The prion-like propagation hypothesis in Alzheimer's and Parkinson's disease

Purpose of review This study, taking the example of Alzheimer's and Parkinson's diseases, presents the experimental and human data that support the hypothesis that A beta, tau, and alpha-synuclein may seed and propagate the pathology and consider the potential clinical consequences. Recent findings A beta aggregates transmit A beta pathology to experimental animals. lnterhuman transmission of A beta pathology has also been observed in iatrogenic Creutzfeldt-Jakob disease, or after dural graft. Tau aggregates also transmit the pathology to mice when injected in the brain and propagates along neuronal pathways. Evidence of interhuman transmission is weak. Finally alpha-synuclein aggregates, when injected in specific areas of the brain may recapitulate Lewy pathology of Parkinson's disease but there is currently no hint of human to human transmission. Summary Since the first evidence that at least A beta pathology of Alzheimer's disease could be transmitted to the animal, data have accumulated indicating that misfolded proteins characteristic of neurodegenerative diseases may seed and propagate pathology in a prion-like manner. The term propagon has been proposed to describe those proteins that act as prions at different levels. Taking the example of Alzheimer's and Parkinson's diseases, the experimental and human data supporting the hypothesis that A beta, tau, and alpha-synuclein are indeed propagons are presented with their clinical consequences.