Lipopolysaccharide affects Golli expression and promotes proliferation of oligodendrocyte progenitors

Contrasting Iron Metabolism in Undifferentiated Versus Differentiated MO3.13 Oligodendrocytes via IL-1β-Induced Iron Regulatory Protein 1

Parkinson's disease (PD) is a prevalent neurodegenerative disorder characterized by the loss of dopaminergic neurons and the accumulation of iron in the substantia nigra. While iron accumulation and inflammation are implicated in PD pathogenesis, their impact on oligodendrocytes, the brain's myelin-forming cells, remains elusive. This study investigated the influence of interleukin-1β (IL-1β), an elevated proinflammatory cytokine in PD, on iron-related proteins in MO3.13 oligodendrocytes. We found that IL-1β treatment in undifferentiated MO3.13 oligodendrocytes increased iron regulatory protein 1 and transferrin receptor 1 (TfR1) expression while decreasing ferroportin 1 (FPN1) expression. Consequently, iron uptake was enhanced, and iron release was reduced, leading to intracellular iron accumulation. Conversely, IL-1β treatment in differentiated MO3.13 oligodendrocytes exhibited the opposite effect, with decreased TfR1 expression, increased FPN1 expression, and reduced iron uptake. These findings suggest that IL-1β-induced dysregulation of iron metabolism in oligodendrocytes may contribute to the pathological processes observed in PD. IL-1β can increase the iron content in undifferentiated oligodendrocytes, thus facilitating the differentiation of undifferentiated MO3.13 oligodendrocytes. In differentiated oligodendrocytes, IL-1β may facilitate iron release, providing a potential source of iron for neighboring dopaminergic neurons, thereby initiating a cascade of deleterious events. This study provides valuable insights into the intricate interplay between inflammation, abnormal iron accumulation, and oligodendrocyte dysfunction in PD. Targeting the IL-1β-mediated alterations in iron metabolism may hold therapeutic potential for mitigating neurodegeneration and preserving dopaminergic function in PD.

Transplantation of Pro-Oligodendroblasts, Preconditioned by LPS-Stimulated Microglia, Promotes Recovery After Acute Contusive Spinal Cord Injury

Spinal cord injury (SCI) is a significant clinical challenge, and to date no effective treatment is available. Oligodendrocyte progenitor cell (OPC) transplantation has been a promising strategy for SCI repair. However, the poor posttransplantation survival and deficiency in differentiation into myelinating oligodendrocytes (OLs) are two major challenges that limit the use of OPCs as donor cells. Here we report the generation of an OL lineage population [i.e., pro-oligodendroblasts (proOLs)] that is relatively more mature than OPCs for transplantation after SCI. We found that proOLs responded to lipopolysaccharide (LPS)-stimulated microglia conditioned medium (L+M) by preserving toll-like receptor 4 (TLR4) expression, improving cell viability, and enhancing the expression of a myelinating OL marker myelin basic protein (MBP), compared to other OL lineage cells exposed to either LPS-stimulated (L+M) or nonstimulated microglia conditioned medium (LM). When L+M-stimulated proOLs were intrathecally delivered through a lumbar puncture after a T10 thoracic contusive SCI, they promoted behavioral recovery, as assessed by the BassoBeattieBresnahan (BBB) locomotor rating scale, stride length, and slips on the grid tests. Histologically, transplantation of L+M proOLs caused a considerable increase in intralesional axon numbers and myelination, and less accumulation of invading macrophages when compared with the vehicle control or OPC transplantation. Thus, transplantation of proOLs, preconditioned by L+M, may offer a better therapeutic potential for SCI than OPCs since the former may have initiated the differentiation process toward OLs prior to transplantation.

Oligodendrocyte, Astrocyte, and Microglia Crosstalk in Myelin Development, Damage, and Repair

Oligodendrocytes are the myelinating glia of the central nervous system. Myelination of axons allows rapid saltatory conduction of nerve impulses and contributes to axonal integrity. Devastating neurological deficits caused by demyelinating diseases, such as multiple sclerosis, illustrate well the importance of the process. In this review, we focus on the positive and negative interactions between oligodendrocytes, astrocytes, and microglia during developmental myelination and remyelination. Even though many lines of evidence support a crucial role for glia crosstalk during these processes, the nature of such interactions is often neglected when designing therapeutics for repair of demyelinated lesions. Understanding the cellular and molecular mechanisms underlying glial cell communication and how they influence oligodendrocyte differentiation and myelination is fundamental to uncover novel therapeutic strategies for myelin repair.

