While transforming growth factor-beta1 (TGF-beta1) regulates proliferation and differentiation of human osteoblast precursor cells, the mechanisms underlying these effects are not known. Several hormones and locally acting growth factors regulate osteoblast functions through changes in the insulin-like growth factors (IGFs) and IGF-binding proteins (IGFBPs). Thus, we studied the effects of TGF-beta1 on IGFs and IGFBPs in human marrow stromal (hMS) osteoblast precursor cells. TGF-beta1 increased the steady-state mRNA level of IGF-I up to 8.5+/-0.6-fold (P<0.001) in a dose- (0.1-10 ng/ml), and time-dependent (12-72 h) manner. No significant effects on IGF-II gene expression were detectable. Employing RNase protection and nuclear run-on assays, these effects on IGF-I were found to take place at the transcriptional level and were not dependent on de novo protein synthesis. Using the transient transfection of various fragments of the IGF-I promoter 1, we found that TGF-beta responsive elements were present in a promoter fragment ranging from-65 bp to+55 bp relative to the major transcription start site in exon 1. In addition, TGF-beta1 treatment resulted in a dose- and time-dependent increase (2-fold) in the IGFBP-3 steady-state mRNA level as well as in protein production but did not affect IGFBP-2 or IGFBP-4 at mRNA or protein levels. Our results indicate that TGF-beta1 exerts significant effects on stimulatory components of the IGF-system and that may represent a mechanism mediating TGF-beta effects on the biological functions of osteoblasts.
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M Kveiborg, A Flyvbjerg, EF Eriksen, and M Kassem
Z Hochberg, T Amit, A Flyvbjerg, and I Dørup
Potassium (K+) deficiency is associated with growth retardation in both man and experimental animals. Growth hormone (GH) administration to such animals prevents, to some extent, weight loss and selective muscle atrophy, but does not affect tail and tibia length even with supraphysiological doses. The present study was undertaken to investigate the possible effect of K+ deficiency on the hepatic GH receptor and GH-binding protein (BP). Young female Wistar rats were maintained on K+-deficient fodder and distilled water, and compared with pair-fed and ad-libitumfed control groups. After 15 days GH-BP and electrolytes were measured in sera, GH receptors were studied in liver membranes by 125I-labeled human GH binding and muscles were weighed and saved for electrolyte measurements. K+-deficient rats showed complete growth arrest compared with an intermediate weight gain of the pair-fed group. Serum K+ was very low, at 1·5 ±0·1 mmol/l, compared with the mean value of 5·3 mmol/l of control animals. Somatogenic and lactogenic receptors in liver membranes and serum GH-BP levels were significantly (P<0·05) lower in K+ deficiency, as compared with their pair-fed controls. Liver GH receptors correlated significantly (P<0·05) with serum GH-BP levels. The growth variables correlated positively with both hepatic somatogenic and lactogenic receptors and serum GH-BP levels, with correlation coefficients that were highest against serum GH-BP and lowest against liver lactogenic receptors. Serum and muscle K+ correlated significantly (P<0·05) with both liver GH receptors and serum GH-BP, with correlation coefficients that were higher against serum GH-BP. Lactogenic receptors had a lower or no correlation. It is concluded that GH receptor deficiency may be involved in the growth retardation of K+ deficiency.
Journal of Endocrinology (1995) 147, 253–258
T Christiansen, H Stødkilde-Jørgensen, and A Flyvbjerg
The aim of the present study was to use magnetic resonance imaging as a non-invasive measure of renal enlargement and regression in experimental diabetes in rats. Rats were randomized into three groups: (1) non-diabetic control animals, (2) diabetic animals, untreated for 30 days after streptozotozin treatment and (3) diabetic animals treated with insulin from day 21 to day 30 after streptozotocin administration. Magnetic resonance images were obtained from anaesthetized rats and kidney, cortex, medulla and pelvis volumes were calculated throughout the experiment until day 30. In untreated diabetic animals, a marked increase in kidney volume was seen 4 days after the induction of diabetes (P<0·05) and after 30 days this increase amounted to 73%, with similar increases in the cortex (63%) and medulla (69%). No change was seen in the pelvis volume. Insulin administration on day 21 to untreated diabetic rats abruptly reduced kidney volume by 21%, cortex volume by 27% and medulla volume by 18%, and after 4 days all three parameters were similar to those seen in non-diabetic controls. In conclusion, the present study has demonstrated the applicability of magnetic resonance imaging as a non-invasive measure of renal enlargement and regression in experimental diabetes in rats. In untreated hyperglycaemic diabetic rats, with manifest diabetic renal enlargement, acute regression in renal volume was observed concomitant with insulin-induced normoglycaemia.
