Neutralization of granulocyte macrophage colony-stimulating factor decreases amyloid beta 1-42 and suppresses microglial activity in a transgenic mouse model of Alzheimer's disease

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Abstract
The purpose of our study was to investigate microglia and astrocytes that are associated with human mutant amyloid precursor protein and amyloid beta (Aβ). We investigated whether the anti-granulocyte–macrophage-colony stimulating factor (GM-CSF) antibody can suppress microglial activity and decrease Aβ production in Alzheimer's disease transgenic mice (Tg2576 line). An antibody to mouse GM-CSF was introduced by intracerebroventricular (ICV) injections into the brains of 10-month-old Tg2576 male mice. We assessed the effect of several GM-CSF-associated cytokines on microglial activities and their association with Aβ using quantitative real-time RT–PCR, immunoblotting, immunohistochemistry analyses in anti-GM-CSF antibody-injected Tg2576 mice. Using sandwich ELISA technique, we measured intraneuronal Aβ in Tg2576 mice injected with GM-CSF antibody and PBS vehicle-injected control Tg2576 mice. Using double-labeling immunofluorescence analysis of intraneuronal Aβ, Aβ deposits and pro-inflammatory cytokines, we assessed the relationship between Aβ deposits and microglial markers in the Tg2576 mice, and also in the anti-GM-CSF antibody-injected Tg2576 mice. Our real-time RT–PCR analysis showed an increase in the mRNA expression of IL6, CD11c, IL1β, CD40 and CD11b in the cerebral cortices of the Tg2576 mice compared with their littermate non-transgenic controls. Immunohistochemistry findings of microglial markers agreed with our real-time RT–PCR results. Interestingly, we found significantly decreased levels of activated microglia and Aβ deposits in anti-GM-CSF antibody-injected Tg2576 mice compared with PBS vehicle-injected Tg2576 mice. Findings from our real-time RT–PCR and immunoblotting analysis agreed with immunohistochemistry results. Our double-labeling analyses of intraneuronal Aβ and CD40 revealed that intraneuronal Aβ is associated with neuronal expression of CD40 in Tg2576 mice. Our quantitative sandwich ELISA analysis revealed decreased levels of soluble Aβ1-42 and increased levels of Aβ1-40 in Tg2576 mice injected with the anti-GM-CSF antibody, suggesting that anti-GM-CSF antibody alone decreases soluble Aβ1-42 production and suppresses microglial activity in Tg2576 mice. These findings indicating the ability of the anti-GM-CSF antibody to reduce Aβ1-42 and microglial activity in Tg2576 mice may have therapeutic implications for Alzheimer's disease.