Diverse requirements for microglial survival, specification, and function revealed by defined-medium cultures

Microglia, the resident macrophages of the central nervous system (CNS), engage in various CNS-specific functions that are critical for development and health. To better study the properties that distinguish microglia from other tissue macrophage populations, we have optimized serum-free culture conditions to permit robust survival of highly purified adult microglia under defined-medium conditions. We find that astrocyte-derived factors prevent microglial death ex vivo and that this activity results from three primary components (CSF-1/IL-34, TGF-b2, and cholesterol). Using microglial cultures that have never been exposed to serum, we demonstrate a dramatic change in intrinsic phagocytic capacity after serum exposure. Finally, we find that mature microglia rapidly lose signature gene expression profiles after isolation, and that this loss can be reversed by engrafting cells back into an intact CNS environment. These data indicate that the specialized gene expression profile of mature microglia require continuous instructive signaling from the intact CNS. This RNA-seq dataset describes changes in rat microglial transcriptome in culture with or without serum exposure. Three to six biological replicates per group were collected: Freshly isolated P21 rat microglia, P21 rat microglia 8 days in culture in serum-free TIC medium, P21 rat microglia 7 days in culture in serum-free TIC medium and 1 day supplemented with 10% fetal calf serum (FCS), P21 rat microglia 5 days in culture in serum-free TIC medium and 3 days supplemented with 10% FCS, or P21 rat microglia 3 days in culture in serum-free TIC medium and 5 days supplemented with 10% FCS.