Exercise training enhances white adipose tissue metabolism in rats selectively bred for low- or high-endurance running capacity

Abstract

Impaired visceral white adipose tissue (WAT) metabolism has been implicated in the pathogenesis of several lifestyle-related disease states, with diminished expression of several WAT mitochondrial genes reported in both insulin-resistant humans and rodents. We have used rat models selectively bred for low- (LCR) or high-intrinsic running capacity (HCR) that present simultaneously with divergent metabolic phenotypes to test the hypothesis that oxidative enzyme expression is reduced in epididymal WAT from LCR animals. Based on this assumption, we further hypothesized that short-term exercise training (6 wk of treadmill running) would ameliorate this deficit. Approximately 22-wk-old rats (generation 22) were studied. In untrained rats, the abundance of mitochondrial respiratory complexes I-V, citrate synthase (CS), and PGC-1 was similar for both phenotypes, although CS activity was greater than 50% in HCR (P = 0.09). Exercise training increased CS activity in both phenotypes but did not alter mitochondrial protein content. Training increased the expression and phosphorylation of proteins with roles in β-adrenergic signaling, including β3-adrenergic receptor (16% increase in LCR; P < 0.05), NOR1 (24% decrease in LCR, 21% decrease in HCR; P < 0.05), phospho-ATGL (25% increase in HCR; P < 0.05), perilipin (25% increase in HCR; P < 0.05), CGI-58 (15% increase in LCR; P < 0.05), and GLUT4 (16% increase in HCR; P < 0.0001). A training effect was also observed for phospho-p38 MAPK (12% decrease in LCR, 20% decrease in HCR; P < 0.05) and phospho-JNK (29% increase in LCR, 20% increase in HCR; P < 0.05). We conclude that in the LCR-HCR model system, mitochondrial protein expression in WAT is not affected by intrinsic running capacity or exercise training. However, training does induce alterations in the activity and expression of several proteins that are essential to the intracellular regulation of WAT metabolism.

Keywords: exercise; lipolysis; metabolism; mitochondria; white adipose tissue.

Figures

Fig. 1.

Body mass (A), epididymal fat pad mass (B), and white adipose tissue (WAT) total protein (C) for low- (LCR; open bars) and high-capacity running rats (HCR; filled bars) with or without exercise training. Values are means ± SE; n = 8–10/group. Significance is reported where P < 0.05. *Main effect for running capacity; †main effect for training; ‡interaction between running capacity and training; adifferent from LCR-sedentary (SED); bdifferent from HCR-SED; cdifferent from LCR-exercise trained (EX); ddifferent from HCR-EX.

Fig. 2.

A: citrate synthase activity of epididymal WAT from LCR (open bars) and HCR rats (filled bars) with or without exercise training. Values are means ± SE; n = 8–10/group. Significance is reported where P < 0.05. †Main effect for training; adifferent from LCR-SED; ddifferent from HCR-EX. B: representative immunoblots of mitochondrial proteins. CI, respiratory complex I; CII, respiratory complex II; CIII, respiratory complex III; CIVIV, respiratory complex IV, subunit IV; PGC-1, peroxisome proliferator-activated receptor-γ coactivator-1.

Fig. 3.

Representative immunoblots and relative protein expression of β3-adrenergic receptor (β3-AR; A), phospho- total adipose triglyceride lipase (ATGL)S406 (B), ATGL (C), perilipin 1 (PLIN1; D), and comparative gene identification-58 (CGI-58; E) in epididymal WAT from LCR (open bars) and HCR rats (filled bars) with or without exercise training. Values are means ± SE; n = 8–10/group. Significance is reported where P < 0.05. *Main effect for running capacity; †main effect for training; ‡interaction between running capacity and training; adifferent from LCR-SED; bdifferent from HCR-SED; cdifferent from LCR-EX; ddifferent from HCR-EX. AU, arbitrary units.

Fig. 4.

Representative immunoblots and relative protein expression of neuron-derived orphan receptor 1 (NOR1; A) and glucose transporter 4 (GLUT4; B) in epididymal WAT from LCR (open bars) and HCR rats (filled bars) with or without exercise training. Values are means ± SE; n = 8–10/group. Significance is reported where P < 0.05. *Main effect for running capacity; †main effect for training; adifferent from LCR-SED; bdifferent from HCR-SED; cdifferent from LCR-EX; ddifferent from HCR-EX.

Fig. 5.

Representative immunoblots and relative protein expression of phospho-p38 MAPKT180/Y182 and total p38 MAPK (A), phospho-JNK1/2T183/Y185 and total JNK1/2 (B), and phospho-ERK1/2T202/Y204 and total ERK1/2 in epididymal WAT (C) from LCR (open bars) and HCR rats (filled bars) with or without exercise training. Values are means ± SE; n = 8–10/group. Significance is reported where P < 0.05. †Main effect for training; adifferent from LCR-SED; cdifferent from LCR-EX; ddifferent from HCR-EX.