Exercise and macrophage phenotype in obese mice • 105

Exercise training inhibits inflammation in adipose
tissue via both suppression of macrophage
infiltration and acceleration of phenotypic switchingfrom M1 to M2 macrophages in high-fat-dietinduced obese mice
Noriaki Kawanishi 1, Hiromi Yano2*, Yuka Yokogawa2, Katsuhiko Suzuki 3
1 Graduate School of Sport Sciences and 3 Faculty of Sport Sciences, Waseda

University, Tokorozawa, Saitama, and 2 Department of Health and Sports Science,
Kawasaki University of Medical Welfare, Kurashiki, Okayama, Japan

ABSTRACT
Purpose: Recent studies suggest that exchange of macrophage phenotype(M1/M2) in adipose tissue is associated with chronic low-grade inflammation in
obesity. M1 macrophages enhance a chronic inflammatory state in adipose tissues, whereas M2 macrophages inhibit it. Although exercise training might inhibit
pro-inflammatory cytokine gene expression in adipose tissue, it remains unclear
whether exercise training affects the phenotypic switch of macrophage polarization in adipose tissue. Therefore, we investigated the effect of exercise training on
the macrophage phenotypic switch in adipose tissue in high-fat-induced obese
mice. Methods: Male C57BL/6 mice were divided into four groups; normal diet(ND) control (n=7), ND exercise (n=7), high-fat-diet (HFD) control (n=12), and
HFD exercise (n=12) groups. All exercised mice ran on a treadmill at 12-20
m/min for 60 min/day for 16 weeks. Tumor necrosis factor (TNF)-α, interleukin(IL)-6, F4/80, monocyte chemotactic protein (MCP)-1, CXCL14, inter-cellularadhesion molecule (ICAM)-1, vascular-cellular adhesion molecule (VCAM)-1,
CD11c, CD163 and toll-like receptor (TLR)4 mRNA expressions in adipose tissue
were evaluated by real time-RT-PCR. Results: In HFD mice, exercise training did
not induce loss of body or adipose tissue mass, exercise training neverthelessmarkedly inhibited TNF-α and F4/80 mRNA expression in adipose tissue. The
exercise training attenuated HFD-induced increase in ICAM-1 mRNA expression,
but not MCP-1, CXCL14 and VCAM-1 mRNA expressions. In addition, increased

Corresponding author: Hiromi Yano*
Department of Health and Sports Science, Kawasaki University of Medical Welfare,
288 Matsushima, Kurashiki, Okayama 701-0193, Japan
Phone: +81-86-462-1111, FAX: +81-86-464-1109
E-mail: yanohiro@mw.kawasaki-m.ac.jp

106 • Exercise and macrophage phenotype in obese miceCD11c mRNA expression, which is a M1 macrophage specific marker, with HFD
treatment was attenuated by exercise training. In contrast, although the mRNA
expression of CD163, a M2 macrophage specific marker, in adipose tissue wassignificantly decreased by HFD, the exercise training significantly increased its
expression. Also, the higher mRNA expression of TLR4, which induces pro-inflammatory cytokine production after fatty acid recognition, was strongly inhibited by
the exercise training in HFD mice. Conclusion: Exercise training might induce
the phenotypic switching from M1 macrophage to M2 macrophage in obese adipose tissue besides inhibiting M1 macrophage infiltration into adipose tissue.
Therefore, chronic exercise might contribute to inhibit inflammation in adipose
tissue via down regulation of TLR4.
Key words: F4/80, CD11c, CD163, TLR4, real-time PCR

