This Article Full Text Full Text (PDF) Submit a related Letter to the Editor Purchase Article View Shopping Cart Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Kruszynska, Y. T. Articles by Olefsky, J. M. Search for Related Content PubMed PubMed Citation Articles by Kruszynska, Y. T. Articles by Olefsky, J. M.

Fatty Acid-Induced Insulin Resistance: Decreased Muscle PI3K Activation But Unchanged Akt Phosphorylation

Department of Endocrinology and Metabolism, University of California San Diego, Veterans Administration Center, La Jolla, California 92093

Address all correspondence and requests for reprints to: Yolanta Kruszynska, M.D., Department of Endocrinology and Metabolism (9111G), Veterans Administration Medical Center, 3350 La Jolla Village Drive, La Jolla, California 92093.

The mechanisms by which elevated plasma nonesterified fatty acid (NEFA) levels induce skeletal muscle insulin resistance remain unclear. A NEFA-induced defect in the activation of PI3K, which plays a key role in insulin’s stimulation of glucose transport, has been invoked. We sought to examine the effects of elevated plasma NEFA (1 mmol/liter) on muscle PI3K activity, insulin receptor substrate (IRS)-1 (important for activation of PI3K), and Akt, which is downstream of PI3K and activated by phosphorylation on serine and threonine in a PI3K-dependent manner. Ten normal men [age, 37 ± 9 yr (mean ± SD); body mass index, 25.2 ± 3.8 kg/m²] underwent two 5-h hyperinsulinemic (80 mU/m²·min) euglycemic clamps with basal and end of clamp biopsies of the vastus lateralis muscle. Plasma NEFAs were increased in one study by infusion of 20% Intralipid (1 ml/min) and heparin (900 U/h) throughout and for 2.5 h beforehand. Skeletal muscle protein levels were quantified by Western blotting. Elevated plasma NEFA reduced whole-body insulin-stimulated glucose disposal by 24% (42.1 ± 4.0 vs. 54.8 ± 3.6 µmol/kg·min; P < 0.001). Basal muscle IRS-1 was the same in the two studies. IRS-1 levels decreased by 40% in the control glucose clamps (P < 0.005), but did not change during the Intralipid study. Total tyrosine phosphorylated IRS-1 increased by 29% during the control clamps (P < 0.05), but by only 18% (NS) during the Intralipid studies. Total levels of p85 subunit of PI3K and Akt were not influenced by plasma NEFA levels either in the basal state or during the glucose clamps. The insulin-induced increase in IRS-1-associated PI3K activity was impaired by elevated NEFA, so that activity at the end of the clamps with Intralipid was 35% lower than in the control clamps (P < 0.05). The percentage reduction in PI3K activation correlated with the reduction in insulin-stimulated glucose disappearance rate that was induced by elevated NEFA (r = 0.70; P < 0.05). Basal P-ser- and P-thr-Akt levels were very low and unaffected by NEFA levels. The glucose clamps resulted in a marked increase in P-ser and P-thr Akt levels. Despite the decrease in PI3K in the Intralipid study, no defect in Akt phosphorylation was found. In summary, NEFA-induced insulin resistance is associated with an impairment of IRS-1 tyrosine phosphorylation and IRS-1-associated PI3K activation. Down-regulation of IRS-1 levels is also impaired. The NEFA-induced defect in muscle glucose uptake appears to be a consequence of a defect in the insulin-signaling pathway leading to impaired PI3K activation. This in turn may lead to impaired glucose transport through an Akt-independent pathway because Akt phosphorylation was unaffected by elevated NEFA levels.

This study was supported by the Whittier Institute, NIH Grant DK 33649, General Clinical Research Center Grant RR00827, and the Medical Service, Department of Veterans Affairs, Veterans Administration Medical Center, San Diego, California.

Abbreviations: Glut 4, Glucose transporter 4; HGO, hepatic glucose output; IR-ß, insulin receptor ß-subunit; IRS, insulin receptor substrate; N, nitrogen; NEFA, nonesterified fatty acid; PI, phosphatidylinositol; PI-3-P, PI-3-phosphate; Ra, rate of appearance; Rd, rate of disappearance.

This article has been cited by other articles:

				G. Frangioudakis and G. J Cooney Acute elevation of circulating fatty acids impairs downstream insulin signalling in rat skeletal muscle in vivo independent of effects on stress signalling J. Endocrinol., May 1, 2008; 197(2): 277 - 285. [Abstract] [Full Text] [PDF]

				C. Le Stunff, A. Dechartres, V. Mariot, C. Lotton, C. Trainor, E. Miraglia Del Giudice, D. Meyre, I. Bieche, I. Laurendeau, P. Froguel, et al. Association Analysis Indicates That a Variant GATA-Binding Site in the PIK3CB Promoter Is a Cis-Acting Expression Quantitative Trait Locus for This Gene and Attenuates Insulin Resistance in Obese Children Diabetes, February 1, 2008; 57(2): 494 - 502. [Abstract] [Full Text] [PDF]