A silver lining of neuroinflammation: Beneficial effects on myelination

Myelin accelerates action potential conduction velocity and provides essential energy support for axons. Unfortunately, myelin and myelinating cells are often vulnerable to injury or disease, resulting in myelin damage, which in turn can lead to axon dysfunction, overt pathology and neurological impairment. Inflammation is a common component of trauma and disease in both the CNS and PNS and therefore an active inflammatory response is often considered deleterious to myelin health. While inflammation can certainly damage myelin, inflammatory processes also can positively affect oligodendrocyte lineage progression, myelin debris clearance, oligodendrocyte metabolism and myelin repair. In the periphery, inflammatory cascades can also augment myelin repair, including processes initiated by infiltrating immune cells as well as by local Schwann cells. In this review, various aspects of inflammation beneficial to myelin repair are discussed and should be considered when designing or implementing anti-inflammatory therapies for CNS and PNS injury involving myelinating cells.

Lipopolysaccharide Upregulates the Expression of CINC-3 and LIX in Primary NG2 Cells

Numerous NG2 cells, also called oligodendrocyte progenitor cells (OPCs), exist ubiquitously in the gray and white matter in the adult central nervous system (CNS). Although NG2 cells could become active by upregulation of NG2 expression and hypertrophy or extension of their processes under various neuropathological conditions, their actual role in the brain remains to be illustrated. In view of the fact that the synergy of cytokine and chemokine networks plays an important role in CNS inflammation and immunity, we have assumed that the NG2 cells might take part in brain inflammation and immunity by making a contribution to the pool of cytokines or chemokines. In the current study, NG2-expressing OPCs were prepared from cerebral hemispheres of postnatal day 0 or 1 Sprague-Dawley rats. Our results showed that NG2-expressing OPCs, verified by immunohistological staining of anti-NG2 antibody and anti-platelet-derived growth factor receptor alpha (PDGFRα) antibody, presented binding affinity to lipopolysaccharide (LPS), a commonly used stimulator in a neuroinflammatory model. Using cytokine antibody array, QPCR and ELISA, we have further shown that LPS could upregulate the expression of cytokine induced neutrophil chemoattractant-3 (CINC-3) and LPS induced CXC chemokine (LIX) in primary NG2-expressing OPCs, without the alteration in cell number of NG2-expressing OPCs. In addition, the cells bearing the receptor for these two cytokines included microglia and OPCs. Taken together, our results suggest that NG2-expressing OPCs could response to LPS and may take part in neuroinflammatory process, through secreting cytokines and chemokines to exert an effect on target cells (OPCs and microglia).

Neuroinflammation and structural injury of the fetal ovine brain following intra-amniotic Candida albicans exposure

BACKGROUND

Intra-amniotic Candida albicans (C. Albicans) infection is associated with preterm birth and high morbidity and mortality rates. Survivors are prone to adverse neurodevelopmental outcomes. The mechanisms leading to these adverse neonatal brain outcomes remain largely unknown. To better understand the mechanisms underlying C. albicans-induced fetal brain injury, we studied immunological responses and structural changes of the fetal brain in a well-established translational ovine model of intra-amniotic C. albicans infection. In addition, we tested whether these potential adverse outcomes of the fetal brain were improved in utero by antifungal treatment with fluconazole.

METHODS

Pregnant ewes received an intra-amniotic injection of 10(7) colony-forming units C. albicans or saline (controls) at 3 or 5 days before preterm delivery at 0.8 of gestation (term ~ 150 days). Fetal intra-amniotic/intra-peritoneal injections of fluconazole or saline (controls) were administered 2 days after C. albicans exposure. Post mortem analyses for fungal burden, peripheral immune activation, neuroinflammation, and white matter/neuronal injury were performed to determine the effects of intra-amniotic C. albicans and fluconazole treatment.

