in central nervous system versus ocular inflammation mediated by the astrocyte-targeted production of IL-12

Adenosine binds predominantly to adenosine receptor A1 subtype in astrocytes and mediates an immunosuppressive effect

The four kinds of adenosine receptor subtypes (ARs), named as ARA1, ARA2A, ARA2B and ARA3, have multiple biological functions. ARs are differently distributed across the body and have distinguished ability of binding adenosine. We try to figure out how these ARs were expressed in astrocytes and which one has the first priority of utilizing adenosine. Firstly, mRNA expressions and membrane localization of all ARs were evaluated by qPCR and western blot. After the membrane localization of all ARs in astrocytes was being confirmed their individual adenosine binding ability was determined by radio-active ligand binding assay respectively. It was revealed that ARA1 had much superior adenosine binding ability than other AR subtypes. Functional study demonstrated that ARA1 potentially mediated an immune suppressive effect in astrocytes. The activation of ARA1 signaling lead to decreased IL-12 and IL-23 production, and decreased chemokine production, including CCL2, CXCL8 and IP-10. When interacted with CD4 cells ARA1 agonist pre-treated astrocytes showed hindered ability of stimulating CD4 cells to secret IL-17 and IFN-γ and inducing CD4 cells' chemo taxi. Finally, in vivo experiment confirmed that local administration of ARA1agonist ameliorated EAE in wild type B6 recipients, but not Ara1-/- recipients. As a conclusion, this paper suggested that adenosine receptor A1 subtype predominantly binds adenosine in astrocytes and mediates an immunosuppressive effect.

Interleukin-12-mediated expression of matrix metalloproteinases in human periodontal ligament fibroblasts involves in NF-κB activation

Interleukin-12 (IL-12) is a proinflammatory cytokine, and its increased level correlates with the severity of periodontitis. However, its role in the pathogenesis of tooth periapical lesions is controversial and has not been completely clarified. The present study aimed to investigate whether IL-12 affects the expression of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) in human periodontal ligament fibroblasts (hPDLFs). After treatment with IL-12 for different times, real-time PCR and Western blotting were used to determine the mRNA and protein levels of MMP-1, MMP-2, MMP-3, MMP-9, MMP-13, TIMP-1, and TIMP-2, respectively. ELISA was applied to measure MMPs and TIMPs secretion production. The results indicated that IL-12 significantly increased the mRNA and protein expression levels of MMP-1, MMP-3, and MMP-13, but down-regulated MMP-2 and MMP-9 mRNA and protein expression in the hPDLFs. Furthermore, IL-12 (10 ng/ml) enhanced the secreted protein production of MMP-1, MMP-3, and MMP-13, and conversely lowered MMP-2 and MMP-9 secretion levels. However, IL-12 treatment did not exert a significant effect on the mRNA and protein levels of TIMP-1 and TIMP-2 and their secreted production. Additionally, IL-12 increased the phosphorylated levels of IκBα and nuclear factor-κB P65 (NF-κB P65), and promoted NF-κB P65 subunit nuclear translocation. Pretreatment with NF-κB inhibitor not only attenuated IL-12-induced IκBα and NF-κB P65 phosphorylation and inhibited NF-κB P65 subunit into nucleus, but also antagonized IL-12-mediated MMP-1, MMP-2, MMP-3, MMP-9, and MMP-13 expression in the hPDLFs. These findings indicate that NF-κB-dependent activation is possibly indispensable for IL-12-mediated MMP expression in hPDLFs.

Astrocytes: Integrative Regulators of Neuroinflammation in Stroke and Other Neurological Diseases

Astrocytes regulate neuroinflammatory responses after stroke and in other neurological diseases. Although not all astrocytic responses reduce inflammation, their predominant function is to protect the brain by driving the system back to homeostasis after injury. They receive multidimensional signals within the central nervous system and between the brain and the systemic circulation. Processing this information allows astrocytes to regulate synapse formation and maintenance, cerebral blood flow, and blood-brain barrier integrity. Similarly, in response to stroke and other central nervous system disorders, astrocytes detect and integrate signals of neuronal damage and inflammation to regulate the neuroinflammatory response. Two direct regulatory mechanisms in the astrocyte arsenal are the ability to form both physical and molecular barriers that seal the injury site and localize the neuroinflammatory response. Astrocytes also indirectly regulate the inflammatory response by affecting neuronal health during the acute injury and axonal regrowth. This ability to regulate the location and degree of neuroinflammation after injury, combined with the long time course of neuroinflammation, makes astrocytic signaling pathways promising targets for therapies.

