EGCG impedes human Tau aggregation and interacts with Tau

Abstract

Tau aggregation and accumulation is a key event in the pathogenesis of Alzheimer's disease. Inhibition of Tau aggregation is therefore a potential therapeutic strategy to ameliorate the disease. Phytochemicals are being highlighted as potential aggregation inhibitors. Epigallocatechin-3-gallate (EGCG) is an active phytochemical of green tea that has shown its potency against various diseases including aggregation inhibition of repeat Tau. The potency of EGCG in altering the PHF assembly of full-length human Tau has not been fully explored. By various biophysical and biochemical analyses like ThS fluorescence assay, MALDI-TOF analysis and Isothermal Titration Calorimetry, we demonstrate dual effect of EGCG on aggregation inhibition and disassembly of full-length Tau and their binding affinity. The IC50 for Tau aggregation by EGCG was found to be 64.2 μM. Abbreviations EGCG Epigallocatechin-3-gallate AD Alzheimer's disease Aβ Amyloid-β IAPP Islet amyloid polypeptide ITC Isothermal titration calorimetry TEM Transmission electron microscopy SEC Size exclusion chromatography MTT 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide ThS Thioflavin S ANS 8-Anilino-1-naphthalenesulfonic acid ammonium salt The direct causal relationship between neurodegenerative disorders and protein misfolding has been debatable over years 1-3. The recent advances in studies of misfolded proteins to some extent have shed the light upon the cause-effect interdependence of proteins and diseases 4. Neurodegenerative diseases are diverse in nature at physiological as well as molecular level. For example, the misfolded proteins involved in Alzheimer's disease (AD) are amyloid-β (Aβ) and Tau (Fig. 1A) whereas 5 ; α-Synuclein is a key player in Parkinson's disease. AD is phenotypically characterized by gradual memory loss due to neuronal death 6. The molecular pathology involves abnormal accumulation of Aβ plaques 7 in the extracellular milieu and cytoplasmic Tau tangles 8,9. Tau aggregation increases load on clearance machinery of neurons, which finally collapses, and results in neuronal death 10,11. The physiological function of Tau is to bind microtubules and stabilize them thus aiding in neuronal functioning 12,13. Tau aggregates abnormally due to multiple factors-like mutations, aberrant post-translational modifications, oxidative stress etc. 14-16. Abnormal phosphorylation of Tau is one of the key factors implied in its aggregation 17,18. The factors leading to Tau aggregation have directed the researchers to design and develop the therapeutics against Tau aggregation and AD. Several classes of compounds showing potency in inhibiting Tau aggregation include phenothiazines 19,20 , anthraquinones 21 , porphyrins, aminothienopyridazines 22 , natural compounds (polyphenols 23 , secondary metabolites 24 , curcumin 25 , Oleocanthal 26 etc.). The phenothiazine compounds inhibit Tau-Tau (repeat domain) binding thus preventing Tau aggregation. These compounds have

(−)-Epigallocatechin-3-Gallate Diminishes Intra-and Extracellular Amyloid-Induced Cytotoxic Effects on Cholinergic-like Neurons from Familial Alzheimer’s Disease PSEN1 E280A

“…At the molecular level, auto-oxidized EGCG reacts with free primary amine groups of proteins, forms a Schiff base, and induces fibril remodeling [ 37 , 38 ]. Interestingly, this mechanism not only might be operative with Aβ and TAU [ 39 ] in AD but also to other neurodegenerative disorders such as α-synuclein (in Parkinson’s disease), Huntingtin protein (in Huntington’s disease), and islet amyloid polypeptide (IAPP, amylin) in the pancreas most probably through a common mechanism, in which EGCG binds to cross-beta sheets amyloid aggregation intermediates remodeling the oligomeric amyloid or pre-formed amyloid fibrils into non-amyloidogenic species [ 21 , 40 ]. According to this view, we found that EGCG significantly reduces (i)sAPPβf aggregates in PSEN 1 E280A ChLNs demonstrated by FM staining, and FC analysis.…”

Microglial remodeling of actin network by Tau oligomers, via G protein‐coupled purinergic receptor, P2Y12R‐driven chemotaxis

“…The structure of oligomers and aggregates were observed by TEM by spotting it onto 400 mesh carbon‐coated copper grids and stained with 2% uranyl acetate. The grids were dried and analyzed by Tecnai T20 at 120 kV for TEM study 82 . Tau oligomers and aggregates were spotted onto a nitrocellulose membrane at a final concentration of 2.5 mg/mL and allowed for complete drying.…”

Green Tea Epigallocatechin-3-gallate (EGCG) Targeting Protein Misfolding in Drug Discovery for Neurodegenerative Diseases

“…This effect was characterized in a study conducted in 2015, which combined cell-free aggregation and a cell-based assay, and found that EGCG could be a potent inhibitor of tau aggregation and toxicity, preventing the aggregation of tau protein into toxic oligomers at substoichiometric ratios [150]. More recently, a study with various biophysical and biochemical analyses suggested a possible dual effect of EGCG on aggregation inhibition and disassembly of full-length tau and their binding affinity [28].…”

“…Studies have revealed that EGCG can interact with a variety of proteins linked to protein misfolding, such as Aβ, tau, α-synuclein (α-syn), transthyretin (TTR), and huntingtin [25][26][27][28]. This review addresses the contribution of EGCG research toward advances in neurodegenerative disease drug discovery.…”