RESULTS

Intra-amniotic exposure to C. albicans caused a severe systemic inflammatory response, illustrated by a robust increase of plasma interleukin-6 concentrations. Cerebrospinal fluid cultures were positive for C. albicans in the majority of the 3-day C. albicans-exposed animals whereas no positive cultures were present in the 5-day C. albicans-exposed and fluconazole-treated animals. Although C. albicans was not detected in the brain parenchyma, a neuroinflammatory response in the hippocampus and white matter was seen which was characterized by increased microglial and astrocyte activation. These neuroinflammatory changes were accompanied by structural white matter injury. Intra-amniotic fluconazole reduced fetal mortality but did not attenuate neuroinflammation and white matter injury.

CONCLUSIONS

Intra-amniotic C. albicans exposure provoked acute systemic and neuroinflammatory responses with concomitant white matter injury. Fluconazole treatment prevented systemic inflammation without attenuating cerebral inflammation and injury.

Oligodendrocyte, Astrocyte, and Microglia Crosstalk in Myelin Development, Damage, and Repair

Oligodendrocytes are the myelinating glia of the central nervous system. Myelination of axons allows rapid saltatory conduction of nerve impulses and contributes to axonal integrity. Devastating neurological deficits caused by demyelinating diseases, such as multiple sclerosis, illustrate well the importance of the process. In this review, we focus on the positive and negative interactions between oligodendrocytes, astrocytes, and microglia during developmental myelination and remyelination. Even though many lines of evidence support a crucial role for glia crosstalk during these processes, the nature of such interactions is often neglected when designing therapeutics for repair of demyelinated lesions. Understanding the cellular and molecular mechanisms underlying glial cell communication and how they influence oligodendrocyte differentiation and myelination is fundamental to uncover novel therapeutic strategies for myelin repair.

Slice Culture Method for Studying Migration of Neuronal Progenitor Cells Derived from Human Embryonic Stem Cells (hESC)

In this unit we describe an overlay brain slice culture assay for studying migration of transgenic neurospheres derived from human embryonic stem cells (hESC). Neuronal progenitor cells were generated from hESC by derivation of embryoid bodies and rosettes. Rosettes were transfected using the PiggyBac transposon system with either control plasmids (GFP) or plasmid encoding a gene important for migration of neuronal progenitor cells, Doublecortin (DCX). Transfected cells were subsequently grown in low-adhesion plates to generate transgenic human neurospheres (t-hNS). Organotypic slice cultures were prepared from postnatal rat forebrain and maintained using the interface method, before transfected t-hNS were overlaid below the cortex of each hemisphere. After 1 to 5 days, forebrain slices were fixed and processed for immunofluorescence. The distance at which cells migrated from the center of neurospheres to the host forebrain tissue was measured using Image J software. This protocol provides details for using the slice culture method for studying migration and integration of human neuronal cells into the host brain tissue.

Astrogliopathy and oligodendrogliopathy are early events in CNS demyelination

We examined the phenotypic composition of cells and the underlying mechanisms of demyelination following injection of lipopolysaccharide (LPS) into the corpus callosum of rats. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay showed fragmented DNA, which co-localized with oligodendrocytes in areas of demyelination following intracerebral injection with LPS. Immunostaining showed the presence of caspase 3 in cells which expressed the oligodendrocyte markers, suggesting activation of the apoptotic pathway. Commensurate reduction in glial fibrillary acid protein (GFAP)+/ gap junction protein connexin43+ (Cx43) cells, was also seen in the corpus callosum prior to histochemical evidence of demyelination. Expression of mRNA for proinflammatory cytokines was maximal 3 day postinjection, at a time when the numbers of TUNEL positive cells in the corpus callosum were declining and the total number of CD68+ cells peaked at day 14 postinjection. Our studies suggest that death of oligodendrocytes is an early event in LPS model of demyelination. We believe that the innate immune model of oligodendrocyte death will be useful in the development of neuroprotective agents capable of rescuing oligodendrocytes from apoptosis.

The multiple roles of myelin protein genes during the development of the oligodendrocyte

It has become clear that the products of several of the earliest identified myelin protein genes perform functions that extend beyond the myelin sheath. Interestingly, these myelin proteins, which comprise proteolipid protein, 2′,3′-cyclic nucleotide 3′-phosphodiesterase and the classic and golli MBPs (myelin basic proteins), play important roles during different stages of oligodendroglial development. These non-myelin-related functions are varied and include roles in the regulation of process outgrowth, migration, RNA transport, oligodendrocyte survival and ion channel modulation. However, despite the wide variety of cellular functions performed by the different myelin genes, the route by which they achieve these many functions seems to converge upon a common mechanism involving Ca²⁺ regulation, cytoskeletal rearrangements and signal transduction. In the present review, the newly emerging functions of these myelin proteins will be described, and these will then be discussed in the context of their contribution to oligodendroglial development.

