Glucose transporter 4-deficient hearts develop maladaptive hypertrophy in response to physiological or pathological stresses

Abstract

Pathological cardiac hypertrophy may be associated with reduced expression of glucose transporter 4 (GLUT4) in contrast to exercise-induced cardiac hypertrophy, where GLUT4 levels are increased. However, mice with cardiac-specific deletion of GLUT4 (G4H^-/-) have normal cardiac function in the unstressed state. This study tested the hypothesis that cardiac GLUT4 is required for myocardial adaptations to hemodynamic demands. G4H^-/- and control littermates were subjected to either a pathological model of left ventricular pressure overload [transverse aortic constriction (TAC)] or a physiological model of endurance exercise (swim training). As predicted after TAC, G4H^-/- mice developed significantly greater hypertrophy and more severe contractile dysfunction. Somewhat surprisingly, after exercise training, G4H^-/- mice developed increased fibrosis and apoptosis that was associated with dephosphorylation of the prosurvival kinase Akt in concert with an increase in protein levels of the upstream phosphatase protein phosphatase 2A (PP2A). Exercise has been shown to decrease levels of ceramide; G4H^-/- hearts failed to decrease myocardial ceramide in response to exercise. Furthermore, G4H^-/- hearts have reduced levels of the transcriptional coactivator peroxisome proliferator-activated receptor-γ coactivator-1, lower carnitine palmitoyl-transferase activity, and reduced hydroxyacyl-CoA dehydrogenase activity. These basal changes may also contribute to the impaired ability of G4H^-/- hearts to adapt to hemodynamic stresses. In conclusion, GLUT4 is required for the maintenance of cardiac structure and function in response to physiological or pathological processes that increase energy demands, in part through secondary changes in mitochondrial metabolism and cellular stress survival pathways such as Akt.NEW & NOTEWORTHY Glucose transporter 4 (GLUT4) is required for myocardial adaptations to exercise, and its absence accelerates heart dysfunction after pressure overload. The requirement for GLUT4 may extend beyond glucose uptake to include defects in mitochondrial metabolism and survival signaling pathways that develop in its absence. Therefore, GLUT4 is critical for responses to hemodynamic stresses.

Keywords: cardiac hypertrophy; exercise training; glucose metabolism; heart failure; mitochondrial metabolism; pressure overload.

Fig. 1.

Loss of cardiac glucose transporter 4 (GLUT4) increases pathological remodeling after transverse aortic constriction (TAC). A: representative gross images of whole hearts from control (Con) and cardiomyocyte-specific GLUT4 knockout (G4H^−/−) mice ~3 wk after sham (Sham) or TAC surgery. B: biventricular heart weight (BV)-to-tibia length (TL) ratios. C: wet lung weight (WLW)-to-TL ratios. D: histological images of hematoxylin and eosin-stained cardiac sections (magnification: ×20). E: histological assessment of fibrosis by picrosirius red staining (magnification: ×20). Graphical data are shown as means ± SE; n = 9–15. *P < 0.05 vs. Con-Sham; $P < 0.05 vs. all. Two-way ANOVA showed a significant genotype effect on BV/TL and a significant treatment effect on BV/TL.

Fig. 2.

Echocardiographic analysis of in vivo cardiac dimensions and function in control (Con) and glucose transporter 4 knockout (G4H^−/−) mice ~3 wk after sham (Sham) or transverse aortic constriction (TAC) surgery. A: representative M-mode echocardiograms. B−F: heart rate (B), ejection fraction (C), and measures at diastole for left ventricular internal diameter (LVIDd), left ventricular posterior wall thickness (LVPWd), and interventricular septum thickness (IVSd; D–F). BPM, beats/min. Graphical data are shown as means ± SE; n = 9–15. $P < 0.05 vs. all. Two-way ANOVA showed a significant interaction of treatment and genotype for ejection fraction and LVIDd.

Fig. 3.

Left ventricular catheterization for in vivo hemodynamic measurements in control (Con) and glucose transporter 4 knockout (G4H^−/−) mice ~3 wk after sham (Sham) or transverse aortic constriction (TAC) surgery. A and B: left ventricular systolic pressure (LV SP) and end-diastolic pressure (LV EDP). C: rate of rise (+dP/dt) and fall (−dP/dt) of LV pressure. D: LV developed pressure (LV DevP). E: isovolumic relaxation constant (τ). Graphical data are shown as means ± SE; n = 5–7. *P < 0.05 vs. Con-Sham; #P < 0.05 vs. Con-TAC; ‡P < 0.05 vs. G4H^−/−-Sham. Two-way ANOVA showed a significant genotype effect on +dP/dt, −dP/dt, LV SP, and LV DevP and significant treatment effect on LV SP, LV EDP, LV DevP, and τ.

