RESUMEN
Primary loss and dysfunction of astrocytes may trigger demyelination, as seen in neuromyelitis optica, an inflammatory disease of the central nervous system. In most patients affected by this disease, injury to astrocytes is initiated by the action of autoantibodies targeting aquaporin 4 (AQP-4), a water channel on astrocytes. We show here that damage of astrocytes and subsequent demyelination can also occur in the absence of autoantibody-mediated mechanisms. Following injection of lipopolysaccharide into the white matter initial microglia activation is followed by a functional disturbance of astrocytes, mainly reflected by retraction of astrocytic foot processes at the glia limitans and loss of AQP-4 and connexins, which are involved in the formation of gap junctions between astrocytes and oligodendrocytes. Demyelination and oligodendrocyte degeneration in this model follows astrocyte pathology. Similar structural abnormalities were also seen in a subset of active lesions in multiple sclerosis. Our studies suggest that astrocyte injury may be an important early step in the cascade of lesion formation in brain inflammation.
Asunto(s)
Astrocitos/inmunología , Sistema Nervioso Central/patología , Encefalomielitis Autoinmune Experimental , Inmunidad Innata , Esclerosis Múltiple/patología , Animales , Acuaporina 4/metabolismo , Astrocitos/patología , Células Cultivadas , Técnicas de Cocultivo/métodos , Modelos Animales de Enfermedad , Encefalomielitis Autoinmune Experimental/etiología , Encefalomielitis Autoinmune Experimental/inmunología , Encefalomielitis Autoinmune Experimental/patología , Regulación de la Expresión Génica/efectos de los fármacos , Regulación de la Expresión Génica/inmunología , Humanos , Proteínas de la Membrana/metabolismo , Microscopía Confocal/métodos , Esclerosis Múltiple/inmunología , Proteínas del Tejido Nervioso/metabolismo , Neuroglía/efectos de los fármacos , Polisacáridos/farmacología , Ratas , Factores de TiempoRESUMEN
Lesions obtained early in the course of multiple sclerosis (MS) have been studied immunocytochemically, and compared with the early stages of the experimental lesion induced in rats by the intraspinal injection of lipopolysaccharide. Large hemispheric or double hemispheric sections were examined from patients who had died in the course of acute or early relapsing multiple sclerosis. In MS patients exhibiting hypoxia-like lesions [Pattern III; Lucchinetti et al. Ann Neurol (2000) 47: 707-17], focal areas in the white matter showed mild oedema, microglial activation and mild axonal injury in the absence of overt demyelination. In such lesions T-cell infiltration was mild and restricted to the perivascular space. Myeloperoxidase and the inducible form of nitric oxide synthase were expressed primarily by microglia, and the activated form of these cells was associated with extracellular deposition of precipitated fibrin. In addition, these lesions showed up-regulation of proteins involved in tissue preconditioning. When active demyelination started, lesions were associated with massive T-cell infiltration and microglia and macrophages expressed all activation markers studied. Similar tissue alterations were found in rats in the pre-demyelinating stage of lesions induced by the focal injection of bacterial lipopolysaccharide into the spinal white matter. We suggest that the areas of microglial activation represent an early stage of tissue injury, which precedes the formation of hypoxia-like demyelinated plaques. The findings indicate that mechanisms associated with innate immunity may play a role in the formation of hypoxia-like demyelinating lesions in MS.
Asunto(s)
Encéfalo/inmunología , Esclerosis Múltiple/inmunología , Linfocitos T/inmunología , Adulto , Anciano , Anciano de 80 o más Años , Animales , Axones/patología , Encéfalo/patología , Estudios de Casos y Controles , Citotoxicidad Inmunológica , Encefalomielitis Autoinmune Experimental , Femenino , Humanos , Hipoxia/inmunología , Hipoxia/metabolismo , Inmunidad Innata , Inmunohistoquímica , Lipopolisacáridos , Macrófagos/patología , Masculino , Microglía/patología , Microscopía Fluorescente , Persona de Mediana Edad , Esclerosis Múltiple/metabolismo , Esclerosis Múltiple/patología , Óxido Nítrico Sintasa/metabolismo , Oligodendroglía/patología , Ratas , Ratas Sprague-Dawley , Estadísticas no ParamétricasRESUMEN
Inflammation is a prominent feature of several disorders characterized by primary demyelination, but it is not clear whether a relationship exists between inflammation and myelin damage. We have found that substantial demyelination results from the focal inflammatory lesion caused by the injection of lipopolysaccharide (LPS; 200 ng) directly into the rat dorsal funiculus. Within 24 h, such injections caused a focal inflammatory response consisting of a substantial number of polymorphonuclear cells and ED1-positive and inducible nitric oxide synthase (iNOS)-positive macrophages/microglia. The number of inflammatory cells was substantially reduced by day 7. OX-52-positive T-cells were less frequently observed but were present in the meninges at 8 h, reached a maximum in the dorsal funiculus at 7 days, and were rare at 14 days. The inflammation was followed by the appearance of a large lesion of primary demyelination that encompassed up to approximately 75% of the cross-sectional area of the dorsal funiculus. Treatment with dexamethasone significantly reduced the number of cells expressing iNOS, but did not prevent the demyelination. By 28 days the lesions were largely remyelinated, usually by Schwann cells. These changes were not observed in control, saline-injected animals. We conclude that the intraspinal injection of LPS results in inflammation and subsequently in prominent demyelination. The mechanisms underlying the demyelination are not clear, but it is notable that it typically begins with disruption of the adaxonal myelin. Indeed, there is an early loss of myelin-associated glycoprotein within the lesion, despite the persistence of proteolipid protein. This combination is a feature of the pattern III lesion recently described in multiple sclerosis (Lucchinetti et al., 2000), and we therefore suggest that LPS-induced demyelination may serve as the first experimental model available for the study of this type of multiple sclerosis lesion.
Asunto(s)
Enfermedades Desmielinizantes/inmunología , Lipopolisacáridos/farmacología , Modelos Animales , Esclerosis Múltiple , Animales , Enfermedades Desmielinizantes/microbiología , Enfermedades Desmielinizantes/patología , Dexametasona/uso terapéutico , Escherichia coli , Ganglios Espinales/inmunología , Ganglios Espinales/microbiología , Ganglios Espinales/patología , Glucocorticoides/uso terapéutico , Inmunohistoquímica/métodos , Inflamación , Inyecciones Espinales , Molécula 1 de Adhesión Intercelular/análisis , Interleucina-1/análisis , Activación de Macrófagos , Masculino , Microglía/inmunología , Infiltración Neutrófila , Óxido Nítrico Sintasa/análisis , Óxido Nítrico Sintasa de Tipo II , Ratas , Ratas Sprague-Dawley , Salmonella , Células de Schwann/patología , Linfocitos T/inmunología , Linfocitos T/metabolismo , Factores de TiempoRESUMEN
Long-term disability in Guillain-Barré syndrome (GBS) is associated with axonal, and some neuronal, degeneration. Brain-derived neurotrophic factor (BDNF) can prevent neuronal death following damage to motor axons and we have therefore examined the ability of BDNF to ameliorate the effects of experimental autoimmune neuritis (EAN), a model of GBS. Treatment of Lewis rats with BDNF (10 mg/kg/day) did not significantly affect the neurological deficit, nor significantly improve survival, motor function or motor innervation. The weight of the urinary bladder was significantly increased in control animals with EAN, but remained similar to normal in animals treated with BDNF. With the exception of a possibly protective effect indicated by bladder weight, this study suggests that BDNF may not provide an effective therapy for GBS, at least in the acute phase of the disease.