INTRODUCTION
It has been reported that obesity and inactivity are associated with chronic inflammatory diseases, such as type II diabetes and arteriosclerosis (1, 2). In fact, highplasma concentrations of pro-inflammatory cytokines (e.g. tumor necrosis factor(TNF)-α and interleukin (IL)-6) in type II diabetes patients are observed (3), andthese cytokines contribute insulin resistance (4). Recent studies have been conducted to examine the influence of obesity on inflammation. There is evidence
that the expression of pro-inflammatory cytokines, chemokines and cell adhesion
molecules in adipose tissue are increased in obese mice (5-8). In addition,
macrophages, which infiltrate adipose tissue in obesity, are known to regulate theinflammatory state of adipose tissue (9-13). Furthermore, a recent study hasreported that the inflammation state of adipose tissue was associated with a phenotypic switch of macrophage polarization in adipose tissue (14). High-fat-dietinduced obesity in mice enhances a phenotypic switching from M2 macrophageto M1 macrophage in adipose tissue (15). Macrophage activation has been operationally defined into two separate polarization states, M1 and M2 (16). The M1
macrophage produces TNF-α, IL-6 and nitric oxide. In contrast, the M2
macrophage produces anti-inflammatory cytokines and arginase. Therefore, it canbe understood that M1 macrophages induce chronic inflammatory states, and M2
macrophages decrease these states in adipose tissue.
Chronic exercise is effective in prevention and improvement of type II diabetes (17), induces down-regulation of plasma pro-inflammatory cytokines andup-regulation of anti-inflammatory cytokines (18). In fact, recent studies haveshown that chronic exercise enhanced down-regulation of TNF-α gene expressionin adipose tissue of obese mice (19, 20). Since it is well known that pathogen andintra- or extra-cellular molecule recognition by toll-like receptors such as Tolllike receptor 4 (TLR4), induces NF-κB activation and then TNF-α mRNA
expression (21), one possibility is that exercise training-induced TNF-α suppression in obese mice might be regulated by down-regulation of TLR4. Song et al.
(22) observed that the mRNA level of TLR4 was enhanced in adipose tissues ofobese mice, and activation of TLR4 with free fatty acids stimulated NF-κB signaling and expression of TNF-α and IL-6 in adipocytes (22). Also, Shi et al. (23)Exercise and macrophage phenotype in obese mice • 107
reported that TLR4 recognizes free fatty acids, and then induces pro-inflammatory cytokine and adhesion molecule production. In a review by Gleeson et al. (24),it was noted that cell-surface TLR4 expression and monocyte pro-inflammatory
cytokine production capacity in physically active subjects are lower than in physically inactive subjects although the precise physiological stimulus mediating an
exercise-induced decrease in cell-surface TLR expression (and TLR mRNA
expression) is not known. Accordingly, it is possible that chronic exercise training-attenuated inflammation in adipose tissue occurs by both suppression ofmacrophage infiltration and acceleration of phenotypic switching from M1 to M2
macrophages in high-fat-diet-induced obese mice. However, it remains unclear if
this is the mechanism of down-regulation of pro-inflammatory cytokine gene
expression that is brought about by chronic exercise training.
Therefore, we investigated the effects of chronic exercise training on M1
macrophage infiltration into adipose tissue and the phenotypic switch ofmacrophage polarization in high-fat-diet-induced obese mice. We hypothesizedthat chronic exercise training would result in decreased macrophage infiltration
and a shift of the macrophage phenotype from M1 to M2 in adipose tissue.

MATERIALS & METHODS
Animals and diets
Male C57BL/6 mice (n =38) were purchased from Clea Japan (Osaka, Japan) at 4
weeks of age, and the four animals were housed together in one cage (27 x 17 x 13cm) in controlled environment under a light-dark cycle (lights on at 20:00 and off at
08:00). The experimental procedures followed the Guiding Principles for the Careand Use of Animals in the KUMW and were approved by the Kawasaki University
Medical Welfare Institutional Animal Care and Use Committee (#08-020). All mice
were randomly divided into four groups: normal diet (ND) control (n=7), ND exercise (n=7), high-fat-diet (HFD) control (n=12), or HFD exercise (n=12) group. All
HFD mice were rendered obese by the HFD (D12492, Research Diets, New
Brunswick, NJ) contained with 60 % from fat, 20% from protein and 20% from carbohydrate (of total calories) starting at 4 weeks of age for 16 weeks. All ND mice
were fed a standard normal diet contained with 13% from fat, 26% from protein and
60% from carbohydrate (MF, Oriental Yeast, Tokyo, Japan). All groups wereallowed to eat food freely. Food ingestion and body weight were measured weekly.
Exercise training protocol
All exercise mice were trained on a motorized treadmill (Natsume, Kyoto, Japan)
for 60 min/day at running speeds of 12-20 m/min, 5 times/week, for 16 weeks.
Electric shock was not used during the treadmill run. All control mice werehoused in cages. Three days after the final exercise training, the exercise trained
and untrained mice were sacrificed under light anesthesia with the inhalant Isoflurane, and then several tissues were collected.
Real-time quantitative PCR
To measure mRNA expressions of TNF-α, IL-6, F4/80, monocyte chemotactic
protein (MCP)-1, CXCL14, inter-cellular adhesion molecule (ICAM)-1, vascular-

