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Eukaryon

Prions: Form Determines Function

Augustana Houcek
Lake Forest College
Lake Forest, Illinois 60045

Prions are misfolded proteins with the unique ability to do what most other proteins cannot: they can transmit their misfolded shape onto the correctly folded versions of the same protein. They are both infectious and destructive and are known to be the source of multiple neurodegenerative diseases that are able to be transmitted across species. Transmission of prion diseases across species usually occurs through the consumption of central nervous system tissues from an animal that is infected with the misfolded proteins. Some of the forms of prion diseases are scrapie (found in sheep), bovine spongiform encephalopathy, also known as mad cow disease (found in cattle), chronic wasting disease (found in deer), and Creutzfeldt-Jakob disease (found in humans). There is currently no effective treatment for these diseases, and therefore, they are  always fatal. 

It is believed that the mechanism that causes prions is the misfolding of endogenous prion protein, PRP(c), into the self-replicating isoform, PRP(res), which binds to the cellular PRP and converts it to the infectious self-replicating form (Skinner, 2015). This misfolding and accumulation is the hallmark of prion diseases and is currently unable to be reversed. The aggregated and misfolded form of the PRP protein is characterized by its inability to be degraded by proteases and chemical disinfection. 

Research done by Skinner et al. in 2015 had hypothesized that one could use the heterologous prion protein - the non-infectious form of the protein that is naturally found in some species - to treat prion diseases. In order to perform this study, Skinner and his colleagues obtained 39 mice that had all been infected with the sheep version of the disease, scrapie. There were three treatment groups; high dose, low dose, and mock dose. The treatments involved the injection of heterologous hamster prions into the central nervous system of the mice. 

Findings of the treatment were substantial, although the proposed form of treatment did not ultimately cure the disease. One of the first findings was that mice that were in the high dose treatment had significantly lower levels of PRP(res) in their central nervous systems than the rest of the treatment groups, with a p-value of .028. The PRP(res) protein was not completely eliminated in the systems of the high-treatment group, however. Along with this, the researchers also found decreased astrocytosis in the high-dose treatment group, as well as delayed loss of motor function, delayed onset of symptoms and prolonged survival of mice that were in the high-dose treatment group. 

Although this form of treatment did not completely cure the mice that were infected with prion disease, it is a large step forward in the treatment and prevention of a disease that is currently a death sentence for those infected. This treatment may also have applications in other diseases that stem from protein misfolding, such as Alzheimer’s disease and Huntington’s disease. 

  1. Skinner PJ, Kim HO, Bryant D, Kinzel NJ, Reilly C, Priola SA, et al. (2015) Treatment of Prion Disease with Heterologous Prion Proteins. PLoS ONE 10(7): e0131993. doi:10.1371/journal. pone.0131993

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