Decades after their discovery, these parasitic mysteries remain to persist in the environment we live in. To date, it is unclear how they metastasise. They don’t contain the fundamental capacity of being alive nor do they possess a nucleic acid genome (DNA sequence).
Rendering them unkillable, prions don’t have any pathogenic bodies to engulf and exterminate by our body’s immune system whilst spreading, deforming, and replicating like viral bacteria. Prions, otherwise recognised as proteinaceous infectious particles are essentially misfolded versions of the normal protein PrPC, found on cell membranes(C, for Cellular). Prions only affect the brain and other neural tissues.
It is bewildering how our body can do such a thing to ourselves. With an abnormal protein tertiary structure (the three-dimensional structure) of a protein molecule, prions are known to demonstrate their infectious properties in collapsing proteins they come near to into the same distorted shape. These collapsed proteins accumulate into irregular aggregates of proteins called amyloids which are observed in neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s. What is especially significant about this transformation is to do with the stability of the new structure. The amyloid is resistant to denaturation by any chemical or physical agents such as ultraviolet radiation, disinfectants, boiling and intense sterilisation. Prions seem to remain infectious even after treatments that destroy nucleic acids are used. They replicate using methods of humanistic and widely known qualities such as epimutation and natural selection. Epimutation, derived from epigenetics, suggests that there are no alterations to the DNA sequence of the protein but only addition, which implies that a newly formed structure of the protein can come to rise with complete eradication of the old one. Normal PrPCs are transformed into PrPscs which are the “scrapie form”. The scrapie form is resistant to protease enzymes that can break down proteins and can change the conformation of PrPCs interconnect. PrPres is a protease-resistant protein but these may not necessarily be infectious.
Aggregations of these abnormal isoforms (a protein with the same function as another protein encoded by a different gene) form amyloid fibres that muster together to form plaques. The ends of the fibres then latch onto whichever free protein molecule and grow with rapid speed. Commonly, only PrP molecules with the same amino acid sequence to the infectious PrPsc are affected. Those affected happen to be not fully understood proteins that misfold and turn into contagious pathogens and recruit any exposed prions to group together into more plaques. It is strange how genetic traits can be passed along through a cell’s cytoplasm rather than via the nucleus where the DNA is stored. This occurs because proteins that are encoded in the nucleus can completely reinvent themselves in the cytoplasm followed by the reconfigured proteins inducing other proteins of the same type to change their configuration as well.
As baffling as it now seems, prions have the invincible ability to eat up our brains, destroying their orientation, capacity to function and agitates the architecture of our central
nervous system. They develop extracellularly and disrupt the normal tissue structure by basically forming holes in the tissue. Vacuole formation in the neurons, atypical in its entirety, the brain turns into a sponge-like structure or something to the likes of swiss cheese. Neurodegenerative symptoms could embody the dysfunction in convulsions, hallucinations, muscle stiffness, dementia, ataxia, difficulty in speaking or behavioural and personality changes. Susan Lindquist, a researcher at the Howard Hughes Medical Institute determined a rather similar phenomenon of prion infection in yeast. But, in this case, the transmission of the infectious agent passed genetic information from mother to daughter cells instead of from an individual cell to another.
Prions cause diseases of the transmissible spongiform encephalopathy type in mammals, including Creutzfeldt-Jakob disease (CJD) in humans or ‘Mad Cow’ Disease (Bovine spongiform encephalopathy). ‘Mad Cow’ Disease infected a large population of cattle in Great Britain which frightened the public and incited newfound haste and urgency to find a cure, seeing that the cows may have been responsible for several new cases of CJD in humans. CJD’s cause was unknown for a long time, occurring with no pattern and absolute randomness with very
low rates of incidence. In the 1950s, an epidemic transmissible disease called kuru (to the left is a photograph of a Fore child with advanced Kuru), similar to CJD, proliferated in the Fore tribe of Papua New Guinea. Astonishingly enough, a ritual of the funeral process which required the brain of a dead tribe member to be removed from the skull, cooked and eaten saw rise to this disease accompanied by a reduction in the number of brain cells. Extracts of brain assembled by D. Carleton of the U.S. National Institute of Health were inoculated into the brain of chimpanzees which suggested the presence of an infectious agent and the inference was corroborated by the unintended transmission of CJD to patients that got corneal transplants and human growth hormone therapy. All these medical treatments are attached to changes of the neural tissue which is where prions do their skilful work.
It is important not to be frightened. Modern medicine and the stoppage of transmissions early on has deemed prion diseases to be extremely rare. Although the disease is always going to be fatal with approximately 70% dying within a year of receiving their diagnosis, it can be prevented by properly cleaning and sterilising medical equipment and not donating organs or tissues if you have CJD. All we know is, prions are existent in this world and who knows whether or not they are directly responsible for the neurocognitive disorders, so common in our elderly society, that make so many suffer and those around them suffer even more.
Barbara Casassus, 2021. “France Issues Moratorium on Prion Research After Fatal Brain Disease STRIKES Two Lab Workers.” Science, Science Magazine, 28 July 2021, www.sciencemag.org/news/2021/07/france-issues-moratorium-prion-research-after-fatal-brain-dise ase-strikes-two-lab.
Gambetti, Pierluigi. “Overview of Prion Diseases - Neurologic Disorders.” MSD Manual Professional Edition, MSD Manuals, July 2020, www.msdmanuals.com/en-sg/professional/neurologic-disorders/prion-diseases/overview-of-prion- diseases.
Lindquist, Susan. “What Is a Prion?” Scientific American, Scientific American, 21 Oct. 1999, www.scientificamerican.com/article/what-is-a-prion-specifica/.
Terry, Cassandra, and Jonathan D. F. Wadsworth. “Recent Advances in Understanding Mammalian Prion Structure: A Mini Review.” Frontiers, Frontiers, 9 July 2019, www.frontiersin.org/articles/10.3389/fnmol.2019.00169/full.