				D. S. Battram, T. E. Graham, and F. Dela Caffeine's impairment of insulin-mediated glucose disposal cannot be solely attributed to adrenaline in humans J. Physiol., September 15, 2007; 583(3): 1069 - 1077. [Abstract] [Full Text] [PDF]

				H. Alkhateeb, A. Chabowski, J. F. C. Glatz, J. F. P. Luiken, and A. Bonen Two phases of palmitate-induced insulin resistance in skeletal muscle: impaired GLUT4 translocation is followed by a reduced GLUT4 intrinsic activity Am J Physiol Endocrinol Metab, September 1, 2007; 293(3): E783 - E793. [Abstract] [Full Text] [PDF]

				B. Lindegaard, C. Frosig, A. M. W. Petersen, P. Plomgaard, S. Ditlevsen, B. Mittendorfer, G. Van Hall, J. F.P. Wojtaszewski, and B. K. Pedersen Inhibition of Lipolysis Stimulates Peripheral Glucose Uptake but Has No Effect on Endogenous Glucose Production in HIV Lipodystrophy Diabetes, August 1, 2007; 56(8): 2070 - 2077. [Abstract] [Full Text] [PDF]

				S. J. Lessard, D. A. Rivas, Z.-P. Chen, A. Bonen, M. A. Febbraio, D. W. Reeder, B. E. Kemp, B. B. Yaspelkis III, and J. A. Hawley Tissue-Specific Effects of Rosiglitazone and Exercise in the Treatment of Lipid-Induced Insulin Resistance Diabetes, July 1, 2007; 56(7): 1856 - 1864. [Abstract] [Full Text] [PDF]

				L. C. Gormsen, N. Jessen, J. Gjedsted, S. Gjedde, H. Norrelund, S. Lund, J. S. Christiansen, S. Nielsen, O. Schmitz, and N. Moller Dose-Response Effects of Free Fatty Acids on Glucose and Lipid Metabolism during Somatostatin Blockade of Growth Hormone and Insulin in Humans J. Clin. Endocrinol. Metab., May 1, 2007; 92(5): 1834 - 1842. [Abstract] [Full Text] [PDF]

				R. Wolk and V. K. Somers Sleep Apnoea & Hypertension: Physiological bases for a causal relation: Sleep and the metabolic syndrome Exp Physiol, January 1, 2007; 92(1): 67 - 78. [Abstract] [Full Text] [PDF]

				S. Shetty, E. R.M. Eckhardt, S. R. Post, and D. R. van der Westhuyzen Phosphatidylinositol-3-Kinase Regulates Scavenger Receptor Class B Type I Subcellular Localization and Selective Lipid Uptake in Hepatocytes Arterioscler. Thromb. Vasc. Biol., September 1, 2006; 26(9): 2125 - 2131. [Abstract] [Full Text] [PDF]

				C. H. Lang Elevated plasma free fatty acids decrease basal protein synthesis, but not the anabolic effect of leucine, in skeletal muscle Am J Physiol Endocrinol Metab, September 1, 2006; 291(3): E666 - E674. [Abstract] [Full Text] [PDF]

				A. T. De Souza, P. D. Cornwell, X. Dai, M. J. Caguyong, and R. G. Ulrich Agonists of the Peroxisome Proliferator-Activated Receptor Alpha Induce a Fiber-Type-Selective Transcriptional Response in Rat Skeletal Muscle Toxicol. Sci., August 1, 2006; 92(2): 578 - 586. [Abstract] [Full Text] [PDF]

				D. S. Battram, T. E. Graham, E. A. Richter, and F. Dela The effect of caffeine on glucose kinetics in humans - influence of adrenaline J. Physiol., November 15, 2005; 569(1): 347 - 355. [Abstract] [Full Text] [PDF]

				L. Chen, X.-H. Yao, and B. L. G. Nyomba In vivo insulin signaling through PI3-kinase is impaired in skeletal muscle of adult rat offspring exposed to ethanol in utero J Appl Physiol, August 1, 2005; 99(2): 528 - 534. [Abstract] [Full Text] [PDF]

				G. K. Bandyopadhyay, J. G. Yu, J. Ofrecio, and J. M. Olefsky Increased p85/55/50 Expression and Decreased Phosphotidylinositol 3-Kinase Activity in Insulin-Resistant Human Skeletal Muscle Diabetes, August 1, 2005; 54(8): 2351 - 2359. [Abstract] [Full Text] [PDF]

				R. Belfort, L. Mandarino, S. Kashyap, K. Wirfel, T. Pratipanawatr, R. Berria, R. A. DeFronzo, and K. Cusi Dose-Response Effect of Elevated Plasma Free Fatty Acid on Insulin Signaling Diabetes, June 1, 2005; 54(6): 1640 - 1648. [Abstract] [Full Text] [PDF]

				Y. I. Miller, S. Viriyakosol, D. S. Worrall, A. Boullier, S. Butler, and J. L. Witztum Toll-Like Receptor 4-Dependent and -Independent Cytokine Secretion Induced by Minimally Oxidized Low-Density Lipoprotein in Macrophages Arterioscler. Thromb. Vasc. Biol., June 1, 2005; 25(6): 1213 - 1219. [Abstract] [Full Text] [PDF]

