title: Binding, trafficking and accumulation of serum amyloid A in peritoneal macrophages.
abstract: Murine serum amyloid A1.1 (SAA1.1) has been conjugated with the fluorophore Texas Red (TxR), and its interaction with peritoneal macrophages has been visualized by scanning confocal microscopy. Binding of TxR-SAA to cell surfaces was inhibited by an excess of unlabelled SAA indicating the involvement of saturable receptors. Internalized TxR-SAA was seen initially as small punctate signals which in some cells evolved into a fine fluorescent network, a pattern typical of tubular endosomes. Colocalization of TxR-SAA with Cy5-labelled low density lipoprotein (LDL) but not with Oregon Green-labelled transferrin suggested that SAA trafficked through endosomes and lysosomes for degradation rather than through recycling compartments. Consistent with this catabolic pathway, macrophages loaded with TxR-SAA lost fluorescence within several days after being shifted to a fluorophore-free medium. In sharp contrast to this, cells maintained under amyloid-forming conditions, i.e. in the presence of unlabelled SAA and amyloid-enhancing factor (AEF) before and after treatment with TxR-SAA, remained brightly fluorescent over the course of 5 days. Immunocytochemistry verified the accumulation of SAA within macrophages. These findings support the hypothesis that a decreased catabolism of internalized SAA plays a role in AA amyloid pathogenesis.
authors: Department of Pathology and Laboratory Medicine, Indiana University School of Medicine, Medical Research and Library Building, Fifth Floor, 975 West Walnut Street, Indianapolis, IN, USA. bkluvebe@iupui.edu
authors: B
authors: B
authors: Kluve-Beckerman
authors: J
authors: J
authors: Manaloor
authors: J J
authors: JJ
authors: Liepnieks
mesh_terms: D000686:Amyloidosis / Q000209:etiology / Q000378:metabolism; D000818:Animals; D001053:Apolipoproteins / Q000378:metabolism*; D001693:Biological Transport, Active; D005456:Fluorescent Dyes; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D017737:Macrophages, Peritoneal / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D011485:Protein Binding; D000685:Serum Amyloid A Protein / Q000378:metabolism*; D014966:Xanthenes
chemical_list: D001053:Apolipoproteins; D005456:Fluorescent Dyes; D000685:Serum Amyloid A Protein; D014966:Xanthenes; C034657:Texas red