Expression of the AQP-1 water channel in normal human tissues: a semiquantitative study using tissue microarray technology

1 Connective Tissue and Molecular Pathogenesis Research Groups, Faculty of Veterinary Science, University of Liverpool, Liverpool L69 7ZJ; and 2 School of Biomedical Sciences, University of Leeds, Leeds LS2 9NQ, United Kingdom Submitted 24 September 2003 ; accepted in final form 23 October 2003 Aquaporin water channels are a family of membrane proteins that facilitate water movement across biological membranes. Aquaporin-1 (AQP-1) has been found to be important in osmotic water movement across cell membranes of epithelial and endothelial barriers. However, the distribution of AQP-1 in many normal human tissues is still unknown. The aim of this study was to use immunohistochemistry and semiquantitative histomorphometric analysis to determine the tissue distribution and relative expression of AQP-1 in normal human tissues using tissue microarray (TMA) technology. The normal human TMAs employed in this study included cardiovascular, respiratory, gastrointestinal, hepatic and pancreatobiliary, oral, salivary, nasal, mammary, fetal, endocrine, genital tract, central and peripheral nervous systems, urinary tract, skin, cartilage, and other soft connective tissues. Immunohistochemistry and semiquantitative histomorphometric analysis confirmed the presence of AQP-1 in endothelial barriers of almost all tissues and in many epithelial barriers. AQP-1 was highly expressed in the renal cortex, choroid plexus, and pancreatic ducts. AQP-1 expression levels were surprisingly high in the anus, gallbladder, and liver; moderate expression was also detected in the hippocampus and ependymal cells of the central nervous system. This is the first report of AQP-1 protein distribution in normal human TMAs. These findings confirm the presence of AQP-1 in human endothelia and selected water-transporting epithelia and several new locations, including mammary epithelium, articular chondrocytes, synoviocytes, and synovial microvessels where AQP-1 may be involved in milk production, chondrocyte volume regulation, synovial fluid secretion, and homeostasis, respectively. aquaporin-1; water channel; human tissue microarrays; immunohistochemistry; histomorphometric analysis Address for reprint requests and other correspondence: A. Mobasheri, Connective Tissue and Molecular Pathogenesis Research Groups, Faculty of Veterinary Science, Univ. of Liverpool, Liverpool L69 7ZJ, United Kingdom (E-mail: a.mobasheri{at}liverpool.ac.uk ).