Effect of tumor necrosis factor alpha and beta on human oligodendrocytes and neurons in culture

Glyphosate infiltrates the brain and increases pro-inflammatory cytokine TNFα: implications for neurodegenerative disorders

BACKGROUND

Herbicides are environmental contaminants that have gained much attention due to the potential hazards they pose to human health. Glyphosate, the active ingredient in many commercial herbicides, is the most heavily applied herbicide worldwide. The recent rise in glyphosate application to corn and soy crops correlates positively with increased death rates due to Alzheimer's disease and other neurodegenerative disorders. Glyphosate has been shown to cross the blood-brain barrier in in vitro models, but has yet to be verified in vivo. Additionally, reports have shown that glyphosate exposure increases pro-inflammatory cytokines in blood plasma, particularly TNFα.

METHODS

Here, we examined whether glyphosate infiltrates the brain and elevates TNFα levels in 4-month-old C57BL/6J mice. Mice received either 125, 250, or 500 mg/kg/day of glyphosate, or a vehicle via oral gavage for 14 days. Urine, plasma, and brain samples were collected on the final day of dosing for analysis via UPLC-MS and ELISAs. Primary cortical neurons were derived from amyloidogenic APP/PS1 pups to evaluate in vitro changes in Aβ40-42 burden and cytotoxicity. RNA sequencing was performed on C57BL/6J brain samples to determine changes in the transcriptome.

RESULTS

Our analysis revealed that glyphosate infiltrated the brain in a dose-dependent manner and upregulated TNFα in both plasma and brain tissue post-exposure. Notably, glyphosate measures correlated positively with TNFα levels. Glyphosate exposure in APP/PS1 primary cortical neurons increases levels of soluble Aβ40-42 and cytotoxicity. RNAseq revealed over 200 differentially expressed genes in a dose-dependent manner and cell-type-specific deconvolution analysis showed enrichment of key biological processes in oligodendrocytes including myelination, axon ensheathment, glial cell development, and oligodendrocyte development.

CONCLUSIONS

Collectively, these results show for the first time that glyphosate infiltrates the brain, elevates both the expression of TNFα and soluble Aβ, and disrupts the transcriptome in a dose-dependent manner, suggesting that exposure to this herbicide may have detrimental outcomes regarding the health of the general population.

Morphological Brain Changes after Climbing to Extreme Altitudes--A Prospective Cohort Study

Background

Findings of cerebral cortical atrophy, white matter lesions and microhemorrhages have been reported in high-altitude climbers. The aim of this study was to evaluate structural cerebral changes in a large cohort of climbers after an ascent to extreme altitudes and to correlate these findings with the severity of hypoxia and neurological signs during the climb.

Methods

Magnetic resonance imaging (MRI) studies were performed in 38 mountaineers before and after participating in a high altitude (7126m) climbing expedition. The imaging studies were assessed for occurrence of new WM hyperintensities and microhemorrhages. Changes of partial volume estimates of cerebrospinal fluid, grey matter, and white matter were evaluated by voxel-based morphometry. Arterial oxygen saturation and acute mountain sickness scores were recorded daily during the climb.

Results

On post-expedition imaging no new white matter hyperintensities were observed. Compared to baseline testing, we observed a significant cerebrospinal fluid fraction increase (0.34% [95% CI 0.10–0.58], p = 0.006) and a white matter fraction reduction (-0.18% [95% CI -0.32–-0.04], p = 0.012), whereas the grey matter fraction remained stable (0.16% [95% CI -0.46–0.13], p = 0.278). Post-expedition imaging revealed new microhemorrhages in 3 of 15 climbers reaching an altitude of over 7000m. Affected climbers had significantly lower oxygen saturation values but not higher acute mountain sickness scores than climbers without microhemorrhages.

Conclusions

A single sojourn to extreme altitudes is not associated with development of focal white matter hyperintensities and grey matter atrophy but leads to a decrease in brain white matter fraction. Microhemorrhages indicative of substantial blood-brain barrier disruption occur in a significant number of climbers attaining extreme altitudes.

Pathophysiology and neuroprotection of global and focal perinatal brain injury: lessons from animal models

BACKGROUND

Arterial ischemic stroke occurs more frequently in term newborns than in the elderly, and brain immaturity affects mechanisms of ischemic injury and recovery. The susceptibility to injury of the brain was assumed to be lower in the perinatal period as compared with childhood. This concept was recently challenged by clinical studies showing marked motor disabilities after stroke in neonates, with the severity of motor and cortical sensory deficits similar in both perinatal and childhood ischemic stroke. Our understanding of the triggers and the pathophysiological mechanisms of perinatal stroke has greatly improved in recent years, but many factors remain incompletely understood.

METHODS

In this review, we focus on the pathophysiology of perinatal stroke and on therapeutic strategies that can protect the immature brain from the consequences of stroke by targeting inflammation and brain microenvironment.

RESULTS

Studies in neonatal rodent models of cerebral ischemia have suggested a potential role for soluble inflammatory molecules as important modulators of injury and recovery. A great effort is underway to investigate neuroprotective molecules based on our increasing understanding of the pathophysiology.

CONCLUSION

In this review, we provide a comprehensive summary of new insights concerning pathophysiology of focal and global perinatal brain injury and their implications for new therapeutic approaches.

Pathophysiology of glia in perinatal white matter injury

Injury to the preterm brain has a particular predilection for cerebral white matter. White matter injury (WMI) is the most common cause of brain injury in preterm infants and a major cause of chronic neurological morbidity including cerebral palsy. Factors that predispose to WMI include cerebral oxygenation disturbances and maternal-fetal infection. During the acute phase of WMI, pronounced oxidative damage occurs that targets late oligodendrocyte progenitors (pre-OLs). The developmental predilection for WMI to occur during prematurity appears to be related to both the timing of appearance and regional distribution of susceptible pre-OLs that are vulnerable to a variety of chemical mediators including reactive oxygen species, glutamate, cytokines, and adenosine. During the chronic phase of WMI, the white matter displays abberant regeneration and repair responses. Early OL progenitors respond to WMI with a rapid robust proliferative response that results in a several fold regeneration of pre-OLs that fail to terminally differentiate along their normal developmental time course. Pre-OL maturation arrest appears to be related in part to inhibitory factors that derive from reactive astrocytes in chronic lesions. Recent high field magnetic resonance imaging (MRI) data support that three distinct forms of chronic WMI exist, each of which displays unique MRI and histopathological features. These findings suggest the possibility that therapies directed at myelin regeneration and repair could be initiated early after WMI and monitored over time. These new mechanisms of acute and chronic WMI provide access to a variety of new strategies to prevent or promote repair of WMI in premature infants.

Cobalamin and normal prions: a new horizon for cobalamin neurotrophism

It is known that cobalamin (Cbl) deficiency damages myelin by increasing tumor necrosis factor (TNF)-α and decreasing epidermal growth factor (EGF) levels in rat central nervous system (CNS), and affects the peripheral nervous system (PNS) morphologically and functionally. It is also known that some polyneuropathies not due to Cbl deficiency are connected with increased TNF-α levels, and that various cytokines (including TNF-α) and growth factors regulate the in vitro synthesis of normal prions (PrP(C)s). Given that there is extensive evidence that PrP(C)s play a key role in the maintenance of CNS and PNS myelin, we investigated whether the PrP(C) octapeptide repeat (OR) region is involved in the pathogenesis of rat Cbl-deficient (Cbl-D) polyneuropathy. After intracerebroventricularly administering antibodies (Abs) against the OR region (OR-Abs) to Cbl-D rats to prevent myelin damage and maximum nerve conduction velocity (MNCV) abnormalities, and PrP(C)s to otherwise normal rats to reproduce PNS Cbl-D-like lesions, we measured PrP(C) levels and MNCV of the sciatic and tibial nerves. PrP(C) and TNF-α levels were increased in sciatic and tibial nerves of Cbl-D and saline-treated rats, and the OR-Abs normalized the myelin ultrastructure, TNF-α levels, and MNCV values of the sciatic and tibial nerves of Cbl-D rats. The same peripheral nerves of the otherwise normal PrP(C)-treated rats showed typical Cbl-D myelin lesions, significantly increased TNF-α levels, and significantly decreased MNCV values. These findings demonstrate that Cbl deficiency induces excess PrP(C)s and thereby excess OR regions, which seem to be responsible for the PNS myelin damage, as has recently been found in the case of CNS myelin damage [66]. Furthermore, excess TNF-α is also involved in the pathogenesis of Cbl-D polyneuropathy. In conclusion, we have extended the list of prion diseases by adding one caused by excess PrP(C)s and the polyneuropathies related to excess TNF-α.

