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      Postreceptor Crosstalk on PI3K/Akt between GH and Insulin in Non-Catch-Up Growth Rats Born Small for Gestational Age

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          Background/Aims: Children born small for gestational age (SGA) are at increased risk for short stature and type 2 diabetes mellitus as a result of growth hormone (GH) resistance and insulin resistance. The mechanisms of multiple hormone resistance remain unclear. This study was designed to investigate the relationship between GH resistance and insulin resistance in non-catch-up growth (NCU-SGA) rats, and how their signaling pathways are related based on their crosstalk on the insulin receptor substrate-1 phosphatidylinositol 3′-kinase (IRS-1-PI3K) pathway. Methods: NCU-SGA rat model was developed by restricting prenatal food intake in pregnant dams. Activated levels of IRS-1 and Akt in liver protein extracts were compared between NCU-SGA and age- and sex-matched controls born appropriate for gestational age rats at baseline, after insulin stimulation, and after pretreatment with AG490 (GH-JAK2 pathway inhibitor) followed by insulin stimulation. Results: GH secretion was positively related to markedly increased insulin levels in NCU-SGA rats. There was no difference of IRS-1 phosphorylation in response to insulin between two groups, however, insulin-stimulated Akt phosphorylation was attenuated in NCU-SGA rats compared to appropriate for gestational age rats. Pretreatment with AG490 restored the Akt response to insulin demonstrated by significantly increased Akt phosphorylation. Conclusion: GH plays a role in inducing insulin resistance via signaling crosstalk with insulin at the level of PI3K/Akt in NCU-SGA rats.

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          Most cited references 19

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          Central role of suppressors of cytokine signaling proteins in hepatic steatosis, insulin resistance, and the metabolic syndrome in the mouse.

          Insulin resistance, obesity, diabetes, dyslipidemia, and nonalcoholic fatty liver are components of the metabolic syndrome, a disease complex that is increasing at epidemic rates in westernized countries. Although proinflammatory cytokines have been suggested to contribute to the development of these disorders, the molecular mechanism is poorly understood. Here we show that overexpression of suppressors of cytokine signaling (SOCS)-1 and SOCS-3 in liver causes insulin resistance and an increase in the key regulator of fatty acid synthesis in liver, sterol regulatory element-binding protein (SREBP)-1c. Conversely, inhibition of SOCS-1 and -3 in obese diabetic mice improves insulin sensitivity, normalizes the increased expression of SREBP-1c, and dramatically ameliorates hepatic steatosis and hypertriglyceridemia. In obese animals, increased SOCS proteins enhance SREBP-1c expression by antagonizing STAT3-mediated inhibition of SREBP-1c promoter activity. Thus, SOCS proteins play an important role in pathogenesis of the metabolic syndrome by concordantly modulating insulin signaling and cytokine signaling.
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            The insulin signalling system and the IRS proteins.

            During the past few years, the insulin signalling system has emerged as a flexible network of interacting proteins. By utilizing the insulin receptor substrate (IRS)-proteins (IRS-1 and IRS-2), the insulin signal can be amplified or attenuated independently of insulin binding and tyrosine kinase activity, providing an extensible mechanism for signal transmission in multiple cellular backgrounds. By employing IRS-proteins to engage various signalling proteins, the insulin receptor avoids the stoichiometric constraints encountered by receptors which directly recruit SH2-proteins to their autophosphorylation sites. Finally, the shared use of IRS-proteins by multiple receptors is likely to reveal important connections between insulin and other hormones and cytokines which were previously unrecognized, or observed but unexplained.
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              Programmed obesity in intrauterine growth-restricted newborns: modulation by newborn nutrition.

              The degree of nutrient enhancement during the newborn period may modulate programming of appetite-regulating hormones, body composition, and propensity to adult obesity in intrauterine growth-restricted (IUGR) newborns. Pregnant rats received, from day 10 to term gestation and throughout lactation, ad libitum food (AdLib) or 50% food restriction (FR) to produce IUGR newborns. AdLib vs. FR offspring were studied at day 1, and, to create two distinct groups of newborn catch-up growth (immediate, delayed) among the IUGR newborns, cross-fostering techniques were employed. The four groups of pups at 3 wk were IUGR immediate catch-up growth (FR/AdLib), IUGR delayed catch-up growth (FR/FR), control (AdLib/AdLib), and lactation FR control (AdLib/FR). From 3 wk to 9 mo, all offspring had AdLib rat chow. Maternal FR during pregnancy resulted in IUGR pups (6.0 +/- 0.3 vs. 7.1 +/- 0.3 g, P < 0.01) with decreased leptin (0.66 +/- 0.03 vs. 1.63 +/- 0.12 ng/ml, P < 0.001) and increased ghrelin (0.43 +/- 0.03 vs. 0.26 +/- 0.02 ng/ml, P < 0.001). Maternal FR during lactation (FR/FR) further impaired IUGR offspring growth at 3 wk. However, by 9 mo, these pups attained normal body weight, percent body fat, and plasma leptin levels. Conversely, IUGR offspring nursed by AdLib dams (FR/AdLib) exhibited rapid catch-up growth at 3 wk and continued accelerated growth, resulting in increased weight, percent body fat, and plasma leptin levels. Thus the degree of newborn nutrient enhancement and timing of IUGR newborn catch-up growth may determine the programming of orexigenic hormones and offspring obesity.

                Author and article information

                Horm Res Paediatr
                Hormone Research in Paediatrics
                S. Karger AG
                July 2008
                21 May 2008
                : 70
                : 1
                : 29-35
                aDepartment of Pediatrics, The First Affiliated Hospital, Sun Yat-Sen University, Guangzhou, China, and bDepartment of Pediatrics, University of Miami School of Medicine, Miami, Fla., USA
                129675 Horm Res 2008;70:29–35
                © 2008 S. Karger AG, Basel

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                Page count
                Figures: 4, Tables: 2, References: 40, Pages: 7
                Original Paper


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