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ABSTRACT
More evidence has recently been obtained indicating that growth hormone (GH) has a direct effect on bone. However, it is not clear which cell type reacts to the hormone. The present study used osteoblast-like cells derived from sequentially digested fetal mouse calvaria. Separately cultured tractions resulted in populations enriched in cells with a more or a less differentiated phenotype. The results showed that GH acts on the cells released last, i.e. those with more characteristics of the osteoblast. In these cells, GH induced strong mitogenic activity. Prolactin was not active.
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ABSTRACT
Specific binding to and proliferative actions of insulinlike growth factors-I and -II (IGF-I and -II) on fetal mouse osteoblasts were tested. Membranes of mouse osteoblasts were shown by binding competition studies to possess specific binding sites for IGF-I and IGF-II. When IGF-I was used as a tracer, half-maximal displacement was obtained with 1·11 μg IGF-I/1 and with 14 μg IGF-II/1. Displacement of 125I-labelled IGF-I was accomplished with 2·33 μg IGF-II/1 and with 55 μg IGF-I/1. Affinity cross-linking showed bands of 130 kDa 125I-labelled IGF-I and 260 kDa 125I-labelled IGF-II under reducing conditions, further indicating the presence of classical type-I and -II receptor sites on mouse osteoblasts. Mitogenic effects of IGFs were weak; a combination with epidermal growth factor or fibroblast growth factor showed strong synergistic action however. The possibility of autocrine/paracrine actions of IGFs is discussed.
Journal of Endocrinology (1990) 125, 271-277
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ABSTRACT
Bone matrix contains a variety of growth factors, but little is known of osteoblastic production of such materials. The present study assesses growth factor activity, chromatographed on acidic Bio-Gel P-100, secreted into conditioned media of primary cultures of fetal mouse calvaria. The cultures produced insulin-like growth factor-I (IGF-I), determined by radioimmuno-assay of molecular weights 20 and 10 kDa. IGF-II, determined by radioreceptor assay, was present at 20–29 and 7 kDa. The IGF peaks at 20, 10 and 7 kDa were all mitogenic in MCF-7 cells. Proteins of several different molecular weights were also present that specifically bound IGF-I and IGF-II. Transforming growth factor-β (TGF-β), assayed in a system for inhibition of growth, was also produced. Both activated and latent forms were present, and part of the TGF-β was TGF-β2. The absence of mitogenic activity in the bmolecular range of platelet-derived growth factor, assayed in 3T3 fibroblasts, makes it unlikely that mouse osteoblasts produce this growth factor.
Journal of Endocrinology (1990) 124, 301–309
