Ch. Schmid

Preferential enhancement of myoblast differentiation by insulin-like growth factors (IGF I and IGF II) in primary cultures of chicken embryonic cells

Cells prepared from the body walls of chicken embryos were plated in the absence of serum. Insulin‐like growth factors (IGFs) barely stimulated cell replication, but preferentially enhanced the differentiation of muscle cells. Myoblast fusion was favoured in the presence of IGF (or insulin). Concomitantly, acetylcholinesterase activity increased. IGF I and IGF II were equipotent and active in low physiological concentrations, in contrast to insulin, which was known for a long time to exert such effects at pharmacological concentrations.

Insulin-like growth factor I supports differentiation of cultured osteoblast-like cells

Rat calvaria cells grown in culture for one week had properties of osteoblasts: a high content in alkaline phosphatase and a marked cyclic AMP response to parathyroid hormone (PTH). In short‐term experiments, insulin‐like growth factor I (IGFI) stimulated the incorporation of (14C]glucose into glycogen. When IGF I was present in the medium during 6 days the cell number increased slightly and there was a substantial, disproportionate rise in alkaline phosphatase activity of the cultures. Thus, IGFI stimulates growth, and in addition, and in contrast to other growth factors, mainly enhances differentiation of osteoblasts.

Insulin-like growth factors stimulate synthesis of nucleic acids and glycogen in cultured calvaria cells

SummaryA (sub)population of cells obtained from newborn rat calvaria by (sequential) collagenase digestion is grown to confluence in serum-containing medium. These cells are osteoblast-like with respect to high alkaline phosphatase activity and marked responsiveness (cAMP) to parathormone.Insulin-like growth factors (IGFs) enhance net incorporation of the labeled precursors thymidine, uridine, and glucose into the respective macromolecules DNA, RNA, and glycogen. Human IGF I is five times as potent as IGF II in evoking these anabolic responses in cultured rat calvaria cells. In contrast to insulin, the factors are effective in concentrations in which they are present in serum.

Regulation of hepatic expression of IGF I and fetal IGF binding protein mRNA in streptozotocin-diabetic rats

Hepatic mRNA levels of insulin‐like growth factor I (IGF I) and of the fetal, nonglycosylated 32 kDa IGF‐binding protein (BP) were analysed in diabetic, diabetic insulin‐ and IGF I‐treated rats as well as in age‐matched, healthy control animals. IGF I mRNA levels are reduced in diabetic rats and increased by insulin treatment. In contrast, the infusion of IGF I does not significantly upregulate IGF I mRNA levels. Fetal IGF BP mRNA expression is very low in healthy control animals, but high levels are found in diabetic rats. Insulin therapy lowers fetal IGF BP mRNA levels, whereas IGF I has no efrect. We propose that insulin is a major regulator of the 32 kDa IGF BP levels in adult rats.

Differential regulation of insulin-like growth factor binding protein (IGFBP)-2 mRNA in liver and bone cells by insulin and retinoic acid in vitro

Isolated cells produce insulin‐like growth factors (IGFs) and their binding proteins (IGFBPs). Two distinct cell types were studied with regard to IGFBP‐2 expression: (i) rat hepatocytes, which produce IGF I at a high rate and thus regulate its plasma concentration; and (ii) rat osteoblasts, which are targets of IGF I action. IGFBP‐2 expression is low in hepatocytes prepared from normal adult rats and high in calvaria cells from newborn rats. Retinoic acid stimulates IGFBP‐2 production by liver cells. Insulin suppresses both basal and retinoic acid‐induced IGFBP‐2 mRNA expression in hepatocytes and has no such effect on osteoblasts. Retinoic acid and insulin regulate IGFBP‐2 expression in a tissue‐specific manner.

