Central nervous system inflammation and neurological disease in transgenic mice expressing the CC chemokine CCL21 in oligodendrocytes

Accelerated senescence exacerbates α-synucleinopathy in senescence-accelerated prone 8 mice via persistent neuroinflammation

Parkinson's disease (PD) is characterized by the formation of α-synuclein (α-syn) aggregates, which lead to dopaminergic neuronal degeneration. The incidence of PD increases with age, and senescence is considered to be a major risk factor for PD. In this study, we evaluated the effect of senescence on PD pathology using α-synuclein preformed fibrils (PFF) injection model in senescence-accelerated mice. We injected PFF into the substantia nigra (SN) of senescence-accelerated prone 8 (SAMP8) mice and senescence-accelerated resistant 1 (SAMR1) mice. At 24 weeks after injection of saline or PFF, we found that SAMP8 mice injected with PFF exhibited robust Lewy pathology and exacerbated degeneration of dopaminergic neurons in the SN compared to PFF-injected SAMR1 mice. We further observed an increase in the number of Iba1-positive cells in the brains of PFF-injected SAMP8 mice. RNA sequencing revealed that several genes related to neuroinflammation were upregulated in the brains of PFF-injected SAMP8 mice compared to SAMR1 mice. Inflammatory chemokine CC-chemokine ligand 21 (CCL21) was upregulated in PFF-injected SAMP8 mice and expressed in the glial cells of these mice. Our research indicates that accelerated senescence leads to persistent neuroinflammation, which plays an important role in the exacerbation of α-synucleinopathy.

Chemokines in neurodegenerative diseases

Neurodegeneration and neuroinflammation disorders are mainly the result of the deposition of various proteins, such as α-synuclein, amyloid-β and prions, which lead to the initiation and activation of inflammatory responses. Different chemokines are involved in the infiltration and movement of inflammatory leukocytes into the central nervous system (CNS) that express chemokine receptors. Dysregulation of several members of chemokines has been shown in the CNS, cerebrospinal fluid and peripheral blood of patients who have neurodegenerative disorders. Upon infiltration of various cells, they produce many inflammatory mediators such as cytokines. Besides them, some CNS-resident cells, such as neurons and astrocytes, are also involved in the pathogenesis of neurodegeneration by producing chemokines. In this review, we summarize the role of chemokines and their related receptors in the pathogenesis of neurodegeneration and neuroinflammation disorders, including multiple sclerosis, Parkinson's disease and Alzheimer's disease. Therapeutic strategies targeting chemokines or their related receptors are also discussed in this article.

Comparative meta-analysis of transcriptomic studies in spinal muscular atrophy: comparison between tissues and mouse models

BACKGROUND

Spinal Muscular Atrophy (SMA), a neuromuscular disorder that leads to weakness in the muscles due to degeneration of motor neurons. Mutations in the survival motor neuron 1 (SMN1) gene leads to the deficiency of SMN protein that causes SMA. The molecular alterations associated with SMA extends across the transcriptome and proteome. Although several studies have examined the transcriptomic profile of SMA, the difference in experimental settings across these studies highlight the need for a comparative meta-analysis to better understand these differences.

METHODS AND DATA

We conducted a systematic comparative meta-analysis of publicly available gene expression data from six selected studies to elucidate variations in the transcriptomic landscape across different experimental conditions, including tissue types and mouse models. We used both microarray and RNA-seq datasets, retrieved from Gene Expression Omnibus (GEO) and ArrayExpress (AE). Methods included normalization, differential expression analysis, gene-set enrichment analysis (GSEA), network reconstruction and co-expression analysis.

RESULTS

Differential expression analysis revealed varying numbers of differentially expressed genes ranging between zero and 1,655 across the selected studies. Notably, the Metallothionein gene Mt2 was common in several of the eight comparisons. This highlights its role in oxidative stress and detoxification. Additionally, genes such as Hspb1, St14 and Sult1a1 were among the top ten differentially expressed genes in more than one comparison. The Snrpa1 gene, involved in pre-mRNA splicing, was upregulated in the spinal cord and has a strong correlation with other differentially expressed genes from other comparisons in our network reconstruction analysis. Gene-set enrichment analysis identified significant GO terms such as contractile fibers and myosin complexes in more than one comparison which highlights its significant role in SMA.

CONCLUSIONS

Our comparative meta-analysis identified only few genes and pathways that were consistently dysregulated in SMA across different tissues and experimental settings. Conversely, many genes and pathways appeared to play a tissue-specific role in SMA. In comparison with the original studies, reproducibility was rather weak.

B355252 Suppresses LPS-Induced Neuroinflammation in the Mouse Brain

B355252 is a small molecular compound known for potentiating neural growth factor and protecting against neuronal cell death induced by glutamate in vitro and cerebral ischemia in vivo. However, its other biological functions remain unclear. This study aims to investigate whether B355252 suppresses neuroinflammatory responses and cell death in the brain. C57BL/6j mice were intraperitoneally injected with a single dosage of lipopolysaccharide (LPS, 1 mg/kg) to induce inflammation. B355252 (1 mg/kg) intervention was started two days prior to the LPS injection. The animal behavioral changes were assessed pre- and post-LPS injections. The animal brains were harvested at 4 and 24 h post-LPS injection, and histological, biochemical, and cytokine array outcomes were examined. Results showed that B355252 improved LPS-induced behavioral deterioration, mitigated brain tissue damage, and suppressed the activation of microglial and astrocytes. Furthermore, B355252 reduced the protein levels of key pyroptotic markers TLR4, NLRP3, and caspase-1 and inhibited the LPS-induced increases in IL-1β, IL-18, and cytokines. In conclusion, B355252 demonstrates a potent anti-neuroinflammatory effect in vivo, suggesting that its potential therapeutic value warrants further investigation.

