DeRen Huang

Chemokines and chemokine receptors in inflammation of the nervous system: manifold roles and exquisite regulation

This article focuses on the production of chemokines by resident glial cells of the nervous system. We describe studies in two distinct categories of inflammation within the nervous system: immune-mediated inflammation as seen in experimental autoimmune encephalomyelitis (EAE) or multiple sclerosis (MS) and post-traumatic inflammation. We provide evidence that chemokines play a role in amplifying the inflammatory reaction in EAE (and, probably, MS). In the context of neural trauma, chemokines appear to be primary stimuli for leukocyte recruitment. Strikingly, expression of monocyte chemoattractant protein (MCP)-1 and interferon-gamma-inducible protein-10 (IP-10) are largely restricted to astrocytes or other glial cells in these diverse pathological states. The remainder of the review focuses on studies that address the molecular mechanisms which underlie transcriptional regulation of three astrocyte-derived chemokines: MCP-1, IP-10 and beta-R1/interferon-gamma-inducible T-cell chemoattractant (I-TAC). Based on these studies, we propose that the complex promoters of these genes are marvelously organized for flexible and efficient response to challenge. In the case of MCP-1, several different stimuli can elicit gene transcription, acting through a conserved mechanism that includes binding of inducible transcription factors and recruitment of the constitutive factor Sp1. For IP-10 and beta-R1/I-TAC, it appears that efficient gene transcription occurs only in highly inflammatory circumstances that produce aggregates of simultaneous stimuli. These characteristics, in turn, mirror the expression patterns of the endogenous genes: MCP-1 is expressed under a variety of circumstances, while IP-10 appears primarily during immune-mediated processes that feature exposure of resident neuroglia to high levels of inflammatory cytokines.

The neuronal chemokine CX3CL1/fractalkine selectively recruits NK cells that modify experimental autoimmune encephalomyelitis within the central nervous system

Leukocyte trafficking to the central nervous system (CNS), regulated in part by chemokines, determines severity of the demyelinating diseases multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). To examine chemokine receptor CX3CR1 in EAE, we studied CX3CR1GFP/GFP mice, in which CX3CR1 targeting by insertion of Green Fluorescent Protein (GFP) allowed tracking of CX3CR1+ cells in CX3CR1+/GFP animals and cells destined to express CX3CR1 in CX3CR1GFP/GFP knockouts. NK cells were markedly reduced in the inflamed CNS of CX3CR1‐deficient mice with EAE, whereas recruitment of T cells, NKT cells and monocyte/macrophages to the CNS during EAE did not require CX3CR1. Impaired recruitment of NK cells in CX3CR1GFP/GFP mice was associated with increased EAE‐related mortality, nonremitting spastic paraplegia and hemorrhagic inflammatory lesions. The absence of CD1d did not affect the severity of EAE in CX3CR1GFP/GFP mice, arguing against a role for NKT cells. Accumulation of NK cells in livers of wild‐type (WT) and CX3CR1GFP/GFP mice with cytomegalovirus hepatitis was equivalent, indicating that CX3CL1 mediated chemoattraction of NK cells was relatively specific for the CNS. These results are the first to define a chemokine that governs NK cell migration to the CNS, and the findings suggest novel therapeutic manipulation of CX3CR1 + NK cells. Huang, D., Shi, F.‐D., Jung, S., Pien, G. C., Wang, J., Salazar‐Mather, T. P., He, T. T., Weaver, J. T., Ljunggren, H. G., Biron, C. A., Littman, D. R., Ransohoff, R. M. FASEB J. 20, 896–905 (2006)

Chronic expression of monocyte chemoattractant protein-1 in the central nervous system causes delayed encephalopathy and impaired microglial function in mice

