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SE Ozanne, CL Wang, MW Dorling, and CJ Petry

Numerous studies have shown a relationship between early growth restriction and Type 2 diabetes. Studies have shown that offspring of rats fed a low protein (LP) diet during pregnancy and lactation have a worse glucose tolerance in late adult life compared with controls. In contrast, in young adult life LP offspring have a better glucose tolerance which is associated with increased insulin-stimulated glucose uptake into skeletal muscle. The aim of the present study was to compare the regulation of glucose uptake and lipolysis in adipocytes by insulin in control and LP offspring. LP adipocytes had increased basal and insulin-stimulated glucose uptake compared with controls. There was no difference in basal rates of lipolysis. Isoproterenol stimulated lipolysis in both groups, but it was more effective on LP adipocytes. Insulin reduced lipolytic rates in controls to basal levels but had a reduced effect in LP adipocytes. Protein kinase B activity matched glucose uptake, with LP adipocytes having elevated activities. These results suggest that early growth retardation has long-term effects on adipocyte metabolism. In addition, they show selective resistance to different metabolic actions of insulin and provide insight into the mechanisms by which insulin regulates glucose uptake and lipolysis.

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SE Ozanne, GS Olsen, LL Hansen, KJ Tingey, BT Nave, CL Wang, K Hartil, CJ Petry, AJ Buckley, and L Mosthaf-Seedorf

Epidemiological studies have revealed a relationship between early growth restriction and the subsequent development of type 2 diabetes. A rat model of maternal protein restriction has been used to investigate the mechanistic basis of this relationship. This model causes insulin resistance and diabetes in adult male offspring. The aim of the present study was to determine the effect of early growth restriction on muscle insulin action in late adult life. Rats were fed either a 20% or an isocaloric 8% protein diet during pregnancy and lactation. Offspring were weaned onto a 20% protein diet and studied at 15 Months of age. Soleus muscle from growth restricted offspring (LP) (of dams fed 8% protein diet) had similar basal glucose uptakes compared with the control group (mothers fed 20% protein diet). Insulin stimulated glucose uptake into control muscle but had no effect on LP muscle. This impaired insulin action was not related to changes in expression of either the insulin receptor or glucose transporter 4 (GLUT 4). However, LP muscle expressed significantly less (P<0.001) of the zeta isoform of protein kinase C (PKC zeta) compared with controls. This PKC isoform has been shown to be positively involved in GLUT 4-mediated glucose transport. Expression levels of other isoforms (betaI, betaII, epsilon, theta) of PKC were similar in both groups. These results suggest that maternal protein restriction leads to muscle insulin resistance. Reduced expression of PKC zeta may contribute to the mechanistic basis of this resistance.

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BS Moonga, OA Adebanjo, HJ Wang, S Li, XB Wu, B Troen, A Inzerillo, E Abe, C Minkin, CL Huang, and M Zaidi

The effects of the related cytokines interleukin-6 (IL-6), leukemia inhibitory factor (LIF) and oncostatin-M on bone resorption and cytosolic Ca(2+) signaling were compared in isolated rat osteoclasts. In the traditional disaggregated osteoclast (pit) assay, IL-6 and LIF, but not oncostatin-M, conserved the bone resorption otherwise inhibited by high extracellular [Ca(2+)] (15 mM). It produced a paradoxical, concentration-dependent stimulation of resorption by elevated extracellular Ca(2+). In the micro-isolated single osteoclast resorption assay, IL-6, high [Ca(2+)] or IL-6 plus high [Ca(2+)] all increased pit formation. In contrast, the IL-6 receptor (IL-6R)-specific agonist antibody MT-18 inhibited bone resorption in a concentration-dependent manner (1:500 to 1:500 000). MT-18 triggered cytosolic Ca(2+) signals in fura 2-loaded osteoclasts within approximately 10 min of application. Each cytosolic Ca(2+) transient began with a peak deflection that persisted in Ca(2+)-free, EGTA-containing extracellular medium, consistent with a release of intracellularly stored Ca(2+). This was followed by a sustained elevation of cytosolic [Ca(2+)] that was abolished in Ca(2+)-free medium, as expected from an entry of extracellular Ca(2+), and by the Ca(2+) channel antagonist Ni(2+). The inclusion of either IL-6 or soluble human (sh) IL-6R specifically reversed both the above effects of MT-18, confirming that both effects were specific for the IL-6R. The findings suggest that IL-6R activation by IL-6 stimulates osteoclastic bone resorption either by reversing the inhibitory effect of high extracellular Ca(2+) in stromal-containing systems or itself stimulating bone resorption along with Ca(2+) by micro-isolated osteoclasts. In contrast, activation of the IL-6R by an agonist antibody produces an inhibition of bone resorption and an associated triggering of the cytosolic Ca(2+) signals previously associated with regulation of bone resorptive function in other situations.