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Acute resistance exercise‐induced IGF1 expression and subsequent GLUT4 translocation

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Acute aerobic exercise (AE) is a major physiological stimulus for skeletal muscle glucose uptake through activation of 5′ AMP-activated protein kinase (AMPK). However, the regulation of glucose uptake by acute resistance exercise (RE) remains unclear. To investigate the intracellular regulation of glucose uptake after acute RE versus acute AE, male Sprague–Dawley rats were divided into three groups: RE, AE, or nonexercise control. After fasting for 12 h overnight, the right gastrocnemius muscle in the RE group was exercised at maximum isometric contraction via percutaneous electrical stimulation (3 × 10 sec, 5 sets). The AE group ran on a treadmill (25 m/min, 60 min). Muscle samples were taken 0, 1, and 3 h after completion of the exercises. AMPK, Ca2+/calmodulin-dependent protein kinase II, and TBC1D1 phosphorylation were increased immediately after both forms of exercise and returned to baseline levels by 3 h. Muscle IGF1 expression was increased by RE but not AE, and maintained until 3 h after RE. Additionally, Akt and AS160 phosphorylation were sustained for 3 h after RE, whereas they returned to baseline levels by 3 h after AE. Similarly, GLUT4 translocation remained elevated 3 h after RE, although it returned to the baseline level by 3 h after AE. Overall, this study showed that AMPK/TBC1D1 and IGF1/Akt/AS160 signaling were enhanced by acute RE, and that GLUT4 translocation after acute RE was more prolonged than after acute AE. These results suggest that acute RE-induced increases in intramuscular IGF1 expression might be a distinct regulator of GLUT4 translocation.
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ORIGINAL RESEARCH
Acute resistance exercise-induced IGF1 expression and
subsequent GLUT4 translocation
Kohei Kido
1
, Satoru Ato
1
, Takumi Yokokawa
2
, Yuhei Makanae
3
, Koji Sato
4
& Satoshi Fujita
1
1 Faculty of Sport and Health Science, Ritsumeikan University, Kusatsu, Japan
2 Laboratory of Sports and Exercise Medicine, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan
3 Department of Physical Education, National Defense Academy, Yokosuka, Japan
4 Graduate School of Human Development and Environment, Kobe University, Kobe, Japan
Keywords
Aerobic exercise, glucose transporter type 4,
insulin-like growth factor 1, resistance
exercise.
Correspondence
Satoshi Fujita, Faculty of Sport and Health
Science, Ritsumeikan University, 1-1-1
Nojihigashi, Kusatsu 525-8577, Japan.
Tel: +81-77-561-3760;
Fax: +81-77-561-3761;
E-mail: safujita@fc.ritsumei.ac.jp
Funding Information
This work was supported by JSPS KAKENHI
Grant nos 25282200 and 25560379 to S.
Fujita. This work was also supported by the
Japanese Council for Science, Technology
and Innovation, SIP (Project ID 14533567),
“Technologies for creating next-generation
agriculture, forestry and fisheries” (funding
agency: Bio-oriented Technology Research
Advancement Institution, NARO).
Received: 18 July 2016; Accepted: 21 July
2016
doi: 10.14814/phy2.12907
Physiol Rep, 4 (16), 2016, e12907,
doi: 10.14814/phy2.12907
Acute aerobic exercise (AE) is a major physiological stimulus for skeletal mus-
cle glucose uptake through activation of 50AMP-activated protein kinase
(AMPK). However, the regulation of glucose uptake by acute resistance exer-
cise (RE) remains unclear. To investigate the intracellular regulation of glucose
uptake after acute RE versus acute AE, male SpragueDawley rats were
divided into three groups: RE, AE, or nonexercise control. After fasting for
12 h overnight, the right gastrocnemius muscle in the RE group was exercised
at maximum isometric contraction via percutaneous electrical stimulation
(3 910 sec, 5 sets). The AE group ran on a treadmill (25 m/min, 60 min).
Muscle samples were taken 0, 1, and 3 h after completion of the exercises.
AMPK, Ca
2+
/calmodulin-dependent protein kinase II, and TBC1D1 phospho-
rylation were increased immediately after both forms of exercise and returned
to baseline levels by 3 h. Muscle IGF1 expression was increased by RE but not
AE, and maintained until 3 h after RE. Additionally, Akt and AS160 phospho-
rylation were sustained for 3 h after RE, whereas they returned to baseline
levels by 3 h after AE. Similarly, GLUT4 translocation remained elevated 3 h
after RE, although it returned to the baseline level by 3 h after AE. Overall,
this study showed that AMPK/TBC1D1 and IGF1/Akt/AS160 signaling were
enhanced by acute RE, and that GLUT4 translocation after acute RE was more
prolonged than after acute AE. These results suggest that acute RE-induced
increases in intramuscular IGF1 expression might be a distinct regulator of
GLUT4 translocation.
Introduction
Aerobic exercise (AE) is a major physiological stimulus that
induces skeletal muscle glucose uptake and improves insu-
lin sensitivity. Acute and chronic AE affect glucose metabo-
lism differently. Specifically, acute AE induces skeletal
muscle glucose uptake incrementally and transiently
(Goodyear et al. 1990). A previous study suggests that the
blood glucose level is decreased approximately 30% for 4 h
by acute AE, as compared with nonexercised controls (Bac-
chi et al. 2012). Daily blood glucose control is critical for
diabetes patients to avoid diabetic complications (Ameri-
can Diabetes Association 2015b). Chronic AE improves
insulin sensitivity, fasting blood glucose, and HbA1c levels
continuously (Umpierre et al. 2011; Mann et al. 2014). The
improvement of these parameters can lead to a complete
ª2016 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of
the American Physiological Society and The Physiological Society.
This is an open access article under the terms of the Creative Commons Attribution License,
which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
2016 | Vol. 4 | Iss. 16 | e12907
Page 1
Physiological Reports ISSN 2051-817X
reversal of type II diabetes. Thus, both acute and chronic
AE are significant for improving glucose metabolism. In a
recent study, chronic resistance exercise (RE), which is a
skeletal muscle hypertrophy model, also improved hyper-
glycemia and HbA1c levels in diabetic patients (Umpierre
et al. 2011). Therefore, recent exercise guidelines from the
American Diabetes Association recommend RE for control-
ling blood glucose (American Diabetes Association 2015a).
However, acute RE-induced augmentation of skeletal mus-
cle glucose uptake and the regulation of this process are still
poorly understood.
