RESUMEN
Microglial activation by blood-borne factors following blood-brain barrier damage may play a significant role in subsequent neuropathogenesis of several neurodegenerative diseases. Exposure of primary cultured rat brain microglia to pure, fatty acid- and lipid-deficient rat serum albumin or fraction V, (fatty acid and lipid-containing rat serum albumin), caused inducible nitric oxide synthase (iNOS) expression, glutamate release, tumour necrosis factor alpha (TNFalpha) and transforming growth factor-beta1 release. iNOS expression was attenuated by the MAPK/extracellular signal-regulated kinase pathway inhibitor U0126 and the phosphorylated forms of extracellular signal-regulated kinase 1 and 2 were detectable in microglia treated with albumin or fraction V. Glutamate release was prevented by l-alpha-aminoadipate and glutathione levels in microglia rose on exposure to albumin. Conditioned medium from microglia exposed to albumin or fraction V was neurotoxic. Peripheral macrophages were resistant to the effects of albumin but both microglia and macrophages responded to lipopolysaccharide, which induced interleukin-1 beta and tumour necrosis factor alpha release, cyclooxygenase-2 and iNOS expression in both cell types, indicating a discrete desensitised pathway in macrophages for albumin which was not desensitised in microglia. Thus, exposure of microglia in the brain to albumin may contribute to neuronal damage following blood-brain barrier breakdown and point to resident microglia rather than infiltrating macrophages as therapeutic targets.
Asunto(s)
Diferenciación Celular/efectos de los fármacos , Macrófagos Peritoneales/efectos de los fármacos , Microglía/efectos de los fármacos , Albúmina Sérica/farmacología , 6-Ciano 7-nitroquinoxalina 2,3-diona/farmacología , Animales , Animales Recién Nacidos , Caspasas/metabolismo , Muerte Celular/efectos de los fármacos , Células Cultivadas , Cerebelo/citología , Medios de Cultivo Condicionados/farmacología , Ciclooxigenasa 2/metabolismo , Citocinas/metabolismo , Relación Dosis-Respuesta a Droga , Antagonistas de Aminoácidos Excitadores/farmacología , Regulación de la Expresión Génica/efectos de los fármacos , Ácido Glutámico/metabolismo , Glutatión/metabolismo , Lipopolisacáridos/farmacología , Macrófagos Peritoneales/química , Microglía/química , Neuronas/efectos de los fármacos , Óxido Nítrico/metabolismo , Óxido Nítrico Sintasa de Tipo II/metabolismo , Polimixina B/farmacología , Ratas , Ratas Wistar , Factores de TiempoRESUMEN
Microglia are present in an activated state in multiple sclerosis lesions. Incubation of primary cultured rat microglia with rat-brain derived myelin (0.1-1 microg/mL) for 24 h induced microglial activation; cells displayed enhanced ED1 staining, expression of inducible nitric oxide synthase, production and release of the cytokine tumour necrosis factor-alpha and glutamate release. Exposure of microglia to myelin induced the expression of neuronal caspases and ultimately neuronal death in cultured cerebellar granule cell neurons; neurotoxicity was directly because of microglial-derived soluble toxins. Co-incubation of microglia with agonists or antagonists of different metabotropic glutamate receptor (mGluR) subtypes ameliorated microglial neurotoxicity by inhibiting soluble neurotoxin production. Activation of microglial mGluR2 exacerbated myelin-evoked neurotoxicity whilst activation of mGluR3 was protective as was activation of group III mGluRs. These data show that myelin-induced microglial neurotoxicity can be prevented by regulation of mGluRs and suggest these receptors on microglia may be promising targets for therapeutic intervention in multiple sclerosis.
