Rick L. Meek

Mouse SAA3: Detection in Mouse Tissues with Specific Antibody

Antibodies to a protein A-SAA3 fusion protein were generated in rabbits. Immunochemical studies using SAA3 antiserum were performed on tissues from LPS treated mice and revealed positive reactions to liver hepatocytes and other tissues.

Kinetics of Selective Deposition of ApoSAA2 During Development of Amyloidosis in Mice

The major murine serum amyloid proteins (apoSAA1, apoSAA2) have been identified, of which only one (apoSAA2) shares amino acid sequence identity with tissue protein AA. To examine the mechanism of this apparent isotype-specific amyloid protein deposition, we have studied apoSAA metabolism at the levels of gene expression and plasma content during amyloidogenesis. In CBA mice, daily intraperitoneal casein administration resulted in a linear increase in splenic amyloid content, beginning within 10 days and reaching approximately 30% of the organ volume at 20 days. Hepatic apoSAA mRNA content, estimated by in vitro translation, was highest at day 1 (3% of total mRNA) and declined thereafter (to 1%, day 20). The relative content of apoSAA2 mRNA compared with that of apoSAA1 was unchanged throughout amyloid induction. Simultaneously, a 2–3 fold drop in total serum apoSAA levels was observed with, by contrast, a 10-fold reduction in the serum ratio of apoSAA2/apoSAA1. These results are consistent with the hypothesis that murine tissue protein AA accumulates by selective deposition of apoSAA2 from the serum.

Serum Amyloid A (SAA) Induction in the Serum High Density Lipoproteins of the Syrian Hamster

SAA elevations in the serum lipoproteins of hamsters were induced by injection of lipopolysaccharide intraperitoneally or turpentine subcutaneously. Lipoprotein fractions isolated by sequential density centrifugation of serum samples obtained 20-hours post-stimulus were examined by SDS-PAGE followed by electroimmunoblotting. We observed a marked enhancement of a 12-kDa doublet in the electrophoretic pattern of the acute-phase HDL3. Antibodies to human or monkey AA reacted preferentially with the leading member of the doublet, whereas antibodies to mouse AA reacted preferentially with the trailing member. Antibodies to human and mouse SAA and to duck AA reacted with both members. The different reactions displayed by the members of the hamster SAA doublet against the several antibody preparations suggest that at least two of the three proteins predicted by a study of SAA-gene expression in the hamster may circulate in the HDL.

Identification of Cells Expressing SAA3 mRNA by in Situ Hybridization

Serum amyloid A (SAA) is a family of proteins found circulating mainly associated with high density lipoproteins.1–3 They behave as acute phase reactants: Only trace amounts are found normally but in response to inflammatory conditions or injury the levels are elevated several hundred fold.4,5 Amyloid A protein is the main protein constituent found in the amyloid fibrils of reactive amyloidosis and is a fragment of serum amyloid A.6–8 in the mouse, serum amyloid A is encoded by a family of three active genes,9 (SAA1, SAA2, SAA3) but only SAA2 is the precursor to amyloid A protein.10 The liver is the major site of SAA synthesis where, following LPS stimulation of mice, messenger RNA for each of the three genes is elevated approximately 1,000 fold.11 Serum amyloid A genes are also expressed in extrahepatic tissues, however this is almost exclusively limited to expression of the SAA3 mRNA.12,13 We wish to determine the source of SAA3 mRNA in extrahepatic sites: Is SAA3 message expressed by a single cell system dispersed throughout the extrahepatic tissues, or are the differentiated cells of the various tissues responsible for SAA3 expression?

Rat Liver and Lung Express Serum Amyloid A Related mRNAs

A vast number of systemic and metabolic changes occur in response to injury or infection. Among these events (the acute phase response) is the rise in concentration of a large number of plasma proteins of hepatic origin termed the acute phase proteins.1 Serum amyloid A is a family of acute phase proteins2,3 of unknown function and are apolipoproteins of HDL.4,5 In reactive amyloidosis amyloid A protein (AA) is the major protein constituent of the amyloid fibrils and amino terminal fragment of the plasma serum amyloid A protein.6,7,8 Not all SAA proteins are amyloidogenic though, since in the mouse there are three transcibed SAA genes (SAA1, SAA2, and SAA3) but only SAA2 is the precursor to murine AA protein.11