Localization of mRNAs for insulin-like growth factor binding proteins 1 to 6 in rat kidney

Insulin-like growth factor-I (IGF-I) is a peptide growth factor whose activity is modulated by interaction with the family of six IGF binding proteins (IGFBPs). IGF-I is detected in rat kidney and has metabolic and growth effects. We have used in situ hybridization to localize mRNAs for the IGFBPs in rat kidney. Messenger RNAs for all six IGFBPs were detected, each with a distinctive distribution. IGFBP-1 mRNA was expressed in the distal nephron, from the thick ascending limb of the loop of Henle to the cortical collecting ducts. IGFBP-2 mRNA expression was confined to epithelial cells of the glomeruli and the thin limbs of the loop of Henle. IGFBP-3 mRNA was localized to the cortical interstitium while IGFBP-4 was the only IGFBP mRNA found in the proximal tubule. IGFBP-5 mRNA, the most abundant and widely distributed of the IGFBP mRNAs in the kidney, occurred in the glomerular mesangium and the medullary interstitium as well as in the epithelial cells of the distal nephron. IGFBP-6 mRNA, the least abundant, was expressed mainly in fibroblasts associated with renal blood vessels and the ureter. This heterogeneous distribution of the IGFBPs may enable IGF action to be regulated by multiple factors in a site-specific manner.