Inflammatory mediators in demyelinating disorders of the CNS and PNS

Immunolocalization and activation of nuclear factor-κB in the sciatic nerves of rats with experimental autoimmune neuritis

Recent data support an important role played by nuclear factor kappa B (NF-kappaB) in peripheral neuropathies. We investigated expression and activation of NF-kappaB in experimental autoimmune neuritis (EAN) in rat sciatic nerves removed after 7, 14 and 21 days after immunization. Immunoreactivity for the activated form of NF-kappaB was found in the nuclei of T cells and macrophages at days 14 and 21, and also in the nuclei of few Schwann cells and of vascular endothelial cells at all time points, especially during the peak stage. Western blot showed a single band corresponding to 65 kDa in all EAN animals. NF-kappaB DNA-binding activity was revealed by electrophoretic mobility shift assay. Our results support NF-kappaB activation in EAN during the induction stage as well as in the disease remission.

Induction and blockage of oligodendrogenesis by differently activated microglia in an animal model of multiple sclerosis

The role of activated microglia (MG) in demyelinating neurodegenerative diseases such as multiple sclerosis is controversial. Here we show that high, but not low, levels of IFN-gamma (a cytokine associated with inflammatory autoimmune diseases) conferred on rodent MG a phenotype that impeded oligodendrogenesis from adult neural stem/progenitor cells. IL-4 reversed the impediment, attenuated TNF-alpha production, and overcame blockage of IGF-I production caused by IFN-gamma. In rodents with acute or chronic EAE, injection of IL-4-activated MG into the cerebrospinal fluid resulted in increased oligodendrogenesis in the spinal cord and improved clinical symptoms. The newly formed oligodendrocytes were spatially associated with MG expressing MHC class II proteins and IGF-I. These results point to what we believe to be a novel role for MG in oligodendrogenesis from the endogenous stem cell pool.

The role of neuroinflammation in neuropathic pain: mechanisms and therapeutic targets

Neuroinflammation is a proinflammatory cytokine-mediated process that can be provoked by systemic tissue injury but it is most often associated with direct injury to the nervous system. It involves neural-immune interactions that activate immune cells, glial cells and neurons and can lead to the debilitating pain state known as neuropathic pain. It occurs most commonly with injury to peripheral nerves and involves axonal injury with Wallerian degeneration mediated by hematogenous macrophages. Therapy is problematic but new trials with anti-cytokine agents, cytokine receptor antibodies, cytokine-signaling inhibitors, and glial and neuron stabilizers provide hope for future success in treating neuropathic pain.

TNF-alpha and phosphorylation of ERK in DRG and spinal cord: insights into mechanisms of sciatica

STUDY DESIGN

Characterize extracellular signal-regulated kinase (ERK) and its phosphorylation (pERK) in neural tissues after topical application of tumor necrosis factor-alpha (TNF-alpha) to L5 nerve root.

OBJECTIVE

Identify time-course, localization, and expression of pERK.

SUMMARY OF BACKGROUND DATA

TNF-alpha has a key role in disc herniation and sciatica as an inflammatory component of the nucleus pulposus. ERK is associated with neuronal signal transduction and nociception.

METHODS

We studied tissue from naive rats, vehicle-treated rats, and rats receiving rat recombinant TNF-alpha using Western blots of total and phosphorylated ERK (pERK). We used immunohistochemistry of pERK with neuronal nuclear (NeuN) antibody to identify its cellular distribution.

RESULTS

Topical application of TNF-alpha to rat nerve root increased pERK in ipsilateral dorsal root ganglion (DRG) neurons and glia within 5 hours. pERK was not expressed in DRG during the first hour after TNF-alpha application, nor was it seen at anytime in spinal cord dorsal horn. DRG satellite cells had increased pERK 5 hours after TNF-alpha or vehicle treatment. TNF-alpha treatment increased pERK in small- and medium-sized DRG neurons and to a lesser degree in large neurons.

CONCLUSIONS

These findings suggest that ERK signaling plays a role in the activation of DRG cells following inflammatory injuries to nerve roots and further documents the importance of inflammation in the pathogenesis of painful spine disorders.

Antioxidants and polyunsaturated fatty acids in multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS). Oligodendrocyte damage and subsequent axonal demyelination is a hallmark of this disease. Different pathomechanisms, for example, immune-mediated inflammation, oxidative stress and excitotoxicity, are involved in the immunopathology of MS. The risk of developing MS is associated with increased dietary intake of saturated fatty acids. Polyunsaturated fatty acid (PUFA) and antioxidant deficiencies along with decreased cellular antioxidant defence mechanisms have been observed in MS patients. Furthermore, antioxidant and PUFA treatment in experimental allergic encephalomyelitis, an animal model of MS, decreased the clinical signs of disease. Low-molecular-weight antioxidants may support cellular antioxidant defences in various ways, including radical scavenging, interfering with gene transcription, protein expression, enzyme activity and by metal chelation. PUFAs may not only exert immunosuppressive actions through their incorporation in immune cells but also may affect cell function within the CNS. Both dietary antioxidants and PUFAs have the potential to diminish disease symptoms by targeting specific pathomechanisms and supporting recovery in MS.

TNFalpha mediates Schwann cell death by upregulating p75NTR expression without sustained activation of NFkappaB

Administration of tumour necrosis factor alpha (TNFalpha) to axotomised mouse neonatal sciatic nerves increased Schwann cell apoptosis in the distal nerve segments, 5-fold greater than axotomy alone. TNFalpha upregulated the low affinity neurotrophin receptor, p75NTR, indicative of phenotype reversion in Schwann cells. Furthermore, re-expression of p75NTR and downregulation of the pro-myelinating transcription factor, Oct 6, in Schwann cells occurred by treatment with TNFalpha, even after the maturation of these cells with brain derived neurotrophic factor (BDNF). TNFalpha treatment of Schwann cells produced only a transient activation of NFkappaB. More importantly, in NFkappaB (p65) mutant mice, axotomy increased Schwann cell apoptosis further than that seen in mice expressing NFkappaB (p65), implicating a survival role for NFkappaB. Collectively, these data suggest that TNFalpha can potentiate Schwann cell death through the modulation of their phenotype. Immature Schwann cells express a high level of p75NTR and as a consequence are susceptible to extracellular death stimuli because of the lack of sustained NFkappaB translocation.

IL-18 Induces Monocyte Chemotactic Protein-1 Production in Macrophages through the Phosphatidylinositol 3-Kinase/Akt and MEK/ERK1/2 Pathways

Macrophages are activated during an inflammatory response and produce multiple inflammatory cytokines. IL-18 is one of the most important innate cytokines produced from macrophages in the early stages of the inflammatory immune response. Monocyte chemoattractant protein (MCP-1) is expressed in many inflammatory diseases such as multiple sclerosis and rheumatoid arthritis, and its expression is correlated with the severity of the disease. Both IL-18 and MCP-1 have been shown to be involved in inflammatory immune responses. However, it has been unclear whether IL-18 is involved in the induction of MCP-1. This investigation was initiated to determine whether IL-18 can induce MCP-1 production, and if so, by which signal transduction pathways. We found that IL-18 induced the production of MCP-1 in macrophages, which was IL-12-independent and was not mediated by autocrine cytokines such as IFN-gamma or TNF-alpha. We then examined signal transduction pathways involved in IL-18-induced MCP-1 production. We found that IL-18 did not activate the IkappaB kinase/NF-kappaB pathway, evidenced by no degradation of IkappaBalpha and no translocation of NF-kappaB p65 to the nucleus in IL-18-stimulated macrophages. Instead, IL-18 activated the PI3K/Akt and MEK/ERK1/2 pathways. Inhibition of either of these pathways attenuated MCP-1 production in macrophages, and inhibition of both signaling pathways resulted in the complete inhibition of MCP-1 production. On the basis of these observations, we conclude that IL-18 induces MCP-1 production through the PI3K/Akt and MEK/ERK1/2 pathways in macrophages.

