Terence Smith

Autoimmune encephalomyelitis ameliorated by AMPA antagonists

Multiple sclerosis is an immune-mediated disorder of the central nervous system leading to progressive decline of motor and sensory functions and permanent disability. The therapy of multiple sclerosis is only partially effective, despite anti-inflammatory, immunosuppresive and immunomodulatory measures. White matter inflammation and loss of myelin, the pathological hallmarks of multiple sclerosis, are thought to determine disease severity. Experimental autoimmune encephalomyelitis reproduces the features of multiple sclerosis in rodents and in nonhuman primates. The dominant early clinical symptom of acute autoimmune encephalomyelitis is progressive ascending muscle weakness. However, demyelination may not be profound and its extent may not correlate with severity of neurological decline, indicating that targets unrelated to myelin or oligodendrocytes may contribute to the pathogenesis of acute autoimmune encephalomyelitis. Here we report that within the spinal cord in the course of autoimmune encephalomyelitis not only myelin but also neurons are subject to lymphocyte attack and may degenerate. Blockade of glutamate AMPA receptors ameliorated the neurological sequelae of autoimmune encephalomyelitis, indicating the potential for AMPA antagonists in the therapy of multiple sclerosis.

Glutamate Receptor Expression in Multiple Sclerosis Lesions

Blockade of receptors for the excitatory neurotransmitter glutamate ameliorates neurological clinical signs in models of the CNS inflammatory demyelinating disease multiple sclerosis (MS). To investigate whether glutamate excitoxicity may play a role in MS pathogenesis, the cellular localization of glutamate and its receptors, transporters and enzymes was examined. Expression of glutamate receptor (GluR) 1, a Ca++‐permeable ionotropic AMPA receptor subunit, was up‐regulated on oligodendrocytes in active MS lesion borders, but Ca++‐impermeable AMPA GluR2 subunit levels were not increased. Reactive astrocytes in active plaques expressed AMPA GluR3 and metabotropic mGluR1, 2/3 and 5 receptors and the GLT‐1 transporter, and a subpopulation was immunostained with glutamate antibodies. Activated microglia and macrophages were immunopositive for GluR2, GluR4 and NMDA receptor subunit 1. Kainate receptor GluR5–7 immunostaining showed endothelial cells and dystrophic axons. Astrocyte and macrophage populations expressed glutamate metabolizing enzymes and unexpectedly the EAAC1 transporter, which may play a role in glutamate uptake in lesions. Thus, reactive astrocytes in MS white matter lesions are equipped for a protective role in sequestering and metabolizing extracellular glutamate. However, they may be unable to maintain glutamate at levels low enough to protect oligodendrocytes rendered vulnerable to excitotoxic damage because of GluR1 up‐regulation.

Altered expression of glutamate transporters in experimental autoimmune encephalomyelitis.

Amelioration of experimental autoimmune encephalomyelitis (EAE) by blockade of the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor, 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(f)quinoxaline (NBQX), has been recently demonstrated [Nat. Med. 6 (2000) 67; Nat. Med. 6 (2000) 62]. However, the mechanisms underlying regulation of the extracellular glutamate concentration in EAE are unclear. To address this, we examined the expression of three distinct Na(+)-dependent glutamate transporters (GLT-1, GLAST and EAAC1) in the spinal cord of the Lewis rat EAE. EAE induced a dramatic increase in EAAC1 protein and mRNA levels, which corresponded closely with the course of neurological symptoms. In contrast, the levels of GLT-1 and GLAST protein were down-regulated in the spinal cord at the peak of disease symptoms, and no recovery was observed after remission. Furthermore, these changes in GLT-1, GLAST and EAAC1 expression were suppressed by treatment with NBQX. These results suggest that AMPA receptor activation precedes the altered expression of glutamate transporters, and that the dysregulation of extracellular glutamate concentration might play a critical role in pathological changes and neuronal dysfunction in EAE.

Multiple Sclerosis and Glutamate

Abstract: Experimental autoimmune encephalomyelitis reproduces in rodents the features of multiple sclerosis, an immune‐mediated, disabling disorder of the human nervous system. No adequate therapy is available for multiple sclerosis, despite anti‐inflammatory, immunosuppressive, and immunomodulatory measures. Increasingly glutamate is implicated in the pathogenesis of neurodegenerative diseases. Here we (1) review changes in the glutamatergic system in multiple sclerosis and (2) reveal the effects of glutamate AMPA antagonists in acute and chronic rodent models of multiple sclerosis. Administration of structurally diverse competitive and non‐competitive AMPA antagonists reduces neurologic disability in rodents subjected to acute experimental autoimmune encephalomyelitis. In addition, AMPA antagonists are active in both the adoptive transfer and in chronic models of experimental autoimmune encephalomyelitis in rats and mice and affect both the acute and chronic relapsing phases. Moreover, short‐term therapy with AMPA antagonists leads to sustained benefit well into the progressive phases. These results imply that therapeutic strategies for multiple sclerosis should be complemented by glutamate AMPA antagonists to reduce neurologic disability.

