Interleukin-1β mediated amyloid plaque clearance is independent of CCR2 signaling in the APP/PS1 mouse model of Alzheimer's disease

Abstract

Neuroinflammation is a key component of Alzheimer's disease (AD) pathogenesis. Particularly, the proinflammatory cytokine interleukin-1 beta (IL-1β) is upregulated in human AD and believed to promote amyloid plaque deposition. However, studies from our laboratory have shown that chronic IL-1β overexpression in the APPswe/PSEN1dE9 (APP/PS1) mouse model of AD ameliorates amyloid pathology, increases plaque-associated microglia, and induces recruitment of peripheral immune cells to the brain parenchyma. To investigate the contribution of CCR2 signaling in IL-1β-mediated amyloid plaque clearance, seven month-old APP/PS1/CCR2−/− mice were intrahippocampally transduced with a recombinant adeno-associated virus serotype 2 containing the cleaved form of human IL-1β (rAAV2-IL-1β). Four weeks after rAAV2-IL-1β transduction, we found significant reductions in 6E10 and Congo red staining of amyloid plaques that was confirmed by decreased levels of insoluble Aβ1–42 and Aβ1–40 in the inflamed hippocampus. Bone marrow chimeric studies confirmed the presence of infiltrating immune cells following IL-1β overexpression and revealed that dramatic reduction of CCR2+ peripheral mononuclear cell recruitment to the inflamed hippocampus did not prevent the ability of IL-1β to induce amyloid plaque clearance. These results suggest that infiltrating CCR2+ monocytes do not contribute to IL-1β-mediated amyloid plaque clearance.