Scrapie: a review of its relation to human disease and ageing

Types and Strains: Their Essential Role in Understanding Protein Aggregation in Neurodegenerative Diseases

Protein misfolding and aggregation is a key event in diseases like Alzheimer’s disease (AD) or Parkinson’s disease (PD) and is associated with neurodegeneration. Factors that initiate protein misfolding and the role of protein aggregation in the pathophysiology of disease pose major challenges to the neuroscientific community. Interestingly, although the accumulation of the same misfolded protein, e.g., α-synuclein is detectable in all idiopathic PD patients, the disease spectrum covers a variety of different clinical presentations and disease courses. In a more recent attempt this clinical variance is being explained in analogy to prion diseases by different protein aggregate conformations. In prion diseases a relationship between protein aggregate conformation properties and the clinical disease course was shown by relating different prion types to a dementia and an ataxic disease course in Creutzfeldt-Jakob patients. This principle is currently transferred to AD, PD and other neurodegenerative diseases with protein aggregation. However, differences in protein aggregate conformation are frequently addressed as disease strains. The term “strain” also derives from prion research and evolved by adopting the virus terminology at a time when transmissible spongiform encephalopathies (TSEs; later called prion diseases) were assumed to be caused by a virus. The problem is that in virus taxonomy the term “type” refers to properties of the disease agent itself and the term “strain” refers to host associated factors that interact with the disease agent and may moderately modify the clinical disease presentation. Strain factors can be discovered only after transmission and passaging of the agent in a host of a different species. The incorrect use of the terminology confuses disease agent and host factors and hampers the understanding of the pathophysiology of protein aggregate-associated neurodegenerative diseases. In this review article the discoveries are reviewed that explain how the terms “type” and “strain” emerged for unconventional disease agents. This may help to avoid confusion in the terminology of protein aggregation diseases and to reflect correctly the impact of protein aggregate conformation as well as host factor contribution on different clinical variations of AD, PD and other neurodegenerative diseases.

Creutzfeld-Jakob disease in the province of Siena: two cases transmitted to monkeys

Two cases of histopathologically documented Creutzfeldt-Jakob disease were observed in the same area of the province of Siena in 1974-1975. The transmission of the disease was obtained through brain homogenates and lymphnodes in one of the two cases. This confirms that the agent is present in other tissues besides the brain and underlines further the analogies between Creutzfeld-Jakob disease and scrapie.

Age-dependent relaxation of gene repression: increase of endogenous murine leukemia virus-related and globin-related RNA in brain and liver of mice

A progressive loss in the ability of cells to maintain their normal specialized states of differentiation could be the common denominator underlying much of the physiology and pathology associated with the mammalian aging process. We investigated this possibility by searching for an age-dependent derepression of endogenous genes in tissues in which they are not normally expected to be expressed. Complementary DNA (cDNA) probes to globin genes and to the murine leukemia type C RNA virus (MuLV) genome were used to detect the presence of RNA complementary to these genes in RNA extracted from brain and liver in young and old mice. Significant amounts of globin RNA were found in brain nuclei and cytoplasm. No age difference was found in the globin RNA sequences present, but the number of globin RNA molecules increased from about 15 in 6-month to 34 in 27-month-old animals for nuclei and 280 in 6-month to 500 in 27-month-old animals for cytoplasm. Similar results were found for liver. RNA complementary to the MuLV cDNA probe was also found but, in contrast to globin, the different RNA sequences increased in both brain and liver nuclei from about 45% of the MuLV genome in 6-month to 72% in 27-month-old animals. The number of MuLV-related RNA molecules remained constant at about 22 and 38 per nuclei for brain and liver, respectively. Derepression of genes of this magnitude could result in a time-dependent increase in virus-related diseases and a general deterioration of the organism.