Binding, trafficking and accumulation of serum amyloid A in peritoneal macrophages.
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.
Kluve-Beckerman
B
B
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
Manaloor
J
J
Liepnieks
J J
JJ
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
D001053:Apolipoproteins; D005456:Fluorescent Dyes; D000685:Serum Amyloid A Protein; D014966:Xanthenes; C034657:Texas red