IL-6 trans-signaling in the brain influences the behavioral and physio-pathological phenotype of the Tg2576 and 3xTgAD mouse models of Alzheimer’s disease

Alzheimer's disease (AD) is the most commonly diagnosed dementia but its underlying pathological mechanisms still unclear. Neuroinflammation and secretion of cytokines such as interleukin-6 (IL-6) accompany the main hallmarks of the disease: amyloid plaques and neurofibrillary tangles. In this study, we analyzed the role of IL-6 trans-signaling in two mouse models of AD, Tg2576 and 3xTg-AD mice. The inhibition of IL-6 trans-signaling partially rescued the AD-induced mortality in females of both models. Before amyloid plaques deposition, it reversed AD-induced changes in exploration and anxiety (but did not affect locomotion) in Tg2576 female mice. However, after plaque deposition the only behavioral trait affected by the inhibition of IL-6 trans-signaling was locomotion. Results in the Morris water maze suggest that cognitive flexibility was reduced by the blocking of the IL-6 trans-signaling in young and old Tg2576 female mice. The inhibition of IL-6 trans-signaling also decreased amyloid plaque burden in cortex and hippocampus, and Aβ40 and Aβ42 levels in the cortex, of Tg2576 female mice. The aforementioned changes might be correlated with changes in blood vessels and matrix structure and organization rather than changes in neuroinflammation. 3xTgAD mice showed a very mild phenotype regarding amyloid cascade, but results were in accordance with those of Tg2576 mice. These results strongly suggest that the inhibition of the IL-6 trans-signaling could represent a powerful therapeutic target in AD.