Title

Pseudophosphorylation of tau at S422 enhances SDS-stable dimer formation and impairs both anterograde and retrograde fast axonal transport.

Journal

Experimental neurology

Volume

283

Issue

None

Pages

318-29

Date

2016-09-01

Authors

Tiernan CT | Brady ST | Combs B | Counts SE | Cox K | Kanaan NM | Morfini G

The amount of total tau captured with pS422 (detected with the pan-tau antibody, Tau5) was significantly higher in AD compared to control (Fig. 7E; t10 = 6.07, p = 0.0001). The level of pS422 tau that also contained PAD exposed tau (i.e., TNT1 reactive) was significantly higher in AD compared to control (Fig. 7F; t10 = 2.31, p = 0.0435). Similarly, the level of pS422 tau that also contained an oligomeric conformation (i.e., TOC1 reactive) was significantly higher in AD compared to control (Fig. 7G; t10 = 1.51, p = 0.0029).

Compared to monomers, aggregation significantly increased PAD exposure for both hT40 and S422E samples (Fig. 3B; F(1,12) = 685.8, p b 0.0001), as indicated by increased TNT1 reactivity. Aggregation also significantly increased oligomer formation (TOC1 reactivity) compared to monomers in both hT40 and S422E samples (Fig. 3C; F(1,12) = 109.3, p b 0.0001).

In contrast, aggregation of either hT40 or S422E significantly increased the amount of SDS-stable dimers at 180 kDa (Fig. 4C; F(1,12) = 110.0; p b 0.0001), as compared to the levels of these species in the respective monomer samples. Furthermore, S422E aggregation significantly increased the amount of SDS-stable dimers compared to hT40 aggregation (p = 0.03).

As previously reported, perfusion of hT40 monomer had no effect on the rate of anterograde FAT in the squid axoplasm (Fig. 5A), whereas perfusion of hT40 aggregates significantly inhibited anterograde FAT as compared to hT40 monomer (Fig. 5B; Fig. 6A; p = 0.003) (LaPointe et al., 2009b). Neither hT40 monomers nor hT40 aggregates altered the rate of retrograde FAT (Fig. 5A, B; Fig. 6B).

However, the rate of polymerization (kapparent) did not differ between hT40 tau and S422E tau. At 360 min, a similar intensity of light scattering was observed for hT40 (122.5 ± 1.2) and S422E tau (134.5±1.7) indicating that the extent of aggregate formation was comparable between these two proteins. ThS fluorescence, measured at 360min, alsowas comparable between hT40 aggregates (946.4 ± 73.8) and S422E aggregates (927.9 ± 63.7).

For both tau constructs, there were significantly more oligomer-type aggregates than short or long filaments formed, but no significant difference between the numbers of short or long filament (Fig. 2E; F(2,12) = 86.64, p b 0.0001). S422E did not differ significantly from hT40 in the number of oligomers, short filaments, or long filaments formed (F(1,12) = 0.05, p = 0.83).

In contrast to hT40 monomer, perfusion of S422E monomer selectively inhibited anterograde transport (Fig. 5C; Fig. 6A; p = 0.028), but not retrograde FAT. Surprisingly, aggregated S422E significantly inhibited both anterograde and retrograde FAT rates (Fig. 5D; Fig. 6A, B) compared to S422E monomer (anterograde, p = 0.012; retrograde, p = 0.002) and hT40 aggregates (retrograde only, p = 0.019).

Staining in fixed tissue sections confirmed several previous reports (Kanaan et al., 2016; Mufson et al., 2014; Patterson et al., 2011a) that pS422 (Fig. 7A) extensively colocalizes with TNT1 (Fig. 7B) and TOC1 (Fig. 7C) in both control and AD brains, despite the relatively sparse appearance of tau pathology in the temporal cortices of control cases (data not shown).

Highlighting the relevance of these findings to human disease, pS422 tau was found to colocalize with tau oligomers and with a fraction of tau showing increased PAD exposure in the human AD brain. This study identifies novel effects of pS422 on tau biochemical properties, including prolonged nucleation and enhanced dimer formation, which correlate with a distinct inhibitory effect on FAT.

BEL Commons is developed and maintained in an academic capacity by Charles Tapley Hoyt and Daniel Domingo-Fernández at the Fraunhofer SCAI Department of Bioinformatics with support from the IMI project, AETIONOMY. It is built on top of PyBEL, an open source project. Please feel free to contact us here to give us feedback or report any issues. Also, see our Publishing Notes and Data Protection information.

If you find BEL Commons useful in your work, please consider citing: Hoyt, C. T., Domingo-Fernández, D., & Hofmann-Apitius, M. (2018). BEL Commons: an environment for exploration and analysis of networks encoded in Biological Expression Language. Database, 2018(3), 1–11.