P-Tau Dephosphorylation Measurement on the Basis of Biomimetic Electrochemical-Polymerized Thin Film Modified Eqcm
Authors: Chien Shang Chi , Wang Yu-Rong , Chen Jung-Chih 
Published: September 2023

Alzheimer’s disease (AD) is characterized by the abnormal protein deposit in the brain, as a most general neurodegenerative disorder in senior. Microtubule-associated tau protein was regarded as a critical biomarker for AD in recent years due to its post-translational modification, especially hyper-phosphorylated tau protein, which would render the protein aggregation and result in neuron degeneration and paired helical filaments (PHF) formation [1]. Unbalanced activities between kinase and phosphatase are the main reason of tau protein hyper-phosphorylation, including overexpression of kinase. Research has recorded that kinases inhibitor would reverse the hyper-phosphorylation induced pathology, showing the possible therapeutic strategy with adjusting the amount of phosphorylated sites. However, this indirect method is insufficient to reverse the neurofibrillary tangle and PHF aggregation [2]. A highly effective method of reversing hyper-phosphorylation need to be investigated. Furthermore, to control the phosphorylation of tau protein, a material with good interaction with biomolecules is required.
In this study, polyaniline (PANI), as one of organic conducting polymers [3], was selected due to its fascinating properties and unparalleled multifunction, including good interaction with proteins, controllable electrical conductivity, ideal stability during electrochemical reactions, and changeable nanostructures, could meet above demands and offer further more bio-applications [4]. Through the electrochemical reaction-driven exchange of ions during oxidation and reduction, PANI mimics change in functional biological organs [5] and plays a key role to create a state-of-the-art biomimetic hippocampus.
A new in vitro experimental architecture was developed based on electrical quartz crystal microbalance (EQCM). First, tau protein was adsorbed on PANI-modified electrodes by electrostatic interaction to mimic captured process on the hippocampus. Then, both the constant-potential method (current-time curve) and Cyclic Voltammetry (CV) were introduced to investigate the electrochemically-driven dephosphorylation-related process and mechanism following the found optimal potential and stimulation time.
As the result, the feasibility of electrochemically-driven dephosphorylation was confirmed. By establishing the relationship between resonant frequency and mass change, this hippocampus-inspired biomimetic polymeric EQCM electrode could detect a trace amount of phosphate and whole protein adsorbed and desorbed to explore the possibility of a non-invasive therapeutic strategy for AD.
[1]Alonso, A. D. C., Grundke-Iqbal, I., & Iqbal, K. "Alzheimer's disease hyperphosphorylated tau sequesters normal tau into tangles of filaments and disassembles microtubules," Nature medicine, 2(7), 783-787. (1996).
[2]Engel, T., Goñi‐Oliver, P., Lucas, J. J., Avila, J., & Hernández, F., "Chronic lithium administration to FTDP-17 tau and GSK‐3β overexpressing mice prevents tau hyperphosphorylation and neurofibrillary tangle formation, but pre-formed neurofibrillary tangles do not revert," Journal of neurochemistry, 99(6), 1445-1455. (2006).
[3]Higgins, M. J., Molino, P. J., Yue, Z., & Wallace, G. G. (2012). Organic conducting polymer–protein interactions. Chemistry of Materials, 24(5), 828-839.
[4]Huang, L., Hu, J., Lang, L., Wang, X., Zhang, P., Jing, X., ... & Wei, Y. (2007). Synthesis and characterization of electroactive and biodegradable ABA block copolymer of polylactide and aniline pentamer. Biomaterials, 28(10), 1741-1751.
[5] Higgins, M. J., Molino, P. J., Yue, Z., & Wallace, G. G. (2012). Organic conducting polymer–protein interactions. Chemistry of Materials, 24(5), 828-839.

Figure 1