Fig. 2: Deficiency of SR in primary microglial cultures enhanced both Aβo phagocytosis and phagocytic uptake of microbeads.

A Primary microglia was cultured from the mice with systemic knockout of Srr (Srr^−/−) or wild-type (WT). FITC-Aβ (0.25 μM) was incubated with microglia for 6, 12, 24, 36, and 48 h. Images were captured with a scale bar of 100 μm shown for all panels. Student’s t-test was used to compare the numbers of microglia phagocytosing FITC-Aβ at all time points, 6–48 h. At 6 h time point, the percentages of microglia phagocytosing FITC-Aβ in Srr^−/− microglia (n = 14) were higher than those in WT microglia (n = 11), t[23] = 4.776, p = 0.0000081. Meanwhile, the FITC-Aβ intensity in Srr^−/− microglia (n = 14) increased compared to WT microglia (n = 11), t[23] = 2.179, p = 0.04. At 36-h time point, there were more Srr^−/− microglia (n = 15) which phagocytosed FITC-Aβ than WT microglia (n = 12), t[25] = 2.192, p = 0.038. No significant differences in the percentage of positive cells ingesting FITC-Aβ were observed between Srr^−/− and WT microglia for 12, 24, and 48 h (Srr^−/− microglia (n = 14), WT (n = 11), t[23] = 0.359, p = 0.723 at 12 h; Srr^−/− (n = 13), WT (n = 13), t[24] = 0.714, p = 0.482 at 24 h; Srr^−/− (n = 12), WT (n = 12), t[22] = 0.358, p = 0.723 at 48 h). FITC-Aβ intensities in Srr^−/− microglia were not different from those in WT microglia for 12, 24, 36, and 48 h (t[23] = 0.890 at 12 h, p = 0.382; t[24] = 0.652, p = 0.521 at 24 h; t[25] = 0.898, p = 0.378 at 36 h; t[17.827] = 1.360, p = 0.191 at 48 h). BF, bright field. B Primary microglial cultures derived from Srr⁻/⁻ and wild-type (WT) mice were co-incubated with latex beads for 2 h. To assess microglial phagocytic capacity, images of red-fluorescent beads and corresponding bright-field views were acquired. Phagocytic activity was quantified as the percentage of microglia that had internalized the beads. All panels in column 1 were presented with a scale bar of 100 μm, whereas column 2 displayed magnified views of the squared areas in column 1 (scale bar = 50 μm). Student’s t-test was performed to compare phagocytic capacity between the two groups, and the results demonstrated that Srr⁻/⁻ microglia exhibited significantly higher phagocytic capacity than WT microglia (t(19.525) = 6.269, p = 0.0000045). Error bars denote the variability of the data.