Continuous fat oxidation in acetyl-CoA carboxylase 2 knockout mice increases total energy expenditure, reduces fat mass, and improves insulin sensitivity

Abstract

Acetyl-CoA carboxylase 2 (ACC)2 is a key regulator of mitochondrial fat oxidation. To examine the impact of ACC2 deletion on whole-body energy metabolism, we measured changes in substrate oxidation and total energy expenditure in Acc2(-/-) and WT control mice fed either regular or high-fat diets. To determine insulin action in vivo, we also measured whole-body insulin-stimulated liver and muscle glucose metabolism during a hyperinsulinemic-euglycemic clamp in Acc2(-/-) and WT control mice fed a high-fat diet. Contrary to previous studies that have suggested that increased fat oxidation might result in lower glucose oxidation, both fat and carbohydrate oxidation were simultaneously increased in Acc2(-/-) mice. This increase in both fat and carbohydrate oxidation resulted in an increase in total energy expenditure, reductions in fat and lean body mass and prevention from diet-induced obesity. Furthermore, Acc2(-/-) mice were protected from fat-induced peripheral and hepatic insulin resistance. These improvements in insulin-stimulated glucose metabolism were associated with reduced diacylglycerol content in muscle and liver, decreased PKC activity in muscle and PKCepsilon activity in liver, and increased insulin-stimulated Akt2 activity in these tissues. Taken together with previous work demonstrating that Acc2(-/-) mice have a normal lifespan, these data suggest that Acc2 inhibition is a viable therapeutic option for the treatment of obesity and type 2 diabetes.

Fig. 1.

Energy balance and substrate selection. Energy expenditure (A and B) and RQ (C and D) were assessed by a comprehensive animal metabolic monitoring system (CLAMS) in Acc2^−/− and WT mice fed a regular diet and a HFD. Metabolic parameters were measured over a 48-h period, and equivalent time points, which were collected during the first and second 24-h periods, were averaged together. The results are a profile of the average energy expenditure of each group per hour during the 24-h course. The data are expressed as mean values ± SEM of five to eight mice per group. *, P < 0.05 (Acc2 ^−/− vs. WT).

Fig. 2.

Knocking out of ACC2 significantly improved hepatic and peripheral insulin sensitivity in high-fat-fed mice. Peripheral and hepatic insulin sensitivity was assessed by means of hyperinsulinemic–euglycemic clamps. (A) Plasma glucose. (B) Glucose infusion rates. (C) Hepatic glucose production during hyperinsulinemic–euglycemic clamps. (D) Whole-body glucose uptake, whole-body glycolysis, and whole-body glycogen synthesis. (E) Skeletal muscle (gastrocnemius) glucose uptake. (F) Epididymal white adipose tissue (WAT) glucose uptake. (G) Suppression of plasma fatty acid concentrations during the clamps. The data are expressed as mean values ± SEM for nine mice per group. *, P < 0.05; †, P < 0.01; ‡, P < 0.001 (Acc2 ^−/− vs. WT); 2DG, 2-deoxy glucose.

Fig. 3.

Knocking out of Acc2 increased Akt2 activity and decreased PKC membrane translocation. (C and D) Improved muscle and hepatic insulin sensitivity are associated with increased Akt2 activity in muscle (C) and liver (D). (A and B) Reduced membrane translocation of PKCθ in muscle (A) and PKCε in liver (B) may be directly involved in improving muscle and hepatic insulin signaling. Akt2 activity was assessed 14 min after i.p. insulin injection of 1 unit per kilogram of body weight. Data are expressed as mean values ± SEM for four to five mice per group. *, P < 0.05; †, P < 0.01; ‡, P < 0.001 (Acc2 ^−/− vs. WT).

Fig. 4.

Decreased triglycerides, diacylglycerol, and long-chain acyl–CoAs in Acc2^−/− mice. (A, B, E, and F) Triglyceride and long-chain acyl–CoA levels were significantly decreased in muscle (A and E) and liver (B and F) in Acc2^−/− mice. (C and D) Skeletal muscle membrane-to-cytosol ratio of diacylglycerols (C) and hepatic diacylglycerols (D) were significantly lower in Acc2^−/− mice compared with WT mice. Data are expressed as mean values ± SEM for five to eight mice per group. *, P < 0.05, †, P < 0.01; ‡, P < 0.001 (Acc2 ^−/− vs. WT).