Disc related cytokines inhibit axonal outgrowth from dorsal root ganglion cells in vitro

STUDY DESIGN

Application of nucleus pulposus and disc related cytokines in vitro on cultured dorsal root ganglion (DRG) cells.

OBJECTIVES

To study if tumor necrosis factor (TNF) and interleukin-1beta (IL-1beta) may induce similar inhibition of axonal outgrowth from cultured DRG cells as application of nucleus pulposus and to compare a new assessment method to previous data.

SUMMARY OF BACKGROUND DATA

Pro-inflammatory cytokines related to the intervertebral disc have been suggested to affect adversely neurons following local application, with implications for the nucleus pulposus-induced nerve injury seen in various studies. Nucleus pulposus is known to inhibit axonal outgrowth from cultured DRG cells, thereby indicating a neurotoxic potential. The mechanisms were not understood, but it was suspected that the effect was mediated by pro-inflammatory cytokines produced by the nucleus pulposus.

METHODS

DRG were harvested from newborn rats and put in culture. The axonal outgrowth was determined 24 hours after starting the culture. Twenty-four hours after exposing the cultured cells to nucleus pulposus, frozen nucleus pulposus, TNF, or IL-1beta, the axonal outgrowth was reassessed, and the outgrowth during the exposure time was calculated.

RESULTS

Nucleus pulposus clearly reduced the axonal outgrowth. Also, application of TNF and IL-1beta reduced the outgrowth but not as pronounced as the nucleus pulposus. Frozen nucleus pulposus had no effects on the outgrowth. Overall, the data were similar regarding frozen and nonfrozen nucleus pulposus compared to a previous study.

CONCLUSIONS

It was evident that the 2 studied cytokines inhibited the outgrowth of axons from cultured DRG cells, thus suggesting a neurotoxic potential. However, the inhibition was not as pronounced as for nucleus pulposus. These data may increase our understanding for cytokine induced nerve injury, with implications for future treatment strategies for such conditions.

Effects of obstructive jaundice on the peripheral nerve: an ultrastructural study in rats

Obstructive jaundice (OJ) and hepatic disorders have been shown to be associated with peripheral neuropathy in several clinical studies. The study evaluated the effect of OJ on the ultrastructure of the rat sciatic nerve. In the OJ group, jaundice was created by ligation of common bile duct in Wistar-Albino rats. In the sham-operated control group the same procedure was performed without ligation of the bile duct. On day 7, all rats were re-operated and sciatic nerves were explored to harvest 2-cm-long nerve segments for quantitative and qualitative histopathological analysis by light and electron microscopy. Bilirubin was measured on serum samples. Bilirubin levels were significantly higher in jaundiced rats compared with that of controls (8.46 +/- 0.45 vs. 0.80 +/- 0.14 mmol/l, means +/- SD, p < 0.01). Control nerves did not show anything other than the normal histology. In the OJ group, degenerative changes such as irregularities, thinning, ruffling and invaginations, irregularshaped bodies, vacuolizations and focal segmental demyelination were observed in the myelin sheath. Myelin clusters were noted in the axoplasm. A varying degree of swelling was noted in the nucleus and cytoplasm of the Schwann cells. Morphometric analysis of specimens obtained from sciatic nerves showed that myelin injury (370.9 +/- 51.3 vs. 11.6 +/- 0.5 axons), axonal edema (142.1 +/- 24.2 vs. 10.6 +/- 0.5 edematous axons) and Schwann cell degeneration (50.3 +/- 11.6 vs. 3.2 +/- 0.2 Schwann cells) was significantly higher in the jaundiced rats than in the control group (p < 0.01). The ultrastructural alterations spotted in the rat peripheral nerve were attributed to hyperbilirubinemia and increased concentrations of several neurotoxic substances released from the Kupffer cells in OJ. Neuropathy in jaundiced patients seems to result from accompanying degenerative changes in the peripheral nervous system. However, the exact nature and initiating factors of this nerve injury remains to be unveiled.

The Age-Related Degeneration of Oligodendrocytes in the Hippocampus of the Senescence-Accelerated Mouse (SAM) P8: A Quantitative Immunohistochemical Study

The senescence-accelerated mouse (SAM) is known as a murine model for accelerated aging. The SAMP8 shows age-related deficits of learning and memory at an earlier age than control mice (SAMR1). We investigated the changes in oligodendrocytes in the brain of SAMP8, using immunohistochemistry for myelin basic protein (MBP) and 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) as an oligodendrocyte marker. SAMP8 at 10 months old showed a decrease in MBP-immunoreactivity (IR) and CNP-IR in the hippocampal CA1 subfield, compared with SAMR1. There were no significant differences in MBP and CNP old in the cerebral cortex and the optic tract between SAMR1 and SAMP8 at 10 months. Furthermore, we measured the area of MBP-IR in the CA1 subfield of both strains and found that the area of MBP-IR in SAMP8 had decreased progressively with age, compared with SAMR1. These results suggest that age-related degeneration of oligodendrocytes had occurred in the hippocampus of SAMP8.

Nitric oxide synthase expression and enzymatic activity in multiple sclerosis

We used post-mortem magnetic resonance imaging (MRI) guidance to obtain paired biopsies from the brains of four patients with clinical definite multiple sclerosis (MS). Samples were analyzed for the immunoreactivity (IR) of the three nitric oxide (NO) synthase isoforms [inducible, neuronal and endothelial nitric oxide synthase (NOS)], and enzymatic NO synthase activity. MRI guided biopsies documented more active plaques than macroscopic examination, and histological examination revealed further lesions. Inducible NOS (iNOS) was the dominant IR isoform, while reactive astrocytes were the dominant iNOS expressing cells in active lesions. NOS IR expressing cells were widely distributed in plaques, in white and gray matter that appeared normal macroscopically, and on MR. Endothelial NOS (eNOS) was highly expressed in intraparenchymal vascular endothelial cells of MS patients. A control group matched for age and sex showed no such changes. Our data support the hypothesis that NO is a pathogenic factor in MS, and that NOS IR is strongly expressed in brain regions appearing normal by MRI.

Interleukin-12 p40-homodimer production in sensory dorsal root ganglion neurons

Recently, the reports that sensory nerves contribute to induction and development of peripheral inflammation have been accumulating. Although neuropeptides have been thought to participate in modulation of inflammation, we supposed the involvement of cytokines. Interleukin-12 (IL-12) is a key regulator of cell-mediated immunity. IL-12 is heterodimer cytokine consisting of a p35 and a p40 subunit, but the results that some of immune cell types secrete p40-homodimer have been reported. In this study, we investigated the expression and secretion of IL-12 in mouse sensory neurons in order to evaluate the involvement of sensory neurons in cell-mediated immunity. Expression of IL-12 p40 mRNA was detected and enhanced by interferon-gamma (IFN-gamma), but another subunit of IL-12 p35 mRNA was not detected in sensory dorsal root ganglion (DRG) neurons in culture. IL-12 p40 molecule was detected in DRG neurons by immunocytochemistry. In addition, cultured DRG neurons secreted p40-homodimer that inhibited IL-12-induced STAT4 phosphorylation in T cells. p40 mRNA expression was accumulated in DRG after administration of IFN-gamma into mouse footpad, and this enhancement was eliminated by a cut of sciatic nerve. These results suggest the possibility that p40-homodimer derived from sensory nerves suppresses the excessive peripheral inflammation.

