Early-Life Immune Activation Shapes Microglial Responses and Reduces Abeta Pathology in 5xFAD mice

Early infection in life has been implicated in increasing the risk for neurological disorders. Here we performed single-cell sequencing of microglia and monocytes from 6-month-old WT and 5xFAD mice subjected to one dose of LPS (1mg/kg) at postnatal day 9. We successfully mapped disease-associated microglia (DAM) and perivascular macrophages in our data and demonstrated a subpopulation of microglia that adopted a monocyte-like profile, marked by Lyz2, Tmsb10, Lgals1and Lgals3. This unique subset appeared in response to early systemic LPS challenge and AD pathology but diminished in the presence of double stimulus. Different cytokines were altered in the brain and periphery as seen using mesoscale plates. GM-CSF and MIP-1 levels were altered in an amyloid-{beta}(A{beta})-dependent manner in hippocampus. MIP-1{beta} and IFN-{gamma} were altered upon early LPS stimulation. In the periphery, we found MMP-9 was significantly increased in serum samples from 5xFAD mice. Interestingly, early LPS stimulation significantly elevated TNF- in serum from WT and 5xFAD mice, but was reduced in the hippocampus due to A{beta} pathology. The LPS treatment in 5xFAD mice had a tendency to improve the short-term memory deficit. Taken together, we observed long-lasting effects from early life stress, including activation of inflammation in the periphery and brain through modulation of different signaling cascades.