Decreased IGF-I mRNA Research Articles

Regulation of insulin-like growth factor (IGF)-I mRNA and peptide and IGF-binding proteins by interleukin-1.

The purpose of the present study was to determine whether interleukin (IL)-1 would alter the insulin-like growth factor (IGF) system in rats and whether this change was mediated by glucocorticoids. The IGF-I concentration was decreased in plasma (32%), liver (35%), skeletal muscle (40-50% depending on fiber type), pituitary (36%), and brain (52%), and increased in kidney (73%) 6 h after intravenous injection of IL-1 beta. IL-1 beta also decreased IGF-I mRNA levels in liver and muscle and increased expression in kidney. These changes were associated with a > 2.5-fold elevation in plasma corticosterone levels. Pretreatment of rats with the glucocorticoid receptor antagonist RU-486 prevented the IL-1 beta-induced decrease in plasma and liver IGF-I concentration and the reduction in hepatic IGF-I mRNA expression. In contrast, RU-486 did not significantly attenuate the fall in IGF-I content in skeletal muscle, heart, brain, or pituitary or the increase in IGF-I observed in kidney after IL-1 beta. Furthermore, pretreatment with RU-486 did not completely prevent the IL-1 beta-induced decrease in IGF-I mRNA in skeletal muscle. The concentration of both IGF-binding protein (BP)-1 and BP-2 was increased in plasma, liver, and muscle in response to IL-1 beta, and these changes were also not prevented by RU-486. These results indicate that the inflammatory cytokine IL-1 beta is capable of influencing multiple components of the IGF system. Whereas the enhanced endogenous production of glucocorticoids appears to mediate the IL-1 beta-induced decrease in IGF-I synthesis in liver, the changes in IGF-I content observed in other tissues and the increase in IGFBP-1 and IGFBP-2 appear to be largely glucocorticoid independent.

Response of the intrarenal insulin-like growth factor-I axis to acute ischemic injury and treatment with growth hormone and epidermal growth factor

We previously reported that following bilateral acute tubular necrosis (ATN) profound changes in the intrarenal insulin-like growth factor-I axis occurs which are unrelated to altered nutritional intake. In this current report we studied rats with unilateral ATN to assess whether these changes reflect a response to acute injury or the accompanying uremia. Compared to the contralateral kidney, the injured kidney showed an increase in IGF-I receptor number without a change in IGF-I receptor mRNA levels, a decrease in IGF-I mRNA and IGF-I protein levels, a decrease in growth hormone (GH) receptor mRNA abundance and receptor binding. There was also a decrease in IGF binding protein-2, -3 and -5 mRNA levels together with a fall in protein products. Since this unilateral ATN model excludes the influence of uremia and reduced nutritional intake, we surmised that these changes reflect a direct response to injury. Next, because of the reduced GH receptor binding noted above and the reported decrease in epidermal growth factor (EGF) expression in ATN, we tested the thesis that the low kidney IGF-I mRNA levels in ATN are partly due to a relative or absolute deficiency of these hormones. Administration of EGF or GH promptly increased ATN kidney IGF-I mRNA levels to control kidney values, lending support to the thesis. The response to EGF also suggests that the salutary effect of EGF treatment in ATN may partly be mediated by stimulating IGF-I production.

IGF-I and serine protease inhibitor 2·1 nuclear transcript abundance in rat liver during protein restriction

Restriction of dietary protein consumption of young male rats results in decreased growth velocity and a reduction in the abundance of hepatic IGF-I mRNA. It is not known whether the reduction of IGF-I mRNA abundance in the liver of protein-restricted rats results from a decrease in IGF-I gene transcription. In the present study, three experiments were performed with 4-week-old male rats to examine the effect of protein restriction on IGF-I gene transcription in liver. In these experiments, we monitored IGF-I nuclear transcripts (pre-mRNA) within total cellular RNA using a ribonuclease protection assay. In the first experiment, a consistent decrease in IGF-I mRNA from animals fed isocaloric diets containing 20% (control), 12%, 8% and 4% protein (dietary effect, P < 0.001) was not paralleled by a decrease (P > 0.50) in IGF-I pre-mRNA. Two additional experiments examining the effect of 4% vs 20% protein diets yielded comparable results. Pooled results from these two studies (n = 12/treatment) demonstrated that a 64% reduction (P < 0.0001) in IGF-I mRNA abundance was not accompanied by a decrease in IGF-I pre-mRNA (1.17 vs 1.31 +/- 0.21 image density units for 4% and 20% protein treatments). Unlike IGF-I, the abundance of carbamyl phosphate synthetase-I (CPS-I) pre-mRNA and mRNA was comparably reduced (approximately 70%, P < 0.001), indicating that the decrease in mRNA of this urea cycle enzyme during protein restriction occurs predominantly by a transcriptional mechanism. A common feature of all experiments was a pronounced variability in the expression of hepatic IGF-I pre-mRNA among animals, which was not diet specific. To test whether the variability in IGF-I gene transcription was correlated with variability in the transcription of another gene that is regulated by GH, we quantified the abundance of nuclear transcripts for the serine protease inhibitor 2.1 (SPI 2.1) gene. A positive association (r = 0.81, P < 0.0001) between SPI 2.1 and IGF-I nuclear transcripts was demonstrated. The correlation between IGF-I and SPI 2.1 transcripts was specific, because the quantity of IGF-I and CPS-I nuclear transcripts was not correlated in this study. Although transcription of the IGF-I and SPI 2.1 genes was similar, the abundance of SPI 2.1 mRNA was not altered by protein deprivation.(ABSTRACT TRUNCATED AT 400 WORDS)