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.

Involvement of cyclooxygenase-1 and -2 in the sciatic nerve of rats with experimental autoimmune neuritis

The expression of both cyclooxygenase (COX)-1 and COX-2, which are representative enzymes in prostaglandin synthesis, was evaluated in the sciatic nerve of rats with experimental autoimmune neuritis (EAN). Western blot analysis showed that both COX-1 and COX-2 were significantly increased in the sciatic nerve at the peak stage of EAN and declined during the recovery stage. Vascular endothelial cells in normal sciatic nerves immunostained for both COX-1 and COX-2. COX-1 was mainly detected in macrophages, and not in other cell types, while COX-2 was detected in Schwann cells and axons as well as inflammatory macrophages in EAN lesions. This suggests that COXs are involved in the pathogenesis of peripheral demyelinating disease, including EAN, and the major cellular source of both COXs in EAN lesions is inflammatory macrophages. Furthermore, COX-2 is enhanced in some Schwann cells and neural elements, possibly mediating peripheral nervous system inflammation.

Metallothionein-I overexpression decreases brain pathology in transgenic mice with astrocyte-targeted expression of interleukin-6

Transgenic expression of interleukin-6 (IL-6) in the CNS under the control of the glial fibrillary acidic protein (GFAP) gene promoter (GFAP-IL6 mice) causes significant damage and alters the expression of many genes, including a dramatic upregulation of metallothionein-I (MT-I). The findings in this report support the idea that the upregulation of MT-I observed in GFAP-IL6 mice is an important mechanism for coping with brain damage. Thus, GFAP-IL6 mice that were crossed with TgMTI transgenic mice (GFAP-IL6xTgMTI) and overexpressed MT-I in the brain showed a decreased upregulation of cytokines such as IL-6 and a diminished recruitment and activation of macrophages and T cells throughout the CNS but mainly in the cerebellum. The GFAP-IL6 mice showed clear evidence of increased oxidative stress, which was significantly decreased by MT-I overexpression. Interestingly, MT-I overexpression increased angiogenesis in GFAP-IL6 mice but not in control littermates. Overall, the results strongly suggest that MT-I+II proteins are valuable factors that protect against cytokine-induced CNS injury.

Beyond neurons: evidence that immune and glial cells contribute to pathological pain states

Chronic pain can occur after peripheral nerve injury, infection, or inflammation. Under such neuropathic pain conditions, sensory processing in the affected body region becomes grossly abnormal. Despite decades of research, currently available drugs largely fail to control such pain. This review explores the possibility that the reason for this failure lies in the fact that such drugs were designed to target neurons rather than immune or glial cells. It describes how immune cells are a natural and inextricable part of skin, peripheral nerves, dorsal root ganglia, and spinal cord. It then examines how immune and glial activation may participate in the etiology and symptomatology of diverse pathological pain states in both humans and laboratory animals. Of the variety of substances released by activated immune and glial cells, proinflammatory cytokines (tumor necrosis factor, interleukin-1, interleukin-6) appear to be of special importance in the creation of peripheral nerve and neuronal hyperexcitability. Although this review focuses on immune modulation of pain, the implications are pervasive. Indeed, all nerves and neurons regardless of modality or function are likely affected by immune and glial activation in the ways described for pain.

Interferon-gamma regulates oxidative stress during experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is an induced inflammatory and demyelinating disease of the central nervous system which shares many clinical and pathological features with and is considered the animal model of multiple sclerosis. There is extensive evidence that EAE is a Th1 disease eliciting secretion of proinflammatory cytokines like IFN-gamma or TNF-alpha, and it has been suggested that cytokine-induced oxidative stress could have a role in EAE neuropathology. However, the individual roles of these and other cytokines in the pathogenesis of the disease are still uncertain. Here we analyze the role of IFN-gamma during EAE by using both IFN-gamma receptor-knockout (IFN-gamma R(-/-)) and wild-type mice, both strains immunized with peptide 40-55 from rat myelin oligodendrocyte glycoprotein. The levels of oxidative stress were determined through the analysis of immunoreactivity for inducible NO synthase, nitrotyrosine, and malondialdehyde, as well as through the expression of the tissue-protective antioxidant factors metallothionein I+II (MT-I+II). We also examined the number of cells undergoing apoptosis as judged by using the TUNEL technique. The levels of oxidative stress, MT-I+II, and apoptotic cell death by EAE were significantly increased in all mice, though more so in IFN-gamma R(-/-) mice compared with wild-type mice. These data support the notion that IFN-gamma has a protective role against EAE.

Local application of disc-related cytokines on spinal nerve roots

STUDY DESIGN

To analyze the effects of tumor necrosis factor-alpha, interleukin-1beta, and interferon-gamma on cauda equina function and to define if any of these cytokines could induce nerve root dysfunction comparable with the situation with application of nucleus pulposus.

SUMMARY OF BACKGROUND DATA

Proinflammatory cytokines derived from the intervertebral disc have been suggested to mediate the nucleus pulposus-induced nerve root injury following local application of nucleus pulposus. However, it is not known if such cytokines may induce similar injury if applied separately.

METHODS

A total of 29 pigs were used. Nucleus pulposus was harvested from lumbar discs and applied to the sacrococcygeal cauda equina following laminectomy of the first coccygeal vertebra in seven pigs. Five pigs received 1.66 microg of tumor necrosis factor-alpha, five pigs received 0.85 microg of interleukin-1beta, and five pigs received 1.66 microg of interferon-gamma. Seven pigs received autologous fat for control. Nerve conduction velocity was studied by local electrical stimulation and recordings in the tail muscles 7 days after the application.

RESULTS

Application of nucleus pulposus and fat induced similar effects as seen in previous studies, with normal nerve conduction velocity for fat and a significant reduction for nucleus pulposus. Application of both interleukin-1beta and IFN-gamma induced slight reductions of nerve conduction velocity compared with fat, but they were not statistically significant. Tumor necrosis factor-alpha, however, induced a reduction of the velocity that was even more pronounced than for nucleus pulposus.

CONCLUSION

Based on previous observations and the data of the present study, one may conclude that tumor necrosis factor-alpha from nucleus pulposus cells seems to be intimately involved with the basic pathophysiologic events leading to both nerve root dysfunction and pain after local, epidural application of nucleus pulposus. One may therefore also suspect that pharmacologic inhibition of tumor necrosis factor-alpha may at least theoretically be considered in the clinical situation with disc herniation and sciatica.

Macrophage biology and pathobiology in the evolution of immune responses: a functional analysis

A number of general principles of macrophage biology and pathobiology are formulated to define the contribution of macrophages to the kinetics and sequencing of innate and adaptive immune responses more precisely. The application of these principles to modelling immune responses and to macrophage-based treatments of immune disorders is discussed. The concept of innate peripheral tolerance is developed. It is suggested that macrophage activation could be a primary determinant of nearly every aspect of immune responsiveness, both normal and abnormal, as might be predicted from the innate immune response to 'danger' being evolutionarily more primitive than the adaptive.