Neutrophil biology in injuries and diseases of the central and peripheral nervous systems

The role of inflammation in nervous system injury and disease is attracting increased attention. Much of that research has focused on microglia in the central nervous system (CNS) and macrophages in the peripheral nervous system (PNS). Much less attention has been paid to the roles played by neutrophils. Neutrophils are part of the granulocyte subtype of myeloid cells. These cells, like macrophages, originate and differentiate in the bone marrow from which they enter the circulation. After tissue damage or infection, neutrophils are the first immune cells to infiltrate into tissues and are directed there by specific chemokines, which act on chemokine receptors on neutrophils. We have reviewed here the basic biology of these cells, including their differentiation, the types of granules they contain, the chemokines that act on them, the subpopulations of neutrophils that exist, and their functions. We also discuss tools available for identification and further study of neutrophils. We then turn to a review of what is known about the role of neutrophils in CNS and PNS diseases and injury, including stroke, Alzheimer's disease, multiple sclerosis, amyotrophic lateral sclerosis, spinal cord and traumatic brain injuries, CNS and PNS axon regeneration, and neuropathic pain. While in the past studies have focused on neutrophils deleterious effects, we will highlight new findings about their benefits. Studies on their actions should lead to identification of ways to modify neutrophil effects to improve health.

Neutrophils in traumatic brain injury (TBI): friend or foe?

Our knowledge of the pathophysiology about traumatic brain injury (TBI) is still limited. Neutrophils, as the most abundant leukocytes in circulation and the first-line transmigrated immune cells at the sites of injury, are highly involved in the initiation, development, and recovery of TBI. Nonetheless, our understanding about neutrophils in TBI is obsolete, and mounting evidences from recent studies have challenged the conventional views. This review summarizes what is known about the relationships between neutrophils and pathophysiology of TBI. In addition, discussions are made on the complex roles as well as the controversial views of neutrophils in TBI.

Differentiation and Transmigration of CD4 T Cells in Neuroinflammation and Autoimmunity

CD4⁺ T cells play a central role in orchestrating protective immunity and autoimmunity. The activation and differentiation of myelin-reactive CD4⁺ T cells into effector (Th1 and Th17) and regulatory (Tregs) subsets at the peripheral tissues, and their subsequent transmigration across the blood–brain barrier (BBB) into the central nervous system (CNS) parenchyma are decisive events in the pathogenesis of multiple sclerosis and experimental autoimmune encephalomyelitis. How the Th1, Th17, and regulatory Tregs transmigrate across the BBB into the CNS and cause CNS inflammation is not clearly understood. Studies with transgenic and gene knockout mice have unraveled that Th1, Th17, and Tregs play a critical role in the induction and resolution of neuroinflammation. However, the plasticity of these lineages and functional dichotomy of their cytokine products makes it difficult to understand what role CD4⁺ T cells in the peripheral lymphoid organs, endothelial BBB, and the CNS parenchyma play in the CNS autoimmune response. In this review, we describe some of the recent findings that shed light on the mechanisms behind the differentiation and transmigration of CD4⁺ T cells across the BBB into the CNS parenchyma and also highlight how these two processes are interconnected, which is crucial for the outcome of CNS inflammation and autoimmunity.

Downregulated Glia Interplay and Increased miRNA-155 as Promising Markers to Track ALS at an Early Stage

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease of unknown cause. Absence of specific targets and biomarkers compromise the development of new therapeutic strategies and of innovative tools to stratify patients and assess their responses to treatment. Here, we investigate changes in neuroprotective-neuroinflammatory actions in the spinal cord of SOD1 ^G93A mice, at presymptomatic and symptomatic stages to identify stage-specific biomarkers and potential targets. Results showed that in the presymptomatic stage, there are alterations in both astrocytes and microglia, which comprise decreased expression of GFAP and S100B and upregulation of GLT-1, as well as reduced expression of CD11b, M2-phenotype markers, and a set of inflammatory mediators. Reduced levels of Connexin-43, Pannexin-1, CCL21, and CX3CL1 further indicate the existence of a compromised intercellular communication. In contrast, in the symptomatic stage, increased markers of inflammation became evident, such as NF-κB/Nlrp3-inflammasome, Iba1, pro-inflammatory cytokines, and M1-polarizion markers, together with a decreased expression of M2-phenotypic markers. We also observed upregulation of the CX3CL1-CX3CR1 axis, Connexin-43, Pannexin-1, and of microRNAs (miR)-124, miR-125b, miR-146a and miR-21. Reduced motor neuron number and presence of reactive astrocytes with decreased GFAP, GLT-1, and GLAST further characterized this inflammatory stage. Interestingly, upregulation of miR-155 and downregulation of MFG-E8 appear as consistent biomarkers of both presymptomatic and symptomatic stages. We hypothesize that downregulated cellular interplay at the early stages may represent neuroprotective mechanisms against inflammation, SOD1 aggregation, and ALS onset. The present study identified a set of inflamma-miRNAs, NLRP3-inflammasome, HMGB1, CX3CL1-CX3CR1, Connexin-43, and Pannexin-1 as emerging candidates and promising pharmacological targets that may represent potential neuroprotective strategies in ALS therapy.

Insights into CCL21's roles in immunosurveillance and immunotherapy for gliomas

Chemokine (C-C) motif ligand 21 (CCL21) is involved in immunosurveillance and has recently garnered the attention of neuro-oncologists and neuroscientists. CCL21 contains an extended C-terminus, which increases binding to lymphatic glycosaminoglycans and provides a mechanism for cell trafficking by forming a stationary chemokine concentration gradient that allows cell migration via haptotaxis. CCL21 is expressed by endothelial cells of the blood-brain barrier in physiologic and pathologic conditions. CCL21 has also been implicated in leukocyte extravasation into the central nervous system. In this review, we summarize the role of CCL21 in immunosurveillance and explore its potential as an immunotherapeutic agent for the treatment of gliomas.

Novel CXCL13 transgenic mouse: inflammation drives pathogenic effect of CXCL13 in experimental myasthenia gravis

Abnormal overexpression of CXCL13 is observed in many inflamed tissues and in particular in autoimmune diseases. Myasthenia gravis (MG) is a neuromuscular disease mainly mediated by anti-acetylcholine receptor autoantibodies. Thymic hyperplasia characterized by ectopic germinal centers (GCs) is a common feature in MG and is correlated with high levels of anti-AChR antibodies. We previously showed that the B-cell chemoattractant, CXCL13 is overexpressed by thymic epithelial cells in MG patients. We hypothesized that abnormal CXCL13 expression by the thymic epithelium triggered B-cell recruitment in MG. We therefore created a novel transgenic (Tg) mouse with a keratin 5 driven CXCL13 expression. The thymus of Tg mice overexpressed CXCL13 but did not trigger B-cell recruitment. However, in inflammatory conditions, induced by Poly(I:C), B cells strongly migrated to the thymus. Tg mice were also more susceptible to experimental autoimmune MG (EAMG) with stronger clinical signs, higher titers of anti-AChR antibodies, increased thymic B cells, and the development of germinal center-like structures. Consequently, this mouse model finally mimics the thymic pathology observed in human MG. Our data also demonstrated that inflammation is mandatory to reveal CXCL13 ability to recruit B cells and to induce tertiary lymphoid organ development.

