Kidney Gpx3 is bound to tubular basement membranes

Abstract

Glutathione peroxidase 3 (Gpx3) is a plasma and extracellular selenoprotein postulated to protect against H2O2 and lipid hydroperoxides. In this study we show that kidney Gpx3 is insoluble, unlike plasma Gpx3. Immunohistochemistry localized Gpx3 to the perimeter of kidney tubules in the cortex and outer medulla of Gpx3+/+ mice. Absence of staining in Gpx3−/− kidneys verified antibody specificity. Tissue overlay experiments using kidney sections from Gpx3−/− mice demonstrated specific Gpx3 binding at the perimeter of the cortical tubules. Basement membranes isolated from Gpx3+/+ kidneys contained Gpx3 and, while basement membranes from Gpx3−/− mice did not contain Gpx3, they displayed Gpx3‐binding activity. Reducing conditions did not disrupt Gpx3 binding to basement membranes, indicating that binding was not mediated by disulfide or selenenylsulfide formation. Feeding selenium‐deficient diet resulted in depletion of the basement membrane‐bound Gpx3 pool. The reducing substrate glutathione is secreted by the tubular epithelium and that may allow the basement membrane‐associated Gpx3 pool to protect plasma membranes of kidney tubule cells. Supported by HD44863 and ES02497.