Rosiglitazone ameliorates insulin resistance in brown adipocytes of Wistar rats by impairing TNF-α induction of p38 and p42/p44 mitogen-activated protein kinases

Abstract

Aims/hypothesis. TNF-α caused insulin resistance on glucose uptake and on insulin signalling in fetal brown adipocytes. Since treatment with TNF-α activates stress kinases, including c-jun NH2 terminal kinase (JNK), and p42/p44 and p38 mitogen-activated protein kinases (MAPK), we explored the contribution of these pathways to insulin resistance by TNF-α. Rosiglitazone is used to treat Type 2 diabetes as it improves insulin sensitivity in vivo. However, its ability to ameliorate TNF-α-induced insulin resistance in brown adipocytes remains to be explored. Methods. We used fetal rat primary brown adipocytes cultured with TNF-α, with or without stress kinase inhibitors or rosiglitazone, and further stimulated with insulin. Then, we measured glucose uptake and GLUT4 translocation. To determine the insulin signalling cascade, we submitted cells to lysis, immunoprecipitation and immunoblotting.

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

“…Incubation of brown adipocytes with insulin for 30 min or with T0901317 for 24 h increased SLC2A4 protein content in plasma membrane (200% and 50%, respectively), which is consistent with the data on glucose uptake. In addition, the redistribution of SLC2A4 in the presence of insulin was precluded after TNFα treatment for 24 h, in agreement with our previous work [22]. Moreover, in these TNFα-induced insulin-resistant conditions pretreatment with T0901317 completely restored SLC2A4 translocation by insulin.…”

“…After protein content determination, equal amounts of protein were immunoprecipitated at 4°C with the corresponding antibody. The immune complexes were collected on protein A-agarose and analysed on SDS-PAGE followed by western blotting or on PI3-kinase activity by in vitro phosphorylation of phosphatidylinositol as previously described [22].…”

“…In this regard, we had previously described that TNFα caused insulin resistance in brown adipocytes by impairing insulin signalling at the level of IRS-2. We had also identified ceramide production and activation of protein phosphatase 2A (PP2A), and induction of p38 and p42/p44 mitogenactivated protein kinase (MAPK) as mediators of insulin resistance by TNFα [22,23]. Moreover, the thiazolidinedione rosiglitazone ameliorates TNFα-induced insulin resistance in brown adipocytes by impairing the stimulation of MAPKs by TNFα [22].…”

“…We had also identified ceramide production and activation of protein phosphatase 2A (PP2A), and induction of p38 and p42/p44 mitogenactivated protein kinase (MAPK) as mediators of insulin resistance by TNFα [22,23]. Moreover, the thiazolidinedione rosiglitazone ameliorates TNFα-induced insulin resistance in brown adipocytes by impairing the stimulation of MAPKs by TNFα [22]. Thiazolidinediones are insulinsensitising drugs, which improve insulin action in vivo across a wide spectrum of insulin-resistant states and which have recently been introduced for the clinical treatment of type 2 diabetes [24,25].…”

Mitochondrial dysfunction and oxidative stress in the pathogenesis of alcohol- and obesity-induced fatty liver diseases

“…Interestingly, the protective effect of metformin in this study did not correlate to AMP kinase activation, but via prevention of plasminogen activator inhibitor (PAI)-I upregulation by alcohol [145]. Rosiglitazone and pioglitazone, thiazolidinedione peroxisomal proliferator-activated receptor (PPAR)-γ agonists, decrease insulin resistance and have been shown to decrease TNF-α levels and inflammation in rodent models of NASH [146][147][148][149][150]. Similarly, the PPAR-γ agonist pioglitazone prevents alcohol induced liver injury through interactions with the c-Met signaling pathway resulting in decreased triglyceride synthesis [151].…”