Deciphering the Effect of Lysine Acetylation on the Misfolding and Aggregation of Human Tau Fragment 171IPAKTPPAPK180 Using Molecular Dynamic Simulation and the Markov State Model

Palmitic Acid Induces Posttranslational Modifications of Tau Protein in Alzheimer's Disease-Related Epitopes and Increases Intraneuronal Tau Levels

Metabolic diseases derived from an unhealthy lifestyle have been linked with an increased risk for developing cognitive impairment and even Alzheimer's disease (AD). Although high consumption of saturated fatty acids such as palmitic acid (PA) has been associated with the development of obesity and type II diabetes, the mechanisms connecting elevated neuronal PA levels and increased AD marker expression remain unclear. Among other effects, PA induces insulin resistance, increases intracellular calcium and reactive oxygen species (ROS) production, and reduces the NAD+/NADH ratio, resulting in decreased activity of the deacetylase Sirtuin1 (SIRT1) in neurons. These mechanisms may affect signaling pathways that impact the posttranslational modifications (PTMs) of the tau protein. To analyze the role played by PA in inducing the phosphorylation and acetylation of tau, we examined PTM changes in human tau in differentiated neurons from human neuroblastoma cells. We found changes in the phosphorylation state of several AD-related sites, namely, S199/202 and S214, that were mediated by a mechanism associated with the dysregulated activity of the kinases GSK3β and mTOR. PA also increased the acetylation of residue K280 and elevated total tau level after long exposure time. These findings provide information about the mechanisms by which saturated fatty acids cause tau PTMs that are similar to those observed in association with AD biochemical changes.

Molecular Mechanism of Tau Misfolding and Aggregation: Insights from Molecular Dynamics Simulation

Tau dysfunction has a close association with many neurodegenerative diseases, which are collectively referred to as tauopathies. Neurofibrillary tangles (NFTs) formed by misfolding and aggregation of tau are the main pathological process of tauopathy. Therefore, uncovering the misfolding and aggregation mechanism of tau protein will help to reveal the pathogenic mechanism of tauopathies. Molecular dynamics (MD) simulation is well suited for studying the dynamic process of protein structure changes. It provides detailed information on protein structure changes over time at the atomic resolution. At the same time, MD simulation can also simulate various conditions conveniently. Based on these advantages, MD simulations are widely used to study conformational transition problems such as protein misfolding and aggregation. Here, we summarized the structural features of tau, the factors affecting its misfolding and aggregation, and the applications of MD simulations in the study of tau misfolding and aggregation.

Identification of Aggregation Mechanism of Acetylated PHF6* and PHF6 Tau Peptides Based on Molecular Dynamics Simulations and Markov State Modeling

The microtubule-associated protein tau (MAPT) has a critical role in the development and preservation of the nervous system. However, tau's dysfunction and accumulation in the human brain can lead to several neurodegenerative diseases, such as Alzheimer's disease, Down's syndrome, and frontotemporal dementia. The microtubule binding (MTB) domain plays a significant, important role in determining the tau's pathophysiology, as the core of paired helical filaments PHF6* (275VQIINK280) and PHF6 (306VQIVYK311) of R2 and R3 repeat units, respectively, are formed in this region, which promotes tau aggregation. Post-translational modifications, and in particular lysine acetylation at K280 of PHF6* and K311 of PHF6, have been previously established to promote tau misfolding and aggregation. However, the exact aggregation mechanism is not known. In this study, we established an atomic-level nucleation-extension mechanism of the separated aggregation of acetylated PHF6* and PHF6 hexapeptides, respectively, of tau. We show that the acetylation of the lysine residues promotes the formation of β-sheet enriched high-ordered oligomers. The Markov state model analysis of ac-PHF6* and ac-PHF6 aggregation revealed the formation of an antiparallel dimer nucleus which could be extended from both sides in a parallel manner to form mixed-oriented and high-ordered oligomers. Our study describes the detailed mechanism for acetylation-driven tau aggregation, which provides valuable insights into the effect of post-translation modification in altering the pathophysiology of tau hexapeptides.

Investigating the Theranostic Potential of Graphene Quantum Dots in Alzheimer's Disease

Alzheimer's disease (AD) is one of the leading causes of death worldwide, with no definitive diagnosis or known cure. The aggregation of Tau protein into neurofibrillary tangles (NFTs), which contain straight filaments (SFs) and paired helical filaments (PHFs), is a major hallmark of AD. Graphene quantum dots (GQDs) are a type of nanomaterial that combat many of the small-molecule therapeutic challenges in AD and have shown promise in similar pathologies. In this study, two sizes of GQDs, GQD7 and GQD28, were docked to various forms of Tau monomers, SFs, and PHFs. From the favorable docked poses, we simulated each system for at least 300 ns and calculated the free energies of binding. We observed a clear preference for GQD28 in the PHF6 (³⁰⁶VQIVYK³¹¹) pathological hexapeptide region of monomeric Tau, while GQD7 targeted both the PHF6 and PHF6* (²⁷⁵VQIINK²⁸⁰) pathological hexapeptide regions. In SFs, GQD28 had a high affinity for a binding site that is available in AD but not in other common tauopathies, while GQD7 behaved promiscuously. In PHFs, GQD28 interacted strongly near the protofibril interface at the putative disaggregation site for epigallocatechin-3-gallate, and GQD7 largely interacted with PHF6. Our analyses revealed several key GQD binding sites that may be used for detecting, preventing, and disassembling the Tau aggregates in AD.