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A, B
To verify the specificity of Cx43‐CreERT mice for astrocytes, mice were crossed to a tdTomato reporter line to induce Cre‐dependent tdTomato expression after tamoxifen administration. TdTomato fluorescence was enhanced with an antibody against red fluorescent protein, and astrocytes were stained with antibodies against GFAP or S100β (not shown). Merged images and quantification show efficient and widespread tdTomato expression specific for astrocytes (arrowheads indicate tdTomato and GFAP overlap) in 8‐ and 11‐month‐old animals. Expression was low in neurons (stained with NeuN, not shown) and negligible in NG2 cells and oligodendrocytes. Scale bars, 250 μm (upper panel) and 50 μm (lower panel).
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C
The majority of peri‐plaque astrocytes in APP/PS1‐Stat3WT were positive for activated/phosphorylated Stat3 (pStat3) in the cortex (Cx) and hippocampus (HC), whereas the fraction of pStat3‐positive astrocytes was significantly lower in APP/PS1‐Stat3KO mice in both regions (n = 8 mice (three females and five males) per group; age, 8 months; *P < 0.05, Mann–Whitney test). The occurrence of pStat3 in WT‐Stat3KO and WT‐Stat3WT mice was negligible (n = 8 mice (four females and four males) per group; age, 8 months; Mann–Whitney test).
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D, E
Examples of Stat3 activation in APP/PS1‐Stat3KO and APP/PS1‐Stat3WT. (D) pStat3 (arrowheads) was abundantly present in reactive astrocytes (identified by GFAP) around plaques (identified by IC16). (E) Only few astrocytes were positive for pStat3 in APP/PS1‐Stat3WT mice. Scale bars, 50 μm.
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F, G
In postmortem brain sections from AD patients, we detected nuclear pStat3 (arrows) in the majority of peri‐plaque reactive astrocytes (identified by GFAP) in the cortex and hippocampus (plaques were stained with methoxy‐XO4, arrowheads). Scale bar, 50 μm. In total, n = 4 cortical and n = 3 hippocampal sections were analyzed.
Data information: Data are represented as mean ± SEM.
