More Like this

1. Narrow equilibrium window for complex coacervation of tau and RNA under cellular conditions

   https://doi.org/10.7554/eLife.42571  

   Lin, Yanxian ; McCarty, James ; Rauch, Jennifer N ; Delaney, Kris T ; Kosik, Kenneth S ; Fredrickson, Glenn H ; Shea, Joan-Emma ; Han, Songi ( April 2019 , eLife)

   Proteins make up much of the machinery of cells and perform many roles that are essential for life. Some important proteins – known as intrinsically disordered proteins – lack any stable three-dimensional structure. One such protein, called tau, is best known for its ability to form tangles in the brain, and a buildup of these tangles is a hallmark of Alzheimer’s disease and many other dementias. Tau is also one of a number of proteins that can undergo a process called liquid-liquid phase separation: essentially, a solution of tau separates into a very dilute solution interspersed with droplets of a concentrated tau solution, similar to an oil-water mixture separating into a very watery solution with drops of oil. Understanding the conditions that lead to spontaneous liquid-liquid phase separation might give insight into how the tau tangles form. However, it was not known whether it is possible in principle for liquid-liquid phase separation of tau to occur in a living brain. Lin, McCarty et al. have now used an advanced computer simulation method together with experiments to map the conditions under which a solution containing tau undergoes liquid-liquid phase separation. Temperature as well as the concentrations of salt and the tau protein all influenced how easily tau droplets formed or dissolved, and the narrow range of conditions that encouraged droplet formation fell within the normal conditions found in the body, also known as “physiological conditions”. This suggested that tau droplets might form and dissolve easily in living systems, and possibly in the brain, depending on the precise physiological conditions. To explore this possibility further, tau protein was added to a dish containing living cells. As the map suggested, slightly adjusting temperature or protein concentrations caused tau droplets to form and dissolve, all while the cells remained alive. The map provided by this study may offer guides to researchers looking for liquid-liquid phase separation in the brain. If liquid-liquid phase separation of tau occurs in living brains, it may be important for determining whether and when damaging tau tangles emerge. For example, the high concentration of tau in droplets might speed up tangle formation. Ultimately, a better understanding of the conditions and mechanism for liquid-liquid phase separation of tau can help researchers understand the role of protein droplet formation in living systems. This may be a process that promotes, or possibly a regulatory mechanism that prevents, the formation of tau tangles associated with dementia. 

   more » « less
2. Liquid–liquid phase separation of Tau by self and complex coacervation

   https://doi.org/10.1002/pro.4101  

   Najafi, Saeed ; Lin, Yanxian ; Longhini, Andrew P. ; Zhang, Xuemei ; Delaney, Kris T. ; Kosik, Kenneth S. ; Fredrickson, Glenn H. ; Shea, Joan‐Emma ; Han, Songi ( May 2021 , Protein Science)

   The liquid–liquid phase separation (LLPS) of Tau has been postulated to play a role in modulating the aggregation property of Tau, a process known to be critically associated with the pathology of a broad range of neurodegenerative diseases including Alzheimer's Disease. Taucan undergo LLPS by homotypic interaction through self‐coacervation (SC) or by heterotypic association through complex‐coacervation (CC) between Tau and binding partners such as RNA. What is unclear is in what way the formation mechanisms for self and complex coacervation of Tau are similar or different, and the addition of a binding partner to Tau alters the properties of LLPS and Tau. A combination ofin vitroexperimental and computational study reveals that the primary driving force for both Tau CC and SC is electrostatic interactions between Tau‐RNA or Tau‐Tau macromolecules. The liquid condensates formed by the complex coacervation of Tau and RNA have distinctly higher micro‐viscosity and greater thermal stability than that formed by the SC of Tau. Our study shows that subtle changes in solution conditions, including molecular crowding and the presence of binding partners, can lead to the formation of different types of Tau condensates with distinct micro‐viscosity that can coexist as persistent and immiscible entities in solution. We speculate that the formation, rheological properties and stability of Tau droplets can be readily tuned by cellular factors, and that liquid condensation of Tau can alter the conformational equilibrium of Tau.

    

   more » « less
3. Yeast surface display of full‐length human microtubule‐associated protein tau

   https://doi.org/10.1002/btpr.2920  

   Wang, Shiyao ; Cho, Yong Ku ( October 2019 , Biotechnology Progress)