CXCR3 promotes plaque formation and behavioral deficits in an Alzheimer's disease model

Chemokines are important modulators of neuroinflammation and neurodegeneration. In the brains of Alzheimer's disease (AD) patients and in AD animal models, the chemokine CXCL10 is found in high concentrations, suggesting a pathogenic role for this chemokine and its receptor, CXCR3. Recent studies aimed at addressing the role of CXCR3 in neurological diseases indicate potent, but diverse, functions for CXCR3. Here, we examined the impact of CXCR3 in the amyloid precursor protein (APP)/presenilin 1 (PS1) transgenic mouse model of AD. We found that, compared with control APP/PSI animals, plaque burden and Aβ levels were strongly reduced in CXCR3-deficient APP/PS1 mice. Analysis of microglial phagocytosis in vitro and in vivo demonstrated that CXCR3 deficiency increased the microglial uptake of Aβ. Application of a CXCR3 antagonist increased microglial Aβ phagocytosis, which was associated with reduced TNF-α secretion. Moreover, in CXCR3-deficient APP/PS1 mice, microglia exhibited morphological activation and reduced plaque association, and brain tissue from APP/PS1 animals lacking CXCR3 had reduced concentrations of proinflammatory cytokines compared with controls. Further, loss of CXCR3 attenuated the behavioral deficits observed in APP/PS1 mice. Together, our data indicate that CXCR3 signaling mediates development of AD-like pathology in APP/PS1 mice and suggest that CXCR3 has potential as a therapeutic target for AD.

Absence of IFN-γ increases brain pathology in experimental autoimmune encephalomyelitis-susceptible DRB1*0301.DQ8 HLA transgenic mice through secretion of proinflammatory cytokine IL-17 and induction of pathogenic monocytes/microglia into the central nervous system

Multiple sclerosis is an inflammatory, demyelinating disease of the CNS of presumed autoimmune origin. Of all the genetic factors linked with multiple sclerosis, MHC class II molecules have the strongest association. Generation of HLA class II transgenic (Tg) mice has helped to elucidate the role of HLA class II genes in chronic inflammatory and demyelinating diseases. We have shown that the human HLA-DRB1*0301 gene predisposes to proteolipid protein (PLP)-induced experimental autoimmune encephalomyelitis (EAE), whereas HLA-DQβ1*0601 (DQ6) was resistant. We also showed that the DQ6 molecule protects from EAE in DRB1*0301.DQ6 double-Tg mice by producing anti-inflammatory IFN-γ. HLA-DQβ1*0302 (DQ8) Tg mice were also resistant to PLP(91-110)-induced EAE, but production of proinflammatory IL-17 exacerbated disease in DRB1*0301.DQ8 mice. To further confirm the role of IFN-γ in protection, we generated DRB1*0301.DQ8 mice lacking IFN-γ (DRB1*0301.DQ8.IFN-γ(-/-)). Immunization with PLP(91-110) peptide caused atypical EAE in DRB1*0301.DQ8.IFN-γ(-/-) mice characterized by ataxia, spasticity, and dystonia, hallmarks of brain-specific disease. Severe brain-specific inflammation and demyelination in DRB1*0301.DQ8.IFN-γ(-/-) mice with minimal spinal cord pathology further confirmed brain-specific pathology. Atypical EAE in DRB1*0301.DQ8.IFN-γ(-/-) mice was associated with increased encephalitogenicity of CD4 T cells and their ability to produce greater levels of IL-17 and GM-CSF compared with DRB1*0301.DQ8 mice. Further, areas with demyelination showed increased presence of CD68(+) inflammatory cells, suggesting an important role for monocytes/microglia in causing brain pathology. Thus, our study supports a protective role for IFN-γ in the demyelination of brain through downregulation of IL-17/GM-CSF and induction of neuroprotective factors in the brain by monocytes/microglial cells.

Enhanced acute immune response in IL-12p35-/- mice is followed by accelerated distinct repair mechanisms in Staphylococcus aureus-induced murine brain abscess

BACKGROUND

Murine Staphylococcus aureus-mediated brain abscess comprises 2 major phases, an initial phase of cerebritis, followed by a healing phase characterized by capsule formation.

METHODS

C57BL/6 wild-type (WT) and IL-12p35(-/-) mice were intracerebrally infected with S. aureus to induce brain abscesses. Clinical disease activity and bacterial load were monitored. The cell populations that were involved, as well as their specific mediators, were analyzed by immunohistochemistry, quantitative real-time polymerase chain reaction, and flow cytometry.

