DEVELOPMENT OF INSULIN RESISTANCE IN GABABKO MICE

BONAVENTURA, M. M.; FERREIRA, ML; LIBERTUN C; LUX LANTOS V

Washington

Congreso; ENDO 2009; 2009

The Endocrine Society

DEVELOPMENT OF INSULIN RESISTANCE IN GABABKO MICE Bonaventura, MM; Ferreira, ML; Libertun C; Lux Lantos V 1.Instituto de Biologia y Medicina Experimental, CONICET.2.Facultad de Medicina-UBA We have previously described alterations in glucose homeostasis in mice with deletion of the B1 subunit of GABAB receptors (GABABKO) with respect to their wild type controls (WT) in both males and females. We have also studied parameters that show the development of insulin resistance in male GABABKO, i.e. significant increase in insulin secretion in an Insulin Secretion Test (IST) and also alterations in an Insulin Tolerance Test (ITT) (1). The aim of the present work was to study the presence of insulin resistance in female GABABKO mice as well as to elucidate the subcellular mechanisms involved in this phenomenon both in males and females. During an IST (Glucose 3g/kg, i.p.) performed in female mice of both genotypes, we observed a marginally significant increase of insulin secretion in GABABKO animals respect to WTs (two way ANOVA for repeated measures: interaction: ns, genotype p<0.06, time p<0.05, n=5). We also study insulin peripheral sensitivity in females with an ITT (0.75 UI/kg i.p.), observing that GABABKO had a diminished sensitivity compared to WT (two way ANOVA for repeated measures: interaction: ns, main effect genotype and time p<0.05, n=8-11). These results coincide with those previously obtained in males. In view of the evidence supporting the development of insulin resistance in both sexes, we evaluated the insulin signaling cascade in peripheral tissue, mainly in skeletal muscle. Anesthetized mice were injected with insulin (2U/kg) into the portal vein and skeletal muscle samples were taken at time points 0, 1 and 5 minutes post injection and analyzed by Western Blot (2). Antibodies against Akt, phospho-Akt (Ser478), IRS1, IRS2 and actin (housekeeper) were assayed. There were no significant differences in the basal levels of any of these proteins. A time-dependent increase in Akt phosphorylation levels was observed WT animals. In contrast, GABABKO mice showed an altered response to the insulin stimulus, in both males and female (pAkt/akt: WT: 5 min > 0 min (n=5), p<0.05; KO: no significant differences were observed between these time points, n=5) In view of these results we conclude that GABABKO animals develop spontaneous insulin resistance at adulthood, and that this resistance is associated to alterations in the insulin signaling cascade in peripheral muscular tissue. This work was supported by grant form: ANPCYT, UBA; CONICET References 1. Bonaventura MM, Catalano PN, Chamson-Reig A, Arany E, Hill D, Bettler B, Saravia F, Libertun C, Lux-Lantos VA 2008 GABAB receptors and glucose homeostasis: evaluation in GABAB receptor knockout mice. Am J Physiol Endocrinol Metab 294:E157-E167 2. Araujo EP, De Souza CT, Gasparetti AL, Ueno M, Boschero AC, Saad MJ, Velloso LA 2005 Short-term in vivo inhibition of insulin receptor substrate-1 expression leads to insulin resistance, hyperinsulinemia, and increased adiposity. Endocrinology 146:1428-1437