Potentiation of indomethacin-induced anti-inflammatory response by pioglitazone in carrageenan-induced acute inflammation in rats: Role of PPARγ receptors

This study aimed to assess the interaction between anti-inflammatory effects of pioglitazone (peroxysome proliferator activated receptor-gamma (PPARγ) agonist, PGL), and indomethacin (cyclooxygenase (COX) inhibitor, IND) and to evaluate the possible underlying mechanisms. Paw edema induced by carrageenan was used to induce inflammation. Different doses of IND (0.3-10mg/kg) and PGL (1-20mg/kg) alone or in combination were administered intraperitoneally to rats. Paw tissue levels of PPARγ, COX-2, and prostaglandin E2 and serum levels of TNF-α and IL-10 were also estimated. Doses of IND and PGL showed a statistically significant anti-inflammatory effect. Combination of a non-effective dose of IND (0.3mg/kg) with increasing doses of PGL (1-10mg/kg) resulted in potentiated anti-inflammation and vise versa. IND, PGL and the combination were able to reduce the COX-2, PGE2 contents and TNF-α level. Moreover, all these treatments caused elevation in PPARγ levels and IL-10 levels. However, when the rats were pre-treated with GW-9662 (a selective PPARγ antagonist), all the anti-inflammation and alterations in the biochemical factors were antagonized. These results showed that PGL markedly enhanced the anti-inflammatory activity of IND and this effect mediated partly at least, through PPARγ. Possible mechanisms of the interaction were that PGL stimulates the PPARγ and inhibits COX-2 by those cytokines that trigger the PPARγ and also inhibit COX-2. This study suggests that combination therapy with pioglitazone and indomethacin may provide an alternative for the clinical control of inflammation especially in patients with diabetes.

Therapeutic Lymphoid Organogenesis in the Tumor Microenvironment

The inflammatory status of the tumor microenvironment (TME) has been heavily investigated in recent years. Chemokine- and cytokine-signaling pathways such as CCR7, CXCR5, lymphotoxin, and IL-36, which are involved in the generation of secondary lymphoid organs and effector immune responses, are now recognized as having value both as prognostic factors and as immunomodulatory therapeutics in the context of cancer. Furthermore, when produced in the TME, these mediators have been shown to promote the recruitment of immune cells, including T cells, B cells, dendritic cells (DCs), and other specialized immune cell subsets such as follicular DCs and T follicular helper cells, in association with the formation of "tertiary" lymphoid structures (TLSs) within or adjacent to sites of disease. Although TLSs are composed of a heterogeneous collection of immune cell types, whose composition differs based on cancer subtype, the qualitative presence of TLSs has been shown to represent a biomarker of good prognosis for cancer patients. A comprehensive understanding of the role each of these pathways plays within the TME may support the rational design of future immunotherapies to selectively promote/bolster TLS formation and function, leading to improved clinical outcomes across the vast range of solid cancer types.

Microglia centered pathogenesis in ALS: insights in cell interconnectivity

Amyotrophic lateral sclerosis (ALS) is the most common and most aggressive form of adult motor neuron (MN) degeneration. The cause of the disease is still unknown, but some protein mutations have been linked to the pathological process. Loss of upper and lower MNs results in progressive muscle paralysis and ultimately death due to respiratory failure. Although initially thought to derive from the selective loss of MNs, the pathogenic concept of non-cell-autonomous disease has come to the forefront for the contribution of glial cells in ALS, in particular microglia. Recent studies suggest that microglia may have a protective effect on MN in an early stage. Conversely, activated microglia contribute and enhance MN death by secreting neurotoxic factors, and impaired microglial function at the end-stage may instead accelerate disease progression. However, the nature of microglial–neuronal interactions that lead to MN degeneration remains elusive. We review the contribution of the neurodegenerative network in ALS pathology, with a special focus on each glial cell type from data obtained in the transgenic SOD1G93A rodents, the most widely used model. We further discuss the diverse roles of neuroinflammation and microglia phenotypes in the modulation of ALS pathology. We provide information on the processes associated with dysfunctional cell–cell communication and summarize findings on pathological cross-talk between neurons and astroglia, and neurons and microglia, as well as on the spread of pathogenic factors. We also highlight the relevance of neurovascular disruption and exosome trafficking to ALS pathology. The harmful and beneficial influences of NG2 cells, oligodendrocytes and Schwann cells will be discussed as well. Insights into the complex intercellular perturbations underlying ALS, including target identification, will enhance our efforts to develop effective therapeutic approaches for preventing or reversing symptomatic progression of this devastating disease.

The biology of chemokines and their receptors

This article summarizes the work done by our laboratory and by our collaborators on the biological role of chemokines and their receptors. Using both gain-of-function and loss of function genetic approaches, we have demonstrated that chemokines are important for the homeostatic distribution of leukocytes in tissues and for their mobilization from the bone marrow. We have also shown that chemokines are important players in inflammation and autoimmunity and that they contribute to lymphoid organogenesis, angiogenesis, and immune regulation. Together, our results and those of the literature suggest an important role for chemokines in homeostasis and disease and characterize chemokines as important targets for therapeutic intervention.

Extrusion of misfolded and aggregated proteins--a protective strategy of aging neurons?