Treatment with BBB022A or rolipram stabilizes the blood-brain barrier in experimental autoimmune encephalomyelitis: an additional mechanism for the therapeutic effect of type IV phosphodiesterase inhibitors

We examined the treatment effects of two structurally distinct phosphodiesterase type IV (PDE IV) inhibitors, BBB022 and rolipram, in murine and rat models of experimental autoimmune encephalomyelitis (EAE). Based on our data, we propose a mechanism of action which may supplement immunomodulatory effects of PDE IV inhibitors. In particular, PDE inhibitors promote elevation of intracellular cAMP levels, increasing the electrical resistance of endothelial monolayers by stabilizing intercellular junctional complexes. Such an effect on central nervous system (CNS) vascular endothelium has the potential to reduce disease severity in EAE, because both inflammatory cells and humoral factors readily cross a disrupted blood-brain barrier (BBB). In this report, we demonstrate the capacity of BBB022 and rolipram to decrease clinical severity of EAE. further, PDE IV inhibitors significantly reduced BBB permeability in the spinal cords of mice with EAE. These results provide evidence that PDE IV-inhibitors may exert therapeutic effects in EAE by modifying cerebrovascular endothelial permeability, reducing tissue edema as well as entry of inflammatory cells and factors.

ADAM-17 and TIMP3 protein and mRNA expression in spinal cord white matter of rats with acute experimental autoimmune encephalomyelitis.

Tumour necrosis factor (TNF) is a major immunomodulatory and proinflammatory cytokine implicated in the pathogenesis of multiple sclerosis (MS) and the animal model experimental autoimmune encephalomyelitis (EAE). ADAM-17 cleaves membrane-bound TNF into its soluble form. The distribution and level of ADAM-17 expression within spinal cords of Lewis rats with EAE was investigated. ADAM-17 was associated with endothelial cells in the naïve and pre-disease spinal cords. In peak disease astrocytic and inflammatory cells expressed ADAM-17. Upregulation of ADAM-17 mRNA expression was coupled with a decrease in mRNA levels of its inhibitor TIMP3 suggesting a role for ADAM-17 in EAE pathogenesis.

INAUGURAL MEETING OF THE BRAIN-IMMUNE NETWORK GROUP (BING)

In recent years a substantial amount of evidence has accumulated to suggest that the central nervous system is not only capable of regulating virtually all aspects of immunity in a wide variety of experimental and real life settings, but that the immune system feeds back information to the central nervous system, modulating its function. Interest in the interactions between the behavioural, immune and neuroendocrine systems is reflected by the number of new journals devoted to this topic. A number of societies have held symposia on some aspect of this work, for example the British Society for Immunology organised John Mason Conference on Stress and Immune Responses held in Newcastle (15/9/95). However, there has not been a specific UK forum for scientists and clinicians interested in this area to meet and discuss their work. It was to provide such a forum and address this perceived need that the Brain-Immune Network Group (BING) was founded. The inaugural meeting was held at The National Hospital for Neurology & Neurosurgery, Queen Square, London on November 10th 1995. This meeting brought together many of the top European and North American scientists in the field to discuss the complexity of the bidirectional communication between the brain and the immune system, and the biological relevance of this data. Despite competition from the Society for Neurosciences meeting in the USA the meeting attracted 95 delegates from 10 countries reflecting the international need for such a forum in Europe. The delegates were evenly split between the three broad subject areas and represented both the basic and the clinical sciences. There were 4 plenary lectures, 8 oral communications and 17 posters which generated a great deal of interest and discussion. We present a summary of that discussion.

The hypothalamo-pituitary-adrenal axis in experimental allergic encephalomyelitis: activation and apoptosis

Myelination in the central nervous system involves interactions between oligodendrocytes, the extracellular matrix and axons; however, few molecules mediating this process have been characterised. A better understanding of myelination may indicate why remyelination fails in multiple sclerosis. Our studies on proteins in isolated myelin membrane preparations led to the identification of a novel myelin/oligodendrocyte-associated metalloprotease (MOM). The cDNA sequence of MOM suggests that it may be involved in cell-cell and cell-extracellular matrix interactions. We now aim to quantify MOM expression relative to periods of myelination and to identify molecules with which MOM interacts.