   Microtubule‐associated protein tau is an intrinsically disordered, highly soluble protein found primarily in neurons. Under normal conditions, tau regulates the stability of axonal microtubules and intracellular vesicle transport. However, in patients of neurodegeneration such as Alzheimer's disease (AD), tau forms neurofibrillary deposits, which correlates well with the disease progression. Identifying molecular signatures in tau, such as posttranslational modification, truncation, and conformational change has great potential to detect earliest signs of neurodegeneration and develop therapeutic strategies. Here, we show that full‐length human tau, including the longest isoform found in the adult brain, can be robustly displayed on the surface of yeastSaccharomyces cerevisiae. Yeast‐displayed tau binds to anti‐tau antibodies that cover epitopes ranging from the N‐terminus to the 4R repeat region. Unlike tau expressed in the yeast cytosol, surface‐displayed tau was not phosphorylated at sites found in AD patients (probed by antibodies AT8, AT270, AT180, and PHF‐1). However, yeast‐displayed tau showed clear binding to paired helical filament (PHF) tau conformation‐specific antibodies Alz‐50, MC‐1, and Tau‐2. Although the tau possessed a conformation found in PHFs, oligomerization or aggregation into larger filaments was undetected. Taken together, yeast‐displayed tau enables robust measurement of protein interactions and is of particular interest for characterizing conformational change.

    

   more » « less
4. Joint Computational/Cell-Based Approach for Screening Inhibitors of Tau Oligomerization: A Proof-of-Concept Study

   https://doi.org/10.3233/JAD-220450  

   Man, Viet Hoang ; Lin, Da ; He, Xibing ; Gao, Jie ; Wang, Junmei ( August 2022 , Journal of Alzheimer's Disease)

   Background: Tau assembly produces soluble oligomers and insoluble neurofibrillary tangles, which are neurotoxic to the brain and associated with Alzheimer’s and Parkinson’s diseases. Therefore, preventing tau aggregation is a promising therapy for those neurodegenerative disorders. Objective: The aim of this study was to develop a joint computational/cell-based oligomerization protocol for screening inhibitors of tau assembly. Methods: Virtual oligomerization inhibition (VOI) experiment using molecular dynamics simulation was performed to screen potential oligomerization inhibitors of PHF6 hexapeptide. Tau seeding assay, which is directly related to the outcome of therapeutic intervention, was carried out to confirm a ligand’s ability in inhibiting tau assembly formation. Results: Our protocol was tested on two known compounds, EGCG and Blarcamesine. EGCG inhibited both the aggregation of PHF6 peptide in VOI and tau assembly in tau seeding assay, while Blarcamesine was not a good inhibitor at the two tasks. We also pointed out that good binding affinity to tau aggregates is needed, but not sufficient for a ligand to become a good inhibitor of tau oligomerization. Conclusion: VOI goes beyond traditional computational inhibitor screening of amyloid aggregation by directly examining the inhibitory ability of a ligand to tau oligomerization. Comparing with the traditional biochemical assays, tau seeding activities in cells is a better indicator for the outcome of a therapeutic intervention. Our hybrid protocol has been successfully validated. It can effectively and efficiently identify the inhibitors of amyloid oligomerization/aggregation processes, thus, facilitate to the drug development of tau-related neurodegenerative diseases. 

   more » « less
5. What’s the cut-point?: a systematic investigation of tau PET thresholding methods

   https://doi.org/10.1186/s13195-022-00986-w  

   Weigand, Alexandra J. ; Maass, Anne ; Eglit, Graham L. ; Bondi, Mark W. ( April 2022 , Alzheimer's Research & Therapy)

   Tau positron emission tomography (PET) is increasing in popularity for biomarker characterization of Alzheimer’s disease (AD), and recent frameworks rely on tau PET cut-points to stage individuals along the AD continuum. Given the lack of standardization in tau PET thresholding methods, this study sought to systematically canvass and characterize existing studies that have derived tau PET cut-points and then directly assess different methods of tau PET thresholding in terms of their concurrent validity.

   First, a literature search was conducted in PubMed to identify studies of AD and related clinical phenotypes that used the Flortaucipir (AV-1451) tau PET tracer to derive a binary cut-point for tau positivity. Of 540 articles screened and 47 full-texts reviewed, 23 cohort studies met inclusion criteria with a total of 6536 participants. Second, we derived and compared tau PET cut-points in a 2 × 2 × 2 design that systematically varied region (temporal meta-ROI and entorhinal cortex), analytic method (receiver operating characteristics and 2 standard deviations above comparison group), and criterion/comparison variable (amyloid-beta negative cognitively unimpaired or cognitively unimpaired only) using a sample of 453 older adults from the Alzheimer’s Disease Neuroimaging Initiative.

   For the systematic review, notable variability in sample characteristics, preprocessing methods, region of interest, and analytic approach were observed, which were accompanied by discrepancy in proposed tau PET cut points. The empirical follow-up indicated the cut-point derived based on 2 standard deviations above a either comparison group in either ROI best differentiated tau positive and negative groups on cerebrospinal fluid phosphorylated tau, Mini-Mental State Examination score, and delayed memory performance.

   Given the impact of discrepant thresholds on tau positivity rates, biomarker staging, and eligibility for future clinical treatment trials, recommendations are offered to select cut-point derivations based on the unique goals and priorities of different studies.

    

   more » « less