Pathogenesis of experimental amyloid protein A amyloidosis in sore hocks-affected rabbits

In vitro and ex vivo expression of serum amyloid A3 in mouse lung epithelia

BACKGROUND AND PURPOSE

Serum amyloid A (SAA), an acute-phase protein whose level tracks infection and inflammation, is the precursor protein of amyloid A (AA) fibrils that is thought to cause AA amyloidosis in human and animals. SAA protein has several isoforms based on the difference of amino acid sequence, such as SAA1 to SAA4 in mice. AA fibrils are associated with chronic inflammation and are mainly originated from SAA1 produced in the liver. SAA3 reportedly contributes to the innate immune response in epithelia; however, little is known about its role at the lung epithelia. Therefore, we investigated SAA3 expression in the lung epithelium activated by bacterial antigens.

MATERIALS AND METHODS

The expressions of SAA3 and SAA1 mRNA were investigated using quantitative real-time PCR, in vitro using mouse Clara (Club) cells and ex vivo using surgically removed mouse lungs, after their stimulation by using either lipopolysaccharide (LPS), the major outer membranous antigen of gram-negative bacteria, or lipoteichoic acid (LTA), the major outer membranous antigen of gram-positive bacteria. In addition, SAA3 and SAA1/2 proteins in treated lung samples were detected by immunohistochemistry (IHC).

RESULTS

SAA3 mRNA expression increased in cells and lungs treated with either LPS or LTA. SAA3 mRNA was more sensitively expressed in LPS than LTA treatment. In contrast, SAA1 mRNA expression did not increase by either LPS or LTA treatment. Furthermore, SAA3 mRNA expression increased in a dose-dependent manner in cells treated with tumor necrosis factor-alpha. By IHC, SAA3 protein was highly expressed in the luminal side of the bronchial epithelium, while SAA1/2 was not expressed.

CONCLUSION

These results obtained from in vitro and ex vivo experiments suggest that SAA3 plays an important role in the innate immune response to bacterial infection in the lung epithelia.

Experimental transmission of systemic AA amyloidosis in autoimmune disease and type 2 diabetes mellitus model mice

AA amyloidosis is a protein misfolding disease characterized by extracellular deposition of amyloid A (AA) fibrils. AA amyloidosis has been identified in food animals, and it has been postulated that AA amyloidosis may be transmissible to different animal species. Since the precursor protein of AA fibrils is serum amyloid A (SAA), which is an inflammatory acute phase protein, AA amyloidosis is considered to be associated with inflammatory diseases such as rheumatoid arthritis. Chronic diseases such as autoimmune disease and type 2 diabetes mellitus could be potential factors for AA amyloidosis. In this study, to examine the relationship between the induction of AA amyloidosis and chromic abnormalities such as autoimmune disease or type 2 diabetes mellitus, amyloid fibrils from mice, cattle, or chickens were experimentally injected into disease model mice. Wild-type mice were used as controls. The concentrations of SAA, IL-6, and IL-10 in autoimmune disease model mice were higher than those of control mice. However, induction of AA amyloidosis in autoimmune disease and type 2 diabetes mellitus model mice was lower than that in control mice, and the amount of amyloid deposits in the spleens of both mouse models was lower than that of control mice according to Congo red staining and immunohistochemistry. These results suggest that factors other than SAA levels, such as an inflammatory or anti-inflammatory environment in the immune response, may be involved in amyloid deposition.

Amyloidosis enhancing activity of bovine amyloid A fibrils in C3H/HeN mice and cynomolgus monkeys (Macaca fascicularis)

BACKGROUND

In experimentally induced cases of AA amyloidosis, the development of disease is enhanced by the administration of homogenous or heterogeneous amyloid fibrils. In recent years, cross-species transmission of animal amyloidosis into human has become of particular concern.

METHODS

Cynomolgus monkeys (Macaca fascicularis) and C3H/HeN mice were inoculated with bovine amyloid fibrils under acute inflammation.

RESULTS

Amyloid A deposits were not detected in any of the monkeys, but mild-to-severe AA deposits were found in all mice.

