Disulfide bond formation in microtubule-associated tau protein promotes tau accumulation and toxicity in vivo

Abstract

Accumulation of microtubule-associated tau protein is thought to cause neuron loss in a group of neurodegenerative diseases called tauopathies. In diseased brains, tau molecules adopt pathological structures that propagate into insoluble forms with disease-specific patterns. Several types of posttranslational modifications in tau are known to modulate its aggregation propensity in vitro, but their influence on tau accumulation and toxicity at the whole-organism level has not been fully elucidated. Herein, we utilized a series of transgenic Drosophila models to compare systematically the toxicity induced by five tau constructs with mutations or deletions associated with aggregation, including substitutions at seven disease-associated phosphorylation sites (S7A and S7E), deletions of PHF6 and PHF6* sequences (ΔPHF6 and ΔPHF6*), and substitutions of cysteine residues in the microtubule binding repeats (C291/322A). We found that substitutions and deletions resulted in different patterns of neurodegeneration and accumulation, with C291/322A having a dramatic effect on both tau accumulation and neurodegeneration. These cysteines formed disulfide bonds in mouse primary cultured neurons and in the fly retina, and stabilized tau proteins. Additionally, they contributed to tau accumulation under oxidative stress. We also found that each of these cysteine residues contributes to the microtubule polymerization rate and microtubule levels at equilibrium, but none of them affected tau binding to polymerized microtubules. Since tau proteins expressed in the Drosophila retina are mostly present in the early stages of tau filaments self-assembly, our results suggest that disulfide bond formation by these cysteine residues could be attractive therapeutic targets.

Mical modulates Tau toxicity via cysteine oxidation in vivo

“…Initial in vivo evidence that Tau forms disulfide bonds in the fly retina was provided by Saito et al [ 61 ], so to quantify oxidized cysteine residues upon Mical overexpression in the fly CNS, we utilized a targeted proteomics approach. Briefly, N-ethyl maleimide (NEM) is known to react with free-thiols resulting in maleimide adducts that are readily observed in the MS spectra as a 125 Da shift in molecular mass.…”

N-Acetyl-Cysteine: Modulating the Cysteine Redox Proteome in Neurodegenerative Diseases

“…For example, the involvement of APOE4 and tau variability in the development of dementia in PD has recently been recognized [ 440 ]. Additionally, the role of oxidative damage and disulfide bond formation in tau [ 441 ] and other SCCPs are critical triggering mechanisms leading to neurodegenerative disorders and pathogenic progression factors. Therefore, NAC may offer an effective therapeutic strategy to decrease the generation and spread of pathological proteins [ 442 ].…”

Dityrosine cross-links are present in Alzheimer’s disease-derived tau oligomers and paired helical filaments (PHF) which promotes the stability of the PHF-core tau (297-391) in vitro

“…Finally, cysteine oxidation can be induced by oxidative stress conditions and is known to influence the functions, properties and toxicity of tau (Landino et al, 2004, Saito et al, 2021, Weismiller et al, 2021). dGAE has a single cysteine residue at position 322, and we have previously shown that it forms PHFs independent of this cysteine and that assembly is enhanced under reducing conditions or using C322A variant (Al-Hilaly et al, 2017, Al-Hilaly et al, 2018).…”