Naphthoquinone-Tryptophan Hybrid Inhibits Aggregation of the Tau-Derived Peptide PHF6 and Reduces Neurotoxicity

Abstract

Tauopathies, such as Alzheimer's disease (AD), are a group of disorders characterized neuropathologically by intracellular toxic accumulations of abnormal protein aggregates formed by misfolding of the microtubule-associated protein tau. Since protein self-assembly appears to be an initial key step in the pathology of this group of diseases, intervening in this process can be both a prophylactic measure and a means for modifying the course of the disease for therapeutic purposes. We and others have shown that aromatic small molecules can be effective inhibitors of aggregation of various protein assemblies, by binding to the aromatic core in aggregation-prone motifs and preventing their self-assembly. Specifically, we have designed a series of small aromatic naphthoquinone-tryptophan hybrid molecules as candidate aggregation inhibitors of β -sheet based assembly and demonstrated their efficacy toward inhibiting aggregation of the amyloid-β peptide, another culprit of AD, as well as of various other aggregative proteins involved in other protein misfolding diseases. Here we tested whether a leading naphthoquinone-tryptophan hybrid molecule, namely NQTrp, can be repurposed as an inhibitor of the aggregation of the tau protein in vitro and in vivo. We show that the molecule inhibits the in vitro assembly of PHF6, the aggregation-prone fragment of tau protein, reduces hyperphosphorylated tau deposits and ameliorates tauopathy-related behavioral defect in an established transgenic Drosophila model expressing human tau. We suggest that NQTrp, or optimized versions of it, could act as novel disease modifying drugs for AD and other tauopathies.

Cl-NQTrp Alleviates Tauopathy Symptoms in a Model Organism through the Inhibition of Tau Aggregation-Engendered Toxicity

“…2c) [43]. Importantly, we previously demonstrated that there is a correlation between the qualitative morphological classification and pigment levels [43].…”

“…2c) [43]. Importantly, we previously demonstrated that there is a correlation between the qualitative morphological classification and pigment levels [43]. The results were normalized compared to the pigment levels of untreated flies that overexpress h tau as well as to the change in the level of pigment that resulted from the treatment of control flies that do not express h tau with Cl-NQTrp (see formula in Materials and Methods).…”

“…We classified qualitatively, via a stereomicroscope, the eye defects of flies that overexpress h tau in their eyes, as previously described [43] (class 1 = normal, class 2 = moderate, through class 4 = most severe; see Materials and Methods). Using this qualitative classification, we observed a remarkable amelioration of eye neurodegeneration when these animals were fed with Cl-NQTrp (fig.…”

“…The eye defects observed were classified into three classes according to their severity, as previously described [43]: class 2 had mucosal eyes but otherwise normal morphology, class 3 exhibited collapsed eye tissue, and class 4 exhibited black spots of apoptotic tissue on their eyes. In order to examine whether the distribution of eye classes in each experimental group was significantly different from the untreated flies overexpressing h tau, a χ 2 test was performed (p < 0.05 was considered to be significantly different).…”

“…The VQIVYK peptide, termed PHF6, is a highly aggregative short segment located in the third repeat of the MT-binding region of the tau protein [17,18], which can assume the β-sheet structures necessary for the aggregation of tau into oligomers and NFTs [17,19]. This peptide is widely used as a model for studying tau aggregation and examining candidate inhibitors [20,21,22,23,24,25,26]. …”