Experimental autoimmune encephalomyelitis (EAE) in CCR2(-/-) mice: susceptibility in multiple strains

Infiltration by monocytes of the central nervous system and its role in multiple sclerosis: reflections on therapeutic strategies

Mononuclear macrophage infiltration in the central nervous system is a prominent feature of neuroinflammation. Recent studies on the pathogenesis and progression of multiple sclerosis have highlighted the multiple roles of mononuclear macrophages in the neuroinflammatory process. Monocytes play a significant role in neuroinflammation, and managing neuroinflammation by manipulating peripheral monocytes stands out as an effective strategy for the treatment of multiple sclerosis, leading to improved patient outcomes. This review outlines the steps involved in the entry of myeloid monocytes into the central nervous system that are targets for effective intervention: the activation of bone marrow hematopoiesis, migration of monocytes in the blood, and penetration of the blood-brain barrier by monocytes. Finally, we summarize the different monocyte subpopulations and their effects on the central nervous system based on phenotypic differences. As activated microglia resemble monocyte-derived macrophages, it is important to accurately identify the role of monocyte-derived macrophages in disease. Depending on the roles played by monocyte-derived macrophages at different stages of the disease, several of these processes can be interrupted to limit neuroinflammation and improve patient prognosis. Here, we discuss possible strategies to target monocytes in neurological diseases, focusing on three key aspects of monocyte infiltration into the central nervous system, to provide new ideas for the treatment of neurodegenerative diseases.

Fc multimers effectively treat murine models of multiple sclerosis

Multiple Sclerosis (MS) is a chronic neurodegenerative disease with limited therapeutic options. Recombinant Fc multimers (rFc), designed to mirror many of the anti-inflammatory activities of Intravenous Immunoglobulin (IVIG), have been shown to effectively treat numerous immune-mediated diseases in rodents. In this study we used the experimental autoimmune encephalomyelitis (EAE) murine model of MS to test the efficacy of a rFc, M019, that consists of multimers of the Fc portion of IgG2, in inhibiting disease severity. We show that M019 effectively reduced clinical symptoms when given either pre- or post-symptom onset compared to vehicle treated EAE induced mice. M019 was effective in reducing symptoms in both SJL model of relapsing remitting MS as well as the B6 model of chronic disease. M019 binds to FcγR bearing-monocytes both in vivo and in vitro and prevented immune cell infiltration into the CNS of treated mice. The lack of T cell infiltration into the spinal cord was not due to a decrease in T cell priming; there was an equivalent frequency of Th17 cells in the spleens of M019 and vehicle treated EAE induced mice. Surprisingly, there was an increase in chemokines in the sera but not in the CNS of M019 treated mice compared to vehicle treated animals. We postulate that M019 interacts with a FcγR rich monocyte intermediary to prevent T cell migration into the CNS and demyelination.

Identification and protective role of CD34+ stromal cells/telocytes in experimental autoimmune encephalomyelitis (EAE) mouse spleen

Experimental autoimmune encephalomyelitis (EAE) is a classical animal model of human multiple sclerosis (MS) that is most commonly used to study the neuropathology and therapeutic effects of the disease. Telocytes (TCs) are a specialized type of interstitial or mesenchymal cell first identified by Popescu in various tissues and organs. However, the existence, distribution and role of CD34⁺ stromal cells (SCs)/TCs in the EAE-induced mouse spleen remain to be elucidated. We conducted immunohistochemistry, immunofluorescence (double staining for CD34 and c-kit, vimentin, F4/80, CD163, Nanog, Sca-1, CD31 or tryptase) and transmission electron microscopy experiments to investigate the existence, distribution and role of CD34⁺ SCs/TCs in the EAE-induced mouse spleen. Interestingly, immunohistochemistry, double-immunofluorescence, and transmission electron microscopy results revealed that CD34⁺ SCs/TCs were significantly upregulated in the EAE mouse spleen. Immunohistochemical or double-immunofluorescence staining of CD34⁺ SCs/TCs showed positive expression for CD34, c-kit, vimentin, CD34/vimentin, c-kit/vimentin and CD34/c-kit, and negative expression for CD31 and tryptase. Transmission electron microscopy (TEM) results demonstrated that CD34⁺ SCs/TCs established close connections with lymphocytes, reticular cells, macrophages, endothelial cells and erythrocytes. Furthermore, we also found that M1 (F4/80) or M2 (CD163) macrophages, and haematopoietic, pluripotent stem cells were markedly increased in EAE mice. Our results suggest that CD34⁺ SCs/TCs are abundant and may play a contributing role in modulating the immune response, recruiting macrophages and proliferation of haematopoietic and pluripotent stem cells following injury to promote tissue repair and regeneration in EAE mouse spleens. This suggests that their transplantation combined with stem cells might represent a promising therapeutic target for the treatment and prevention of multiple autoimmune and chronic inflammatory disorders.

ETV3 and ETV6 enable monocyte differentiation into dendritic cells by repressing macrophage fate commitment

In inflamed tissues, monocytes differentiate into macrophages (mo-Macs) or dendritic cells (mo-DCs). In chronic nonresolving inflammation, mo-DCs are major drivers of pathogenic events. Manipulating monocyte differentiation would therefore be an attractive therapeutic strategy. However, how the balance of mo-DC versus mo-Mac fate commitment is regulated is not clear. In the present study, we show that the transcriptional repressors ETV3 and ETV6 control human monocyte differentiation into mo-DCs. ETV3 and ETV6 inhibit interferon (IFN)-stimulated genes; however, their action on monocyte differentiation is independent of IFN signaling. Instead, we find that ETV3 and ETV6 directly repress mo-Mac development by controlling MAFB expression. Mice deficient for Etv6 in monocytes have spontaneous expression of IFN-stimulated genes, confirming that Etv6 regulates IFN responses in vivo. Furthermore, these mice have impaired mo-DC differentiation during inflammation and reduced pathology in an experimental autoimmune encephalomyelitis model. These findings provide information about the molecular control of monocyte fate decision and identify ETV6 as a therapeutic target to redirect monocyte differentiation in inflammatory disorders.