Expression of constitutive endothelial and inducible nitric oxide synthase in the sciatic nerve of Lewis rats with experimental autoimmune neuritis

This study examined the expression of constitutive endothelial nitric oxide synthase (eNOS) and inducible NOS (iNOS) in the sciatic nerve of Lewis rats with experimental autoimmune neuritis (EAN). Western blot analysis showed that both eNOS and iNOS expressions in the sciatic nerves of rats increased significantly during the peak stage of EAN, but declined thereafter. Only minimal amounts of these enzymes were identified in normal rat sciatic nerves. Immunohistochemical studies showed that eNOS was increased in vascular endothelial cells and Schwann cells, but not in inflammatory cells, during the peak stage of EAN. However, iNOS was found mainly in inflammatory macrophages in sciatic nerve EAN lesions.These findings suggest that, depending on the stage of peripheral nervous system autoimmune disease, the increased expressions of both eNOS and iNOS might be involved in either the production of detrimental effects during the induction stage of EAN or in the recovery from EAN paralysis.

Metallothionein-1+2 deficiency increases brain pathology in transgenic mice with astrocyte-targeted expression of interleukin 6

Transgenic expression of IL-6 under the control of the GFAP gene promoter (GFAP-IL6 mice) in the CNS causes significant damage and alters the expression of many genes, including the metallothionein (MT) family, especially in the cerebellum. The crossing of GFAP-IL6 mice with MT-1+2 knock out (MTKO) mice provided evidence that the increased MT-1+2 expression normally observed in the GFAP-IL6 mice is an important mechanism for coping with brain damage. Thus, the GFAP-IL6xMTKO mice showed a decreased body weight gain and an impaired performance in the rota-rod test, as well as a higher upregulation of cytokines such as IL-6, IL-1alpha,beta, and TNFalpha and recruitment and activation of macrophages and T cells throughout the CNS but mainly in the cerebellum. Clear symptoms of increased oxidative stress and apoptotic cell death caused by MT-1+2 deficiency were observed in the GFAP-IL6xMTKO mice. Interestingly, MT-1+2 deficiency also altered the expected frequency of the offspring genotypes, suggesting a role of these proteins during development. Overall, the results suggest that the MT-1+2 proteins are valuable factors against cytokine-induced CNS injury.

Neuregulin: an oligodendrocyte growth factor absent in active multiple sclerosis lesions

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS) which results in demyelination and axonal injury. Conventional therapy for MS is immune suppression in the absence of agents that promote neural and glial survival or remyelination. Neuregulins are a family of ligands that exert trophic effects on both neurons and glia. Using mice bearing a null mutation in the neuregulin gene, here we demonstrate that neuregulins are necessary for the normal development of oligodendrocytes. In addition, neuregulins are produced in the normal human CNS by astrocytes as well as neurons. Astrocyte-derived neuregulin is functionally active in bioassays and exists in secreted and membrane-associated beta-isoforms. In active and chronic active MS lesions, however, the expression of astrocyte neuregulin is dramatically reduced. The absence of neuregulin in active MS lesions may contribute to the paucity of remyelination in MS.

Metallothionein-1+2 protect the CNS after a focal brain injury

We have evaluated the physiological relevance of metallothionein-1+2 (MT-1+2) in the CNS following damage caused by a focal cryolesion onto the cortex. In comparison to normal mice, transgenic mice overexpressing the MT-1 isoform (TgMTI* mice) showed a significant decrease of the number of activated microglia/macrophage and of CD3+ T lymphocytes in the area surrounding the lesion, while astrocytosis was increased. The TgMTI* mice showed a diminished peripheral macrophage but not CD3 T cell response to the cryolesion. This altered inflammatory response produced a decreased expression of the proinflammatory cytokines IL-1beta, IL-6, and TNF-alpha and an increased expression of the growth factors bFGF, TGFbeta1, and VEGF in the TgMTI* mice relative to control mice, which might be related to the increased angiogenesis and regeneration of the parenchyma of the former mice. The overexpression of MT-1 dramatically reduced the cryolesion-induced oxidative stress and neuronal apoptosis. Remarkably, these effects were also obtained by the intraperitoneal administration of MT-2 to both normal and MT-1+2 knock-out mice. These results fully support the notion that MT-1+2 are essential in the CNS for coping with focal brain injury and suggest a potential therapeutic use of these proteins.

Sublytic C5b-9-stimulated Schwann cell survival through PI 3-kinase-mediated phosphorylation of BAD

Sublytic C5b-9 induces cell cycle activation, proliferation, and rescue from apoptosis in Schwann cells. The signaling pathways for C5b-9-mediated rescue were investigated. Following serum withdrawal, DNA fragmentation, detected by TUNEL and FACS analysis, was 56.7% +/- 7.3 and 91.9% +/- 2.4 in cultured sciatic nerve Schwann cells from 6-day-old rats after 18 h and 24 h, respectively. Apoptosis was confirmed by inhibition of DNA fragmentation in a dose-dependent manner by DMQD-CHO, a caspase-3 inhibitor. Treatment with sublytic C5b-9 generated with purified components (C5*9) or Ab+C7-depleted serum (C7dHS)+C7 rescued 89% and 86% of Schwann cells, respectively, as compared with cells treated with C5*6, C8, C9, or Ab+C7dHS. Sublytic C5b-9 increased Schwann cell PI-3 kinase and Akt activity maximally at 5 min 3.14 +/- 0.5-fold and 3.56 +/- 0.4-fold, respectively, over controls. ERK-1 activity was maximally stimulated 2.98-fold at 15 min. Inhibition of PI-3 kinase by LY294002 abrogated the C5b-9-mediated Schwann cell rescue from apoptosis, while inhibition of ERK-1 with PD098,059 did not. PI-3 kinase-Akt pathway activation by C5b-9 induced, within 15 min, a 6.34 +/- 1.2-fold increase in BAD phosphorylation at Ser 136, but not at Ser 112. Downstream Bcl-x(L) protein was increased 2.61-fold +/- 0.34-fold by 18 h and 3.9-fold +/- 0.84-fold by 24 h over controls. LY294002 prevented both BAD phosphorylation at Ser 136 and Bcl-x(L) protein induction, while PD098,059 did not. Our data indicated that sublytic C5b-9 rescued Schwann cell from apoptosis via activation of PI-3 kinase-Akt, BAD phosphorylation on Ser 136 and increased expression of Bcl-x(L). Sublytic C5b-9 detected on Schwann cell in vivo during inflammatory neuropathy may facilitate survival of Schwann cell capable of remyelination.

Hypoxic-ischemic injury results in acute disruption of myelin gene expression and death of oligodendroglial precursors in neonatal mice

