Enhanced susceptibility of S‐100B transgenic mice to neuroinflammation and neuronal dysfunction induced by intracerebroventricular infusion of human β‐amyloid

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Abstract
S-100B is an astrocyte-derived protein that is increased in focal areas of the brain most severely affected by neuropathological changes in Alzheimer's disease (AD). Cell-based and clinical studies have implicated S-100B in progression of a pathologic, glial-mediated pro-inflammatory state in the CNS. However, the relationship between S-100B levels and susceptibility to AD-relevant neuroinflammation and neuronal dysfunction in vivo has not been determined. To test the hypothesis that overexpression of S-100B increases vulnerability to β-amyloid (Aβ)-induced damage, we used S-100B-overexpressing transgenic (Tg) and S-100B knockout (KO) mice in a mouse model that involves intracerebroventricular infusion of human oligomeric Aβ1-42. This model mimics many features of AD, including robust neuroinflammation, Aβ plaques, synaptic damage and neuronal loss in the hippocampus. S-100B Tg, KO, and wild-type (WT) mice were infused with Aβ for 28 days, sacrificed at 60 days, and hippocampal endpoints analyzed. We found that Tg mice showed increased vulnerability to Aβ-induced neuropathology relative to either WT or KO mice. Specifically, Tg mice exhibited enhanced glial activation and neuroinflammation, increased nitrotyrosine staining (a marker of glial-induced neuronal damage), and more pronounced loss of synaptic markers. Interestingly, Tg mice showed no significant differences in Aβ plaque burden compared with WT or KO mice, suggesting that, as in the human situation, the severity of neuronal dysfunction did not correlate with amyloid deposition. Our data are consistent with a model in which S-100B overexpression in AD enhances glial activation and leads to an augmented neuroinflammatory process that increases the severity of neuropathologic sequelae.