Metanephric osteopontin regulates nephrogenesis in vitro

Renal expression of osteopontin is enhanced in the setting of acute ischemic injury. Because of the parallels that exist between recovery from renalischemia and renal development, we characterized the role that osteopontin plays during metanephrogenesis in the rat. Osteopontin mRNA is present in kidneys obtained from rat embryos as early as embryonic day 13 (E13). Immunohistochemical staining of metanephroi obtained from E16 rat embryos and metanephroi obtained from E13 embryos and cultured for 3 days in vitro demonstrated that osteopontin is expressed both in the developing nephron and in the ureteric bud. Addition of anti-osteopontin antibodies to metanephric organ cultures results in failure of the metanephrio blastema to undergo normal tubulogenesis. Addition of the arginine-glycine-aspartic acid- containing peptide, cyclo-RGDfV, or the anti-α(v)β₃-integrin antibody, LM609, to cultures has a similar effect. These findings establish that osteopontin is produced within the rat metanephros during development in vivo and suggest that the binding of osteopontin to the α(v)β₃-integrin is required for tubulogenesis to occur in vitro. Blastemal cells within metanephroi cultured in the presence of OP199 manifest increased apoptosis compared with controls. It is possible that osteopontin plays an important anti-apoptotic role during the process of metanephric blastema condensation that is a prerequisite for the formation of nephrons in vivo.