A temporal and ultrastructural relationship between heparan sulfate proteoglycans and AA amyloid in experimental amyloidosis.

Abstract

Previous histochemical studies have suggested a close temporal relationship between the deposition of highly sulfated glycosaminoglycans (GAGs) and amyloid during experimental AA amyloidosis. In the present investigation, we extended these initial observations by using specific immunocytochemical probes to analyze the temporal and ultrastructural relationship between heparan sulfate proteoglycan (HSPG) accumulation and amyloid deposition in a mouse model of AA amyloidosis. Antibodies against the basement membrane-derived HSPG (either protein core or GAG chains) demonstrated a virtually concurrent deposition of HSPGs and amyloid in specific tissue sites regardless of the organ involved (spleen or liver) or the induction protocol used (amyloid enhancing factor + silver nitrate, or daily azocasein injections). Polyclonal antibodies to AA amyloid protein and amyloid P component also demonstrated co-localization to sites of HSPG deposition in amyloid sites, whereas no positive immunostaining was observed in these locales with a polyclonal antibody to the protein core of a dermatan sulfate proteoglycan (known as "decorin"). Immunogold labeling of HSPGs (either protein core or GAG chains) in amyloidotic mouse spleen or liver revealed specific localization of HSPGs to amyloid fibrils. In the liver, heparan sulfate GAGs were also immunolocalized to the lysosomal compartment of hepatocytes and/or Kupffer cells adjacent to sites of amyloid deposition, suggesting that these cells are involved in HSPG production and/or degradation. The close temporal and ultrastructural relationship between HSPGs and AA amyloid further implies an important role for HSPGs during the initial stages of AA amyloidosis.

Structural mechanism of serum amyloid A-mediated inflammatory amyloidosis

“…Glycosaminoglycans (GAGs), in particular heparin/heparan sulfate (HS), are known to associate with AA amyloidosis (21,22). Previous studies showed that the binding of mouse SAA to HS depends primarily on charge interactions, and that the association promotes the HDL release of SAA and facilitates their aggregation (23)(24)(25).…”

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

“…Purified RNA was separated on 1.2% agarose gels containing 2.2 M formaldehyde as previously described [24]. The RNA was then hybridized overnight at 42ЊC with [a 32 P]-dCTP-(Amersham, Oakville, Ontario, Canada) labelled probes using a nick translation system (GIBCO/BRL). A tumour necrosis factor-a (TNF-a) cDNA probe (1.3 kb) was kindly provided by Dr A. Cerami (Rockefeller University, NY, USA).…”

“…Moreover, SDS-PAGE analysis of culture medium did not show any appearance of the 8 kDa protein band which would further suggest that AA fibrils were not formed. Other components present in vivo, such as the different common elements found in several types of amyloid deposits (serum amyloid P, heparan sulphate proteoglycan, Apo-E) [30][31][32][33][34][35], may be required for inducing a partial degradation and/or fibril formation. These common elements may be relevant to test in vitro to determine whether they play a role in the initiation phase of fibril formation.…”

“…However, when we consider that macrophages from susceptible mice show a slower SAA degradative processing between 24 and 48 h, one can wonder whether a similar intermittent block in SAA degradation occurring in vivo, where co-factors are present, may represent a 'window of opportunity' for the extracellular fibril formation and deposition. In vivo, co-factors such as heparan sulphate proteoglycans, amyloid P component and/or Apolipoprotein-E (Apo-E) could play a role in the initiation or perpetuation of the fibril formation in the presence of SAA [30][31][32][33][34][35].…”

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

“…The procedure causes amyloid formation in affected organs within 24 h (7). Experiments with this model have revealed an intimate structural and temporal relationship between AA amyloidosis and heparan sulfate (HS) (8), a sulfated polysaccharide expressed on the cell surfaces and in the extracellular matrix, suggesting a role for HS in SAA amyloidogenesis. Further, cell surface HS converts HDL-associated SAA into AA amyloid fibrils in cell culture, a process that can be inhibited by a C-terminal SAA peptide selectively binding to HS (9).…”