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 albumin^2,3. 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.