Transmissible spongiform encephalopathies (TSEs or prion diseases) are a group of rare neurodegenerative diseases which include scrapie in sheep, bovine spongiform encephalopathy (BSE), and chronic wasting disease (CWD) in mule deer and elk. In humans, the most common type of prion disease is Creutzfeldt-Jakob disease (CJD) which can occur in several forms. Sporadic CJD (sCJD) makes up the majority of the cases and occurs randomly at an incidence of 1-2 per million people worldwide. Iatrogenic CJD (iCJD) is associated with exposure to prion contaminated medical instruments or products while familial CJD (fCJD) is associated with mutations in the prion protein gene. The infectious agent of TSE diseases is called a prion and is largely composed of an abnormally refolded, protease resistant form (PrPSc) of the normal, protease-sensitive prion protein, PrPC. PrPSc can be deposited in the brain as either diffuse, amyloid negative deposits or as dense, amyloid positive deposits. Amyloid forms of prion disease appear to be less transmissible than non-amyloid forms. Furthermore, it is unclear whether or not prion diseases where PrPSc is deposited primarily as amyloid follow the same pathogenic processes as prion diseases where PrPSc is primarily deposited as non-amyloid. Interestingly, PrPSc formation and spread appear to be mechanistically similar to the formation and spread of amyloid in other neurodegenerative disease of protein misfolding, including Alzheimers disease and Parkinsons disease. Thus, the results of our prion studies will likely be broadly applicable to other diseases of protein misfolding and deposition. We are interested in understanding the molecular mechanisms underlying PrP amyloid formation and have begun to approach this issue using both in vitro and in vivo model systems. This project focuses on: 1) Understanding the pathways of PrP amyloid formation and spread and, 2) Studying how mutations in PrP influence PrPSc amyloid formation in familial forms of prion disease. Using LC-MS/MS Nanospray Ion Trap Mass Spectrometry, in 2016 we completed the protein profiles of PrPSc isolated from over 20 cases of CJD where PrPSc is deposited as diffuse, amyloid negative deposits and/or as amyloid plaques. Our results show that the protein profiles differ depending upon whether PrPSc is derived from sCJD or iCJD suggesting pathogenic differences between the two different disease types. In 2016 we continued long term in vivo work to study the pathogenesis of different forms of amyloid and non-amyloid human prion disease in transgenic mice expressing either mutant or wild-type human PrP. Multiple different CJD isolates have been inoculated into these mice and, in some cases, multiple brain regions from the same patient have also been inoculated. While we completed transmission data for some of these isolates in 2016, mice inoculated with multiple isolates are still being monitored for disease. This experiment represents another approach in delineating the mechanisms underlying amyloid and non-amyloid forms of prion disease. These studies will take several years to complete but will provide important information in several poorly understood areas of human prion disease including 1) the contribution of the host versus the contribution of the prion strain to different in vivo disease phenotypes and, 2) the mechanisms of amyloid versus non-amyloid prion formation. Multiple studies have shown that amyloid formed from amyloid beta (A) protein, alpha synuclein and tau can propagate via a prion-like mechanism and spread from cell-to-cell in transgenic mouse models e.g. Science 313: 1781-1784 (2006), Nat Cell Biol 11: 909-913 (2009), J Exp Med 209: 975-986 (2012). Based on these data, it has been suggested that amyloid formation in neurodegenerative proteinopathies such as Alzheimers Disease (AD) and Parkinsons disease (PD) occur via prion-like mechanisms and that proteins such as AD-associated A may also be transmissible, infectious prions. Co-deposition of misfolded proteins during neurodegeneration, such as the co-localization of PrPSc and A to plaques in some cases of sCJD ACTA Neuropathol 96:116-122 (1998), also suggest that interactions between these proteins could contribute to disease pathogenesis. In 2016, we initiated a collaboration with Dr. Pedro Piccardo to use mass spectrometry to study BSE-infected non-human primates which develop a neurodegenerative disease characterized by accumulation of PrPSc, hyper-phosphorylated tau, and alpha synuclein J Gen Virol 95:1612-16-18 (2014). This experimental model will enable us to better understand the molecular mechanisms behind neurodegeneration in complex proteinopathies.