Infliximab administration reduces neuronal apoptosis on the optic pathways in a rabbit hydrocephalus model: a preliminary report

OBJECT

This study was designed to explore the effects of infliximab on the optic pathway in kaolin induced hydrocephalus rabbit model.

METHODS

After injection of kaolin to the cisterna magna of 12 New Zealand rabbits for induction of hydrocephalus, animals were divided into 2 groups and received either infliximab or normal saline. The intracranial pressure measurement was performed 2 times; firstly, before kaolin injection and secondly, before decapitation to ensure that the rabbits had hydrocephalus. After 2 weeks, animals were decapitated.

RESULTS

Apoptotic cells in the lateral geniculate body, optic radiation, and optic disc were counted with TUNEL method. Apoptotic cell counts of the lateral geniculate body and the optic radiation were showed statistically significant difference between the infliximab group and the control group.

CONCLUSIONS

This study suggests that infliximab may have a neuroprotective effect through its anti-apoptotic property on hydrocephalus induced optic pathways injury.

Attenuation of proliferation in oligodendrocyte precursor cells by activated microglia

Activated microglia can influence the survival of neural cells through the release of cytotoxic factors. Here, we investigated the interaction between Toll-like receptor 4 (TLR4)-activated microglia and oligodendrocytes or their precursor cells (OPC). Primary rat or N9 microglial cells were activated by exposure to TLR4-specifc lipopolysaccharide (LPS), resulting in mitogen-activated protein kinase activation, increased CD68 and inducible nitric oxide synthase expression, and release of the proinflammatory cytokines tumor necrosis factor (TNF) and interleukin-6 (IL-6). Microglial conditioned medium (MGCM) from LPS-activated microglia attenuated primary OPC proliferation without inducing cell death. The microglial-induced inhibition of OPC proliferation was reversed by stimulating group III metabotropic glutamate receptors in microglia with the agonist L-AP4. In contrast to OPC, LPS-activated MGCM enhanced the survival of mature oligodendrocytes. Further investigation suggested that TNF and IL-6 released from TLR4-activated microglia might contribute to the effect of MGCM on OPC proliferation, insofar as TNF depletion of LPS-activated MGCM reduced the inhibition of OPC proliferation, and direct addition of TNF or IL-6 attenuated or increased proliferation, respectively. OPC themselves were also found to express proteins involved in TLR4 signalling, including TLR4, MyD88, and MAL. Although LPS stimulation of OPC did not induce proinflammatory cytokine release or affect their survival, it did trigger JNK phosphorylation, suggesting that TLR4 signalling in these cells is active. These findings suggest that OPC survival may be influenced not only by factors released from endotoxin-activated microglia but also through a direct response to endotoxins. This may have consequences for myelination under conditions in which microglial activation and cerebral infection are both implicated. , Inc.

Polymorphonuclear leukocytes promote neurotoxicity through release of matrix metalloproteinases, reactive oxygen species, and TNF-α

As the first immune cells to infiltrate the nervous system after traumatic PNS and CNS injury, neutrophils (polymorphonuclear leukocytes, PMNs) may promote injury by releasing toxic soluble factors that may affect neuronal survival. Direct neurotoxicity of matrix metalloproteinases (MMPs), reactive oxygen species (ROS), and cytokines released by PMNs was investigated by culturing dorsal root ganglion (DRG) cells with PMN-conditioned media containing MMP inhibitor (GM6001), ROS scavengers, or tumor necrosis factor alphaR (TNF-alphaR) neutralizing antibody. Although DRGs exposed to PMN-conditioned media had 53% fewer surviving neurons than controls, neuronal cell loss was prevented by GM6001 (20 micromol/L), catalase (1000 U/mL), or TNF-alphaR neutralizing antibody (1.5 microg/mL), elevating survival to 77%, 94%, and 95%, respectively. In accordance with protection by GM6001, conditioned media collected from MMP-9 null PMNs was less neurotoxic than that collected from wild-type PMNs. Additionally, MMP inhibition reduced PMN-derived ROS; removal of ROS reduced PMN-derived MMP-9 activity; and TNF-alpha inhibition reduced both PMN-derived MMP-9 activity and ROS in PMN cultures. Our data provide the first direct evidence that PMN-driven neurotoxicity is dependent on MMPs, ROS, and TNF-alpha, and that these factors may regulate PMN release of these soluble factors or interact with one another to mediate PMN-driven neurotoxicity.

Hypoxic-ischemic injury in the immature brain--key vascular and cellular players

Over the past decade, much has been learned about the cellular and molecular mechanisms underlying hypoxic-ischemic (H-I) injury in the preterm human brain. The pathogenesis of H-I brain injury is now understood to be multifactorial and quite complex, depending on (i) the severity, intensity and timing of asphyxia, (ii) selective ischemic vulnerability, (iii) the degree of maturity of the brain, and (iv) the characteristics of the ensuing reoxygenation/reperfusion phase. Each of these factors has differential effects on the distinct cell populations in the brain, with certain specific cell types being particularly vulnerable in the developing brain. In this review, we discuss the role of the blood vessels and the distinct cell populations, which are the mayor constitutive elements of the immature brain, in the pathophysiology of H-I lesion. The presence of fragile and poorly anastomosed blood vessels and the existence of disturbances in the blood-brain barrier alter blood flow, vascular tone and nutrient delivery. Brain cells are sensitive to the overstimulation of neurotransmitter receptors, particularly glutamate receptors, which can provoke excitotoxicity leading to the death of neurons and other cells such as astrocytes and oligodendrocyte progenitors. Microglial activation by means of excitatory amino acids and by leukocyte migration initiates the inflammatory response giving rise to an increase in regional cerebral blood flow and promoting astrocyte and oligodendrocyte injuries. A better understanding of these aspects of H-I injury will contribute to more efficient strategies for the management of the associated damage.

IGF-1 protects oligodendrocyte progenitors against TNFα-induced damage by activation of PI3K/Akt and interruption of the mitochondrial apoptotic pathway

Proinflammatory cytokine-mediated injury to oligodendrocyte progenitor cells (OPCs) has been proposed as a cause of periventricular leukomalacia (PVL), the most common brain injury found in preterm infants. Preventing death of OPCs is a potential strategy to prevent or treat PVL. In the current study, we utilized an in vitro cell culture system to investigate the effect of insulin-like growth factor-1 (IGF-1) on tumor necrosis factor-alpha (TNFalpha)-induced OPC injury and the possible mechanisms involved. OPCs were isolated from neonatal rat optic nerves and cultured in chemically defined medium (CDM) supplemented with platelet-derived growth factor and basic fibroblast growth factor. Exposure to TNFalpha resulted in death of OPCs. IGF-1 protected OPCs from TNFalpha cytotoxicity in a dose-dependent manner as measured by the XTT and TUNEL assays. IGF-1 activates both the PI3K/Akt and the extracellular signal-regulated kinase (ERK) pathway. However, IGF-1-enhanced cell survival signals were mediated by the PI3K/Akt, but not by the ERK pathway, as evidenced by the observation that IGF-1-enhanced cell survival was partially abrogated by Akti, the Akt inhibitor, or wortmannin, the PI3K inhibitor, but not by PD98,059, the MAPK kinase/ERK kinase inhibitor. The downstream events of IGF-1-triggered survival signals included phosphorylation of BAD, blockade of TNFalpha-induced translocation of Bax from the cytosol to the mitochondrial membrane, and suppression of caspase-9 and caspase-3 activation. These observations indicate that the protection of OPCs by IGF-1 is mediated, at least partially, by interruption of the mitochondrial apoptotic pathway via activation of PI3K/Akt.

