Environmental enrichment potently prevents microglia-mediated neuroinflammation by human amyloid β-protein oligomers

Microglial dysfunction is increasingly recognized as a key contributor to the pathogenesis of Alzheimer’s disease (AD). Environmental enrichment (EE) is well documented to enhance neuronal form and function, but almost nothing isknownabout whether andhowit alters the brain’s innate immune system. Here we found that prolonged exposure of naive wild-type mice to EE significantly altered microglial density and branching complexity in the dentate gyrus of hippocampus. In wild-type mice injected intraventricularly with soluble Aβ oligomers (oAβ) from hAPP-expressing cultured cells, EE prevented several morphological features of microglial inflammation and consistently prevented oAβ-mediated mRNA changes in multiple inflammatory genes both in vivo and in primary microglia cultured from the mice. Microdialysis in behaving mice confirmed that EE normalized increases in the extracellular levels of the key cytokines (CCL3, CCL4, TNFα) identified by the mRNA analysis. Moreover, EE prevented the changes in microglial gene expression caused by ventricular injection of oAβ extracted directly from AD cerebral cortex. We conclude that EE potently alters the form and function of microglia in a way that prevents their inflammatory response tohumanoAβ, suggesting that prolonged environmental enrichment could protect against AD by modulating the brain’s innate immune system.