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.

Methodology: 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.

Principal findings: 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/interpretation: 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.

Figure 1. Respiration rates of isolated mitochondria from mouse skeletal muscle on pyruvate and palmitoyl-CoA+carnitine.

(A) ADP-stimulated (state 3) respiration on pyruvate, (B) oligomycin-insensitive (state 4) respiration on pyruvate, (C) maximally uncoupled (state UnC) respiration on pyruvate, (D) state 3 respiration on palmitoylCoA + carnitine, (E) state 4 respiration on palmitoyl-CoA + carnitine and (F) State UnC respiration on palmitoyl-CoA + carnitine. Black and white bars represent LFD mice and HFD mice, respectively. Values are means ± SE (n = 7–8). D, significant diet effect with p<0.01; T, significant time effect with p<0.05 in state 3 and state 4 and with p<0.01 in state UnC; D*T, significant diet * time effect with p<0.05; HFD, high fat diet; LFD, low fat diet; TA, tibialis anterior; UnC, uncoupled.