The phosphatidylinositol/AKT/atypical PKC pathway is involved in the improved insulin sensitivity by DHEA in muscle and liver of rats in vivo.

DHEA improves insulin sensitivity and has anti-obesity effect in animal models and men. However, the molecular mechanisms by which DHEA improves insulin action have not been clearly understood. In the present study, we examined the protein levels and phosphorylation state of insulin receptor (IR), IRS-1 and IRS-2, the association between IRSs and PI3K and SHP2, the insulin-induced IRSs associated PI 3-kinase activities, and the phosphorylation status of AKT and atypical PKCzeta/lambda in the liver and the muscle of 6 month-old Wistar rats treated with DHEA. There was no change in IR, IRS-1 and IRS-2 protein levels in both tissues of treated rats analysed by immunoblotting. On the other hand, insulin-induced IRS-1 tyrosine phosphorylation was increased in both tissues while IRS-2 tyrosyl phosphorylation was increased in liver of DHEA treated group. The PI3-kinase/AKT pathway was increased in the liver and the PI3K/atypical PKCzeta/lambda pathway was increased in the muscle of DHEA treated rats. These data indicate that these regulations of early steps of insulin action may play a role in the intracellular mechanism for the improved insulin sensitivity observed in this animal model.

[1]  P. Cohen,et al.  Mechanism of activation and function of protein kinase B. , 1998, Current opinion in genetics & development.

[2]  T. Yagi,et al.  Insulin resistance and growth retardation in mice lacking insulin receptor substrate-1 , 1994, Nature.

[3]  J. Clore,et al.  Suppression of serum dehydroepiandrosterone sulfate levels by insulin: an evaluation of possible mechanisms. , 1989, The Journal of clinical endocrinology and metabolism.

[4]  H. Nawata,et al.  Effect of dehydroepiandrosterone on glucose uptake in cultured human fibroblasts. , 1995, Metabolism: clinical and experimental.

[5]  L. Velloso,et al.  Effect of Captopril, Losartan, and Bradykinin on Early Steps of Insulin Action , 1997, Diabetes.

[6]  H. Nawata,et al.  Effect of Dehydroepiandrosterone on Glucose Uptake in Cultured Rat Myoblasts , 1995, Hormone and metabolic research = Hormon- und Stoffwechselforschung = Hormones et metabolisme.

[7]  G. Shulman,et al.  Disruption of IRS-2 causes type 2 diabetes in mice , 1998, Nature.

[8]  Hsien-yu Wang,et al.  Gαi2 Enhances Insulin Signaling via Suppression of Protein-tyrosine Phosphatase 1B* , 2001, The Journal of Biological Chemistry.

[9]  H. Sekihara,et al.  Dehydroepiandrosterone Decreases Serum Tumor Necrosis Factor-α and Restores Insulin Sensitivity: Independent Effect from Secondary Weight Reduction in Genetically Obese Zucker Fatty Rats. , 1998, Endocrinology.

[10]  S. Satoh,et al.  Dehydroepiandrosterone (DHEA) ameliorates the insulin sensitivity in older rats , 1998, The Journal of Steroid Biochemistry and Molecular Biology.

[11]  M. Greenberg,et al.  Prevention of obesity in Avy/a mice by dehydroepiandrosterone , 1977, Lipids.

[12]  C. Kahn,et al.  Insulin stimulation of phosphatidylinositol 3-kinase activity and association with insulin receptor substrate 1 in liver and muscle of the intact rat. , 1992, The Journal of biological chemistry.

[13]  D. Jakubowicz,et al.  The calcium channel blocker amlodipine raises serum dehydroepiandrosterone sulfate and androstenedione, but lowers serum cortisol, in insulin-resistant obese and hypertensive men. , 1993, The Journal of clinical endocrinology and metabolism.

[14]  C R Carvalho,et al.  Effect of aging on insulin receptor, insulin receptor substrate-1, and phosphatidylinositol 3-kinase in liver and muscle of rats. , 1996, Endocrinology.

[15]  William Arbuthnot Sir Lane,et al.  Role of IRS-2 in insulin and cytokine signalling , 1995, Nature.

