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Transmissible spongiform encephalopathies or prion disorders--current views
1Department of Oncology, School of Medicine Lodz.
Abstract:
Basic hypotheses concerning nature of an infectious agent of the transmissible spongiform encephalopathies are reported here. The agent may consist of a protein only (PrPsc), and for such a molecular structure the term "prion" has been coined. It may consist of a yet-to-be-discovered small oligonucleotide and a shell protein and this is the "virino" concept. Or, the agent may be a virus which has still eluded detection. The experiments with transgenic and knock-out mice proved that PrPsc is crucial for pathogenesis of spongiform encephalopathies. However, presence of strains of scrapie agent strongly favour a nucleic acid as a template of genetic information, which is difficult to reconcile with the "protein only" hypothesis. On the other hand, the development of spontaneous neurodegenerative disorder in Tg(GSS MoPrP) mice, if independently confirmed, strongly supports the "prion" hypothesis. Furthermore, the linkage of mutations within the PRNP gene with phenotypic appearance of Creutzfeldt-Jakob disease and Gerstmann-Sträussler-Scheinker syndrome points to importance of the PrP gene. In conclusion, it must be said that the molecular structure of the agent is still uncertain.
Insights
The infectious agent causing transmissible spongiform encephalopathies may be a protein-only prion or a virino. While prion protein (PrPsc) is crucial for disease, the existence of strains suggests a nucleic acid component, leaving the agent's exact structure uncertain.
Area of Science:
- Neuroscience
- Molecular Biology
- Infectious Diseases
Background:
- Transmissible spongiform encephalopathies (TSEs) are fatal neurodegenerative diseases.
- The precise molecular nature of the infectious agent underlying TSEs remains a subject of debate.
Purpose of the Study:
- To review and evaluate the primary hypotheses regarding the molecular structure of the TSE infectious agent.
- To discuss experimental evidence supporting or refuting these hypotheses.
Main Methods:
- Review of existing literature and experimental findings.
- Analysis of data from transgenic and knock-out mouse models.
- Consideration of genetic linkage studies in human prion diseases.
Main Results:
- Transgenic mouse experiments confirm the essential role of the prion protein (PrPsc) in TSE pathogenesis.
- The existence of distinct prion strains suggests a non-protein-based genetic template, challenging the protein-only hypothesis.
- Spontaneous neurodegenerative disorders in specific mouse models and genetic links to human diseases (Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker syndrome) support the prion hypothesis.
Conclusions:
- The molecular identity of the TSE infectious agent is not definitively established.
- While the prion protein (PrPsc) is central to disease, the possibility of a nucleic acid component or alternative structures like the 'virino' cannot be excluded.