108 • Exercise and macrophage phenotype in obese micecellular adhesion molecule (VCAM)-1, CD11c, CD163 and TLR4 in adipose tissue, epididymal fat pads in mice were quickly immersed in RNAlater (Applied
Biosystems, Carlsbad, CA) and stored at –80°C. Total RNA was extracted using
Trizol reagent (Invetrogen, Carlsbad, CA) and RNeasy Mini Kit (Qiagen, Valencia, CA) according to the manufacturer's instructions and assessed for purity
using the NanoDrop system (NanoDrop Technologies, Wilmington, DE). Total
mRNA was reverse transcribed to cDNA using High Capacity cDNA Reverse
Transcription Kit (Applied Biosystems) according to the manufacturer's instructions. RT-PCR was performed using the Fast 7500 real-time PCR system (Applied
Biosystems) using Power SYBR® Green PCR Master Mix kits (Applied Biosystems). The thermal profiles consisted of 10 min at 95°C for denaturing followed
by 40 cycles of 95°C for 15 s, annealing at 60°C for 1 min.
Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA was used as
the housekeeping gene, and all data are represented relative to its expression (i.e.,
using standard curve methods) as fold change from ND control group. Specific
PCR primer pairs for each studied gene are shown in Table 1.
Table 1. Primer sequences for real-time RT-PCR analysis
geneforwardreverseGAPDH TGAAGCAGGCATCTGAGGGTNFCCTCCCTCTCATCAGTTCTAIL-6
TAGTCCTTCCTACCCCAATTTCC
F4/80
CTTTGGCTATGGGCTTCCAGTC
MCP-1 CTTCTGGGCCTGCTGTTCACXCL14 CCAAGATTCGCTATAGCGAC
ICAM-1 CCTGATGGGCAGTCAACAGCTA
VCAM-1 CTTCATCCCCACCATTGAAG
CD11c
CTGGATAGCCTTTCTTCTGCTG
CD163
GGGTCATTCAGAGGCACACTG
TLR4
ATGGCATGGCTTACACCACCCGAAGGTGGAAGAGTGGGAG
ACTTGGTGGTTTGCTACGAC
TTGGTCCTTAGCCACTCCTTCGCAAGGAGGACAGAGTTTATCGTG
CCAGCCTACTCATTGGGATCACCTGCGCTTCTCGTTCCAGG
ACAGCTGGCTCCCGTTTCATGAGCAGGTCAGGTTCACAGGCACACTGTGTCCGAACTCCTGGCTGTCCTGTCAAGGCTGAGGCCAATTTTGTCTCCACA

Statistical analysis
Data are presented as means ± SEM. Gene expressions were analyzed using a
two-way analysis of variance (ANOVA) with post-hoc Tukey HSD. All analyses
were performed using SPSS V17.0 (SPSS, Chicago, IL). Statistical significancewas set at p<0.05.

RESULTS
Food intake, which was measured in terms of energy intake, varied as a main
effect of diet: F(1,66)=89.43, p<0.01, but the ANOVA revealed no statisticallysignificant effect for exercise training: F(1,66)=1.39, not significant (n.s.) and dietx exercise interaction: F(1,66)=0.218, n.s. Thus, in this study, the exercise training did not affect the food intake in both ND and HFD mice (Table 2). In addition,

Exercise and macrophage phenotype in obese mice • 109
body mass was also affected by diet: F(1,34)=54.18, p<0.01, but the ANOVA
revealed no statistically significant effect for exercise training: F(1,34)=1.98, n.s.
and diet x exercise interaction: F(1,34)=0.24, n.s. The change in epididymal fat
mass varied as an effect of diet: F(1,34)=111.92, p<0.01, but the exercise training:F(1,34)=0.32, n.s. and interaction: F(1,34)=0.157, n.s. were not statistically significant.
Table 2. The comparsion of food intake, body mass and fat mass between normal (ND) andhigh fat (HFD) diets in control and exercise trained mice

ND

HFD
control
exercisecontrol

exercise

Caloric intake ((kcal/week)**
)

