The Two Cysteines of Tau Protein Are Functionally Distinct and Contribute Differentially to Its Pathogenicityin Vivo

Abstract

Although Tau accumulation is clearly linked to pathogenesis in Alzheimer's disease and other Tauopathies, the mechanism that initiates the aggregation of this highly soluble protein in vivo remains largely unanswered. Interestingly, in vitro Tau can be induced to form fibrillar filaments by oxidation of its two cysteine residues, generating an intermolecular disulfide bond that promotes dimerization and fibrillization. The recently solved structures of Tau filaments revealed that the two cysteine residues are not structurally equivalent since Cys-322 is incorporated into the core of the fibril, whereas Cys-291 projects away from the core to form the fuzzy coat. Here, we examined whether mutation of these cysteines to alanine affects differentially Tau mediated toxicity and dysfunction in the well-established Drosophila Tauopathy model. Experiments were conducted with both sexes, or with either sex. Each cysteine residue contributes differentially to Tau stability, phosphorylation status, aggregation propensity, resistance to stress, learning, and memory. Importantly, our work uncovers a critical role of Cys-322 in determining Tau toxicity and dysfunction.

Mical modulates Tau toxicity via cysteine oxidation in vivo

“…Flies were cultured in standard sugar-wheat flour food supplemented with soy flour and CaCl 2 [ 26 ]. Panneuronal transgene expression was achieved using the elav C155 -GAL4 or the elav C155 -GAL4;Ras2-GAL4 double driver as already described [ 7 , 27 ]. Fly crosses and experiments were performed at 25 °C unless noted otherwise.…”

“…The fly line carrying UAS-htau 0N4R was a gift of Dr. M. Feany (Harvard Medical School, [ 29 ]) and UAS-hTau 0N3R of Dr. Stefan Thor (Linkoping University, [ 30 ]). The generation of UAS-htau FLAG−2N4R , UAS-htau FLAG−2N4RC291A and UAS-htau FLAG−2N4RC322A transgenes has been described previously in [ 7 , 31 ]. Fly lines carrying UAS transgenes of full-length GFPMical and Mical G → W mutation (MicalΔredox) were kindly provided by Dr. Jonathan Terman (University of Texas Southwestern Medical Center) [ 22 , 32 ].…”

“…Post-translationally modified Tau is the primary component of intracellular aggregates, a pathological hallmark of AD and other Tauopathies [ 1 , 6 ]. Although phosphorylation at both physiological and non-physiological sites is the most extensively studied Tau post-translational modification (PTM), the protein undergoes additional such modifications including acetylation, ubiquitination, glycosylation and oxidation [ 6 , 7 ]. Tau presents high conformational flexibility primarily arising from the excess of polar amino acids, the relatively small fraction of bulky hydrophobic amino acid side-chains and its high proline content [ 6 , 8 ].…”

“…As we are interested in understanding the nature of the interaction between Tau and Mical and given the importance of cysteine residues for specific physiological and patho-physiological functions of Tau [ 7 ], we hypothesized that they are the most likely candidate amino acids to be post-translationally modified by the enzyme. We describe the genetic interactions between the two proteins with respect to Tau normal function as a cytoskeletal protein, Tau-associated toxicity and dysfunction.…”

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

“…During the preparation of this manuscript, Prifti et al. also reported that alanine substitutions at C291 and C322 decrease tau accumulation and toxicity in a Drosophila model ( 39 ). Although deletion of PHF6 or PHF6 * and cysteine substitutions are all reported to disrupt fibril formation in vitro ( 13 , 15 , 40 ), our results suggest that mechanisms by which these regions contribute to tau toxicity are different, and blocking cysteine residues decreases neurodegeneration via enhancement of tau degradation.…”