Prions Play the Good Guy: A Role in Brain Development

Prion proteins get a lot of bad press. Now understood to be the causative agent of such neurodegenerative afflictions as mad cow disease, scrapie (which affects sheep), and Creutzfeldt-Jakob disease (which affects humans), prions are not normally thought of as vital for normal brain function. However, new research points to an interesting role for prions in the developing brains of mice, specifically in the hippocampus, a region critical in learning and memory.

Prions were first identified in the 1980s by Dr. Stanley Prusiner, who set out to determine the cause of the transmissible scrapie and Creutzfeldt-Jakob diseases. These fatal disorders were widely thought to be unidentified viruses. Prusiner found that the causative agent was actually a protein. He coined the term prion from “protein infection” and found that the protein was present in both healthy and diseased brains, with the exception that the protein in diseased tissue had a completely different 3-dimensional conformation. These proteins spread disease even without having a genome. The prions replicate by causing healthy prion proteins to re-configure in something like a chain reaction (Petersson 1997). This was a completely novel concept at the time of its discovery, and eventually resulted in a Nobel Prize for Dr. Prusiner (Weiss 1997).

The abnormal folding and spreading of prion proteins leads to brain damage and ultimately, death. Prions such as those that cause mad cow disease can decimate populations. But, there is another side to this coin: some necessary brain functions require normally-folded prion proteins. Prion proteins are necessary for myelin sheath creation, and are also expressed abundantly at synapses, especially during development.

The authors of a current publication in the Journal of Neuroscience used prion protein-null mice to determine a role for prions in synaptic plasticity in the developing hippocampus at postnatal 3-7 days. They found that activation of hippocampal brain slice sections produced an increase in synaptic strength between mossy fiber and CA3 neurons in wild-type mice, but showed a decrease in synaptic strength in prion-null mice with the same stimulation conditions. The strengthening of synapses in the wild-type mice was dependent on prion function via PKA signaling.

While the whole prion story is far from complete, this work demonstrates that prion protein is likely a vital player in normal brain function, and one that should not be overlooked.

What do you think?

Further Reading:

Caiati MD, Safiulina VF, Fattorini G, Sivakumaran S, Legname G, Cherubini E. PrPC Controls via Protein Kinase A the Direction of Synaptic Plasticity in the Immature Hippocampus. J Neurosci. 2013 Feb 13;33(7):2973-83.

Pettersson Ralf F. (1997, December). Award Ceremony Speech. Speech presented at the Nobel Prize Award Ceremony, The Karolinska Institute, Stockholm, Sweden.

Weiss, R. “U.S. Neurologist Wins Nobel Prize for Discovery of Prions.” The Tech. 7 Oct. 1997. Web.

A fun piece on visualizing protein structure:

http://www.npr.org/blogs/krulwich/2013/02/14/172006052/close-your-eyes-and-imagine-a-protein-see-anything-a-housefly-maybe?ft=1&f=1007