Osteopontin expression in fetal and mature human kidney

Osteopontin is a secreted phosphoprotein that is expressed by normal kidney , and has been associated with a number of functions including cell adhesio n, migration, signaling, and biomineralization. Although there is a vast li terature detailing osteopontin localization in various rodent models of bot h development and disease, this article presents the first comprehensive de scription of osteopontin localization in human kidney. In this study, immun ohistochemistry, immunoelectron microscopy. in situ hybridization, and Nort hern blotting are used to analyze osteopontin protein rind mRNA expression in human fetal and normal mature renal tissue. Osteopontin is expressed in the human embryonic renal tubular epithelium beginning on approximately day 75 to 80 of gestation. In the fetal kidney, osteopontin can also be: seen occasionally expressed in the ureteric buds and in some interstitial cells. As localized at the protein and mRNA level, the tubular expression of oste opontin increases with increasing gestational age and persists into adultho od. In the normal adult kidney, osteopontin is localized primarily to the d istal nephron and is strongly expressed by the thick ascending limb of the loops of Henle. Osteopontin expression can also be observed in some collect ing duct epithelium. In cases that exhibit foci of interstitial fibrosis an d an associated influx of interstitial macrophages, osteopontin expression is significantly upregulated in all tubular segments, including proximal tu bules.