Studies of ischemic brain injury in neonatal rodents have focused upon the pathophysiology of neuronal damage. Much less consideration has been given to white matter injury, even though it is a major contributor to chronic neurological dysfunction in children. In the human neonate, particularly in those born prematurely, periventricular white matter is highly susceptible to hypoxic--ischemic (H--I) injury. To understand the basis for this selective vulnerability, we examined myelin gene expression and cell death in the subventricular layer and the surrounding white matter of neonatal mice following H--I insult. Using an in situ hybridization technique that gives high resolution and is very sensitive, we examined myelin basic protein and proteolipid protein gene expression three and twenty-four hours after a H-I insult. To elicit unilateral forebrain hypoxic and ischemic injury, 9--10-day-old mice underwent right carotid artery ligation followed by timed (40--70 min) exposure to 10% oxygen. Twenty-four hours following H--I, myelin basic protein and proteolipid protein transcripts were markedly reduced in striatum, external capsule, fornix, and corpus callosum in the injured side. Three hours after lesioning (ligation+70 min hypoxic exposure) myelin basic protein gene transcripts were visibly reduced in the ipsilateral white matter tracts. Interestingly, some cells in the subventricular layer expressed proteolipid protein transcripts, and 3 h after a H--I insult they were degenerating in the injured but not contralateral side. TUNEL staining showed an increase in the number of positive cells in the injured subventricular layer and corpus callosum but the adjacent striatum did not show a corresponding change in the number of TUNEL labeled cells. Ultrastructural studies of the subventricular zone and corpus callosum 3 h after H--I revealed that many subventricular cells, glial cells in the corpus callosum, and callosal axons in the injured side had already degenerated. However, the subventricular cells, glia and axons in the contralateral corpus callosum were spared. Many cells in the injured corpus callosum exhibited a apoptotic morphology; yet more mature oligodendrocytes in this region appeared normal. Our results show that a H--I insult causes a surprisingly swift and dramatic degenerative response in the subventricular layer and adjacent white matter. Within 3 h after H--I, the programmed cell death cascade was initiated; internucleosomal DNA degradation took place in subventricular and glial cells; oligodendrocyte progenitors died and axonal degeneration in the ipsilateral corpus callosum was extensive. The swiftness of the subventricular and glial cell degeneration suggests the H--I insult directly targets glia, as well as neurons, and raises the provocative question of whether glia exert damaging effects upon neurons and axons. Since the severity of the H--I insult can be modulated by varying the duration of hypoxia, the model is ideal to study whether oligodendrocyte progenitors are more susceptible to death than mature oligodendrocytes, whether mature oligodendrocytes de-differentiate and then are induced to remyelinate surviving axons, and/or whether oligodendrocyte progenitors in the subventricular layer can be stimulated to proliferate, migrate, and remyelinate the surviving axons.

Calcium signalling in cells of oligodendroglial lineage

Intracellular Ca2+ is the key signal that regulates the efficacy of neurotransmitter release and synaptic plasticity in neurons but is also an important second messenger involved in the signal transduction and modulation of gene expression in both excitable and non-excitable cells. Glial cells, including cells of oligodendroglial (OLG) lineage, are capable of responding to extracellular stimuli via changes in the intracellular Ca2+. This review article focuses on the mechanisms of Ca2+ signalling in cells of OLG lineage with the goal of providing the basis for understanding the relevance of receptor- and non-receptor-mediated signalling to oligodendroglial development, myelination, and demyelination. Conclusions to date indicate that cells of OLG lineage exhibit remarkable plasticity with regard to the expression of ion channels and receptors linked to Ca2+ signalling and that perturbation of [Ca2](i) homeostasis contributes to the pathogenesis of demyelinating diseases.

Autoantibodies to TNFalpha in HIV-1 infection: prospects for anti-cytokine vaccine therapy

Tumor necrosis factor alpha (TNFalpha) is a proinflammatory cytokine principally involved in the activation of lymphocytes in response to viral infection. TNFalpha also stimulates the production of other cytokines, activates NK cells and potentiates cell death and/or lysis in certain models of viral infection. Although TNFalpha might be expected to be a protective component of an antiviral immune response, several lines of evidence suggest that TNFalpha and other virally-induced cytokines actually may contribute to the pathogenesis of HIV infection. Based on the activation of HIV replication in response to TNFalpha, HIV appears to have evolved to take advantage of host cytokine activation pathways. Antibodies to TNFalpha are present in the serum of normal individuals as well as in certain autoimmune disorders, and may modulate disease progression in the setting of HIV infection. We examined TNFalpha-specific antibodies in HIV-infected non-progressors and healthy seronegatives; anti-TNFalpha antibody levels are significantly higher in GRIV seropositive slow/non-progressors (N = 120, mean = 0.24), compared to seronegative controls (N= 12, mean = 0.11). TNFalpha antibodies correlated positively with viral load, (P = 0.013, r = 0.282), and CD8+ cell count (P = 0.03, r = 0.258), and inversely with CD4+ cell count (P = 0.003, r = - 0.246), percent CD4+ cells (P = 0.008, r = -0.306), and CD4 :CD8 ratio (P = 0.033, r = - 0.251). TNFalpha antibodies also correlated positively with antibodies to peptides corresponding to the CD4 binding site of gp160 (P = 0.001, r = 0.384), the CD4 identity region (P = 0.016, r = 0.29), the V3 loop (P = 0.005, r = 0.34), and the amino terminus of Tat (P = 0.001, r = 0.395); TNFalpha antibodies also correlated positively with antibodies to Nef protein (P = 0.008, r = 0.302). The production of anti-TNFalpha antibodies appears to be an adaptive response to HIV infection and suggests the potential utility of modified cytokine vaccines in the treatment of HIV infections as well as AIDS-related and unrelated autoimmune and CNS disorders.

2000 Volvo Award winner in basic science studies: Exogenous tumor necrosis factor-alpha mimics nucleus pulposus-induced neuropathology. Molecular, histologic, and behavioral comparisons in rats

STUDY DESIGN

This study tested the hypothesis that the 17-kDa form of tumor necrosis factor-alpha is the pathophysiologic agent expressed by herniated nucleus pulposus in vivo that is primarily responsible for the histologic and behavioral manifestations of experimental sciatica associated with herniated lumbar discs.

OBJECTIVE

The authors determined the molecular weight and concentration of active tumor necrosis factor-alpha in rat herniated disc and used exogenous tumor necrosis factor-alpha at the same molecular weight to study its neuropathologic effect on rat nerve root and dorsal root ganglion preparations in vivo.

SUMMARY OF BACKGROUND DATA

Expressed by herniated nucleus pulposus in culture, tumor necrosis factor-alpha causes neuropathologic injury in nerve roots and neuropathic pain states in which mechanical allodynia is seen in response to peripheral stimuli.

METHODS

Western blotting was used to identify the molecular weight of the operative tumor necrosis factor-alpha protein form, and measures of optical density were used for semiquantitative determination of concentration. Plastic-embedded nerve roots and dorsal root ganglion were used for neuropathologic evaluation, and von Frey stimulation was used to quantify mechanical allodynia.

RESULTS

The 17-kDa form of tumor necrosis factor-alpha is expressed by herniated nucleus pulposus at a concentration of approximately 0.48 ng per herniated rat lumbar disc. Exogenous tumor necrosis factor-alpha applied in vivo to rat nerve roots produced neuropathologic changes and behavior deficits that mimicked experimental studies with herniated nucleus pulposus applied to nerve roots.

CONCLUSIONS

The data reinforce other evidence that tumor necrosis factor-alpha is involved in mechanisms of neuropathic pain.

Peptide T does not ameliorate experimental autoimmune encephalomyelitis (EAE) in Lewis rats

Peptide T has been shown to inhibit T cell activation and cytokine production and function. Moreover, it has been reported to be a safe treatment in humans. We have studied the ability of peptide T to prevent or ameliorate EAE in Lewis rats. Peptide T was administered subcutaneously at different doses and phases of the disease according to several treatment protocols, but we could not observe a consistent effect of peptide T ameliorating the disease. Lymph node cell proliferation and IL-4 and interferon-gamma production were also studied. We conclude that peptide T neither prevents nor ameliorates EAE in Lewis rats.

Reactions of oligodendrocytes to spinal cord injury: cell survival and myelin repair

The aim of this study was to elucidate whether oligodendrocytes die in fiber tracts that are spared by a spinal cord injury but are in close vicinity of inflammatory cells. Adult rat spinal cords were studied histologically 1 day to 2 weeks after a contusion lesion that left the ventral white matter largely intact. Massive oligodendrocyte death occurred in the lesion center, along with the death of neurons, microglia, and astrocytes. Oligodendrocytes, specifically positive for proteolipid protein (PLP) mRNA, were counted in the ventral white matter where axons at the rostral and caudal edges of the lesion were histologically intact. Although these regions contained many macrophages and neutrophils hypothesized to contribute to secondary tissue loss, there was no significant loss of oligodendrocytes. In the ventral funiculus, 3 and 6 mm rostral and caudal to the lesion, oligodendrocyte numbers were also unchanged, in spite of the presence of many activated microglial cells. From day 7 on, oligodendrocytes in close vicinity to the lesion increased their expression of PLP mRNA. We conclude that, at least within the first 2 weeks after a spinal cord contusion lesion, there is no major devastating influence of inflammatory cells or their mediators on oligodendrocytes. When death occurs, it may be due to mechanical trauma, ischemia, or excitotoxicity within the lesion or it may occur as a result of axonal degeneration.

