Trophic effect of insulin-like growth factor-I on metanephric development: Relationship to proteoglycans

Many hormones/factors influence the total body growth and development during embryonic life, and very few studies have been carried out to ascertain their effects on the individual organ system. In this study, the effect of exogenous insulin-like growth factor-I (IGF-I) on embryonic kidneys was investigated, and correlated with phenotypic and gene expression and synthesis of extracellular matrix (ECM) proteoglycans (PGs). Antisense experiments were carried out to elucidate the role of endogenous (IGF-I in metanephric development. Mouse metanephroi, harvested at 13th day of gestation, were exposed to IGF-I (100 ng/ml) in an organ culture for 7 days. An enlargement of the metanephroi with accentuation of its lobules, and increase in the nephron population and [³H]thymidine incorporation was observed. Immunofluorescence studies and Southern blot analysis of polymerase chain reaction products indicated augmented expression of the ECM PGs. A heavy concentration of [³⁵S]sulfate-associated radioactivity over the tips of ureteric bud branches and ECM components of maturing glomeruli was seen. Maximal effect of radioincorporation was observed on day-4 of the culture, the period when the concentration of endogenous IGF-I is the highest. PGs synthesized had elevated proportions of chondroitin sulfate vs heparan sulfate and of free chains, and reduced charge-density characteristics. Immunoprecipitation studies of [³⁵S]methionine-labeled glycoproteins revealed an increased synthesis of core-peptide of the PGs. IGE-I antisense oligonucleotide caused retardation in the growth of the kidneys along with the decrease in de novo synthesis of PGs. These findings indicate that IGF-I, a polypeptide essential to the renal growth and development, has a trophic effect on the embryonic kidney during the postinductive period of metanephric development, and the observed response has a temporal relationship with the increased synthesis of the PGs.