PROJECT SUMMARY/ABSTRACT The co-occurrence of more than one pathogenic protein is a frequent event in acquired and idiopathic neurodegenerative diseases. Amyloid beta (Aβ) and tau pathologies coexist in Alzheimer's disease; α-synuclein and Aβ in Parkinson's disease with dementia; TAR DNA-binding protein 43 and tau in corticobasal degeneration. Recently, I studied iatrogenic Creutzfeldt-Jakob disease (iCJD), a human prion disease acquired by infection, and chronic traumatic encephalopathy/post-traumatic stress disorder (CTE/PTSD), a neurodegenerative condition secondary to repetitive trauma. A subset of iCJD featured the co-occurrence of pathogenic or disease- related prion protein (PrPD) and Aβ, both of which I suggested result from human-to-human transmission. Similarly, a subset of CTE/PTSD harbored PrPD and pathogenic tau (tauD). The co-existence of multiple pathogenic proteins in neurodegenerative conditions has not yet been fully understood. In this K99/R00 I propose to investigate molecular characteristics of co-occurring proteinopathies in iCJD, sporadic CJD (sCJD) and CTE/PTSD as well as in animal models. Iatrogenic CJD and CTE/PTSD offer the unique advantage to study the mechanisms of non-age related multiprotein neurodegeneration. Three interrelated specific aims are proposed. Specific aim 1 focuses on conformational properties of PrPD and Aβ aggregates from cases with iCJD and sCJD associated with Aβ pathology compared to PrPD features in Aβ- negative iCJD and sCJD; late onset Alzheimer's disease will provide control data from classic Aβ. Specific aim 2 deals with conformational features of PrPD and tauD harvested from CTE/PTSD cases with both proteinopathies compared to corresponding CTE/PTSD cases affected by tauD but not PrPD; cases of prion disease will serve as classic PrPD controls. The methodologies proposed for these studies comprise mass spectrometry-based approaches to assess the conformational features of the co-existing pathogenic proteins, seeding kinetics by protein misfolding cyclic amplification (PMCA) technology and cytotoxicity assay employing primary neuronal cultures. Specific aim 3 dissects further aspects of the co-occurring proteinopathies by transmission of the aforementioned conditions to novel transgenic mouse models co-expressing the human cellular PrP and human amyloid precursor protein (APP). The bioassay will examine critical dynamic aspects of multiprotein neurodegeneration, including timing and route of propagation, existence of interactions of the pathogenic proteins during propagation and stages in the formation of the disease phenotype. I believe that together these studies that take advantage of newly-described conditions comprising multi- and single- proteinopathies along with novel experimental models, will generate significant and needed information on an important area of research. Through these studies and under the dedicated guidance of my two primary mentors, Drs. Surewicz and Zhu, and of the ...