Changes in cerebral blood flow and distribution associated with acute increases in plasma sodium and osmolality of chronic hyponatremic rats

The cause of the osmotic demyelination syndrome that follows too rapid correction of chronic hyponatremia (CHN) is unknown. Recently, we reported in CHN rats an association between blood-brain barrier (BBB) disruption occurring as early as 3 h into correction and subsequent demyelination. Given the changes in brain water and blood volume which occur during correction of CHN, we hypothesized that the same correction protocol that causes demyelination might alter cerebral blood flow (CBF) during correction, thereby possibly contributing to BBB disruption and demyelination. Ten CHN rats were given hypertonic sodium intraperitoneally and its effect on CBF was continuously monitored for 3 h by magnetic resonance flow imaging. Over the subsequent 3 h, plasma sodium rose from 110.8 to 127.6 mEq/liter (P < 0.001) but neither mean arterial blood pressure nor arterial CO(2) tension changed significantly. By 30 min, CBF increased by 50% in cortical and subcortical areas (P < 0.001) and remained elevated for the next 60 min. After 2 h, cortical flow was no longer elevated significantly and by 3 h it had returned to control values. Subcortical flow, however, significantly exceeded control values throughout the 3 h so that after 2 h the ratio of cortical to subcortical blood flow had fallen from 1.17 to 0.91 (P < 0.05). Although the mechanism by which increased plasma sodium and osmolality alters CBF is uncertain, the results suggest that changes in CBF may be part of a cascade of cerebrovascular disturbances including endothelial or parenchymal damage, mechanical events, metabolic disturbances, or cytokine release which eventually lead to BBB disruption and subsequent demyelination.

Depletion of macrophages reduces axonal degeneration and hyperalgesia following nerve injury

Inflammatory mechanisms are believed to play an important role in hyperalgesia resulting from nerve injury. Hyperalgesia following nerve injury is temporally linked with Wallerian degeneration and macrophage recruitment, and is reduced in WLD mice, in which Wallerian degeneration is delayed. We sought more direct evidence that macrophages contribute to hyperalgesia and Wallerian degeneration by depleting macrophages with liposomes loaded with dichloromethylene diphosphonate (clodronate, Cl(2)MDP). Rats were subjected to partial ligation of the sciatic nerve. Intravenous injection of liposome-encapsulated clodronate reduced the number of macrophages in the injured nerve, alleviated thermal hyperalgesia and protected both myelinated and unmyelinated fibres against degeneration. The results confirm the role of circulating monocytes/macrophages in the development of neuropathic hyperalgesia and Wallerian degeneration due to partial nerve injury. Macrophage depletion immediately after nerve injury could have some clinical potential in prevention of neuropathic pain.

Effects of aging on myelinated nerve fibers in monkey primary visual cortex

In monkeys, myelin sheaths of the axons in the vertical bundles of nerve fibers passing through the deeper layers of primary visual cortex show age-related alterations in their structure. These alterations have been examined by comparing the myelin sheaths in young monkeys, 5-10 years old, with those in old monkeys, between 25 and 33 years of age. The age-related alterations are of four basic types. In some sheaths, there is local splitting of the major dense line to accommodate dense cytoplasm derived from the oligodendrocytes. Other sheaths balloon out, and in these locations, the intraperiod line in that part of the sheath opens up to surround a fluid-filled space. Other alterations are the formation of redundant myelin so that a sheath is too large for the enclosed axon and the formation of double sheaths in which one layer of compact myelin is surrounded by another one. These alterations in myelin increase in frequency with the ages of the monkeys, and there is a significant correlation between the breakdown of the myelin and the impairments in cognition exhibited by individual monkeys. This correlation also holds even when the old monkeys, 25 to 33 years of age, are considered as a group. It is suggested that the correlation between the breakdown of myelin in the old monkeys and their impairments in cognition has not to do specifically with visual function but to the role of myelin in axonal conduction throughout the brain. The breakdown of myelin could impair cognition by leading to a change in the conduction rates along axons, resulting in a loss of synchrony in cortical neuronal circuits.

Axonal damage induced by cerebrospinal fluid from patients with relapsing-remitting multiple sclerosis

The importance of axonal damage in multiple sclerosis (MS) has been recently stressed in proton magnetic resonance spectroscopy and pathological studies, but the exact mechanism producing this damage is unknown. The aim of our study was to ascertain whether soluble mediators present in the cerebrospinal fluid (CSF) of patients with relapsing-remitting MS could induce neuron injury in culture. Different biochemical and cytochemical parameters were determined in primary embryonal rat neuron cultures following 8 days of exposure to CSF. Cytotoxic activity was evaluated with a blue formazan production colorimetric assay. Morphological and immunocytochemical studies performed with antibodies against beta-tubulin revealed neuritic fragmentation, axonal damage and cellular shrinkage indicating apoptosis. Detection of apoptosis was carried out using the fluorescent DNA-binding dye Hoechst 33342, as well as by a Terminal deoxynucleotidyl transferase-mediated dUTP Nick End-Labeling assay. We observed that soluble factors in CSF from patients with "aggressive" MS i.e, those with poor recovery after relapses, induced neurite breakdown and neuronal apoptosis in cultures. Neuron injury is not related with blood-brain barrier dysfunction nor with IgG index. Interestingly, CSF from patients with "non-aggressive" MS i.e., relapsing-remitting patients with a good recovery after relapses, did not induce any damage. In conclusion, we report that CSF from patients with aggressive MS bears soluble mediators that induce axonal damage and apoptosis of neurons in culture. These mediators can be present during the first attack of the disease, and the neuronal damage caused could be related to the functional deficit of these MS patients.

Cytokines in CNS disorders: neurotoxicity versus neuroprotection

Cytokines orchestrate T cell-mediated immune responses. In experimental autoimmune encephalomyelitis (EAE) the proinflammatory cytokines interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, IL-6, IL-12 and IL-18 are critically involved in the initiation and amplification of the local immune response in the CNS which is counter-balanced by upregulation of antiinflammatory cytokines such as IL-10. The predicted function of individual cytokines during EAE has recently been challenged by transgenic animal studies and neutralization experiments. Cytokine induction is not restricted to autoimmunity in the nervous system. Cytokines are involved in nerve regeneration and induced in focal cerebral ischemia both at the site of infarction and in remote nonischemic brain regions. In cerebral ischemia TNF-alpha and IL-1beta probably have dual functions: In concert with upregulation of inducible NO synthase (iNOS) they exert neurotoxicity while in the absence of iNOS, TNF-alpha and IL-1beta may contribute to neuroprotection and plasticity. The interplay between glial cells, infiltrating leukocytes and induced cytokines leading to CNS pathology is complex and incompletely understood. Further assessment of the functional contribution of cytokines critically depends on the elucidation of downstream secondary signaling mechanisms.