Tetramerization of STAT5 promotes autoimmune-mediated neuroinflammation

Signal tranducer and activator of transcription 5 (STAT5) plays a critical role in mediating cellular responses following cytokine stimulation. STAT proteins critically signal via the formation of dimers, but additionally, STAT tetramers serve key biological roles, and we previously reported their importance in T and natural killer (NK) cell biology. However, the role of STAT5 tetramerization in autoimmune-mediated neuroinflammation has not been investigated. Using the STAT5 tetramer-deficient Stat5a-Stat5b N-domain double knockin (DKI) mouse strain, we report here that STAT5 tetramers promote the pathogenesis of experimental autoimmune encephalomyelitis (EAE). The mild EAE phenotype observed in DKI mice correlates with the impaired extravasation of pathogenic T-helper 17 (Th17) cells and interactions between Th17 cells and monocyte-derived cells (MDCs) in the meninges. We further demonstrate that granulocyte-macrophage colony-stimulating factor (GM-CSF)-mediated STAT5 tetramerization regulates the production of CCL17 by MDCs. Importantly, CCL17 can partially restore the pathogenicity of DKI Th17 cells, and this is dependent on the activity of the integrin VLA-4. Thus, our study reveals a GM-CSF-STAT5 tetramer-CCL17 pathway in MDCs that promotes autoimmune neuroinflammation.

CCR2 mediates the adverse effects of LPS in the pregnant mouse

In our earlier work, we found that intrauterine (i.u.) and intraperitoneal (i.p.) injection of LPS (10-μg serotype 0111:B4) induced preterm labor (PTL) with high pup mortality, marked systemic inflammatory response and hypotension. Here, we used both i.u. and i.p. LPS models in pregnant wild-type (wt) and CCR2 knockout (CCR2-/-) mice on E16 to investigate the role played by the CCL2/CCR2 system in the response to LPS. Basally, lower numbers of monocytes and macrophages and higher numbers of neutrophils were found in the myometrium, placenta, and blood of CCR2-/- vs. wt mice. After i.u. LPS, parturition occurred at 14 h in both groups of mice. At 7 h post-injection, 70% of wt pups were dead vs. 10% of CCR2-/- pups, but at delivery 100% of wt and 90% of CCR2-/- pups were dead. Myometrial and placental monocytes and macrophages were generally lower in CCR2-/- mice, but this was less consistent in the circulation, lung, and liver. At 7 h post-LPS, myometrial ERK activation was greater and JNK and p65 lower and the mRNA levels of chemokines were higher and of inflammatory cytokines lower in CCR2-/- vs. wt mice. Pup brain and placental inflammation were similar. Using the IP LPS model, we found that all measures of arterial pressure increased in CCR2-/- but declined in wt mice. These data suggest that the CCL2/CCR2 system plays a critical role in the cardiovascular response to LPS and contributes to pup death but does not influence the onset of inflammation-induced PTL.

Role of CCR2+ Myeloid Cells in Inflammation Responses Driven by Expression of a Surfactant Protein-C Mutant in the Alveolar Epithelium

Acute inflammatory exacerbations (AIE) represent precipitous deteriorations of a number of chronic lung conditions, including pulmonary fibrosis (PF), chronic obstructive pulmonary disease and asthma. AIEs are marked by diffuse and persistent polycellular alveolitis that profoundly accelerate lung function decline and mortality. In particular, excess monocyte mobilization during AIE and their persistence in the lung have been linked to poor disease outcome. The etiology of AIEs remains quite uncertain, but environmental exposure and genetic predisposition/mutations have been identified as two contributing factors. Guided by clinical evidence, we have developed a mutant model of pulmonary fibrosis leveraging the PF-linked missense isoleucine to threonine substitution at position 73 [I73T] in the alveolar type-2 cell-restricted Surfactant Protein-C [SP-C] gene [SFTPC]. With this toolbox at hand, the present work investigates the role of peripheral monocytes during the initiation and progression of AIE-PF. Genetic ablation of CCR2⁺ monocytes (SP-C^I73TCCR2^KO) resulted in improved lung histology, mouse survival, and reduced inflammation compared to SP-C^I73TCCR2^WT cohorts. FACS analysis of CD11b⁺CD64^-Ly6C^hi monocytes isolated 3 d and 14 d after SP-C^I73T induced injury reveals dynamic transcriptional changes associated with “Innate Immunity’ and ‘Extracellular Matrix Organization’ signaling. While immunohistochemical and in situ hybridization analysis revealed comparable levels of tgfb1 mRNA expression localized primarily in parenchymal cells found nearby foci of injury we found reduced effector cell activation (C1q, iNOS, Arg1) in SP-C^I73TCCR2^KO lungs as well as partial colocalization of tgfb1 mRNA expression in Arg1⁺ cells. These results provide a detailed picture of the role of resident macrophages and recruited monocytes in the context of AIE-PF driven by alveolar epithelial dysfunction.

Genetic Background and Sex: Impact on Generalizability of Research Findings in Pharmacology Studies

Animal models consisting of inbred laboratory rodent strains have been a powerful tool for decades, helping to unravel the underpinnings of biological problems and employed to evaluate potential therapeutic treatments in drug discovery. While inbred strains demonstrate relatively reliable and predictable responses, using a single inbred strain alone or as a background to a mutation is analogous to running a clinical trial in a single individual and their identical twins. Indeed, complex etiologies drive the most common human diseases, and a single inbred strain that is a surrogate of a single genome, or data generated from a single sex, is not representative of the genetically diverse patient populations. Further, pharmacological and toxicology data generated in otherwise healthy animals may not translate to disease states where physiology, metabolism, and general health are compromised. The purpose of this chapter is to provide guidance for improving generalizability of preclinical studies by providing insight into necessary considerations for introducing systematic variation within the study design, such as genetic diversity, the use of both sexes, and selection of appropriate age and disease model. The outcome of implementing these considerations should be that reproducibility and generalizability of significant results are significantly enhanced leading to improved clinical translation.

Nanomodulation of Macrophages in Multiple Sclerosis

Multiple Sclerosis (MS) is a chronic demyelinating autoimmune disease primarily affecting young adults. Despite an unclear causal factor, symptoms and pathology arise from the infiltration of peripheral immune cells across the blood brain barrier. Accounting for the largest fraction of this infiltrate, macrophages are functionally heterogeneous innate immune cells capable of adopting either a pro or an anti-inflammatory phenotype, a phenomenon dependent upon cytokine milieu in the CNS. This functional plasticity is of key relevance in MS, where the pro-inflammatory state dominates the early stage, instructing demyelination and axonal loss while the later anti-inflammatory state holds a key role in promoting tissue repair and regeneration in later remission. This review highlights a potential therapeutic benefit of modulating macrophage polarisation to harness the anti-inflammatory and reparative state in MS. Here, we outline the role of macrophages in MS and look at the role of current FDA approved therapeutics in macrophage polarisation. Moreover, we explore the potential of particulate carriers as a novel strategy to manipulate polarisation states in macrophages, whilst examining how optimising macrophage uptake via nanoparticle size and functionalisation could offer a novel therapeutic approach for MS.

