Rat oligodendroglial cell lines express a functional receptor for the chemokine CCL3 (macrophage inflammatory protein-1alpha)

A CCR5 antagonist, maraviroc, alleviates neural circuit dysfunction and behavioral disorders induced by prenatal valproate exposure

BACKGROUND

Valproic acid (VPA) is a clinically used antiepileptic drug, but it is associated with a significant risk of a low verbal intelligence quotient (IQ) score, attention-deficit hyperactivity disorder and autism spectrum disorder in children when it is administered during pregnancy. Prenatal VPA exposure has been reported to affect neurogenesis and neuronal migration and differentiation. In addition, growing evidence has shown that microglia and brain immune cells are activated by VPA treatment. However, the role of VPA-activated microglia remains unclear.

METHODS

Pregnant female mice received sodium valproate on E11.5. A microglial activation inhibitor, minocycline or a CCR5 antagonist, maraviroc was dissolved in drinking water and administered to dams from P1 to P21. Measurement of microglial activity, evaluation of neural circuit function and expression analysis were performed on P10. Behavioral tests were performed in the order of open field test, Y-maze test, social affiliation test and marble burying test from the age of 6 weeks.

RESULTS

Prenatal exposure of mice to VPA induced microglial activation and neural circuit dysfunction in the CA1 region of the hippocampus during the early postnatal periods and post-developmental defects in working memory and social interaction and repetitive behaviors. Minocycline, a microglial activation inhibitor, clearly suppressed the above effects, suggesting that microglia elicit neural dysfunction and behavioral disorders. Next-generation sequencing analysis revealed that the expression of a chemokine, C-C motif chemokine ligand 3 (CCL3), was upregulated in the hippocampi of VPA-treated mice. CCL3 expression increased in microglia during the early postnatal periods via an epigenetic mechanism. The CCR5 antagonist maraviroc significantly suppressed neural circuit dysfunction and post-developmental behavioral disorders induced by prenatal VPA exposure.

CONCLUSION

These findings suggest that microglial CCL3 might act during development to contribute to VPA-induced post-developmental behavioral abnormalities. CCR5-targeting compounds such as maraviroc might alleviate behavioral disorders when administered early.

A Preventive Role of RANTES Genetic Variation against Undifferentiated Schizophrenia

AIM

Due to conflicting data from relevant studies, evidence for chemokine alterations in the pathophysiology of schizophrenia (Scz) remains inconclusive. Thus, we aimed to investigate the impact of rs2107538, rs2280788, and rs2280789 polymorphisms in CCL5 gene, as well as rs333 within CCR5 gene and the development of Scz in a Tunisian cohort.

METHODS

We performed a case-control study composed of 200 patients and 200 controls using RFLP-PCR.

RESULTS

Among the analyzed polymorphisms, only rs2107538 imparted protection against Scz and more specifically to male sex. This protective effect remained valid for the undifferentiated form. Moreover, this SNP had an impact on patients' symptomatology. When focusing on haplotypes, we noticed that the rs2107538-rs2280788-rs2280789 ACT genetic combination, with only one mutated allele rs2107538A, displayed reduced frequency in both Scz (as a whole group) and undifferentiated subtype. The haplotype distribution profile implies that the A allele at rs2107538 could induce a protective effect by increasing RANTES production.

CONCLUSION

Additional independent analyses are required to corroborate these findings and elucidate the functional implications of the discovered preventing genotypes and haplotypes in Scz.

Multiple sclerosis risk gene Mertk is required for microglial activation and subsequent remyelination

In multiple sclerosis (MS) and other neurological diseases, the failure to repair demyelinated lesions contributes to axonal damage and clinical disability. Here, we provide evidence that Mertk, a gene highly expressed by microglia that alters MS risk, is required for efficient remyelination. Compared to wild-type (WT) mice, Mertk-knockout (KO) mice show impaired clearance of myelin debris and remyelination following demyelination. Using single-cell RNA sequencing, we characterize Mertk-influenced responses to cuprizone-mediated demyelination and remyelination across different cell types. Mertk-KO brains show an attenuated microglial response to demyelination but an elevated proportion of interferon (IFN)-responsive microglia. In addition, we identify a transcriptionally distinct subtype of surviving oligodendrocytes specific to demyelinated lesions. The inhibitory effect of myelin debris on remyelination is mediated in part by IFNγ, which further impedes microglial clearance of myelin debris and inhibits oligodendrocyte differentiation. Together, our work establishes a role for Mertk in microglia activation, phagocytosis, and migration during remyelination.