RESULTS

In the acute phase, IL-12p35(-/-) mice were protected from disease. This was associated with enhanced recruitment of granulocytes, accompanied by upregulated expression of Il17a, Csf2 (which encodes granulocyte-macrophage colony-stimulating factor), Cxcl1, and Cxcl5, as well as increased expression of proinflammatory mediators, including Nos2 (which encodes inducible nitric oxide synthase), Ptgs2 (which encodes cyclooxygenase 2), and Tnf, that were primarily produced by granulocytes and activated microglia/macrophages. Furthermore, mechanisms associated with beneficial wound healing, including an accelerated formation of a fibrous capsule, were demonstrated by prominent VEGF-A production and collagen deposition driven by an earlier onset of T-helper 2 immunity in the absence of interleukin 12 (IL-12).

CONCLUSIONS

Brain abscess development is orchestrated by IL-12 at different stages of disease. Our data indicate that IL-12 has a nonprotective role in the acute phase and that IL-12 deficiency results in the accelerated formation of a protective capsule during the healing phase, which we consider crucial for early recovery from disease.

CNS-targeted production of IL-17A induces glial activation, microvascular pathology and enhances the neuroinflammatory response to systemic endotoxemia

Interleukin-17A (IL-17A) is a key cytokine modulating the course of inflammatory diseases. Whereas effector functions of IL-17A like induction of antimicrobial peptides and leukocyte infiltration could clearly be demonstrated for peripheral organs, CNS specific effects are not well defined and appear controversial. To further clarify the functional significance of IL-17A in the CNS, we generated a transgenic mouse line with astrocyte-restricted expression of the IL-17A gene. GFAP/IL-17A transgenic mice develop normally and do not show any signs of neurological dysfunction. However, histological characterization revealed astrocytosis and activation of microglia. Demyelination, neurodegeneration or prominent tissue damage was not observed but a vascular pathology mimicking microangiopathic features was evident. Histological and flow cytometric analysis demonstrated the absence of parenchymal infiltration of immune cells into the CNS of GFAP/IL-17A transgenic mice. In GFAP/IL-17A mice, LPS-induced endotoxemia led to a more pronounced microglial activation with expansion of a distinct CD45(high)/CD11b(+) population and increased induction of proinflammatory cytokines compared with controls. Our data argues against a direct role of IL-17A in mediating tissue damage during neuroinflammation. More likely IL-17A acts as a modulating factor in the network of induced cytokines. This novel mouse model will be a very useful tool to further characterize the role of IL-17A in neuroinflammatory disease models.

Increased expression of CD200 on circulating CD11b+ monocytes in patients with neovascular age-related macular degeneration

OBJECTIVE

Dysregulation of retinal microglial activity has been implicated in the pathogenesis of neovascular age-related macular degeneration. Microglia activity can be regulated through the membrane protein CD200 and its corresponding receptor, the CD200 receptor (CD200R). Because both the ligand and the receptor are expressed on a broad spectrum of cell types, we set out to study the expression of CD200 and CD200R on CD11b+ monocytes, granulocytes, and subsets of T lymphocytes.

DESIGN

Prospective, case-control study.

PARTICIPANTS

The study population consisted of 62 patients with neovascular age-related macular degeneration (AMD) and 44 age-matched controls without AMD.

METHODS

The participants were aged 60 years or older, had no history of immune dysfunction or cancer, and were not receiving immune-modulating therapy. All participants were subjected to a structured interview, and detailed retinal imaging was performed: fundus autofluorescence imaging, digital color fundoscopy, and spectral-domain optical coherence tomography. Fluorescein and indocyanine green angiography were performed in patients with suspected neovascular AMD. Visual acuity was measured in both eyes. Fresh venous blood was obtained and stained with monoclonal antibodies and analyzed using flow cytometry within 6 hours of phlebotomy.

MAIN OUTCOME MEASURES

The percentage of CD11b+ monocytes, granulocytes, and CD4+/CD8+ T lymphocytes positive for CD200 or CD200R in patients and controls, respectively.

RESULTS

Patients with neovascular AMD had a higher percentage of CD11b+CD200+ monocytes and CD200+ monocytes compared with controls. Multiple regression analysis revealed that the intergroup differences observed were independent of age. Moreover, an age-related increment in CD200 expression on monocytes was observed in controls with healthy eyes, but not in patients with neovascular AMD. We did not find any differences in CD200 and CD200R expression between patients with subretinal fibrosis and patients without subretinal fibrosis.

CONCLUSIONS

The surface expression of CD200 on circulating CD11b+ monocytes was found to be increased in patients with neovascular AMD compared with controls with healthy eyes. This novel finding supports the notion that altered regulation of the inflammatory response plays an integral role in the pathogenesis of AMD.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.