ABSTRACT
AIMS: Lower androgen level in elderly men is a risk factor of Alzheimer's disease (AD). It has been reported that androgen reduces amyloid peptides (Aß) production and increases Aß degradation by neurons. Activated microglia are involved in AD by either clearing Aß deposits through uptake of Aß or releasing cytotoxic substances and pro-inflammatory cytokines. Here, we investigated the effect of androgen on Aß uptake and clearance and Aß-induced inflammatory response in microglia, on neuronal death induced by Aß-activated microglia, and explored underlying mechanisms. METHODS: Intracellular and extracellular Aß were examined by immunofluorescence staining and Western blot. Amyloid peptides (Aß) receptors, Aß degrading enzymes, and pro-inflammatory cytokines were detected by RT-PCR, real-time PCR, and ELISA. Phosphorylation of MAP kinases and NF-κB was examined by Western blot. RESULTS: We found that physiological concentrations of androgen enhanced Aß42 uptake and clearance, suppressed Aß42 -induced IL-1ß and TNFα expression by murine microglia cell line N9 and primary microglia, and alleviated neuronal death induced by Aß42 -activated microglia. Androgen administration also reduced Aß42 -induced IL-1ß expression and neuronal death in murine hippocampus. Mechanistic studies revealed that androgen promoted microglia to phagocytose and degrade Aß42 through upregulating formyl peptide receptor 2 and endothelin-converting enzyme 1c expression, and inhibited Aß42 -induced pro-inflammatory cytokines expression via suppressing MAPK p38 and NF-κB activation by Aß42 , in an androgen receptor independent manner. CONCLUSION: Our study demonstrates that androgen promotes microglia to phagocytose and clear Aß42 and inhibits Aß42 -induced inflammatory response, which may play an important role in reducing the neurotoxicity of Aß.
