Expression and release of insulin-like growth factor binding proteins in isolated epiphyseal growth plate chondrocytes from the ovine fetus

Insulin-like growth factor-ii (IGF-II) is an autocrine modulator of epiphys eal chondrogenesis in the fetus. The cellular availability of ICFs are infl uenced by the IGF-binding proteins (ICFBPs). In this study, we investigated the control of expression and release of ICFBPs from isolated epiphyseal g rowth plate chondrocytes from the ovine fetus by hormones and growth factor s implicated in the chondrogenic process. Chondrocytes were isolated from t he proliferative zone of the fetal ovine proximal tibial growth plate and m aintained in monolayer culture at early passage number. Culture media condi tioned by chondrocytes under basal conditions released ICFBPs of 24, 34, an d 29 kDa, and a less abundant species of 39-43 kDa that were identified imm unologically as IGFBP-4, IGFBP-2, IGFBP-5, and IGFBP-3, respectively. Messe nger RNAs encoding each species were identified by Northern blot analysis w ithin chondrocytes, as was mRNA encoding IGFBP-6. Exposure to ICF-I or IGF- II (13 or 26 nM) caused an increase in expression and release of 1GFBP-3. T he release of 1GFBP-2 and IGFBP-5 were also potentiated without changes to steady state mRNA, and for IGFBP-5 this was due in part to a release from t he cell membrane in the presence of ICF-II. Insulin (16.7 or 167 nM)selecti vely increased mRNA and the release of IGFBP-3, while cortisol il or 5 mu M ) inhibited both mRNA and release of IGFBP-2 and ICFBP-5, Transforming grow th factor-beta 1 (TGF-beta 1) (0.1 or 0.2 nM) increased the expression and release of IGFBP-3. and caused an increase in mRNAs encoding IGFBP-2 and IC FBP-5. Neither growth hormone (GH), Fibroblast growth factor-2, nor thyroxi ne (T-4) had any effect on IGFBP expression or release. The results suggest that IGFBP expression and release within the developing growth plate can b e modulates by IGF-II and other trophic factors, thus controlling IGF avail ability and action. (C) 2000 Wiley-Liss, Inc.