ABSTRACT
Maternal insulin resistance is essential for efficient provision of glucose to the fetus. Although elevation of placental hormones is known to relate to the development of insulin resistance, the precise underlying mechanism of maternal insulin resistance is unknown. Therefore, we examined the molecular mechanisms of progesterone causing insulin resistance in 3T3-L1 adipocytes. Progesterone at 10(-4) M, but not 10(-5) M, reduced the amount of IRS-1. As a result, insulin-induced phosphorylation of IRS-1, the association of IRS-1 with p85alpha, and subsequent phosphorylation of Akt1 and -2 was decreased moderately by 10(-4) M progesterone. Subsequently, insulin-induced translocation of GLUT4 to the plasma membrane evaluated by immunostaining on the plasma membrane sheet by confocal laser microscope was also decreased by 10(-4) M progesterone. In contrast, 2-[(3)H]deoxyglucose (2DG) uptake was markedly inhibited by both 10(-5) and 10(-4) M progesterone in a dose-dependent manner. Surprisingly, 2DG uptake elicited by adenovirus-mediated expression of constitutive-active mutant of PI 3-kinase (myr-p110) and Akt (myr-Akt) was suppressed by progesterone. Interestingly, insulin-induced tyrosine phosphorylation of Cbl and activation of TC10 were inhibited by progesterone at 10(-5) M. These results indicate that progesterone is implicated in insulin resistance during pregnancy by inhibiting the PI 3-kinase pathway at the step of 1) IRS-1 expression and 2) distal to Akt and 3) by suppressing the PI 3-kinase-independent pathway of TC10 activation by affecting Cbl phosphorylation.
Subject(s)
Adipocytes/metabolism , Glucose/metabolism , Insulin/physiology , Progesterone/pharmacology , Signal Transduction/drug effects , 3T3-L1 Cells , Adipocytes/drug effects , Animals , Antimetabolites , Blotting, Western , Cell Differentiation/drug effects , Cell Membrane/drug effects , Cell Membrane/metabolism , Cell Membrane/ultrastructure , Deoxyglucose , Female , Glucose Transporter Type 4/metabolism , Insulin Receptor Substrate Proteins/metabolism , Insulin Resistance/physiology , Mice , Microscopy, Confocal , Oncogene Protein v-akt/metabolism , Phosphoinositide-3 Kinase Inhibitors , Phosphorylation , Pregnancy , Protein Transport/drug effects , rho GTP-Binding Proteins/metabolismABSTRACT
Glargine and detemir are long-acting human insulin analogues with a smooth peakless profile of action. Although their binding affinities to the insulin receptor have been studied, little is known about the subsequent signalling properties activated after the binding. We directly compared intracellular signalling properties of them in various cultured cells. Regarding the metabolic signalling, glargine and insulin-induced comparable dose-dependent phosphorylation of insulin receptor, IRS-1, Akt, and GSK3, whereas detemir-induced kinetics were markedly lower in 3T3-L1 adipocytes and L6 myocytes. A similar pattern of phosphorylation induction was observed in primary hepatocytes and vascular smooth muscle cells (VSMCs). Because of the binding of detemir to albumin with high affinity, the phosphorylation kinetics and glucose uptake of detemir, but not glargine, decreased with increasing concentrations of BSA. Concerning the mitogenic properties, glargine and insulin-induced comparable dose-dependent phosphorylation of MAP kinase (MAPK) and 5-bromo-2'-deoxyuridine (BrdU) incorporation. Detemir-induced phosphorylation of MAPK was apparently reduced, whereas it stimulated BrdU incorporation with relatively similar dose-dependent manner in VSMCs. These results indicate that glargine has comparable properties to human insulin in metabolic and mitogenic signalling and action. In contrast, detemir-induced metabolic signaling is less potent in all cell types studied, and is reduced further by increasing concentrations of albumin.