Toll-Like Receptor 4 Promotes Th17 Lymphocyte Infiltration Via CCL25/CCR9 in Pathogenesis of Experimental Autoimmune Encephalomyelitis

Toll-like receptor 4 (TLR4) is a key component in innate immunity and has been linked to central nervous system (CNS) inflammation diseases, such as multiple sclerosis (MS), an inflammatory disorder induced by autoreactive Th17 cells. In our study, we found that TLR4 deficient (TLR4^-/-) mice were inadequate to induce experimental autoimmune encephalomyelitis (EAE), characterized by low clinic score and weight loss, alleviative demyelinating, as well as decreased inflammatory cell infiltration in the spinal cord. In the lesion area of EAE mice, loss of TLR4 down-regulated the secretion of inflammatory cytokines and chemokine CCL25. Furthermore, the expression of CCR9 was decreased and chemotactic migration was attenuated in TLR4^-/- Th17 cells. Our results demonstrate that TLR4 may mediate Th17 infiltration through CCL25/CCR9 signal during pathogenesis of EAE. Graphical Abstract Immunofluorescent staining of RORγt (green) and CCR9 (red) in spinal cords. TLR4 deficiency down-regulates CCR9 expression in infiltrating lymphocytes.

Myeloid-Derived Suppressor Cells: Ductile Targets in Disease

Myeloid-derived suppressor cells (MDSCs) represent a heterogeneous population of immature myeloid cells with major regulatory functions and rise during pathological conditions, including cancer, infections and autoimmune conditions. MDSC expansion is generally linked to inflammatory processes that emerge in response to stable immunological stress, which alter both magnitude and quality of the myelopoietic output. Inability to reinstate physiological myelopoiesis would fall in an “emergency state” that perpetually reprograms myeloid cells toward suppressive functions. While differentiation and reprogramming of myeloid cells toward an immunosuppressive phenotype can be considered the result of a multistep process that originates in the bone marrow and culminates in the tumor microenvironment, the identification of its driving events may offer potential therapeutic approaches in different pathologies. Indeed, whereas expansion of MDSCs, in both murine and human tumor bearers, results in reduced immune surveillance and antitumor cytotoxicity, placing an obstacle to the effectiveness of anticancer therapies, adoptive transfer of MDSCs has shown therapeutic benefits in autoimmune disorders. Here, we describe relevant mechanisms of myeloid cell reprogramming leading to generation of suppressive MDSCs and discuss their therapeutic ductility in disease.

Janus-Faced Myeloid-Derived Suppressor Cell Exosomes for the Good and the Bad in Cancer and Autoimmune Disease

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells originally described to hamper immune responses in chronic infections. Meanwhile, they are known to be a major obstacle in cancer immunotherapy. On the other hand, MDSC can interfere with allogeneic transplant rejection and may dampen autoreactive T cell activity. Whether MDSC-Exosomes (Exo) can cope with the dangerous and potentially therapeutic activities of MDSC is not yet fully explored. After introducing MDSC and Exo, it will be discussed, whether a blockade of MDSC-Exo could foster the efficacy of immunotherapy in cancer and mitigate tumor progression supporting activities of MDSC. It also will be outlined, whether application of native or tailored MDSC-Exo might prohibit autoimmune disease progression. These considerations are based on the steadily increasing knowledge on Exo composition, their capacity to distribute throughout the organism combined with selectivity of targeting, and the ease to tailor Exo and includes open questions that answers will facilitate optimizing protocols for a MDSC-Exo blockade in cancer as well as for strengthening their therapeutic efficacy in autoimmune disease.

miR-23b Suppresses Leukocyte Migration and Pathogenesis of Experimental Autoimmune Encephalomyelitis by Targeting CCL7

MicroRNAs (miRNAs) are small, non-coding RNAs involved in immune response regulation. Specific miRNAs have been linked to the development of various autoimmune diseases; however, their contribution to the modulation of CNS-directed cellular infiltration remains unclear. In this study, we found that miR-23b, in addition to its reported functions in the suppression of IL-17-associated autoimmune inflammation, halted the progression of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS), by directly inhibiting the migration of pathogenic leukocytes to the CNS. We demonstrated that miR-23b was specifically decreased during the acute phase of EAE and that overexpression of miR-23b resulted in a defect in leukocyte migration and strong resistance to EAE. Furthermore, we found that miR-23b suppressed leukocyte migration of EAE by targeting CCL7, a chemokine that attracts monocytes during inflammation and metastasis. Finally, in the adoptive transfer model, miR-23b reduced the severity of EAE by inhibiting the migration of pathogenic T cells to the CNS rather than diminishing the encephalitogenesis of T cells. Taken together, our results characterize a novel aspect of miR-23b function in leukocyte migration, and they identify miR-23b as a potential therapeutic target in the amelioration of MS and likely other autoimmune diseases.

Peripheral monocyte entry is required for alpha-Synuclein induced inflammation and Neurodegeneration in a model of Parkinson disease

Accumulation of alpha-synuclein (α-syn) in the central nervous system (CNS) is a core feature of Parkinson disease (PD) that leads to activation of the innate immune system, production of inflammatory cytokines and chemokines, and subsequent neurodegeneration. Here, we used heterozygous reporter knock-in mice in which the first exons of the fractalkine receptor (CX3CR1) and of the C-C chemokine receptor type 2 (CCR2) are replaced with fluorescent reporters to study the role of resident microglia (CX3CR1+) and infiltrating peripheral monocytes (CCR2+), respectively, in the CNS. We used an α-syn mouse model induced by viral over-expression of α-syn. We find that in vivo, expression of full-length human α-syn induces robust infiltration of pro-inflammatory CCR2+ peripheral monocytes into the substantia nigra. Genetic deletion of CCR2 prevents α-syn induced monocyte entry, attenuates MHCII expression and blocks the subsequent degeneration of dopaminergic neurons. These results demonstrate that extravasation of pro-inflammatory peripheral monocytes into the CNS plays a key role in neurodegeneration in this model of PD synucleinopathy, and suggest that peripheral monocytes may be a target of neuroprotective therapies for human PD.

Chemokines as new inflammatory players in the pathogenesis of epilepsy

A large series of clinical and experimental studies supports a link between inflammation and epilepsy, indicating that inflammatory processes within the brain are important contributors to seizure recurrence and precipitation. Systemic inflammation can precipitate seizures in children suffering from epileptic encephalopathies, and hallmarks of a chronic inflammatory state have been found in patients with temporal lobe epilepsy. Research performed on animal models of epilepsy further corroborates the idea that seizures upregulate inflammatory mediators, which in turn may enhance brain excitability and neuronal degeneration. Several inflammatory molecules and their signaling pathways have been implicated in epilepsy. Among these, the chemokine pathway has increasingly gained attention. Chemokines are small cytokines secreted by blood cells, which act as chemoattractants for leukocyte migration. Recent studies indicate that chemokines and their receptors are also produced by brain cells, and are involved in various neurological disorders including epilepsy. In this review, we will focus on a subset of pro-inflammatory chemokines (namely CCL2, CCL3, CCL5, CX3CL1) and their receptors, and their increasingly recognized role in seizure control.

