Effect of growth hormone treatment in the quantity and phosphorylation of the insulin receptor substrate -1 and -3 (IRS-1) and (IRS-3) and their associations with PI 3-kinase

Author(s)

Fernanda Campos de Paiva Castro

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2001-04-27
• Advisor: Dante Pazzanese Duarte Lanna

Abstract

The growth hormone treatment (GH) decreases the adipose tissue sensitivity to the insulin action. However, the exact molecular mechanism remains unclear. ln the present study, we have employed an organ maintenance system for adipose tissue in order to better characterize the cellular basis of the insulin resistance effect of GH. The objective of this project was to amplify the knowledge of the growth hormone effects on the insulin signal cascade through determination of the insulin receptor substrate -1 (IRS-1), -3 (IRS-3) and PI 3-kinase (PI-3K) concentrations, IRS-1 and IRS-3 phosphorylation’s and the associations of these substrates with PI 3-kinase. ln order to analyze the effects of the adipose tissue exposition to GH, explants were subjected to two essays in 199 medium containing: Essay I (48 horas): a) I + D (100 ng/ml insulin + 10 mM dexamethasone); b) I + D + GH (100 ng/ml insulin + 10 mM dexamethasone + 100 ng/ml GH). Essay II (24 horas): a) control (no hormone addition); b) GH (100 ng/ml). After 24 hours’ culture, half of the essay II explants were stimulated with insulin (1 µg/ml) for 20 min. The results, consistent with the literature, showed a reduction of the same magnitude (~30%) in the concentration of IRS-1 in both essays where adipocytes where chronically treated with growth hormone for 24 and 48 hours. The IRS-3 protein levels varied between essays, being a reduction of 15% encountered in the 24 hours’ essay, and a reduction of 27% in the 48 hours. The PI 3-kinase concentration reduced 27% in both GH treatments for 24 and 48 hours. The IRS-1 and IRS-3 showed a reduction of 44 e 28%, respectively, in their associations with PI 3-kinase after 20 min insulin stimulation in the 24 hours GH treated explants and, in the same explants, after insulin stimulus, the IRS-3 phosphorylation was reduced 28%. These data suggest that chronically GH treatment alters the early steps of insulin signal transduction pathway, possibly cooperating with an alteration in the adipose tissue sensitivity to insulin. (AU)