An in vitro model for the study of microglia-induced neurodegeneration: involvement of nitric oxide and tumor necrosis factor-alpha

The precise function of activated microglia and their secretory products re mains controversial. In order to assess the role of microglial secretion pr oducts, we established an in vitro model of an inflammatory reaction in the brain by co-culturing microglial and neuronal cell lines. Upon stimulation with interferon-gamma and lipopolysaccharides, the microglial cells adopte d an activated phenotype and secreted tumor necrosis factor-alpha (TNF-alph a), prostaglandin E-2 and nitric oxide (NO). Neuronal degeneration was quan tified by measuring the concentrations of microtubule associated protein ta u and neuron specific enolase, which are also used as diagnostic tool in Al zheimer's disease, in supernatants. In activated contact co-cultures, the l evels of these neuronal markers were significantly raised compared to non-a ctivated co-cultures. NO-synthase inhibitors significantly diminished the r ise of tau in activated co-cultures, while indomethacin, superoxide dismuta se, or a neutralizing TNF-alpha antibody did not. When a chemical NO-donor or TNF-alpha were added to pure neuronal cultures, cell viability was signi ficantly reduced. TNF-alpha increased neuronal sensitivity towards NO. Ther e were indications that a part of the cells died by apoptosis. This model d emonstrates a neurotoxic role for NO in microglia-induced neurodegeneration and provides a valuable in vitro tool for the study of microglia-neuron in teractions during inflammation in the brain. (C) 2001 Elsevier Science Ltd. All rights reserved.