Fig. 4

Age-associated gene expression signatures of human microglia. A Gene ontology analysis of top 100 highly variable genes whose expression incrementally decreased with age. B Heatmap depicting expression of phagocytosis related genes. Red and blue color indicate up and down regulation of genes, respectively. C Gene ontology analysis of top 100 highly variable genes whose expression incrementally increased with age. D Heatmap depicting expression of pro-inflammatory molecules. Red and blue color indicate up and down regulation of genes, respectively. E Human pre-natal and adult microglia were treated with LPS 100 ng/ml for 24 h. Release of TNF and IL-6 was measured by ELISA. Wilcoxon–Mann–Whitney t test was used to check significance of the result. F Representative RNAscope images of AIF1 (green), CXCR4 (orange), IL18 (red), and CD36 (magenta) expression in fresh-frozen pre-natal and adult human brain tissue (n = 1 pre-natal; n = 1 adult). The absolute number of microglia is vastly reduced in pre-natal brain tissue compared to adult brain tissue, as visualized by AIF1 expression. A selection of microglia is denoted by white arrowheads for ease of interpretation. Scale bar = 40 μM Enlarged images of individual cells expressing markers of interest are included and their position indicated by white boxes. G Bar plot of corrected total cell fluorescence (CTCF; a standardized intensity measurement) values for CXCR4, IL18 and CD36 for AIF1 + cells. CXCR4 and IL18 expression are increased in adult microglia compared to pre-natal microglia. Conversely, CD36 expression in pre-natal microglia far exceeds that of adult microglia