Cellular senescence is the consequence of repetitive exposures to oxidative stress, perturbed energy homeostasis, accumulation of damaged proteins and lesions in their nucleic acids. Whereas mitotic cells are equipped with efficient cell replacement strategies; postmitotic neurons have--with a few exceptions--no mechanism to substitute dysfunctional cells within a complex neuronal network. Here we propose a potential strategy by which aging neurons contend against abnormal accumulation of damaged/misfolded proteins. The suggested mechanism involves the formation of 'budding-like' extrusions and their subsequent clearance by glia. This hypothesis emerged from our previous investigations of the aged hippocampus revealing layer-specific accumulations of Reelin, a glycoprotein with fundamental roles during brain development and adult synaptic plasticity. We showed that Reelin deposits constitute a conserved neuropathological feature of aging, which is significantly accelerated in adult wild-type mice prenatally exposed to a viral-like infection. Here, we employed two- and three-dimensional immunoelectron microscopy to elucidate their morphological properties, localization and origin in immune challenged vs. control mice. In controls, Reelin-positive deposits were dispersed in the neuropil, some being engulfed by glia. In immune challenged mice, however, significantly more Reelin-immunoreactive deposits were associated with neuritic swellings containing mitochondria, vacuoles and cellular debris, pointing to their intracellular origin and suggesting that 'budding-like' neuronal extrusions of misfolded proteins and glial clearance may represent a protective strategy to counteract aging-associated impairments in proteosomal/lysosomal degradation. Neurons exposed to chronic neuroinflammation with increased levels of misfolded/damaged proteins, however, may fail to combat intraneuronal protein accumulations, a process probably underlying neuronal dysfunction and degeneration during aging.

Role of C-C chemokine receptor type 7 and its ligands during neuroinflammation

For decades, chemokines and their receptors have received a great deal of attention for their multiple roles in controlling leukocyte functions during inflammation and immunity. The ability of chemokines to convey remarkably versatile but context-specific signals identifies them as powerful modulators of immune responses generated in response to diverse pathogenic or non-infectious insults. A number of recent studies have speculated that the C-C chemokine receptor type 7 (CCR7), plays important roles in immune-cell trafficking in various tissue compartments during inflammation and in immune surveillance. Using computational modeling and microfluidics-based approaches, recent studies have explored leukocyte migration behavior in response to CCR7 ligands in a complex chemokine environment existing with other coexisting chemokine fields. In this review, we summarize the current understanding of the effects of soluble versus immobilized ligands and of the downstream signaling pathways of CCR7 that control leukocyte motility, directionality, and speed. This review also integrates the current knowledge about the role of CCR7 in coordinating immune responses between secondary lymphoid organs and peripheral tissue microenvironments during primary or secondary antigen encounters. CCR7 seems to influence distinct immunological events during inflammatory responses in the central nervous system (CNS) including immune-cell entry and migration, and neuroglial interactions. The clinical and pathological outcome may vary depending on its contribution in the inflamed CNS microenvironment. Understanding these mechanisms has direct implications for therapeutic developments favoring more protective and efficient immune responses.

On the occurrence of hypomyelination in a transgenic mouse model: a consequence of the myelin basic protein promoter?

Central nervous system hypomyelination is a feature common to a number of transgenic (Tg) mouse lines that express a variety of unrelated exogenous (i.e. non-central nervous system) transgenes. In this report, we document hypomyelination structurally by immunocytochemistry and functionally in the Tg line MBP-JE, which over expresses the chemokine CCL2 (MCP-1) within oligodendrocytes targeted by a myelin basic protein (MBP) promoter. Analysis of hypomyelinated optic nerves of Tg mice revealed progressive decrease in oligodendrocyte numbers with age (p < 0.01). Although molecular mechanisms underlying hypomyelination in this and other Tg models remain largely unknown, we present preliminary findings on oligodendrocyte progenitor cell (OPC) cultures in which, although OPC expressed CCR2, the receptor for CCL2, treatment with CCL2 had no significant effect on OPC proliferation, differentiation, or apoptosis. We suggest that hypomyelination in the MBP-JE model might not be due to CCL2 expression but rather the result of transcriptional dysfunction related to random insertion of the MBP promoter that disrupts myelinogenesis and leads to oligodendrocyte demise. Because an MBP promoter is a common denominator in most Tg lines displaying hypomyelination, we hypothesize that use of myelin gene sequences in the regulator region of Tg constructs might underlie this perturbation of myelination in such models.

CNS-derived CCL21 is both sufficient to drive homeostatic CD4+ T cell proliferation and necessary for efficient CD4+ T cell migration into the CNS parenchyma following Toxoplasma gondii infection

Injury, infection and autoimmune triggers increase CNS expression of the chemokine CCL21. Outside the CNS, CCL21 contributes to chronic inflammatory disease and autoimmunity by three mechanisms: recruitment of lymphocytes into injured or infected tissues, organization of inflammatory infiltrates into lymphoid-like structures and promotion of homeostatic CD4+ T-cell proliferation. To test if CCL21 plays the same role in CNS inflammation, we generated transgenic mice with astrocyte-driven expression of CCL21 (GFAP-CCL21 mice). Astrocyte-produced CCL21 was bioavailable and sufficient to support homeostatic CD4+ T-cell proliferation in cervical lymph nodes even in the absence of endogenous CCL19/CCL21. However, lymphocytes and glial-activation were not detected in the brains of uninfected GFAP-CCL21 mice, although CCL21 levels in GFAP-CCL21 brains were higher than levels expressed in inflamed Toxoplasma-infected non-transgenic brains. Following Toxoplasma infection, T-cell extravasation into submeningeal, perivascular and ventricular sites of infected CNS was not CCL21-dependent, occurring even in CCL19/CCL21-deficient mice. However, migration of extravasated CD4+, but not CD8+ T cells from extra-parenchymal CNS sites into the CNS parenchyma was CCL21-dependent. CD4+ T cells preferentially accumulated at perivascular, submeningeal and ventricular spaces in infected CCL21/CCL19-deficient mice. By contrast, greater numbers of CD4+ T cells infiltrated the parenchyma of infected GFAP-CCL21 mice than in wild-type or CCL19/CCL21-deficient mice. Together these data indicate that CCL21 expression within the CNS has the potential to contribute to T cell-mediated CNS pathology via: (a) homeostatic priming of CD4+ T-lymphocytes outside the CNS and (b) by facilitating CD4+ T-cell migration into parenchymal sites following pathogenic insults to the CNS.