Differential contribution of immune effector mechanisms to cortical demyelination in multiple sclerosis

Cortical demyelination is a widely recognized hallmark of multiple sclerosis (MS) and correlate of disease progression and cognitive decline. The pathomechanisms initiating and driving gray matter damage are only incompletely understood. Here, we determined the infiltrating leukocyte subpopulations in 26 cortical demyelinated lesions of biopsied MS patients and assessed their contribution to cortical lesion formation in a newly developed mouse model. We find that conformation-specific anti-myelin antibodies contribute to cortical demyelination even in the absence of the classical complement pathway. T cells and natural killer cells are relevant for intracortical type 2 but dispensable for subpial type 3 lesions, whereas CCR2⁺ monocytes are required for both. Depleting CCR2⁺ monocytes in marmoset monkeys with experimental autoimmune encephalomyelitis using a novel humanized CCR2 targeting antibody translates into significantly less cortical demyelination and disease severity. We conclude that biologics depleting CCR2⁺ monocytes might be attractive candidates for preventing cortical lesion formation and ameliorating disease progression in MS.

GM-CSF is not essential for experimental autoimmune encephalomyelitis but promotes brain-targeted disease

Experimental autoimmune encephalomyelitis (EAE) has been used as an animal model of multiple sclerosis to identify pathogenic cytokines that could be therapeutic targets. Granulocyte-macrophage colony-stimulating factor (GM-CSF) is the only cytokine reported to be essential for EAE. We investigated the role of GM-CSF in EAE in C3HeB/FeJ mice that uniquely exhibit extensive brain and spinal cord inflammation. Unexpectedly, GM-CSF-deficient C3HeB/FeJ mice were fully susceptible to EAE because IL-17 activity compensated for the loss of GM-CSF during induction of spinal cord-targeted disease. In contrast, both GM-CSF and IL-17 were needed to fully overcome the inhibitory influence of IFN-γ on the induction of inflammation in the brain. Both GM-CSF and IL-17 independently promoted neutrophil accumulation in the brain, which was essential for brain-targeted disease. These results identify a GM-CSF/IL-17/IFN-γ axis that regulates inflammation in the central nervous system and suggest that a combination of cytokine-neutralizing therapies may be needed to dampen central nervous system autoimmunity.

Cytokine networks in neuroinflammation

Cytokines provide cells with the ability to communicate with one another and orchestrate complex multicellular behaviour. There is an emerging understanding of the role that cytokines play in normal homeostatic tissue function and how dysregulation of these cytokine networks is associated with pathological conditions. The central nervous system (CNS), where few blood-borne immune cells circulate, seems to be particularly vulnerable to dysregulated cytokine networks. In degenerative diseases, such as proteopathies, CNS-resident cells are the predominant producers of pro-inflammatory cytokines. By contrast, in classical neuroinflammatory diseases, such as multiple sclerosis and encephalitides, pro-inflammatory cytokines are mainly produced by tissue-invading leukocytes. Whereas the effect of dysregulated cytokine networks in proteopathies is controversial, cytokines delivered to the CNS by invading immune cells are in general detrimental to the tissue. Here, we summarize recent observations on the impact of dysregulated cytokine networks in neuroinflammation.

Schizophrenia associated sensory gating deficits develop after adolescent microglia activation

Maternal infection during pregnancy is a well-established risk factor for schizophrenia in the adult offspring. Consistently, prenatal Poly(I:C) treatment in mice has been validated to model behavioral and neurodevelopmental abnormalities associated with schizophrenia. By using the Poly(I:C) BALB/c mouse model, we investigated the functional profile of microglia by flow cytometry in relation to progressive behavioral changes from adolescence to adulthood. Prenatal Poly(I:C) treatment induced the expected sensory gating deficits (pre-pulse inhibition (PPI) of the acoustic startle response) in 100day-old adult offspring, but only in female not in male descendants. No PPI-deficits were present in 30day-old adolescent mice. Sensory gating deficits in adult females were preceded by a strong M1-type microglia polarization pattern during puberty as determined by flow cytometric analysis of multiple pro- and anti-inflammatory surface markers. Microglia activation in females did not persist until adulthood and was absent in behaviorally unaffected male descendants. Further, the specific activation pattern of microglia was not mirrored by a similar activation of peripheral immune cells. We conclude that prenatal Poly(I:C) treatment induces post pubertal deficits in sensory gating which are specifically preceded by a pro-inflammatory activation pattern of microglia during puberty.

Regulator of G-protein Signaling (RGS)1 and RGS10 Proteins as Potential Drug Targets for Neuroinflammatory and Neurodegenerative Diseases

Regulator of G-protein signaling (RGS) proteins were originally identified as negative regulators of G-protein-coupled receptor (GPCR) signaling via their GTPase-accelerating protein (GAP) activity. All RGS proteins contain evolutionarily conserved RGS domain; however, they differ in their size and regulatory domains. RGS1 and RGS10 are smaller than other RGS proteins, and their functions involve various inflammatory responses including autoimmune responses in both the periphery and the central nervous system (CNS). Neuroinflammation is the chronic inflammatory response in the CNS. Acute inflammatory response in the CNS is believed to be beneficial by involving the neuroprotective actions of immune cells in the brain, particularly microglia, to limit tissue damage and to aid in neuronal repair. However, chronically elevated levels of cytokines serve to maintain activation of abundant numbers of immune cells potentiating prolonged inflammatory responses and creating an environment of oxidative stress, which further hastens oxidative damage of neurons. In this review, we describe the implications and features of RGS proteins (specifically RGS1 and RGS10) in neuroinflammation and neurodegenerative diseases. We will discuss the experimental and epidemiological evidence on the benefits of anti-inflammatory interventions by targeting RGS1 and/or RGS10 protein function or expression in order to delay or attenuate the progression of neurodegeneration, particularly in multiple sclerosis (MS) and Parkinson's disease (PD).