Production of carrier proteins for insulin-like growth factors (IGFs) by rat osteoblastic cells Regulation by IGF I and cortisol

A bone‐derived rat cell line, PyMS, releases IGF I and IGF carrier proteins which are similar to those found in rat serum. Western blot analysis of culture media conditioned by hormone‐treated cells shows that growth hormone and IGF I stimulate and cortisol inhibits production of IGF carrier proteins in vitro. A glycosylated carrier protein species of 49‐42 kDa is closely related to the subunits of the growth hormone‐dependent carrier protein complex found in rat serum. In addition, rhIGF I rapidly induces a 32 kDa, non‐glycosylated IGF‐binding protein whose accumulation is markedly increased by cortisol.

1α,25-Dihydroxyvitamin D3 stimulates sodium-dependent phosphate transport in osteoblast-like cells

1α,25-Dihydroxyvitamin D3 [1,25(OH)2D3] stimulate calcium and phosphate absorption in the duodenum. Because osteoblastic cells appear to be responsible for Pi deposition in bone, we analyzed the effect of 1,25(OH)2D3 on sodium-dependent phosphate (NadPi) transport in newborn rat calvaria-derived osteoblasts and in a rat bone-derived cell line, PyMS. 1,25(OH)2D3 at 10−9 mol/L stimulated NadPi uptake 1.6-fold in PyMS and 1.8-fold in calvaria cells after 24 h, but not after 2 h and 6 h. Insulin-like growth factor (IGF)-I stimulated NadPi transport 1.8-fold in both cell types within 2 h. There was no change in Na-dependent alanine transport or in Na-independent uptake of Pi and alanine, and the effects of 1,25(OH)2D3 on NadPi transport were not associated with corresponding changes in cell number, protein content, or alkaline phosphatase activity. Actinomycin D, an inhibitor of transcription, prevented the stimulatory effect of 1,25(OH)2D3 (but not that of IGF-I) on NadPi transport; stimulation of NadPi transport by 1,25(OH)2D3 may depend on an increased de novo synthesis of transporters. Our studies confirm that IGF-I stimulates NadPi uptake and show, for the first time, a specific stimulatory effect of 1,25(OH)2D3 on NadPi transport in osteoblasts in vitro.

Effects of Insulin‐Like Growth Factor I in Man

ABSTRACT. A 6‐day period of subcutaneous infusion with recombinant human insulin‐like growth factor I in three healthy male volunteers resulted in an increase in the ratio of insulin to C‐peptide levels and significant decreases in triglyceride levels and the ratio of total to high density lipoprotein—cholesterol in serum. Increased renal plasma flow and glomerular filtration rates were also observed.

Parathormone promotes glycogen formation from [14C]glucose in cultured osteoblast-like cells

Parathyroid hormone stimulates [U‐14C]glucose incorporation into glycogen of cultured osteoblast‐like calvaria cells. This effect is detectable only several hours after the addition of PTH and it is mimicked by dibutyryl cyclic AMP. In contrast to insulin (in pharmacological concentrations), PTH enhances glycogen formation only in calvaria cells, but not in fibroblasts. Insulin‐like growth factor I in physiological concentrations promotes glycogen‐synthesis shortly after addition.

Differential effects of fluoride and insulin-like growth factor I on sodium-dependent alanine and phosphate transport in a human osteoblast-like cell line

The effects of fluoride and insulin-like growth factor (IGF)-I on sodium-dependent (Na(d)) alanine and phosphate (Pi) transport were compared in a human osteosarcoma cell line, SAOS-2/B-10. Fluoride stimulated Na(d) alanine but not Pi uptake in a dose-dependent manner, whereas IGF-I stimulated both alanine and Na(d)Pi transport. IGF-I and low concentrations of fluoride stimulated Na(d) alanine transport rapidly. Genistein, an inhibitor of tyrosine kinase blocked IGF-I- but not fluoride-stimulated Na(d) alanine transport. The effects of fluoride and IGF-I were additive and not associated with corresponding changes in cell number or protein content. In conclusion, low concentrations of fluoride rapidly and selectively stimulate Na(d) alanine transport in SAOS-2 cells.