Proteomic characterization of serum amyloid A protein in different porcine body fluids

Abstract

Serum Amyloid A (SAA) proteins constitute a superfamily of small proteins (14–15 kDa) composed by a number of isoforms1, of which SAA1/2 (pI 5–6) are the main circulating forms in most of the species, and SAA3 is the predominant SAA isoform produced extrahepatically (pI higher than 9)1. Although its structure has not been determined, human SAA is considered an apolipoprotein, and can be found in biological fluids as monomers, aggregated as different-order multimers or associated with other proteins, such as HDL or albumin2,3. Exact functions of SAA remain unclear, although immunomodulatory, antimicrobial and lipid metabolism-related functions have been described in the literature1. Recent reports have established a relationship between functionality and conformation, and so the exact function of SAA would depend on its aggregation state4. SAA is also involved in the pathogenesis of AA-amyloidosis, a disease that is rare in pigs5. It has been postulated that porcine resistance to AA amyloidosis could be a consequence of a singular SAA isoform pattern5. In fact, we recently described that the theoretical characteristics of the SAA cDNA sequences obtained from different pig tissues indicated a singular isoform pattern in this species, since the pig SAA main circulating form showed properties of local SAA6. To the author’s knowledge, no studies have been performed to characterize pig SAA proteins by proteomics, probably due to the lack of pig-specific reagents. In the present study, the SAA conformation and isoforms were investigated in different porcine body fluids by 1-DE (SDS-PAGE) and 2-DE analysis and subsequent immunoblotting employing a specific in-house produced anti-pig SAA monoclonal antibody6.