Intranasal delivery of E-selectin reduces atherosclerosis in ApoE-/- mice

Mucosal tolerance to E-selectin prevents stroke and protects against ischemic brain damage in experimental models of stroke studying healthy animals or spontaneously hypertensive stroke-prone rats. A reduction in inflammation and neural damage was associated with immunomodulatory or “tolerogenic” responses to E-selectin. The purpose of the current study on ApoE deficient mice is to assess the capacity of this stroke prevention innovation to influence atherosclerosis, a major underlying cause for ischemic strokes; human E-selectin is being translated as a potential clinical prevention strategy for secondary stroke. Female ApoE−/− mice received intranasal delivery of E-selectin prior to (pre-tolerization) or simultaneously with initiation of a high-fat diet. After 7 weeks on the high-fat diet, lipid lesions in the aorta, serum triglycerides, and total cholesterol were assessed as markers of atherosclerosis development. We also assessed E-selectin-specific antibodies and cytokine responses, in addition to inflammatory responses that included macrophage infiltration of the aorta and altered gene expression profiles of aortic mRNA. Intranasal delivery of E-selectin prior to initiation of high-fat chow decreased atherosclerosis, serum total cholesterol, and expression of the leucocyte chemoattractant CCL21 that is typically upregulated in atherosclerotic lesions of ApoE−/− mice. This response was associated with the induction of E-selectin specific cells producing the immunomodulatory cytokine IL-10 and immunosuppressive antibody isotypes. Intranasal administration of E-selectin generates E-selectin specific immune responses that are immunosuppressive in nature and can ameliorate atherosclerosis, a major risk factor for ischemic stroke. These results provide additional preclinical support for the potential of induction of mucosal tolerance to E-selectin to prevent stroke.

Transgenic mouse models of multiple sclerosis

Multiple sclerosis (MS) is an inflammatory demyelinating disease affecting the central nervous system (CNS) and a frequent cause of neurological disability in young adults. Multifocal inflammatory lesions in the CNS white matter, demyelination, oligodendrocyte loss, axonal damage, as well as astrogliosis represent the histological hallmarks of the disease. These pathological features of MS can be mimicked, at least in part, using animal models. This review discusses the current concepts of the immune effector mechanisms driving CNS demyelination in murine models. It highlights the fundamental contribution of transgenesis in identifying the mediators and mechanisms involved in the pathophysiology of MS models.

The blood-brain barrier, chemokines and multiple sclerosis

The infiltration of leukocytes into the central nervous system (CNS) is an essential step in the neuropathogenesis of multiple sclerosis (MS). Leukocyte extravasation from the bloodstream is a multistep process that depends on several factors including fluid dynamics within the vasculature and molecular interactions between circulating leukocytes and the vascular endothelium. An important step in this cascade is the presence of chemokines on the vascular endothelial cell surface. Chemokines displayed along the endothelial lumen bind chemokine receptors on circulating leukocytes, initiating intracellular signaling that culminates in integrin activation, leukocyte arrest, and extravasation. The presence of chemokines at the endothelial lumen can help guide the movement of leukocytes through peripheral tissues during normal immune surveillance, host defense or inflammation. The expression and display of homeostatic or inflammatory chemokines therefore critically determine which leukocyte subsets extravasate and enter the peripheral tissues. Within the CNS, however, infiltrating leukocytes that cross the endothelium face additional boundaries to parenchymal entry, including the abluminal presence of localizing cues that prevent egress from perivascular spaces. This review focuses on the differential display of chemokines along endothelial surfaces and how they impact leukocyte extravasation into parenchymal tissues, especially within the CNS. In particular, the display of chemokines by endothelial cells of the blood brain barrier may be altered during CNS autoimmune disease, promoting leukocyte entry into this immunologically distinct site. Recent advances in microscopic techniques, including two-photon and intravital imaging have provided new insights into the mechanisms of chemokine-mediated capture of leukocytes within the CNS.

Lymphoid chemokines in the CNS

Lymphoid chemokines, including CCL19, CCL21 and CXCL13, are critical in the development and organization of secondary lymphoid tissues and in the generation of adaptive immune responses. These molecules have also been implicated in the development of ectopic lymphoid structures in the setting of chronic inflammation. Here we review current knowledge on the production of lymphoid chemokines in the central nervous system during both homeostatic conditions and in disease states. Accumulating evidence suggests that constitutive expression of CCL19 plays a critical immunosurveillance role in healthy individuals. In contrast, aberrant induction of CCL19, CCL21 and CXCL13 may support the establishment of chronic autoimmunity and hematopoietic tumors within the CNS.

CD93/AA4.1: a novel regulator of inflammation in murine focal cerebral ischemia

The stem-cell marker CD93 (AA4.1/C1qRp) has been described as a potential complement C1q-receptor. Its exact molecular function, however, remains unknown. By using global expression profiling we showed that CD93-mRNA is highly induced after transient focal cerebral ischemia. CD93 protein is upregulated in endothelial cells, but also in selected macrophages and microglia. To elucidate the potential functional role of CD93 in postischemic brain damage, we used mice with a targeted deletion of the CD93 gene. After 30 min of occlusion of the middle cerebral artery and 3 d of reperfusion these mice displayed increased leukocyte infiltration into the brain, increased edema, and significantly larger infarct volumes (60.8 +/- 52.2 versus 23.9 +/- 16.6 mm(3)) when compared with wild-type (WT) mice. When the MCA was occluded for 60 min, after 2 d of reperfusion the CD93 knockout mice still showed more leukocytes in the brain, but the infarct volumes were not different from those seen in WT animals. To further explore CD93-dependent signaling pathways, we determined global transcription profiles and compared CD93-deficient and WT mice at various time points after induction of focal cerebral ischemia. We found a highly significant upregulation of the chemokine CCL21/Exodus-2 in untreated and treated CD93-deficient mice at all time points. Induction of CCL21 mRNA and protein was confirmed by PCR and immunohistochemistry. CCL21, which was formerly shown to be released by damaged neurons and to activate microglia, contributes to neurodegeneration. Thus, we speculate that CD93-neuroprotection is mediated via suppression of the neuroinflammatory response through downregulation of CCL21.