Stroke and T-cells

The microvasculature of the brain region affected by a stroke assumes an inflammatory phenotype that is characterized by endothelial cell activation and barrier dysfunction and the recruitment of adherent leukocytes. Although most attention has been devoted to the possible role of neutrophils in the tissue responses to ischemic stroke there is evidence that T-lymphocytes also accumulate in the postischemic brain. Although comparable detailed analyses of lymphocyte involvement in ischemic brain injury have not been performed, emerging findings suggest a role for T-cells in the pathogenesis of ischemic stroke. The recruitment of T-cells to the site of brain injury is critically dependent on the coordinated expression of adhesion molecules on the activated capillary endothelium. Whether the recruited lymphocytes are acting directly on brain tissue or indirectly through activation of other circulating blood cells and/or extravascular cells remain unclear. Cytotoxic CD8+ T-cells may induce brain injury through molecules released from their cytotoxic granules. CD4+ T-helper 1 (TH1) cells, which secrete proinflammatory cytokines, including interleukin-2 (IL-2), IL-12, interferon-gamma, and tumor necrosis factor-alpha, may play a key role in the pathogenesis of stroke, whereas CD4+TH2 cells may play a protective role through anti-inflammatory cytokines such as IL-4, IL-5, IL-10, and IL-13. T-cells should be considered as therapeutic targets for ischemic stroke. However, because infection is a leading cause of mortality in the postacute phase of ischemic stroke, and considering anti-inflammatory role of CD4+TH2, treatment targeting T-cells should be carefully designed to reduce deleterious and enhance protective actions of T-cells.

A sublethal dose of TNFalpha potentiates kainate-induced excitotoxicity in optic nerve oligodendrocytes

Glutamate receptor-induced cell death, known as excitotoxicity in both neurons and oligodendrocytes, has been implicated as a common pathway of cell death in numerous central nervous system (CNS) diseases and trauma. Research in both neuronal and oligodendrocyte excitotoxicity has examined glutamate's receptor-mediated effects on CNS cells, and explored strategies to protect cells exposed to the elevated glutamate levels that occur in CNS trauma and disease. Proinflammatory cytokines are also elevated in the injured CNS, and have also been implicated in CNS cell death. Recently, several laboratories have examined cytokines' effects on neuronal and glial excitotoxicity. Here, we review literature concerning the dynamic susceptibility of both neurons and oligodendrocytes to excitotoxicity, and present new data from our laboratory showing that the susceptibility of oligodendrocytes to excitotoxicity is acutely potentiated by the proinflammatory cytokine TNFalpha.

Perinatal white matter injury: The changing spectrum of pathology and emerging insights into pathogenetic mechanisms

Perinatal brain injury in survivors of premature birth has a unique and unexplained predilection for periventricular cerebral white matter. Periventricular white-matter injury (PWMI) is now the most common cause of brain injury in preterm infants and the leading cause of chronic neurological morbidity. The spectrum of chronic PWMI includes focal cystic necrotic lesions (periventricular leukomalacia; PVL) and diffuses myelination disturbances. Recent neuroimaging studies support that the incidence of PVL is declining, whereas focal or diffuse noncystic injury is emerging as the predominant lesion. Factors that predispose to PVL during prematurity include hypoxia, ischemia, and maternal-fetal infection. In a significant number of infants, PWMI appears to be initiated by perturbations in cerebral blood flow that reflect anatomic and physiological immaturity of the vasculature. Ischemic cerebral white matter is susceptible to pronounced free radical-mediated injury that particularly targets immature stages of the oligodendrocyte lineage. Emerging experimental data supports that pronounced ischemia in the periventricular white matter is necessary, but not sufficient to generate PWMI. The developmental predilection for PWMI to occur during prematurity appears to be related to both the timing of appearance and regional distribution of susceptible oligodendrocyte progenitors. Injury to oligodendrocyte progenitors may contribute to the pathogenesis of PWMI by disrupting the maturation of myelin-forming oligodendrocytes. Chemical mediators that may contribute to white-matter injury include reactive oxygen species glutamate, cytokines, and adenosine. As our understanding of the pathogenesis of PWMI improves, it is anticipated that new strategies for directly preventing brain injury in premature infants will develop.

Neutralization of the chemokine CXCL10 reduces apoptosis and increases axon sprouting after spinal cord injury

Spinal cord injury (SCI) is followed by a secondary degenerative process that includes cell death. We have previously demonstrated that the chemokine CXCL10 is up-regulated following SCI and plays a critical role in T-lymphocyte recruitment to sites of injury and inhibition of angiogenesis; antibody-mediated functional blockade of CXCL10 reduced inflammation while enhancing angiogenesis. We hypothesized, based on these findings, that the injury environment established by anti-CXCL10 antibody treatment would support greater survival of neurons and enhance axon sprouting compared with the untreated, injured spinal cord. Here, we document gene array and histopathological data to support our hypothesis. Gene array analysis of treated and untreated tissue from spinal cord-injured animals revealed eight apoptosis-related genes with significant expression changes at 3 days postinjury. In support of these data, quantification of TUNEL-positive cells at 3 days postinjury indicated a 75% reduction in the number of dying cells in treated animals compared with untreated animals. Gene array analysis of treated and untreated tissue also revealed six central nervous system growth-related genes with significant expression changes in the brainstem at 14 days postinjury. In support of these data, quantification of anterograde-labeled corticospinal tract fibers indicated a 60-70% increase in axon sprouting caudal to the injury site in treated animals compared with untreated animals. These findings indicate that anti-CXCL10 antibody treatment provides an environment that reduces apoptosis and increases axon sprouting following injury to the adult spinal cord.

Suppression of glial activation is involved in the protection of IL-10 on maternal E. coli induced neonatal white matter injury

White matter damage (WMD) is an important cause of disability including cerebral palsy in preterm, low birth-weight infants. Maternal infection is now recognized as one of the risk factors for WMD. Previously we reported that intrauterine inoculation of Escherichia coli to pregnant rats resulted in WMD in offspring and interleukin-10 (IL-10) was protective against this damage. The objective of this study was to elucidate the mechanism involved in the protective effect of IL-10 against neonatal WMD. We found that E. coli treatment in dams resulted in significant apoptosis in periventricular white matter of rat pups on postnatal day 0 (P0). On P8, a remarkable increase in ED-1 immunostaining (indicating either microglial activation or macrophage infiltration) was detected in brains of pups in the E. coli-treated group. Astrogliosis was also noticed in brain white matter of pups in the E. coli-treated group. In addition to the strong activation of microglia and astrocytes, oligodendrocytes (OLs) were significantly reduced in periventricular areas in the brains of pups from the E. coli-treated group. Later, on P15, hypomyelination was also noticed in rat brains from the E. coli-treated group, using myelin basic protein (MBP) immunostaining. Treatment with IL-10 after E. coli inoculation significantly reduced TUNEL staining and caspase-3 activation, and partially restored the impaired immunostaining markers for immature and mature OLs, such as CNPase, O4, adenomatous polyposis coli (APC) and MBP. These results indicate that the protective effect of IL-10 against brain WMD is linked with suppression of microglial activation/macrophage infiltration, as shown by significantly reduced ED-1+ cells in the white matter.

Effect of tumor necrosis factor-alpha on developing optic nerve oligodendrocytes in culture

There is increasing evidence that proinflammatory cytokines are involved in the development of periventricular leukomalacia (PVL), a condition in which developing oliodendrocytes (OLs) are preferentially injured. In the present study, we utilized an in vitro assay to demonstrate that the A2B5+ OL progenitors as well as the O4+ prooligodendrocytes (pro-OLs) were more susceptible to tumor necrosis factor-alpha (TNF-alpha) cytotoxicity than the O4+/O1+ immature OLs. OL progenitors were isolated from optic nerves of 7-day-old rat pups and cultured in chemically defined medium supplemented with platelet-derived growth factor and basic fibroblast growth factor. OL progenitors were allowed to differentiate into pro-OLs and immature OLs under special cultural conditions. Cells at three different developmental stages were subjected to TNF-alpha treatment. Cell death, presumably by apoptosis as evidenced by TUNEL staining and caspase-3 activation, was observed following TNF-alpha treatment. Corresponding to TNF-alpha-induced apoptosis, cell survival rate decreased in a time- and dose-dependent manner. The sensitivity of different OL developmental stages to TNF-alpha decreased with the progression of cell maturation. However, this differential response was not related to differentially expressed TNF-alpha receptors. Consistent with reports that progenitor cells are preferentially injured in PVL, our results may further support the role of TNF-alpha as a potential mediator of PVL.

