Volume 7, Issue 1, Pages (January 2008)

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1 Volume 7, Issue 1, Pages 45-56 (January 2008)
Mitochondrial Overload and Incomplete Fatty Acid Oxidation Contribute to Skeletal Muscle Insulin Resistance  Timothy R. Koves, John R. Ussher, Robert C. Noland, Dorothy Slentz, Merrie Mosedale, Olga Ilkayeva, James Bain, Robert Stevens, Jason R.B. Dyck, Christopher B. Newgard, Gary D. Lopaschuk, Deborah M. Muoio  Cell Metabolism  Volume 7, Issue 1, Pages (January 2008) DOI: /j.cmet Copyright © 2008 Elsevier Inc. Terms and Conditions

2 Figure 1 Chronic High-Fat Feeding Increases Postprandial Serum Nonesterified Fatty Acids and Acylcarnitines Serum samples were harvested in the ad lib fed or 24 hr starved state from rats fed either standard chow (SC) or high-fat (HF) diet for 12 weeks. Data represent means ± SEM from 4–5 animals per group. ∗p < 0.05 relative to HF diet. (A) Total nonesterified fatty acid (NEFA) levels. (B) Individual serum NEFA species in the fed state measured by gas chromatography/mass spectrometry. (C) Acylcarnitine species in the fed state measured by tandem mass spectrometry. Cell Metabolism 2008 7, 45-56DOI: ( /j.cmet ) Copyright © 2008 Elsevier Inc. Terms and Conditions

3 Figure 2 Skeletal Muscle Acylcarnitine Profiles Reveal Excessive β-Oxidation in Multiple Forms of Insulin Resistance (A) Acylcarnitine levels in whole gastrocnemius muscles harvested in the ad lib fed or 24 hr starved state from rats fed either SC or HF diet for 12 weeks. Data represent means ± SEM from 4–5 animals per group. (B) Acylcarnitine levels in whole gastrocnemius muscles harvested in the ad lib fed state from lean or obese Zucker diabetic fatty (ZDF) rats. Data represent means ± SEM from 3 animals per group. Main effects of starvation (p < 0.01), diet (p < 0.01), and genotype (p < 0.01) were detected by two-way ANOVA or Student's t test, but symbols were excluded for simplicity. Cell Metabolism 2008 7, 45-56DOI: ( /j.cmet ) Copyright © 2008 Elsevier Inc. Terms and Conditions

4 Figure 3 Skeletal Muscle Organic Acid Profiles Reveal Diminished Levels of TCA Cycle Intermediates in Multiple Forms of Insulin Resistance (A–C) Organic acid levels in whole gastrocnemius muscles harvested in the ad lib fed or 24 hr starved state from rats fed either SC or HF diet for 12 weeks. Data represent means ± SEM from 4–5 animals per group. ∗p < 0.05 for main diet effect between individual species by two-way ANOVA. (D) Organic acid levels in whole gastrocnemius muscles harvested in the ad lib fed state from lean Zucker and obese ZDF rats. Data are expressed as percent decrease in ZDF animals compared to lean control animals. Data represent means ± SEM from 9 animals per group. ‡p < 0.05 for genotype difference by Student's t test. Cell Metabolism 2008 7, 45-56DOI: ( /j.cmet ) Copyright © 2008 Elsevier Inc. Terms and Conditions

5 Figure 4 High-Fat Feeding Promotes Incomplete β-Oxidation and Metabolic Inflexibility in Skeletal Muscle Muscles were harvested from rats fed either SC or HF diet for 12 weeks. Data represent means ± SEM from 4–5 animals per group. ∗p < 0.05 relative to SC diet; ‡p < 0.05 relative to no pyruvate condition. (A) Complete oxidation of 200 μM [1-14C]oleate to CO2 in muscle homogenates prepared from deep (Red Quad) or superficial (White Quad) quadriceps. (B) Incomplete oxidation of 200 μM [1-14C]oleate to acid-soluble metabolites (ASM) in muscle homogenates prepared from deep (Red Quad) or superficial (White Quad) quadriceps. (C) Complete oxidation of 200 μM [1-14C]oleate to CO2 in isolated mitochondria from whole gastrocnemius muscle, incubated with or without 2 mM pyruvate. (D) Incomplete oxidation of 200 μM [1-14C]oleate to ASM in isolated mitochondria from whole gastrocnemius muscle, incubated with or without 2 mM pyruvate. Cell Metabolism 2008 7, 45-56DOI: ( /j.cmet ) Copyright © 2008 Elsevier Inc. Terms and Conditions