Myelin basic protein binds to and inhibits the fibrillar assembly of Abeta42 in vitro

The deposition of amyloid beta-protein (Abeta) fibrils into plaques within the brain parenchyma and along cerebral blood vessels is a hallmark of Alzheimer's disease. Abeta peptides are produced through the successive cleavage of the Abeta precursor protein by beta- and gamma-secretase, producing peptides between 39 and 43 amino acids in length. The most common of these are Abeta40 (the most abundant) and Abeta42. Abeta42 is more fibrillogenic than Abeta40 and has been implicated in early Abeta plaque deposition. Our previous studies determined that myelin basic protein (MBP) was capable of inhibiting fibril formation of a highly fibrillogenic Abeta peptide containing both E22Q (Dutch) and D23N (Iowa) mutations associated with familial forms of cerebral amyloid angiopathy [Hoos, M. D., et al. (2007) J. Biol. Chem. 282, 9952-9961]. In this study, we show through a combination of biochemical and ultrastructural techniques that MBP is also capable of inhibiting the beta-sheet fibrillar assembly of the normal Abeta42 peptide. These findings suggest that MBP may play a role in regulating the deposition of Abeta42 and thereby also may regulate the early formation of amyloid plaques in Alzheimer's disease.

Human fetal radial glia cells generate oligodendrocytes in vitro

Limited knowledge about human oligodendrogenesis prompted us to explore the lineage relationship between cortical radial glia (RG) cells and oligodendrocytes (OLs) in the human fetal forebrain. RG cells were isolated from cortical ventricular/subventricular zone and their progeny was followed in vitro. One portion of RG cells differentiated into cells of OL lineage identified by cell-type specific antibodies, including platelet-derived growth factor receptor-alpha (PDGFRalpha), NG2, O4, myelin basic protein, and myelin oligodendrocyte glycoprotein. Moreover, using Cre Lox fate mapping (brain lipid binding protein-Cre/Floxed-yellow fluorescent protein) we established a direct link between RG cells and OL progenitors. In vitro generation of RG-derived O4(+) OL progenitors was enhanced by addition of sonic hedgehog (SHH) and reduced by the SHH inhibitor, cyclopamine, suggesting the role of SHH signaling in this process. In summary, our in vitro experiments revealed that a portion of cortical RG cells isolated from human forebrain at the second trimester of gestation generates OL progenitors and this suggests a role of SHH in this process.

Iron is essential for oligodendrocyte genesis following intraspinal macrophage activation

Progenitor proliferation and differentiation are necessary for oligodendrocyte replacement. Previously, we showed that intraspinal activation of microglia and macrophages with the TLR4 agonist lipopolysaccharide (LPS) induced robust oligodendrocyte genesis. In this study we investigated whether this process involves iron since LPS can alter macrophage regulation of iron and its storage protein ferritin, and oligodendrocytes require iron for proper development and myelination. Further, activated macrophages can sequester and release iron and ferritin. We first examined whether iron or ferritin was present following LPS microinjection. Using Perl's stain, we noted a slight increase in iron at 1d, and peak iron levels 3d post-injection coincident with maximal macrophage activation. Ferritin+ cells were prevalent by 3d and included macrophages and NG2 cells (putative oligodendrocyte progenitors). At 7d, ferritin was mainly expressed by new oligodendrocytes prevalent throughout the lesions. Because of the timing and distribution of iron and ferritin after LPS, we next used an iron chelator to test whether free iron was necessary for maximal LPS-induced oligodendrocyte genesis. Chelating iron by Deferasirox (Exjade) after LPS microinjection significantly reduced the number of proliferating NG2 cells and new oligodendrocytes. Of the remaining oligodendrocytes, there was a 2-fold decrease in those expressing ferritin, revealing that the number of oligodendrocytes with high iron stores was reduced. Collectively, these results establish that iron accumulates after intraspinal TLR4 activation and is required for maximal TLR4-induced oligodendrogenesis. Since TLR4 agonists are abundant in CNS injury/disease sites, these results suggest that iron may be essential for macrophage/oligodendrocyte communication and adult glial replacement.