Fig. 4.

Systemic and cardiac changes in control (Con) and glucose transporter 4 knockout (G4H^−/−) mice after ~3 wk of swim training (Swim). A−D: biventricular weight (BV)-to-body weight (BW) ratio (A), BW (B), BV-to-tibia length (TL) ratio (C), and gastrocnemius skeletal muscle whole cell lysate citrate synthase (CS) activity (D). E and F: histological examination using wheat germ agglutinin (WGA) with quantification. G and H: histological examination using picrosirius red and trichrome. Sed, sedentary. Graphical data are shown as means ± SE; n = 15–26 for A–C and n = 3–7 for D–H. *P < 0.05 vs. Con-Sed; #P < 0.05 vs. Con-Swim; ‡P < 0.05 vs. G4H^−/−-Sed. $P < 0.05 for two-way ANOVA genotype effect. There was a significant treatment effect on body weight, genotype effect on BV/TL, and interaction of treatment and genotype for CS activity.

Fig. 5.

Echocardiography for in vivo cardiac measurements ~3 wk after swim training (Swim) or in sedentary (Sed) control (Con) and glucose transporter 4 knockout (G4H^−/−) mice. A−F: representative M-mode echocardiograms (A), heart rate (B), ejection fraction (C), and measures at diastole for left ventricular internal diameter (LVIDd), left ventricular posterior wall thickness (LVPWd), and interventricular septum thickness (IVSd; D–F). BPM, beats/min. Graphical data are shown as means ± SE; n = 12–18. *P < 0.05 vs. Con-Sed; #P < 0.05 vs. Con-Swim. Two-way ANOVA showed a significant genotype effect on LVIDd and a significant interaction of treatment and genotype for LVPWd.

Fig. 6.

Substrate oxidation and contractile function in isolated perfused working hearts (IWH). Palmitate oxidation (A), myocardial O₂ consumption (MV̇o₂; B), cardiac power (C), heart rate (D), cardiac output (E), left ventricular diastolic pressure (LVDP; F), and rate-pressure product (RPP; G) measured in IWH are shown. In a separate cohort of mice, cardiac tissue was snap frozen and used for diacylglycerol (H) or ceramide (I) measurements. Sed, sedentary; Swim, swim training; Con, control; dhw, dry heart weight; whw, wet heart weight; BPM, beats/min. Graphical data are shown as means ± SE; n = 6–11 for A–G and n = 5 for H and I. *P < 0.05 vs. Con-Sed; #P < 0.05 vs. Con-Swim. Two-way ANOVA showed a significant genotype effect on LVDP, a significant treatment effect on heart rate and cardiac output, and significant interaction of treatment and genotype for palmitate oxidation and MV̇o₂.

Fig. 7.

Histological examination of cardiac changes in control (Con) and glucose transporter 4 knockout (G4H^−/−) mouse hearts after ~3 wk of swim training (Swim). A−C: cleaved caspase-3 (A), TUNEL (B), and 4-hydroxynonenal (4-HNE; C). Sed, sedentary. Graphical data are shown as means ± SE; n = 3. *P < 0.05 vs. Con-Sed; #P < 0.05 vs. Con-Swim. Two-way ANOVA showed a significant genotype effect on 4-HNE.

Fig. 8.

Protein examination of cardiac changes in control (Con) and glucose transporter 4 knockout (G4H^−/−) mouse hearts after ~3 wk of swim training (Swim) and changes in gene expression and markers of mitochondrial oxidative capacity in nonstressed G4H^−/− mouse hearts. A: Western blot analysis of whole cell lysate from biventricular tissue. B: gene expression analysis by quantitative PCR (qPCR; see Table 2 for full gene names). C−E: carnitine palmitoyl-transferase (CPT) activity (C), hydroxyacyl-CoA dehydrogenase (HADH) activity (D), and citrate synthase activity (E). Sed, sedentary; a.u., arbitrary units. Graphical data are shown as means ± SE; n = 4–6 for A, n = 3 for B, and n = 4–6 for C–E. *P < 0.05 vs. Con-Sed; #P < 0.05 vs. Con-Swim; $P < 0.05 vs. G4H^−/−-Sed. Two-way ANOVA showed a significant genotype effect on the protein phosphatase 2A C-subunit (PP2A-C) and inhibitor 2 of PP2A (I2PP2A) and a significant interaction of treatment and genotype for phosphorylated (P-)Ser⁴⁷³ Akt.