Chronic IL-1β-Mediated Neuroinflammation Mitigates Amyloid Pathology in a Mouse Model of Alzheimer's Disease without Inducing Overt Neurodegeneration

Neuroinflammation is a local tissue response to injurious stimuli in the central nervous system (CNS) and is characterized by glial reactivity, induction of cytokines and chemokines, and vascular permeability. The cytokine interleukin (IL)-1 beta is rapidly induced following CNS insult, and is chronically expressed in neurodegenerative disorders such as Alzheimer's disease (AD). We recently developed a novel method of sustained IL-1 beta production in the brain to study the link between IL-1 beta and AD pathogenesis. Utilizing this model, we have previously demonstrated reduction of plaque size and frequency accompanied by a robust neuroinflammatory response. These observations were limited to a single early time point in the course of AD plaque deposition and did not investigate other neurodegenerative endpoints. To extend these observations to other stages of disease progression and evaluate additional pathologic markers, we investigated the effects of age and duration of IL-1 beta overexpression in the APPswe/PS-1dE9 AD model on a congenic C57BL/6 background. We now report that IL1 beta overexpression leads to decreased 6E10 immunopositive plaque pathology regardless of age or duration. We also investigated whether IL-1 beta overexpression led to neuronal apoptosis or cholinergic axonal degeneration in the context of this AD model. Although we could demonstrate apoptosis of infiltrating inflammatory cells, we found no evidence for IL-1 associated apoptosis of neurons or cholinergic axon degeneration even after 5 months of chronic neuroinflammation. Together, these observations point to a neuroprotective role for IL-1 beta in AD neuropathogenesis.