Regulation of store-operated and voltage-operated Ca2+ channels in the proliferation and death of oligodendrocyte precursor cells by golli proteins

OPCs (oligodendrocyte precursor cells) express golli proteins which, through regulation of Ca²⁺ influx, appear to be important in OPC process extension/retraction and migration. The aim of the present study was to examine further the role of golli in regulating OPC development. The effects of golli ablation and overexpression were examined in primary cultures of OPCs prepared from golli-KO (knockout) and JOE (golli J37-overexpressing) mice. In OPCs lacking golli, or overexpressing golli, differentiation induced by growth factor withdrawal was impaired. Proliferation analysis in the presence of PDGF (platelet-derived growth factor), revealed that golli enhanced the mitogen-stimulated proliferation of OPCs through activation of SOCCs (store-operated Ca²⁺ channels). PDGF treatment induced a biphasic increase in OPC intracellular Ca²⁺, and golli specifically increased Ca²⁺ influx during the second SOCC-dependent phase that followed the initial release of Ca²⁺ from intracellular stores. This store-operated Ca²⁺ uptake appeared to be essential for cell division, since specific SOCC antagonists completely blocked the effects of PDGF and golli on OPC proliferation. Additionally, in OPCs overexpressing golli, increased cell death was observed after mitogen withdrawal. This phenomenon could be prevented by exposure to VOCC (voltage-operated Ca²⁺ channel) blockers, indicating that the effect of golli on cell death involved increased Ca²⁺ influx through VOCCs. The results showed a clear effect of golli on OPC development and support a role for golli in modulating multiple Ca²⁺-regulatory events through VOCCs and SOCCs. Our results also suggest that PDGF engagement of its receptor resulting in OPC proliferation proceeds through activation of SOCCs.

Cytokines and myelination in the central nervous system

Myelin abnormalities that reflect damage to developing and mature brains are often found in neurological diseases with evidence of inflammatory infiltration and microglial activation. Many cytokines are virtually undetectable in the uninflamed central nervous system (CNS), so that their rapid induction and sustained elevation in immune and glial cells contributes to dysregulation of the inflammatory response and neural cell homeostasis. This results in aberrant neural cell development, cytotoxicity, and loss of the primary myelin-producing cells of the CNS, the oligodendrocytes. This article provides an overview of cytokine and chemokine activity in the CNS with relevance to clinical conditions of neonatal and adult demyelinating disease, brain trauma, and mental disorders with observed white matter defects. Experimental models that mimic human disease have been developed in order to study pathogenic and therapeutic mechanisms, but have shown mixed success in clinical application. However, genetically altered animals, and models of CNS inflammation and demyelination, have offered great insight into the complexities of neuroimmune interactions that impact oligodendrocyte function. The intracellular signaling pathways of selected cytokines have also been highlighted to illustrate current knowledge of receptor-mediated events. By learning to interpret the actions of cytokines and by improving methods to target appropriate predictors of disease risk selectively, a more comprehensive understanding of altered immunoregulation will aid in the development of advanced treatment options for patients with inflammatory white matter disorders.

The effect of CXCL1 on human fetal oligodendrocyte progenitor cells

Chemokine CXCL1 is abundantly present in proliferative zones during brain development and in regions of remyelination, suggesting that it influences development of oligodendrocyte progenitors (OPC) in these regions. We studied in vitro the effects and possible mechanisms by which CXCL1 acts on human fetal OPC. In organotypic slice cultures of human fetal cortical ventricular/subventricular (VZ/SVZ) zones, blocking of CXCL1 signaling reduced significantly the proliferation of OPC. Moreover, exogenously added CXCL1 induced increase of OPC proliferation. Treatments of purified OPC cultures and cell depletion experiments demonstrated that this effect of CXCL1 was mainly indirect, mediated through astrocytes. We identified that CXCL1 acted through the extracellular signal regulated kinase (ERK1/2) pathway, activated primarily in astrocytes. In vitro, astrocytes stimulated with CXCL1 released several cytokines, but only the release of interleukin-6 (IL-6) was completely blocked by inhibition of ERK1/2 pathway. When released IL-6 was neutralized in slices, a decrease in OPC proliferation was demonstrated, while addition of IL-6 was able to return OPC proliferation in astrocyte-depleted slices to the control level. These results suggest that in the human fetal brain CXCL1 promotes proliferation of early OPC, acting in part through an ERK1/2-dependent pathway and release of IL-6 from astrocytes.