73.2

1.0

70.5

2.2

88.6 2.0

87.4 1.7

Body mass (g)**

27.3

0.6

25.8

1.0

40.4 1.5

37.2 1.5

Epididymal fat mass (g)**

0.58

0.02

0.43

0.01

2.12 0.06

2.09 0.08

The values are the means

SEM. ** p<0.01: effect of the diets

To identify the effect of exercise training on HFD-induced inflammation,
we examined gene expressions of TNF-α and IL-6 as key inflammatory markers
in adipose tissue (Fig. 1). TNF-α mRNA expression was significantly affected bydiet and the exercise training [an effect of diet: F(1,32)=14.96, p<0.01, exercise
training: F(1,32)=4.71, p<0.05, and diet x exercise training interaction:
F(1,32)=2.60, n.s.]. Post-hoc comparisons revealed that, in the control condition,
TNF-α mRNA expression in HFD mice was significantly higher than that in ND

A

B
3.5

5

3

TNF-α
A expression
α mRNA

IL-6 mRN
NA expression

4

3

2

2.5

2

1.5

1

1

0.5

0

0

control exercise control exercise
ND
HFD

control exercise control exercise
ND
HFD

Fig. 1 Effects of exercise training on TNF-α (A) and IL-6 (B) mRNA expression in adipose tissue in both normal- and high-fat-diet fed mice. The values are the means ± SEM. ND: normal diet and HFD: high-fat-diet. *p<0.05 and **p<0.01.

110 • Exercise and macrophage phenotype in obese mice

F4/80
0 mRNA expression

mice (p<0.01). However, the higher expression of TNF-α mRNA was significantly attenuated by exercise training in HFD mice (p<0.01, Fig. 1A). In addition, IL6 mRNA expression was also affected by the diets [an effect of diet:F(1,32)=5.88, p<0.05, exercise training: F(1,32)=3.62, n.s., and diet x exercise
training interaction: F(1,32)=1.24, n.s.]. IL-6 mRNA expression in adipose tissue
was also increased by HFD treatment in the control condition (p<0.05, Fig. 1B).
As an ANOVA result, although the exercise training did not significantly affect
IL-6 mRNA expression (p=0.066), its level in the HFD exercise group decreased(~51% compared with the HFD control group).
F4/80 mRNA expression, reflecting the presence of monocytes andmacrophages, varied as an effect of diet: F(1,32)=21.37, p<0.01, exercise training: F(1,32)=7.68, p<0.01, and diet x exercise training interaction: F(1,32)=4.93,
p<0.05. Expression of F4/80 mRNA was significantly increased in the HFD control group compared with the ND
control group (p<0.01), and the high5expression of F4/80 mRNA in HFD
control mice was significantly
decreasedby exercise training
4(p<0.01, Fig. 2). Therefore, exercise
training might reduce macrophage3
infiltration of adipose tissues in
HFD mice.
The results of mRNA expres2
sions of macrophage chemokines(MCP-1 and CXCL14) are shown in
Fig.
3A and B. For both MCP-1 and1
CXCL14 mRNA expressions, twoway ANOVA revealed no statistical0
ly significant effect for exercise
control exercise
control exercise
training, but there were a statistically
ND
HFD
significant
effect for diet [MCP-1:
Fig. 2 Effects of exercise training on F4/80
mRNA expression in adipose tissue in both nor- an effect of the diet: F(1,32)=28.03,
exercisetraining:
mal- and high-fat-diet-fed mice. The values are p<0.01,
the means ± SEM. ND: normal diet and HFD: F(1,32)=2.32, n.s., and diet x exerhigh-fat-diet. **p<0.01.
cise
training
interaction:
F(1,32)=1.99, n.s., and CXCL14: aneffect of diet: F(1,32)=5.18, p<0.05, exercise training: F(1,32)=3.16, n.s., and dietx exercise training interaction: F(1,32)=2.24, n.s.]. Post-hoc comparisonsrevealed significant differences between the ND control group and the HFD control group (MCP-1; p<0.01, and CXCL14; p<0.05, respectively).
In addition, Fig. 3 also shows adhesion molecules (ICAM-1; Fig. 3C andVCAM-1; Fig. 3D, respectively) mRNA expression in adipose tissue. For ICAM1 mRNA, two-way ANOVA indicated an effect of diet: F(1,32)=25.65, p<0.01,
exercise training: F(1,32)=26.98, p<0.01, and diet x exercise training interaction:
F(1,32)=0.00, n.s. There were statistically significant differences between the ND
control and the ND exercise (p<0.05), the ND control and the HFD control(p<0.01), and the HFD control and the HFD exercise groups (p<0.01), respectively. For VCAM-1 mRNA, two-way ANOVA revealed no statistically significant

