Sustained Interleukin-1β Overexpression Exacerbates Tau Pathology Despite Reduced Amyloid Burden in an Alzheimer's Mouse Model

Neuroinflammation is an important component of Alzheimer's disease (AD) pathogenesis and has been implicated in neurodegeneration. Interleukin-1 (IL-1), a potent inflammatory cytokine in the CNS, is chronically upregulated in human AD and believed to serve as part of a vicious inflammatory cycle that drives AD pathology. To further understand the role of IL-1 beta in AD pathogenesis, we used an inducible model of sustained IL-1 beta overexpression (IL-1 beta(XAT)) developed in our laboratory. The triple transgenic mouse model of AD, which develops plaques and tangles later in its life cycle, was bred with IL-1 beta(XAT) mice, and effects of IL-1 beta overexpression on AD pathology were assessed in F1 progeny. After 1 and 3 months of transgene expression, we found robust increases in tau phosphorylation despite an similar to 70-80% reduction in amyloid load and fourfold to sixfold increase in plaque-associated microglia, as well as evidence of greater microglial activation at the site of inflammation. We also found evidence of increased p38 mitogen-activated protein kinase and glycogen synthase kinase-3 beta activity, which are believed to contribute to tau phosphorylation. Thus, neuroinflammation regulates amyloid and tau pathology in opposing ways, suggesting that it provides a link between amyloid accumulation and changes in tau and raising concerns about the use of immunomodulatory therapies in AD.