Submitted to: Journal of Cells Tissues and Organs
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/10/2003
Publication Date: 5/22/2003
Citation: Talbot, N.C., Garrett, W.M., Caperna, T.J. 2003. Analysis of the expression of aquaporins in pig liver tissue: comparison with rat liver tissue. Journal of Cells Tissues and Organs. 174:117-128. Interpretive Summary: In vitro models of pig liver tissue are needed to better study the metabolic and homeostatic functions of this centrally important body organ. To get an understanding of how good the model of the pig liver may be, pertinent in vivo characteristics of pig liver tissue need to be defined. The present study defined the presence and location of a class of important water-transporting proteins, called aquaporins (AQPs), in the liver of the fetal pig and the adult pig. The results of the study indicated that two-aquaporins, AQP-1 and AQP-9, were expressed in the bile duct tissue of the pig, and for AQP-9, this is in contrast to its expression in the rat liver where no expression in the bile duct tissue was found. AQP-1 was also present in the blood cells of the fetal liver, and this was consistent with its demonstrated expression in the blood cells of other species. The study indicates that the previous finding of AQP-1 and -9 in pig bile ductules grown in an in vitro model is consistent with the in vivo condition of the tissue and validates the model. The work will support efforts to study the pig liver and its functions, and may have utility in biomedical studies of cross-species organ transplantation.
Technical Abstract: Aquaporins (AQPs) are cellular proteins involved with water movement across cell membranes and are fundamentally important to the fluid transport in bile ducts and liver ductules. An immunohistochemical analysis of several AQPs was undertaken to describe their expression in fetal and adult pig liver. Anti-AQP-1 antibody reacted with the bile duct of the portal space and bile ductules at the periphery of liver lobules. Histological identification of bile ductules was confirmed by positive reactivity with anti-cytokeratin-7 and anti-laminin immunostaining. Anti-AQP-1 signals were also pronounced in the endothelium of the portal space blood vessels and peripheral venules. Antibody to AQP-9 reacted strongly with small ductules peripheral to the liver lobules, but only weakly with bile ducts of the portal space. Anti-AQP-adipose antibody bound to smooth muscle cells of arteries in the portal space and sporadically with certain dinucleated cells in the liver lobules. Antibodies to AQP-3,4,7, and 8 were non reactive with any of the tissues of the adult pig liver. For comparative purposes, immunohistochemical analysis of rat liver tissue was done with the anti-AQP-1 and -9 antibodies. Anti-AQP-1 reacted weakly with the rat liver's bile ducts, but robustly with the endothelium of liver's veins and arteries. It also reacted strongly with the central vein of the rat liver lobules, and, because the staining was continuous with hepatic sinusoids, it appeared that reactivity was specific to endothelial cells. Anti-AQP-9 antibodies reacted with rat hepatocytes and was not associated with canaliculi, as judged by concurrent phallodin staining of actin. Results indicate that specific aquaporins are expressed in pig liver tissues and that AQP-9 expression is distinct from its expression in the rat liver.