Systematic Review of the Neurobiological Relevance of Chemokines to Psychiatric Disorders

Psychiatric disorders are highly prevalent and disabling conditions of increasing public health relevance. Much recent research has focused on the role of cytokines in the pathophysiology of psychiatric disorders; however, the related family of immune proteins designated chemokines has been relatively neglected. Chemokines were originally identified as having chemotactic function on immune cells; however, recent evidence has begun to elucidate novel, brain-specific functions of these proteins of relevance to the mechanisms of psychiatric disorders. A systematic review of both human and animal literature in the PubMed and Google Scholar databases was undertaken. After application of all inclusion and exclusion criteria, 157 references were remained for the review. Some early mechanistic evidence does associate select chemokines with the neurobiological processes, including neurogenesis, modulation of the neuroinflammatory response, regulation of the hypothalamus–pituitary–adrenal axis, and modulation of neurotransmitter systems. This early evidence however does not clearly demonstrate any specificity for a certain psychiatric disorder, but is primarily relevant to mechanisms which are shared across disorders. Notable exceptions include CCL11 that has recently been shown to impair hippocampal function in aging – of distinct relevance to Alzheimer’s disease and depression in the elderly, and pre-natal exposure to CXCL8 that may disrupt early neurodevelopmental periods predisposing to schizophrenia. Pro-inflammatory chemokines, such as CCL2, CCL7, CCL8, CCL12, and CCL13, have been shown to drive chemotaxis of pro-inflammatory cells to the inflamed or injured CNS. Likewise, CX3CL has been implicated in promoting glial cells activation, pro-inflammatory cytokines secretion, expression of ICAM-1, and recruitment of CD4+ T-cells into the CNS during neuroinflammatory processes. With further translational research, chemokines may present novel diagnostic and/or therapeutic targets in psychiatric disorders.

Chemokines and chemokine receptors in mood disorders, schizophrenia, and cognitive impairment: a systematic review of biomarker studies

The search for immune biomarkers in psychiatric disorders has primarily focused on pro-inflammatory cytokines. Other immune proteins including chemokines have been relatively neglected in such studies. Recent evidence has implicated chemokines in many neurobiological processes potentially relevant to psychiatric disorders, beyond their classical chemotactic functions. These may include neuromodulator effects, neurotransmitter-like effects, and direct/indirect regulation of neurogenesis. This systematic review presents the existing early evidence which supports an association of many chemokines with the psychiatric disorders: depression, bipolar disorder, schizophrenia, mild cognitive impairment and Alzheimer's disease. The non-specific association of chemokines including CXCL8 (IL-8), CCL2 (MCP-1), CCL3 (MIP-1α) and CCL5 (RANTES) with these disorders across diagnostic categories implies a generalised involvement of many chemokine systemic with psychiatric disease. Additional chemokines with great mechanistic relevance including CXCL12 (SDF-1) and CX3CL1 (fractalkine) have been rarely reported in the existing human literature and should be included in future clinical studies. The potential utility of these proteins as pathologically relevant biomarkers or therapeutic targets should be considered by future clinical and translational research.

The "window of susceptibility" for inflammation in the immature central nervous system is characterized by a leaky blood-brain barrier and the local expression of inflammatory chemokines

Early in postnatal development, the immature central nervous system (CNS) is more susceptible to inflammation than its adult counterpart. We show here that this "window of susceptibility" is characterized by the presence of leaky vessels in the CNS, and by a global chemokine expression profile which is clearly distinct from the one observed in the adult CNS and has three important characteristics. First, it contains chemokines with known roles in the differentiation and maturation of glia and neurons. Secondly, these chemokines have been described before in inflammatory lesions of the CNS, where they are important for the recruitment of monocytes and T cells. Lastly, the chemokine profile is shaped by pathological changes like oligodendrocyte stress and attempts of myelin repair. Changes in the chemokine expression profile along with a leaky blood-brain barrier pave the ground for an accelerated development of CNS inflammation.

