Mechanisms of tau proteotoxicity in neurodegeneration

Background: Brain lesions in the form of protein deposits are instrumental pathological markers for neurodegenerative diseases. It is now accepted, supported by genetic findings, that fibrillar protein deposition and concomitant proteotoxicity are features underlying most neurodegenerative diseases. Neurodegeneration-associated proteins normally display an intrinsically disordered structure that changes into a fibrillization-prone cross ß-sheet rich conformation. This conformation switch correlates with aging, aberrant post-translational modifications, impaired clearance and increased toxicity. In addition, the prion-like intermolecular and transcellular propagation of pathological protein forms is shared by most neurodegenerative disorders. Hypothesis: Protein toxicity results from the interplay between a particular subcellular location and specific modifications, conformations or multimeric/fibrillar assemblies. The elucidation of the processes reciprocally regulating subcellular location and abnormal protein forms will allow a better understanding of the proteotoxic mechanism. This is required for much-needed disease-modifying therapies and for the development of early diagnostic approaches for neurodegenerative disorders.Aims: The identification of conditions and cellular processes regulating selective post-translational modifications followed/preceded by specific subcellular (mis)location of neurodegeneration-associated proteins (tau, a-synuclein, huntingtin) and how these affect their prion-like properties. Strategy: We propose to use a fluorescent protein-complementing technology, which offers multiple analytic approaches such as a) confocal microscopy to study in live time-dependent subcellular location, b) biochemical isolation of subcellular protein pools for the identification of abnormal protein modifications and conformation, and c) fluorimetric methods for the study of transcellular pathological protein propagation. As a model protein, we selected tau, which is involved in different neurodegenerative tauopathies. Parkinson’s disease-linked a-synuclein and Huntington’s disease-linked huntingtin will be analyzed in comparative studies to highlight specific, or common, pathogenic events.Expected value: Prion-like behavior is a repetitive chain of events of abnormal protein folding and assembly, recruitment of monomers, resistance to cellular clearance, amplification of seeding species and transcellular spreading. Our proposal aims at dissecting some of these events and finds impact in a medicine domain - protein misfolding disorders - where disease-modifying therapies and early markers of an ongoing pre-symptomatic neurodegeneration are still missing.