Developmental stage of oligodendrocytes determines their response to activated microglia in vitro

Background

Oligodendrocyte progenitor cells (OPCs) and mature oligodendrocytes are both lost in central nervous system injury and disease. Activated microglia may play a role in OPC and oligodendrocyte loss or replacement, but it is not clear how the responses of OPCs and oligodendrocytes to activated microglia differ.

Methods

OPCs and microglia were isolated from rat cortex. OPCs were induced to differentiate into oligodendrocytes with thyroid hormone in defined medium. For selected experiments, microglia were added to OPC or oligodendrocyte cultures. Lipopolysaccharide was used to activate microglia and microglial activation was confirmed by TNFα ELISA. Cell survival was assessed with immunocytochemistry and cell counts. OPC proliferation and oligodendrocyte apoptosis were also assessed.

Results

OPCs and oligodendrocytes displayed phenotypes representative of immature and mature oligodendrocytes, respectively. Activated microglia reduced OPC survival, but increased survival and reduced apoptosis of mature oligodendrocytes. Activated microglia also underwent cell death themselves.

Conclusion

Activated microglia may have divergent effects on OPCs and mature oligodendrocytes, reducing OPC survival and increasing mature oligodendrocyte survival. This may be of importance because activated microglia are present in several disease states where both OPCs and mature oligodendrocytes are also reacting to injury. Activated microglia may simultaneously have deleterious and helpful effects on different cells after central nervous system injury.

Induction of Golli-MBP expression in CNS macrophages during acute LPS-induced CNS inflammation and experimental autoimmune encephalomyelitis (EAE)

Microglia are the tissue macrophages of the CNS. Microglial activation coupled with macrophage infiltration is a common feature of many classic neurodegenerative disorders. The absence of cell-type specific markers has confounded and complicated the analysis of cell-type specific contributions toward the onset, progression, and remission of neurodegeneration. Molecular screens comparing gene expression in cultured microglia and macrophages identified Golli-myelin basic protein (MBP) as a candidate molecule enriched in peripheral macrophages. In situ hybridization analysis of LPS/IFNg and experimental autoimmune encephalomyelitis (EAE)–induced CNS inflammation revealed that only a subset of CNS macrophages express Golli-MBP. Interestingly, the location and morphology of Golli-MBP+ CNS macrophages differs between these two models of CNS inflammation. These data demonstrate the difficulties of extending in vitro observations to in vivo biology and concretely illustrate the complex heterogeneity of macrophage activation states present in region- and stage-specific phases of CNS inflammation. Taken altogether, these are consistent with the emerging picture that the phenotype of CNS macrophages is actively defined by their molecular interactions with the CNS microenvironment.

Cell cycle related signaling in neuro2a cells proceeds via the receptor for advanced glycation end products

Re-expression of cell cycle related genes such as cyclin-dependent kinases (cdk), cyclins, or cdk inhibitors in differentiated neurons in Alzheimer's disease (AD) is rooted in aberrant mitogenic signaling. Since microglia and astroglia proliferate in the vicinity of amyloid plaques, it is likely that plaque components or factors secreted from plaque-activated glia induce mitogenic signaling in neurons. Mitogenic compounds might be S100B, overexpressed by activated astrocytes, or advanced glycation end products (AGEs), a component of plaques. Both S100B and AGEs may interact with the multiligand receptor for AGEs (RAGE) and trigger for the activation of the p42/44 mitogen-activated protein kinase (p42/44 MAPK), whether they also count for cell cycle related signaling in neurons remains unresolved. By immunohistochemical staining, we confirmed that cyclin D(1) positive neurons are surrounded by AGE deposits, demonstrating the potential relevance in vivo. For exploring the mitogenic signal cascade, we used Neuro2a cells overexpressing human full-length RAGE (FL-RAGE) or the cytosolic deletion mutant (Delta-RAGE). In both cell lines, S100B and AGEs induced the production of reactive oxygen species but not in a RAGE-dependent manner. By contrast, in FL-RAGE cells but not in Delta-RAGE cells S100B and AGEs activate p42/44 MAPK, augment cyclin D(1)/cdk4 protein and RNA levels and the transition into the S-phase. Moreover, in FL-RAGE cells, decreased protein levels of the cdk inhibitor p16 were observed, and the p42/44 MAPK inhibitor UO126 prevented AGE and S100B stimulated cyclin D(1) expression and hindered cells to enter the S-phase. Our results demonstrate that S100B and AGE may serve as mitogenic sources for the stimulation of neurons to progress through the cell cycle whereby signaling proceeds via RAGE --> p42/44 MAPK --> cyclin D(1)/cdk4.