AMP-activated protein kinase (AMPK), which is acti-
vated by increases in the cellular AMP/ATP ratio, is a key
intracellular signaling protein for glucose uptake (Musi
et al. 2003; Jessen and Goodyear 2005; O’Neill 2013). The
activation of AMPK is mediated by acute AE that induces
glucose transporter type 4 (GLUT4) translocation to the
cell membrane, resulting in glucose uptake (Musi et al.
2003; Jessen and Goodyear 2005; O’Neill et al. 2011;
O’Neill 2013), but no study confirmed the signaling
response after RE. Ca
2+
/calmodulin-dependent protein
kinase II (CaMKII) is another important signaling protein
for glucose uptake following acute AE. Previous studies
demonstrated that CaMKII activates AMPK as an
upstream event in response to AE or muscle contraction
(Raney and Turcotte 2008; Morales-Alamo et al. 2013),
but other studies indicated that CaMKII may also induce
glucose uptake independent of AMPK signaling pathways
(Raney and Turcotte 2008; Witczak et al. 2010). Although
CaMKII may have important roles in skeletal muscle glu-
cose uptake following AE, the regulation of CaMKII sig-
naling remains unclear. Some previous studies showed
that both AMPK and CaMKII were phosphorylated fol-
lowing acute RE, which might contribute to glucose
uptake (Witczak et al. 2010; Ogasawara et al. 2014).
However, no study showed the roles of AMPK and CaM-
KII in acute RE-induced glucose uptake.
Phosphorylation of TBC1D1 and AS160 occurs down-
stream of AMPK and CaMKII (Funai and Cartee 2008;
Vendelbo et al. 2014). Through the phosphorylation of
TBC1D1 and AS160, AMPK and CaMKII enhance GLUT4
translocation (Chavez et al. 2008; Witczak et al. 2010).
However, the relationship between AMPK/CaMKII phos-
phorylation and TBC1D1/AS160 phosphorylation remains
unknown. Moreover, acute RE-induced TBC1D1/AS160
responses are not fully clarified.
Insulin-like growth factor 1 (IGF1) is increased in
skeletal muscle by acute RE (Ogasawara et al. 2013a,b). In
contrast, there is no evidence of acute AE inducing the
expression of skeletal muscle IGF1. In a cell culture study,
IGF1 phosphorylated Akt which then phosphorylated
AS160 at Thr642 resulting in enhanced GLUT4 transloca-
tion and glucose uptake (Ciaraldi et al. 2002; Roach et al.
2007; Baus et al. 2008; Taylor et al. 2008; Morissette et al.
2009; Peck et al. 2009). Accordingly, IGF1 may play cru-
cial roles as a stimulator of both AMPK- and CaMKII-
independent glucose uptake through the activation of Akt
and AS160 signaling pathways. In general, it is poorly
understood how different modes of exercise, that is, acute
RE and AE, differentially regulate IGF1/Akt/AS160 signal-
ing and subsequent GLUT4 translocation.
The purpose of this study was to identify specific cellu-
lar signal responses to acute RE, including IGF1 signaling,
as compared with those to acute AE in respect with glu-
cose metabolism. We additionally investigated the role of
IGF1 on TBC1D1/AS160 phosphorylation and glucose
uptake by using an in vitro model.
Materials and Methods
In vitro experiments
Mouse C2C12 myoblasts (American Type Culture Collec-
tion, Manassas, VA) were cultured as described previously
(Yokokawa et al. 2015). Briefly, cells were grown in Dul-
becco’s modified Eagle’s medium (DMEM; 4.5 g glucose/L,
Nacalai Tesque, Kyoto, Japan) containing 10% fetal bovine
serum and 1% penicillin-streptomycin (P/S). To initiate
myogenic differentiation, the culture medium was replaced
by DMEM containing 2% horse serum and 1% P/S. After
4 days of differentiation, myotubes were serum-starved
overnight and then incubated for 30 min in serum-free
medium containing 5 lmol/L 5-aminoimidazole-4-carbox-
amide ribonucleoside (AICAR; Wako, Osaka, Japan),
1lmol/L insulin (Novolin; Novo Nordisk, Bagsvaerd, Den-
mark), or 200 ng/mL IGF1 (PeproTech, Rocky Hill, NJ).
In vivo experiments
The study protocol was approved by the Ethics Commit-
tee for Animal Experiments at Ritsumeikan University,
and was conducted in accordance with the Declaration of
Helsinki. Forty-two male SpragueDawley rats, aged
10 weeks (320360 g), were obtained from CLEA Japan
(Tokyo, Japan). The rats were divided into three groups:
nonexercise control, RE, or AE. All rats were housed for
1 week in an environment maintained at 2224°C with a
12:12-h lightdark cycle, and were allowed food (CE2;
CLEA Japan) and water ad libitum.
The time course of changes in signaling protein levels
was evaluated following RE and AE initiated after a 12-h
overnight fast, as detailed below. Rats were sacrificed 0, 1,
or 3 h after completion of the exercise routine. Control
rats were sacrificed at the basal state. Dissected gastrocne-
mius muscles were frozen rapidly in liquid nitrogen and
stored at 80°C until use.
2016 | Vol. 4 | Iss. 16 | e12907
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ª2016 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of
the American Physiological Society and The Physiological Society.
Glucose Uptake Regulation by Resistance Exercise K. Kido et al.
RE protocol
Under isoflurane anesthesia, hair was shaved off the
right lower leg of each rat; the area was then cleaned
with alcohol wipes. The rats were kept in a prone posi-
tion with their right foot on the footplate and the
ankle joint angle positioned at 90°. The triceps surae
muscle was stimulated percutaneously with electrodes
(Vitrode V, Ag/AgCl; Nihon Kohden, Tokyo, Japan)
that were cut to 10 95 mm and connected to an elec-
tric stimulator and an isolator (SS-104J; Nihon Koh-
den) (Nakazato et al. 2010). The right gastrocnemius
muscle was exercised isometrically by stimulation with
ten 3-sec contractions per set for 5 sets. There was a
7-sec interval between contractions and 3-min rest
intervals between sets. Voltage (~30 V) and stimulation
frequency (100 Hz) were adjusted to produce maximal
isometric tension. This exercise protocol is used widely
as a RE model for animals (Ogasawara et al. 2013a,b,
2014; Tsutaki et al. 2013; Kido et al. 2015) and
induces significant muscle hypertrophy (Ogasawara et al.
2013a,b).
AE protocol
Rats in the AE group were habituated to the treadmill by
running for 30 min at 15 m/min, 45 min at 20 m/min,
and 60 min at 25 m/min over a week. Three to five days
after the last running habituation, rats were placed on a
flat treadmill and made to run for 60 min at 25 m/min
(Langfort et al. 1996).