6 Figure 5 Fatty Acid Metabolism and Insulin Resistance in L6 Skeletal Myotubes (A and B) Triacylglycerol (TAG) synthesis and turnover were assessed in L6 myotubes treated for 24 hr with 500 μM oleate, palmitate, or a 1:1 oleate:palmitate blend with or without 1 mM L-carnitine. Cellular triacylglycerol content (A) and glycerol release into medium (B) were quantified spectrophotometrically. Data represent means ± SD from two independent experiments performed in duplicate. (C) Cytotoxicity was assayed by measuring adenylate kinase activity in the medium after 24 hr exposure to 0, 200, or 500 μM oleate (OA), palmitate (PA), or a 1:1 mix of oleate:palmitate (OP). Data are normalized to total adenylate kinase activity per well and represent means ± SD from two independent experiments performed in duplicate. ∗p < 0.05 relative to BSA control; ‡p < 0.05 relative to no carnitine condition. (D) Acylcarnitine accumulation was measured in L6 myotubes treated with 1 mM L-carnitine and 0.5% BSA, alone or complexed with 500 μM oleate:palmitate (1:1) with or without 100 μM etomoxir. Data are presented as means ± SD from experiments performed in triplicate and are representative of at least two experiments with similar results. (E and F) L6 myotubes were pretreated for 24 hr with 0.5% BSA alone or complexed with 500 μM 1:1 oleate:palmitate (FA) ± 2 mM L-carnitine, followed by a 2 hr incubation with [UL-14C]glucose ± 100 nM insulin, to determine rates of glycogen synthesis (E) and glucose oxidation to CO2 (F). Data are presented as means ± SD from experiments performed in triplicate and are representative of at least two experiments with similar results. (G and H) L6 myotubes were pretreated for 24 hr with 0.5% BSA alone or complexed with 500 μM 1:1 oleate:palmitate and increasing concentrations of L-carnitine (G) or 2 mM carnitine ± 100 μM etomoxir (H), followed by 15 min stimulation ± 100 nM insulin and western blot analysis of phosphorylated AKT2. MemCode (memc) staining was used to normalize protein transfer. Data are means ± SD from experiments performed in triplicate and are representative of at least three other experiments with similar results. ∗p < 0.05 comparing fatty acid exposure to BSA under the respective conditions by Student's t test. Cell Metabolism 2008 7, 45-56DOI: ( /j.cmet ) Copyright © 2008 Elsevier Inc. Terms and Conditions

7 Figure 6 mcd−/− Mice Are Protected against Diet-Induced Glucose Intolerance (A–C) Metabolic profiling was performed on gastrocnemius muscle lysates from wild-type (WT) and mcd−/− (KO) mice fed a HF diet for 12 weeks. Tissues were harvested in the postprandial state and analyzed for malonylcarnitine (A), fatty acylcarnitine species (B), and organic acids (C). (D and E) Long-chain acyl-CoAs (LC-Acyl-CoA) (D) and TAG content (E) were measured in mice fed either low-fat (LF) or HF diet for 12 weeks. (F and G) Whole-body glucose tolerance (F) and insulin sensitivity (G) tests were performed in mice fed a HF diet for 12 weeks. ∗p < 0.05 versus WT; ‡p < 0.05 versus animals of same genotype on SC diet. Data represent means ± SEM from 6 animals per group. Cell Metabolism 2008 7, 45-56DOI: ( /j.cmet ) Copyright © 2008 Elsevier Inc. Terms and Conditions

8 Figure 7 Whole-Body Substrate Oxidation in Wild-Type and mcd−/− Mice
Indirect calorimetry was performed using an eight-chamber Oxymax system (Columbus Instruments). Mice were acclimatized to the system prior to measurement. Respiratory exchange ratio (RER) was calculated as VCO2/ VO2. Data represent means ± SEM from 6–11 animals per group. (A) Wild-type mice were fed either a 10% fat (LF) or 60% fat (HF) diet for 2 weeks prior to whole-body metabolic assessments. Measurements were recorded every 40 min. (B) mcd−/− (KO) and wild-type (WT) littermates were fed a HF diet for 3 weeks prior to whole-body metabolic assessments. Measurements were recorded every 11 min; data points shown represent the average of each 55 min interval. Data were analyzed by Student's t test. Mean RER during the dark cycle was greater in KO versus WT mice (p < 0.01). Cell Metabolism 2008 7, 45-56DOI: ( /j.cmet ) Copyright © 2008 Elsevier Inc. Terms and Conditions