Jason C Bartz

Prion diseases are fatal neurodegenerative disorders with no approved therapies that halt or reverse disease progression. Given that cellular prion protein (PrP C ) expression is required for prion propagation and neurotoxicity, reducing its expression is a promising therapeutic strategy. However, complete PrP ablation, as seen in knockout models, causes subtle developmental and behavioral abnormalities, raising concerns about long-term safety. Here, we explore a complementary strategy that harnesses the dominant-negative effect of the naturally protective G127V PrP variant found in kuru-resistant individuals in Papua New Guinea. In CAD5 cell lines, we demonstrate that inducible expression of G126V PrP (the mouse equivalent of human G127V) along with WT PrP prevents and suppresses prion infection in a dose-dependent manner. Extending this approach to CAD5 cells that express bank vole PrP, we further show that the protective effect of G127V spans a wide range of naturally and artificially derived prion strains, highlighting the generality of the dominant-negative approach. Remarkably, prion resistance persists even after G126V expression had ceased, indicating a sustained protective effect that could obviate the need for continuous transgene expression in a therapeutic setting. Finally, we find that anchorless, recombinant G127V PrP retains a potent dominant-negative activity, suggesting the use of this protein as a biological therapeutic. Together, these findings define a framework for development of G127V, a naturally protective and evolutionarily selected PrP variant, as a therapeutic agent to treat or prevent prion diseases.Prion diseases are fatal neurodegenerative disorders with no approved therapies that halt or reverse disease progression. Given that cellular prion protein (PrP C ) expression is required for prion propagation and neurotoxicity, reducing its expression is a promising therapeutic strategy. However, complete PrP ablation, as seen in knockout models, causes subtle developmental and behavioral abnormalities, raising concerns about long-term safety. Here, we explore a complementary strategy that harnesses the dominant-negative effect of the naturally protective G127V PrP variant found in kuru-resistant individuals in Papua New Guinea. In CAD5 cell lines, we demonstrate that inducible expression of G126V PrP (the mouse equivalent of human G127V) along with WT PrP prevents and suppresses prion infection in a dose-dependent manner. Extending this approach to CAD5 cells that express bank vole PrP, we further show that the protective effect of G127V spans a wide range of naturally and artificially derived prion strains, highlighting the generality of the dominant-negative approach. Remarkably, prion resistance persists even after G126V expression had ceased, indicating a sustained protective effect that could obviate the need for continuous transgene expression in a therapeutic setting. Finally, we find that anchorless, recombinant G127V PrP retains a potent dominant-negative activity, suggesting the use of this protein as a biological therapeutic. Together, these findings define a framework for development of G127V, a naturally protective and evolutionarily selected PrP variant, as a therapeutic agent to treat or prevent prion diseases.

In synucleinopathies, the protein α-synuclein misfolds into Lewy bodies (LBs) in patients with Lewy body disease (LBD) or into glial cytoplasmic inclusions (GCIs) in patients with multiple system atrophy (MSA). The ability of a single misfolded protein to cause disparate diseases is explained by the prion strain hypothesis, which argues that protein conformation is a major determinant of disease. While structural, biochemical, and biological studies show that LBD and MSA patient samples contain distinct α-synuclein strains, we recently reported the unexpected finding of a novel α-synuclein strain in a Parkinson’s disease with dementia patient sample containing GCI-like co-pathology along with widespread LB pathology. This finding led us to question if two α-synuclein strains can interact with one another in a patient and, if so, can strain competition occur. Notably, this would not only impact the clinical presentation of disease but would also have profound impacts on successful therapeutic development. To test this possibility, we used the strain interference superinfection model developed in the prion field, in which a slower replicating strain—in this study, mouse-passaged MSA—is used to compete with a faster replicating strain—here, recombinant preformed fibrils (PFFs)— following sciatic nerve (sc.n.) inoculation. Unexpectedly, we found that PFFs generated using the same method differed in their ability to neuroinvade following sc.n. inoculation based on α-synuclein monomer source. Using a PFF preparation that does spread from the periphery, we conducted strain competition studies by first injecting TgM83 +/− mice with mouse-passaged MSA into the sc.n. followed by a second injection with PFFs at 30, 45, and 60% of the MSA incubation period. Unlike in the prion field, where the faster replicating strain inhibits the slower strain at the 30 and 45% time points, we found that the two α-synuclein strains exhibited a synergistic effect during neuroinvasion. Notably, disease onset across the three cohorts was shortened compared to MSA inoculation alone, and brains from terminal animals showed evidence of both the PFF and mouse-passaged MSA strains, suggesting the two strains worked together to accelerate neuroinvasion in the mice. These findings have important implications for disease progression in patients with α-synuclein co-pathologies. The finding that two strains can synergize with one another to accelerate the progression of clinical disease represents a novel outcome in mixed infection studies and more broadly expands our understanding of the effect of prion strain biology on disease pathogenesis.