Now that I’ve gained a marginally better understanding of prions over the last couple months, I went back and re-read Spontaneous Generation of Prion Infectivity in Fatal Familial Insomnia Knockin Mice (full text here), Walker Jackson’s original paper announcing the creation of FFI knock-in mice.

The major emphasis of the paper is its confirmation of the “protein-only” hypothesis of prion infectivity.  Jackson showed that expressing a D178N 129M prion protein in mice is sufficient to bring about FFI symptoms (as distinct from CJD or GSS symptoms), and that this disease can then be transmitted to other mice through brain injection.  This is very strong evidence that proteins are the only thing needed for prion disease and that prion disease is not due to a virus acting behind the scenes.

Of course, what is most interesting to us at is that Jackson created these FFI kn0ck-in mice, which can now be used for testing therapeutics.  In the paper Jackson hits at how these mice are a better, more accurate model than most murine models of human disease, in part because the murine amino acid sequences were “humanized” to match the human PrP sequence.

The study shows that PrP knockout mice are immune to variant introduction of FFI infectious material and seem to do well.  (Of course, we can’t interview the mice to find out exactly how well they’re doing in terms of memory, cognition, etc. but this at least hints that PrP suppression might be a viable way to treat FFI in humans).  Interestingly, even wild type mice proved insusceptible to the introduction of infectious material– only the Tga20 mice, which have heightened levels of PrP expression, became ill after being infected with disease prions from FFI knock-in mice.  Jackson hypothesizes that the resistance of wild type mice shows that the infectious material is subject to “transmission barriers” — presumably referring to the fact that the humanization of the mouse PrP gene created some amount of species barrier.