Exercise and macrophage phenotype in obese mice • 111
A

B

CXCL14 mRNA expression

8

6

4

2

0

2

ICAM-1 mRNA expression

5

3

2

1

0

control exercise control exercise
ND
HFD

C

2

D

1.5

1

0.5

0

4

control exercise control exercise
ND
HFD

VCAM-1 mRNA expression

MCP-1 mRNA expression

10

control exercise control exercise
ND
HFD

1.5

1

0.5

0

control exercise control exercise
ND
HFD

Fig. 3 Effects of exercise training on mRNA expression of the chemokines MCP-1 (A) andCXCL14 (B), and adhesion molecules ICAM-1(C) and VCAM-1 (D) in adipose tissue in bothnormal diet- and high-fat-diet-fed mice. The values are the means ± SEM. ND: normal dietand HFD: high-fat-diet. *p<0.05 and **p<0.01.

effect of diet: F(1,32)=1.65, n.s., but there were a statistically significant effects
for exercise training: F(1,32)=9.25, p<0.01, and diet x exercise training interaction: F(1,32)=0.21, n.s. Post-hoc comparisons revealed a significant difference
between the HFD control and the HFD exercise groups (p<0.05).
To assess the effects of exercise training on HFD-induced phenotypic switch
in adipose tissue macrophage polarization, we examined gene expression of M1
and M2 macrophage markers in adipose tissue. As the result of two-way ANOVA,
the expression of CD11c mRNA, reflecting the presence of M1 macrophage, varied as an effect of diet: F(1,32)=16.11, p<0.01, exercise training: F(1,32)=4.47,
p<0.05, and diet x exercise training interaction: F(1,32)=3.97, n.s. (Fig. 4A).
Post-hoc comparisons revealed that CD11c mRNA expression in the HFD control
group was significantly higher than that in the ND control group (p<0.01). However, the expression in the HFD exercise group was significantly lower than thatin the HFD control group (p<0.01). Moreover, there were statistically significant
differences in CD163 mRNA expression, reflecting the presence of M2
macrophage, in adipose tissue due to diet and diet x exercise training interaction

112 • Exercise and macrophage phenotype in obese mice

A

B
1.5

CD163 mRN
NA expression

CD11c mRN
NA expression

25

20

15

10

5

0

1

0.5

0

control exercise
ND

control exercise
HFD

control exercise
ND

control exercise
HFD

Fig. 4 Effects of exercise training on CD11c as a M1 marker (A) and CD163 as a M2 marker(B) mRNA expression in adipose tissue in both normal- and high-fat-diet-fed mice. The values are the means ± SEM. ND: normal diet and HFD: high-fat-diet. *p<0.05 and **p<0.01.

TL
LR4 mRNA expression[an effect of diet: F(1,31)=7.26, p<0.05, exercise training: F(1,31)=0.46, n.s., anddiet x exercise training interaction: F(1,31)=10.74, p<0.01]. Post-hoc comparisons revealed that the expression of CD163 mRNA in HFD control mice was significantly lower than that in ND con2
trol mice (p<0.01). However, theexpression in the HFD exercisegroup was significantly higher thanthat in the HFD control group1.5(p<0.05, Fig. 4B). These data
demonstrate that chronic exercise
might induce a decrease in M1
1macrophages and an increase in M2
macrophages in adipose tissue in
HFD mice.
05
0.5Interestingly, the mRNA
expression of TLR4, which induces
production of pro-inflammatory
0cytokines after recognition of a fatty
control exercise control exercise
acid, varied as an effect of diet:
ND
HFD
F(1,32)=15.91, p<0.01, exercise
Fig. 5 Effects of exercise training on TLR4 mRNA
expression in adipose tissue in both normal diet- training: F(1,32)=10.42, p<0.01, andand high-fat-diet-fed mice. The values are the diet x exercise training interaction:means ± SEM. ND: normal diet and HFD: high- F(1,32)=10.52, p<0.01 (Fig.5). Postfat-diet. **p<0.01.
hoc comparisons revealed that there

Exercise and macrophage phenotype in obese mice • 113
were statistically significant differences between ND control and HFD control(p<0.01), and HFD control and HFD exercise groups (p<0.01), respectively.

