Insulin-Resistant Brain State after Intracerebroventricular Streptozotocin Injection Exacerbates Alzheimer-like Changes in Tg2576 AβPP-Overexpressing Mice

For studying rare hereditary Alzheimer's disease (AD), transgenic (Tg) animal models overexpressing amyloid-beta protein precursor (AbetaPP) followed by increased amyloid-beta (Abeta) formation are used. In contrast, sporadic AD has been proposed to start with an insulin-resistant brain state (IRBS).We investigated the effect of IRBS induced by intracerebroventricularly (icv) administered streptozotocin (STZ) on behavior, glycogen synthase kinase-3 (GSK) alpha/beta content, and the formation of AD-like morphological hallmarks Abeta and tau protein in AbetaPP Tg2576 mice. Nine-month-old Tg mice were investigated 6 months after a single icv injection of STZ or placebo. Spatial cognition was analyzed using the Morris water maze test. Soluble and aggregated Abeta40/42 fragments, total and phosphorylated tau protein, and GSK-3alpha/beta were determined by ELISA. Cerebral (immuno)histological analyses were performed. In Tg mice, STZ treatment increased mortality, reduced spatial cognition, and increased cerebral aggregated Abeta fragments, total tau protein, and congophilic amyloid deposits. These changes were associated with decreased GSK-3alpha/beta ratio (phosphorylated/total). A linear negative correlation was detected between Abeta42 and cognition, and between GSK-3alpha/beta ratio and aggregated Abeta40+42. No marked necrotic and apoptotic changes were observed. In conclusion, IRBS may aggravate AD-like changes such as behavioral and increase the formation of pathomorphological AD hallmarks via GSK-3alpha/beta pathway in AbetaPP-overexpressing mice.