Protein Disulfide Isomerase Interacts with Tau Protein and Inhibits Its Fibrillization

PLOS ONE, Dec 2019

Background Tau protein is implicated in the pathogenesis of neurodegenerative disorders such as tauopathies including Alzheimer disease, and Tau fibrillization is thought to be related to neuronal toxicity. Physiological inhibitors of Tau fibrillization hold promise for developing new strategies for treatment of Alzheimer disease. Because protein disulfide isomerase (PDI) is both an enzyme and a chaperone, and implicated in neuroprotection against Alzheimer disease, we want to know whether PDI can prevent Tau fibrillization. In this study, we have investigated the interaction between PDI and Tau protein and the effect of PDI on Tau fibrillization. Methodology/Principal Findings As evidenced by co-immunoprecipitation and confocal laser scanning microscopy, human PDI interacts and co-locates with some endogenous human Tau on the endoplasmic reticulum of undifferentiated SH-SY5Y neuroblastoma cells. The results from isothermal titration calorimetry show that one full-length human PDI binds to one full-length human Tau (or human Tau fragment Tau244–372) monomer with moderate, micromolar affinity at physiological pH and near physiological ionic strength. As revealed by thioflavin T binding assays, Sarkosyl-insoluble SDS-PAGE, and transmission electron microscopy, full-length human PDI remarkably inhibits both steps of nucleation and elongation of Tau244–372 fibrillization in a concentration-dependent manner. Furthermore, we find that two molecules of the a-domain of human PDI interact with one Tau244–372 molecule with sub-micromolar affinity, and inhibit both steps of nucleation and elongation of Tau244–372 fibrillization more strongly than full-length human PDI. Conclusions/Significance We demonstrate for the first time that human PDI binds to Tau protein mainly through its thioredoxin-like catalytic domain a, forming a 1∶1 complex and preventing Tau misfolding. Our findings suggest that PDI could act as a physiological inhibitor of Tau fibrillization, and have applications for developing novel strategies for treatment and early diagnosis of Alzheimer disease.

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Protein Disulfide Isomerase Interacts with Tau Protein and Inhibits Its Fibrillization

Citation: Xu L-R, Liu X-L, Chen J, Liang Y ( Protein Disulfide Isomerase Interacts with Tau Protein and Inhibits Its Fibrillization Li-Rong Xu 0 Xiao-Ling Liu 0 Jie Chen 0 Yi Liang 0 Jie Zheng, University of Akron, United States of America 0 State Key Laboratory of Virology, College of Life Sciences, Wuhan University , Wuhan , China Background: Tau protein is implicated in the pathogenesis of neurodegenerative disorders such as tauopathies including Alzheimer disease, and Tau fibrillization is thought to be related to neuronal toxicity. Physiological inhibitors of Tau fibrillization hold promise for developing new strategies for treatment of Alzheimer disease. Because protein disulfide isomerase (PDI) is both an enzyme and a chaperone, and implicated in neuroprotection against Alzheimer disease, we want to know whether PDI can prevent Tau fibrillization. In this study, we have investigated the interaction between PDI and Tau protein and the effect of PDI on Tau fibrillization. Methodology/Principal Findings: As evidenced by co-immunoprecipitation and confocal laser scanning microscopy, human PDI interacts and co-locates with some endogenous human Tau on the endoplasmic reticulum of undifferentiated SH-SY5Y neuroblastoma cells. The results from isothermal titration calorimetry show that one full-length human PDI binds to one full-length human Tau (or human Tau fragment Tau244-372) monomer with moderate, micromolar affinity at physiological pH and near physiological ionic strength. As revealed by thioflavin T binding assays, Sarkosyl-insoluble SDSPAGE, and transmission electron microscopy, full-length human PDI remarkably inhibits both steps of nucleation and elongation of Tau244-372 fibrillization in a concentration-dependent manner. Furthermore, we find that two molecules of the a-domain of human PDI interact with one Tau244-372 molecule with sub-micromolar affinity, and inhibit both steps of nucleation and elongation of Tau244-372 fibrillization more strongly than full-length human PDI. Conclusions/Significance: We demonstrate for the first time that human PDI binds to Tau protein mainly through its thioredoxin-like catalytic domain a, forming a 1:1 complex and preventing Tau misfolding. Our findings suggest that PDI could act as a physiological inhibitor of Tau fibrillization, and have applications for developing novel strategies for treatment and early diagnosis of Alzheimer disease. - Funding: This study was supported by National Key Basic Research Foundation of China (http://www.most.gov.cn/, Grant nos. 2013CB910702 and 2012CB911003, YL), National Natural Science Foundation of China (http://www.nsfc.gov.cn/, Grant nos. 31170744 and 31370774, YL), and Fundamental Research Funds for the Central Universities of China (http://www.moe.edu.cn/, Grant no. 1104006, YL). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Tau protein is implicated in the pathogenesis of neurodegenerative disorders such as tauopathies including Alzheimer disease, and Tau fibrillization is thought to be related to neuronal toxicity [13]. There is no efficient treatment available for Alzheimer disease so far, and the mechanism of Alzheimer disease is still unclear [4,5]. Thus on one hand, the characterization of factors regulating Tau fibrillization is of great importance to clarify the etiology of Alzheimer disease and to assist in the establishment of medical treatment [4,5]. On the other hand, physiological inhibitors for Tau fibrillization, such as molecular chaperone heat shock protein 70 (Hsp70) [6,7], hold promise for development of novel strategies for treatment and early diagnosis of Alzheimer disease. Tau protein does not adopt the compact folded structure typical of most cytosolic proteins because of its hydrophilic character [8]. Instead, Tau protein adopts a natively unfolded or intrinsically disordered structure in solution [9,10]. Tau protein consists of two distinct domains, the projection domain and the microtubule binding domain, and four or three imperfect repeats (R1, R2, R3, and R4) make up the microtubule binding domain [10,11]. Tau244372 contains the four-repeat microtubule binding domain forming the core of bundles of filaments in Alzheimer disease, and can form fibrils with the help of heparin in vitro in a relatively short time [4,1215]. Thus it is a frequently used model for Tau fibrillization [16]. The endoplasmic reticulum (ER), a central player in cell physiology, not only is an important organelle for protein folding and protein posttranslational modification, but also acts as a significant intracellular calcium store [17]. The accumulation of misfolded proteins and Ca2+ influx can cause ER stress in neurons, and severe ER stress can induce apoptosis [18,19]. However, the ER can withstand relatively mild insults through the expression o (...truncated)


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Li-Rong Xu, Xiao-Ling Liu, Jie Chen, Yi Liang. Protein Disulfide Isomerase Interacts with Tau Protein and Inhibits Its Fibrillization, PLOS ONE, 2013, 10, DOI: 10.1371/journal.pone.0076657