Severity-dependent expression of pro-inflammatory cytokines in traumatic spinal cord injury in the rat

The post-traumatic inflammatory response in acute spinal cord contusion injury was studied in the rat. Mild and severe spinal cord injury (SCI) was produced by dropping a 10 g weight from 3 and 12 cm at the T12 vertebral level. Increased immunoreactivity of TNF-alpha in mild and severe SCI was detected in neurons at 1 h post-injury, and in neurons and microglia at 6 h post-injury, with a less significant increase in mild SCI. Expression was short-lived and declined sharply by 1 d post-injury. RT-PCR showed an early significant up-regulation of IL-1 beta, IL-6 and TNF-alpha mRNAs, maximal at 6 h post-injury with return to control levels by 24 h post-injury, the changes being less statistically significantly in mild SCI. Western blot showed early transient increases of IL-1 beta, IL-6 and TNF-alpha proteins in severe SCI but not mild SCI. Immunocytochemical, western blotting and RT-PCR analyses suggest that endogenous cells (neurons and microglia) in the spinal cord, not blood-borne leucocytes, contribute to IL-1 beta, IL-6 and TNF-alpha production in the post-traumatic inflammatory response and that their up-regulation is greater in severe than mild SCI.

Emerging concepts in periventricular white matter injury

Approximately 10% of newborns are born prematurely. Of these children, more than 10% will sustain neurological injuries leading to significant learning disabilities, cerebral palsy, or mental retardation, with very low birth weight infants having an even higher incidence of brain injury. Whereas intraventricular hemorrhage was the most common form of serious neurological injury a decade ago, periventricular white matter injury (PWMI) is now the most common cause of brain injury in preterm infants. The spectrum of chronic PWMI includes focal cystic necrotic lesions (periventricular leukomalacia; PVL) and diffuse myelination disturbances. Recent neuroimaging studies support that the incidence of PVL is declining, whereas diffuse cerebral white matter injury is emerging as the predominant lesion. Factors that predispose to PVL include prematurity, hypoxia, ischemia, and inflammation. It is believed that injury to oligodendrocyte (OL) progenitors contributes to the pathogenesis of myelination disturbances in PWMI by disrupting the maturation of myelin-myelin-forming oligodendrocytes. Other potential mechanisms of injury include activation of microglia and axonal damage. Chemical mediators that may contribute to white matter injury include reactive oxygen (ROS) and nitrogen species (RNS), glutamate, cytokines, and adenosine. As our understanding of the pathogenesis of PWMI improves, it is anticipated that new strategies for directly preventing brain injury in premature infants will evolve.

Maternal infection-induced white matter injury is reduced by treatment with interleukin-10

OBJECTIVE

The purpose of this study was to test the hypothesis that interleukin-10 can prevent white matter injury in neonatal rats that are born to infected dams.

STUDY DESIGN

Timed pregnant rats (day 17) were assigned to the following treatment groups: (1) saline control (n = 5 rats), (2) Escherichia coli- infected (n = 10 rats), and (3) E coli + interleukin-10 (n = 5 rats). E coli was administered at a titer of 1 x 10(7) colony-forming units by intrauterine inoculation just above the cervix at the bifurcation of the uterine horns. Rat interleukin-10 was administered intravenously at a dose of 1 microg/kg of body weight. After delivery, the pups were maintained with dams until day 8, at which time they were placed under general anesthesia and perfused with saline solution followed by 10% paraformaldehyde. The brains were removed, placed in 30% sucrose solution, and then frozen at -20 degrees C until the preparation of the frozen sections. Standard hematoxylin/eosin staining was performed, and the brains were evaluated for matter necrosis, apoptotic cells, and ventricular swelling.

RESULTS

In pups that were born to infected dams, 11 of 38 pups (29%) displayed symmetric lesions around the lateral ventricles. These lesions were characterized by marked looseness/edema of the neuropil, foamy-appearing histiocytes, and granular neuropil breakdown. None of the pups (n = 17) that were born to interleukin-10-treated infected dams displayed this pattern of severe white matter injury.

CONCLUSION

These results suggest that maternal interleukin-10 therapy could provide neuroprotection for infants who are born to mothers with intrauterine infection.

Infection with an endemic human herpesvirus disrupts critical glial precursor cell properties

Human herpesvirus 6 (HHV-6), a common resident virus of the human CNS, has been implicated in both acute and chronic inflammatory--demyelinating diseases. Although HHV-6 persists within the human CNS and has been described to infect mature oligodendrocytes, nothing is known about the susceptibility of glial precursors, the ancestors of myelin-producing oligodendrocytes, to viral infection. We show that HHV-6 infects human glial precursor cells in vitro. Active infection was demonstrated by both electron microscopy and expression of viral gene transcripts and proteins, with subsequent formation of cell syncytia. Infection leads to alterations in cell morphology and impairment of cell replication but not increased cell death. Infected cells showed decreased proliferation as measured by bromodeoxyuridine uptake, which was confirmed by blunting of the cell growth rate of infected cells compared with uninfected controls over time. The detailed analysis using novel, fluorescent-labeled HHV-6A or HHV-6B reagents demonstrated strong G1/S phase inhibition in infected precursor cells. Cell cycle arrest in HHV-6-infected cells was associated with a profound decrease in the expression of the glial progenitor cell marker A2B5 and a corresponding increase in the oligodendrocyte differentiation marker GalC. These data demonstrate for the first time that infection of primary human glial precursor cells with a neurologically relevant human herpesvirus causes profound alterations of critical precursor cell properties. In light of recent observations that repair of CNS demyelination is dependent on the generation of mature oligodendrocytes from the glial precursor cell pool, these findings may have broad implications for both the ineffective repair seen in demyelinating diseases and the disruption of normal glial maturation.

Cytokine-induced cell death in human oligodendroglial cell lines: I. Synergistic effects of IFN-gamma and TNF-alpha on apoptosis

Multiple sclerosis is a chronic inflammatory disease of the central nervous system. Myelin and oligodendrocytes are considered the major targets of injury caused by a cell-mediated immune response. There is circumstantial evidence that proinflammatory cytokines like tumor necrosis factor alpha (TNF-alpha) and interferon gamma (IFN-gamma) could have disease-promoting roles in multiple sclerosis (MS). In the present study, the cytotoxic effects of IFN-gamma and TNF-alpha on the human oligodendroglial cell lines human oligodendroglioma (HOG) and MO3.13 were analyzed. When the oligodendroglial cell lines were cultured in the presence of IFN-gamma or TNF-alpha, apoptotic cell death was observed in both cell lines after >24 hr incubation. Apoptosis was evidenced by a decrease in cell viability, apoptotic changes in cell and nucleus morphology, and disruption of the membrane asymmetry. Our data show that TNF-alpha and IFN-gamma induce apoptosis in a dose-dependent fashion in both oligodendroglial cell lines and that their synergistic effect results in enhanced cell death. Understanding the regulation of cell death pathways in oligodendrocytes is critical for protecting myelin-producing cells and their associated axons during injury in patients with MS.

Oligodendrocytes and progenitors become progressively depleted within chronically demyelinated lesions

To understand mechanisms that may underlie the progression of a demyelinated lesion to a chronic state, we have used the cuprizone model of chronic demyelination. In this study, we investigated the fate of oligodendrocytes during the progression of a demyelinating lesion to a chronic state and determined whether transplanted adult oligodendrocyte progenitors could remyelinate the chronically demyelinated axons. Although there is rapid regeneration of the oligodendrocyte population following an acute lesion, most of these newly regenerated cells undergo apoptosis if mice remain on a cuprizone diet. Furthermore, the oligodendrocyte progenitors also become progressively depleted within the lesion, which appears to contribute to the chronic demyelination. Interestingly, even if the mice are returned to a normal diet following 12 weeks of exposure to cuprizone, remyelination and oligodendrocyte regeneration does not occur. However, if adult O4+ progenitors are transplanted into the chronically demyelinated lesion of mice treated with cuprizone for 12 weeks, mature oligodendrocyte regeneration and remyelination occurs after the mice are returned to a normal diet. Thus, the formation of chronically demyelinated lesions induced by cuprizone appears to be the result of oligodendrocyte depletion within the lesion and not due to the inability of the chronically demyelinated axons to be remyelinated.

Early expression and cellular localization of proinflammatory cytokines interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha in human traumatic spinal cord injury

STUDY DESIGN

Post-traumatic inflammatory response was studied in 11 human cases of acute spinal cord contusion injury.

OBJECTIVES

To examine the inflammatory cellular response and the immunocytochemical expression and localization of interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha in human spinal cord after contusion injury.

SUMMARY OF BACKGROUND DATA

: The post-traumatic inflammatory response plays an important role in secondary injury mechanisms after spinal cord injury, and interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha are key inflammatory mediators.