Analyses
In vitro glucose uptake assay
Glucose uptake was determined by measuring the glucose
concentration of the medium as described previously
(Yokokawa et al. 2015). In brief, culture media were col-
lected and the glucose concentrations assayed spectropho-
tometrically using a Glucose II test kit (Wako).
Measurements of serum IGF1, insulin, and
glucose, and muscle IGF1 concentrations
Insulin-like growth factor 1 levels in the serum and skele-
tal muscle were determined using the mouse/rat IGF1
Quantikine ELISA kit (R&D Systems, Minneapolis, MN).
Serum insulin levels were detected using a rat insulin
ELISA kit (Shibayagi, Gunma, Japan), according to the
manufacturer’s instructions. Serum glucose concentrations
were measured by the YSI 2300 STAT Plus analyzer (Yel-
low Springs Instrument, Yellow Springs, OH).
Western blotting analyses
Western blotting analyses were performed as reported
previously (Goodman et al. 2011). Briefly, stimulated
C2C12 myotubes were washed once with cold phosphate-
buffered saline (PBS) and lysed in radioimmunoprecipita-
tion assay buffer containing 10 mmol/L Tris HCl (pH
7.4), 1% NP-40, 1% sodium deoxycholate, 0.1% sodium
dodecyl sulfate (SDS), 150 mmol/L NaCl, and 5 mmol/L
EDTA. The extracts were centrifuged at 13,700 gfor
20 min at 4°C. Protein concentrations of the supernatants
were determined using a protein assay kit (Nacalai Tes-
que). The lysates were mixed with 69sample buffer con-
taining 350 mmol/L TrisHCl (pH 6.8), 10% SDS, 30%
glycerol, 9.3% dithiothreitol, and 0.03% bromophenol
blue, then boiled at 95°C for 5 min.
Gastrocnemius muscles were homogenized in buffer
containing 100 mmol/L TrisHCl (pH 7.8), 1% NP-40,
0.1% SDS, 0.1% sodium deoxycholate, 1 mmol/L EDTA,
150 mmol/L NaCl, and protease and phosphatase inhibi-
tor cocktail (Thermo Fisher Scientific, Waltham, MA).
Homogenates were centrifuged at 13,700 gfor 20 min at
4°C. The supernatant was removed, and the protein con-
centration determined using the Protein Assay Rapid kit
(Wako).
Samples were diluted in 39sample buffer (1.0%
b-mercaptoethanol, 4.0% SDS, 0.16 mol/L TrisHCl (pH
6.8), 43% glycerol, and 0.2% bromophenol blue), and
boiled at 95°C for 5 min. Using 812% SDS-polyacryla-
mide gels, 5 lg (for cell lysates) or 20 lg of protein (for
muscle lysates) was separated by electrophoresis and
transferred to polyvinylidene difluoride membranes. After
the transfer, membranes were washed in Tris-buffered
saline containing 0.1% Tween 20 (TBST). Membranes
were then blocked with 5% powdered milk in TBST for
1 h at room temperature. After blocking, the membranes
were washed and incubated overnight at 4°C with pri-
mary antibodies against p-Akt (Thr308), p-Akt (Ser473),
total Akt, p-AMPK (Thr172), total AMPK, p-AS160
(Thr642), total AS160, p-CaMKII (Thr286), a-tubulin
(Cell Signaling Technology, Danvers, MA), total CaMKII
(Santa Cruz Biotechnology, Santa Cruz, CA), or
p-TBC1D1 (Ser237) (Merck Millipore, Damstadt, Ger-
many). The membranes were then washed again in TBST
and incubated for 1 h at room temperature with the
appropriate secondary antibodies. Chemiluminescent
reagents (Luminata Forte Western HRP Substrate; Merck
Millipore) were used to facilitate the detection of protein
bands. Images were scanned using a chemiluminescence
detector (ImageQuant LAS 4000; GE Healthcare, Buck-
inghamshire, UK). Band intensities were quantified using
ImageJ 1.46 software (National Institutes of Health,
Bethesda, MD).
ª2016 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of
the American Physiological Society and The Physiological Society.
2016 | Vol. 4 | Iss. 16 | e12907
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K. Kido et al.Glucose Uptake Regulation by Resistance Exercise
To assess the plasma membrane localization of GLUT4,
plasma membranes were extracted as modified methods of
previous study (Sato et al. 2009). Briefly, gastrocnemius
muscles were homogenized into buffer A (20 mmol/L
Tris [pH 7.4], 1 mmol/L EDTA, 0.25 mmol/L EGTA,
0.25 mol/L sucrose, 1 mmol/L DTT, 50 mmol/L
NaF, 25 mmol/L sodium pyrophosphate, and 40 mmol/L
b-glycerophosphate). The homogenates were centrifuged
at 400 gfor 15 min at 4°C. The supernatant was
centrifuged again at 249,138 g(Hitachi CS100GXII, Ibar-
aki, Japan) for 1 h at 4°C. The fractions were resus-
pended in buffer A and then homogenized to add equal
volume buffer B containing 20 mmol/L Tris (pH 7.4),
1 mmol/L EDTA, 0.25 mmol/L EGTA, 2% Triton X-100,
50 mmol/L NaF, 25 lmol/L sodium pyrophosphate, and
40 mmol/L b-glycerophosphate. The homogenates were
centrifuged at 274,052 gfor 1 h at 4°C (Hitachi
CS100GXII) and the supernatant was used as plasma
membrane fraction. Prepared plasma membrane fraction
was used for the measurement of plasma membrane
GLUT4 level, which was determined by Western blotting
analysis using antibodies against GLUT4 (Merck Milli-
pore) (Sato et al. 2009).
Statistical analysis
All results are expressed as means SE. A one-way
ANOVA with a least significant difference post hoc test
was used to evaluate changes among multiple groups, and
the unpaired Student t-test was used for two-group com-
parisons (Yang et al. 2012).
Results
In vitro experiments
AICAR stimulation
AICAR, an AMPK activator, significantly increased the
phosphorylation of AMPK (Thr172), TBC1D1 (Ser237),
and AS160 (Thr642). Additionally, AICAR induced signif-
icant decreases in media glucose concentrations indicating
an increase in glucose uptake (Fig. 1).
Insulin and IGF1 stimulation
Akt phosphorylation at Thr308 and Ser473, and AS160
phosphorylation at Thr642, were increased significantly
by stimulation with insulin and IGF1, whereas TBC1D1
phosphorylation at Ser237 was not changed. Additionally,
insulin and IGF1 induced significant decreases in glucose
concentrations in the media indicating an increase in glu-
cose uptake (Fig. 2).
