Antioxidant Molecular Brain Changes Parallel Adaptive Cardiovascular Response to Forced Running in Mice

Abstract

Physically active lifestyle has huge implications for the health and well-being of people of all ages. However, excessive training can lead to severe cardiovascular events such as heart fibrosis and arrhythmia. In addition, strenuous exercise may impair brain plasticity. Here we investigate the presence of any deleterious effects induced by chronic high-intensity exercise, although not reaching exhaustion. We analyzed cardiovascular, cognitive, and cerebral molecular changes in young adult male mice submitted to treadmill running for eight weeks at moderate or high-intensity regimens compared to sedentary mice. Exercised mice showed decreased weight gain, which was significant for the high-intensity group. Exercised mice showed cardiac hypertrophy but with no signs of hemodynamic overload. No morphological changes in the descending aorta were observed, either. High-intensity training induced a decrease in heart rate and an increase in motor skills. However, it did not impair recognition or spatial memory, and, accordingly, the expression of hippocampal and cerebral cortical neuroplasticity markers was maintained. Interestingly, proteasome enzymatic activity increased in the cerebral cortex of all trained mice, and catalase expression was significantly increased in the high-intensity group; both first-line mechanisms contribute to maintaining redox homeostasis. Therefore, physical exercise at an intensity that induces adaptive cardiovascular changes parallels increases in antioxidant defenses to prevent brain damage.

Keywords: brain resilience; cardiac remodeling; catalase; physical exercise; proteasome; redox homeostasis; treadmill running; young male mice.

Figure 1

Daily treadmill training induced a body weight decrease in mice. (a) Body weight curves; (b) relative body weight curves. Experimental groups: SED, sedentary; MOD, moderate training; INT, high-intensity training. Values are mean ± SEM ((a,b) SED n = 15, MOD n = 15, INT n = 12). ANOVA statistics: Ex, factor exercise; Ti, factor time; see text for post hoc results.

Figure 2

Exercise training induced a resting heart rate decrease. Individually paired data of electrocardiograms previous (PRE) and posterior (POST) to the training period. (a) Heart rate and paired electrocardiograms of a representative INT mouse with indication of RR interval; (b) PR interval; (c) QRS interval; (d) QTc interval. Experimental groups: SED, sedentary; MOD, moderate training; INT, high-intensity training. Values are individual mouse data for each group ((a,b) SED n = 11, MOD n = 9, INT n = 10; (c,d) SED n = 11, MOD n = 8, INT n = 10). ANOVA statistics: Ex, factor exercise; Ti, factor time. Bonferroni test *** p < 0.001.

Figure 3

Exercise training induced mild cardiac hypertrophy. (a) Heart weight; (b) relative heart weight; (c) tibial length; (d) N-terminal pro B-type natriuretic peptide (NT-proBNP). Experimental groups: SED (orange circles), sedentary; MOD (green squares), moderate training; INT (blue triangles), high-intensity training. Values are mean ± SEM ((a–c) SED n = 15, MOD n = 15, INT n = 12); (d) SED n = 14, MOD n = 14, INT n = 12). Statistics: There was a significant ANOVA effect of exercise treatment without post hoc test significances in (a) and a borderline significant effect in (b).

Figure 4

Exercise training did not induce gross morphological changes in the aorta. (a) Area of the aorta lumen; (b) area of a transversal section of the tunica media; (c) representative histological images of the aorta section with arrows pointing to dots indicating the internal and external limit of the tunica media. Experimental groups: SED (orange circles), sedentary; MOD (green squares), moderate training; INT (blue triangles), high-intensity training. Values are mean ± SEM ((a,b) SED n = 7, MOD n = 10, INT n = 10). Scale bar = 100 µm in (c).

Figure 5

Exercise training improved motor coordination and maintained learning and memory skills. (a) Distance traveled on a squared wooden rod; (b) distance traveled on a round metal rod; (c) discrimination index (D.I.) in the novel object recognition test (NORT); (d) discrimination index (D.I.) in the novel object location test (NOLT). Experimental groups: SED (orange circles), sedentary; MOD (green squares), moderate training; INT (blue triangles), high-intensity training. Values are mean ± SEM ((a–d) SED n = 6, MOD n = 5, INT n = 6). Statistics: There was a significant ANOVA effect of exercise treatment in (a) without post hoc test significance.

Figure 6

Synaptic markers synaptophysin and PSD95 were not modified by exercise in young mice. (a–c) Levels of synaptophysin in the cerebral cortex (CC) and hippocampus (HC), as indicated, and representative blots of experimental groups; (d–f) levels of PSD95 in cerebral cortex and hippocampus and representative blots. Experimental groups: SED (orange circles), sedentary; MOD (green squares), moderate training; INT (blue triangles), high-intensity training. Values are mean ± SEM ((a) SED n = 14, MOD n = 15, INT n = 14; (b,e) SED n = 8, MOD n = 8, INT n = 8; (d) SED n = 14, MOD n = 13, INT n = 11).

Figure 7

Proteolytic activity of the proteasome was increased by exercise. Caspase-like enzymatic activity (a), trypsin-like activity (b), and chymotrypsin-like activity (c) were determined in cerebral cortical tissue. Experimental groups: SED (orange circles), sedentary; MOD (green squares), moderate training; INT (blue triangles), high-intensity training. Values are mean ± SEM ((a) SED n = 13, MOD n = 15, INT n = 12; (b) SED n = 13, MOD n = 14, INT n = 12; (c) SED n = 14, MOD n = 15, INT n = 12). Statistics: There was a significant ANOVA effect of exercise treatment in (b) with post hoc test *** p < 0.001 for both MOD and INT in comparison to the SED group.

Figure 8

Protein levels of proteasome subunits were modified by exercise. HSP70 (a), 19S proteasome cap (b), and representative blots of each experimental group (c); 20S proteasome core (d) proteasome subunit β2 (e) and representative blots (f). Proteins were determined in cerebral cortical tissue. Experimental groups: SED (orange circles), sedentary; MOD (green squares), moderate training; INT (blue triangles), high-intensity training. Values are mean ± SEM ((a) SED n = 14, MOD n = 15, INT n = 12; (b) SED n = 8, MOD n = 8, INT n = 8; (d) SED n = 12, MOD n = 11, INT n = 11; (e) SED n = 14, MOD n = 15, INT n = 13). Statistics: There was a significant ANOVA effect of exercise treatment in (f) with post hoc test *** p < 0.001 in comparison to the SED group.

Figure 9

Increase in antioxidant defense and absence of oxidative stress in exercised mice. Levels of proteins labeled with 4-HNE (a) and nitrotyrosine (b), including corresponding representative blots; mRNA levels of Nfe2l2 (c), Cat (d), and Sod2 genes (e). Analyses were performed on cerebral cortical tissue. Experimental groups: SED (orange circles), sedentary; MOD (green squares), moderate training; INT (blue triangles), high-intensity training. Values are mean ± SEM ((a,b) SED n = 6, MOD n = 6, INT n = 6; (c,e) SED n = 11, MOD n = 11, INT n = 11; (d) SED n = 11, MOD n = 11, INT n = 10). Statistics: There was a significant ANOVA effect of exercise treatment in (d) with post hoc test * p < 0.05 in comparison to the SED group.