Intestinal Lymphatic Tissue Important For The Absorption And Spread Of The Scrapie Prion

ScienceDaily (Jan. 17, 2009) — Scrapie is a transmissible, degenerative and ultimately fatal disease of the nervous system of sheep. The cause of the disease is a prion protein, and absorption from the intestine is assumed to be the natural route of infection. Lymphatic tissue associated with the intestine is important for the early accumulation of prion protein and its subsequent spread to the central nervous system.

Transmissible prion diseases occur in both animals and man, two well-known ones being mad cow disease of cattle and Creutzfeldt Jacobs disease of man. These diseases produce symptoms in the central nervous system, with classical scrapie being characterised by intense itching with subsequent loss of wool, smacking of the lips, abnormal gait, and eventually collapse.

Protein molecules may show different properties when their structures become altered, for example, proteins in egg white are hardened by heat treatment. The assumed cause of prion diseases is that the structure of the normal prion protein (called PrPC) becomes altered. The abnormal, disease-associated form of the prion protein (called PrPSc) is assumed to be the infectious agent.

Infection most likely occurs across the intestine, and one first sees an accumulation of PrPSc in the lymphatic tissue associated with the intestine, especially in areas of the small intestine called Peyer's patches. The infection then spreads to the central nervous system and the brain, where, in the final stages of the disease, one sees an accumulation of PrPSc and also structural changes such as sponge-like "holes" in the brain mass.

We understand as yet very little of just how the infectious PrP is absorbed from the intestine. It is assumed that infection requires the presence of the normal form of the protein PrP, and it is known that the gene for PrP is active in a series of different types of cells and tissues.

For his doctorate, Lars Austbø investigated the activity of the gene for prion protein (PrP mRNA) by looking at where in the intestinal tissue it is formed and in what quantity. He also identified other genes of possible significance for the early phase of scrapie.

Austbø used advanced gene technology and molecular biology to study both prion gene activity (PrP mRNA) and the presence of the protein PrPC in the Payer's patches of the small intestine and in the spleen - two organs where lymphoreticular tissue is assumed to be important for the absorption of the infective substance (PrPSc) and its spread to the brain.

Austbø and his colleagues have compiled new knowledge of the tissues that the PrPC protein and its mRNA is expressed in and the degree to which the gene is active. In addition, the study has shown that accumulation of the disease-related prion protein (PrPSc) is not necessarily associated with high levels of the normal prion protein. This conflicts with earlier assumptions and may force a re-evaluation of earlier theories on the absorption and distribution of the disease-related prion protein.

In addition, Lars Austbø worked with the identification of other genes that may play a role in the development of scrapie. Many genes contribute to, or are affected by, any disease progression. By mapping such genes, one can gain a better impression of the processes that are initiated and thereby a better understanding of disease development.

Cand. scient. Lars Austbø defended his Ph. D. thesis, entitled "Studies on gene expression during the lymphoreticular phase of scrapie in sheep", on June 26, 2008. The work for the thesis was done at the Department of Basal Sciences and Aquatic Medicine, the Norwegian School of Veterinary Science.