METHODS

: The study group comprised 11 patients with spinal cord contusion injury and 2 normal individuals. Histologic and immunocytochemical assessments were undertaken to evaluate the inflammatory cellular response and the immunoexpression of interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha in the injured human spinal cord. The cellular sources of interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha were elucidated by immunofluorescence double-labeled confocal imaging.

RESULTS

: Increased immunoreactivity of interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha was detected in neurons 0.5 hour after injury, and in neurons and microglia 5 hours after injury, but the expression of these proinflammatory cytokines was short-lived and declined sharply to baseline by 2 days after injury. In the inflammatory cellular response, as early as 0.5 hour after spinal cord injury, activated microglia were detected, and axonal swellings and axons were surrounded by microglial processes. Numerous neutrophils appeared in the injured cord 1 day after injury, and then their number declined dramatically, whereas macrophages progressively increased after day 1.

CONCLUSIONS

Endogenous cells (neurons and microglia) in the human spinal cord, not the blood-borne leukocytes, contribute to the early production of interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha in the post-traumatic inflammatory response, and microglia are involved the early response to traumatic axonal injury.

Molecular biology of cervical myelopathy and spinal cord injury: role of oligodendrocyte apoptosis

BACKGROUND CONTEXT

Rational design of treatment strategies for cervical myelopathy and spinal cord injury requires a working knowledge of the molecular biology underlying these pathological processes. The cellular process of apoptosis is an important component of tissue and organ development as well as the natural response to disease and injury. Recent studies have convincingly demonstrated that apoptosis also plays a pivotal role in numerous pathological processes, contributing to the adverse effects of various diseases and traumatic conditions. A growing body of evidence has implicated apoptosis as a key determinant of the extent of neurological damage and dysfunction after acute spinal cord injury and in chronic cervical myelopathy.

PURPOSE

To provide clinicians and research investigators interested in spinal cord injury and myelopathy with a practical and up-to-date basic science review of cellular apoptosis in the context of spinal cord pathology.

STUDY DESIGN/SETTING

A review of recently published or presented data from molecular biological, animal model and human clinical studies.

METHODS

A computer-based comprehensive review of the English-language scientific and medical literature was performed in order to identify relevant publications with emphasis given to more recent studies.

RESULTS

Investigation into the role of apoptosis in spinal cord injury and myelopathy has drawn the interest of an increasing number of researchers and has yielded a substantial amount of new information.

CONCLUSIONS

Apoptosis is a fundamental biological process that contributes to preservation of health as well as development of disease. There is now strong evidence to support a significant role for apoptosis in secondary injury mechanisms after acute spinal cord injury as well in the progressive neurological deficits observed in such conditions as spondylotic cervical myelopathy.

Normal pressure hydrocephalus triggers intrathecal production of TNF-alpha

Normal pressure hydrocephalus (NPH) is associated with periventricular white matter lesions and demyelination. The aim of the present study was to examine the cerebrospinal fluid (CSF) levels of tumor necrosis factor-alpha (TNF-alpha), a proinflammatory cytokine mediating myelin damage, in patients with NPH. TNF-alpha levels were analyzed by ELISA and measured before and after shunt operation in 35 patients with NPH. The levels of this cytokine were related to the symptomatology and to magnetic resonance imaging (MRI) verified white matter lesions. They were also related to intrathecal levels of sulfatide, a marker for white matter degradation and to levels of neurofilament, a marker for neuronal degeneration. The preoperative levels of TNF-alpha were increased in the CSF of NPH patients compared to controls, and correlated to the levels of sulfatide. The intrathecal TNF-alpha levels were higher in NPH patients with impairment of wakefulness than in those without this symptom. The preoperative TNF-alpha levels were significantly correlated to the improvement of psychometrical test scores, and of wakefulness and to the overall improvement of the patients following shunt operation. Importantly, shunt operation led to complete disappearance of intrathecal TNF-alpha. We conclude that NPH is correlated with intrathecal TNF-alpha production being reversed following shunt operation in parallel with the clinical improvement. The positive correlation between preoperative TNF-alpha and sulfatide levels in the CSF suggest that intrathecal TNF-alpha may contribute to the damage of the white matter known to occur in patients with NPH.

Cerebral pattern of pro- and anti-inflammatory cytokines in dementias

The knowledge regarding putative inflammatory component(s) participating in Alzheimer's disease (AD) and vascular dementia (VAD) is scarce. Recently, we have demonstrated the presence of certain inflammatory cytokines in the cerebrospinal fluid (CSF) of demented patients. Although the initial event(s) triggering the neurodegenerative processes in AD versus VAD may be different and lead to different neuropathological changes, it may initiate a similar cascade of cytokine production in response to neuronal injury. The cytokines released in the central nervous system (CNS) may, in turn, act in a similar manner in both diseases, amplifying some pathological changes such as amyloidogenesis and white matter lesions or on the contrary acting as neuroprotective molecules. This review will focus on the intracerebral production of the pro- and anti-inflammatory cytokines interleukin IL-1beta, IL-1 receptor antagonist (IL-1ra), IL-6 and TNF-alpha in dementia, and their relation to gene polymorphism, to cerebral neuronal damage, apoptosis, and to clinical variables of dementia. Our results, which show for the first time strikingly increased CSF levels of TNF-alpha but not of TNF-beta, IL-1beta or IL-6 in AD and VAD, may form a conceptual framework for further studies of neuroprotective mechanisms in dementias.

Activated/effector CD4+ T cells exacerbate acute damage in the central nervous system following traumatic injury

CD4(+) helper T cells (Th) have been demonstrated to participate in the chronic phase of traumatic injury repair in the central nervous system (CNS). Here, we show that CD4(+) T cells can also contribute to the severity of the acute phase of CNS traumatic injury. We compared the area of tissue damage and the level of cellular apoptosis in aseptic cerebral injury (ACI) sites of C57BL/6 wild type and RAG1(-/-) immunodeficient mice. We demonstrate that ACI is attenuated in RAG1(-/-) mice compared to C57BL/6 animals. Adoptive transfer of CD4(+)CD62L(low)CD44(high) activated/effector T cells 24 h prior to ACI into RAG1(-/-) mice resulted in a significantly enhanced acute ACI that was comparable to ACI in the C57BL/6 animals. Adoptive transfer of CD4(+)CD62L(high)CD44(low) naive/non-activated T cells did not increase ACI in the brains of RAG1(-/-) mice. T cell inhibitory agents, cyclosporin A (CsA) and FK506, significantly decreased ACI-induced acute damage in C57BL/6 mice. These results suggest a previously undescribed role for activated/effector CD4(+) T cells in exacerbating ACI-induced acute damage in the CNS and raise a novel possibility for acute treatment of sterile traumatic brain injury.

Disturbance of oligodendrocyte development, hypomyelination and white matter injury in the neonatal rat brain after intracerebral injection of lipopolysaccharide

Increasing data provide support for the hypothesis that brain inflammation plays an important role in injury to developing white matter. In the present study, inflammatory responses in the neonatal rat brain were investigated following lipopolysaccharide (LPS) administration at postnatal day 5. LPS-induced brain injury was examined in brain sections 24 h, 3 and 9 days after LPS injection. White matter rarefaction was observed in 50% of the rat brains (three out of six) 24 h after LPS injection. Lateral ventricle enlargement was found in 100% (four out of four) and 89% (eight out of nine) of rat brains 3 and 9 days after LPS administration, respectively. White matter necrosis was found in three out of nine brains injected with LPS on P14. None of these injuries was observed in any control rat brains. No histological changes in gray matter were noted in the LPS-injected rat brain. Proinflammatory cytokines, tumor necrosis factor-alpha (TNFalpha), interleukin-1beta (IL-1beta) and interleukin-6 (IL-6), and inducible nitric oxide synthase (iNOS) in the rat brain were greatly induced after LPS administration. Activated astrocytes and microglia/macrophages were found in the affected rat brains. Double-labeling showed that IL-1beta and iNOS expressing cells were microglia/macrophages. Injury to or delayed development of immature oligodendrocytes (OLs) was evident by decreased immunostaining for both O4 and O1 antibodies, markers for developing immature OLs, in the LPS-injected as compared to the control rat brain. LPS also resulted in hypomyelination, as indicated by reduced myelin basic protein (MBP) immunostaining in the P8 rat brain. Co-administration of IL-1 receptor antagonist (IL-1Ra) with LPS reduced brain injury by improving myelination and subsequent reduction of lateral ventricle enlargement. These results indicate that developing OLs may be the target cells for LPS-induced brain injury and inflammatory cytokines are possible mediators of LPS-induced brain injury.