In vivo experiments
Blood parameters
Table 1 shows the changes in serum insulin, IGF1, and
glucose levels. Serum insulin was not changed by RE and
AE. Serum IGF1 was decreased significantly at 3 h after
AE (P<0.05) but not changed by RE. In the RE group,
serum glucose was increased significantly immediately
after exercise (P<0.05), and returned to the baseline
level by 3 h after exercise. In the AE group, serum glucose
was increased significantly immediately after exercise
(P<0.05). Glucose dropped to below the baseline level at
1h(P<0.05) and returned to the baseline level by 3 h
after AE.
Skeletal muscle parameters
AMPK was phosphorylated significantly immediately after
both RE and AE (P<0.05). AMPK phosphorylation
remained high at 1 h after RE (P<0.05). This was in
contrast to AE-induced AMPK phosphorylation that
returned to baseline by 1 h after exercise (Fig. 3).
CaMKII phosphorylation was increased significantly
immediately after RE and returned to the baseline level
by 1 h after exercise. In the AE group, CaMKII was phos-
phorylated significantly immediately after exercise and
returned to the baseline level at 3 h after AE (Fig. 4).
TBC1D1 was phosphorylated significantly at Ser237
immediately after RE. The phosphorylation level returned
to baseline by 3 h after RE. In the AE group, TBC1D1
phosphorylation tended to increase immediately after
exercise and reached significance at 1 h. Phosphorylation
levels returned to baseline by 3 h after exercise (Fig. 5).
Resistance exercise induced a significant (63%) increase
in IGF1 expression in skeletal muscle at 1 h after exercise.
This increase was maintained until 3 h after exercise.
However, AE-induced IGF1 expression was decreased sig-
nificantly at every time point (P<0.05) (Fig. 6).
Both RE and AE induced significant phosphorylation
of Akt at Thr308 immediately after exercise (P<0.05). p-
Akt (Thr308) levels returned to baseline by 1 h after exer-
cise. Akt was also phosphorylated at Ser473 immediately
after RE and AE (P<0.05). Although AE-induced p-Akt
(Ser473) returned to the baseline level at 1 h after exer-
cise, this phosphorylation was maintained for 3 h after
RE (P<0.05) (Fig. 7).
Phosphorylation of AS160 at Thr642 increased signifi-
cantly at 1 h after RE (P<0.05). This increase was sus-
tained for 3 h (P<0.05). In contrast, AE-induced
phosphorylation of AS160 occurred immediately after
exercise (P<0.05) and returned to the baseline level by
3 h (Fig. 8).
2016 | Vol. 4 | Iss. 16 | e12907
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ª2016 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of
the American Physiological Society and The Physiological Society.
Glucose Uptake Regulation by Resistance Exercise K. Kido et al.
The expression of GLUT4 on the plasma membrane
was increased significantly 1 h after RE (P<0.05). This
increase was maintained until 3 h after RE (P<0.05). AE
induced a significant increase in plasma membrane
GLUT4 immediately and 1 h after exercise (P<0.05).
Plasma membrane GLUT4 expression returned to the
baseline level by 3 h after AE (Fig. 9).
Discussion
In this study, we investigated intracellular signaling and
GLUT4 translocation in response to an acute bout of RE
or AE in rat skeletal muscle. Skeletal muscle IGF1 expres-
sion was increased after RE but not AE, and subsequent
GLUT4 translocation was sustained longer after RE as
compared with AE. Additionally, we used an in vitro
study to show that activation of AMPK/TBC1D1 and
IGF1/Akt/AS160 signaling enhanced glucose uptake inde-
pendently. These data provided crucial new information
to explain the regulation of glucose uptake by acute RE
through specific signals, and showed differences between
acute RE and AE at the molecular level.
The results of this study indicated that RE- and AE-
induced AMPK phosphorylation were similar. In previous
studies, AMPK was also found to be phosphorylated
immediately after exercise by both RE and AE, and no
significant difference was observed between the responses
to RE and AE (Rasmussen et al. 1998; McConell et al.
2008; Vissing et al. 2013; Ogasawara et al. 2014; Ahti-
ainen et al. 2015). The activation of AMPK was found
previously to depend upon skeletal muscle contraction
tension (Ihlemann et al. 1999). Additionally, the
16
17
18
19
20
21
22
CON AICAR
Glucose concentraon (mmol/L)
0
0.5
1
1.5
2
2.5
CON AICAR
Phospho/total AMPK (AU)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
CON AICAR
Phospho-TBC1D1/α-tubulin
(AU)
0
0.5
1
1.5
2
2.5
3
3.5
CON AICAR
Phospho/total AS160 (AU)
*
*
**
Phospho
Total
Phospho
Phospho
Total
α-tubulin
AB
CD
Figure 1. Effects of AICAR on mouse C2C12 myotubes. Phosphorylation of AMPK at Thr172 (A), TBC1D1 at Ser237 (B), and AS160 at Thr642
(C) following stimulation with AICAR. Media glucose concentration indicating glucose uptake (D) relative to control (CON) following stimulation
with AICAR. Data are presented as means SE (n=5). *P<0.05 versus CON.
ª2016 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of
the American Physiological Society and The Physiological Society.
2016 | Vol. 4 | Iss. 16 | e12907
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K. Kido et al.Glucose Uptake Regulation by Resistance Exercise
phosphorylation of AMPK depended upon the intensity
of AE (i.e., %VO
2
max) (Chen et al. 2003; Sriwijitkamol
et al. 2007). According to these previous studies, the
magnitude of AMPK phosphorylation in response to RE
and AE depends on exercise intensity. Therefore, further
studies are needed to identify the magnitude of AMPK
0
2
4
6
8
10
12
AB
C
E
D
Thr308
Ser473
Total
0
2
1
3
4
5
6
Phospho/total Akt at Thr308
(AU)
0
0.2
0.4
0.6
0.8
1
1.2
Phospho-TBC1D1/α-Tubulin
(AU)
16
17
18
19
20
21
22
Glucose concentraon (mmol/L)
Phospho/total Akt at Ser473
(AU)
CON INSULIN IGF1
CON INSULIN IGF1 CON INSULIN IGF1
CON INSULIN IGF1
CON INSULIN IGF1
Phospho
Total
0
0.5
1
1.5
2
2.5
Phospho/total AS160 (AU)
Phospho
α-tubulin
Figure 2. Effects of insulin and IGF1 on mouse C2C12 myotubes. Phosphorylation of Akt at Thr308 (A) and Ser473 (B), AS160 at Thr642 (C),
and TBC1D1 at Ser237 (D) following stimulation by insulin or IGF1. Media glucose concentration indicating glucose uptake (E) relative to
control (CON) following stimulation by insulin or IGF1. Data are expressed as means SE (n=6). *P<0.05 versus CON.