Increased central nervous system (CNS) levels of monocyte chemoattractant protein 1 [CC chemokine ligand 2 (CCL2) in the systematic nomenclature] have been reported in chronic neurological diseases such as human immunodeficiency virus type 1‐associated dementia, amyotrophic lateral sclerosis, and multiple sclerosis. However, a pathogenic role for CCL2 has not been confirmed, and there is no established model for the effects of chronic CCL2 expression on resident and recruited CNS cells. We report that aged (>6 months) transgenic (tg) mice expressing CCL2 under the control of the human glial fibrillary acidic protein promoter (huGFAP‐CCL2hi tg+ mice) manifested encephalopathy with mild perivascular leukocyte infiltration, impaired blood brain barrier function, and increased CD45‐immunoreactive microglia, which had morphologic features of activation. huGFAP‐CCL2hi tg+ mice lacking CC chemokine receptor 2 (CCR2) were normal, showing that chemokine action via CCR2 was required. Studies of cortical slice preparations using video confocal microscopy showed that microglia in the CNS of huGFAP‐CCL2hi tg+ mice were defective in expressing amoeboid morphology. Treatment with mutant CCL2 peptides, a receptor antagonist and an obligate monomer, also suppressed morphological transformation in this assay, indicating a critical role for CCL2 in microglial activation and suggesting that chronic CCL2 exposure desensitized CCR2 on microglia, which in the CNS of huGFAP‐CCL2hi tg+ mice, did not up‐regulate cell‐surface expression of major histocompatibility complex class II, CD11b, CD11c, or CD40, in contrast to recruited perivascular macrophages that expressed enhanced levels of these markers. These results indicate that huGFAP‐CCL2hi tg+ mice provide a useful model to study how chronic CNS expression of CCL2 alters microglial function and CNS physiology.—Huang, D., Wujek, J., Kidd, G., He, T. T., Cardona, A., Sasse, M. E., Stein, E. J., Kish, J., Tani, M., Charo, I. F., Proudfoot, A. E., Rollins, B. J., Handel, T., Ransohoff, R. M. Chronic expression of monocyte chemoattractant protein‐1 in the central nervous system causes delayed encephalopathy and impaired microglial function in mice. FASEB J. 19, 761–772 (2005)

Isolation of murine microglial cells for RNA analysis or flow cytometry

There is increasing interest in the isolation of adult microglia to study their functions at a morphological and molecular level during normal and neuroinflammatory conditions. Microglia have important roles in brain homeostasis, and in disease states they exert neuroprotective or neurodegenerative functions. To assay expression profiles or functions of microglia, we have developed a method to isolate microglial cells and infiltrating leukocytes from adult mouse brain. This protocol uses a digestion cocktail containing collagenase and dispase, and it involves separation over discontinuous percoll gradients. Isolated cells can be used for RNA analysis, including RNase protection analysis (RPA), quantitative RT-PCR, high-density microarray, proteomic or flow cytometric characterization of cell surface markers or adoptive transfer. Cell isolation can be completed in less than 4 h.

Severe Disease, Unaltered Leukocyte Migration, and Reduced IFN-γ Production in CXCR3−/− Mice with Experimental Autoimmune Encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is a CD4+ Th1 T cell-mediated disease of the CNS, used to study certain aspects of multiple sclerosis. CXCR3, the receptor for CXCL10, CXCL9, and CXCL11, is preferentially expressed on activated Th1 T cells and has been proposed to govern the migration of lymphocytes into the inflamed CNS during multiple sclerosis and EAE. Unexpectedly, CXCL10-deficient mice were susceptible to EAE, leaving uncertain what the role of CXCR3 and its ligands might play in this disease model. In this study, we report that CXCR3−/− mice exhibit exaggerated severity of EAE compared with wild-type (CXCR3+/+) littermate mice. Surprisingly, there were neither quantitative nor qualitative differences in CNS-infiltrating leukocytes between CXCR3+/+ and CXCR3−/− mice with EAE. Despite these equivalent inflammatory infiltrates, CNS tissues from CXCR3−/− mice with EAE showed worsened blood-brain barrier disruption and more von Willebrand factor-immunoreactive vessels within inflamed spinal cords, as compared with CXCR3+/+ mice. Spinal cords of CXCR3−/− mice with EAE demonstrated decreased levels of IFN-γ, associated with reduced inducible NO synthase immunoreactivity, and lymph node T cells from CXCR3−/− mice primed with MOG35–55 secreted less IFN-γ in Ag-driven recall responses than cells from CXCR3+/+ animals. CXCR3−/− lymph node T cells also showed enhanced Ag-driven proliferation, which was reduced by addition of IFN-γ. Taken with prior findings, our data show that CXCL10 is the most relevant ligand for CXCR3 in EAE. CXCR3 does not govern leukocyte trafficking in EAE but modulates T cell IFN-γ production and downstream events that affect disease severity.

