Submitted to: Domestic Animal Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2015
Publication Date: 7/1/2015
Citation: Caperna, T.J., Shannon, A.E., Stoll, M.J., Blomberg, L., Ramsay, T.G. 2015. Regulation of alpha-1 acid glycoprotein synthesis by porcine hepatocytes in monolayer culture. Domestic Animal Endocrinology. 52(7):51-59.
Interpretive Summary: Alpha 1-acid glycoprotein (AGP) is a unique multifunctional protein. It is synthesized primarily in the liver by hepatocytes and at birth it represents about half of the circulating protein within the blood of newborn pigs. Moreover, the levels of AGP in the blood have been shown to be related to pre-weaning growth rate in piglets. The purpose of the present study was to investigate the regulation of AGP synthesis in hepatocytes prepared from suckling pigs and to provide a framework to compare its regulation with that of a typical stress-related or acute phase protein, haptoglobin (HP). Hepatocytes were isolated from 5-22 day old piglets and maintained in serum-free culture for up to 72 h. The influences of hormones, and inflammatory modifiers on AGP and HP were determined by measuring the gene expression and the amount of each protein of secreted into culture medium. The gene expression and secretion of AGP protein were enhanced by the cytokines (interleukins 1 and 17a), and by the antioxidant, resveratrol; AGP expression was inhibited by a panel of other cytokines including tumor necrosis factor and oncostatin M. The overall mRNA expression levels at 24 h were in agreement with the secreted protein levels confirming that control of these proteins in hepatocytes is largely at the transcriptional level. Moreover, these data support the idea that AGP is regulated by cytokines and hormones in a way largely opposite that of the positive acute phase protein, HP. This is the first report to determine what molecules regulate the expression of AGP and these data can be used to determine what metabolic conditions enhance and suppress the production of AGP. Since AGP has been shown to play a key role in the immune response and is a protein whose levels fluctuate during infection in other animal species, this initial study will help identify the role of this protein in the regulation of growth and health status in the pig.
Technical Abstract: Alpha 1-acid glycoprotein (AGP, ORM-1) is a highly glycosylated mammalian acute phase protein, which is synthesized primarily in the liver and represents the major serum protein in newborn pigs. Recent data have suggested that the pig is unique in that AGP is a negative acute phase protein in this specie and its circulating level appears to be associated with growth rate. The purpose of the present study was to investigate the regulation of AGP synthesis in hepatocytes prepared from suckling piglets and to provide a framework to compare its regulation with that of haptoglobin (HP) a positive acute phase protein. Hepatocytes were isolated from 5-22 day old piglets and maintained in serum-free monolayer culture for up to 72 h. The influences of hormones, cytokines and redox modifiers on the expression and secretion of AGP and HP were determined by relative PCR and by measuring the levels of each protein secreted into culture medium. The mRNA expression and/or synthesis/secretion of AGP protein was enhanced by IL-17a, IL-1 and resveratrol and inhibited by TNF, oncostatin M (OSM), IL-6, and thyroid hormone (P<0.05), while HP synthesis was up-regulated by, OSM, IL-6, dexamethasone and thyroid hormone and down-regulated by TNF and IL-1 (P<0.05). The overall mRNA expression levels at 24 h were in agreement with the secreted protein levels confirming that control of these proteins in hepatocytes, is largely transcriptional. Moreover, these data support the consideration that AGP is a negative acute phase reactant and appears to be regulated by cytokines (with the exception of TNF) and hormones in a way largely opposite that of the positive acute phase protein, HP.