Investigation of the effect and underlying mechanism of microglia on beta-amyloid protein mediated neurotoxicity

• Main Authors: Chia-ping Chen, 陳嘉萍
• Other Authors: Young-ji Shiao
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/44173164912324616500

碩士 === 國立陽明大學 === 生物藥學研究所 === 92 === There are two pathological hallmarks in the patients of Alzheimer’s disease (AD), including extracellular senile plaque and intracellular neurofibrillary tangels in the cortex and hippocampus. Senile plaque is composed of amyloid fibril and surrounded by activated microglial cells. Therefore, both amyloid beta-peptide (A□) and microglia are pivotal in the pathogensis of AD. Nevertheless, it is still unclear that A□-mediated activation of microgla causes the neuronal toxicity or the activation of microglia is only the consequence of neural death induced by A□. In the present study we attempt to delineate the interaction between A□, neurons, and microglial cells. The results will address the cause-consequence relationship between these three items. Two types of microglia, type A and B, had been identified by specific culture condition in the present study. Type A and type B microglia were morphologically similar to microglial progenitor and resting microglia, respectively. Two types of microglia expressed the microphage marker cluster of differentiation 11b (CD11b) and CD68, whereas they did not contain CD11c, microphage inflammatory protein-1□ (MIP-1□), interleukin-1□ (IL-1□), tumor necrosis factor-□ (TNF-□), and inducible nitric oxide synthase (iNOS). Two types of cells displayed distinct responses to LPS stimulation including 1) LPS induced the expression of CD11c and MIP-1□ in type B but not type A cells, 2) LPS elevated the level of CD 68 in type B cells but showed opposite effect for type A cells, 3) the LPS-mediated secretion of IL-1□, TNF-□, and nitric oxide was prominent for type B cells and to lesser extent for type A cells, and 4) LPS provoked the proliferation of type A but not type B cells. Interferon-□ (IFN-□) promoted the proliferation of both type A and type B cells, whereas it exerted differential effect on the nitric oxide production in both types of cells. Treatment with IFN-□ induced the production of nitric oxide in type B cells only, but it did increase the LPS-induced production of nitric oxide in type A cells. The effects of three kinds of A□ (A□25-35, oligomer form of A□1-42, and fibril form of A□1-42) and conditioned medium of A□-stimulated neuron (CMAN) on type A and type B microglia were further investigated. Only treatment of A□25-35 induced the expression of MIP-1□ in type A microglia. All three kinds of A□ provoked the secretion of TNF-□ in type B cells, whereas only A□25-35 induced the secretion of IL-1□ in both types of microglia. The A□25-35-CMAN exerted lesser cytotoxicity than the A□25-35 alone for type B microglia. The adjacent distance co-culture type A but not type B microglia with neurons showed protective effect on the toxicity of A□25-35. The conditioned medium from A□-stimulated microglia was used to elucidate the interaction of A□, microglia and neurons. The results demonstrated that the conditioned medium from either type A microglia treated with high concentration of A□25-35 or type B microglia treated with fibril A□1-42 exerted higher toxicity than A□ alone. Therefore, two types of microglia displayed specific characteristic in response to different insults in several respects including the expression of chemoattractive factor, secretion of proinflammatory cytokines, and neuron toxicity. These events may be implicated in the pathogenesis of AD.