Size Matters: Aggregate Structure Affects CWD Prion Replication Kinetics, Brain Region Tropism, and Transcriptomic Response.

The infectious prion protein (PrPSc) is the main component of prions, which can exist as distinct strains defined, in part, by PrPSc quaternary structure distribution and regional deposition in the brain. The mechanisms driving brain region tropism remain unclear. We hypothesize that prion quaternary structure directs regional targeting.

We inoculated mice with CWD prions of low (LMW) and high (HMW) molecular weight derived from infected elk and collected brains at defined timepoints post-inoculation. We assessed clinical signs, prion replication kinetics, protease-resistant PrPSc, astrogliosis, and vacuolation across brain regions.

LMW and HMW groups exhibited distinct clinical signs. A control group receiving sonicated HMW inoculum showed the same signs as LMW. LMW prions seeded strongly across brain regions within one month post-inoculation (MPI) and induced early vacuolation in cortex and corpus callosum. HMW prions showed lower early seeding but induced protease-resistant PrPSc and hippocampal vacuolation at one MPI. To investigate pathways underlying distinct signs, we performed single-nucleus RNA sequencing at an early preclinical timepoint. Both groups showed substantial astrogliosis, cell population shifts, and transcriptomic changes as early as one MPI.

Our results provide the first evidence that PrPSc quaternary structure is causally linked to clinical presentation. Based on our data, PrPSc quaternary structure dictates localization to, interactions with, and replication in distinct brain region environments which, taken together, result in distinct clinical presentations.

Given heterogeneity of PrPSc quaternary structures among prion strains, our findings reveal key determinants of strain-specific brain tropism and clinical presentation: structural conformer interactions with brain microenvironments.