2016 | Vol. 4 | Iss. 16 | e12907
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ª2016 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of
the American Physiological Society and The Physiological Society.
Glucose Uptake Regulation by Resistance Exercise K. Kido et al.
phosphorylation following RE and AE with various inten-
sities.
This is the first study comparing the time course of
changes in CaMKII phosphorylation between RE and AE.
The results showed that CaMKII was phosphorylated
immediately after both acute RE and AE. This was consis-
tent with a previous study showing that the phosphoryla-
tion of CaMKII was increased significantly immediately
after acute AE (Rose et al. 2006). Together, these results
demonstrate that both acute RE and AE induce CaMKII
phosphorylation immediately after exercise.
The phosphorylation of CaMKII apparently depended
on Ca
2+
released from the sarcoplasmic reticulum. Ca
2+
release is increased by higher skeletal muscle contraction
tension (Chin and Allen 1997). Accordingly, RE, which
induces higher contraction tension than AE, might
phosphorylate CaMKII to a greater extent than AE. How-
ever, the phosphorylation of CaMKII after acute RE
returned to the baseline level faster than after acute AE.
Thus, contraction tension might not be the most signifi-
cant regulatory factor for CaMKII phosphorylation after
AE.
As a downstream signal of AMPK and CaMKII, the
phosphorylation of TBC1D1 (Ser237) was measured after
acute RE and AE and found to match the time course of
changes in AMPK phosphorylation. To better support
the functional relationship between these changes,
TBC1D1 phosphorylation was measured in response to
AICAR-induced AMPK phosphorylation or insulin/IGF1
stimulation in vitro. The results showed that AMPK
phosphorylation induced TBC1D1 phosphorylation. In
contrast, insulin/IGF1-induced Akt signal activation did
Table 1. Blood parameters.
CON RE AE
0H 1H 3H 0H 1H 3H
Insulin (pmol/l) 11.3 3.0 9.7 1.4 7.7 3.2 12.7 2.1 10.3 1.8 10.9 1.0 9.12 0.9
IGF1 (ng/mL) 1281.4 51.6 1203.9 115.6 1262.3 60.1 1200.0 54.1 1491.9 57.1 1178.1 115.3 937.9 72.7*
Glucose (mmol/L) 3.7 0.3 7.2 0.8*9.9 1.0*4.0 1.7 7.4 0.3*2.6 0.1*3.0 0.2
Data are presented as means SE (n=6).
CON, control; RE, resistance exercise; AE, aerobic exercise.
*
P<0.05 versus CON.
0
0.5
1
1.5
2
2.5
3
3.5
CON RE0H RE1H RE3H
Phospho/total AMPK (AU)
0
0.5
1
1.5
2
2.5
3
3.5
CON AE0H AE1H AE3H
Phospho/total AMPK (AU)
*
*
*
Phospho
Total
AB
Figure 3. Effects of RE and AE on AMPK. Phosphorylation of AMPK at Thr172 relative to total AMPK protein content following RE (A) or AE
(B). Data are expressed as means SE (n=6). *P<0.05 versus CON. CON, control; RE, resistance exercise; AE, aerobic exercise.
ª2016 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of
the American Physiological Society and The Physiological Society.
2016 | Vol. 4 | Iss. 16 | e12907
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K. Kido et al.Glucose Uptake Regulation by Resistance Exercise
not affect TBC1D1 phosphorylation at Ser237. A previous
animal study showed that p-TBC1D1 (Ser237) increased
immediately after acute AE, and was diminished in
AMPK knockout mice (Fentz et al. 2015). Based on these
results, acute RE-induced TBC1D1 phosphorylation at
Ser237 may be also caused by AMPK phosphorylation.
0
0.5
1
1.5
2
2.5
3
3.5
4
CON AE0H AE1H AE3H
Phospho/total CaMKII (AU)
0
0.5
1
1.5
2
2.5
3
3.5
4
CON RE0H RE1H RE3H
Phospho/total CaMKII (AU)
Phospho
Total
***
AB
Figure 4. Effects of RE and AE on CaMKII. Phosphorylation of CaMKII at Thr286 relative to total CaMKII protein content following RE (A) or
AE (B). Data are expressed as means SE (n=6). *P<0.05 versus CON. CON, control; RE, resistance exercise; AE, aerobic exercise.
0
0.5
1
1.5
2
2.5
3
CON RE0H RE1H RE3H
Phospho-TBC1D1/α-tubulin (AU)
Phospho-TBC1D1/α-tubulin (AU)
0
0.5
1
1.5
2
2.5
3
CON AE0H AE1H AE3H
*
*
*
P = 0.07
Phospho
α-tubulin
AB
Figure 5. Effects of RE and AE on TBC1D1. Phosphorylation of TBC1D1 at Ser237 relative to total TBC1D1 protein content following RE (A) or
AE (B). Data are expressed as means SE (n=6). *P<0.05 versus CON. CON, control; RE, resistance exercise; AE, aerobic exercise.
2016 | Vol. 4 | Iss. 16 | e12907
Page 8
ª2016 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of
the American Physiological Society and The Physiological Society.
Glucose Uptake Regulation by Resistance Exercise K. Kido et al.
Acute RE-induced IGF1 expression was assessed previ-
ously as a regulator of skeletal muscle hypertrophy
(Ogasawara et al. 2013b). As a glucose uptake regulator,
IGF1 was measured after acute RE and AE. The results
showed that skeletal muscle IGF1 was increased 1 h after
acute RE and maintained until 3 h. In contrast, acute
0
50
100
150
200
250
CON RE0H RE1H RE3H
Skeletal muscle IGF1
expression (ng/protein)
0
50
100
150
200
250
CON AE0H AE1H AE3H
Skeletal muscle IGF1
expression (ng/protein)
*
**
*
*
AB
Figure 6. Effects of RE and AE on IGF1. The expression of skeletal muscle IGF1 relative to CON following RE (A) or AE (B). Data are expressed
as means SE (n=6). *P<0.05 versus CON. CON, control; RE, resistance exercise; AE, aerobic exercise.