Chemokine Receptor CXCR3: An Unexpected Enigma

CXCR3, the receptor for CXCL9/MIG, CXCL10/IP-10, and CXCL11/I-TAC, is preferentially expressed on activated Th1 T cells and has been predicted to play an important role in their trafficking. However, this simplistic view of the function of CXCR3 and its ligands has not been borne out by studies of disease models, including experimental autoimmune encephalomyelitis (EAE), using varied methods of receptor blockade, as well as knockout or transgenic mice. This review focuses on the current understanding of the enigmatic role of CXCR3 and its ligands in CNS inflammatory/autoimmune disorders. The conflicting results among varied models of CNS inflammation suggest complex and multiple roles for CXCR3 and its ligands in the pathogenesis of CNS inflammatory/autoimmune diseases. Thus, further study is needed to determine how CXCL10 neutralizing agents or CXCR3 receptor antagonists might be applied to treating human disease.

TNF-α mediates SDF-1α–induced NF-κB activation and cytotoxic effects in primary astrocytes

Stromal-derived cell factor-1 alpha (SDF-1 alpha; CXCL12) and its receptor, CXCR4, are constitutively expressed on neuroepithelial cells and are believed to be involved in both development and pathological processes, such as AIDS-associated neurologic disorders. Here, we demonstrate that SDF-1 alpha activates NF-kappa B, stimulates production of chemokines and cytokines, and induces cell death in primary astrocytes, effects that depend on ongoing secretion of TNF-alpha. SDF-1 alpha upregulated TNF-alpha mRNA and protein secretion, as well as TNF receptor 2 expression. TNF-alpha treatment mimicked SDF-1 alpha induction of NF-kappa B, IL-1 alpha/beta, and RANTES, as well as cell death; neutralizing antibodies against TNF-alpha opposed these responses. We also found that SDF-1 alpha activated Erk1 and Erk2 (Erk1/2) MAPK in a biphasic fashion. Early Erk1/2 activation was stimulated directly by SDF-1 alpha and late activation was mediated by TNF-alpha. PD98059 suppression of early Erk1/2 activation correlated with reduction of SDF-1 alpha-induced TNF-alpha expression. Late Erk1/2 activation was involved in TNF-alpha-stimulated NF-kappa B activation and cytokine induction. SDF-1 alpha was induced in reactive CXCR4-positive astrocytes near axotomized spinal cord motor neurons, consistent with autocrine SDF-1/CXCR4 signaling in these cells. We propose that these novel effects of SDF-1 alpha are relevant to the pathogenic and developmental roles of SDF-1 alpha in the CNS.

Cortical demyelination in PML and MS: Similarities and differences.

