Expression of a truncated human tau protein induces aqueous-phase free radicals in a rat model of tauopathy: implications for targeted antioxidative therapy

Oxidative stress has been implicated in the pathogenesis of many neurodegenerative diseases including Alzheimer's disease (AD). We investigated the effect of a truncated form of the human tau protein in the neurons of transgenic rats. Using electron paramagnetic resonance we observed significantly increased accumulation of ascorbyl free radicals in brains of transgenic animals (up to 1.5-fold increase; P < 0.01). Examination of an in vitro model of cultured rat corticohippocampal neurons revealed that even relatively low level expression of human truncated tau protein (equal to 50% of endogenous tau) induced oxidative stress that resulted in increased depolarization of mitochondria (approximately 1.2-fold above control, P < 0.01) and increases in reactive oxygen species (approximately 1.3-fold above control, P < 0.001). We show that mitochondrial damage-associated oxidative stress is an early event in neurodegeneration. Furthermore, using two common antioxidants (vitamin C and E), we were able significantly eliminate tau-induced elevation of reactive oxygen species. Interestingly, vitamin C was found to be selective in the scavenging activity, suggesting that expression of truncated tau protein preferentially leads to increases in aqueous phase oxidants and free radicals such as hydrogen peroxide and hydroxyl and superoxide radicals. Our results suggest that antioxidant strategies designed to treat AD should focus on elimination of aqueous phase oxidants and free radicals.

Preserving free thiols of intrinsically disordered tau protein without the use of a reducing agent

Intrinsically disordered proteins (IDPs) represent key mediators in many physiological as well as pathological processes. Solution-exposed cysteines of IDPs are highly reactive and therefore reducing agents are frequently included during their preparation to prevent formation of nonnative disulfides. However, reductants can potentially interfere with subsequent assays performed on the purified IDPs. Herein we report a method for purification of IDP tau in an atmosphere of inert argon, which eliminates the need for reducing agents. We have used this method for preparing several IDP tau isoforms and found it useful in the investigation of monomeric tau toxicity in rat cerebral neurons.