0
1
2
3
4
5
6
7
CON AE0HAE1HAE3H
0
1
2
3
4
5
6
7
CON RE0H RE1H RE3H
Phospho/total Akt at
Ser473 (AU)
0
1
2
3
4
5
6
7
CON RE0H RE1H RE3H
Phospho/total Akt at
Thr308 (AU)
Phospho/total Akt at
Ser473 (AU)
Phospho/total Akt at
Thr308 (AU)
0
1
2
3
4
5
6
7
CON AE0HAE1HAE3H
*
*
*
*
*
*
Thr308
Ser473
Tot a l
AB
CD
Figure 7. Effects of RE and AE on Akt. Phosphorylation of Akt at Thr308 and Ser473 relative to total Akt protein content following RE (A and
C) or AE (B and D). Data are expressed as means SE (n=6). *P<0.05 versus CON. CON, control; RE, resistance exercise; AE, aerobic
exercise.
ª2016 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of
the American Physiological Society and The Physiological Society.
2016 | Vol. 4 | Iss. 16 | e12907
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K. Kido et al.Glucose Uptake Regulation by Resistance Exercise
AE did not augment intramuscular IGF1. Following aug-
mented IGF1 expression, the increase in Akt phosphory-
lation seen in the RE was more prolonged than that in
the AE group. As a downstream signal of Akt, AS160
phosphorylation was also maintained longer than AE.
Moreover, using an in vitro model, we also determined
that IGF1 stimulated Akt and AS160 phosphorylation.
According to these results, Akt and AS160 phosphoryla-
tion after RE may be modulated by RE-induced IGF1
expression, which may have contributed to prolonged
increase in Akt and AS160 phosphorylation. Taken
together, the IGF1 signaling, including prolonged Akt
and AS160 phosphorylation, may be a specific signal
response to acute RE.
The early-phase phosphorylation of Akt by both RE
and AE may occur independently of IGF1 expression
because there was no change in IGF1 expression immedi-
ately after exercise. Moreover, according to a previous
study, the integrin/Akt signaling response occurred imme-
diately after exercise (Klossner et al. 2009). Thus, Akt
phosphorylation immediately after acute RE and AE may
be caused by an integrin/Akt signal.
0
0.5
1
1.5
2
2.5
3
CON RE0H RE1H RE3H
Phospho/total AS160 (AU)
0
0.5
1
1.5
2
2.5
3
CON AE0H AE1H AE3H
Phospho/total AS160 (AU)
****
Phospho
Total
AB
P = 0.05
Figure 8. Effects of RE and AE on AS160. Phosphorylation of AS160 at Thr642 relative to total AS160 protein content following RE (A) or AE
(B). Data are expressed as means SE (n=6). *P<0.05 versus CON. CON, control; RE, resistance exercise; AE, aerobic exercise.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
CON RE0H RE1H RE3H
GLUT4 in plasma membrane (AU)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
CON AE0H AE1H AE3H
GLUT4 in plasma membrane (AU)
***
*
AB
Figure 9. Effects of RE and AE on GLUT4. Total GLUT4 expression in plasma membrane following RE (A) or AE (B) relative to CON. Data are
expressed as means SE (n=6). *P<0.05 versus CON. CON, control; RE, resistance exercise; AE, aerobic exercise.
2016 | Vol. 4 | Iss. 16 | e12907
Page 10
ª2016 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of
the American Physiological Society and The Physiological Society.
Glucose Uptake Regulation by Resistance Exercise K. Kido et al.
This is the first study which directly compared AS160
phosphorylation in response to RE and AE. Previous
studies showed that AS160 phosphorylation in rat skeletal
muscle after swimming increased immediately after exer-
cise, and it maintained until 3 h after exercise (Arias et al.
2007; Funai et al. 2009; Castorena et al. 2014). This is
contrary to this study which demonstrated that AS160
phosphorylation returned to baseline level by 3 h after
exercise. However, these previous studies used different
mode of exercise (i.e., swimming vs. running) and ana-
lyzed epitrochlearis muscle. Acute swimming exercise-
induced PGC1aexpression, which is downstream of
AMPK, was different with acute running exercise on sev-
eral skeletal muscles including epitrochlearis and gastroc-
nemius muscle (Terada and Tabata 2004). Additionally,
epitrochlearis and gastrocnemius muscle have different
muscle fiber composition (Castorena et al. 2011). These
methodological differences between previous and this
studies may have caused the differences in AS160 phos-
phorylation level and time course of response.
This is also the first report that compared the time
course of changes in GLUT4 translocation and upstream
signal responses after acute RE and AE. Interestingly,
enhanced GLUT4 translocation after acute RE was found
at later time points, but was maintained longer than after
acute AE. Previously, acute AE was reported to augment
GLUT4 translocation immediately after exercise, and
GLUT4 translocation returned to the baseline level by 2 h
after exercise (Goodyear et al. 1990). Additional impor-
tant results were that the RE-induced increase in AS160
phosphorylation was more prolonged than TBC1D1 phos-
phorylation, and that acute RE-induced GLUT4 transloca-
tion was also prolonged until the same time point.
Furthermore, the induction of AS160/TBC1D1 phospho-
rylation and GLUT4 translocation was not as prolonged
with AE as with RE. These findings may underscore the
significance of AS160 signal activation on RE-induced
GLUT4 translocation. In the future study, we need to
directly assess the glucose uptake to confirm our findings
on GLUT4 translocation.
Overall, our data showed that AMPK/TBC1D1 and
IGF1/Akt/AS160 signal activation enhanced glucose
uptake independently, and that acute RE activated these
signals. Moreover, acute RE increased the expression of
skeletal muscle IGF1 as a RE-specific GLUT4 transloca-
tion regulator. Further studies might clarify the contribu-
tion of IGF1 signals to acute RE-induced GLUT4
translocation by using an IGF1 knockout model.
Conflicts of Interest
The authors declare no conflicts of interest, financial or
otherwise.
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... The CaMK family consists of CaMK I, II, and IV isoforms [17,18]. It has been reported that increased calcium from exercise activates CaMKs while also increasing the activity of markers that enhance glucose uptake [18,19]. The peroxisome proliferatoractivated receptor gamma coactivator (PGC)-1α plays a central role in energy metabolism as a transcriptional coactivator of fat metabolism and carbohydrate metabolism and also plays an important role in mitochondrial biogenesis induced by exercise [20]. ...
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Diabetes is a metabolic syndrome characterized by inadequate blood glucose control and is associated with reduced quality of life and various complications, significantly shortening life expectancy. Natural phytochemicals found in plants have been traditionally used as medicines for the prevention of chronic diseases including diabetes in East Asia since ancient times. Many of these phytochemicals have been characterized as having few side effects, and scientific research into the mechanisms of action responsible has accumulated mounting evidence for their efficacy. These compounds, which may help to prevent metabolic syndrome disorders including diabetes, act through relevant intracellular signaling pathways. In this review, we examine the anti-diabetic efficacy of several compounds and extracts derived from medicinal plants, with a focus on AMP-activated protein kinase (AMPK) activity.