Lymphoid chemokines in chronic neuroinflammation

Lymphoid chemokines play an essential role in the establishment and maintenance of lymphoid tissue microarchitecture and have been implicated in the formation of tertiary (or ectopic) lymphoid tissue in chronic inflammatory conditions. Here, we review recent advances in lymphoid chemokine research in central nervous system inflammation, focusing on multiple sclerosis and the animal model experimental autoimmune encephalomyelitis. We also highlight how the study of lymphoid chemokines, particularly CXCL13, has led to the identification of intrameningeal B-cell follicles in the multiple sclerosis brain paving the way to the discovery that these abnormal structures are highly enriched in Epstein–Barr virus-infected B cells and plasma cells.

CXCR3 signaling reduces the severity of experimental autoimmune encephalomyelitis by controlling the parenchymal distribution of effector and regulatory T cells in the central nervous system

The chemokine receptor CXCR3 promotes the trafficking of activated T and NK cells in response to three ligands, CXCL9, CXCL10, and CXCL11. Although these chemokines are produced in the CNS in multiple sclerosis and experimental autoimmune encephalomyelitis (EAE), their role in the pathogenesis of CNS autoimmunity is unresolved. We examined the function of CXCR3 signaling in EAE using mice that were deficient for CXCR3 (CXCR3(-/-)). The time to onset and peak disease severity were similar for CXCR3(-/-) and wild-type (WT) animals; however, CXCR3(-/-) mice had more severe chronic disease with increased demyelination and axonal damage. The inflammatory lesions in WT mice consisted of well-demarcated perivascular mononuclear cell infiltrates, mainly in the spinal cord and cerebellum. In CXCR3(-/-) mice, these lesions were more widespread throughout the CNS and were diffused and poorly organized, with T cells and highly activated microglia/macrophages scattered throughout the white matter. Although the number of CD4(+) and CD8(+) T cells infiltrating the CNS were similar in CXCR3(-/-) and WT mice, Foxp3(+) regulatory T cells were significantly reduced in number and dispersed in CXCR3(-/-) mice. The expression of various chemokine and cytokine genes in the CNS was similar in CXCR3(-/-) and WT mice. The genes for the CXCR3 ligands were expressed predominantly in and/or immediately surrounding the mononuclear cell infiltrates. We conclude that in EAE, CXCR3 signaling constrains T cells to the perivascular space in the CNS and augments regulatory T cell recruitment and effector T cell interaction, thus limiting autoimmune-mediated tissue damage.

Intracranial glioblastoma models in preclinical neuro-oncology: neuropathological characterization and tumor progression

Although rodent glioblastoma (GBM) models have been used for over 30 years, the extent to which they recapitulate the characteristics encountered in human GBMs remains controversial. We studied the histopathological features of dog GBM and human xenograft GBM models in immune-deficient mice (U251 and U87 GBM in nude Balb/c), and syngeneic GBMs in immune-competent rodents (GL26 cells in C57BL/6 mice, CNS-1 cells in Lewis rats). All GBMs studied exhibited neovascularization, pleomorphism, vimentin immunoreactivity, and infiltration of T-cells and macrophages. All the tumors showed necrosis and hemorrhages, except the U87 human xenograft, in which the most salient feature was its profuse neovascularization. The tumors differed in the expression of astrocytic intermediate filaments: human and dog GBMs, as well as U251 xenografts expressed glial fibrillary acidic protein (GFAP) and vimentin, while the U87 xenograft and the syngeneic rodent GBMs were GFAP(-) and vimentin(+). Also, only dog GBMs exhibited endothelial proliferation, a key feature that was absent in the murine models. In all spontaneous and implanted GBMs we found histopathological features compatible with tumor invasion into the non-neoplastic brain parenchyma. Our data indicate that murine models of GBM appear to recapitulate several of the human GBM histopathological features and, considering their reproducibility and availability, they constitute a valuable in vivo system for preclinical studies. Importantly, our results indicate that dog GBM emerges as an attractive animal model for testing novel therapies in a spontaneous tumor in the context of a larger brain.

Neuronal chemokines: versatile messengers in central nervous system cell interaction

Whereas chemokines are well known for their ability to induce cell migration, only recently it became evident that chemokines also control a variety of other cell functions and are versatile messengers in the interaction between a diversity of cell types. In the central nervous system (CNS), chemokines are generally found under both physiological and pathological conditions. Whereas many reports describe chemokine expression in astrocytes and microglia and their role in the migration of leukocytes into the CNS, only few studies describe chemokine expression in neurons. Nevertheless, the expression of neuronal chemokines and the corresponding chemokine receptors in CNS cells under physiological and pathological conditions indicates that neuronal chemokines contribute to CNS cell interaction. In this study, we review recent studies describing neuronal chemokine expression and discuss potential roles of neuronal chemokines in neuron-astrocyte, neuron-microglia, and neuron-neuron interaction.

Experimental models of spontaneous autoimmune disease in the central nervous system

Animal models have become essential tools for studying the human autoimmune disease. They are of vital importance in explorations of disease aspects, where, for diverse reasons, human material is unavailable. This is especially true for disease processes preceding clinical diagnosis and for tissues, which are inaccessible to routine biopsy. Early developing multiple sclerosis (MS) makes an excellent point in case for these limitations. Useful disease models should be developing spontaneously, without a need of artificial, adjuvant-supported induction protocols, and they should reflect credibly at least some of the complex features of human disease. The aim of this review is to compile models that exhibit spontaneous organ-specific autoimmunity and explore their use for studying MS. We first evaluate a few naturally occurring models of organ-specific autoimmune diseases and then screen autoimmunity in animals with compromised immune regulation (neonatal thymectomy, transgenesis, etc.). While most of these models affect organs other than the nervous tissues, central nervous system (CNS)-specific autoimmune disease is readily noted either after transgenic overexpression of cytokines or chemokines within the CNS or by introducing CNS-specific immune receptors into the lymphocyte repertoire. Most recently, spontaneous autoimmunity resembling MS was obtained by transgenic expression of self-reactive T cell receptors and B cell receptors. These transgenic models are not only of promise for studying directly disease processes during the entire course of the disease but may also be helpful in drug discovery.

