Fig. 3. Extrinsic Tau proteins induce nuclear translocation of NFκB and expression of pro-inflammatory genes in microglia.

a Immunocytochemistry of primary microglia prepared from newborn C57BL/6 mice reveals nuclear translocation of NFκB at 48 h after addition of recombinant full-length Tau 410, Tau 441, Tau 410 P179A, Tau 410 P216A, or Tau 410 P179A/P216A protein in the non-polymerized or polymerized state to culture medium. Images were obtained by confocal microscopy. Red or white arrows indicate microglia with or without nuclear translocation of NFκB. Lower panels show high magnification of representative cells. In the presence of tau proteins in culture medium, nuclear translocation of NFκB was induced in most microglia, while in the absence of tau proteins NFκB remained in the cytoplasm. b The effects of various tau species in the polymerized and non-polymerized state on nuclear translocation of NFκB were compared. Aggregation of Tau 410/441 reduces the frequency of NFκB nuclear translocation. PQBP1-binding proline single mutants (Tau 410 P179A, Tau 410 P216A) partially, while double proline mutant (Tau 410 P179A/P216A) substantially, lost the ability to induce NFκB nuclear translocation. N = 5, n = 20 (cells). ^##P < 0.01 in Tukey’s HSD test. c Isoforms, mutations, and aggregation states of tau affect induction of Tnf and Isg54 gene expression. Consistent with immunocytochemistry of NFκB, non-polymerized Tau 410 induced pro-inflammatory genes most efficiently, while Tau 441 possesses 60–80% of the induction ability. PQBP1-binding proline single mutants (Tau 410 P179A, Tau 410 P216A) partially, while double proline mutant (Tau 410 P179A/P216A) substantially, lost transactivation of Tnf and Isg54 gene expression. RT-qPCR reverse transcriptase quantitative polymerase chain reaction. N = 3. ^##P < 0.01 in Tukey’s HSD test. Box plots show the median, quartiles, and whiskers that represent data outside the 25th to 75th percentile range.