The role of myelin in Theiler's virus persistence in the central nervous system

Theiler's virus, a picornavirus, persists for life in the central nervous system of mouse and causes a demyelinating disease that is a model for multiple sclerosis. The virus infects neurons first but persists in white matter glial cells, mainly oligodendrocytes and macrophages. The mechanism, by which the virus traffics from neurons to glial cells, and the respective roles of oligodendrocytes and macrophages in persistence are poorly understood. We took advantage of our previous finding that the shiverer mouse, a mutant with a deletion in the myelin basic protein gene (Mbp), is resistant to persistent infection to examine the role of myelin in persistence. Using immune chimeras, we show that resistance is not mediated by immune responses or by an efficient recruitment of inflammatory cells into the central nervous system. With both in vivo and in vitro experiments, we show that the mutation does not impair the permissiveness of neurons, oligodendrocytes, and macrophages to the virus. We demonstrate that viral antigens are present in cytoplasmic channels of myelin during persistent infection of wild-type mice. Using the optic nerve as a model, we show that the virus traffics from the axons of retinal ganglion cells to the cytoplasmic channels of myelin, and that this traffic is impaired by the shiverer mutation. These results uncover an unsuspected axon to myelin traffic of Theiler's virus and the essential role played by the infection of myelin/oligodendrocyte in persistence.

Theiler's virus persists in the central nervous system of mice and causes a chronic disease that resembles multiple sclerosis, a common demyelinating disease of humans. The virus infects neurons for one to two weeks, but later on it persists in the white matter, in oligodendrocytes and also in macrophages. Oligodendrocytes are the myelin-making cells of the central nervous system. Strikingly, in mice with a genetic defect of myelin, the virus infects neurons normally but is unable to persist. Understanding the reason for the lack of persistence in this mutant mouse should pinpoint an essential step in the complex process resulting in persistence. In this article, we show that resistance to persistent infection is not mediated by the immune system and is not due to inefficient viral replication in oligodendrocytes or macrophages. Instead, we show that virus transported in axons traffics into the myelin, and that this traffic is interrupted by the myelin mutation. This unsuspected axon to myelin traffic of Theiler's virus is necessary for viral persistence. Our results warrant looking for a similar phenomenon in other persistent infections of the nervous system, including in humans.

Effect of inflammation on central nervous system development and vulnerability: review

PURPOSE OF REVIEW

Preterm infants are at high risk for neurological sequelae and cognitive dysfunction. These problems have been attributed to a high occurrence of central nervous system (CNS) lesions, but suboptimal brain development appears to be just as important. In this brief review we present the hypothesis that systemic infection/inflammation can severely interfere with normal CNS function and development.

RECENT FINDINGS

We focus on the effects of lipopolysaccharide because it is often used to model the systemic inflammatory response induced by infections. The inflammatory signals are propagated across the intact or ruptured blood-brain barrier to the CNS by proinflammatory cytokines, prostaglandins, or lipopolysaccharide. Subsequently, microglia are triggered to release cytokines, oxygen free radicals and trophic factors, which will influence the CNS in various ways. Cognition, dendritic length and spine density, dopaminergic cells, neurogenesis and glial proliferation will be affected. Furthermore, CNS vulnerability and, in some instances, cerebral anomalies and white matter damage are produced.

SUMMARY

Hypothetically, all of these effects on the CNS triggered by inflammation may have severe consequences for the individual's ability to cope with environmental exposures during childhood and adulthood.