88 Chapter 4 over the range 2-10000 ng/mL, then preparing and analysing as for the study samples. Lower limit of detection was 2 ng/mL. Results TSPO expression and epigenetic regulation in primary macrophages To investigate TSPO gene expression changes in human and mouse a meta-analysis was performed using publicly available macrophage and microglia transcriptomic datasets upon pro-inflammatory stimulation (Fig. 1). We found 10 datasets (Fig. 1a) derived from mouse macrophages and microglia in samples from 68 mice and with inflammatory stimuli including activation with LPS, Type 1 interferon (IFN), IFNγ, and LPS plus IFNγ. We performed a metaanalysis and found that Tspo was upregulated under pro-inflammatory conditions (Fig. 1a). In the individual datasets, Tspo was significantly upregulated in 9 of the 10 experiments. We then interrogated 42 datasets from primary human macrophages and microglia involving samples from 312 participants, with stimuli including inflammatory activation with LPS, IFNγ, IL1, IL6, Poly I:C, viruses, and bacteria (Fig. 1b). c a b d Figure 1. TSPO gene expression and epigenetic profile in human and mouse macrophages. a,b Forest plot of the meta-analysis for TSPO expression in a mouse and b human myeloid cells treated with a pro-inflammatory stimulus. The random-effect model was applied when combining the gene expression. The black squares represent the logFC value of each dataset. The horizontal lines indicate the 95% confidence intervals of each study. The diamond represents the pooled logFC. c,d ChIP-seq data, generated from c mouse and d human myeloid cells treated with IFNγ, visualisation of histone modification peaks (H3K27Ac, H3K4me3, H3K4me1) and PU.1 binding peaks at TSPO loci in IFNγ-treated (pink) and baseline (blue) conditions. Yellow vertical shading corresponds to the TSS along with promoter and light blue shading corresponds to the enhancer region of the loci.
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