Clearly, the different phosphorylations sites affect protein processing in different ways; therefore the chronology of these selleck chemicals llc events becomes crucial in order to further elucidate the mechanism of abnormal tau processing that could lead to deposition.
Here, by using moderate and severe AD cases, we found that AD markers AT8 and PHF-1 have different chronological appearance in relation to pathology severity, with AT8 correlating with more severe stages. Conversely, we observed that PHF-1 was able to recognize more tau pathology when compared with the AT8 marker at all AD stages. Furthermore, phosphorylation at Ser396 was found closely related to early tau pathological events such as cleavage at site D421, as well as to the late E391 cleavage, validating PHF-1 as neuropathological markers of AD progression. To further analyse our findings, we evaluate the processing of tau protein
in DS. Here we found that tau pathological processing mimics what is seen during early stages of AD. In other words, our data showed a well-defined pathway with phosphorylation at sites Ser396–404 as the earliest event, followed by phosphorylation at sites Ser199–202–Thr205 and cleavage at site D421. Taken together, the data suggest that phosphorylation of tau protein at those sites labelled by PHF-1 precedes find more the phosphorylation at sites labelled by AT8, and PHF-1 phosphorylation is present even before the classical aggregate in β-sheet conformation.
The brain tissues were collected, stored and used for research following approval Immune system from the institutional ethics committee and written informed consent from close legal relatives of the subjects. We studied brains (ages 56–91 years) received from the Case Western Reserve University Brain Bank (Cleveland, OH, USA). All of the patients had a clinical diagnosis of either AD or DS. All of the pathological cases stained for phosphorylated tau and exhibited Alzheimer pathology, NFTs and senile plaques. The mean duration of illness was 9.1 years (range 1–20 years) for the AD cases. The mean post mortem interval in these cases averaged 15 h (± 8). Further, control brains, with no evidence of clinical dementia or other neurological diseases, were examined and were found to be negative for the presence of tau atrophy. The control group showed negative or low staining when stained with PHF-1, an antibody that recognizes the early stages of a NFT. Brain hippocampal tissue was fixed in routine formalin, dehydrated and embedded in paraffin, 6-μm sections were placed on saline-coated slides. After rehydration through xylene and graded ethanols, sections were treated with 3% H2O2, for 30 min to reduce endogenous peroxidase activity and blocked with 10% normal goat serum (NGS; Sigma, St. Louis, MO, USA) in Tris-buffered saline (TBS) (50 mM Tris, 150 mM NaCl, pH 7.6) for 45 min.