Keystones in lymph node development

New molecular markers are constantly increasing our knowledge of developmental processes. In this review article we have attempted to summarize the keystones of lymphoid tissue development in embryonic and pathological conditions. During embryonic lymph node development in the mouse, cells from the anterior cardinal vein start to bud and sprout, forming a lymph sac at defined sites. The protrusion of mesenchymal tissue into the lymph sacs forms the environment, where so-called 'lymphoid tissue inducer cells' and 'mesenchymal organizer cells' meet and interact. Defects of molecules involved in the recruitment and signalling cascades of these cells lead to primary immunodeficiency diseases. A comparison of molecules involved in the development of secondary lymphoid organs and tertiary lymphoid organs, e.g. in autoimmune diseases, shows that the same molecules are involved in both processes. This has led to the hypothesis that the development of tertiary lymphoid organs is a recapitulation of embryonic lymphoid tissue development at ectopic sites.

Lymphoid neogenesis in chronic inflammatory diseases

The frequent observation of organized lymphoid structures that resemble secondary lymphoid organs in tissues that are targeted by chronic inflammatory processes, such as autoimmunity and infection, has indicated that lymphoid neogenesis might have a role in maintaining immune responses against persistent antigens. In this Review, we discuss recent progress in several aspects of lymphoid neogenesis, focusing on the similarities with lymphoid tissue development, the mechanisms of induction, functional competence and pathophysiological significance. As more information on these issues becomes available, a better understanding of the role of lymphoid neogenesis in promoting chronic inflammation might eventually lead to new strategies to target immunopathological processes.

The ins and outs of T-lymphocyte trafficking to the CNS: anatomical sites and molecular mechanisms

This review addresses current knowledge of the molecular trafficking signals involved in the migration of circulating leukocytes across the highly specialized blood-central nervous system (CNS) barriers during immunosurveillance and inflammation. In this regard, adhesion molecules and activating and chemotactic factors are also discussed and the regional variability in the brain and spinal cord parenchyma are also considered. Furthermore, direct passage into cerebrospinal fluid (CSF) is discussed, in the context of CNS immunosurveillance. The potential differences that characterize leukocyte entry into these varied anatomical sites are highlighted, with special emphasis on studies of the pathogenesis of multiple sclerosis and its animal models. An update on findings from clinical trials of natalizumab is also provided.

Neutrophils that infiltrate the central nervous system regulate T cell responses

Regulation of inflammatory responses is critical to progression of organ-specific autoimmune disease. Although many candidate cell types have been identified, immunoregulatory activity has rarely been directly assayed and never from the CNS. We have analyzed the regulatory capability of Gr-1high neutrophils isolated from the CNS of mice with experimental autoimmune encephalomyelitis. Proportions of neutrophils were markedly increased in the CNS of IFN-gamma-deficient mice. Strikingly, CNS-derived neutrophils, whether or not they derived from IFN-gamma-deficient mice, were potent suppressors of T cell responses to myelin or adjuvant Ags. Neutrophil suppressor activity was absolutely dependent on IFN-gamma production by target T cells, and suppression was abrogated by blocking NO synthase. These data identify an immunoregulatory capacity for neutrophils, and indicate that interplay between IFN-gamma, NO, and activated Gr-1high neutrophils within the target organ determines the outcome of inflammatory and potentially autoimmune T cell responses.

A stromal address code defined by fibroblasts

To navigate into and within tissues, leukocytes require guidance cues that enable them to recognize which tissues to enter and which to avoid. Such cues are partly provided at the time of extravasation from blood by an endothelial address code on the luminal surface of the vascular endothelium. Here, we review the evidence that fibroblasts help define an additional stromal address code that directs leukocyte behaviour within tissues. We examine how this stromal code regulates site-specific leukocyte accumulation, differentiation and survival in a variety of physiological stromal niches, and how the aberrant expression of components of this code in the wrong tissue at the wrong time contributes to the persistence of chronic inflammatory diseases.

A novel model for lymphocytic infiltration of the thyroid gland generated by transgenic expression of the CC chemokine CCL21

Lymphocytic infiltrates and lymphoid follicles with germinal centers are often detected in autoimmune thyroid disease (AITD), but the mechanisms underlying lymphocyte entry and organization in the thyroid remain unknown. We tested the hypothesis that CCL21, a chemokine that regulates homeostatic lymphocyte trafficking, and whose expression has been detected in AITD, is involved in the migration of lymphocytes to the thyroid. We show that transgenic mice expressing CCL21 from the thyroglobulin promoter (TGCCL21 mice) have significant lymphocytic infiltrates, which are topologically segregated into B and T cell areas. Although high endothelial venules expressing peripheral lymph node addressin were frequently observed in the thyroid tissue, lymphocyte recruitment was independent of L-selectin or lymphotoxin-alpha but required CCR7 expression. Taken together, these results indicate that CCL21 is sufficient to drive lymphocyte recruitment to the thyroid, suggest that CCL21 is involved in AITD pathogenesis, and establish TGCCL21 transgenic mice as a novel model to study the formation and function of lymphoid follicles in the thyroid.

Expression of CCR7 in multiple sclerosis: implications for CNS immunity

It is unclear how immune cells traffic between the lymphoid compartment and the central nervous system (CNS), which lacks lymphatic vessels and is shielded by the blood-brain barrier. We studied the expression of CCR7, a chemokine receptor required for migration of T cells and dendritic cells (DCs) to lymphoid organs, in the CNS of patients with multiple sclerosis (MS) to gain insight into pathways for CNS immune cell trafficking. Inflamed MS lesions contained numerous CCR7+ myeloid cells expressing major histocompatibility complex class II, CD68 and CD86, consistent with maturing DCs. CCR7+ DCs also were identified in cerebrospinal fluid (CSF). These observations suggested that the afferent limb of CNS immunity is comprised, in part, of DCs, which are generated within the CNS and migrate to deep cervical lymph nodes through the CSF after antigen capture. Ninety percent of CSF T cells expressed CCR7 and CSF from patients with MS was relatively depleted of CCR7-negative effector-memory T cells. In contrast, all T cells in parenchymal MS lesions lacked CCR7, indicating local retention and differentiation of central-memory T cells upon restimulation by antigen within the CNS. These data suggested that the efferent limb of CNS immunity is executed by central-memory T cells, which enter CSF directly from the circulation.

