Akt mediates insulin induction of glucose uptake and up‐regulation of GLUT4 gene expression in brown adipocytes

Abstract

Insulin acutely stimulated glucose uptake in rat primary brown adipocytes in a PI3-kinase-dependent but p70S6-kinase-independent manner. Since Akt represents an intermediate step between these kinases, this study investigated the contribution of Akt to insulin-induced glucose uptake by the use of a chemical compound, ML-9, as well as by transfection with a dominant-negative form of Akt (v vAkt). Pretreatment with ML-9 for 10 min completely inhibited insulin stimulation of (1) Akt kinase activity, (2) Akt phosphorylation on the regulatory residue Ser473 but not on Thr308, and (3) mobility shift in Akt1 and Akt2. However, ML-9 did not affect insulin-stimulated PI3-kinase nor PKCj j activities. In consequence, ML-9 precluded insulin stimulation of glucose uptake and GLUT4 translocation to plasma membrane (determined by Western blot), without any effect on the basal glucose uptake. Moreover, v vAkt impaired insulin stimulation of glucose uptake and GFP-tagged GLUT4 translocation to plasma membrane in transiently transfected immortalised brown adipocytes and HeLa cells, respectively. Furthermore, ML-9 treatment for 6 h down-regulated insulininduced GLUT4 mRNA accumulation, without affecting GLUT1 expression, in a similar fashion as LY294002. Indeed, co-transfection of brown adipocytes with v vAkt precluded the transactivation of GLUT4-CAT promoter by insulin in a similar fashion as a dominant-negative form of PI3-kinase. Our results indicate that activation of Akt may be an essential requirement for insulin regulation of glucose uptake and GLUT4 gene expression in brown adipocytes. ß

Liver X receptor agonists ameliorate TNFα-induced insulin resistance in murine brown adipocytes by downregulating protein tyrosine phosphatase-1B gene expression

“…Results are the mean±SEM of triplicate measurements made in three to five independent cultures. *p<0.01 for differences vs control; Δ p<0.01 for difference vs Ins; ♦ p<0.01 for difference vs TNFα plus Ins [15]. Insulin sensitisation on glucose uptake was only observed when cells were treated with rosiglitazone, but not when they were treated with NR1HR ligands, TTNPB or phytanic acid.…”

“…Glucose transport determination Glucose uptake was measured by incorporating 2-deoxy-D-[1-3 H]glucose into cells during the last 10 min of culture as described previously [15]. Results are expressed as pmol glucose mg protein −1 10 min −1 .…”

“…Next, we investigated in the downstream PI3-kinase pathways the role of PKB and PKCζ, which have been proposed to mediate glucose uptake in brown adipocytes [15,16], as shown in Fig. 4.…”

“…Brown adipose tissue is a target tissue for insulin action, especially during late fetal development, when insulin promotes adipogenic and thermogenic differentiation and regulates glucose uptake, as reviewed [14]. Acute insulin treatment stimulates glucose transport in fetal brown adipocytes largely by mediating translocation of SLC2A4 to the plasma membrane, a process involving the activation of phosphatidylinositol (PI) 3-kinase, protein kinase B (PKB) and protein kinase C (PKC)ζ [15,16]. Brown adipose tissue is also a target for nuclear receptor agonists, since it produces abundant PPARγ, NR1HRα and β [9,17].…”

Statins in the Treatment of Polycystic Ovary Syndrome

“…In contrast, mevastatin has no effect on either basal or insulin-stimulated Akt/protein kinase B (PKB) phosphorylation in theca-interstitial cells 151 . The above findings underscore the potential therapeutic importance of selective inhibition of Erk1/2, but not Akt/PKB by statins, such that insulinmediated cellular proliferation of the theca-interstitial compartment may be abrogated without significantly affecting insulin-dependent glucose uptake, a process that appears to rely mostly on the Akt/PKB pathway 153,154 .…”