Degradation of Amyloid A Precursor Protein SAA by Macrophage Cell Lines Obtained from Amyloid Resistant and Susceptible Strains of Mice

Abstract

1997;45:354-360 Reactive AA amyloidosis can be induced in mice in a model of sustained inflammation following daily casein subcutaneous injections. However, the development of AA amyloidosis is known to vary in different strains of mice. The C57BL/6 strain is susceptible to the development of amyloidosis while the A/J strain is resistant. The degradation of purified serum amyloid A (SAA) protein by human monocytes as well as by mouse macrophages has been shown. The resistance/susceptibility of different mouse strains to the development of systemic amyloidosis may therefore be related to a difference in the ability of macrophages to degrade SAA. The authors have used bone marrow-derived macrophage cell lines obtained from susceptible C57BL/6 (ANA-1) and resistant A/J (A/J 10) mouse strains to compare their ability to degrade HDL-SAA in vitro. Cells were incubated with HDL-SAA for up to 72 h and the culture medium was analysed by SDS-PAGE to determine the rate of SAA degradation by the macrophages. The A/J 10 cells (resistant) were found to initiate a constant HDL-SAA degradation promptly whereas ANA-1 cells (susceptible) showed an intermittent block in the degradation of the precursor. Activation of macrophages by lipopolysaccharide (LPS) or interferon-g (IFN-g) hampered the precursor degradation suggesting that the activation process may favour extracellular accumulation of the precursor leading to a partial degradation and fibril formation.

Comparison of the binding and endocytosis of high-density lipoprotein from healthy (HDL) and inflamed (HDL SAA ) donors by murine macrophages of four different mouse strains

“…In contrast, the SAA-degradative capacity of mØ obtained from mice undergoing an amyloidosis induction protocol showed no difference from that of mØ obtained from healthy control animals [20]. Although it appears that the degradative capacity of mØ is influenced by their orgin and not by the amyloid induction protocol, neither of the two studies investigated the pathway by which SAA was degraded and whether mØ from C57BL/6 and A/J mice apply different pathways to degrade SAA [18,20].…”

“…In this respect, quantitative rather than qualitative differences may need to be demonstrated. Ham et al [18] have found that mØ obtained from C57BL/6 mice, in contrast to those obtained from A/J mice, show an intermittent block in the degradation of SAA as analyzed by in vitro degradation experiments with HDL SAA . In contrast, the SAA-degradative capacity of mØ obtained from mice undergoing an amyloidosis induction protocol showed no difference from that of mØ obtained from healthy control animals [20].…”

Serum Amyloid A Regulates Granulomatous Inflammation in Sarcoidosis through Toll-like Receptor-2

“…Second, the up-regulation of hepatic release of SAA induced as part of a systemic acutephase response may increase levels of plasma SAA available to bind to cells/matrix within the developing granulomatous inflammation. Third, IFN-g directly impairs the degradation of SAA by macrophages, which would enhance local accumulation and persistence of SAA (26). Although the dominant mechanism(s) remain unknown, we posit that the actual level of SAA up-regulation is not as critical as the factors that lead to aggregation and persistence of SAA (both nonfibrillar and fibrillar forms) that promotes further accumulation of SAA within the sarcoidosis granulomas.…”

“…CD3 1 T cells could also regulate trafficking of SAA-expressing inflammatory cells to sites of granulomatous inflammation. Importantly, IFN-g has been shown to directly impair the degradation of SAA by macrophages favoring extracellular accumulation and fibril formation (26), an effect that can directly link Th1 responses to enhanced aggregation and persistence of SAA. Together, these histopathologic observations provide the spatial context for the hypothesis that SAA is a bridge between the innate and adaptive immune responses that determine a specific pathobiologic development of granulomatous inflammation in sarcoidosis.…”

Pathology, diagnosis and pathogenesis of AA amyloidosis

“…It may be degraded completely without the occurrence of fragments [13,38,64] or incompletely with the generation of fragments resembling the AA fibril proteins in size, antigenicity and/or amino acid sequence [38,39,69,86,87,88], depending on the technique used to analyse proteolysis. Complete degradation of SAA without fragments was observed following degradation by m∅ [13,38] and neutrophils [64] and was assigned to the activity of serine proteases [38,64]. Incomplete degradation by m∅ has also been attributed to serine proteases and elastase [38,39,69].…”