Octarepeat Mutation of PrP in Cells and Transgenic Mice

       Prion diseases have become a subject worthy of considerable scientific scrutiny for two main reasons. Firstly , prions are a novel class of infectious agent with properties that distinguish them from conventional pathogens such as viruses. Virions contain all of the genetic information that directs synthesis of their structural components – mostly protein molecules – within the infectious particle. When a virus infects a cell it exploits the host cell’s “machinery” to decode this information and create new copies for the formation of new infectious particles . Prions do not work in this manner. In contrast, it appears that all or most of the genetic information that is required to synthesize a prion is supplied by the host cell. In fact the only known component of the infectious particle is the ” prion protein” , an altered form of a protein that is a normal component of the host animal which the prion infects. The mystery of the prion to molecular biologists concerns the nature of the information that specifies the creation of new prions . Normally, information of this type would be stored in a nucleic acid molecule, termed a “genome”, contained within the infectious particle. However, numerous efforts to identify such a molecule have been fruitless. The absence of this “prion genome ” suggests that all of the information required to synthesize a new prion might be contained either within a novel molecule that is not a nucleic acid or perhaps even within the prion protein itself. The ramifications of this concept are enormous and extend in principle to every field of biological research , including Alzheimer’s disease.            The second major reason for our interest in prions concerns the study of degenerative neurological diseases in humans . Although prion diseases exist in humans, they are relatively rare , affecting only about one in a million individuals. Alzheimer’s disease (AD), in contrast, is a major threat to a large section of the population . The absence of an experimental animal model for AD has severely impeded progress in the fight eradicate the disease. There are, however , many similarities between prion disease and AD, most importantly the prion protein forms deposits, termed amyloid, in the brains of afflicted individuals. A similar protein, ß-amyloid, is found in patients with AD . Since the formation of amyloid deposits in AD is believed to be fundamental to AD, it is likely that the study of prion diseases will yield some vital clues to establishing the mechanism of AD. It is certainly feasible – although there is currently no evidence to support this hypothesis – that AD is also a prion disease. Even if this is not the case the mechanisms that cause the formation of the amyloid deposits which are observed in AD may be similar to those that occur in prion diseases.         We have created artificial prion proteins which closely resemble the normal protein found in cells . This resemblance is sufficiently great for the cells to be “fooled” into using the artificial prion protein as if it were a completely normal molecule. However, the structure of this protein has been subtly modified so that we can track thes e altered proteins in the cells of genetically engineered animals. Because these proteins are specifically marked , they may be distinguished from normal prion proteins, allowing us to use genetic engineering techniques to systematically alter the protein and study the consequences of thes e manipulations upon the function of the prot ein. Using this approach we have created prions with synthetic properties. In this proposal, we wish to extend this approach to study gene mutations which ca use prion diseases in humans. By doing so, we hope to determine the precise molecular mechanism by which they cause neurodegenerative disease, and by which they lead to the formation of amyloid deposits in experimental animals.