Metabolomic analysis of akt1-mediated muscle hypertrophy in models of diet-induced obesity and age-related fat accumulation

Abstract

Akt1 is a serine/threonine kinase that promotes cell growth and survival. Previously, Akt1 activation in a double transgenic (DTG) mouse model fed a high-fat/high-sucrose (HF/HS) diet was found to promote type IIb muscle growth and to lead to a significant reduction in obesity. Here, we have used metabolomics to examine the metabolic perturbations in blood serum and liver and gastrocnemius tissues of the DTG mice. Multivariate statistics highlighted consistent metabolic changes in gastrocnemius muscle following Akt1 activation, which included significant reductions of serine and histidine-containing dipeptides (anserine and carnosine), in addition to increased concentrations of phosphorylated sugars. In addition, Akt1-mediated regression in obesity could be associated with increased glycolysis in gastrocnemius muscle as well as increased gluconeogenesis, glycogenolysis, and ketogenesis in the liver. In old DTG animals, Akt1 activation was found to improve glucose metabolism and confer a beneficial effect in the regression of age-related fat accumulation. This study identifies metabolic changes induced by Akt1-mediated muscle growth and demonstrates a cross-talk between distant organs that leads to a regression of fat mass. The current findings indicate that agents that promote Akt1 induction in muscle have utility in the regression of obesity.

Keywords: Protein kinase B; metabonomics; obesity; type 2 diabetes.

Figure 1

Obesity induced by a high-fat/high-sucrose diet could be regressed by Akt1 induction (A). The corresponding changes in tissue weight (B). Akt1 induction also conferred a reduction in age-related fat accumulation (C).

Figure 2

PLS-DA scores plot of the NMR spectra of gastrocnemius muscle tissue show separation between the controls (black squares) and DTG (red dots) mice (R²X = 43%, R²Y = 75%, Q² = 72%, for the first component) (A). Satisfactory cross-validation plot for the PLS-DA model demonstrating a robust PLS-DA model (B). Changes in a number of metabolites induced by Akt1 activation were found to be consistent across both diet and aging effects: anserine (C), anserine and carnosine (D), DHA (E), serine (F), phosphate (G), and phosphorylated sugars (H). Peak areas for young controls (C–G) or young DTG mice (H) from the aging study were normalized to 100 for comparison. (*P < 0.05, ** P < 0.01, and *** P < 0.001.)

Figure 3

Multiple sections of ¹H NMR spectra showing (A) a marked reduction of serum glucose concentration (glucose region: δ 3.22–3.91) following Akt1 activation in HF/HS-fed mice, (B) an increased hepatic concentration of β-hydroxybutyrate and reductions of lactate and alanine in the DTG mice, and (C) an increased concentration of betaine and a marked reduction of hepatic glucose concentration (glucose region: δ 3.22–3.92) in the DTG mice. The NMR spectra were obtained from an individual sample of each class after 4 weeks of Akt1 activation: black spectrum, the HF/HS-fed controls; red spectrum, the HF/HS-fed DTG mice. Spectra were scaled to the same relative noise level.

Figure 4

Increased blood glucose concentration associated with aging was reduced by Akt1 induction (A). This may be associated with increased glycolysis, as an increased concentration of lactate was detected in the hypertrophic muscle of the DTG animals (B).

Figure 5

PLS-DA scores plot of the LC–MS lipidomic data of liver tissue show separation between DTG mice fed the chow and HF/HS diets (A). Satisfactory cross-validation plot for the PLS-DA model demonstrating a robust PLS-DA model (B). Group separation was also observed between controls and the DTG mice fed with the HF/HS diet (C). PLS-DA scores plot of the LC–MS lipidomic data of gastrocnemius tissue showed separation between DTG mice fed the chow and HF/HS diets (D); the model passed cross-validation by random permutation test (E).

Figure 6

Profound metabolic perturbation as a result of Akt1 induction in the skeletal muscle of the HF/HS-fed DTG mice (red, increase in concentration; blue, decrease in concentration) as compared with the controls fed the same diet. Increased Cori cycle activity and hepatic fatty acid oxidation were evident in the DTG mice. Abbreviations: α-KG, α-ketoglutarate; β-HB, β-hydroxybutyrate; DMG, dimethylglycine; G6P, glucose-6-phosphate; M6P, mannose-6-phosphate.

Figure 7

For the HF/HS-fed animals, the concentrations of anserine and carnosine were negatively correlated with the lactate concentration in the gastrocnemius muscle (Pearson correlation coefficient, r = −0.90). A weaker correlation was observed when all data from both diet and aging studies were considered (r = −0.63).