Secondary lymphoid organ chemokines are elevated in the cerebrospinal fluid during central nervous system inflammation

Secondary lymphoid organ chemokines have been implicated in chronic inflammation. Their expression in the central nervous system (CNS) has not been studied. Here, levels of secondary lymphoid organ chemokines CCL19 (Exodus-3, MIP-3beta), CCL21 (Exodus-2, 6Ckine, SLC) and CXCL12 (SDF-1alpha) were analysed by ELISA in cerebrospinal fluid (CSF) and plasma from patients with multiple sclerosis (MS); acute optic neuritis (ON) with oligoclonal IgG in the CSF (i.e., first bout of MS); acute ON without oligoclonal IgG (non-MS-type ON); other inflammatory neurological diseases (OIND); and non-inflammatory neurological diseases (NIND). NIND CSF contained CCL19 and CXCL12, while CCL21 was not detected. Intrathecal production of CCL19 and CCL21 was elevated in MS, MS-type ON, and OIND, but not in non-MS-type ON. In MS, CSF levels of CCL19 weakly correlated with CSF cell counts. Intrathecal production of CXCL12 was elevated only in OIND. The role of elevated CCL19 and CCL21 in MS could be retention of mature dendritic cells (DC) in the CNS, recruitment of nai;ve T cells and activated B cells, as well as de novo formation of secondary lymphoid structures in MS plaques.

Lymphoid chemokines CCL19 and CCL21 are expressed in the central nervous system during experimental autoimmune encephalomyelitis: implications for the maintenance of chronic neuroinflammation

The simultaneous presence of dendritic, T- and B-cells in the central nervous system (CNS) of mice with experimental autoimmune encephalomyelitis (EAE), a model for multiple sclerosis, suggests that interactions among these cell types might be instrumental in the local induction and maintenance of autoimmune reactions. In this study, we explored the possibility that such aberrant leukocyte recruitment in the CNS could be sustained by "lymphoid" chemokines which orchestrate dendritic cell and lymphocyte homing to lymphoid organs. Transcripts for CCL19 and CCL21 and their common receptor CCR7 were induced in the CNS of mice undergoing relapsing-remitting and chronic-relapsing EAE. While CCL21 immunoreactivity was confined to the endothelium of some inflamed blood vessels, CCL19 was expressed by many infiltrating leukocytes and some astrocytes and microglia in the CNS parenchyma. CCR7+ cells accumulated in inflammatory lesions during EAE progression, when abundant infiltration of the CNS by mature dendritic cells, B-cells and cells expressing naive T-cell markers also occurred. These findings suggest that CCL19 and CCL21 produced in the EAE-affected CNS may be critical for the homing of antigen presenting cells and lymphocytes, resulting in continuous local antigenic stimulation and maintenance of chronic neuroinflammation.

Microglia as liaisons between the immune and central nervous systems: functional implications for multiple sclerosis

Multiple sclerosis is a chronic demyelinating inflammatory disease of the central nervous system (CNS). As the tissue macrophage of the CNS, microglia have the potential to regulate and be regulated by cells of the CNS and by CNS-infiltrating immune cells. The exquisite sensitivity of microglia to these signals, coupled with their ability to develop a broad range of effector functions, allows the CNS to tailor microglial function for specific physiological needs. However, the great plasticity of microglial responses can also predispose these cells to amplify disproportionately the irrelevant or dysfunctional signals provided by either the CNS or immune systems. The consequences of such an event could be the conversion of self-limiting inflammatory responses into chronic neurodegeneration and may explain in part the heterogeneous nature of multiple sclerosis.

Leukocyte infiltration, but not neurodegeneration, in the CNS of transgenic mice with astrocyte production of the CXC chemokine ligand 10

The CXC chemokine ligand (CXCL)10 is induced locally in the CNS in diverse pathologic states. The impact of CXCL10 production in the CNS was examined in transgenic mice with astrocyte-directed production of this chemokine. These glial fibrillary acidic protein (GF)-CXCL10 transgenic mice spontaneously developed transgene dose- and age-related leukocyte infiltrates in perivascular, meningeal, and ventricular regions of the brain that were composed of, surprisingly, mainly neutrophils and, to a lesser extent, T cells. No other overt pathologic or physical changes were evident. In addition, the cerebral expression of a number of inflammation-related genes (e.g., cytokines) was not significantly altered in the transgenic mice. The extent of leukocyte recruitment to the brain could be enhanced markedly by peripheral immunization of GF-CXCL10 mice with CFA and pertussis toxin. This was paralleled by a modest, transient increase in the expression of some cytokine and chemokine genes. Analysis of the expression of the CXCL10 receptor, CXCR3, by the brain-infiltrating leukocytes from immunized GF-CXCL10 transgenic mice revealed a significant enrichment for CXCR3-positive cells in the CNS compared with spleen. The majority of cells positive for CXCR3 coexpressed CD3, whereas Gr1-positive granulocytes were negative for CXCR3 expression. Thus, while astrocyte production of CXCL10 can promote spontaneous and potentiate immune-induced recruitment of leukocytes to the CNS, this is not associated with activation of a degenerative immune pathology. Finally, the accumulation of neutrophils in the brain of GF-CXCL10 transgenic mice is apparently independent of CXCR3 and involves an unknown mechanism.

Ectopic expression of the murine chemokines CCL21a and CCL21b induces the formation of lymph node-like structures in pancreas, but not skin, of transgenic mice

The CC chemokine CCL21 is a potent chemoattractant for lymphocytes and dendritic cells in vitro. In the murine genome there are multiple copies of CCL21 encoding two CCL21 proteins that differ from each other by one amino acid at position 65 (either a serine or leucine residue). In this report, we examine the expression pattern and biological activities of both forms of CCL21. We found that although both serine and leucine forms are expressed in most tissues examined, the former was the predominant form in lymphoid organs while the latter was predominantly expressed in nonlymphoid organs. When expressed in transgenic pancreas, both forms of CCL21 were capable of inducing the formation of lymph node-like structures composed primarily of T and B cells and a few dendritic cells. Induction of lymph node-like structures by these CCL21 proteins, however, could not be reproduced in every tissue. For instance, no lymphocyte recruitment or accumulation was observed when CCL21 was overexpressed in the skin. We conclude that both forms of CCL21 protein are biologically equivalent in promoting lymphocyte recruitment to the pancreas, and that their ability to induce the formation of lymph node-like structures is dependent on the tissues in which they are expressed.