Microglia Replenished OHSC: A Culture System to Study In Vivo Like Adult Microglia

Recent data suggest that ramified microglia fulfil various tasks in the brain. However, to investigate this unique cell type cultured primary microglia are only a poor model. We here describe a method to deplete and repopulate organotypic hippocampal slice cultures (OHSC) with ramified microglia isolated from adult mouse brain creating microglia-replenished OHSC (Mrep-OHSC). Replenished microglia integrate into the tissue and ramify to a degree indistinguishable from their counterparts in the mouse brain. Moreover, wild-type slices replenished with microglia from TNF alpha-deficient animals provide similar results as OHSC prepared from microglia-specific TNF alpha-knockout mice (CX3CR1(cre)/TNF alpha(fl/fl)). Furthermore, this study demonstrates that replenished microglia in OHSC maintain original functions and properties acquired in vivo. Microglia from ERCC1(Delta/ko) mice, a mouse model of accelerated aging, maintain enhanced Mac2 expression and their activated phenotype after replenishment to wild-type OHSC tissue. Thus, the present study demonstrates that Mrep-OHSC are a unique tool to construct chimeric brain slices allowing studying the function of different phenotypes of in vivo like microglia in a tissue culture setting.