Endogenous adaptation to low oxygen modulates T-cell regulatory pathways in EAE

Background

In the brain, chronic inflammatory activity may lead to compromised delivery of oxygen and glucose suggesting that therapeutic approaches aimed at restoring metabolic balance may be useful. In vivo exposure to chronic mild normobaric hypoxia (10 % oxygen) leads to a number of endogenous adaptations that includes vascular remodeling (angioplasticity). Angioplasticity promotes tissue survival. We have previously shown that induction of adaptive angioplasticity modulates the disease pattern in myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE). In the present study, we define mechanisms by which adaptation to low oxygen functionally ameliorates the signs and symptoms of EAE and for the first time show that tissue hypoxia may fundamentally alter neurodegenerative disease.

Methods

C57BL/6 mice were immunized with MOG, and some of them were kept in the hypoxia chambers (day 0) and exposed to 10 % oxygen for 3 weeks, while the others were kept at normoxic environment. Sham-immunized controls were included in both hypoxic and normoxic groups. Animals were sacrificed at pre-clinical and peak disease periods for tissue collection and analysis.

Results

Exposure to mild hypoxia decreased histological evidence of inflammation. Decreased numbers of cluster of differentiation (CD)4+ T cells were found in the hypoxic spinal cords associated with a delayed Th17-specific cytokine response. Hypoxia-induced changes did not alter the sensitization of peripheral T cells to the MOG peptide. Exposure to mild hypoxia induced significant increases in anti-inflammatory IL-10 levels and an increase in the number of spinal cord CD25+FoxP3+ T-regulatory cells.

Conclusions

Acclimatization to mild hypoxia incites a number of endogenous adaptations that induces an anti-inflammatory milieu. Further understanding of these mechanisms system may pinpoint possible new therapeutic targets to treat neurodegenerative disease.

C-C chemokine receptor type 4 antagonist Compound 22 ameliorates experimental autoimmune encephalomyelitis

Chemokines and chemokine receptors play important roles in the immune response. We previously reported the pathogenic role of C-C chemokine receptor type 4 (CCR4) in experimental autoimmune encephalomyelitis (EAE). Here, we examined whether CCR4 antagonism modulates the disease course of EAE. Wild-type and CCR4-knockout mice were induced EAE and were administered Compound 22, an antagonist of CCR4. Compound 22 significantly ameliorated the severity of EAE in wild-type mice, but not in the CCR4-knockout mice. Compound 22 inhibited Th1 and Th17 polarization of antigen-induced T-cell responses. Therefore, CCR4 antagonists might be potential therapeutic agents for multiple sclerosis.

CCR2 defines in vivo development and homing of IL-23-driven GM-CSF-producing Th17 cells

IL-17-producing helper T (Th17) cells are critical for host defense against extracellular pathogens but also drive numerous autoimmune diseases. Th17 cells that differ in their inflammatory potential have been described including IL-10-producing Th17 cells that are weak inducers of inflammation and highly inflammatory, IL-23-driven, GM-CSF/IFNγ-producing Th17 cells. However, their distinct developmental requirements, functions and trafficking mechanisms in vivo remain poorly understood. Here we identify a temporally regulated IL-23-dependent switch from CCR6 to CCR2 usage by developing Th17 cells that is critical for pathogenic Th17 cell-driven inflammation in experimental autoimmune encephalomyelitis (EAE). This switch defines a unique in vivo cell surface signature (CCR6⁻CCR2⁺) of GM-CSF/IFNγ-producing Th17 cells in EAE and experimental persistent extracellular bacterial infection, and in humans. Using this signature, we identify an IL-23/IL-1/IFNγ/TNFα/T-bet/Eomesodermin-driven circuit driving GM-CSF/IFNγ-producing Th17 cell formation in vivo. Thus, our data identify a unique cell surface signature, trafficking mechanism and T-cell intrinsic regulators of GM-CSF/IFNγ-producing Th17 cells.

Little is known regarding migration of Th17 cells that produce distinct cytokines implicated in protection and pathology. Kara et al. show that a switch from CCR6 to CCR2 by Th17 cells defines a signature (CCR6⁻CCR2⁺) of GM-CSF⁺ Th17 cells and drives pathology in a mouse model of autoimmunity.

Bone marrow-derived macrophages and the CNS: An update on the use of experimental chimeric mouse models and bone marrow transplantation in neurological disorders

The central nervous system (CNS) is a very unique system with multiple features that differentiate it from systemic tissues. One of the most captivating aspects of its distinctive nature is the presence of the blood brain barrier (BBB), which seals it from the periphery. Therefore, to preserve tissue homeostasis, the CNS has to rely heavily on resident cells such as microglia. These pivotal cells of the mononuclear lineage have important and dichotomous roles according to various neurological disorders. However, certain insults can overwhelm microglia as well as compromising the integrity of the BBB, thus allowing the infiltration of bone marrow-derived macrophages (BMDMs). The use of myeloablation and bone marrow transplantation allowed the generation of chimeric mice to study resident microglia and infiltrated BMDM separately. This breakthrough completely revolutionized the way we captured these 2 types of mononuclear phagocytic cells. We now realize that microglia and BMDM exhibit distinct features and appear to perform different tasks. Since these cells are central in several pathologies, it is crucial to use chimeric mice to analyze their functions and mechanisms to possibly harness them for therapeutic purpose. This review will shed light on the advent of this methodology and how it allowed deciphering the ontology of microglia and its maintenance during adulthood. We will also compare the different strategies used to perform myeloablation. Finally, we will discuss the landmark studies that used chimeric mice to characterize the roles of microglia and BMDM in several neurological disorders. This article is part of a Special Issue entitled: Neuro Inflammation edited by Helga E. de Vries and Markus Schwaninger.

Bioenergetics of the spinal cord in experimental autoimmune encephalitis of rats

Background

Mitochondrial dysregulation is important in axonal damage and demyelination in multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). There is however, no evidence in the literature of any study that has examined cellular bioenergetics of the central nervous system (CNS) during the early development and clinical course of EAE. EAE, a rodent model of relapsing/remitting MS, is a CD4⁺ T cell-mediated disease of the CNS. We hypothesize that CNS bioenergetics might predict prognosis, and that preserved bioenergetics might underlie the remission from disease. The study aims therefore, to determine whether the clinical history of EAE is influenced by cellular respiration of the CNS in susceptible Dark Agouti (DA) and resistant Albino Oxford (AO) rats.

Methods

Experimental autoimmune encephalomyelitis was induced by myelin basic protein in complete Freud Adjuvant in the footpads of DA and AO rats. A phosphorescence analyzer that determines cellular respiration was used to monitor oxygen consumption and ATP concentration was measured using the Enliten ATP assay system. Disease pathology was demonstrated by H&E and Luxol fast blue staining of sections of the lumbar regions of the spinal cord. Mitochondrial size in relation to axonal size was determined by electron microscopy. Apoptosis was studied by HPLC measurement of intracellular caspase-3 activity and caspase immunohistochemistry. Role and source of caspase 1 was studied by double immunofluorescence with antibodies for caspase-1, microglia (anti-Iba1) and astrocytes (anti-GFAP).

