Characterization of MACS isolated microglia cells (CD11b positive cells) in comparison to all non-CD11b positive cells (termed non-target cell fraction (NTCF)) with proteomics

Microglia isolation from adult mouse brains remains difficult in comparison to microglia isolation from brains from newborn mouse brains as connective tissue, extracellular matrix materials and thicker myelin sheaths substantially influence traditional isolation protocols used with newborn mouse brains. Since the introduction of magnetic activated cell sorting (MACS), it has been reported that it is possible to also obtain microglia cells from adult mouse brains with a very good purity. However, most studies only used flow cytometry and/or qPCR to determine microglia enrichment and enrichment of traditional microglia marker proteins. Therefore we wanted to characterize in an unbiased way the proteomes of with MACS isolated microglia cells (CD11b positive cells) in comparison to all non-CD11b positive cells (termed non-target cell fraction (NTCF)), which consist of primarily astrocytes, neurons and oligodendrocytes. Therefore, we isolated from three adult mouse brains via MACS CD11b positive cells as well as the remaining CD11b negative cells (NTCF) to characterize the proteome of both cell fractions. The obtained proteomes were compared to a dataset of proteomic signatures for all CNS cell types determined by Sharma et al., (2015, doi: 10.1038/nn.4160) to determine the amount of enrichment of microglia-specific proteins.