Edited by: Jun Sugawara, National Institute of Advanced Industrial Science and Technology (AIST), Japan
Reviewed by: Noriaki Kawanishi, Chiba Institute of Technology, Japan; Mitsuharu Okutsu, Nagoya City University, Japan
This article was submitted to Exercise Physiology, a section of the journal Frontiers in Sports and Active Living
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Age-induced chronic inflammation is prevented by aerobic and resistance exercise training. However, the effects of the mechanism of exercise on chronic inflammation in each tissue remains unclear. The aim of this study was to investigate the effects of resistance and aerobic training on gene expression profiles for macrophage infiltration and polarization (M1/M2 ratio) with chronic inflammation in various tissues of aged model mice. Male 38-week-old SAMP1 (senescence-accelerated prone mouse 1) mice were randomly divided into three groups—sedentary (Aged-Sed-SAMP1), aerobic training (Aged-AT-SAMP1; voluntary running), and resistance training—for 12 weeks (Aged-RT-SAMP1; climbing ladder). Resistance and aerobic exercise training prevented an increase in circulating TNF-α levels (a marker of systemic inflammation) in aged SAMP1 mice, along with decreases in tissue inflammatory cytokine (TNF-α and IL-1β) mRNA expression in the heart, liver, small intestine, brain, aorta, adipose, and skeletal muscle, but it did not change the levels in the lung, spleen, and large intestine. Moreover, resistance and aerobic exercise training attenuated increases in F4/80 mRNA expression (macrophage infiltration), the ratio of CD11c/CD163 mRNA expression (M1/M2 macrophage polarization), and MCP-1 mRNA expression (chemokine: a regulator of chronic inflammation) in the chronic inflamed tissues of aged SAMP1 mice. These results suggested that resistance and aerobic exercise training-induced changes in gene expression for macrophage infiltration and polarization in various tissues might be involved in the prevention of age-related tissue chronic inflammation, and lead to a reduction of the increase in circulating TNF-α levels, as a marker of systemic inflammation, in aged SAMP1 mice.
Aging induces the dysregulation of immune function and leads to systemic inflammation (Woods et al.,
Regular aerobic exercise reduces the circulating levels of inflammatory markers, such as TNF-α and IL-6, in aged mice and humans (Packer and Hoffman-Goetz,
In this study, we aimed to elucidate whether resistance and aerobic exercise training altered the gene expression profiles for macrophages in various tissues of aged mice, which could potentially result in the attenuation of age-related chronic inflammation. We hypothesized that the effect of continuous exercise training on chronic inflammation-related gene profiles may differ between aerobic and resistance training. To test the specificity of different exercise training on age-related macrophage profiles in various tissues, we investigated the effects of resistance and aerobic training on gene expression for macrophage infiltration as well as polarization (from M1 to M2) with chronic inflammatory responses in various tissues of senescence-accelerated prone mouse 1 (SAMP1) mice, a model of aging mice. SAMP1 mice exhibit accelerated senescence and early occurrence of age-related chronic diseases, such as chronic inflammation of the arterial wall and adipose tissue, dysregulated immune function, senile amyloidosis, sarcopenia, and degenerative joint disease, without any experimental manipulation (Takeda et al.,
Ethical approval for this study was obtained from the Committee on Animal Care at Ritsumeikan University. Male senescence-accelerated prone mouse 1 (SAMP1) mice (8 weeks old) were obtained from Japan SLC (Shizuoka, Japan) and cared for according to the Guiding Principles for the Care and Use of Animals, based on the Declaration of Helsinki. The mice were housed individually in cages under controlled conditions on a 12:12 h light-dark cycle and were allowed
Post-treatment experiments on Aged-AT-SAMP1 and Aged-RT-SAMP1 mice were performed more than 48 h after the last exercise session to avoid the acute effects of each training exercise intervention. Additionally, chow was removed from the cages of all mice for 12 h, and after measuring the body weight, the blood samples were obtained from the orbital eye vessel under general anesthesia. The blood samples were collected in EDTA-coated tubes and immediately placed on ice. Plasma was isolated from whole blood by centrifugation (2,000 × g, 20 min at 4°C) and stored at −80°C until other assays were performed. In addition, the brain, heart, lung, liver, kidney, spleen, aorta, epididymal fat, small intestine, large intestine, quadriceps femoris muscle, and tibialis anterior (TA) muscle samples were resected quickly, rinsed in ice-cold saline, frozen in liquid nitrogen, and stored at −80°C for further analysis.