Journal of Endocrinology (1997) 153, 193–198
H Grønbæk, J Frystyk, H Ørskov, and A Flyvbjerg
Selenium is an essential trace element although at higher doses it is also known to be a toxic agent causing a wide range of symptoms including growth retardation. In order to investigate the effect of sodium selenite on growth, insulin-like growth factor-binding proteins (IGFBPs) and insulin-like growth factor-I (IGF-I), 30 male Wistar rats were randomized into three groups. Group A was treated with sodium selenite in the drinking water (3·3 mg selenium/l). Group B was ad libitum fed with free access to standard fodder and tap water and group C was pair fed relative to the selenium-treated rats. Serum IGF-I and IGFBPs were determined on days 0, 14 and at the end of the study on day 35. Selenium-treated rats had significantly lower body weights compared with group B rats on day 9 and group C rats on day 14 (P<0·05). Tibia length was measured at the end of the study and no difference was observed between groups B and C (3·77 ± 0·04 cm vs 3·60±0·02 cm); however, selenium-treated rats had significantly shorter tibia lengths (3·46±0·03 cm) compared with rats in groups B (P<0·001) and C (P<0·05). Selenium treatment induced a significant reduction in circulating IGF-I by the end of the study compared with ad libitum and pair fed rats (P<0·05). Serum subjected to Western ligand blots showed four distinct IGFBP bands with apparent relative molecular weights of 38–47 kDa (doublet) (IGFBP-3), 30 kDa (IGFBP-1 and/or IGFBP-2) and 24 kDa (IGFBP-4). At the end of the study a significant reduction in IGFBP-3 was observed in group A compared with groups B and C (P<0·05). Selenium treatment also caused a reduction in IGFBP-1 and/or IGFBP-2 compared with ad libitum fed rats; in addition, a reduction was observed in pair fed controls. In conclusion, sodium selenite treatment leads to growth retardation accompanied by reduced circulating levels of IGF-I, IGFBP-3, and IGFBP-1 and/or IGFBP-2. The reduction in IGF-I and IGFBP-3 could not be attributed to reduced caloric intake but seems to be a specific action of selenium.
Journal of Endocrinology (1995) 145, 105–112
C Hill, A Flyvbjerg, R Rasch, M Bak, and A Logan
Diabetic nephropathy is characterised by an increase in glomerular and tubular fibrosis that compromises kidney function. The transforming growth factor-betas (TGF-betas) have been shown to play a major role in fibrosis and we have shown that TGF-beta2, in particular, increases co-ordinately with fibrogenesis in the diabetic kidney. The aim of this study was to investigate the changes in expression of extracellular matrix molecules in the diabetic kidney, with and without systemic administration of a recombinant human monoclonal antibody to TGF-beta2. Streptozotocin-induced diabetic rats were split into two groups. The first were treated with 5 mg/kg irrelevant control IgG4 (placebo) and the second treated with 5 mg/kg isoform-specific recombinant monoclonal anti-TGF-beta2 IgG4 (termed CAT-152) systemically every second day for 14 days. A further group of six non-diabetic rats was also used as a control. Various biological parameters were measured daily throughout the experimental period, and on termination of the experiment at 14 days Western blotting was performed on kidney cortices for procollagen-I C-propeptide, which is an indicator of the rate of collagen-I synthesis within the kidney. In the placebo-treated diabetic rats, blood glucose, food consumption, urinary albumin excretion (UAE) and kidney weights were all significantly higher than in the non-diabetic group (P<0.05, n=24, by ANOVA). In the anti-TGF-beta2-treated diabetic rats, kidney weights and UAE levels were decreased when compared with those in placebo-treated diabetics. Western blotting for the procollagen-I C-propeptide in kidney cortices showed a significant increase in levels in placebo-treated diabetic rats compared with non-diabetic controls over the 14 day diabetic period, indicating initiation of fibrogenesis. By contrast, in anti-TGF-beta2-treated diabetic rats, levels of the propeptide remained at non-diabetic levels. In summary, a significant suppression of kidney fibrosis was seen in anti-TGF-beta2-treated diabetic rats, compared with placebo-treated diabetic rats. We conclude that systemic delivery of CAT-152, a neutralising anti-TGF-beta2 antibody, during the acute stages of diabetic nephropathy reduces the rate of pathogenic fibrosis in the kidney.