DISCUSSION
Previous studies have shown that voluntary physical activity and forced treadmill
exercise training inhibit the expression of pro-inflammatory cytokines in adipose
tissue of obese mice (19, 20). These studies concluded that the exercise-induced
loss of body mass might be the important factor in the reduction of inflammation,
because obese mice exhibited enhanced pro-inflammatory cytokine expression in
adipose tissue (5-8). However, in this study, exercise training did not induce theloss of body and epididymal fat mass in HFD mice: the exercise training nevertheless markedly inhibited TNF-α mRNA expression in adipose tissue. Although
we can only speculate about the reason for this, our results suggest that exercise
training may directly attenuate pro-inflammatory cytokine expression in adipose
tissue without requiring exercise-induced loss of overweight. Our results agreewith the findings of the other recent studies which have reported that chronic
exercise enhances down-regulation of TNF-α gene expression in adipose tissue ofobese mice (19, 20).
Furthermore, we observed that higher expression of F4/80 mRNA in adipose tissue was greatly attenuated by exercise training in obese mice. Previous
studies have shown that the high expression of pro-inflammatory cytokines after
high-fat-diet treatment were attenuated by inhibition of macrophage infiltration inobese mice (9, 10, 25). In fact, increase in F4/80 mRNA expression in adipose tissue relates well to macrophage (Mac3- or CD11b-stained cell) infiltrations into
adipose tissue (9). Moreover, Kamei et al. (11) indicated that acceleration ofmacrophage infiltration into adipose tissue induced high expression of proinflammatory cytokines even in normal (non-obese) mice. Therefore, obesityinduced macrophage infiltration into adipose tissue is an important factor for proinflammatory cytokine expression, and may be decreased by chronic exercise
training. The factors affecting the inhibition of macrophage infiltration into adipose tissue by moderate exercise are presently unknown. We found that HFD fed
mice showed higher mRNA expression of ICAM-1 and VCAM-1 in adipose tissue. Previous studies also reported that expression of adhesion molecules in adipose tissue was increased by obesity (26, 27). In addition, obese mice did notexhibit macrophage infiltration into adipose tissue after ICAM-1 antagonist treatment (28). Thus, adhesion molecules affect obesity-induced macrophage infiltration into adipose tissue. However, the effect of exercise training on ICAM-1
expression in adipose tissue has been unclear until now. Interestingly, weobserved that ICAM-1, but not VCAM-1, was significantly reduced by exercise
training. Another study also showed that plasma ICAM-1 concentrations weremarkedly decreased by moderate exercise training in type II diabetic patients
without a concomitant weight loss (29). Although it needs more study to clearly
establish in detail for the effect of exercise training on ICAM-1 in adipose tissue,
attenuated ICAM-1 might be one of the causes of exercise training-induced suppression of macrophage infiltration. On the other hand, it is known that mice whoare deficient for the macrophage specific chemokines, such as MCP-1 and114 • Exercise and macrophage phenotype in obese mice
CXCL14, do not exhibit inflammation despite their obesity (9, 12). However, in
this study, inhibitory effects of exercise training on the expression of MCP-1 andCXCL14 in adipose tissue were not observed, although we clearly found that
HFD fed mice showed high expression of those chemokines in adipose tissue.
Taken together, our data indicate that exercise training-induced down-regulationof pro-inflammatory cytokine mRNA expression is caused by depression ofmacrophage infiltration into adipose tissue in HFD-induced obese mice.
Our study, however, revealed another possible mechanism for the exercise
training-induced decrease in pro-inflammatory cytokine expression. Down-regulation of CD11c mRNA, reflecting the presence of M1 macrophage, and upregulation of CD163 mRNA, reflecting the presence of M2 macrophage, in adipose tissue were observed in HFD exercised mice. Thus, our data indicated thatexercise training induced macrophage phenotypic switching from M1 to M2 inadipose tissue. We speculate that moderate exercise might inhibit M1
macrophage infiltration into adipose tissue. Indeed, infiltrated macrophages into
adipose tissue in obesity are mainly M1 macrophages. Patsouris et al. (14)showed that a treatment of CD11c antagonist attenuated inflammation via inhibition of M1 macrophage infiltration in obese mice. These studies suggest thatthe phenotypic switch of M1/M2 macrophages causes obesity-induced proinflammatory cytokine production in adipose tissue. In this study, we also
observed both a phenotypic switch of M1/M2 macrophages and obesity-induced
pro-inflammatory cytokine production in adipose tissue. Moreover, exercise
training in these obese mice not only induced inhibition of the M1 macrophage
marker but also increased the M2 macrophage marker, while the exercise attenuated higher TNF-α mRNA expression in adipose tissue. In fact, the M1/M2 ratioin HFD-treated mice was greatly inhibited by exercise training (HFD control vs.
HFD exercise: 57% vs. 11%), although the ratio in ND treated mice was 1.1% in
both control and exercised animals. However, it is difficult to explain why
down-regulation of CD163 mRNA occured in our study. Another possibility isthat exercise training induces differentiation from M1 to M2 macrophages inadipose tissue. This hypothesis was based on data that glucocorticoid treatment
interfered with the increase in M1 macrophages in adipose tissue, and inhibited
inflammation in obese mice (30) and moderate exercise induces glucocorticoid(31). In addition, a recent study reported that monocytes up-regulated CD163
after treatment with dexamethasone (32). We also observed that dexamethasone
treatment induced a decrease in CD11c mRNA expression and an increase in
CD163 mRNA expression in vitro (data not shown). Therefore, moderate exercise-induced glucocorticoid secretion may affect macrophage differentiationfrom M1 to M2.
Glucocorticoid inhibits the expression of TLR2 and TLR4 (33). It is possible that the attenuation of TLR4 expression in exercised mice was caused by exercise-induced glucocorticoid stimulation. Furthermore, an exercise traininginduced reduction in TNF-α mRNA expression might be regulated by the downregulation of TLR4. Activation of TLR4 with free fatty acids stimulates NF-κB
signaling and expression of TNF-α and IL-6 in adipocytes (22, 23). Therefore,
our results suggest that exercise-induced down-regulation of TLR4 expression,
which is occurred by both suppression of macrophage infiltration and acceleration of phenotypic switching from M1 to M2 macrophages in adipose tissue,

