title: High fat diet-induced changes in mouse muscle mitochondrial phospholipids do not impair mitochondrial respiration despite insulin resistance.
abstract: BACKGROUND
  Type 2 diabetes mellitus and muscle insulin resistance have been associated with reduced capacity of skeletal muscle mitochondria, possibly as a result of increased intake of dietary fat. Here, we examined the hypothesis that a prolonged high-fat diet consumption (HFD) increases the saturation of muscle mitochondrial membrane phospholipids causing impaired mitochondrial oxidative capacity and possibly insulin resistance.
  
  
  METHODS
  C57BL/6J mice were fed an 8-week or 20-week low fat diet (10 kcal%; LFD) or HFD (45 kcal%). Skeletal muscle mitochondria were isolated and fatty acid (FA) composition of skeletal muscle mitochondrial phospholipids was analyzed by thin-layer chromatography followed by GC. High-resolution respirometry was used to assess oxidation of pyruvate and fatty acids by mitochondria. Insulin sensitivity was estimated by HOMA-IR.
  
  
  RESULTS
  At 8 weeks, mono-unsaturated FA (16∶1n7, 18∶1n7 and 18∶1n9) were decreased (-4.0%, p<0.001), whereas saturated FA (16∶0) were increased (+3.2%, p<0.001) in phospholipids of HFD vs. LFD mitochondria. Interestingly, 20 weeks of HFD descreased mono-unsaturated FA while n-6 poly-unsaturated FA (18∶2n6, 20∶4n6, 22∶5n6) showed a pronounced increase (+4.0%, p<0.001). Despite increased saturation of muscle mitochondrial phospholipids after the 8-week HFD, mitochondrial oxidation of both pyruvate and fatty acids were similar between LFD and HFD mice. After 20 weeks of HFD, the increase in n-6 poly-unsaturated FA was accompanied by enhanced maximal capacity of the electron transport chain (+49%, p = 0.002) and a tendency for increased ADP-stimulated respiration, but only when fuelled by a lipid-derived substrate. Insulin sensitivity in HFD mice was reduced at both 8 and 20 weeks.
  
  
  CONCLUSIONS
  Our findings do not support the concept that prolonged HF feeding leads to increased saturation of skeletal muscle mitochondrial phospholipids resulting in a decrease in mitochondrial fat oxidative capacity and (muscle) insulin resistance.
authors.affiliation: Department of Human Biology, NUTRIM School for Nutrition, Toxicology and Metabolism, Maastricht University Medical Center, Maastricht, The Netherlands.
authors.forename: Joris
authors.initials: J
authors.lastname: Hoeks
authors.forename: Janneke de
authors.initials: Jd
authors.lastname: Wilde
authors.forename: Martijn F M
authors.initials: MF
authors.lastname: Hulshof
authors.forename: Sjoerd A A van den
authors.initials: SA
authors.lastname: Berg
authors.forename: Gert
authors.initials: G
authors.lastname: Schaart
authors.forename: Ko Willems van
authors.initials: KW
authors.lastname: Dijk
authors.forename: Egbert
authors.initials: E
authors.lastname: Smit
authors.forename: Edwin C M
authors.initials: EC
authors.lastname: Mariman
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D001835:Body Weight; D019069:Cell Respiration; D059305:Diet, High-Fat; D004734:Energy Metabolism; D005227:Fatty Acids / Q000378:metabolism; D006614:Hindlimb / Q000378:metabolism; D006706:Homeostasis / Q000187:drug effects; D007328:Insulin / Q000097:blood; D007333:Insulin Resistance; D020738:Leptin / Q000097:blood; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008931:Mitochondria, Muscle / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism; D010085:Oxidative Phosphorylation; D010743:Phospholipids / Q000378:metabolism*
chemical_list: D001786:Blood Glucose; D005227:Fatty Acids; D007328:Insulin; D020738:Leptin; D010743:Phospholipids