Oxidative Stress Conditions Result in Trapping of PHF-Core Tau (297–391) Intermediates

Abstract

The self-assembly of tau into paired helical filaments (PHFs) in neurofibrillary tangles (NFTs) is a significant event in Alzheimer’s disease (AD) pathogenesis. Numerous post-translational modifications enhance or inhibit tau assembly into NFTs. Oxidative stress, which accompanies AD, induces multiple post-translational modifications in proteins, including the formation of dityrosine (DiY) cross-links. Previous studies have revealed that metal-catalysed oxidation (MCO) using Cu2+ and H2O2 leads to the formation of DiY cross-links in two misfolding proteins, Aβ and α-synuclein, associated with AD and Parkinson’s disease respectively. The effect of MCO on tau remains unknown. Here, we examined the effect of MCO and ultra-violet oxidation to study the influence of DiY cross-linking on the self-assembly of the PHF-core tau fragment. We report that DiY cross-linking facilitates tau assembly into tau oligomers that fail to bind thioflavin S, lack β-sheet structure and prevents their elongation into filaments. At a higher concentration, Cu2+ (without H2O2) also facilitates the formation of these tau oligomers. The DiY cross-linked tau oligomers do not cause cell death. Our findings suggest that DiY cross-linking of pre-assembled tau promotes the formation of soluble tau oligomers that show no acute impact on cell viability.

Salpyran: A Cu(II) Selective Chelator with Therapeutic Potential

“…One known product of oxidation induced by Cu­(II) is dityrosine cross-links on proteins, such as Aβ . Dityrosine (DiY) formation, whereby closely spaced tyrosines covalently cross-link by ortho–ortho coupling at C3 of their benzene rings, has been used as a marker of oxidative stress, and DiY has been shown to form under Cu­(I/II)/H 2 O 2 oxidative conditions for Aβ and tau in vitro − and within AD amyloid plaques in vivo . In the presence of H 2 O 2 , Cu­(II) induces dityrosine cross-linking more efficiently, serving as an excellent marker of oxidation .…”

“…Dityrosine (DiY) formation, whereby closely spaced tyrosines covalently cross-link by ortho–ortho coupling at C3 of their benzene rings, has been used as a marker of oxidative stress, and DiY has been shown to form under Cu­(I/II)/H 2 O 2 oxidative conditions for Aβ and tau in vitro − and within AD amyloid plaques in vivo . In the presence of H 2 O 2 , Cu­(II) induces dityrosine cross-linking more efficiently, serving as an excellent marker of oxidation . Also, Cu­(II) is known to bind tau and induce tau oxidation, dimerization, and aggregation. , Recently, it was demonstrated that Cu­(II) alone or in the presence of H 2 O 2 induces oxidation and dityrosine cross-linking of a tau297–391 fragment which contains one tyrosine at position 310. , To further demonstrate the antioxidant ability of Salpyran , we performed a series of reactions using tau297–391 and Cu­(II) (1:10 ratio) in combination with H 2 O 2 to induce oxidation and dityrosine formation, which were quenched after 1 h with the addition of EDTA.…”

“…In the presence of H 2 O 2 , Cu­(II) induces dityrosine cross-linking more efficiently, serving as an excellent marker of oxidation . Also, Cu­(II) is known to bind tau and induce tau oxidation, dimerization, and aggregation. , Recently, it was demonstrated that Cu­(II) alone or in the presence of H 2 O 2 induces oxidation and dityrosine cross-linking of a tau297–391 fragment which contains one tyrosine at position 310. , To further demonstrate the antioxidant ability of Salpyran , we performed a series of reactions using tau297–391 and Cu­(II) (1:10 ratio) in combination with H 2 O 2 to induce oxidation and dityrosine formation, which were quenched after 1 h with the addition of EDTA. The appearance of the dityrosine species was observed by monitoring the intensity of the peak at 410 nm (Figure ).…”

“…87 In the presence of H 2 O 2 , Cu(II) induces dityrosine cross-linking more efficiently, serving as an excellent marker of oxidation. 89 Also, Cu(II) is known to bind tau and induce tau oxidation, dimerization, and aggregation. 90,91 Recently, it was demonstrated that Cu(II) alone or in the presence of H 2 O 2 induces oxidation and dityrosine crosslinking of a tau297−391 fragment which contains one tyrosine at position 310.…”

Tau-targeting therapy in Alzheimer’s disease: critical advances and future opportunities

“…Lysine methylation is part of the normal PTMs of tau in the human brain and can partially serve to protect against pathological tau aggregation [44] . Dityrosine (DiY) cross-links, another tau PTM induced by oxidative stress, was observed on human AD-derived tau oligomers and PHFs [45] . DiY cross-links of tau dGAE (tau297-391 fragment of the full-length tau) can facilitate the formation of non-toxic, soluble tau oligomers, inhibit the formation of β-sheets and further extension of prefibrils [46] , and increase the insolubility and stability of tau fibrils in AD [45] .…”