				M. Gaster, A. C. Rustan, and H. Beck-Nielsen Differential Utilization of Saturated Palmitate and Unsaturated Oleate: Evidence From Cultured Myotubes Diabetes, March 1, 2005; 54(3): 648 - 656. [Abstract] [Full Text] [PDF]

				F. Tremblay, A. Gagnon, A. Veilleux, A. Sorisky, and A. Marette Activation of the Mammalian Target of Rapamycin Pathway Acutely Inhibits Insulin Signaling to Akt and Glucose Transport in 3T3-L1 and Human Adipocytes Endocrinology, March 1, 2005; 146(3): 1328 - 1337. [Abstract] [Full Text] [PDF]

				M. E. Cleasby, N. Dzamko, B. D. Hegarty, G. J. Cooney, E. W. Kraegen, and J.-M. Ye Metformin Prevents the Development of Acute Lipid-Induced Insulin Resistance in the Rat Through Altered Hepatic Signaling Mechanisms Diabetes, December 1, 2004; 53(12): 3258 - 3266. [Abstract] [Full Text] [PDF]

				J. M. Rumberger, T. Peters Jr, C. Burrington, and A. Green Transferrin and Iron Contribute to the Lipolytic Effect of Serum in Isolated Adipocytes Diabetes, October 1, 2004; 53(10): 2535 - 2541. [Abstract] [Full Text] [PDF]

				S. R. Kashyap, R. Belfort, R. Berria, S. Suraamornkul, T. Pratipranawatr, J. Finlayson, A. Barrentine, M. Bajaj, L. Mandarino, R. DeFronzo, et al. Discordant effects of a chronic physiological increase in plasma FFA on insulin signaling in healthy subjects with or without a family history of type 2 diabetes Am J Physiol Endocrinol Metab, September 1, 2004; 287(3): E537 - E546. [Abstract] [Full Text] [PDF]

				M. Roden How Free Fatty Acids Inhibit Glucose Utilization in Human Skeletal Muscle Physiology, June 1, 2004; 19(3): 92 - 96. [Abstract] [Full Text] [PDF]

				A. D. Krisan, D. E. Collins, A. M. Crain, C. C. Kwong, M. K. Singh, J. R. Bernard, and B. B. Yaspelkis III Resistance training enhances components of the insulin signaling cascade in normal and high-fat-fed rodent skeletal muscle J Appl Physiol, May 1, 2004; 96(5): 1691 - 1700. [Abstract] [Full Text] [PDF]

				M. Straczkowski, I. Kowalska, A. Nikolajuk, S. Dzienis-Straczkowska, I. Kinalska, M. Baranowski, M. Zendzian-Piotrowska, Z. Brzezinska, and J. Gorski Relationship Between Insulin Sensitivity and Sphingomyelin Signaling Pathway in Human Skeletal Muscle Diabetes, May 1, 2004; 53(5): 1215 - 1221. [Abstract] [Full Text] [PDF]

				H. Storgaard, C. B. Jensen, M. Bjornholm, X. M. Song, S. Madsbad, J. R. Zierath, and A. A. Vaag Dissociation between Fat-Induced in Vivo Insulin Resistance and Proximal Insulin Signaling in Skeletal Muscle in Men at Risk for Type 2 Diabetes J. Clin. Endocrinol. Metab., March 1, 2004; 89(3): 1301 - 1311. [Abstract] [Full Text] [PDF]

				H. Bays, L. Mandarino, and R. A. DeFronzo Role of the Adipocyte, Free Fatty Acids, and Ectopic Fat in Pathogenesis of Type 2 Diabetes Mellitus: Peroxisomal Proliferator-Activated Receptor Agonists Provide a Rational Therapeutic Approach J. Clin. Endocrinol. Metab., February 1, 2004; 89(2): 463 - 478. [Full Text] [PDF]

				Y. I. Miller, D. S. Worrall, C. D. Funk, J. R. Feramisco, and J. L. Witztum Actin Polymerization in Macrophages in Response to Oxidized LDL and Apoptotic Cells: Role of 12/15-Lipoxygenase and Phosphoinositide 3-Kinase Mol. Biol. Cell, October 1, 2003; 14(10): 4196 - 4206. [Abstract] [Full Text] [PDF]

				J. W. Helge and F. Dela Effect of Training on Muscle Triacylglycerol and Structural Lipids: A Relation to Insulin Sensitivity? Diabetes, August 1, 2003; 52(8): 1881 - 1887. [Abstract] [Full Text] [PDF]

				H. Ruan, P. D. G. Miles, C. M. Ladd, K. Ross, T. R. Golub, J. M. Olefsky, and H. F. Lodish Profiling Gene Transcription In Vivo Reveals Adipose Tissue as an Immediate Target of Tumor Necrosis Factor-{alpha}: Implications for Insulin Resistance Diabetes, November 1, 2002; 51(11): 3176 - 3188. [Abstract] [Full Text] [PDF]