Exercise and macrophage phenotype in obese mice • 115
attenuates pro-inflammatory cytokine expression in adipose tissue of high-fatdiet-induced obese mice.
The limitation of this study was that the experiment was carried out without isolation of macrophages from adipose tissue. Several parameters, such as
TNF-α, MCP-1 and TLR4, are expressing on/in adipocytes as well as
macrophages. However, macrophages, but neither adipocytes nor other cells, inmice specifically express F4/80. In addition, expression of CD11c and CD163
has never been observed in adipocytes in previous studies, although future studies need to study using an analysis of isolated macrophage functions from adipose tissue. Another limitation was that the evaluation of protein levels in eachparameter was not carried out. Altough mRNA expression levels are commonlyused as a proxy for estimating functional differences that occur at the protein
level, future investigations need to identify exercise-induced CD11c and CD163mRNA expressions as the phenotypic switch of macrophage polarization in adipose tissue.

CONCLUSION
Exercise training is now considered to be a crucial event leading to a reduction of
inflammation in adipose tissue. However, it has still been unclear how exercise
training down-regulates the inflammatory states of adipose tissue. The present
study demonstrates that exercise training markedly inhibits TNF-α and F4/80
mRNA expression in adipose tissue of obese mice. Furthermore, both decreased
CD11c mRNA and increased CD163 mRNA expression in adipose tissue wereobserved with the exercise training. Also, the higher mRNA expression of TLR4
was reduced by the exercise training. These results suggest that exercise training
might induce the phenotypic switching from M1 to M2 macrophages in adipose
tissue as well as inhibiting M1 macrophage infiltration into adipose tissue. Therefore, chronic exercise might contribute to inhibition of inflammation in adipose
tissue via down regulation of TLR4.

ACKNOWLEDGEMENTS
This work was supported by a Grant-in-Aid for the Global COE ‘‘Sport Sciences for the Promotion of Active Life’’ from the Ministry of Education, Culture, Sports, Science and Technology of Japan (to K. Kanosue), and the Interdepartmental Research Fund of Kawasaki University of Medical Welfare (to H.
Yano).

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