CHARACTERIZATION OF TYPE-I IGF RECEPTOR AND IGF-I MESSENGER-RNA EXPRESSION IN CULTURED HUMAN AND BOVINE GLOMERULAR CELLS

Glomerular hypertrophy is reported in several endocrine disorders such as acromegaly and diabetes mellitus, where abnormalities of growth ho rmone and insulin-like growth factor (IGF-I) have been reported. In th e present report, we have cultured bovine and human glomerular endothe lial cells, and bovine glomerular epithelial and mesangial cells, and characterized the expression of IGF-I mRNA and its receptor in these c ells. High affinity, specific receptors for IGF-I were identified in a ll three types of cells by radioreceptor assays. Receptor number (R(o) ) derived by Scatchard analysis revealed an unusually high number of T ype I IGF receptors, approx. 1.2-105 receptors/cell in glomerular endo thelial cells. Affinity crosslinking studies and immunoprecipitation w ith antibodies against the Type I IGF receptor identified the alpha-su bunit of the IGF-I receptor as having a molecular mass of 140 kDa. Bio logically, IGF-I was more potent than insulin or IGF-II in stimulating DNA synthesis in glomerular endothelial cells. Northern blot analysis showed that glomerular and aortic endothelial cells expressed IGF-I m RNA of 1.7 kb. In contrast, renal glomeruli showed several IGF-I mRNAs of 7.5, 1.7 and 1.2 kb. Thus, the demonstration of both a prepondence of Type I IGF receptors coupled with the growth promoting effects of IGF-I in glomerular endothelial and epithelial cells, as well as the l ocal production of IGF-I mRNA suggests that IGF-I serves an important role as an autocrine or paracrine regulator of the growth of renal glo meruli.