Tumor necrosis factor alpha and human Schwann cells: signalling and phenotype modulation without cell death

The aim of the study was to evaluate the biological response of human Schwann cells (SC) to tumor necrosis factor alpha (TNFalpha) in vitro and to the inflammatory milieu of chronic inflammatory demyelinating polyradiculoneuritis (CIDP). By immunocytochemical and functional assays, we found that SC expressed TNF receptors and that TNFalpha promoted in SC cultures transient activation of transcription factors NFkappaB and c-jun in the absence of apoptosis. In addition, TNFalpha significantly increased the proportion of non-myelin-forming SC expressing the p75 nerve growth factor receptor. Such phenotypic effect was dose-dependent and partially mediated by NFkappaB, as assessed by functional blockage with acetylsalicylic acid. We then extended our study to a human disease in which SC are exposed to TNFalpha. Increased signals for NFkappaB, but not c-jun, molecules were observed by immunohistochemistry on SC nuclei in nerve biopsies from patients with CIDP, as compared with controls. Irrespective of the presence of nerve inflammation, SC showed no evidence of apoptosis. Taken together, our results suggested that SC are potential targets of TNFalpha and that this cytokine exerted no cytotoxic effects either in vivo or in vitro. Rather, TNFalpha may influence the fate of SC by activating transcriptional pathways and modulating their phenotype.

The action mechanism of cyclooxygenase-2 inhibitor for treatment of experimental allergic neuritis

We previously reported the effect of a cyclooxygenase (COX)-2 inhibitor, nimesulide, on experimental allergic neuritis (EAN) in both the induction and effector phases, in contrast to the usual COX inhibitor, which was effective only when administered in the induction phase. To assess the mechanism of action of a COX-2 inhibitor, we studied the expression of COX-2 and assayed plasma levels of prostaglandins, and also compared the clinical effect of a COX-2 inhibitor with a 5-lipoxygenase (LO) inhibitor, which is responsible for another pathway of arachidonic acid metabolism. Nerves of EAN rats showed distinct expression of COX-2, which is derived mostly from endoneurial macrophages. Treatment with a COX-2 inhibitor had no effect on its expression. However, prostaglandin estradiol (E(2)) concentration of plasma was significantly lower compared with the control group. The LO inhibitor showed no clinical effect. These results suggest that a selective COX-2 inhibitor is effective in the effector phase by its influence on macrophages that are responsible for nerve degeneration.

Molecular pathogenesis of multiple sclerosis

Multiple sclerosis (MS) is best understood as an inflammatory disease of the central nervous system (CNS) white matter characterized by demyelination, focal T cell and macrophage infiltrates, axonal injury and loss of neurological function. Our current understanding invokes proinflammatory cells and mediators that may be triggered by environmental factors to mediate disease in a genetically susceptible host. Five major themes which have been associated with the pathogenesis of MS lesions will be discussed: (1) The differential activation states of myelin-reactive T cells from MS patients vs. normal individuals, (2) the selective expression of chemokines, adhesion molecules and matrix metalloproteinases, (3) the proposed roles of the B7 costimulatory pathway, (4) the proinflammatory cytokines and (5) the role of molecular mimicry.

Multiple sclerosis and central nervous system demyelination

Multiple sclerosis (MS) is characterized by multifocal areas within the CNS of demyelination with relative but not absolute axonal sparing. Initial lesion development appears dependent on T cell infiltration into the CNS; however, lesion expansion may reflect tissue injury induced by additional effector mechanisms derived from cells of the immune system and endogenous CNS cells (glial cells). This relative susceptibility to injury in MS of myelin and its cell of origin, the oligodendrocyte (OL), could reflect either the properties of the effectors or the targets. Effector-determined susceptibility could relate to presence of OL/myelin-restricted T cells or antibody. OLs, at least in vitro, express MHC class I molecules and are susceptible to CD8(+)T cell-mediated cytotoxicity. OL/myelin-specific antibodies are identified in MS lesions and could induce injury via complement- or ADCC-dependent mechanisms. OLs are susceptible to injury-mediated by non-specific cell effectors including NK cells, NK-like T cells (CD56(+)), and gamma/delta T cells via perforin/granzyme-dependent mechanisms. In vitro studies of OL injury mediated via tumor necrosis factor (TNF) and CD95 indicate that differential glial cell susceptibility to injury can depend on cell surface receptor expression and intracellular signaling pathways that are activated. These target-determined susceptibility factors may be amenable to neuroprotective therapies.

Secretory sphingomyelinase

Several physiologic and pathophysiologic processes in which sphingomyelinases (SMases) have been implicated may involve extracellular sphingomyelin (SM) hydrolysis. A candidate enzyme for these processes is a recently discovered SMase called secretory SMase, or S-SMase. S-SMase arises from the acid sphingomyelinase (ASM) gene via differential protein trafficking of a common protein precursor; this precursor can be targeted to either lysosomes or the Golgi secretory pathway. S-SMase is activated by physiologic levels of Zn2+, although the S-SMase from endothelial cells, which secrete abundant amounts of the enzyme, is partially Zn2+-independent. S-SMase functions best at acid pH but can hydrolyze certain physiologic substrates, such as atherogenic lipoproteins, at neutral pH. In endothelial cells, the secretion of S-SMase is regulated at the level of protein trafficking by inflammatory cytokines. Current work implicates a role for S-SMase in atherogenesis, and future work will be directed at understanding the potential roles of S-SMase in other processes, such as ceramide-mediated cell-signaling and the host inflammatory response.

The non-steroidal anti-inflammatory drug tepoxalin inhibits interleukin-6 and alpha1-anti-chymotrypsin synthesis in astrocytes by preventing degradation of IkappaB-alpha

Tepoxalin is a structurally and functionally novel non-steroidal anti-inflammatory drug (NSAID) with potent anti-inflammatory and analgesic properties. Apart from its inhibitory effect on cyclooxygenase activity, tepoxalin is able to inhibit production of cytokines in peripheral cells outside the CNS. No data, however, are available concerning the effects of this drug in the CNS. Since cytokines such as interleukin-1 (IL-1) or interleukin-6 (IL-6) as well as acute-phase proteins such as alpha1-anti-chymotrypsin (ACT) participate in the etiopathology of Alzheimer's disease (AD), we were interested whether tepoxalin is able to inhibit the synthesis of these immunomodulators in primary rat microglia and astrocytes as well as in the human astrocytoma cell line U373 MG. We found that tepoxalin markedly inhibits IL-1beta-induced IL-6 and ACT synthesis in astrocytes and the synthesis of IL-1beta and IL-6 in lipopolysaccharide (LPS)-stimulated microglial cells. Electrophoretic mobility shift and reporter gene assays revealed that tepoxalin exerts its inhibitory effect through the inhibition of nuclear factor kappaB (NF-kappaB), a transcription factor involved in the induction of IL-1, IL-6 and ACT gene expression. We show that inhibition of NF-kappaB activation by tepoxalin is mediated by preventing IkappaB-alpha degradation. Based on this inhibitory effect of tepoxalin on cytokine and ACT synthesis and the documented therapeutic efficacy of NSAIDs in AD, we conclude that tepoxalin may be of therapeutic benefit for the treatment of AD patients and should therefore be tested in clinical trials.

