Increasingly, evidence argues that many
neurodegenerative diseases, including
progressive supranuclear palsy (PSP), are caused by
prions, which are alternatively folded
proteins undergoing self-propagation. In earlier studies, PSP
prions were detected by infecting human embryonic kidney (HEK) cells expressing a tau fragment [TauRD(LM)] fused to yellow fluorescent
protein (YFP). Here, we report on an improved bioassay using selective precipitation of tau
prions from human PSP brain homogenates before
infection of the HEK cells. Tau
prions were measured by counting the number of cells with TauRD(LM)-YFP aggregates using confocal fluorescence microscopy. In parallel studies, we fused α-
synuclein to YFP to bioassay α-
synuclein prions in the brains of patients who died of
multiple system atrophy (MSA). Previously, MSA
prion detection required ∼120 d for transmission into transgenic mice, whereas our cultured cell assay needed only 4 d. Variation in MSA
prion levels in four different brain regions from three patients provided evidence for three different MSA
prion strains. Attempts to demonstrate α-
synuclein prions in brain homogenates from
Parkinson's disease patients were unsuccessful, identifying an important
biological difference between the two
synucleinopathies. Partial purification of tau and α-
synuclein prions facilitated measuring the levels of these
protein pathogens in human brains. Our studies should facilitate investigations of the pathogenesis of both tau and α-
synuclein prion disorders as well as help decipher the basic biology of those
prions that attack the CNS.