Periventricular leukomalacia, inflammation and white matter lesions within the developing nervous system

Periventricular leukomalacia (PVL) occurring in premature infants, represents a major precursor for neurological and intellectual impairment, and cerebral palsy in later life. The disorder is characterized by multifocal areas of necrosis found deep in the cortical white matter, which are often symmetrical and occur adjacent to the lateral ventricles. There is no known cure for PVL. Factors predisposing to PVL include birth trauma, asphyxia and respiratory failure, cardiopulmonary defects, premature birth/low birthweight, associated immature cerebrovascular development and lack of appropriate autoregulation of cerebral blood flow in response to hypoxic-ischemic insults. The intrinsic vulnerability of oligodendrocyte precursors is considered as central to the pathogenesis of PVL. These cells are susceptible to a variety of injurious stimuli including free radicals and excitotoxicity induced by hypoxic-ischemic injury (resulting from cerebral hypoperfusion), lack of trophic stimuli, as well as secondary associated events involving microglial and astrocytic activation and the release of pro-inflammatory cytokines TNF-alpha and IL-6. It is yet unclear whether activated astrocytes and microglia act as principal participants in the development of PVL lesions, or whether they are representatives of an incidental pathological response directed towards repair of tissue injury in PVL. Nevertheless, the accumulated evidence points to a pathological contribution of microglia towards damage. The topography of lesions in PVL most likely reflects a combination of the relatively immature cerebrovasculature together with a failure in perfusion and/or hypoxia during the greatest period of vulnerability occurring around mid-to-late gestation. Mechanisms underlying the pathogenesis of PVL have so far been related to prenatal ischemic injury to the brain initiated within the third trimester, which result in global cognitive and developmental delay and motor disturbances. Over the past few years, several epidemiological and experimental studies have implicated intrauterine infection and chorioamnionitis as causative in the pathogenesis of PVL. In particular, recent investigations have shown that inflammatory responses in the fetus and neonate can contribute towards neonatal brain injury and development-related disabilities including cerebral palsy. This review presents current concepts on the pathogenesis of PVL and emphasizes the increasing evidence for an inflammatory pathogenic component to this disorder, either resulting from hypoxic-ischemic injury or from infection. These findings provide the basis for clinical approaches targeted at protecting the premature brain from inflammatory damage, which may prove beneficial for treating PVL, if identified early in pathogenesis.

Molecular mechanisms of enhanced susceptibility to apoptosis in differentiating oligodendrocytes

Several studies have shown that the progression of oligodendrocyte progenitors along the lineage correlates with increased susceptibility to death stimuli. The molecular basis of this phenomenon remains unclear. This study demonstrates that the protein levels of several proapoptotic molecules, including Bax, Bad (nonphosphorylated form), and certain caspase proforms, increase during oligodendrocyte development. In contrast, the steady-state levels of antiapoptotic molecules, such as Bcl2 and Bcl(XL), remain constant. This altered equilibrium between proapoptotic and antiapoptotic molecules correlates with increased cytochrome C in the cytosol. We conclude that, as oligodendrocytes mature, their susceptibility to apoptosis increases because of a change in the balance between protective mechanisms and proapoptotic pathways. This suggests the possible existence of a death susceptibility program, which is intrinsic to differentiating oligodendrocyte progenitors.

Chronic ischemia preferentially causes white matter injury in the neonatal rat brain

Chronic ischemic brain injuries were studied in 7- and 14-day-old rat pups, which were subjected to bilateral carotid artery occlusion (BCAO) on postnatal day 1. BCAO preferentially injured white matter in the corpus callosum, subcortex and internal capsule areas while largely spared cortical neurons. White matter rarefaction in the corpus callosum was observed in 12 out of the 17 BCAO rat brains and significantly enlarged lateral ventricles were found in five out of seven P14 BCAO rat brains. These white matter changes were similar to injuries found in newborn infants with periventricular leukomalacia (PVL). White matter injuries in the 7-day-old BCAO rat brain were accompanied with increased activation of microglia/macrophages, as indicated by ED1 and OX42 positive immunostaining. Immature oligodendrocytes in the 7-day-old BCAO rat brain, as indicated by O4+/O1+ staining, were much fewer than in the sham-operated rat brain. Immunostaining for myelin basic protein (MBP) at the fimbria hippocampus and the internal capsule areas in the 7-day-old BACO rat brain was also much less than in the control rat brain. Consistent with the immunostaining data, MBP mRNA expression in the 7-day-old, but not in the 14-day-old, BCAO rat brain was significantly less than in the control rat brain. The overall results suggest that pre-oligodendrocytes and immature oligodendrocytes might be major targets for chronic ischemic insults and activated microglia/macrophages are possibly involved in the process of white matter injury.

Effects of lipopolysaccharide on oligodendrocyte progenitor cells are mediated by astrocytes and microglia

Oligodendrocytes are the primary cells injured in periventricular leukomalacia (PVL), a predominant form of brain white matter lesion in preterm infants. To explore the possible linkage between white matter injury and maternal infection, purified rat O-2A progenitor (Oligodendrocyte-type 2 astrocyte progenitor) cell cultures were used as a model in studying the effects of lipopolysaccharide (LPS), an endotoxin, on survival and differentiation of oligodendrocytes and the involvement of other glial cells in the effects of LPS. O-2A progenitor cells were cultured from optic nerves of 7-day-old rat pups in a chemically defined medium (CDM). Astrocyte and microglia cell cultures were prepared from the cortex of 1-day-old rat brains in the CDM. Direct treatment of LPS (1 microg/ml) to O-2A cells had no effect on viability or differentiation of these cells. When O-2A progenitor cells were cultured in the conditioned medium obtained from either astrocyte or microglial cell cultures for 48 hr, survival rate and differentiation of O-2A cells into mature oligodendrocytes were greatly enhanced as measured by the MTT assay and immunocytochemistry. The conditioned medium obtained from astrocytes or microglia treated with LPS for 48 hr, however, failed to show such a promotional effect on viability and differentiation of O-2A cells. When 5 microg/ml LPS was used to stimulate astrocytes or microglia, the conditioned medium from these glial cell cultures caused O-2A cell injury. The overall results indicate that astrocytes and microglia may promote viability and differentiation of O-2A progenitor cells under physiological conditions, but they may also mediate cytotoxic effects of LPS on oligodendrocytes under an infectious disease biochemical environment.

Mature oligodendrocyte apoptosis precedes IGF-1 production and oligodendrocyte progenitor accumulation and differentiation during demyelination/remyelination

We have documented changes in the oligodendrocyte population during demyelinating insult to the adult CNS. Feeding of cuprizone to adult mice led to apoptotic death of mature oligodendrocytes followed by profound demyelination of the corpus callosum. A regenerative response was initiated even during active demyelination. Oligodendrocyte progenitors have begun to proliferate and then accumulate within the lesion. Many of these cells may have migrated from the sub-ventricular zone and fornix before their accumulation in the demyelinating corpus callosum. The accumulation of differentiating oligodendrocyte progenitors was followed closely by the reappearance of mature oligodendrocytes and remyelination. Interestingly, an increase in IGF-1 mRNA was detected at Week 3 through Week 7, suggesting potential involvement in remyelination. Other factors, however, such as PDGF, NT3, FGF, jagged, and notch remained unchanged. These results suggest that the mature oligodendroglial population depleted by apoptosis is replaced by a newly formed oligodendroglial population derived from progenitors; these accumulate and seem to differentiate during remyelination.

Inositol stereoisomers stabilize an oligomeric aggregate of Alzheimer amyloid beta peptide and inhibit abeta -induced toxicity

Inositol has 8 stereoisomers, four of which are physiologically active. myo-Inositol is the most abundant isomer in the brain and more recently shown that epi- and scyllo-inositol are also present. myo-Inositol complexes with Abeta42 in vitro to form a small stable micelle. The ability of inositol stereoisomers to interact with and stabilize small Abeta complexes was addressed. Circular dichroism spectroscopy demonstrated that epi- and scyllo- but not chiro-inositol were able to induce a structural transition from random to beta-structure in Abeta42. Alternatively, none of the stereoisomers were able to induce a structural transition in Abeta40. Electron microscopy demonstrated that inositol stabilizes small aggregates of Abeta42. We demonstrate that inositol-Abeta interactions result in a complex that is non-toxic to nerve growth factor-differentiated PC-12 cells and primary human neuronal cultures. The attenuation of toxicity is the result of Abeta-inositol interaction, as inositol uptake inhibitors had no effect on neuronal survival. The use of inositol stereoisomers allowed us to elucidate an important structure-activity relationship between Abeta and inositol. Inositol stereoisomers are naturally occurring molecules that readily cross the blood-brain barrier and may represent a viable treatment for AD through the complexation of Abeta and attenuation of Abeta neurotoxic effects.

