Amyloid-β peptides inhibit the expression of AQP4 and glutamate transporter EAAC1 in insulin-treated C6 glioma cells

Astrocytic aquaporin 4 (AQP4) facilitates glutamate clearance via regulation of the glutamate transporter function, involved in the modulation of brain plasticity and cognitive function to prevent neurodegenerative disorders such as Alzheimer's disease (AD). In in vitro studies, the C6 rat glioma cell line is a widely applied aging model system to investigate changes in glial cells associated with aging or AD. However, the neurotoxicity mechanism whether AQP4 mediate glutamate uptake in A beta-stimulated C6 cell remain uncertain. In this study, we examined the effects of A beta on the expression of AQP4, Glu transporters, Glu uptake, and cell viability in insulintreated C6 cells. Our results showed that the expression of AQP4 mRNA and protein was significantly enhanced by insulin in older cultures (passage 45), and the expression was inhibited by A beta at 10 mu M. In addition, the cell viability and glutamate uptake in A beta-treated C6 cells were decreased in dose-dependent manners. GFAP showed similar changes in gene and protein expression patterns as AQP4, but no significant alterations were seen in GLAST expression. In C6 cells, the glutamate transport was found to be EAAC1, not GLT-1. EAAC1 expression was decreased by the treatment of A beta. Taken together, our findings suggest that C6 cells may have astrocytic characteristics, and the astrocytic cytotoxicity induced by A beta was mediated by reduction of glutamate uptake through AQP4/EAAC1 pathway in C6 cells. This indicates that C6 glioma cells could be used to study the roles of AQP4 on astrocyte function in AD.