Tauopathic Changes in the Striatum of A53T α-Synuclein Mutant Mouse Model of Parkinson's Disease

Abstract

Tauopathic pathways lead to degenerative changes in Alzheimer's disease and there is evidence that they are also involved in the neurodegenerative pathology of Parkinson's disease [PD]. We have examined tauopathic changes in striatum of the α-synuclein (α-Syn) A53T mutant mouse. Elevated levels of α-Syn were observed in striatum of the adult A53T α-Syn mice. This was accompanied by increases in hyperphosphorylated Tau [p-Tau], phosphorylated at Ser202, Ser262 and Ser396/404, which are the same toxic sites also seen in Alzheimer's disease. There was an increase in active p-GSK-3β, hyperphosphorylated at Tyr216, a major and primary kinase known to phosphorylate Tau at multiple sites. The sites of hyperphosphorylation of Tau in the A53T mutant mice were similar to those seen in post-mortem striata from PD patients, attesting to their pathophysiological relevance. Increases in p-Tau were not due to alterations on protein phosphatases in either A53T mice or in human PD, suggesting lack of involvement of these proteins in tauopathy. Extraction of striata with Triton X-100 showed large increases in oligomeric forms of α-Syn suggesting that α-Syn had formed aggregates the mutant mice. In addition, increased levels of p-GSK-3β and pSer396/404 were also found associated with aggregated α-Syn. Differential solubilization to measure protein binding to cytoskeletal proteins demonstrated that p-Tau in the A53T mutant mouse were unbound to cytoskeletal proteins, consistent with dissociation of p-Tau from the microtubules upon hyperphosphorylation. Interestingly, α-Syn remained tightly bound to the cytoskeleton, while p-GSK-3β was seen in the cytoskeleton-free fractions. Immunohistochemical studies showed that α-Syn, pSer396/404 Tau and p-GSK-3β co-localized with one another and was aggregated and accumulated into large inclusion bodies, leading to cell death of Substantia nigral neurons. Together, these data demonstrate an elevated state of tauopathy in striata of the A53T α-Syn mutant mice, suggesting that tauopathy is a common feature of synucleinopathies.

GSK-3β dysregulation contributes to parkinson’s-like pathophysiology with associated region-specific phosphorylation and accumulation of tau and α-synuclein

“…25,26 The aforementioned studies combined with our current results suggest that hyperactivation of GSK-3β may be the primary mechanism by which this protein is linked to PD (Figure 7). Indeed, a growing body of evidence from our laboratory and others define the important roles, kinases, such as GSK-3β, CK2, PLK2 and 3, and GRK1-5 have in the development and pathology of PD through the phosphorylation of α-Syn and Tau 16,[18][19][20][21][22][23][24][53][54][55][56][57] (Supplementary Table S3 and associated references).…”

“…Tissues were prepared as previously described. 12,19,20 See supplementary material and methods for further details.…”

“…IHC analysis of mouse brain coronal sections was performed as previously described. 19,65 See supplementary material and methods for further details.…”

“…11 We 12,13 and others 14,15 have also identified p-Tau in different brain regions of PD, dementia with Lewy bodies, and AD. High levels of p-Tau have also been observed in vivo in several toxin [16][17][18] and transgenic α-Syn models of PD, 19,20 suggesting that p-Tau may be an important common factor in the neurodegeneration of not only tauopathies but also of synucleinopathies, such as PD. [21][22][23][24] Most studies to date have focused on the formation and accumulation of Tau and p-Tau in idiopathic PD.…”

“…12,13,16,19,20 In in vitro studies of MPTPtreated SH-SY5Y cells, blockade of GSK-3β with lithium, or with the highly selective non-ATP competitive inhibitor, TDZD--8, prevented the induction of p-GSK-3β-Y216, abolished p-Tau formation, and reversed the accumulation and aggregation of both p-Tau and α-Syn, averting cell death. 16 Other studies using Rotenone or MPTP/MPP+ in chemical PD models, have shown similar results of decreased neuronal viability during treatments accompanied by dose-and timedependent increases in GSK-3β activation, with decreased cytotoxicity detected when GSK-3β was inhibited or knockeddown through the use of GSK-3β-specific small molecule inhibitors or through RNAi.…”