Sequential mRNA expression for immediate early genes, cytokines, and neurotrophins in spinal cord injury

In this communication, we demonstrate the sequential expression of endogenous molecules, including immediate early genes (IEGs), cytokines, neurotrophins, and neurotrophin receptors in the injured spinal cord. In the acute phase, expression of IEGs and cytokines mRNAs were rapidly upregulated within 1 h in nonneuronal cells in the lesioned sites and the surrounding spinal white and gray matter. Maximal expression was observed at 1 h for c-fos and TNF-alpha mRNAs, at 3 h for c-jun and IL-6 mRNAs, and at 6 h for IL-1 beta mRNA, and these signals were virtually nondetectable after 6-12 h from the onset of the injury. Some of these genes products may promote the degeneration of damaged cells and tissues, while others may be involved in the subsequent repair processes. In the subacute phase, expression of NGF, BDNF, NT-3, p75LNGFR and Trk B mRNAs began to increase in the nonneuronal cells and neuronal cells from 6 h, and peaked at 24-72 h in the area where expression of mRNAs for IEGs and cytokines overlapped. Signals for IL-6 mRNA were also observed in motoneurons at 24-72 h after the injury, with the suggestion that these molecules may be involved in promoting axonal sprouting in the injured spinal cord. Of further interest was the finding that this upregulation of IL-1 beta, BDNF, and NT-3 mRNAs in injured spinal cord was attenuated by treatment with high dose glucocorticoids, with the suggestion that the downregulation of BDNF and NT-3 might be disadvantageous to survival and axonal sprouting of spinal neurons.

Cell death in the oligodendrocyte lineage: a molecular perspective of life/death decisions in development and disease

Cell death in the oligodendrocyte lineage occurs during development and in pathological conditions as the result of a balance between opposing molecular signals. This review focuses on the molecular mechanisms of activation of signal transduction pathways affecting life/death decisions in progenitor cells and in mature oligodendrocytes. Loss of trophic support, cytokine receptor activation, and oxidative stress may differentially contribute to the induction of cell death at specific stages of development and to the pathogenesis of demyelinating disorders. The execution of the death program leading to the morphological changes of apoptosis and/or necrosis is then determined by the generation of reactive oxygen species and the level of impairment of mitochondrial function. The final decision of a cell to die or survive is determined by a competition between survival and death signals. Depending on ligand availability, type, and levels of receptor expression and downstream cross-talks between distinct signaling pathways, the cell may activate a death execution program that will be affected by its stage of differentiation and its energetic metabolism.

Caspases mediate C2-ceramide-induced apoptosis of the human oligodendroglial cell line, MO3.13

The signalling molecule ceramide participates in the sphingomyelin pathway and accumulates intracellularly in response to inflammatory mediators. Here we show that membrane permeable C2-ceramide is apoptogenic in the immortalised human oligodendroglial cell line MO3.13. Apoptosis (defined by cell shrinkage and chromatin condensation) is accompanied by caspase enzyme activation. Immunoblotting analysis of extracts from differentiated MO3.13 cells revealed the presence of caspase-3 proenzyme, activation by cleavage of pro-caspase-3 in cells treated with C2-ceramide and cleavage of the caspase substrates fodrin and rabaptin. Lysates also showed cleavage of a fluorogenic peptide substrate. Addition of the general caspase inhibitor BAF markedly attenuated apoptosis of MO3.13 oligodendroglia. A role for caspase-3-like enzymes in ceramide-induced apoptosis of oligodendroglia may have important implications for approaches to treatment of demyelinating diseases.

Cytokine induction in fetal rat brains and brain injury in neonatal rats after maternal lipopolysaccharide administration

Induction of proinflammatory cytokines has been proposed to be a link between prenatal maternal intrauterine infection and neonatal brain damage. It is known that the endotoxin, lipopolysaccharide (LPS), released during bacterial infection crosses the placenta. Cytokine induction in the fetal rat brain after maternal administration of LPS was determined by reverse transcriptase-polymerase chain reaction method. LPS suspension in pyrogen-free saline was administered (i.p.) to pregnant rats at 18 d of gestation. The control group was treated with pyrogen-free saline. Expression of the proinflammatory cytokines, tumor necrosis factor-alpha and IL-1beta mRNA, in the fetal rat brain was increased in a dose-dependent manner at 1 h after LPS administration. The great increase in expression of IL-1beta mRNA was only observed at 1 h after injection of LPS (4 mg/kg), whereas the increased expression of tumor necrosis factor-alpha was still detectable from 4 to 24 h after LPS administration. Brain injuries were examined by immunohistochemistry in 8-d-old rat pups born to the dams that were consecutively treated with LPS (500 microg/kg) or pyrogen-free saline on gestation d 18 and 19. No apparent necrotic tissue damage was found in either the LPS group or the control group. Myelin basic protein staining, as a marker of myelin, was clearly observed in the internal capsule and the fimbria hippocampus in the rat brain from the control group. Myelin basic protein staining was much less and weaker in the brains of the LPS-treated group. Glial fibrillary acidic protein-positive astrocytes were observed in both the control and the LPS-treated groups. The LPS-treated group appeared to have more glial fibrillary acidic protein-positive astrocytes in the hippocampal and the cortex areas of the brain than the control group. Immunoblotting data showed that glial fibrillary acidic protein content in the cortex or the hippocampus of the LPS-treated rat brain was higher than in the control group. OX-42-positive staining (a marker of the type 3 complement receptors) of microglial cells was greatly reduced in the 8-d-old rat brain after maternal LPS administration. However, histochemistry with tomato lectin showed that staining of both amoeboid and ramified microglial cells in the LPS-treated rat brain was similar to that in the control group. The overall results indicate that maternal LPS administration induces an increased expression of IL-1beta and tumor necrosis factor-alpha mRNA in the fetal brain. Maternal LPS administration also increases glial fibrillary acidic protein-positive astrocytes, decreases myelin basic protein and alters immunoreactivity of microglia in the brain of offspring. Although results from the current study do not provide direct evidence linking LPS-induced cytokines with the abnormalities in the neonatal rat brain, our animal model may be appropriate for exploring the mechanisms involved in the effects of maternal infection on glial cells in the brains of offspring.

Intracerebral administration of interleukin-1beta and induction of inflammation, apoptosis, and vasogenic edema

OBJECT

The proinflammatory cytokines interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNFalpha) are produced intracerebrally in brain disorders such as trauma, ischemia, meningitis, and multiple sclerosis. This investigation was undertaken to analyze the effect of intracerebral administration of IL-1beta and TNFalpha on inflammatory response, cell death, and edema development.

METHODS

Intracerebral microinjections of these cytokines were administered to rats. The animals were killed 24 or 72 hours after the injections, and their brains were analyzed by using deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) with digoxigenin-labeled deoxyuridine triphosphate, immunohistochemical studies, and brain-specific gravity measurement. The IL-1beta induced a transient inflammatory response (p < 0.001) and TUNEL staining (p < 0.001), indicating cell death, in intrinsic central nervous system (CNS) cells and infiltrating inflammatory cells. In 73.8+/-6.77% of the TUNEL-positive cells, small, fragmented nuclei were found. All TUNEL-positive cells expressed the proapoptotic gene Bax, and 69.6+/-4.6% of the TUNEL-positive cells expressed the antiapoptotic gene Bcl-2; the Bax expression was stronger than the Bcl-2 expression. Taken together, the data indicate that cell death occurred via the apoptotic pathway. The TNFalpha did not induce inflammation or DNA fragmentation within the analyzed time period. Both IL-1beta (p < 0.001) and TNFalpha (p < 0.01) caused vasogenic edema, as measured by specific gravity and albumin staining. The edematous effect of TNFalpha persisted 72 hours after injection (p < 0.01), whereas the IL-1beta-treated animals had normalized by that time.

CONCLUSIONS

Intracerebral inflammation, death of intrinsic CNS cells, and vasogenic edema can be mediated by IL-1beta, and TNFalpha can cause vasogenic edema. Suppression of these cytokines in the clinical setting may improve outcome.

