Age-Dependent Skeletal Muscle Mitochondrial Response to Short-Term Increased Dietary Fructose

Abstract

The harmful effect of a long-term high-fructose diet is well established, but the age-dependent physiological responses that can be triggered by a short-term high-fructose diet in skeletal muscles have not been deeply explored. Therefore, the aim of this work was to compare the alterations in mitochondrial energetic and insulin responsiveness in the skeletal muscle induced by a short-term (2 weeks) fructose feeding in rats of different ages. For this purpose, fructose and uric acid levels, insulin sensitivity, mitochondrial bioenergetics and oxidative status were evaluated in the skeletal muscles from young (30 days old) and adult (90 days old) rats. We showed that, even in the short term, a high-fructose diet has a strong impact on skeletal muscle metabolism, with more marked effects in young rats than in adults ones. In fact, despite both groups showing a decrease in insulin sensitivity, the marked mitochondrial dysfunction was found only in the young rats, thus leading to an increase in the mitochondrial production of ROS, and therefore, in oxidative damage. These findings underscore the need to reduce fructose consumption, especially in young people, to preserve the maintenance of a metabolically healthy status.

Keywords: fructose; insulin resistance; mitochondria; oxidative stress; proton leak; skeletal muscle.

Figure 1

Skeletal muscle insulin signalling. (a) Skeletal muscle insulin sensitivity index, Western blot quantification (with representative Western blots) of (b) p-Akt, (c) p-GSK, (d) glucose transporter 4 (GLUT-4) and (e) content of glycogen in skeletal muscle in young and adult rats fed a control (young-C and adult-C) or fructose-rich diet (young-F and adult-F) for 2 weeks. Values are the means ± SEM of eight different rats. * p < 0.05, ** p < 0.01 compared to respective controls (two-way ANOVA followed by Tukey post-test).

Figure 2

Composition of skeletal muscle (a) Content of fructose, (b) uric acid, (c) glucose transporter 5 (GLUT-5), (d) fatty acid synthase (FAS) activity, (e) triglycerides and (f) ceramide in skeletal muscles of young and adult rats fed a control (young-C and adult-C) or fructose-rich diet (young-F and adult-F) for 2 weeks. Values are the means ± SEM of eight different rats. * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001 compared to respective controls (two-way ANOVA followed by Tukey post-test).

Figure 3

Markers of oxidative status. (a) Lipid peroxidation in skeletal muscle homogenates and (b) isolated mitochondria, (c) activities of NADPH oxidase, (d) xanthine oxidase, (e) antioxidant enzymes catalase, (f) cellular superoxide dismutase (SOD) and (g) mitochondrial SOD in young and adult rats fed a control (young-C and adult-C) or fructose-rich diet (young-F and adult-F) for 2 weeks. Values are the means ± SEM of eight different rats. * p < 0.05, *** p < 0.001, **** p < 0.0001 compared to respective controls; # p < 0.05, ## p < 0.01, #### p < 0.0001 compared to young-C rats (two-way ANOVA followed by Tukey post-test). TBARS = thiobarbituric acid related substances.

Figure 4

Mitochondrial markers. (a–d) Mitochondrial oxygen consumption and activities of (e) cytochrome oxidase and (f) citrate synthase measured in skeletal muscle isolated mitochondria of young and adult rats fed a control (young-C and adult-C) or fructose-rich diet (young-F and adult-F) for 2 weeks. Values are the means ± SEM of eight different rats. * p < 0.05, ** p < 0.01, *** p < 0.001 compared to respective controls; # p < 0.05, ### p < 0.001 compared to young-C rats (two-way ANOVA followed by Tukey post-test).

Figure 5

Mitochondrial complexes. (e) Complex I, (d) complex II, (b) complex III, (c) complex IV, and (a) complex V, together with representative Western blots, which were normalized via Ponceau staining (f), assessed in isolated mitochondria from young and adult rats fed a control (young-C and adult-C) or fructose-rich diet (young-F and adult-F) for 2 weeks. Values are the means ± SEM of eight different rats. * p < 0.05 compared to respective controls (two-way ANOVA followed by Tukey post-test).

Figure 6

Mitochondrial proton leak. (a) Basal and (b) palmitate-induced proton leak kinetics, (c,d) oxygen consumption at the highest common membrane potential, (e) Western blot quantification via Ponceau staining (with representative Western blots) of UCP-3 and (f) ANT in isolated mitochondria from skeletal muscles of young and adult rats fed a control (young-C and adult-C) or fructose-rich diet (young-F and adult-F) for 2 weeks. Values are the means ± SEM of eight different rats. * p < 0.05, **** p < 0.0001, compared to respective controls; # p < 0.05, #### p < 0.0001 compared to young-C rats (two-way ANOVA followed by Tukey post-test).