Exercise reduces metabolic burden while altering the immune system in aged mice

Abstract

Although several evidence has suggested the impact of exercise on the prevention of aging phenotypes, few studies have been conducted on the mechanism by which exercise alters the immune-cell profile, thereby improving metabolism in senile obesity. In this study, we confirmed that 4-week treadmill exercise sufficiently improved metabolic function, including increased lean mass and decreased fat mass, in 88-week-old mice. The expression level of the senescence marker p16 in the white adipose tissue (WAT) was decreased after 4-weeks of exercise. Exercise induced changes in the profiles of immune-cell subsets, including natural killer (NK) cells, central memory CD8⁺ T cells, eosinophils, and neutrophils, in the stromal vascular fraction of WAT. In addition, it has been shown through transcriptome analysis of WAT that exercise can activate pathways involved in the interaction between WAT and immune cells, in particular NK cells, in aged mice. These results suggest that exercise has a profound effect on changes in immune-cell distribution and senescent-cell scavenging in WAT of aged mice, eventually affecting overall energy metabolism toward a more youthful state.

Keywords: NK cell; aging; exercise; immunosenescence; metabolism.

Figure 1

Schematic design for exercise protocol. 9-week-old and 84-week-old mice were divided into sedentary or exercise group. After 1day habituation in the room where treadmill is, mice were adapted in treadmill for 2 days. Then speed of treadmill was gradually increased (2 m/min weekly) during 4 weeks.

Figure 2

Analysis of energy metabolism during exercise in young and aged mice. (A–F) Metabolic measurements were performed in young control, young exercise, old control, and old exercise groups (n = 5, respectively) in CLAMS metabolic cages after 4-week of exercise. (A) Kinetic data for VO₂ (mg/kg/hr) consumption are shown as mean for each time point in young control (YC; blue circles), young exercise (YE; red rectangles), old control (OC; green triangles) and old exercise (OE, purple reversed triangles) groups. (B) Average VO₂ (mg/kg/hr) are shown for total, night (dark) and day (light) cycles. (C) Kinetic data for VCO₂ (mg/kg/hr) production are shown as mean for each time point in YC, YE, OC, and OE groups. (D) Average VCO₂ (mg/kg/hr) production are shown for total, night (dark) and day (light) cycles. (E) Kinetic data for respiratory exchange ratio (RER) is shown as mean for each time point in YC, YE, OC, and OE groups. (F) Average RER are shown for total, night (dark) and day (light) cycles. (G–H) Average percent body fat (G) and lean mass (H) for YC, YE, OC, and OE were measured using Minispec LF-50. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001.

Figure 3

Effect of exercise on Immune cell profiling in SVF and spleen of young and aged mice. Bar graph and dot plots depict the frequencies of central memory (CM, CD62L⁺CD44⁺) CD4⁺ T cells (A); the frequencies of CM CD8⁺ T cells (B); the frequencies of NK (NK1.1⁺TCRβ^-) cells (C); the frequencies of eosinophils (F4/80⁺Siglec-F⁺) (D); and the frequencies of neutrophils (F4/80^-CD11c^-CD11b⁺Ly6G⁺) (E) in SVF.

Figure 4

Impact of exercise on a senescence marker, p16 and energy regulating enzyme in adipose tissues of aged mice. (A) p16 and GAPDH were measured through immuno-blotting in the white adipose tissue (WAT) of both young and old mice after 4-week of treadmill exercise or sedentariness. Representative 3 samples per group are shown (total n=5, each group). (B) Bar graph depicts the mean (± standard error of the mean, SEM) intensity ratio of p16 to GAPDH bands measured using ImageJ program. *p < 0.05 compared to old sedentary controls, **p < 0.01 compared to young sedentary controls or exercise groups.

Figure 5

Exercise-induced altered gene expression in adipose tissue of aged mice. Gene ontology based- bioinformatic analysis (A) Heatmap represents grouping of genes through Hierarchical clustering (Euclidean Method, Complete Linkage) using the expression level (normalized value). (B) Panel shows the similarity between samples in two dimensions using the normalized signal of each sample.

Figure 6

Gene Ontology Enrichment analysis. (A, B) Enrichment results for the top 20 GO terms in (A) OC vs YC and (B) OE vs OC that satisfy adjusted p-value < 0.05 for each GO category are plotted. Dot size indicates Gene Ratio.