Chronic rosiglitazone treatment restores AMPKα2 activity in insulin-resistant rat skeletal muscle

Abstract

(RSG) is an insulin-sensitizing thiazolidinedione (TZD) that exerts peroxisome proliferator-activated receptor-␥ (PPAR␥)-dependent and -independent effects. We tested the hypothesis that part of the insulinsensitizing effect of RSG is mediated through the action of AMPactivated protein kinase (AMPK). First, we determined the effect of acute (30 -60 min) incubation of L6 myotubes with RSG on AMPK regulation and palmitate oxidation. Compared with control (DMSO), 200 M RSG increased (P Ͻ 0.05) AMPK␣1 activity and phosphorylation of AMPK (Thr 172 ). In addition, acetyl-CoA carboxylase (Ser 218 ) phosphorylation and palmitate oxidation were increased (P Ͻ 0.05) in these cells. To investigate the effects of chronic RSG treatment on AMPK regulation in skeletal muscle in vivo, obese Zucker rats were randomly allocated into two experimental groups: control and RSG. Lean Zucker rats were treated with vehicle and acted as a control group for obese Zucker rats. Rats were dosed daily for 6 wk with either vehicle (0.5% carboxymethylcellulose, 100 l/100 g body mass), or 3 mg/kg RSG. AMPK␣1 activity was similar in muscle from lean and obese animals and was unaffected by RSG treatment. AMPK␣2 activity was ϳ25% lower in obese vs. lean animals (P Ͻ 0.05) but was normalized to control values after RSG treatment. ACC phosphorylation was decreased with obesity (P Ͻ 0.05) but restored to the level of lean controls with RSG treatment. Our data demonstrate that RSG restores AMPK signaling in skeletal muscle of insulin-resistant obese Zucker rats.lipids; peroxisome proliferator-activated receptor-␥; thiazolidinedione; Zucker rats; adenosine monophosphate-activated protein kinase-␣2 SKELETAL MUSCLE INSULIN RESISTANCE is a common state associated with inactivity, aging, genetic predisposition, and environmental factors and is a hallmark feature of a variety of disease states, including obesity, hyperlipidemia, hypertension, and type 2 diabetes (31). Rosiglitazone (RSG) is a member of the thiazolidinedione (TZD) class of oral antidiabetic agents that improve insulin sensitivity in a range of insulin-resistant states (15,18). TZDs are peroxisome proliferator-activated receptor-␥ (PPAR␥) agonists that, upon activation by fatty acids (FA) or FA-derived compounds, bind to responsive elements located in the promoter regions of many genes and modulate their transcriptive activities (1, 32). Although PPAR␥ plays a role in the TZD-induced insulin sensitization, metabolic responses to TZDs can be dissociated from PPAR␥-induced gene transcription (4,14,29). Furthermore, we (23) have recently reported that RSG improves glucose tolerance by mechanisms other than a reduction of FA accumulation within skeletal muscle. Hence, it is likely that there exists PPAR␥-independent mechanisms by which TZDs improve insulin sensitivity.The AMP-activated protein kinase (AMPK) is a cellular energy sensor that regulates glucose and lipid metabolism by phosphorylating key regulatory enzymes (21, 39). AMPK activation causes many metabolic changes that would be benef...

Activation of Protein Phosphatase 2A by Palmitate Inhibits AMP-activated Protein Kinase

“…Also, high fat diet feeding significantly decreases phospho-AMPK in the liver and muscles of rodents (13,14). AMPK activity is reduced in aortic endothelium or skeletal muscle of obese rats compared with lean animals (15,16). These data raise the possibility that chronic exposure of fatty acids to cells inhibit AMPK activation.…”

Tissue-Specific Effects of Rosiglitazone and Exercise in the Treatment of Lipid-Induced Insulin Resistance

“…In this regard, we have previously demonstrated that chronic rosiglitazone restores AMPK activation in the skeletal muscle of fa/fa Zucker rats, a model that displays reduced AMPK activation as a result of deficient leptin signaling (20). In contrast, high-fat feeding in the present study resulted in a ϳ36% increase in AMPK␣2 activity (Fig.…”

“…AMPK activity and AMPK subunit protein expression. AMPK activity, pT172 phosphorylation, and total protein content were analyzed as previously described (20). Activities were calculated as picomoles of phosphate incorporated into the SAMS peptide per minute, per milligram of protein subjected to immunoprecipitation.…”

“…Activities were calculated as picomoles of phosphate incorporated into the SAMS peptide per minute, per milligram of protein subjected to immunoprecipitation. Acetyl CoA carboxylase (ACC) was affinity purified and quantified using post-AMPK immunoprecipitation supernatants as previously described (20).…”

Inflammation in Obesity is a Common Link Between Defects in Fatty Acid Metabolism and Insulin Resistance

“…89,90 Since AMPK is important for mitochondrial biogenesis through it's effects on the transcriptional coactivator PGC-1α, 91,92 it seems reasonable that mitochondrial dysfunction may be due to reduced AMPK activity and that the prolonged inhibition of TNF signaling as observed in ob/ob TNFR -/-may be effective in reversing these defects due to increased mitochondrial biogenesis. Supporting this idea are findings that the chronic treatment of ob/ob mice with the commonly used anti-diabetic drug rosiglitazone, which is an AMPK activator 93,94 and suppressor of TNFα production, 95,96 reverses defects in mitochondrial density in adipose tissue. 97 Similarly, a recent study has shown that chronic activation of AMPK by the hormone adiponectin, which alike to rosiglitazone also reduces TNFα production, increases muscle mitochondrial biogenesis.…”