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.Workingtogethercloselyinaniterativemannerweintendtodeterminethepathwayfromnormal 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 amountsofheparin,segmentsofTaudramaticallyextendbyananometertosolvent-exposethehydrophobic 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 dropletsheldtogetherbyweakelectrostaticforces.Attheinvivocellularlevel,theKosiklabdiscoveredTau- tRNAcomplexes,therebyaddingTautothegrowinglistofRNA-bindingproteinsinvolvedinneurodegeneration, andcapableofestablishingliquid-liquidphaseseparationinthecytoplasm.TheTau-tRNAcomplexesmaybea physiologic or pathological entity?we will obtain clues by determining their loci in neuronal cells. Finally, we intendtolearnwhethertheconformationofTau,asmodulatedbydiseasemutationsorco-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 #
1R01AG056058-01
Application #
9224771
Study Section
Special Emphasis Panel (ZRG1-BCMB-T (02)M)
Program Officer
Yang, Austin Jyan-Yu
Project Start
2017-04-01
Project End
2022-03-31
Budget Start
2017-04-01
Budget End
2018-03-31
Support Year
1
Fiscal Year
2017
Total Cost
$434,174
Indirect Cost
$133,349
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