99 TSPO in neurodegeneration EAE. o TSPO+ pixels are not increased in acute and subacute lesions in marmoset EAE relative to control. Statistical significance in f-j,o was determined by a one way ANOVA or Kruskal-Wallis test when not normally distributed, and by a two-tailed unpaired t-test or Mann-Whitney U-test when not normally distributed in c,k and l. Holm-Sidak’s and Dunn’s multiple comparisons were performed. Box and whiskers mark the 25th to 75th percentiles and min to max values, respectively, with the median indicated. Scale bar = 50µm, inserts are digitally zoomed in (200%). In summary, and consistent with the AD and ALS data, we have shown that individual cellular TSPO expression is increased in microglia in EAE in both young and aged mouse models, but it is not increased in microglia from MS lesions nor marmoset EAE acute lesions. Again, consistent with previous data, astrocytes did not show an increase in TSPO expression in either MS or EAE. Single cell RNAseq shows TSPO gene expression is upregulated in activated mouse microglia, but not in activated human microglia Methods for protein quantification by immunohistochemistry in postmortem brain are semiquantitative and therefore we also assessed ex vivo species-specific TSPO gene expression of microglial under pro-inflammatory conditions to add further confidence to our findings. We employed publicly available human and mouse scRNAseq datasets37-42. We first examined evidence for a pro-inflammatory microglial phenotype by quantifying the differential expression of homeostatic and/or activation markers. We then quantified the differential expression of TSPO in pro-inflammatory activated microglia using MAST47. In a model of LPS exposure in the mouse40, scRNAseq yielded 2019 microglial cells that showed evidence of pro-inflammatory activation including a downregulation of the homeostatic marker P2ry12 and an upregulation of activation markers Fth1 and Cd74 (Fig. 7a). In this population, TSPO was significantly upregulated. In a mouse model of acute EAE42, scRNAseq yielded 8470 pro-inflammatory activated microglial cells that showed significant downregulation of P2ry12, and a significant upregulation of Fth1 and Cd74 (Fig. 7b). TSPO was significantly upregulated. Finally, in the 5XFAD mouse model of AD41, scRNAseq yielded over 6203 microglial cells. Among them, 223 showed enrichment in disease-associated microglia (DAM) markers41, including increased expression of Apoe, Trem2, Tyrobp and Cst7 (Fig. 7c). Compared to non-DAM cells, DAM cells showed a significant upregulation of TSPO. In cerebrospinal fluid (CSF)-derived cells isolated from people with AD37, microglia-like cells (n=522) had an activated phenotype with a significant upregulation of APOE, FTH1 and SPI1 relative to controls. However, TSPO was not differentially expressed (Fig. 7d). In CSF isolated from people with MS38, microglia-like cells (n=1650) showed evidence of activation: TREM2, C1QA, C1QB, SPI1, and HLA-DQA1 all were significantly upregulated38. However, TSPO was not differentially expressed in these cells (Fig. 7e). In a similarly designed study also using CSF-derived cells, microglia showing upregulation of HLA-DRB1, HLA-DRB5 and SPI1 also downregulated TSPO39 (Fig. 7f). These experiments are consistent at the gene expression level with our own data at the protein expression level showing that the TSPO gene is not increased in microglia in AD or EAE, but is increased in their respective commonly used mouse models.
RkJQdWJsaXNoZXIy MTk4NDMw