Objective: To characterize pathologic changes in the cerebral cortex of patients with multiple sclerosis (MS) and progressive multifocal leukoencephalopathy (PML). Methods: Autopsy brain tissue was obtained from 13 patients with PML, 4 patients with MS, 2 patients with HIV encephalopathy, and 1 subject without neurologic pathology. Immunohistochemistry for myelin proteins, inflammatory cells, and neurofilaments was performed to evaluate the distribution of cortical lesions, their inflammatory activity, and neuritic pathology. Confocal microscopy was applied to examine pathologic changes in neurites in PML cortex. Results: Leukocortical, intracortical, and subpial patterns of cortical demyelination were represented in MS brain tissue. In PML brain tissue intracortical and leukocortical but not subpial lesions were observed. Cortical lesions in PML and MS contained fewer inflammatory cells than demyelinated areas in the white matter. Neuritic pathology in cortical PML lesions was represented by dystrophic and transected neurites. Pathologic modifications in neuritic processes in PML were more evident in highly inflamed white matter than in gray matter areas of demyelination, reminiscent of previous reports of neuritic pathology in MS. JC virus-infected cells were associated with PML white matter, leukocortical and intracortical lesions. Conclusions: Cortical pathology represents a distinct feature of progressive multifocal leukoencephalopathy. Similarities and differences with regard to multiple sclerosis cortical pathology were noted and may be informative regarding the pathogenesis of both disorders. GLOSSARY: AP = alkaline phosphatase; DAB = diaminobenzidine; HAART = highly active antiretroviral therapy; HIVE = HIV encephalopathy; MBP = myelin basic protein; MS = multiple sclerosis; NNTC = NeuroAIDS Tissue Consortium; PLP = proteolipid protein; PML = progressive multifocal leukoencephalopathy; SPMS = secondary progressive multiple sclerosis; X-ALD = X-linked adrenoleukodystrophy.

Polymorphisms in IL-1β and IL-1 receptor antagonist genes are associated with myasthenia gravis

Interleukin 1 (IL-1)β TaqI restriction fragment length polymorphism (RFLP) in exon 5 and IL-1 receptor antagonist (IL-1Ra) polymorphism, variable numbers of an 86-bp tandem repeat (VNTR), were analysed in 107 patients with myasthenia gravis (MG) and 82 ethnically matched healthy control (HC) individuals. Positive association was found with IL-1β TaqI RFLP allele 2 carriage in MG (OR=2.007), while allele 1 was negatively associated with MG (OR=0.498). When homozygous individuals for allele 2 were considered, the association was stronger (OR=4.630), indicating a dose effect of allele 2. Analysis of IL-1β TaqI RFLP in relation to HLA-B8 demonstrated that the allelic association was more pronounced in patients without HLA-B8 (OR=2.813). There was no difference in IL-1Ra VNTR allelic distribution in MG patients compared with HC. However, MG patients who were noncarriers of IL-Ra allele 2 had a significantly higher percentage of IL-1β TaqI RFLP allele 2 carriage (OR=3.085), while there was no such difference in IL-1Ra allele 2 carriers. Our results demonstrate a new genetic marker in MG, which exerts its maximum effect in patients with the lowest MHC-associated susceptibility. We propose a possible pathogenetic role of IL-1β and a possible intrinsic dyregulation of IL-1 in MG.

Transgenic expression of CCL2 in the central nervous system prevents experimental autoimmune encephalomyelitis

CC chemokine ligand 2 (CCL2)/monocyte chemotactic protein‐1, a member of the CC chemokine family, is a chemoattractant for monocytes and T cells through interaction with its receptor CCR2. In the present study, we examined a T helper cell type 1 (Th1)‐dependent disease, proteolipid protein‐induced experimental autoimmune encephalomyelitis, in a transgenic mouse line that constitutively expressed low levels of CCL2 in the central nervous system (CNS) under control of the astrocyte‐specific glial fibrillary acidic protein promoter. CCL2 transgenic mice developed significantly milder clinical disease than littermate controls. As determined by flow cytometry, mononuclear cell infiltrates in the CNS tissues of CCL2 transgenic and littermate‐control mice contained equal numbers of CD4+ and CD8+ T cells, and the CCL2 transgenic mice showed an enhanced number of CNS‐infiltrating monocytes. CNS antigen‐specific T cells from CCL2 transgenic mice produced markedly less interferon‐γ. Overexpression of CCL2 in the CNS resulted in decreased interleukin‐12 receptor expression by antigen‐specific T cells. Collectively, these results indicate that sustained, tissue‐specific expression of CCL2 in vivo down‐regulates the Th1 autoimmune response, culminating in milder clinical disease.