... 66,67 Mechanisms by which exercise increases insulin-stimulated glucose disposal are often associated with increased muscle blood flow, decreased muscle glycogen, and an increase in enzymes responsible for nonoxidative glucose disposal. [68][69][70] In addition to those, in recent years, an increase in AMPK has been implicated as an important mediator of postexercise insulin sensitivity. 52,53,71 Similarly, as previously described, metformin shares AMPK as a common target for glucose regulation, but the combination of these two modalities seems to be unclear and potentially conflicting (Table 1). ...
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Excess nutrient intake and lack of exercise characterize the problem of obesity and are common factors in insulin resistance (IR). With an increasing number of prediabetic, and type 2 diabetic populations, metformin is still the most prescribed glucose-lowering drug and is often accompanied by recommendations for regular physical exercise. Metformin, by the inhibition of complex 1 of the electron transport chain, and exercise, by increasing energy expenditure, both elicit a low cellular energy state that leads to improvements in glucose control via activation of adenosine 5' monophosphate-activated protein kinase (AMPK). An augmented stimulation of the energy-sensing enzyme AMPK by either of the two modalities leads to an increase in glycogenolysis, glucose uptake, fat oxidation, a decrease in glycogen and protein synthesis, and gluconeogenesis in muscle and the liver, which are remarked as having positive effects on metabolic pathophysiology observed in IR and type 2 diabetes mellitus (T2DM). While both modalities exploit the energy-sensing enzyme AMPK to attain glucose homeostasis, the synergistic effect of these two treatments is not distinctly supported by the literature. Further, an antagonistic dynamic has been observed in cases where metformin and exercise were combined. Reduction of insulin-sensitizing effects of exercise and an overall hindrance of exercise performance and adaptations have been reported and could suggest the possible incongruity of these two modalities. The aim of this review is to elucidate the effect that metformin and exercise have on the management of the metabolic abnormalities observed in T2DM and to provide an insight into the interaction of these two modalities.
... Similarly, small but statistically nonsignificant decreases in insulin level and HOMA-IR were found in an AET group compared to that of an RT group [34]. Reportedly, glucose uptake and utilization are increased with AET intervention via activation of AMP-activated protein kinase, whereas RT intervention can enhance glucose uptake and reduce blood glucose by resistance exercise-induced glucose transporter 4 translocation [35]. The effect of RT and AET interventions on glucose uptake regulation have different mechanisms. ...
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The aim of this study was to compare activation of cellular signaling pathways regulating protein synthesis and glucose uptake in skeletal muscle between resistance and endurance exercise. Moreover, the effect of resistance exercise volume was examined. Three groups of male volunteers (26 ± 3 years) were examined: 5 × 10 repetition maximum (RM) resistance exercise (RE) with leg press device (5 × 10 RE; n = 8), 10 × 10 RE (n = 11), and endurance exercise (strenuous 50-min walking with extra load on a treadmill; EE; n = 8). Muscle biopsies were obtained from m.vastus lateralis 30 min pre- and post-exercise. Downstream markers of mTORC1, p-p70S6K(Thr421/Ser424) and p-rpS6(Ser240/244), increased more after 10 × 10 RE than after 5 × 10 RE (p < 0.05) and EE (p < 0.01-0.001). Exercise-induced changes in p-IRS-I(Ser636/639) that inhibit IRS-I signaling via negative feedback from hyperactivated mTORC1 signaling were greater (p < 0.05) after 10 × 10 RE compared with 5 × 10 RE and EE. The changes in energy sensor p-AMPKα(Thr172) were greater after 10 × 10 RE and EE (p < 0.05-0.01) than after 5 × 10 RE. A major regulator of glucose uptake in muscle, p-AS160(Thr642), increased more after 10 × 10 RE than after 5 × 10 RE (p < 0.01) and EE (p < 0.05). 10 × 10 RE induced greater activation of important signaling proteins regulating glucose uptake (p-AS160) and protein synthesis (p-p70S6K, p-rpS6) than 5 × 10 RE and EE. The present findings further suggest that, especially after 10 × 10 RE, IRS-I signaling is downregulated and that AS160 is activated through AMPK signaling pathway.
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The importance of AMPK in regulation of fatty acid (FA) oxidation in skeletal muscle with contraction/exercise is unresolved. Using a mouse model lacking both AMPKα1 and -α2 in skeletal muscle specifically (mdKO), we hypothesized that FA utilization would be impaired in skeletal muscle. AMPKα mdKO mice displayed normal respiratory exchange ratio (RER) when fed chow or a high-fat diet, or with prolonged fasting. However, in vivo treadmill exercise at the same relative intensity induced a higher RER in AMPKα mdKO mice compared to wild-type (WT = 0.81 ± 0.01 (sem); mdKO = 0.87 ± 0.02 (sem); P < 0.01), indicating a decreased utilization of FA. Further, ex vivo contraction-induced FA oxidation was impaired in AMPKα mdKO muscle, suggesting that the increased RER during exercise originated from decreased skeletal muscle FA oxidation. A decreased muscle protein expression of CD36 (cluster of differentiation 36) and FABPpm (plasma membrane fatty acid binding protein) (by ∼17-40%), together with fully abolished TBC1D1 (tre-2/USP6, BUB2, cdc16 domain family member 1) Ser(237) phosphorylation during contraction/exercise in AMPKα mdKO mice, may impair FA transport capacity and FA transport protein translocation to sarcolemma, respectively. AMPKα is thus required for normal FA metabolism during exercise and muscle contraction.-Fentz, J., Kjøbsted, R., Birk, J. B., Jordy, A. B., Jeppesen, J., Thorsen, K., Schjerling, P., Kiens, B., Jessen, N., Viollet, B., Wojtaszewski, J. F. P. AMPKα is critical for enhancing skeletal muscle fatty acid utilization during in vivo exercise in mice. © FASEB.