Results

The cellular respiration of the CNS did not vary between diseased and normal rats. We also demonstrate here, that at the peak of disease, inflammation as shown by caspase-1, produced by activated microglia and infiltrating cells, was significant in susceptible DA rats. The mitochondrial:axonal size ratio did not vary in the different groups although mitochondria were smaller in spinal cords of diseased DA rats. Demyelination, observed only in areas of mononuclear infiltration of the spinal cord of diseased DA rats, was demonstrated by light microscopy and electron microscopy.

Conclusion

We conclude that EAE at this early stage does not significantly affect CNS cellular respiration and this might underlie the reason for the recovery of diseased rats.

Microglia Versus Myeloid Cell Nomenclature during Brain Inflammation

As immune sentinels of the central nervous system (CNS), microglia not only respond rapidly to pathological conditions but also contribute to homeostasis in the healthy brain. In contrast to other populations of the myeloid lineage, adult microglia derive from primitive myeloid precursors that arise in the yolk sac early during embryonic development, after which they self-maintain locally and independently of blood-borne myeloid precursors. Under neuro-inflammatory conditions such as experimental autoimmune encephalomyelitis, circulating monocytes invade the CNS parenchyma where they further differentiate into macrophages or inflammatory dendritic cells. Often it is difficult to delineate resident microglia from infiltrating myeloid cells using currently known markers. Here, we will discuss the current means to reliably distinguish between these populations, and which recent advances have helped to make clear definitions between phenotypically similar, yet functionally diverse myeloid cell types.

Insights into Myeloid-Derived Suppressor Cells in Inflammatory Diseases

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of cells involved in immune regulation. This population subdivides into granulocytic MDSCs and monocytic MDSCs, which regulate immune responses via the production of various molecules including reactive oxygen species, nitric oxide, arginase-1, interleukin-10, and transforming growth factor-β. Most studies of MDSCs focused on their role in tumors. MDSCs protect tumor cells from immune responses, and thus the frequency of MDSCs associates with poor prognosis. Many recent studies reported an important role for MDSCs in inflammatory diseases via the regulation of immune cells. In addition, the utilization of MDSCs by infectious pathogens suggests an immune evasion mechanism. Thus, MDSCs are important immune regulators in inflammatory diseases, as well as in tumors. This review focuses on the role of MDSCs in the regulation of inflammation in non-tumor settings.

The Role and Potential Therapeutic Application of Myeloid-Derived Suppressor Cells in Allo- and Autoimmunity

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of cells that consists of myeloid progenitor cells and immature myeloid cells. They have been identified as a cell population that may affect the activation of CD4(+) and CD8(+) T-cells to regulate the immune response negatively, which makes them attractive targets for the treatment of transplantation and autoimmune diseases. Several studies have suggested the potential suppressive effect of MDSCs on allo- and autoimmune responses. Conversely, MDSCs have also been found at various stages of differentiation, accumulating during pathological situations, not only during tumor development but also in a variety of inflammatory immune responses, bone marrow transplantation, and some autoimmune diseases. These findings appear to be contradictory. In this review, we summarize the roles of MDSCs in different transplantation and autoimmune diseases models as well as the potential to target these cells for therapeutic benefit.

Absence of CCL2 and CCL3 Ameliorates Central Nervous System Grey Matter But Not White Matter Demyelination in the Presence of an Intact Blood-Brain Barrier

A broad spectrum of diseases is characterized by myelin abnormalities, oligodendrocyte pathology, and concomitant glia activation, among multiple sclerosis (MS). Our knowledge regarding the factors triggering gliosis and demyelination is scanty. Chemokines are pivotal for microglia and astrocyte activation and orchestrate critical steps during the formation of central nervous system (CNS) demyelinating lesions. Redundant functions of chemokines complicate, however, the study of their functional relevance. We used the cuprizone model to study redundant functions of two chemokines, CCL2/MCP1 and CCL3/MIP1α, which are critically involved in the pathological process of cuprizone-induced demyelination. First, we generated a mutant mouse strain lacking functional genes of both chemokines and demonstrated that double-mutant animals are viable, fertile, and do not present with gross abnormalities. Astrocytes and peritoneal macrophages, cultured form tissues of these animals did neither express CCL2 nor CCL3. Exposure to cuprizone resulted in increased CCL2 and CCL3 brain levels in wild-type but not mutant animals. Cuprizone-induced demyelination, oligodendrocyte loss, and astrogliosis were significantly ameliorated in the cortex but not corpus callosum of chemokine-deficient animals. In summary, we provide a novel powerful model to study the redundant function of two important chemokines. Our study reveals that chemokine function in the CNS redounds to region-specific pathophysiological events.

CCR2-dependent dendritic cell accumulation in the central nervous system during early effector experimental autoimmune encephalomyelitis is essential for effector T cell restimulation in situ and disease progression

Dendritic cells (DCs)--although absent from the healthy CNS parenchyma--rapidly accumulate within brain and spinal cord tissue during neuroinflammation associated with experimental autoimmune encephalomyelitis (EAE; a mouse model of multiple sclerosis). Yet, although DCs have been appreciated for their role in initiating adaptive immune responses in peripheral lymphoid organ tissues, how DCs infiltrate the CNS and contribute to ongoing neuroinflammation in situ is poorly understood. In this study, we report the following: 1) CD11c(+) bone marrow-derived DCs and CNS-infiltrating DCs express chemokine receptor CCR2; 2) compared with CCR2(+/+) cells, adoptively transferred CCR2(-/-) bone marrow-derived DCs or DC precursors do not accumulate in the CNS during EAE, despite abundance in blood; 3) CCR2(-/-) DCs show less accumulation in the inflamed CNS in mixed bone marrow chimeras, when compared with CCR2(+/+) DCs; and 4) ablation of CCR2(+/+) DCs during EAE clinical onset delays progression and attenuates cytokine production by infiltrating T cells. Whereas the role of CCR2 in monocyte migration into the CNS has been implicated previously, the role of CCR2 in DC infiltration into the CNS has never been directly addressed. Our data suggest that CCR2-dependent DC recruitment to the CNS during ongoing neuroinflammation plays a crucial role in effector T cell cytokine production and disease progression, and signify that CNS-DCs and circulating DC precursors might be key therapeutic targets for suppressing ongoing neuroinflammation in CNS autoimmune diseases.