H Grønbæk, B Nielsen, J Frystyk, H Ørskov, and A Flyvbjerg
IGF-I acts as a renotropic factor in early streptozotocin-induced diabetes. Somatostatin analogue (octreotide) treatment initiated at the onset of diabetes prevents kidney IGF-I accumulation and renal growth. Seven days of octreotide treatment initiated after 3, 5, 7 or 9 days of untreated diabetes was investigated. Diabetic renal hypertrophy was followed by renal hyperplasia. Compared with placebo-treated diabetic rats, the earliest octreotide intervention was followed by a greater reduction in renal growth compared with intervention later on (days 3 to 10, 12%; days 5 to 12, 10%; days 7 to 14, 9%; days 9 to 16, 6%; P<0·05). Octreotide treatment was unable to reduce protein accumulation and kidney DNA increase consistently. No difference in glomerular volume fraction or total glomerular volume was observed between placebo- and octreotide-treated diabetic rats. Octreotide treatment was followed by reduced kidney and serum IGF-I especially following early intervention, while no effect over that of diabetes was observed in the later intervention periods. The results confirm the notion that initial renal IGF-I accumulation is a prerequisite for early diabetic kidney hypertrophy in rats and show that delayed octreotide treatment cannot reverse renal and glomerular growth which is already manifest.
Journal of Endocrinology (1995) 147, 95–102
JW van Neck, NF Dits, V Cingel, IA Hoppenbrouwers, SL Drop, and A Flyvbjerg
The effects of growth hormone (GH) in regulating the expression of the hepatic and renal GH and insulin-like growth factor (IGF) system were studied by administering a novel GH receptor antagonist (GHRA) (B2036-PEG) at different doses (0, 1.25, 2.5, 5 and 10 mg/kg/day) to mice for 7 days. No differences were observed in the groups with respect to body weight, food consumption or blood glucose. However, a dose-dependent decrease was observed in circulating IGF-I levels and in hepatic and renal IGF-I levels at the highest doses. In contrast, in the 5 and 10 mg/kg/day GHRA groups, circulating and hepatic transcriptional IGF binding protein-3 (IGFBP-3) levels were not modified, likely resulting in a significantly decreased IGF-I/IGFBP-3 ratio. Hepatic GH receptor (GHR) and GH binding protein (GHBP) mRNA levels increased significantly in all GHRA dosage groups. Endogenous circulatory GH levels increased significantly in the 2.5 and 5 mg/kg/day GHRA groups. Remarkably, increased circulating IGFBP-4 and hepatic IGFBP-4 mRNA levels were observed in all GHRA administration groups. Renal GHR and GHBP mRNA levels were not modified by GHRA administration at the highest doses. Also, renal IGFBP-3 mRNA levels remained unchanged in most GHRA administration groups, whereas IGFBP-1, -4 and -5 mRNA levels were significantly increased in the 5 and 10 mg/kg/day GHRA administration groups. In conclusion, the effects of a specific GHR blockade on circulating, hepatic and renal GH/IGF axis reported here, may prove useful in the future clinical use of GHRAs.
L Vinter-Jensen, C Orloff Juhl, J Frystyk, E Z Dajani, N Oksbjerg, and A Flyvbjerg
It has recently been demonstrated that epidermal growth factor (EGF) administration to neonatal rodents causes growth retardation with concomitant reductions in circulation levels of IGF-I. We describe the effects of systemic EGF administration for 4 weeks on circulating levels of IGF-I and IGF-binding proteins (IGFBPs) and on thyroid hormones (tri-iodothyronine, T3; thyroxine, T4) in sexually mature pigs. Goettingen minipigs of either sex were treated with placebo (n=5) or EGF (30 μg/kg per day, n=6) s.c. for 4 weeks (in relation to an oesophageal sclerotherapy regimen). Blood samples were taken under anaesthesia before and after 1, 2, 3 and 4 weeks of treatment. Circulating levels of IGF-I, insulin, glucose, T3 and T4 were analysed every week and IGFBPs every second week. IGF-I was not reduced significantly after 1 week but significantly reduced after 2 and 3 weeks of EGF treatment. A similar decline was observed for the major IGFBP, IGFBP-3, which was reduced after 2 and 4 weeks. IGFBP-1, IGFBP-2 and IGFBP-4 increased throughout the treatment period (all significantly at week 4). EGF treatment induced increased circulating T3 after 2, 3 and 4 weeks of EGF treatment. In conclusion, we report that EGF treatment for 4 weeks in Goettingen minipigs reduces circulating IGF-I and IGFBP-3, increases circulating IGFBP-1, IGFBP-2 and IGFBP-4, and induces a slight hyperthyroidism as judged from increased circulating levels of T3.
