Pathogenesis Of AA Amyloidosis Research Articles

Effect of amino acid variations in the central region of human serum amyloid A on the amyloidogenic properties

Human serum amyloid A (SAA) is a precursor protein of the amyloid fibrils that are responsible for AA amyloidosis. Of the four human SAA genotypes, SAA1 is most commonly associated with AA amyloidosis. Furthermore, SAA1 has three major isoforms (SAA1.1, 1.3, and 1.5) that differ by single amino acid variations at two sites in their 104-amino acid sequences. In the present study, we examined the effect of amino acid variations in human SAA1 isoforms on the amyloidogenic properties. All SAA1 isoforms adopted α-helix structures at 4°C, but were unstructured at 37°C. Heparin-induced amyloid fibril formation of SAA1 was observed at 37°C, as evidenced by the increased thioflavin T (ThT) fluorescence and β-sheet structure formation. Despite a comparable increase in ThT fluorescence, SAA1 molecules retained their α-helix structures at 4°C. At both temperatures, no essential differences in ThT fluorescence and secondary structures were observed among the SAA1 isoforms. However, the fibril morphologies appeared to differ; SAA1.1 formed long and curly fibrils, whereas SAA1.3 formed thin and straight fibrils. The peptides corresponding to the central regions of the SAA1 isoforms containing amino acid variations showed distinct amyloidogenicities, reflecting their direct effects on amyloid fibril formation. These findings may provide novel insights into the influence of amino acid variations in human SAA on the pathogenesis of AA amyloidosis.

Heparan Sulfate Dissociates Serum Amyloid A (SAA) from Acute-phase High-density Lipoprotein, Promoting SAA Aggregation

Inflammation-related (AA) amyloidosis is a severe clinical disorder characterized by the systemic deposition of the acute-phase reactant serum amyloid A (SAA). SAA is normally associated with the high-density lipoprotein (HDL) fraction in plasma, but under yet unclear circumstances, the apolipoprotein is converted into amyloid fibrils. AA amyloid and heparan sulfate (HS) display an intimate relationship in situ, suggesting a role for HS in the pathogenic process. This study reports that HS dissociates SAA from HDLs isolated from inflamed mouse plasma. Application of surface plasmon resonance spectroscopy and molecular modeling suggests that HS simultaneously binds to two apolipoproteins of HDL, SAA and ApoA-I, and thereby induce SAA dissociation. The activity requires a minimum chain length of 12-14 sugar units, proposing an explanation to previous findings that short HS fragments preclude AA amyloidosis. The results address the initial events in the pathogenesis of AA amyloidosis.

Increased susceptibility of serum amyloid A 1.1 to degradation by MMP-1: potential explanation for higher risk of type AA amyloidosis

Genetic polymorphisms in serum amyloid A (SAA) have been shown to substantially influence the risk of developing type AA amyloidosis. Recently, a role for MMP-1 has been suggested in the pathogenesis of AA amyloidosis. Therefore, we investigated if the SAA1 isotypes are differentially degraded by MMP-1. Degradation of different SAA isotypes by MMP-1 was assessed by immunoblotting. MALDI-TOF mass spectrometry was used to identify degradation fragments. We found that SAA1.5 is more resistant to degradation by MMP-1 than SAA1.1. This difference is caused by the capacity of MMP-1 to cleave at the site of the polymorphism at position 57. These results may explain the higher risk of amyloidosis in patients with a SAA1.1/1.1 genotype vs SAA1.5/1.5 or SAA1.1/1.5 genotype. In addition, the impaired degradation of SAA1.5 by MMP-1 could also explain the higher serum SAA concentrations in persons with a SAA1.5 genotype.

Serum amyloid A: production by human white adipocyte and regulation by obesity and nutrition

The acute-phase proteins, serum amyloid As (SAA), are precursors of amyloid A, involved in the pathogenesis of AA amyloidosis. This work started with the characterisation of systemic AA amyloidosis concurrent with SAA overexpression in the subcutaneous white adipose tissue (sWAT) of an obese patient with a leptin receptor deficiency. In the present study a series of histopathological, cellular and gene expression studies was performed to assess the importance of SAA in common obesity and its possible production by mature adipocytes. Gene expression profiling was performed in the sWAT of two extremely obese patients with a leptin receptor deficiency. Levels of the mRNAs of the different SAA isoforms were quantified in sWAT cellular fractions from lean subjects and from obese subjects before and after a very-low-calorie diet. These values were subsequently compared with serum levels of SAA in these individuals. In addition, histopathological analyses of sWAT were performed in lean and obese subjects. In sWAT, the expression of SAA is more than 20-fold higher in mature adipocytes than in the cells of the stroma vascular fraction (p<0.01). Levels of SAA mRNA expression and circulating levels of the protein are sixfold (p<0.001) and 3.5-fold (p<0.01) higher in obese subjects than in lean subjects, respectively. In lean subjects, 5% of adipocytes are immunoreactive for SAA, whereas the corresponding value is greater than 20% in obese subjects. Caloric restriction results in decreases of 45-75% in levels of the transcripts for the SAA isoforms and in circulating levels of the protein. The results of the present study indicate that SAA is expressed by sWAT, and its production at this site is regulated by nutritional status. If amyloidosis is seen in the context of obesity, it is possible that production of SAA by adipocytes could be a contributory factor.