Chronic pelvic allodynia is mediated by CCL2 through mast cells in an experimental autoimmune cystitis model

The cause of chronic pelvic pain in interstitial cystitis/painful bladder syndrome (IC/PBS) remains unclear; autoimmunity is a possible etiology. We have recently shown that injection of a single immunogenic peptide of uroplakin 3A (UPK3A 65-84) induces experimental autoimmune cystitis (EAC) in female BALB/cJ mice that is unique among experimental models in accurately reflecting both the urinary symptoms and pelvic pain of IC/PBS. The aim of this project was to identify the roles of mast cells and mast cell chemoattractant/activator monocyte chemoattractant protein-1 [chemokine (C-C motif) ligand 2 (CCL2)] in the allodynia in this model. We immunized 6- to 8-wk-old female BALB/cJ mice with UPK3A 65-84 peptide and, 5-40 days later, observed increased responses to stimulation of the suprapubic abdominal and hindpaw surfaces with von Frey monofilaments compared with mice injected with adjuvant alone. Suprapubic and hindpaw tactile allodynia responses by EAC mice were blocked by instillation of lidocaine into the bladder but not by lidocaine in the uterus, confirming the bladder as the source of the hypersensitivity. Markedly increased numbers of activated mast cells and expression of CCL2 were found in the bladder after immunization with UPK3A 65-84. Hypersensitive responses were inhibited by mast cell stabilizer cromolyn sodium and antagonists of histamine receptors 1 and 2. Furthermore, BALB/cJ mice with deletion of the Ccl2 or chemokine (C-C motif) receptor 2 gene exhibited markedly reduced allodynia and accumulation of mast cells after UPK3A 65-84 immunization. These results show that UPK3A 65-84 immunization causes chronic visceral allodynia and suggest that it is mediated by CCL2-driven mast cell accumulation in the bladder.

Role of CCR2 in inflammatory conditions of the central nervous system

CC chemokine receptor 2 (CCR2) plays important roles in extravasation and transmigration of monocytes under inflammatory conditions. CCR2 and its ligands have been extensively studied in a range of inflammatory diseases in the central nervous system (CNS), including multiple sclerosis, Alzheimer's disease and ischemic stroke. This brief review summarizes our current understanding of the physiologic and pathologic roles of CCR2, focusing on its involvement in CNS inflammatory diseases. There appears to be a rationale for exploring therapies involving CCR2 inhibition in multiple sclerosis and ischemic stroke, but there is also evidence for immunomodulatory and protective effects of CCR2 activity during CNS inflammation. The critical balance between protective and detrimental roles of CCR2-dependent recruitment of leukocytes must therefore be carefully examined to guide safe and effective development of any therapies involving CCR2 modulation.

Thymic CCL2 influences induction of T-cell tolerance

Thymic epithelial cells (TEC) and dendritic cells (DC) play a role in T cell development by controlling the selection of the T cell receptor repertoire. DC have been described to take up antigens in the periphery and migrate into the thymus where they mediate tolerance via deletion of autoreactive T cells, or by induction of natural regulatory T cells. Migration of DC to thymus is driven by chemokine receptors. CCL2, a major ligand for the chemokine receptor CCR2, is an inflammation-associated chemokine that induces the recruitment of immune cells in tissues. CCL2 and CCR2 are implicated in promoting experimental autoimmune encephalomyelitis (EAE), a mouse model for multiple sclerosis. We here show that CCL2 is constitutively expressed by endothelial cells and TEC in the thymus. Transgenic mice overexpressing CCL2 in the thymus showed an increased number of thymic plasmacytoid DC and pronounced impairment of T cell development. Consequently, CCL2 transgenic mice were resistant to EAE. These findings demonstrate that expression of CCL2 in thymus regulates DC homeostasis and controls development of autoreactive T cells, thus preventing development of autoimmune diseases.

High-resolution intravital imaging reveals that blood-derived macrophages but not resident microglia facilitate secondary axonal dieback in traumatic spinal cord injury

After traumatic spinal cord injury, functional deficits increase as axons die back from the center of the lesion and the glial scar forms. Axonal dieback occurs in two phases: an initial axon intrinsic stage that occurs over the first several hours and a secondary phase which takes place over the first few weeks after injury. Here, we examine the secondary phase, which is marked by infiltration of macrophages. Using powerful time-lapse multi-photon imaging, we captured images of interactions between Cx3cr1(+/GFP) macrophages and microglia and Thy-1(YFP) axons in a mouse dorsal column crush spinal cord injury model. Over the first few weeks after injury, axonal retraction bulbs within the lesion are static except when axonal fragments are lost by a blebbing mechanism in response to physical contact followed by phagocytosis by mobile Cx3Cr1(+/GFP) cells. Utilizing a radiation chimera model to distinguish marrow-derived cells from radio-resistant CNS-resident microglia, we determined that the vast majority of accumulated cells in the lesion are derived from the blood and only these are associated with axonal damage. Interestingly, CNS-resident Cx3Cr1(+/GFP) microglia did not increasingly accumulate nor participate in neuronal destruction in the lesion during this time period. Additionally, we found that the blood-derived cells consisted mainly of singly labeled Ccr2(+/RFP) macrophages, singly labeled Cx3Cr1(+/GFP) macrophages and a small population of double-labeled cells. Since all axon destructive events were seen in contact with a Cx3Cr1(+/GFP) cell, we infer that the CCR2 single positive subset is likely not robustly involved in axonal dieback. Finally, in our model, deletion of CCR2, a chemokine receptor, did not alter the position of axons after dieback. Understanding the in vivo cellular interactions involved in secondary axonal injury may lead to clinical treatment candidates involving modulation of destructive infiltrating blood monocytes.

GM-CSF-responsive monocyte-derived dendritic cells are pivotal in Th17 pathogenesis

Although multiple dendritic cell (DC) subsets have the potential to induce Th17 differentiation in vitro, the key DC that is critical in Th17 induction and Th17-mediated disease remains moot. In this study, we revealed that CCR2(+) monocyte-derived DCs (moDCs), but not conventional DCs, were critical for in vivo Th17 induction and autoimmune inflammation. Functional comparison in vitro indicated that moDCs are the most potent type of Th17-inducing DCs compared with conventional DCs and plasmacytoid DCs. Furthermore, we demonstrated that the importance of GM-CSF in Th17 induction and Th17-mediated disease is its endowment of moDCs to induce Th17 differentiation in vivo, although it has little effect on moDC numbers. Our findings identify the in vivo cellular targets that can be selectively manipulated to ameliorate Th17-mediated inflammatory diseases, as well as the mechanism of GM-CSF antagonism in such diseases.

