Tauisamicrotubule-stabilizingproteinthatisabundantinneurons.Itisahighlysoluble,intrinsicallydisordered protein(IDP)withlittletendencyforaggregationundernativeconditions.However,underseveralexperimental conditionsandinavarietyofneurodegenerativedisordersincludingAlzheimer?sdisease,Taucanspreadfrom cell to cell and aggregates as intra-cellular ?-sheet fibrilar deposits. Our laboratories have critical new data concerningthetemporal,structuralandcellbiologicaldetailsofTaumisfoldingandfluid-phaseassembly?the basis of this proposal. Our research team consists of a cell biologist, a physical chemist, and a theoretical biophysicist. Working together closely in an iterative mannerwe intend to determine the pathway from normal Tautodisease-relatedTaufibrils.Thetoolsforthisanalysisinclude(a)cellularsystemscapableofaddressing invivoTauinteractions,andindirectlyitsconformationalstatebasedonavarietyofmolecularprobes;?(b)site- directedspinlabeling,electronparamagneticresonance(EPR)lineshapeanalysisandpulseddipolarEPRto determine conformational signatures of Tau;? and (c) fully atomistic modeling of IDP conformations, their populationsandenergetics,andcoarse-grainedsimulationofhigher-orderassembliesofTau.Theconceptual flowoftheproposalbeginswitharemarkableobservationfromtheHanlab:Whenexposedtosub-stoichiometric amounts of heparin, segments of Tau dramatically extend by a nanometer to solvent-expose the hydrophobic PHF6(*) segment capable of stacking into neat ?-sheets. This observation correlates with the appearance of fibrils,andthuswerefertothisinitiatingstepas?onpathway?seeding.Invivo,Tauisknowntopopulateavast conformationallandscapecontrolledbyalternativesplicing,mutationsandpost-translationalmodifications.We propose that the IDP Tau populates an ensemble of different conformations with different aggregation propensities, fibril morphologies and interaction partners, depending on the exact Tau variant. However, the defining and specific conformational signatures within this ensemble are unknown. Determining the conformationalsignaturesofaggregation-proneTauvariantsisourcoreobjective,whileamissingpuzzlepiece inconnectingTauconformationtocellularinteractionsistheexistenceandnatureofaggregationintermediates. Inthisvein,theHanlabdiscoveredthatRNAinducesliquid-liquidphaseseparationofTauinvitrointoprotein droplets held together by weak electrostatic forces. At the in vivo cellular level, the Kosik lab discovered Tau- tRNAcomplexes,therebyaddingTautothegrowinglistofRNA-bindingproteinsinvolvedinneurodegeneration, andcapableofestablishingliquid-liquidphaseseparationinthecytoplasm.TheTau-tRNAcomplexesmaybea physiologic or pathological entity?we will obtain clues by determining their loci in neuronal cells. Finally, we intend to learn whether the conformation of Tau, as modulated by disease mutations or co-factors, influences thestabilityandinvivolocalityoftheTau-tRNAcomplexes.Ourgoalistodiscoveradetailedroutefromsoluble Tautofibrils,fromthenanometertothecellularlevel,anddiscoverthepathologicalentitiesofTauaggregation.

Public Health Relevance

Tauself-assemblyintofibrilsthatformcellularinclusionsisfoundationaltothepathologyofAlzheimer?sDisease (AD) and other Tauopathies. However, the factors that initiate the aggregation of Tau are unknown. A cell biologist,aphysicalchemist,andatheoreticalbiophysicistproposetoworktogetherinaniterativemannerand exploitnoveltoolstodeterminethepathwayfromnormalTautodisease-relatedTaufibrilsinaquesttodiscover thepathologicallyrelevantspeciesandfactors.

Agency
National Institute of Health (NIH)
Institute
National Institute on Aging (NIA)
Type
Research Project (R01)
Project #
3R01AG056058-02S1
Application #
9695490
Study Section
Program Officer
Yang, Austin Jyan-Yu
Project Start
2018-07-01
Project End
2019-06-30
Budget Start
2018-09-15
Budget End
2019-06-30
Support Year
2
Fiscal Year
2018
Total Cost
Indirect Cost
Name
University of California Santa Barbara
Department
Chemistry
Type
Schools of Arts and Sciences
DUNS #
094878394
City
Santa Barbara
State
CA
Country
United States
Zip Code
93106