Cellular assays reveal a decline in Aβ and tau pathological conformers in Alzheimer’s disease brain samples.

Significance: Dementia with Lewy bodies (DLB) and multiple system atrophy (MSA) are caused by α-synuclein prions that differ from each other and from those causing Parkinson’s disease (PD). DLB prions differ in their infectivity from those causing MSA or PD. The wild-type, normal version of the α-synuclein protein has the acidic amino acid glutamate (E) at residue 46, while in cases of inherited PD, it is mutated to the basic amino acid lysine (K). Using genetically engineered α-synuclein, we identified unique conditions for propagating MSA and DLB prions. Being able to distinguish among strains of naturally occurring α-synuclein prions may make it possible to develop strain-specific therapeutics for MSA, DLB, and PD.

Multiple system atrophy (MSA), a progressive neurodegenerative disease characterized by autonomic dysfunction and motor impairment, is caused by the self-templated misfolding of the protein α-synuclein. With no treatment currently available, we sought to characterize the spread of α-synuclein in a transgenic mouse model of MSA prion propagation to support drug discovery programs for synucleinopathies. Brain homogenates from MSA patient samples or mouse-passaged MSA were inoculated either by standard freehand injection or stereotactically into TgM83^+/- mice, which express human α-synuclein with the A53T mutation. Following disease onset, brains from the mice were tested for biologically active α-synuclein prions using a cell-based assay and examined for α-synuclein neuropathology. Inoculation studies using homogenates prepared from brain regions lacking detectable α-synuclein neuropathology transmitted neurological disease to mice. Terminal animals contained similar concentrations of α-synuclein prions; however, a time-course study where mice were terminated every five days through disease progression revealed that the kinetics of α-synuclein prion replication in the mice were variable. Stereotactic inoculation into the thalamus reduced variability in disease onset in the mice, although incubation times were consistent with standard inoculations. Using human samples with and without neuropathological lesions, we observed that α-synuclein prion formation precedes neuropathology in the brain, suggesting that disease in patients is not limited to brain regions containing neuropathological lesions. The underlying cause of disease in a group of rapidly progressing neurodegenerative disorders called prion diseases is the misfolding of the prion protein (PrP) into a conformation that can self-template and spread disease throughout the brain. Diseases caused by this phenomenon include Creutzfeldt–Jakob disease (CJD), chronic wasting disease, and bovine spongiform encephalopathy (“mad cow” disease). In 2015, we demonstrated that this same mechanism is responsible for the neurodegenerative disease multiple system atrophy (MSA); however, the disease is caused by the misfolding of the protein α-synuclein rather than PrP. Having shown that α-synuclein prions in MSA patient samples exhibit a number of properties consistent with PrP prions in CJD patients, we sought to establish and define a rigorous transgenic mouse model of α-synuclein prion propagation to support ongoing drug discovery efforts for MSA therapeutics. In this study, we identified optimized methods for transmitting MSA in a transgenic mouse model of α-synuclein prion spreading and defined disease pathogenesis in these mice. These results are needed to properly evaluate compounds that may prevent α-synuclein prion spreading. We also showed that in both human and mouse brain, α-synuclein prion spreading precedes the formation of neuropathological lesions traditionally used to define disease, yielding new insights into the progression of MSA.