[16]  S. Aizawa,et al.  Disruption of insulin receptor substrate 2 causes type 2 diabetes because of liver insulin resistance and lack of compensatory beta-cell hyperplasia. , 2000, Diabetes.

[17]  D. Coleman,et al.  Therapeutic Effects of Dehydroepiandrosterone (DHEA) in Diabetic Mice , 1982, Diabetes.

[18]  R. Farese,et al.  Protein Kinase C-ζ as a Downstream Effector of Phosphatidylinositol 3-Kinase during Insulin Stimulation in Rat Adipocytes , 1997, The Journal of Biological Chemistry.

[19]  E. Ghigo,et al.  Dehydroepiandrosterone sulfate levels in women. Relationships with age, body mass index and insulin levels , 1999, Journal of endocrinological investigation.

[20]  B. Margolis,et al.  Phosphatidylinositol 3′‐kinase is activated by association with IRS‐1 during insulin stimulation. , 1992, The EMBO journal.

[21]  M. Birnbaum,et al.  Different Signaling Roles of SHPTP2 in Insulin-induced GLUT1 Expression and GLUT4 Translocation (*) , 1995, The Journal of Biological Chemistry.

[22]  G. Pergola.  The adipose tissue metabolism: role of testosterone and dehydroepiandrosterone , 2000, International Journal of Obesity.

[23]  M. White,et al.  Irs-2 coordinates Igf-1 receptor-mediated β-cell development and peripheral insulin signalling , 1999, Nature Genetics.

[24]  C. Kahn,et al.  Structure of the insulin receptor substrate IRS-1 defines a unique signal transduction protein , 1991, Nature.

[25]  Y. Yarden,et al.  Insulin and insulinomimetic agents induce activation of phosphatidylinositol 3'-kinase upon its association with pp185 (IRS-1) in intact rat livers. , 1992, The Journal of biological chemistry.

[26]  C. Zancanaro,et al.  Estimates of in vivo insulin action in man: comparison of insulin tolerance tests with euglycemic and hyperglycemic glucose clamp studies. , 1989, The Journal of clinical endocrinology and metabolism.

[27]  Dongmin Liu,et al.  Dehydroepiandrosterone Activates Endothelial Cell Nitric-oxide Synthase by a Specific Plasma Membrane Receptor Coupled to Gαi2,3 * , 2002, The Journal of Biological Chemistry.

[28]  R. J. Richards,et al.  Serum Leptin, Lipids, Free Fatty Acids, and Fat Pads in Long-Term Dehydroepiandrosterone-Treated Zucker Rats (44488) , 2000, Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine.

[29]  G. Shulman,et al.  Contrasting Effects of IRS-1 Versus IRS-2 Gene Disruption on Carbohydrate and Lipid Metabolism in Vivo * , 2000, The Journal of Biological Chemistry.

[30]  D. Jakubowicz,et al.  Effects of nitrendipine on glucose tolerance and serum insulin and dehydroepiandrosterone sulfate levels in insulin-resistant obese and hypertensive men. , 1993, The Journal of clinical endocrinology and metabolism.

[31]  J. Blenis,et al.  Phosphatidylinositol 3-kinase activation is required for insulin stimulation of pp70 S6 kinase, DNA synthesis, and glucose transporter translocation , 1994, Molecular and cellular biology.

[32]  M. White,et al.  Insulin signal transduction and the IRS proteins. , 1996, Annual review of pharmacology and toxicology.

[33]  C. Kahn,et al.  Alternative pathway of insulin signalling in mice with targeted disruption of the IRS-1 gene , 1994, Nature.

[34]  N. Sonenberg,et al.  Insulin signalling and insulin actions in the muscles and livers of insulin-resistant, insulin receptor substrate 1-deficient mice , 1996, Molecular and cellular biology.

[35]  C. Kahn,et al.  Insulin action and the insulin signaling network. , 1995, Endocrine reviews.

[36]  E. Barrett-Connor,et al.  A prospective study of dehydroepiandrosterone sulfate, mortality, and cardiovascular disease. , 1986, The New England journal of medicine.

[37]  T. Pawson,et al.  The insulin receptor substrate 1 associates with the SH2-containing phosphotyrosine phosphatase Syp. , 1993, The Journal of biological chemistry.