As indicated in previous studies, the Aged-RT-SAMP1 group completed resistance training three times a week for 12 weeks using a climbing ladder (90 cm, 1 cm grid, 80° incline) (Matheny et al.,
As indicated in previous studies, the Aged-AT-SAMP1 group exercised by voluntary running on a wheel (diameter 15.5 cm, Brain science idea, Osaka, Japan) (Littlefield et al.,
Quadriceps femoris muscle tissues (20 mg) were homogenized in 10 volumes of 250 mM sucrose, 1 mM Tris·HCl (pH 7.4), and 130 mM NaCl on ice using a Teflon homogenizer. The homogenate was centrifuged at 9,000 g for 20 min at 0°C, and the pellet was resuspended in homogenate buffer and centrifuged at 600 g for 10 min at 0°C. The resultant supernatant was centrifuged at 8,000 g for 15 min at 0°C, and the pellet was resuspended in 250 mM sucrose. To determine the citrate synthase activity, 8 μl of each sample was incubated for 2 min at 30°C in a 182-μl incubation mixture containing 100 mM Tris·HCl (pH 8.0), 1 mM 5,5-dithiobis [2-nitrobenzoic acid], and 10 mM acetyl-CoA. The reaction was initiated by the addition of 10 μl of 10 mM oxaloacetate and was then determined spectrophotometrically at 412 nm for 3 min.
Plasma TNF-α (R&D Systems, Minneapolis, MN, USA) concentration was determined using a high sensitivity TNF-α sandwich enzyme-linked immunosorbent assay (ELISA) kit. The absorbance was measured at 450 nm by microplate reader using an xMark microplate spectrophotometer (Bio-Rad Laboratories, Hercules, CA, USA).
Total tissue RNA in brain, lung, heart, liver, kidney, spleen, small intestine, large intestine, aorta, and TA tissues was isolated using the ISOGEN reagent (Nippon Gene, Toyama, Japan) and the RNeasy mini kit (QIAGEN, Hilden, Germany), as previously described (Matheny et al.,
All values are expressed as the mean ± SEM. Statistical evaluations were performed using one-way ANOVA. The Fisher
Thirty-eight-week-old senescence accelerated prone mouse 1 (SAMP1) mice carried out aerobic training (Aged-AT-SAMP1 group), resistance training (Aged-RT-SAMP1 group), or remained sedentary (Aged-Sed-SAMP1 group) for 12 weeks. Additionally, 25-week-old SAMP1 mice were used as a young sedentary (Young-Sed-SAMP1 group). Body weight was significantly lower in the Aged-RT-SAMP1 and Aged-AT-SAMP1 groups than in the Aged-Sed-SAMP1 group but did not change compared with that in the Young-Sed-SAMP1 group (
Animal characteristics.
Body weight (g) | 35.3 ± 1.1 | 36.4 ± 1.2 | 36.0 ± 3.7 |
33.9 ± 1.5 |
LV mass (mg) | 177.9 ± 13.1 | 196.2 ± 11.3 | 213.3 ± 6.2 | 182.7 ± 6.2 |
LV mass/body weight (mg/g) | 5.0 ± 0.3 | 5.4 ± 0.3 | 6.4 ± 0.3 |
5.7 ± 0.2 |
Adipose tissue mass (g) | 1.7 ± 0.1 | 1.4 ± 0.2 | 1.0 ± 0.2 |
1.2 ± 0.2 |
Tibialis anterior muscle mass (mg) | 53.8 ± 0.7 | 49.2 ± 1.5 | 51.7 ± 1.6 | 58.3 ± 1.1 |
TA muscle mass/body weight (mg/g) | 1.5 ± 0.04 | 1.4 ± 0.06 | 1.5 ± 0.08 | 1.8 ± 0.04 |
Muscle citrate synthase activity (mol/min/gtissue) | 13.2 ± 0.8 | 11.1 ± 0.7 |
15.2 ± 0.4 |
13.0 ± 0.7 |
Food intake (g/day) | 3.5 ± 0.1 | 3.2 ± 0.1 | 4.2 ± 0.5 |
3.2 ± 0.1 |
This study examined plasma TNF-α levels, which are a marker of systemic inflammation, in young and aged SAMP1 mice. Plasma TNF-α levels significantly increased in the Aged-Sed-SAMP1 group compared to those in the Young-Sed-SAMP1 group (
Effects of aging and exercise training on plasma TNF-α level. Young-Sed-SAMP1, young sedentary group; Aged-Sed-SAMP1, aged sedentary group; Aged-AT-SAMP1, aged aerobic training group; Aged-RT-SAMP1, aged resistance training group. The values are expressed as means ± SEM. **
To confirm the chronic inflammatory state in various tissues, we assessed mRNA expressions of inflammatory cytokines in various tissues. IL-6 mRNA expression in the adipose and the small intestine significantly increased in the Aged-Sed-SAMP1 group compared to that in the Young-Sed-SAMP1 group (
Effect of aging and exercise training on
To examine macrophage infiltration and polarization, we analyzed the expression of macrophage markers by mRNA in inflamed tissues. In the heart, liver, small intestine, aorta, adipose, and TA muscle samples of the Aged-Sed-SAMP1 group, F4/80 mRNA expression was significantly higher than that in the Young-Sed-SAMP1 group but was not altered in the brain (
