In mild AD cases we found considerable cytopathology around the affected areas, that is, tau early aggregates, mature

NFTs and neurites, all of them comprising phosphorylated tau at the Ser396–404 and Ser199–202–Thr205 sites (Figure 1). Such pathology was also present in severe AD cases (Figure 1). Interestingly, in mild and severe AD cases, phosphorylation at sites Ser396–404 was found in higher density when compared with phosphorylations at sites Ser199–202–Thr205 (Figure 2). More importantly, 50% of the total structures containing phosphorylation at sites Ser396–404 were found as early phospho-tau aggregates BAY 80-6946 cost with a well-preserved neuronal soma (Figures 2 and 3). Importantly, this early aggregated state does not showed https://www.selleckchem.com/products/Deforolimus.html fibrillar conformation as revealed by TR labelling (Figure 3). Similar findings were reported by

using AD2 antibody that also labels Ser396–404 [35]. These data clearly suggest that phosphorylation at sites Ser396–404 is an early phenomenon, which could be happening in tau protein even before phosphorylations at sites Ser199–202–Thr205, or conformational modifications. In addition, our data open a new perspective in terms of chronology and pathogenesis as both events are present in different sites of the molecule, suggesting that phosphorylation at the carboxyl terminal could be crucially related as pivotal events for further processing and aggregation of tau protein. To further develop our hypothesis we studied the association of this particular phosphorylation to early and late tau processing events, cleavage at the D421 and E391 sites respectively. Here we found that phosphorylation is strongly coincident with both cleavage events (Figure 4). Interestingly, when we analysed the relationship between phosphorylation at Ser396 and the early cleavage at site D421 we found mainly two NFT populations;

one containing just phosphorylation and the other containing phosphorylation and cleavage (Figure 4). These data suggest that phosphorylation at this particular site does not require cleavage Casein kinase 1 at site D421 to be present. Conversely, the majority of structures comprising cleavage at site D421 were found in coexistence with phosphorylation events, suggesting that cleavage requires phosphorylation in order to be present. When phosphorylation was studied in relationship to the late cleavage at E391 we found two populations as well, one with significantly elevated phosphorylation and the other with significantly elevated cleavage at E391 (Figure 4). These data suggested a sequential pattern, where phosphorylation appears as the earliest insult probably promoting early cleavage and remaining into the NFT maturation until events like cleavage at E391 take place. But, why is the remaining fragment not longer labelled by pS396? Here we believed that the small tau fragment containing this epitope could be undergoing degradation (Figure 4).