How substrate dosage drives prion disease kinetics

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PROJECT SUMMARY Prion disease is a uniquely rapid, universally fatal progressive neurodegenerative disease of humans and other mammals. It arises from a single protein, the native prion protein (PrP), which is capable of post-translationally misfolding into a self-templating and deadly “prion.” Genetic and pharmacological proofs of concept increasingly identify PrP dosage as the key to understanding, and ultimately intercepting this pathogenic cascade. In mice with genetically altered PrP levels, lower PrP levels lead to longer survival following prion infection, while excess PrP hastens disease. PrP-lowering antisense oligonucleotides (ASOs) now show promise as a potential therapeutic strategy. However, effective implementation will hinge on a deeper understanding of how PrP level controls the rates of prion nucleation, replication and neurotoxicity, and how this control translates across disease timepoints, species and strains. Though almost all human prion disease originates in the brain, PrP-lowering interventions have not yet been tested in spontaneous, rather than inoculated, prion models. Meanwhile, the magnitude of protection conveyed by 50% genetic PrP reduction can vary between model systems; the relative contributions of slowed prion replication and slowed neurotoxicity to observed survival benefit in different species and prion strains remain to be disentangled. Finally, PrP lowering must be studied in the context of patient-derived human prions, to assess how above learnings extrapolate to strains of public health interest. We will fill these gaps by assessing the following. 1) Kinetics of spontaneous prion formation. Using a new mouse model of spontaneous prion disease, we will track the spontaneously disease process through serial molecular measurements of neuronal damage and prion seeding activity. Through PrP-lowering tool compounds administered at different timepoints, we will disentangle how PrP dosage modulates prion formation, amplification, neurotoxicity and symptomatic progression. 2) Rapid and slow prion subtypes as a function of PrP dosage. Using newly engineered PrP knockout hamster and rat models, we will characterize the kinetics of pathological biomarker rise relative to disease onset and terminal illness as a function of PrP expression level in both canonically rapid (hamster) and more slowly progressive (rat) prion disease systems. 3) Impact of PrP lowering on human prions. Using a series of novel “humanized” mouse lines expressing human PrP at six different dosage levels, that have been shown susceptible to multiple clinically relevant human prion strains, we will characterize time to pathology, symptom onset, and terminal illness. PrP level will be varied on a lifelong basis through genetically manipulation, as well as through postnatal, precisely timed intervention with PrP-lowering tool compounds. Taken together, these studies will illuminate PrP’s control of disease kinetics across a spectrum of prion disease paradigms, while building a scientific foundation to guide future development of PrP-lowering therapeutics.