By Horace Gore, Wildlife Biologist
A recent study by a research team at UC San Diego has shown that a small loop in the human prion protein prevents corruption of human proteins when exposed to elk prions. This study, published Feb. 23, 2017 in the Journal of Clinical Investigations identified the small loop in the human prion protein that confers resistance to chronic wasting disease. CWD is an infectious disease caused by prions that affect cervids (elk, deer, moose), but has not shown to affect humans. The importance of this finding cannot be over-emphasized, since Texans consume some fifteen million pounds of deer and elk venison annually.
“Since the loop has been found to be a key segment in prion protein aggregation, this site could be targeted for the development of new therapeutics designed to block prion conversions,” said Christine Sigurdson, DVM, PhD, associate professor of UC San Diego and UC Davis and senior author of the study.
Prions aren’t microorganisms like bacteria and viruses; they are simply protein aggregates. Some protein diseases are caused by an inherited genetic mutation, while others are caused by exposure to infectious prions in food. Acquired protein diseases are triggered when a foreign, misfolded prion protein causes the body’s own natural prion proteins to misfold and aggregate.
“We suspected that a loop in the human prion protein structure may block the cervid (elk) prions from binding, as the sequences did not appear to be complete.” Sigurdson said.
To test this hypothesis, Sigurdson and her team developed a transgenic mouse that expresses a prion protein that is identical to the human version—except for a small loop that was swapped out for the elk sequence. When these mice were exposed to the cervid (elk) prions, they developed chronic wasting disease (CWD).
In contrast, control mice expressing the normal human sequences, resisted infection when exposed to the same material—just as humans seem to, even those who consume venison meat.
“This finding suggests that the loop structure is crucial to prion conversion, and that sequence compatibility with the host prion protein at this site is required for the transmission of certain prion diseases,” Sigurdson said.
Co-authors of the study were Timothy D. Kurt, Cyrus Bett, Jun Liu, Tom Yang, UC San Diego; Lin Jiang, David Eisenberg, UC Los Angles and Howard Hughes Medical Institute; Natalia Fernandez-Borges, CIC bio GUNE, Spain; Terry R. Spraker, Colorado State University, Fort Collins; Joaquin Castilla, CIC bio GUNE and Basque Foundation for Science, Spain; and Qingzhong Kong, Case Western Reserve University.
Author’s Note: The clinical effects of CWD on cervids is much too slow to cause population reductions in elk, deer, and moose herds. Reproduction far exceeds mortality, and coupled with the results of this study, which suggests that CWD cannot affect humans as a result of eating venison, Texans should continue to enjoy America’s healthiest red meat.
“The California study has merit, and explains why the consumption of ten-of-millions of pounds of venison has shown no ill effect on humans,” said Dr. James “Dr.Deer” Kroll in a recent interview.
It appears that State and Federal Agencies have spent a lot of time, resources, and money trying to control or eradicate a malady that is irrelevant and immaterial.
