This study investigated the effects of gonadal hormone loss and immobilization or high fat diet on skeletal muscle insulin signaling in female rats. The researchers found that gonadal hormone loss decreased insulin-mediated pAKT/total AKT expression in quadriceps muscle after immobilization-induced disuse atrophy, but not body or quadriceps weight. A high fat diet increased body weight, energy intake, and tended to increase pAKT/total AKT expression in quadriceps muscle irrespective of gonadal hormone status. Ongoing studies will examine other insulin signaling proteins and muscle recovery after disuse atrophy with hormone loss and high fat diet.

1. Gonadal Hormone Loss Impairs Skeletal Muscle Insulin Signaling
Natalie Raia, Alice Yeh, Riley Nguyen, Flavia Souza-Smith, Patricia Molina, Liz Simon
Department of Physiology, LSUHSC
Ø Decreased gonadal hormone levels and shift in fat distribution
contribute to weight gain postmenopause
Ø Weight gain is exacerbated in postmenopausal women consuming a
Western Diet, which is high in fatty foods and correlated with increased
rates of insulin resistance, diabetes, and obesity
Ø Incidence of skeletal muscle disuse atrophy is also high in
postmenopausal women primarily due to osteoporotic fractures
requiring limb immobilization and other conditions.
Ø Both disuse atrophy and consuming a high-fat diet hinder insulin-
mediated glucose uptake into muscle, the most abundant insulin-
sensitive tissue.
Ø Disuse atrophy:
o ↓ in quadriceps weight irrespective of gonadal hormone status
o ↓ in quadriceps pAKT: total AKT expression due to gonadal
hormone loss
.This research was supported by the Entergy Workforce Training Grant.
Methods
Fisher-344 Female Rats
OVX
Immobilized
limb
Non-immobilized
limb
Non-OVX
Immobilized
limb
Non-immobilized
limb
Experiment 1
Disuse Atrophy
Fisher-344 Female Rats
OVX
HFD
(45% fat)
LFD
(10% fat)
Non-OVX
HFD
(45% fat)
LFD
(10% fat)
Experiment 2
High Fat Diet
Gonadal hormone loss pAKT/total AKT in quadriceps after disuse atrophy
Figure 1: There was no significant difference in body weight
between the control and the ovariectomized group. There was
a main effect of immobilization to decrease quadriceps muscle
weight. Statistical analysis was done using t-tests and two-
way ANOVA. N=4/group *P<0.05.
Figure 4: There was a main effect of
ovariectomy and HFD to increase
body weight and energy. Data
analyzed using two-way ANOVA.
N=4/group * Effect of HFD P<0.05, $
Effect of OVX p<0.05.
Hypothesis
Introduction
Gonadal hormone loss
decreases skeletal
muscle insulin signaling
protein expression
following disuse
atrophy, or with high fat
diet in female rodents
Summary
LFD
+INS
LFD
-INS
HFD
+INS
HFD
-INS
LFD
+INS
LFD
-INS
HFD
+INS
HFD
-INS
Control OVX
Ø Seven-day unilateral hind limb immobilization ten weeks post-ovariectomy
Ø Casts were removed and animals were allowed to recover for 14 days
Ø Quadriceps muscle was collected
Ø Western blot analysis performed on homogenized tissue
Ø Animals were ovariectomized and fed ad libitum on a HFD or LFD
Ø Quadriceps muscle tissue was collected and stimulated with insulin (10 nM)
for 1 hr
Ø Western blot analysis performed on homogenized tissue
Body weight
g
Control OVX
0
50
100
150
200
Quad Weight
g/inch(tibiallength)
NI I NI I
0.0
0.5
1.0
1.5
* *
Control OVX
Ø High fat diet:
o ↑ in body weight due to high fat diet and gonadal hormone loss
o Potential ↑ in quadriceps pAKT: total AKT expression due to high
fat diet
pAKT/Total AKT
Relativveproteinexpression
NI I NI I
0.0
0.5
1.0
1.5
2.0
2.5
* *
Control OVX
Figure 2: Representative blots of pAKT, total AKT and GRB2. There was a main effect of ovariectomy
to decrease pAKT/total AKT expression in the quadriceps muscle. There was no significant change in
pAKT/ total AKT due to immobilization. Expression of pAKT and AKT were normalized to the loading
control, GRB2. Data analyzed using two-way ANOVA. N=4/group * P<0.05.
Body weight
g
LFD HFD LFD HFD
100
150
200
250
* $
*$
Control OVX
Energy Intake
LFD HFD LFD HFD
0
100
200
300
400
*
*$
kcal
$
Control OVX
pAKT/Total AKT
LFD HFD LFD HFD
0
10
20
40
60
Relativveproteinexpression
Insstimulated/non-insstimulated
Main effect of diet, p=0.08
Control OVX
Control OVX
Figure 3: HFD increased
pAKT/total AKT expression in the
quadriceps muscle, although it
did not achieve statistical
significance. Muscle pAKT/ total
AKT was expressed as the ratio
of insulin-stimulated over non-
insulin stimulated pAKT/ total AKT
ratios. Data analyzed using two-
way ANOVA. N=4/group * P<0.05
Gonadal hormone loss and high fat diet body weight and energy intake
Non-immobilized
pAKT
AKT
GRB2
Immobilized
pAKT
AKT
GRB2
Ø Ongoing studies will determine expression of other insulin signaling proteins in the muscle in both the studies
Ø Future studies will determine whether high fat diet and gonadal hormone loss impairs recovery after disuse atrophy
pAKT
AKT
GRB2