CONCLUSIONS

These results suggest that unlike in rodents, cross-species transmission of AA amyloidosis is less likely to develop, at least during acute inflammation, in primates.

Systemic AA amyloidosis as a prion-like disorder

Amyloidosis is a collective term for a group of disorders that induce functional impairment of organs and occurs through the accumulation of amyloid, or misfolded protein in beta-sheets. AA amyloidosis is a lethal systemic amyloidosis with SAA as the precursor protein, and is observed in various animal species, including humans. AA amyloidosis can be induced artificially by continuously administering inflammatory stimuli in experimental animal models. In this process of experimental induction, the administration of AA amyloids from either the same or different species is known to markedly expedite AA amyloidosis development, and this is also termed transmission of AA amyloidosis. Similarly to prion disease, AA amyloidosis is considered to be transmitted via a "seeding-nucleation" process. In this manuscript, we reviewed the pathology and transmissibility of AA amyloidosis in animals.

Prion and prion-like diseases in animals

Transmissible spongiform encephalopaties (TSEs) are fatal neurodegenerative diseases characterized by the aggregation and accumulation of the misfolded prion protein in the brain. Other proteins such as β-amyloid, tau or Serum Amyloid-A (SAA) seem to share with prions some aspects of their pathogenic mechanism; causing a variety of so called prion-like diseases in humans and/or animals such as Alzheimer's, Parkinson's, Huntington's, Type II diabetes mellitus or amyloidosis. The question remains whether these misfolding proteins have the ability to self-propagate and transmit in a similar manner to prions. In this review, we describe the prion and prion-like diseases affecting animals as well as the recent findings suggesting the prion-like transmissibility of certain non-prion proteins.

Failure of heterogeneous amyloid-enhancing factor in geriatric squirrel monkeys (Saimiri boliviensis)

BACKGROUND

Cross-species transmission of AA amyloidosis between primates and other animals has not been previously reported.

METHODS

Eight geriatric squirrel monkeys were intravenously administered chimpanzee, bovine, or chicken amyloid fibrils and simultaneously received inflammatory stimulation.

RESULTS

AA amyloid deposition was not detected in any of the monkeys histopathologically or immunohistochemically.

CONCLUSIONS

These results suggest that heterogeneous AA amyloidosis may not be easily transmitted into primates.

Transmission of systemic AA amyloidosis in animals

Amyloidoses are a group of protein-misfolding disorders that are characterized by the deposition of amyloid fibrils in organs and/or tissues. In reactive amyloid A (AA) amyloidosis, serum AA (SAA) protein forms deposits in mice, domestic and wild animals, and humans that experience chronic inflammation. AA amyloid fibrils are abnormal β-sheet-rich forms of the serum precursor SAA, with conformational changes that promote fibril formation. Extracellular deposition of amyloid fibrils causes disease in affected animals. Recent findings suggest that AA amyloidosis could be transmissible. Similar to the pathogenesis of transmissible prion diseases, amyloid fibrils induce a seeding-nucleation process that may lead to development of AA amyloidosis. We review studies of possible transmission in bovine, avian, mouse, and cheetah AA amyloidosis.

Experimental induction and oral transmission of avian AA amyloidosis in vaccinated white hens

Avian AA amyloidosis is commonly observed in adult birds afflicted with bacterial infections or chronic inflammatory disorders. Experimental AA amyloidosis in birds can be induced by repeated inflammatory stimulation, such as injection with casein or vaccination with oil-emulsified bacterins. However, the transmission of amyloidosis among avian species has not been studied well to date. In the present study, we confirm the potential induction of avian AA amyloidosis by inoculation of Salmonella enteritidis (SE) vaccine or Mycoplasma gallisepticum vaccine. To determine the transmission of chicken AA amyloidosis among white hens, we induced experimental AA amyloidosis in vaccinated chickens by intravenous or oral administration of chicken AA fibrils. Amyloid deposits were observed in chickens injected with SE and inoculated with chicken AA fibrils intravenously (21/26: 81%) and orally (8/12: 67%). These results suggest that chicken AA amyloidosis can be induced by vaccinations, and may be transmitted among like species by oral administration.