Basic fibroblast growth factor regulates IGF-I binding proteins in the clonal osteoblastic cell line MC3T3-E1

In previous studies, we reported that basic fibroblast growth factor (bFGF) regulates insulin-like growth factor messenger RNAs and protein levels in the osteoblastic MC3T3-E1 cells. In the present study, we examined the expression of insulin-like growth factor binding proteins (IGFBPs) in MC3T3-E1 cells and determined whether bFGF altered IGFBP mRNAs and protein levels. Since previous studies suggested that IGFBPs can inhibit DNA synthesis stimulated by IGF-I, we wondered whether the mitogenic effect of bFGF was altered by exogenous IGFBP-3. Confluent MC3T3-E1 cells were serum-deprived for 24 h and then treated with bFGF for 6-24 h. In control cultures, MC3T3-E1 cells expressed the mRNAs for IGF-I, IGF-II, and IGFBP-2, 4, 5, and 6 but not IGFBP-1 or 3. A 24 h treatment with bFGF at 10(-8) M decreased IGF-I mRNA by 97%, IGF-II mRNA by 73%, IGFBP-2 by 64%, IGFBP-4 by 73%, IGFBP-5 by 95%, and IGFBP-6 by 65%. The inhibitory effect of bFGF on IGF-I and IGFBP mRNA levels was not altered by aphidicolin, an inhibitor of cell replication. bFGF 10 nM decreased IGF-I levels determined by radioimmunoassay after acidification by 45% and 72% at 24 and 48 h, respectively. Western ligand blot for IGF binding proteins revealed that MC3T3-E1 cells expressed IGFBPs of 24, 30, and 34 kD. Treatment with bFGF 10(-8) M decreased the levels of the 24 and 30 kD band at 24 h but increased the 34 kD band.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin-like growth factor and growth hormone receptor in nephrotic rats.

In an attempt to elucidate the mechanism of growth retardation in the nephrotic syndrome, specific serum and hepatic growth factors were measured in Sprague-Dawley rats in which nephrotic syndrome was produced by administration of puromycin (1.5 mg.100 g body wt-1.day-1) for 12 days. On the 13th day, the results of these nephrotic animals were compared with those of an equal number of pair-fed and control animals: the mean dietary intake of the nephrotic group was 71% that of the control group (P < 0.001). Serum insulin-like growth factor (IGF) binding protein-3 was significantly reduced (P < 0.005) in the nephrotic rats, compared with the pair-fed and the control groups. Hepatic IGF-I mRNA in the nephrotic rats averaged 36% that of control (P < 0.001) and 46% that of the pair-fed animals (P < 0.001). Hepatic growth hormone receptor (GHr) mRNA in the nephrotic rats averaged 19% of that of the control (P < 0.001) and 27% of that of the pair-fed rats (P < 0.001). These results indicate that the growth retardation of the nephrotic rats may be associated with the significant decrease in IGF-I mRNA and reduction in GHr mRNA.

Insulin-Like Growth Factor-I and -II Messenger RNA Expression in Muscle, Heart, and Liver of Streptozotocin-Diabetic Swine*

We have investigated the effects of streptozotocin-diabetes and fasting in juvenile swine by monitoring IGF-I and -II gene expression in muscle, heart, and liver tissues. In diabetic pigs, IGF-I messenger RNAs (mRNA) were decreased by 50% in muscle and liver tissues, and by 70% in heart. The imposition of fasting on diabetic animals tended to further decrease IGF-I mRNA levels, and fasting alone also decreased IGF-I mRNA abundance in the three tissues (P less than 0.05). Insulin therapy restored IGF-I mRNA levels to normal in muscle and livers but was less effective in hearts of diabetic pigs. Relative IGF-I mRNA expression in heart and muscle tissues was 2-fold and 4-fold higher, respectively, than in liver tissues under normal conditions in these animals. Serum IGF-I concentrations and tissue extractable immunoreactive IGF-I levels were also measured. Serum IGF-I was markedly decreased in the diabetic state, dropping to 70% below control levels (P less than 0.01). Extractable IGF-I in liver declined by 50% with diabetes (P less than 0.01), and by 30% in muscle with diabetes and fasting (P less than 0.05), but no significant changes in heart levels of IGF-I protein were detected. Expression levels of IGF-II mRNAs in the three tissues were unaffected by diabetes or fasting. These results are consistent with earlier observations in rat liver and further demonstrate that IGF-I expression in muscle and heart is altered by diabetes and fasting, whereas IGF-II mRNAs do not change.

Regulation of insulin-like growth factor-I and growth hormone receptor gene expression by diabetes and nutritional state in rat tissues

Insulin-like growth factor-I (IGF-I) mRNA and GH receptor mRNA levels were analysed in different tissues from rats made diabetic with streptozotocin, fasted rats and rats fed with a protein-reduced diet. Diabetes decreased IGF-I mRNA levels in liver, heart, diaphragm, kidney and aorta, but not in brain. GH receptor mRNA levels were decreased in heart and diaphragm, but not in liver and kidney. Fasting decreased IGF-I mRNA in all tissues studied except brain, and decreased GH receptor mRNA in liver, heart and diaphragm, but not in kidney. A protein-reduced diet decreased hepatic IGF-I mRNA levels but did not significantly affect other tissues, while GH receptor mRNA levels were reduced in liver and diaphragm. In conclusion, both diabetes and limited nutrition affected IGF-I and GH receptor mRNA in different tissues, but the two mRNAs were not co-ordinately regulated in all tissues studied. While reduced GH receptor gene expression may thus be responsible for decreased IGF-I gene expression in some states and tissues, additional regulatory mechanisms may be of importance.