Pathology, diagnosis and pathogenesis of AA amyloidosis.

Amyloid is defined as a proteinaceous tissue deposit that shows a typical green birefringence in polarised light after staining with Congo red, the presence of non-branching linear fibrils of indefinite length with an approximate diameter of 10-12 nm and a distinct X-ray diffraction pattern consistent with Pauling's model of a cross-beta fibril. Approximately 45% of generalised amyloidoses are secondary or reactive (AA) amyloidosis. Among the causes of AA amyloidosis are rheumatic diseases, idiopathic diseases, inherited diseases, infectious diseases and malignant tumours. Recent decades have provided significant advances in our understanding of the pathology and pathogenesis of AA amyloidosis. Its pathogenesis is multifactorial involving many variables such as primary structure of the precursor protein, acute phase response, the presence of non-fibril proteins (e.g. amyloid P component, apolipoprotein E, glycosaminoglycans, proteoglycans and basement membrane proteins), receptors, lipid metabolism and proteases. Study of the pathogenesis of AA amyloidosis has provided many insights into the nature of conformational diseases, which may help in the understanding of other members of this particularly heterogeneous group of diseases, such as Alzheimer's disease and transmissible spongiform encephalopathies.

Amyloid proteins in pathogenesis of AA amyloidosis

Amyloid proteins in pathogenesis of AA amyloidosis

Binding and endocytosis of murine high density lipoprotein from healthy (HDL) and inflamed donors (HDLSAA) by murine macrophages in vitro. A light and electronmicroscopic investigation

Serum amyloid A (SAA), an acute phase protein found primarily on high density lipoproteins (HDLsaa), is the precursor protein of AA-amyloidosis. Though extensivly studied, the pathway by which SAA bound to HDL becomes deposited as a fibril protein in AA-amyloidosis, is unknown. Macrophages (Mø) have been implicated in the pathogen-esis of AA amyloidosis and are known to bind, endocytose and retro-endocytose HDL. Studies were therefore performed to examine whether HDLsaa is handled in a manner similar to HDLHDL and HDLsaa binding and intemalisation experiments were performed with cultured, cholesterol-laden murine MpH using either native or colloidal gold-labelled HDL and HDLsaa, and visualized either directly by light and electronmicroscopy, or by immunocytochemical means. Pre-treatment of MpH with heparinase examined the potential importance of membrane-bound glycosaminoglycans on the binding and uptake of HDL and HDLsaaThe binding of HDL and HDLsaa by MpH depended on culture conditions. Short-term cultures (2 vs 5 days), or cells treated with heparinase reduced the binding of both HDL and HDLsaa. Gold-labelled HDL and HDLsaa were found in compartments of the receptor-mediated pathway, such as coated pits, coated vesicles, endosomes, outer leaflets of multivesicular bodies as well as in lipid droplets and compartments which appear to be part of the exocytotic pathway. Only after prolonged incubation periods were signifcant numbers of gold-particles found in lysosomes. No differences were observed between the route followed by HDL and HDLsaaThese studies are consistent with the view that inter-nalization of HDLsaa by cells of the reticuloendothelial system is similar to that of HDL, and that its binding may involve a surface heparan sulfate proteoglycan and a receptor

Serum amyloid A (SAA): Biochemistry, genetics and the pathogenesis of AA amyloidosis

Serum amyloid A (apoSAA) is a polymorphic protein encoded by a family of SAA genes in which new members continue to be identi3ed. Those isoforms or allelic forms that are precursors for the amyloid...

Amyloid-enhancing factor (AEF) in the pathogenesis of AA-amyloidosis in the hamster.

AA-amyloidosis was induced in hamsters receiving amyloid-enhancing factor (AEF) by daily subcutaneous injection with either an aged casein solution or casein supplemented with lipopolysaccharide (LPS). Both amyloid inducers gave similar results with respect to amyloid development in spleen, liver and kidneys and to serum amyloid A (SAA) concentrations and plasma cathepsin D activities. AEF was isolated from amyloid-containing tissue by the method described by Hol et al. (1985), and amyloid-enhancing material was also extracted from isolated hamster amyloid fibrils by intensive sonification. This fibril-derived amyloid-enhancing material lacked typical green birefringence after staining with Congo red and appeared as amorphous material on electron microscopy. AEF shortened the pre-amyloid phase for splenic and hepatic amyloid development and also the subsequent interval before renal amyloid deposition. This indicates that endogenous AEF, unlike passively transferred preformed AEF, is not distributed throughout the body and is probably generated at the site of amyloid deposition. Moreover, these results suggest that amyloid deposition in the kidneys, like that in the spleen and liver, involves an AEF-dependent pathway. Thus redistribution of amyloid is probably not an important cause of renal amyloid involvement. In addition to the reduction in the lag phase for splenic and hepatic amyloid deposition, AEF also speeds the changes in SAA concentration and plasma cathepsin D activity. This indicates that AEF accelerates rather than eliminates the pre-amyloid phase.