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Background: phosphorylation of AS160 and TBC1D1 plays an important role for GLUT4 mobilization to the cell surface. The phosphorylation of AS160 and TBC1D1 in humans in response to acute exercise is not fully characterized. Objective: to study AS160 and TBC1D1 phosphorylation in human skeletal muscle after aerobic exercise followed by a hyperinsulinemic euglycemic clamp. Design: eight healthy men were studied on two occasions: 1) in the resting state and 2) in the hours after a 1-h bout of ergometer cycling. A hyperinsulinemic euglycemic clamp was initiated 240 min after exercise and in a time-matched nonexercised control condition. We obtained muscle biopsies 30 min after exercise and in a time-matched nonexercised control condition (t = 30) and after 30 min of insulin stimulation (t = 270) and investigated site-specific phosphorylation of AS160 and TBC1D1. Results: phosphorylation on AS160 and TBC1D1 was increased 30 min after the exercise bout, whereas phosphorylation of the putative upstream kinases, Akt and AMPK, was unchanged compared with resting control condition. Exercise augmented insulin-stimulated phosphorylation on AS160 at Ser(341) and Ser(704) 270 min after exercise. No additional exercise effects were observed on insulin-stimulated phosphorylation of Thr(642) and Ser(588) on AS160 or Ser(237) and Thr(596) on TBC1D1. Conclusions: AS160 and TBC1D1 phosphorylations were evident 30 min after exercise without simultaneously increased Akt and AMPK phosphorylation. Unlike TBC1D1, insulin-stimulated site-specific AS160 phosphorylation is modified by prior exercise, but these sites do not include Thr(642) and Ser(588). Together, these data provide new insights into phosphorylation of key regulators of glucose transport in human skeletal muscle.
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Concurrent training, a combination of endurance (EE) and resistance exercise (RE) performed in succession, may compromise the muscle hypertrophic adaptations induced by RE alone. However, little is known about the molecular signaling interactions underlying the changes in skeletal muscle adaptation during concurrent training. Here, we used an animal model to investigate whether EE before or after RE affects the molecular signaling associated with muscle protein synthesis, specifically the interaction between RE-induced mammalian target of rapamycin complex 1 (mTORC1) signaling and EE-induced AMP-activated protein kinase (AMPK) signaling. Male Sprague-Dawley rats were divided into 5 groups: an EE (treadmill, 25 m/min, 60 min) group, an RE (maximum isometric contraction via percutaneous electrical stimulation for 3 s × 10, 5 sets) group, an EE before RE group, an EE after RE group, and a non-exercise control (CON) group. Phosphorylation of p70S6K, a marker of mTORC1 activity, was significantly increased 3 h after RE in both the EE before RE and EE after RE groups, but the increase was smaller in latter. Further, protein synthesis was greatly increased 6 h after RE in the EE before RE group. Increases in the phosphorylation of AMPK and Raptor were observed only in the EE after RE group. Akt and mTOR phosphorylation were increased in both groups with no between-group differences. Our results suggest that the last bout of exercise dictates the molecular responses, and that mTORC1 signaling induced by any prior bout of RE may be downregulated by a subsequent bout of EE.
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Earlier research on rats with normal insulin sensitivity demonstrated that acute exercise increased insulin-stimulated glucose uptake (GU) concomitant with greater phosphorylation of Akt Substrate of 160 kDa (pAS160). Because mechanisms for exercise-effects on glucose uptake in insulin-resistant muscle are unknown, our primary objective was to assess insulin-stimulated GU, proximal insulin signaling (insulin receptor tyrosine phosphorylation, IRS-1-phosphatidylinositol-3-kinase, and Akt phosphorylation and activity) and pAS160 in muscles from acutely exercised (one-session) and sedentary rats fed either chow (low fat diet, LFD; normal insulin sensitivity) or high fat diet (for 2wk; HFD; insulin resistant). At 3h post-exercise (3hPEX), isolated epitrochlearis muscles were used for insulin-stimulated GU and insulin signaling measurements. Although exercise did not enhance proximal signaling in either group, insulin-stimulated glucose uptake at 3hPEX exceeded respective sedentary controls in both diet-groups. Furthermore, insulin-stimulated GU for LFD-3hPEX was greater than HFD-3hPEX values. For HFD-3hPEX muscles, pAS160 exceeded HFD-Sedentary controls, but in muscle from LFD-3hPEX rats, pAS160 was greater still than HFD-3hPEX values. These results implicated pAS160 as a potential determinant of the exercise-induced elevation in insulin-stimulated GU for each diet-group and also revealed pAS160 as a possible mediator of greater post-exercise GU of insulin-stimulated muscles from the insulin-sensitive versus insulin-resistant group.
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Type 2 Diabetes is an increasingly prevalent condition with complications including blindness and kidney failure. Evidence suggests that Type 2 Diabetes is associated with a sedentary lifestyle, with physical activity demonstrated to increase glucose uptake and improve glycemic control. Proposed mechanisms for these effects include the maintenance and improvement of insulin sensitivity via increased GLUT 4 production. The optimal mode, frequency, intensity and duration of exercise for the improvement of insulin sensitivity are however yet to be identified. We review the evidence from 34 published studies addressing the effects on glycemic control and insulin sensitivity of aerobic exercise (AE), resistance training (RT), and both combined (COM). Effect sizes and confidence intervals are reported for each intervention and meta-analysis presented. The quality of the evidence is tentatively graded, and recommendations for best practice proposed. This article is protected by copyright. All rights reserved.
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Objectives: Kamishimotsuto (KST) is a supplement containing 13 different herbs including Phellodendron bark, Anemarrhena rhizome and ginseng that have been shown to activate mammalian target of rapamycin complex 1 (mTORC1) and thereby increase muscle protein synthesis in vitro. However, the combined effect of KST and resistance exercise on muscle protein anabolism has not been investigated in vivo. Therefore, the purpose of this study was to investigate the effect of KST supplementation, resistance exercise on (mTORC1) signaling and subsequent muscle protein synthesis. Methods: Male Sprague-Dawley rats were divided into two groups: one group received KST (500 mg/kg/d in water) and the other group received placebo (PLA) for 7 d. After 12 h of fasting, the right gastrocnemius muscle was isometrically exercised via percutaneous electrical stimulation. Muscle samples were analyzed for muscle protein synthesis (MPS) and by western blotting analysis to assess the phosphorylation of p70S6K (Thr389), rpS6 (Ser240/244), and Akt (Ser473 and Thr308). Results: KST supplementation for 7 d significantly increased basal p-Akt (Ser473) levels compared with PLA, phosphorylation of the signaling proteins and MPS at baseline were otherwise unaffected. p-p70S6K and p-rpS6 levels significantly increased 1 h and 3 h after exercise in the PLA group, and these elevations were augmented in the KST group (P < 0.05). Furthermore, MPS at 6 h after resistance exercise was greater in the KST group than in the PLA group (P < 0.05). Conclusions: While resistance exercise alone was able to increase p70S6K and rpS6 phosphorylation, Kamishimotsuto supplementation further augmented resistance exercise-induced muscle protein synthesis through mTORC1 signaling.