Effects of aging and exercise training on
Since macrophage infiltration is regulated by MCP-1, we evaluated MCP-1 mRNA expression levels in inflamed tissues. MCP-1 mRNA expression in the heart, liver, small intestine, brain, aorta, adipose, and TA muscle significantly increased in the Aged-Sed-SAMP1 group compared to that in the Young-Sed-SAMP1 group, and the expression was significantly reduced by aerobic and resistance training (
Effects of aging and exercise training on
In this study, we revealed the preventive effects of different exercise programs (including aerobic and resistance training) on chronic inflammation in various tissues in aging mice. In aged SAMP1 mice, the elevation of circulating TNF-α levels, a marker of systemic inflammation, were attenuated by both exercise types, and this effect did not differ between the two types of training. Additionally, an increase in TNF-α and IL-1β mRNA expression levels in the aorta, heart, liver, small intestine, adipose, and skeletal muscle in the aged mice was observed; these elevated expression levels were attenuated by both exercise programs. Interestingly, no significant change in TNF-α and IL-1β mRNA expression levels in the spleen, large intestine, and lung were seen in the two trained mice. Thus, the preventative effects of exercise on age-induced increases in TNF-α and IL-1β mRNA expression levels in local tissues may contribute to the attenuated effect of increase in circulating TNF-α level, as a marker of systemic inflammation. Moreover, even if the exercise manner is different, as with aerobic and resistance training programs, the effects gained from the exercises may be similarly obtained.
Macrophage infiltration and the balance of macrophage polarization are key regulators of chronic inflammation in tissues, and chemokine, such as MCP-1, is required for macrophage infiltration (Oh et al.,
MCP-1 plays a crucial role in macrophage migration and inflammatory reaction under inflammatory conditions (Mantovani et al.,
In this study, we revealed for the first time that there is no difference in the preventive effect of resistance and aerobic training on chronic inflammation with aging. However, the mechanism underlying these immune responses is unclear. Acute exercise-induced secretions of catecholamine may be involved in an underlying mechanism for the inhibition of chronic inflammation. In previous human studies, resistance training has shown to increase blood catecholamine levels (Okamoto et al.,
Furthermore, macrophages are involved in chronic inflammation in tissues. Previous studies have observed that aged mice exhibit a high expression of inflammatory markers and macrophage markers in the liver, adipose, and aorta (Lesniewski et al.,
This study examined the mRNA expression levels of several inflammatory parameters, such as TNF-α, IL-1β, IL-6, and MCP-1. Since changes in protein expression levels reflect functional adaptations, future studies should examine not only mRNA levels but also protein expression and concentration levels. Furthermore, we investigated the mRNA expression levels of F4/80, CD11c, and CD206, the molecular markers of macrophage infiltration and M1 and M2 macrophages, respectively. However, F4/80 mRNA expression in the adipose tissue of obese mice reflected macrophage activation rather than infiltration (Bassaganya-Riera et al.,
In summary, resistance and aerobic exercise training might ameliorate gene expression profiles for macrophage infiltration and polarization in various tissues of aged SAMP1 mice, and these alterations might be involved in the prevention of age-related tissue chronic inflammation and lead to a reduction of the increase in circulating TNF-α level, as a marker of systemic inflammation, in aged SAMP1 mice.
All datasets generated for this study are included in the manuscript/supplementary files.
Ethical approval for this study was obtained from the Committee on Animal Care at Ritsumeikan University (BKC2017-024).
MI, MU, and NHo designed research and wrote the paper. MI, MU, NHo, NHa, SF, EO, and HY performed research. MU and NHo analyzed data.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.