Inflammation stimulates myelination by transplanted oligodendrocyte precursor cells

Inflammation associated with CNS demyelination provides an important stimulus for the activation of endogenous oligodendrocyte precursor cells (OPCs) and subsequent remyelination. This view is largely based on "loss-of-function" studies, whereby remyelination is impaired following depletion of inflammatory cells or mediators. However, "gain-of-function" approaches, asking whether inflammation directly enhances remyelination, have received less attention. We have addressed this issue using a model in which OPCs transplanted into the adult rat retina myelinate retinal ganglion cell axons around the point of injection. Inflammation (characterized by increased expression of the macrophage marker ED1 and the astrocyte marker GFAP, and the up-regulation of multiple cytokines) was induced in the retina by the administration of the TLR-2 ligand zymosan. Myelination, revealed by MBP+ myelin sheaths, was substantially increased when OPCs were injected into the inflamed retina compared to that achieved following transplantation into the normal, noninflamed retina. Our results have important implications for the development of immunomodulatory treatments for acute demyelinating disease and for the therapeutic creation of proremyelination environments in chronic demyelinating disease.

Modulation of rat oligodendrocyte precursor cells by the chemokine CXCL12

Migration, proliferation, and differentiation of oligodendrocyte precursor cells are essential for the assembly of myelin in the central nervous system. Knowledge on the regulation of these precursor cells is therefore of great importance for the understanding of developmental myelination and remyelination in demyelinating diseases. Here, we show that primary rat oligodendrocyte precursor cells express the chemokine receptor CXCR4. Stimulation with the ligand CXCL12 (SDF-1 alpha) leads to intracellular Ca elevation. Furthermore, 10 ng/ml CXCL12 augmented differentiation of precursors into mature oligodendrocytes. Migration toward growth factor conditioned medium was inhibited by CXCL12, while proliferation was only slightly modulated. The effect of CXCL12 on both migration and differentiation was blocked using a G protein antagonist. These data suggest a role for CXCL12 and oligodendroglial CXCR4 receptors during developmental myelination and repair in demyelinating diseases of the central nervous system.

Oligodendrocyte precursor cells express a functional chemokine receptor CCR3: Implications for myelination

Myelination in the central nervous system requires an accurate interplay between oligodendrocyte precursor cells (OPC) and axons. By as yet not fully understood mechanisms, OPC proliferate, migrate to the axon to be myelinated and finally differentiate into mature oligodendrocytes. The recent finding that OPC express CXC chemokine receptors led us to the investigation of the expression and functional importance of CC chemokine receptors. Using RT-PCR, we show that primary OPC from neonatal rats express CCR3, while CCR1, CCR2, CCR4, CCR5, and CCR7 are not expressed. Immunofluorescence staining of OPC could further demonstrate protein expression of CCR3. A rise of intracellular Ca2+ upon stimulation with the appropriate ligand CCL11 showed that this receptor is functional. Moreover, CCL11 led to a concentration specific increase in proliferation, inhibition of migration, and augmentation of differentiation in primary OPC. Thus, CCR3 may influence the process of myelination. This is of general importance for both developmental tissue patterning and for repair processes in demyelinating diseases like multiple sclerosis.

Differential effects of chemokines on oligodendrocyte precursor proliferation and myelin formation in vitro

Chemokines have recently been postulated to have important functions in the central nervous system (CNS) in addition to their principal role of directional migration of leukocytes. In particular, it has been shown that chemokines may play a role in the regulation of oligodendrocyte biology. Here, we have chosen to study the role of certain chemokines in regulating myelination. We have used the murine oligodendrocyte precursor-like cell line, Oli-neu, and primary mixed cortical cultures as experimental systems to assess their activities on oligodendrocyte precursor proliferation and developmental in vitro myelination. GRO-alpha, IL-8, SDF-1alpha and RANTES dose-dependently increased proliferation of this mouse A2B5 precursor-like cell line, while MCP-1 did not. Furthermore, the CXC chemokines GRO-alpha, IL-8 and SDF-1alpha stimulated myelin basic protein synthesis in a dose-dependent manner in primary myelinating cultures and enhanced myelin segment formation in this system, while the CC chemokines MCP-1 and RANTES did not. We also demonstrate that the receptor for SDF-1alpha, CXCR4, is expressed in mixed cortical cultures by PDGFalphaR positive oligodendrocyte precursors (OLPs) as well as by Oli-neu cells. SDF-1alpha induced proliferation in primary mixed cultures and the Oli-neu cell line was mediated through this receptor. We propose, therefore, that CXC chemokines and in particular SDF-1alpha regulates CNS myelination via their effects on cells of the oligodendrocyte lineage, specifically stimulation of OLP proliferation.