92 Chapter 4 CON AD CON AD 0 10 20 30 40 TSPO+ μm2/ cell microglia astrocytes CON AD 0 100 200 300 400 500 600 GFAP+ cells / mm² CON AD 0 100 200 300 400 500 600 HLA-DR+ cells / mm² CON AD 0 100 200 300 400 500 600 IBA1+ cells / mm² CON AD 0 100 200 300 400 500 600 TSPO+ cells / mm² CON AD 0 100 200 300 400 500 600 TSPO+GFAP+ cells / mm² CON AD 0 100 200 300 400 500 600 TSPO+HLA-DR+ cells / mm² CON AD 0 100 200 300 400 500 600 TSPO+IBA1+ cells / mm² TSPO/IBA1 a AD b c TSPO/HLA-DR TSPO/GFAP d e f g h i j k Figure 3. TSPO expression is not altered in the AD hippocampus. a-c Representative images of TSPO expression in microglia and astrocytes in AD hippocampus. d-g No increases were observed in microglia (P=0.5159, U=7, ranks=17, 28), activated microglia (P = 0.8997, t=0.1301, df=8) astrocytes (P = 0.8599, t=0.1831, df=7) or TSPO+ cells (P = 0.7329, t=0.3534, df=8) in the AD hippocampus. h-j Concurrently no increases were observed in the number of TSPO+IBA1+ microglia (P = 0.3573, t=0.9854, df=7), TSPO+HLA-DR+ microglia (P = 0.7239, t=0.3659, df=8) and astrocytes (P = 0.7181, t=0.3760, df=7). k Even though microglia in the AD brain show signs of activation microglia do not upregulate TSPO expression in the hippocampus (P = 0.6717, t=0.4398, df=8), nor do astrocytes (P = 0.6475, t=0.4750, df=8). Statistical significance in d-k was determined by a two-tailed unpaired t-test or Mann-Whitney U-test when not normally distributed. 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%). Density is elevated due to the combined effects of three mutations associated with familial AD (NL; Swedish, G: Arctic, F: Iberian). The AppNL-G-F line is characterised by formation of amyloid plaques, microgliosis and astrocytosis18. We also investigated TSPO expression in a model of tauopathy, TAUP301S mice, which develop tangle-like inclusions in the brain parenchyma associated with microgliosis and astrocytosis19. The use of these two models allows differentiation of effects of the amyloid plaques and neurofibrillary tangles on the expression of TSPO in the mouse hippocampus. In AppNL-G-F mice, an increase in the density of microglia was observed at 28-weeks (Fig. 4c), but not in the density of astrocytes (Fig. 4d). An increase in TSPO+ cells was also observed (Fig. 4e), due to an increase in numbers of TSPO+ microglia and macrophages (Fig. 4f). No differences were observed in the density of TSPO+ astrocytes in AppNL-G-F at 10 weeks, although a small (relative to that with microglia) increase was observed at 28 weeks (Fig. 4g). Finally, we then quantified TSPO+ area in microglia and astrocytes as an index of TSPO expression in individual cells. In contrast to the human data, expression of TSPO in individual cells was increased by 3-fold in microglia in the AppNL-G-F mice at 28 weeks (Fig. 4h). It was unchanged in astrocytes. In the TAUP301S mice, no differenceswere
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