ABSTRACT Alzheimer's disease (AD) is the most common form of dementia and may contribute to 60--70% of cases, followed in prevalence by Lewy body dementia (LBD), responsible for 17% of the cases. AD and related dementias are thought to be caused by the accumulation of misfolded protein aggregates in the brain. In AD, protein aggregates mostly appear in the form of amyloid plaques and neurofibrillary tangles composed of amyloid-beta (ABeta) and hyperphosporylated Tau, respectively. In LBD the main component of the aggregates is the alpha-synuclein (aSyn) protein. However, there is a substantial overlap of pathological abnormalities, leading to the relatively frequent appearance of mixed pathologies, characterized by the presence of multiple protein aggregates in the same brain. Indeed, up to 30-40% of AD patients display aSyn Lewy bodies in their brains. Although, much investigation has been devoted to understand the role of A~ and Tau aggregates in AD, little research has been done to evaluate the contribution of aSyn in AD and related dementias. Recently, we implemented and developed a highly sensitive and specific assay (termed aSyn-PMCA) to faithfully amplify aSyn seeds present in brain and biological fluids of patients affected by various synucleinopathies, including LBD. Using this technology we were able to amplify seeding competent aSyn aggregates from patients' samples and identify conformational strains associated to different diseases. The major goal of this project is to take advantage of the reliability of the aSyn-PMCA technology to massively amplify aSyn polymorphic variants in order to produce and distribute to the scientific community well-characterized aSyn aggregates amplified from patient's samples. Materials will be characterized for their size, biochemical, biophysical, structural and biological properties using various in vitro, cellular and animal models. Specific aims include: (1) Production of aSyn aggregates by aSyn-PMCA amplification from brain and CSF of patients affected by AD and LBD (as well as other synucleinopathies) and comprehensive analysis of the size, biochemical and biophysical properties of these aggregates; (2) Study the structural basis differentiating different synucleinopathies, in particular we propose to elucidate the structural fold at atomic resolution for aSyn aggregates implicated in different diseases; (3) Study the biological properties of aSyn aggregates derived from AD, LBD and other synucleinopathies using in vitro and in vivo models. (4) Produce and distribute to the scientific community well-characterized and biologically relevant aSyn aggregates. The resources generated in this project will be made fully available to researchers in order to standardize reagents and ensure the biological relevance of the findings.