Journal of Endocrinology (1996) 151, 401–407
S. M. Marshall, A. Flyvbjerg, K. D. Jørgensen, J. Weeke, and H. Ørskov
The effects of treatment for 11 days with human growth hormone (hGH; 140 μg/day), thyroxine (T4; 3 μg/day) and hGH + T4 on renal growth and content of insulin-like growth factor-I (IGF-I) in hypophysectomized rats have been compared with saline-treated hypophysectomized animals and intact control animals. Right kidney weight and kidney weight/body weight ratio remained low in the saline-treated group (313±9 vs 694±28 mg in controls on day 11, P<0·001 and 3·4±0·12 × 10−3 vs 4·2±0·10× 10−3, P< 0·005 respectively). In T4- and hGH-treated animals, kidney weight gain was similar (to 420 ± 14 and 450±22 mg on day 11 respectively, P>0·05), whilst the increase was greater in the group given hGH + T4 (to 572 ±34 mg, P< 0·001 compared with hGH- and T4-treated groups). The kidney weight/body weight ratio became normal in the T4- and hGH + T4-treated animals but remained low in the hGH-treated group. The renal content of IGF-I was low in the salinetreated animals throughout the study (92±10 ng/g on day 11 vs 219±8 ng/g in control animals, P< 0·001), but increased to a maximum of 88% above baseline on day 1 in the group given T4. In the hGH-and hGH + T4-treated groups, renal IGF-I concentration rose to a peak of 317% above baseline on days 2 to 4, then fell to the values seen in control animals on day 11 (hGH: 242±18 ng/g; hGH + T4: 320 ± 41 ng/g; controls: 219 ± 8 ng/g; P> 0·05 for all comparisons). Thus treatment with hGH or T4 results in similar kidney weight gain, despite a greater rise in the renal concentration of IGF-I in the hGH-treated animals. Treatment with both hGH + T4 leads to an increase in the renal concentration of IGF-I similar to that seen with hGH treatment alone, but a larger increase in kidney weight, suggesting that T4 does not stimulate renal growth via the IGF-I pathway and that growth promotion by hGH and T4 is additive.
Journal of Endocrinology (1993) 136, 399–406
H Gronbaek, B Nielsen, B Schrijvers, I Vogel, R Rasch, and A Flyvbjerg
It was recently discovered that the streptozotocin (STZ)-diabetic mouse model is characterised by GH hypersecretion in contrast to the STZ-diabetic rat, the former thus mimicking the changes in GH in human type 1 diabetes. Inhibition of circulating and renal IGF-I by long-acting somatostatin analogues reduces renal and glomerular growth and urinary albumin excretion in diabetic rats. The aim of the present study was to examine renal and glomerular growth in early experimental diabetes in mice along with changes in the GH/IGF-I axis following treatment with the somatostatin analogue octreotide. Balb/C(a) mice were randomised into non-diabetic controls, placebo-treated and octreotide-treated diabetic (50 microg/day) mice and examined 7 and 14 days after induction of diabetes. There was no effect of octreotide treatment on body weight, glycaemic control or food intake. However, octreotide treatment significantly inhibited renal and glomerular growth by the end of the study period when compared with placebo treatment. In addition, octreotide prevented an increase in kidney IGF-I by day 7. GH hypersecretion was observed in the diabetic groups but octreotide treatment reduced GH levels compared with placebo treatment by day 14. No significant differences in serum or kidney IGF-binding protein-3 levels were observed between placebo- and octreotide-treated diabetic mice. In conclusion, this new diabetic mouse model mimicking human type 1 diabetes is characterised by GH hypersecretion and the somatostatin analogue octreotide is able to prevent renal and glomerular growth, probably mediated through changes in circulating GH and local kidney IGF-I levels.