Molecular mechanisms of actions of interleukin-6 on the brain, with special reference to serotonin and the hypothalamo-pituitary-adrenocortical axis

Biological activities of the multifunctional cytokine, interleukin-6 (IL-6) include stimulation of B cell proliferation, immunoglobulin production, and initiation of the acute-phase response. IL-6 affects the CNS in that it activates the hypothalamo-pituitary-adrenocortical (HPA) axis and increases brain tryptophan and serotonin metabolism. IL-6 has been proposed as an important mediator of interaction between the neuroendocrine and immune systems. The peripheral and central effects of IL-6 are presumably mediated through its membrane receptor (IL-6R). IL-6, IL-6R and their respective mRNAs have been detected in several brain regions. Although the functions of cytokines overlap considerably, each displays its own characteristic properties. Expression of IL-6 in the brain has been observed in several CNS disorders, some of which have been associated with disorders of serotonin metabolism. It is proposed that interactions between IL-6 and brain serotonin is a complex process which involves corticotropin-releasing factor (CRF) and opioid peptides. It is likely that the molecular mechanisms underlying the actions of IL-6 on the HPA axis and its other brain functions involve the integrated effects of glutamate, Ca2+, 3',5'-cyclic AMP, protein kinase C, and other metabolic pathways.

Nerve injury, axonal degeneration and neural regeneration: basic insights

Axotomy or crush of a peripheral nerve leads to degeneration of the distal nerve stump referred to as Wallerian degeneration (WD). During WD a microenvironment is created that allows successful regrowth of nerve fibres from the proximal nerve segment. Schwann cells respond to loss of axons by extrusion of their myelin sheaths, downregulation of myelin genes, dedifferentiation and proliferation. They finally aline in tubes (Büngner bands) and express surface molecules that guide regenerating fibres. Hematogenous macrophages are rapidly recruited to the distal stump and remove the vast majority of myelin debris. Molecular changes in the distal stump include upregulation of neurotrophins, neural cell adhesion molecules, cytokines and other soluble factors and their corresponding receptors. Axonal injury not only induces muscle weakness and loss of sensation but also leads to adaptive responses and neuropathic pain. Regrowth of nerve fibres occurs with high specificity with formerly motor fibres preferentially reinnervating muscle. This involves recognition molecules of the L2/HNK-1 family. Nerve regeneration occurs at a rate of 3-4 mm/day after crush and 2-3 mm/day after sectioning a nerve. Nerve regeneration can be fostered pharmacologically. Upon reestablishment of axonal contact Schwann cells remyelinate nerve sprouts and downregulate surface molecules characteristic for precursor/premyelinating or nonmyelinating Schwann cells. At present it is unclear whether axonal regeneration after nerve injury is impeded in neuropathies.

Oligodendroglial response to the immune cytokine interferon gamma

In the human demyelinating disorder multiple sclerosis, and its animal model experimental allergic encephalomyelitis, there is a breakdown of the blood-brain barrier and an infiltration of immune cells into the CNS. Infiltrating T lymphocytes and macrophages are believed to be key mediators of the disease process. Considerable circumstantial and experimental evidence has suggested that the pleiotropic cytokine interferon gamma (IFN-gamma), which is exclusively expressed by T cells and natural killer cells, is a deleterious component of the immune response in these disorders. When experimentally introduced into the CNS IFN-gamma promotes many of the pathological changes that occur in immune-mediated demyelinating disorders. In vitro, this cytokine elicits a number of effects on oligodendrocytes, including cell death. The harmful actions of IFN-gamma on CNS myelin are likely mediated through direct effects on the myelinating cells, as well as through the activation of macrophages and microglia. In this review we summarize relevant studies concerning the action of IFN-gamma in demyelinating disorders and discuss possible mechanisms for the observed effects.

Effect of rhTNF-alpha injection into rat sciatic nerve

To assess whether TNF-alpha causes inflammatory demyelination or axonal degeneration, we injected into rat sciatic nerve saline, 100 U and 1000 U of rhTNF-alpha and studied the electrophysiological and pathological effects. At day 1 electrophysiology showed a slight reduction of proximal compound muscle action potential amplitude and pathology showed edema, inflammatory infiltration of vessel walls and endoneurium only in nerves injected with 1000 U of rhTNF-alpha. At day 5, there was no demyelination and a percentage of degenerated fibers similar in the three groups. To study the blood-nerve barrier, fluorescein isothiocyanate-labelled albumin was given intravenously after intraneural injection. The nerves injected with 1000 U rhTNF-alpha showed a leakage of the tracer in the endoneurium. TNF-alpha does not appear, at the doses used, to have myelinotoxic or axonopathic properties. The electrophysiological effect at day 1 may be due to mechanical compression of nerve fibers as a result of the blood-nerve barrier damage with consequent endoneurial edema.

Tumor necrosis factor alpha and nucleus-pulposus-induced nerve root injury

STUDY DESIGN

The effects of nucleus pulposus and various treatments to block tumor necrosis factor alpha activity were evaluated in an experimental set-up using immunohistochemistry and nerve conduction velocity recordings.

OBJECTIVES

To assess the presence of tumor necrosis factor alpha in pig nucleus pulposus cells, and to see if block of tumor necrosis factor alpha also blocks the nucleus-pulposus-induced reduction of nerve root conduction velocity.

SUMMARY AND BACKGROUND DATA

A meta-analysis of observed effects induced by nucleus pulposus revealed that these effects might relate to one specific cytokine-tumor necrosis factor alpha.

METHODS

Series-1: Cultured nucleus pulposus cells were stained immunohistologically with a monoclonal antibody for tumor necrosis factor alpha. Series-2: Nucleus pulposus was harvested from lumbar discs and applied to the sacrococcygeal cauda equina in 13 pigs autologously. Four pigs received 100 mg of doxycycline intravenously; five pigs had a blocking monoclonal antibody to tumor necrosis factor alpha applied locally in the nucleus pulposus, and four pigs remained nontreated, forming a control group. Three days after the application, the nerve root conduction velocity was determined over the application zone by local electrical stimulation.

RESULTS

Series-1: Tumor necrosis factor alpha was found to be present in the nucleus pulposus cells. Series-2: The selective antibody to tumor necrosis factor alpha limited the reduction of nerve conduction velocity, although in comparison with the control group this was not statistically significant. However, treatment with doxycycline significantly blocked the nucleus-pulposus-induced reduction of conduction velocity.

CONCLUSION

For the first time, a specific substance, tumor necrosis factor alpha, has been linked to the nucleus-pulposus-induced effects of nerve roots after local application. Although the effects of this substance may be synergistic with those of other similar substances, the data of the current study may be of significant importance for the continued understanding of nucleus pulposus' biologic activity, and of possible potential use for future strategies in managing sciatica.

Cytokine-induced transcription of protein-tyrosine-phosphatases in human astrocytoma cells

Interleukin-1 (IL-1) and Tumor Necrosis Factor-a (TNFalpha) are potent mediators of inflammatory reactions in the brain. Although much is known about the effects of IL-1 on expression of secretory proteins, few studies have addressed the question of a selective, IL-1-dependent expression of genes involved in neuromodulatory effects of inflammation. Protein-tyrosine-phosphatases (PTP's) have been shown to regulate signal transduction and adhesion processes in the developing nervous system. They are candidates for inflammation-induced neuromodulation. Therefore, we investigated if IL-1 regulates expression of PTP's. We applied a DNA-fingerprinting method based on the PCR-amplification of conserved domains of gene families and observed IL-1-dependent induction of two PTP's, cytoplasmic PTPvarepsilon and receptor-PTPgamma, RPTPgamma, in human U373-MG astrocytoma cells. Using Northern blot analysis, we confirmed this result and also show that in addition to IL-1, TNFalpha but not IL-6 induces the transcription of cytoplasmic PTPvarepsilon and RPTPgamma in human astrocytoma cells. Given the important role for PTP's in neuromodulatory aspects such as axonal guidance and neurite outgrowth, cytokine-induced induction of PTP's may play an important pathenogenic role in the development of chronic inflammatory diseases in the brain.