Mechanisms of damage to myelin and oligodendrocytes and their relevance to disease

Oligodendrocytes synthesize and maintain myelin in the central nervous system (CNS). Damage may occur to these cells in a number of conditions, including infections, exposure to toxins, injury, degeneration, or autoimmune disease, arising both in the course of human disease and in experimental animal models of demyelination and dysmyelination; multiple sclerosis is the commonest human demyelinating disorder. Conventional classical accounts of the pathology of this and other myelin diseases have given great insights into their core features, but there remain considerable uncertainties concerning the timing, means and cause(s) of oligodendrocyte and myelin damage. At present, therapeutic efforts largely concentrate on immune manipulation and damage limitation, an approach that has produced only modest effects in multiple sclerosis. One reason for this must be the limited understanding of the mechanisms underlying cell damage - clearly, successful therapeutic strategies for preserving the oligodendrocyte-myelin unit must depend on knowledge of how oligodendrocyte damage and death occurs. In this review, mechanisms of oligodendrocyte and myelin damage are considered, and attempts made to relate them to disease processes, clinical and experimental. The hallmarks of different cell death processes are described, and oligodendrocyte-myelin injury by cellular and soluble mediators is discussed, both in vitro and invivo. Recent developments concerning the pathological involvement of oligodendrocytes in neurodegenerative disease are summarized. Finally, these neuropathological and applied neurobiological observations are drawn together in the context of multiple sclerosis.

Expression of a homologue of rat NG2 on human microglia

The expression of NG2 chondroitin sulfate has been widely associated with oligodendrocyte precursors in rodents. We used a monoclonal antibody (9.2.27) against the human homologue of the rat NG2 to determine whether expression of this molecule was associated with a specific glial cell population present in dissociated cell preparations derived from adult and fetal human brain tissue. Our data, derived using FACS and immunocytochemical analyses of immediately ex vivo or cultured glial cells, indicate that the large majority of NG2 expressing cells belonged to the microglial lineage (CD68, CD11c) rather than to the oligodendrocyte lineage (O4, A2B5, GalC). In situ immunohistochemistry performed on non-fixed normal spinal cord tissue confirmed the observation that NG2 is expressed by mononuclear phagocytes of the CNS. In contrast, peripheral blood-derived monocytes were NG2(-). Cells from fetal brain tissue showed only small numbers of NG2(+) cells, which was consistent with the number of microglial cells in this preparation. In absence of additional markers, we cannot exclude that this anti-NG2 mAb might also recognize human oligodendrocyte progenitor cells.

Intracerebral production of tumor necrosis factor-alpha, a local neuroprotective agent, in Alzheimer disease and vascular dementia

The local pattern of proinflammatory cytokine release was studied in Alzheimer disease (AD) and vascular dementia (VAD), by measuring intrathecal levels of IL-1 beta, IL-6, TNF-alpha, and its naturally occurring antagonists, soluble TNF receptors I and II. The cytokine levels were related to neuronal damage, as measured by the intrathecal tau concentration, to cerebral apoptosis assessed by levels of Fas/APO-1 and bcl-2, and to clinical variables. In vitro analysis was performed to study the effect of TNF-alpha on the production of bcl-2, an antiapoptotic factor, by human neuronal cells. Patients with both AD and VAD displayed significantly higher intrathecal levels of TNF-alpha compared to controls. In addition, patients with AD showed significantly negative correlations between the intrathecal levels of TNF-alpha and the levels of Fas/APO-1 as well as of tau protein. The level of bcl-2 in supernatants of TNF-alpha-exposed cultures of human neuronal cells was up to three times higher than in control supernatants. Our study demonstrates intrathecal production of TNF-alpha in patients with dementias, suggesting that this cytokine may have a neuroprotective role in these neurodegenerative conditions as evidenced by negative correlations between this cytokine and (i) levels of intrathecal Fas/APO-1 and (ii) levels of tau protein, both parameters closely related to brain damage. Our in vitro data suggest that TNF-alpha exerts its neuroprotective effect by stimulating neuronal cells to express bcl-2, a molecule which downregulates apoptosis.

Myelinolytic lesions in spinal cord of cobalamin-deficient rats are TNF-alpha-mediated

Repeated intracerebroventricular (i.c.v.)microinjection of tumor necrosis factor-alpha (TNF-alpha) into normal rats causes intramyelin and interstitial edema in the white matter of the spinal cord (SC). This response is identical to that observed in the SC white matter of rats made cobalamin (Cbl) deficient by total gastrectomy (TG). Immunoblot analysis showed that: 1) the level of the biologically active form of the TNF-alpha protein (17 kDa) is higher in the SC of totally gastrectomized (TGX) rats 2 months after TG, i.e., at the postoperative time when edema is observed; 2) SC levels of TNF-alpha protein (17 kDa) in 2-mo-TGX-, Cbl-treated rats are reduced to control. Repeated i.c.v. microinjections of anti-TNF-alpha antibodies, transforming growth factor-beta1 (TGF-beta1) or interleukin-6 (IL-6) into TGX rats, begun shortly after TG, substantially reduced both intramyelin and interstitial edema in the SC white matter. This study provides the first evidence that the hallmark myelin damage of Cbl-deficient central neuropathy, which is a pure myelinolytic disease, is not caused directly by the withdrawal of the vitamin itself, but reflects enhanced production of the biologically active form of TNF-alpha by SC cells. This study thus supports the view that TGF-beta1 and IL-6 may act as neuroprotective agents in Cbl deficiency central neuropathy.

Comparison of TNFalpha and TNFbeta cytolytic mechanisms in human ovarian and cervical carcinoma cell lines

OBJECTIVES

The aim of this study was to determine the potential and mechanism of tumor necrosis factor beta (TNFbeta) mediated cytolysis in human ovarian and cervical carcinoma cells.

METHODS

The cytolytic potential of tumor necrosis factor alpha (TNFalpha) and TNFbeta was determined using the TNF reference cell line L929 and human ovarian (SK-OV-3, CaOV-3) and cervical (SiHa, HT-3) carcinoma cell lines. We have previously reported the effects of the lipoxygenase enzyme inhibitor, nordihydroguaiaretic acid, the oxygen radical scavenger glutathione, and fragmented DNA-specific staining with diamidino-2-phenylindole and ApopTag on TNFalpha-mediated cytolysis in these cells. The effects of these agents on TNFbeta-mediated cytolysis were determined.

RESULTS

All of the cell lines express a protein-synthesis-dependent TNFalpha and TNFbeta resistance mechanisms. When protein synthesis is inhibited the cytolytic activity of TNFbeta was fivefold greater than that of TNFalpha in L929 cells. In contrast, the cytolytic activity of TNFalpha was fivefold greater than that of TNFbeta in the human cells. Like the TNFalpha cytolytic mechanism, the TNFbeta cytolytic mechanism is dependent on lipoxygenase enzymes, but not oxygen radicals, and results in apoptosis.

CONCLUSIONS

To date there is little information about the cytolytic potential of TNFbeta in human cells. The fact that the cytolytic mechanism of TNFbeta appears very similar to that of TNFalpha could be important to our understanding of the potential of these closely related cytokines in anticancer therapies. Although the cytolytic potential of TNFbeta is greater than that of TNFalpha in mouse cells, this is not true in human cells and could limit the efficacy of TNFbeta in anticancer therapies.

Human oligodendroglial development: relationship to periventricular leukomalacia

Periventricular leukomalacia in the premature infant is a lesion of cerebral white matter with its greatest period of risk when white matter is immature, that is, when oligodendrocyte precursors are proliferating and differentiating, and before myelin sheaths are actively synthesized. Although the pathogenesis of perinatal cerebral white matter damage involves multiple factors, the correlation of the timing of the lesion with dominance of oligodendrocyte precursors in cerebral white matter suggests that intrinsic factors related to oligodendrocyte precursors are critical. Ischemia and infection have both been implicated as causes of perinatal white matter damage. Major mechanisms underlying oligodendrocyte injury in ischemia include glutamate toxicity, free-radical injury, and cytokine damage mediated by macrophages accompanying ischemia-induced inflammation. Factors related to a vulnerability of immature oligodendrocytes to ischemia potentially include a developmental lack of antioxidant enzymes to mediate oxidative stress. Cytokine-mediated injury to oligodendrocytes is also potentially important. A complete understanding of the role of immature white matter in the pathogenesis of periventricular leukomalacia is essential for developing strategies to prevent it.