Fig. 4.
Naked mole-rat tau phosphorylation partly contributes to the age-associated increase in molecular weight. (A) Adult and neonatal naked mole-rat tau is heavily phosphorylated at AD-associated epitope Ser396/404. Naked mole-rat tau is most heavily phosphorylated during development and significantly changes with age (ANOVA, p < 0.0001). (B) Densitometric analysis indicates that PHF1 immunoreactivity decreases 32% after first week of life (ANOVA, p = 0.0159) and then drops significantly again between 20 days and 6 months (52% decrease; ANOVA, p = 0.0081) where levels then remain statistically similar throughout the rest of life. (C) Protein dephosphorylation with calf intestinal phosphatase (CIP) indicates that phosphorylation contributes to a large portion of the total molecular weight. While untreated tau from two-week old animals migrates as a 62, 66, 72 kDa triplet, dephosphorylated tau migrates as a single dense tau species ~60kDa immunoreactive to Tau1 but not PHF1. Recombinant human 4R2N tau migrates at 49kDa. Untreated two-year old animals express a prominent 88kDa tau band whereas dephosphorylation reveals a strong ~66kDa tau species immunoreactive to Tau1 but not PHF1. (D) In accord with capillary electrophoresis data, immunohistochemistry with phospho-Ser202/Thr205 tau antibody, CP13, shows highest levels of phospho-tau in development, a dramatic decrease at 6 months and with maintained levels throughout life in the cortex and hippocampal CA1. Scale bars: 100μm.