This episode of Brain Celebrities will take us to the mountainous highlands of New Guinea, where the Fore people live. Until the 1960’s, the Fore had an interesting habit: they ate their dead. This gruesome tradition might help us understand neurological diseases such as Creutzfeldt-Jakob and Alzheimer’s disease.
Fore father and son. From http://rstb.royalsocietypublishing.org/content/363/1510/3715
In the 1950’s a horrible epidemic plagued the Fore tribe: a fatal disease that started with shivers, slurred speech and unsteady gait, followed by emotional lability and incontinence, eventually causing a fatal inability to eat. The Fore called the disease Kuru, which means shiver. Women seemed to be more affected than men, and it appeared to be more common in certain families.
Since the disease ran in specific families, researchers who initially studied the disease in the 50’s assumed it was a genetic disorder. However, as more and more people died, a genetic cause seemed less and less likely. In the 1960’s brain material of a victim was injected in a chimpanzee, which started to develop very similar symptoms as the Fore, proving that Kuru was not a genetic disease but instead infectious and transmittable. Researchers quickly linked this fact to the cannibalistic ritual of the Fore: the cannibalism was mostly executed by women of kin; they prepared the body and ate the brains while the man only ate the skin. This could explain why women were most affected.
So what kind of infectious disease is Kuru, and how does it help us understand Creutzfeldt-Jakob and Alzheimer’s disease? Since the disease takes a couple of years to develop after infection, researchers assumed that Kuru was caused by a slow virus. They saw that the symptoms were very similar to Creutzfeldt-Jakob disease, mad cows disease, and scrapie and hypothesized that these diseases were caused by similar viruses. After seeing one of his patients die from Creutzfeldt-Jakob disease, Stanley Prusiner started studying this class of slow viruses. In 1982 he showed that theses diseases were not caused by a virus or any of the other infectious agents we had known before. He found a whole new class of infectious agents, next to the bacteria, viruses, fungi and parasites, he called it a prion.
A prion is a misfolded version of a protein normally found in cell membranes throughout the body. When it is normally folded, this protein is soluble and easily degenerated. The prion however, is insoluble and cannot be degenerated. It accumulates and clogs up the cell. In addition, by unclear mechanisms, it converts the normal version of this protein into prions as well, clogging up the cell even more until it dies. How exactly prions infect people and replicate themselves by converting healthy proteins is still unknown.
Moreover, prions are interesting because they resemble the cellular mechanisms causing Parkinson’s and Alzheimer’s disease. In these diseases specific proteins beta-amyloid, alpha-synuclein or tau proteins) accumulate and clog up the brain cells, causing the cells to die. Understanding how we can prevent prions to accumulate might thus also help us understand the etiology of Alzheimer’s and Parkinson’s disease.
Normal and misfolded prion protein and the chain reaction leading to disease. From http://www.macalester.edu/academics/psychology/whathap/ubnrp/tse10/introduction.html
So how did eating it help in treating it? As it turns out, some people in the Fore tribe developed a resistance against Kuru. A study published by the Collinge lab last June investigated the genome of the Fore people. They found out that some people had a mutation in the gene of the prion protein. When they gave mice this mutation, the mice were resistant not only to Kuru, but also to Creutzfeldt-Jakob and mad cows disease. The reason was that the mutated version of this protein was unable to be misfolded into prions
What exactly it is that protects this mutated version of the protein from converting to prions is still unknown. However, it is a very promising start in searching a treatment for this type of diseases. The researchers found that even when only half of the normal proteins were mutated, the mice were protected against Kuru and Creutzfeldt-Jakob disease (although not against mad cows disease). It thus seems that as long as there are sufficient unconvertible proteins in our cells, prions will not be able to accumulate and aggregate enough to clog up the cells. Treating people by introducing unconvertible versions of the prion protein or of disease-state beta-amyloid, alpha-synuclein or tau proteins might thus be a way we can fight these diseases.
Although a great amount of research is still necessary to find out if and how we can translate the current study into a treatment for protein aggregation diseases, it seems like the Fore’s cannibalism has provided us a clue!
Asante, E.A., Smidak, M., Grimshaw, A., Houghton, R., Tomlinson, A., Jeelani, A., Jakubcova, T., Hamdam, S., Richard-Londt, A., Linehan, J., Brandner, S., Alpers, M., Whitfield, J., Mead, S., Wadsworth, J.D.F., Collinge, J. (2015). A naturally occuring variant of the human prion protein completely prevents prion disease. Nature, 522, 478-481.