Seminar

Prions. Unraveling their mysteries through their in vitro handling

Joaquín Castilla, PhD

Prion diseases or transmissible spongiform encephalopathies (TSEs) are fatal neurodegenerative disorders affecting both humans and animals. TSEs can be of genetic, sporadic or infectious origin. The infectious agent associated with TSEs, termed prion, consists of a single protein, an abnormal conformer (PrPSc) of a natural host protein (PrPC), which propagates by converting host PrPC into a replica of itself. One of the most intriguing characteristic of prions is that they occur in the form of different strains, which show distinct pathological and physicochemical properties, even though they are encoded by PrP with the same amino acid sequence, albeit in presumably different conformations. Interestingly, each strain shows the ability to infect some species and not others, a phenomenon known as transmission barrier. The self-propagating process has been definitively proven by in vitro systems able to induce misfolding of PrP to its infectious conformation in the absence of elements derived from mammalian tissues. Particularly, using a version of PMCA (Protein Misfolding Cyclic Amplification) based on recombinant PrP as substrate (recPMCA) our group has created a diversity of infectious recombinant prion strains. We use different cofactors able to drive the evolution of prion populations toward specific strains. Infectivity is being tested in our transgenic mouse models, showing high infectivity and the generation of new prion strains. recPMCA is also being used for estimating the transmission barrier in a more reliable and accurate way. The use of recombinant proteins and the possibility to propagate, direct, and select a variety of infectious strains bring us a step closer to deciphering the strain and the transmission barrier phenomena. In addition, we are taking the advantage of this technique to propagate bona fide infectious prions in a high throughput manner and producing unprecedented quantities to use this methodology for screening of potential anti-prion compounds and to definitely decipher the structure of an infectious prion.