Dr Paul Simons, from University College London, has used an NC3Rs project grant to develop a refined mouse model for studying amyloidosis which eliminates some of the animal welfare concerns associated with standard models.
Principal Investigator: Paul Simons, Senior Lecturer in Inflammation
Organisation: University College London
Award: £302,128, in 2008, over 36 months
Title: A refined mouse model to study systemic amyloidosis
Read more about Dr Simons' research.
Amyloid deposits are found in a range of diseases including arthritis and diabetes
Amyloidosis is a disorder of protein metabolism which leads to the extracellular deposition of insoluble amyloid fibrils. The accumulation and persistence of amyloid disrupts the structure and function of affected tissues. Amyloid deposition is also a characteristic feature of Alzheimer’s disease and type II diabetes.
Systemic amyloidosis accounts for one in every 1,000 deaths in developed countries. Amyloid A (AA) amyloidosis is the second most common type of systemic amyloidosis in humans. It occurs in up to 5% of patients with chronic inflammatory diseases such as rheumatoid arthritis. Inflammation causes increased production of the acute phase serum amyloid A protein (SAA) by the liver, which leads to amyloid A deposits and systemic amyloidosis, mainly affecting the spleen, liver and kidneys. Renal damage is usually the first clinical manifestation of the disease. There are currently no specific treatments and it is a major unmet medical need.
A mouse model first developed over 80 years ago is used to study systemic AA amyloidosis
The mouse is widely used to model systemic AA amyloidosis using an approach which was developed in the early 20th century. The disease is induced experimentally by repeated injection of casein which causes persistent inflammation. The mouse model mirrors some aspects of the human disease, however, amyloid deposits are rarely seen in the kidneys – clinically the most important organ affected – and there are limited deposits in the liver. In the mouse, both development and regression of the disease can be highly variable between animals, making studies difficult to reproduce.
A transgenic mouse model which allows amyloidosis to be turned on and off
With NC3Rs funding, Dr Paul Simons, University College London, has developed and characterised a refined transgenic model of systemic AA amyloidosis which better represents the human disease.
An inducible transgenic line has been generated in which expression of the SAA gene can be controlled by the inclusion of the antibiotic, doxycycline, in the drinking water. Amyloidogenesis, that is the production of amyloid fibrils, can then be accelerated by a single intravenous injection of Amyloid Enhancing Factor.
The transgenic mice express more SAA protein than is seen in the traditional model, with amyloid fibrils being observed in the spleen, liver and kidneys. The model has further advantages in that the inducible system allows the level of SAA protein to be carefully modulated and it therefore presents the opportunity to study the spontaneous regression of amyloidosis seen in some patients. Moreover, amyloidogenesis is rapid taking six to ten days rather than two to eight weeks.
Less animal suffering by avoiding repeat injections and widespread inflammation
The transgenic model of systemic AA amyloidosis is a refinement over the traditional model. It avoids the daily subcutaneous injections of inflammatory agents for up to eight weeks and the concomitant systemic inflammation.
Use of the transgenic mice is classified as mild severity under the Animals (Scientific Procedures) Act 1986; the traditional model involving chronic administration of casein is classified as moderate severity.
The SAA line has now been bred to homozygosity, avoiding the wastage of animals associated with other breeding strategies and the need to take biopsies to genotype. The control over the expression of the SAA protein in the transgenic mice has provided a more robust and reproducible model. As a result, group sizes for experiments have been reduced from approximately 12 mice with the standard model to eight with the transgenic mice.
New insights into the disease
Using the transgenic model it has been possible to dissociate SAA expression from inflammation. This has shown for the first time that high circulating concentrations of SAA alone, in the absence of inflammation, are sufficient for amyloidogenesis. The only essential aspect of the inflammatory response is the up-regulation of SAA expression.
This work has been presented at a range of conferences including the XIIth International Symposium on Amyloidosis in 2010.
This case study was published in a review of our research portfolio in September 2011.