Mice lacking natural killer T cells are more susceptible to metabolic alterations following high fat diet feeding

Current estimates suggest that over one-third of the adult population has metabolic syndrome and three-fourths of the obese population has non-alcoholic fatty liver disease (NAFLD). Inflammation in metabolic tissues has emerged as a universal feature of obesity and its co-morbidities, including NAFLD. Natural Killer T (NKT) cells are a subset of innate immune cells that abundantly reside within the liver and are readily activated by lipid antigens. There is general consensus that NKT cells are pivotal regulators of inflammation; however, disagreement exists as to whether NKT cells exert pathogenic or suppressive functions in obesity. Here we demonstrate that CD1d^−/− mice, which lack NKT cells, were more susceptible to weight gain and fatty liver following high fat diet (HFD) feeding. Compared with their WT counterparts, CD1d^−/− mice displayed increased adiposity and greater induction of inflammatory genes in the liver suggestive of the precursors of NAFLD. Calorimetry studies revealed a significant increase in food intake and trends toward decreased metabolic rate and activity in CD1d^−/− mice compared with WT mice. Based on these findings, our results suggest that NKT cells play a regulatory role that helps to prevent diet-induced obesity and metabolic dysfunction and may play an important role in mechanisms governing cross-talk between metabolism and the immune system to regulate energy balance and liver health.

Th1-mediated experimental autoimmune encephalomyelitis is CXCR3 independent

Drugs that block leukocyte trafficking ameliorate multiple sclerosis (MS). Occurrences of opportunistic infection, however, highlight the need for novel drugs that modulate more restricted subsets of T cells. In this context, chemokines and their receptors are attractive therapeutic targets. CXCR3, a Th1-associated chemokine receptor, is preferentially expressed on T cells that accumulate in MS lesions and central nervous system (CNS) infiltrates of mice with experimental autoimmune encephalomyelitis (EAE). Surprisingly, mice genetically deficient in either CXCR3 or CXCL10 succumb to EAE following active immunization with myelin antigens. EAE is mediated by a heterogeneous population of T cells in myelin-immunized mice. Hence, disease might develop in the absence of CXCR3 secondary to the compensatory action of encephalitogenic CCR6(+) Th17 cells. However, in the current study, we show for the first time that blockade or genetic deficiency of either CXCR3 or of its primary ligand has no impact on clinical EAE induced by the adoptive transfer of highly polarized Th1 effector cells. Our data illustrate the fact that, although highly targeted immunotherapies might have more favorable side effect profiles, they are also more likely to be rendered ineffective by inherent redundancies in chemokine and cytokine networks that arise at sites of neuroinflammation.

Possible association between expression of chemokine receptor-2 (CCR2) and amyotrophic lateral sclerosis (ALS) patients of North India

Background and Objectives

We earlier reported elevated chemokine ligand-2 (CCL2) in Indian amyotrophic lateral sclerosis (ALS) patients. We now analysed chemokine receptor-2 (CCR2), the receptor of CCL2, in these ALS patients.

Methods

Indian sporadic ALS patients (n = 50) were included on the basis of El Escorial criteria. Percentage (%) of CCR2 expressing peripheral blood mononuclear cells (PBMCs) was evaluated using Flow Cytometry. Real Time Polymerase Chain Reaction (PCR) was used to quantitate CCR2 mRNA expression in PBMCs. Normal controls (n = 40) were also included for comparison.

Results

Flow Cytometry revealed significantly reduced CCR2 expressing PBMCs in the ALS patients. We also found a significant decline in number of CCR2 expressing PBMCs in limb onset ALS when compared to bulbar onset ALS. PBMCs from ALS patients showed substantial down-regulation of CCR2 mRNA. CCR2 mRNA expression was found to be decreased among limb ALS patients as compared to bulbar onset ALS. Further, the count of CCR2+ PBMCs and CCR2 mRNA transcript in PBMCs was significantly lower in severe and moderate ALS as compared to ALS patients with mild impairments.

Conclusions

Downregulation of PBMCs CCR2 may indicate its etio-pathological relevance in ALS pathogenesis. Reduced PBMCs CCR2 may result in decreased infiltration of leukocytes at the site of degeneration as a compensatory response to ALS. CCR2 levels measurements in hematopoietic stem cells and estimation of comparative PBMCs count among ALS, disease controls and normal controls can unveil its direct neuroprotective role. However, the conclusions are restricted by the absence of neurological/non-neurological disease controls in the study.

G protein-coupled receptors as therapeutic targets for multiple sclerosis

G protein-coupled receptors (GPCRs) mediate most of our physiological responses to hormones, neurotransmitters and environmental stimulants. They are considered as the most successful therapeutic targets for a broad spectrum of diseases. Multiple sclerosis (MS) is an inflammatory disease that is characterized by immune-mediated demyelination and degeneration of the central nervous system (CNS). It is the leading cause of non-traumatic disability in young adults. Great progress has been made over the past few decades in understanding the pathogenesis of MS. Numerous data from animal and clinical studies indicate that many GPCRs are critically involved in various aspects of MS pathogenesis, including antigen presentation, cytokine production, T-cell differentiation, T-cell proliferation, T-cell invasion, etc. In this review, we summarize the recent findings regarding the expression or functional changes of GPCRs in MS patients or animal models, and the influences of GPCRs on disease severity upon genetic or pharmacological manipulations. Hopefully some of these findings will lead to the development of novel therapies for MS in the near future.

CC chemokine receptor 4 is required for experimental autoimmune encephalomyelitis by regulating GM-CSF and IL-23 production in dendritic cells

Dendritic cells (DCs) are pivotal for the development of experimental autoimmune encephalomyelitis (EAE). However, the mechanisms by which they control disease remain to be determined. This study demonstrates that expression of CC chemokine receptor 4 (CCR4) by DCs is required for EAE induction. CCR4(-/-) mice presented enhanced resistance to EAE associated with a reduction in IL-23 and GM-CSF expression in the CNS. Restoring CCR4 on myeloid cells in bone marrow chimeras or intracerebral microinjection of CCR4-competent DCs, but not macrophages, restored EAE in CCR4(-/-) mice, indicating that CCR4(+) DCs are cellular mediators of EAE development. Mechanistically, CCR4(-/-) DCs were less efficient in GM-CSF and IL-23 production and also T(H)-17 maintenance. Intraspinal IL-23 reconstitution restored EAE in CCR4(-/-) mice, whereas intracerebral inoculation using IL-23(-/-) DCs or GM-CSF(-/-) DCs failed to induce disease. Thus, CCR4-dependent GM-CSF production in DCs required for IL-23 release in these cells is a major component in the development of EAE. Our study identified a unique role for CCR4 in regulating DC function in EAE, harboring therapeutic potential for the treatment of CNS autoimmunity by targeting CCR4 on this specific cell type.

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.