ABSTRACT
In the present study, we investigated the protein levels and phosphorylation status of the insulin receptor and insulin receptor substrates (IRS-1, IRS-2, and IRS-3) as well as their association with PI(3)-kinase in the rat adipose tissue of two models of insulin resistance: dexamethasone treatment and aging. AKT and atypical PKC phosphorylation detection were also performed. Both models showed decreased insulin-induced IRS-1 and IRS-2 tyrosine phosphorylation, accompanied by reduced protein levels of IRS-1 and IRS-2. Nevertheless, IRS-3 protein level was unchanged in aging but increased in dexamethasone-treated rats. PI(3)-kinase association with IRS-1 was reduced in aged rats, whereas dexamethasone-treated rats showed a reduced IRS-2/ PI(3)-kinase association. However, IRS-3 association with PI(3)-kinase was reduced in both models, as well as insulin-induced AKT and PKC phosphorylation. The alterations described in the present study show that the action of insulin is differently impaired depending on the origin of insulin resistance. These differences might be directly linked to the singular metabolic features of the models we tested.
Subject(s)
Adipose Tissue/metabolism , Aging/physiology , Dexamethasone/pharmacology , Intracellular Signaling Peptides and Proteins/metabolism , Obesity/metabolism , Phosphoproteins/metabolism , Adipose Tissue/drug effects , Animals , Blood Glucose/analysis , Body Weight , Insulin/blood , Insulin Receptor Substrate Proteins , Insulin Resistance , Isoenzymes/metabolism , Male , Phosphatidylinositol 3-Kinases/metabolism , Phosphorylation , Protein Kinase C/metabolism , Rats , Rats, Wistar , Receptor, Insulin/metabolism , Signal Transduction/drug effectsABSTRACT
The adaptation of pancreatic islets to pregnancy includes increased beta cell proliferation, expansion of islet mass, and increased insulin synthesis and secretion. Most of these adaptations are induced by prolactin (PRL). We have previously described that in vitro PRL treatment increases ERK3 expression in isolated rat pancreatic islets. This study shows that ERK3 is also upregulated during pregnancy. Islets from pregnant rats treated with antisense oligonucleotide targeted to the PRL receptor displayed a significant reduction in ERK3 expression. Immunohistochemical double-staining showed that ERK3 expression is restricted to pancreatic beta cells. Transfection with antisense oligonucleotide targeted to ERK3 abolished the insulin secretion stimulated by glucose in rat islets and by PMA in RINm5F cells. Therefore, we examined the participation of ERK3 in the activation of a cellular target involved in secretory events, the microtubule associated protein MAP2. PMA induced ERK3 phosphorylation that was companied by an increase in ERK3/MAP2 association and MAP2 phosphorylation. These observations provide evidence that ERK3 is involved in the regulation of stimulus-secretion coupling in pancreatic beta cells.
Subject(s)
Insulin-Secreting Cells/metabolism , Insulin/metabolism , Microtubule-Associated Proteins/metabolism , Mitogen-Activated Protein Kinase 6/biosynthesis , Receptors, Prolactin/metabolism , Animals , Cells, Cultured , Female , Glucose/metabolism , Insulin-Secreting Cells/drug effects , Models, Animal , Oligonucleotides, Antisense , Phosphorylation , Pregnancy , Rats , Rats, Wistar , Tetradecanoylphorbol Acetate/pharmacology , Up-RegulationABSTRACT
The effect of dehydroepiandrosterone (DHEA) on pancreatic islet function of aged rats, an animal model with impaired glucose-induced insulin secretion, was investigated. The following parameters were examined: morphological analysis of endocrine pancreata by immunohistochemistry; protein levels of insulin receptor, IRS-1, IRS-2, PI 3-kinase, Akt-1, and Akt-2; and static insulin secretion in isolated pancreatic islets. Pancreatic islets from DHEA-treated rats showed an increased beta-cell mass accompanied by increased Akt-1 protein level but reduced IR, IRS-1, and IRS-2 protein levels and enhanced glucose-stimulated insulin secretion. The present results suggest that DHEA may be a promising drug to prevent diabetes during aging.