Phosphorylation of Tau at Thr212, Thr231, and Ser262 Combined Causes Neurodegeneration

Abstract

Abnormal hyperphosphorylation of the microtubule-associated protein Tau is a hallmark of Alzheimer disease and related diseases called tauopathies. As yet, the exact mechanism by which this pathology causes neurodegeneration is not understood. The present study provides direct evidence that Tau abnormal hyperphosphorylation causes its aggregation, breakdown of the microtubule network, and cell death and identifies phosphorylation sites involved in neurotoxicity. We generated pseudophosphorylated Tau proteins by mutating Ser/Thr to Glu and, as controls, to Ala. These mutations involved one, two, or three pathological phosphorylation sites by site-directed mutagenesis using as backbones the wild type or FTDP-17 mutant R406W Tau. Pseudophosphorylated and corresponding control Tau proteins were expressed transiently in PC12 and CHO cells. We found that a single phosphorylation site alone had little influence on the biological activity of Tau, except Thr 212 , which, upon mutation to Glu in the R406W background, induced Tau aggregation in cells, suggesting phosphorylation at this site along with a modification on the C-terminal of the protein facilitates self-assembly of Tau. The expression of R406W Tau pseudophosphorylated at Thr 212 , Thr 231 , and Ser 262 triggered caspase-3 activation in as much as 85% of the transfected cells, whereas the corresponding value for wild type pseudophosphorylated Tau was 30%. Cells transfected with pseudophosphorylated Tau became TUNEL-positive.

Tau-induced neurodegeneration: mechanisms and targets

“…We have shown that phosphorylation of tau is suffi cient to promote tau self-assembly into fi laments [29] and that phosphorylation at Ser 199 and 262 and Thr 212 and 231 is sufficient to convert tau into an D-like protein in cells [101] and in vivo in transgenic Drosophila [126] . On the basis of our results and the evidence reviewed here, we propose that the hyperphosphorylation of tau leads to neurodegeneration through microtubule disruption and the consequent decreases in neurotransmission a n d a x o p l a s m i c t r a n s p o r t ( F i g .…”

“…1 ) . B e s i d e s t h e microtubule disruption, we have evidence that abnormal tau translocates into the nucleus [101] and also impacts mitochondrial health in neurons. The consequences of these facts deserve further investigation.…”

“…This is also reported in the brains of Drosophila that express Until recently, the majority of evidence that linked mitochondria to AD was the accumulation of Aβ in mitochondria (reviewed in [100] ). The phosphorylation state of tau has been implicated in the degeneration of neurons [101] and linked to mitochondrial dysfunction [102] . Tau has also been shown to be ubiquitinated and to be involved in the cellular distribution of mitochondria in mouse neurons [103,104] .…”

JNK Signaling: Regulation and Functions Based on Complex Protein-Protein Partnerships

“…This MAP2 region is similar to an FBW7 phosphodegron of Tau (Thr231 and Ser235 [underlined in the above sequence]), which is modified in cooperation with GSK3. Although phosphorylation was originally reported to inhibit the microtubule-binding ability of Tau, more recent research suggests that modification of these sites may not be sufficient to induce Tau dissociation from microtubules (354,355). The phosphorylation of the latter motif may still contribute to neurotoxicity and filament forming when Tau is released from microtubules in Alzheimer's disease (355).…”

“…Furthermore, as JNK2 does not display any preference (245). e In addition, Tau can be subjected to more complex regulation (354,355).…”