Recombinant Mouse Serum Amyloid A1 Protein, CF

Mouse Serum Amyloid A protein‑1 (SAA1; previously SAA2 in mouse) is a multifunctional apolipoprotein produced by hepatocytes in response to pro‑inflammatory cytokines (1 ‑ 4). It is secreted as a 12 kDa, 103 amino acid (aa), nonglycosylated protein and circulates as part of the HDL complex (1 ‑ 4). The SAA1 gene is one of five SAA genes in mouse (3). Mature mouse SAA1 shares 72%, 72% and 67% amino acid (aa) sequence identity with human, rabbit and equine SAA1, respectively. SAA1 and SAA2 share 113 of their 122 amino acids and are termed A‑SAA (acute phase SAA) (2, 3). SAA1 is produced in the liver in both human and mouse (3, 4). SAA1 is prominently produced in human adipose tissue, but is absent in mouse adipose, which instead expresses adipose SAA3 (a pseudogene in humans) (5). In mouse, however, circulating SAA1 is elevated by insulin resistance (6). A‑SAA can increase by as much as 1000‑fold during inflammation (3). When highly expressed, A‑SAA can displace ApoA1 as the major apolipoprotein in HDL complexes, weakening its role as a reverse (lipid clearing) cholesterol transporter (4). A highly charged region of SAA1 and 2 (aa 36 ‑ 68) contains putative fibronectin and laminin binding motifs (3). This region also binds heparan sulfate proteoglycans at mildly acidic pH and promotes aggregation of A‑SAA; however, pathogenic amyloid fibrils contain fragments of mouse SAA2, not SAA1 (3, 7, 8). Mouse strains can differ in SAA sequence, expression, and amyloid formation (1, 8 ‑ 10). SAA1 is a ligand for CD36/SR‑B3, SR‑B1, FPRL1, TLR2, and RAGE on monocytes/macrophages, inducing chemotaxis and generation of cytokines and tissue factor (12 ‑ 14). SAA1 can bind the surface of invading gram‑negative bacteria, acting as an opsonin to aid clearance by macrophages (11). SAA1 also binds platelets, probably by engaging fibrinogen on the platelet surface (15).