ORIGINAL ARTICLE
Insulin stimulation of Akt/PKB phosphorylation in the
placenta of preeclampsia patients
Estimulação com insulina da fosforilação da Akt/PKB em placenta de pacientes
com pré-eclâmpsia
Gustavo Dias FerreiraI, Rafael Bueno OrcyII, Sérgio Hofmeister Martins-CostaIII, José Geraldo Lopes RamosIV, Ilma Simoni BrumV,
Helena von Eye CorletaVI, Edison CappVII
Master’s degree program in Biological Sciences (Physiology), Molecular, Endocrine and Tumor Biology Laboratory and Department of
Gynecology and Obstetrics, Universidade Federal do Rio Grande do Sul (UFRGS), and Gynecology and Molecular Obstetrics Laboratory,
Gynecology and Obstetrics Research Center, Hospital de Clínicas de Porto Alegre, Porto Alegre, Rio Grande do Sul, Brazil
I
MSc, Molecular, Endocrine and Tumor Biology
Laboratory, Universidade Federal do Rio Grande do
Sul (UFRGS), and PhD Student in Gynecology and
Molecular Obstetrics Laboratory, Research Center,
Hospital de Clínicas de Porto Alegre, Porto Alegre,
Rio Grande do Sul, Brazil.
II
PhD. Physiologist, Molecular, Endocrine and
Tumor Biology Laboratory, Universidade Federal
do Rio Grande do Sul (UFRGS), and Researcher in
Gynecology and Molecular Obstetrics Laboratory,
Research Center, Hospital de Clínicas de Porto
Alegre, Porto Alegre, Rio Grande do Sul, Brazil.
III
MD, PhD. Adjunct Professor, Gynecology and
Obstetrics Service, Hospital de Clínicas de Porto Alegre,
and Department of Gynecology and Obstetrics, School
of Medicine, Universidade Federal do Rio Grande do
Sul (UFRGS), Porto Alegre, Rio Grande do Sul, Brazil.
IV
MD, PhD. Associate Professor, Gynecology and
Obstetrics Service, Hospital de Clínicas de Porto Alegre,
and Department of Gynecology and Obstetrics, School
of Medicine, Universidade Federal do Rio Grande do
Sul (UFRGS), Porto Alegre, Rio Grande do Sul, Brazil.
V
MD, PhD. Associate Professor, Department of
Physiology, Molecular, Endocrine and Tumor Biology
Laboratory, Universidade Federal do Rio Grande do
Sul (UFRGS), Gynecology and Molecular Obstetrics
Laboratory, Research Center, Hospital de Clínicas de
Porto Alegre, Porto Alegre, Rio Grande do Sul, Brazil.
VI
MD. Associate Professor, Gynecology and Obstetrics
Service, Hospital de Clínicas de Porto Alegre, and
Department of Gynecology and Obstetrics, School of
Medicine, Universidade Federal do Rio Grande do Sul
(UFRGS), Porto Alegre, Rio Grande do Sul, Brazil.
VII
MD, PhD. Associate Professor, Department of
Gynecology and Obstetrics, Universidade Federal do
Rio Grande do Sul (UFRGS), and Coordinator of Master’s
degree program in Biological Sciences (Physiology),
Molecular, Endocrine and Tumor Biology Laboratory,
UFRGS, Porto Alegre, Rio Grande do Sul, Brazil.
KEY WORDS:
Pre-eclampsia.
Placenta.
Insulin resistance.
Receptor, insulin.
Proto-oncogene proteins c-akt.
ABSTRACT
CONTEXT AND OBJECTIVE: Preeclampsia is a multi-systemic disease and one of the most frequent severe
health problems during pregnancy. Binding of insulin triggers phosphorylation and activates cytoplasmic
substrates such as phosphatidylinositol 3 kinase (PI3K). Phosphorylation of membrane phosphoinositide
2 (PIP2) to phosphoinositide 3 (PIP3) by PI3K starts Akt/PKB activation. Defects in phosphorylation of the
insulin receptor and its substrates have an important role in insulin resistance. Studies have shown that
insulin resistance is associated with preeclampsia and its pathophysiology. The aim here was to investigate
insulin stimulation of the Akt/PKB pathway in the placenta, in normal and preeclampsia parturients.
DESIGN AND SETTING: Cross-sectional study in a tertiary public university hospital.
METHODS: Placentas were collected from 12 normal and 12 preeclampsia patients. These were stimulated and analyzed using Western blot to quantify the Akt/PKB phosphorylation.
RESULTS: The insulin stimulation was conirmed through comparing the stimulated group (1.14 ± 0.10)
with the non-stimulated group (0.91 ± 0.08; P < 0.001). The phosphorylation of Akt/PKB did not differ between the placenta of the normal patients (1.26 ± 0.16) and those of the preeclampsia patients
(1.01 ± 0.11; P = 0.237).
CONCLUSIONS: In vitro insulin stimulation of the human placenta has been well established. There was
no diference in Akt/PKB phosphorylation, after stimulation with insulin, between placentas of normal and
preeclampsia patients. Nevertheless, it cannot be ruled out that the Akt/PKB signaling pathway may have a
role in the pathophysiology of preeclampsia, since the substrates of Akt/PKB still need to be investigated.
RESUMO
CONTEXTO E OBJETIVO: Pré-eclâmpsia (PE) é uma doença multissistêmica das mais frequentes e graves
durante a gestação. A ligação da insulina inicia a fosforilação e ativação de substratos citoplasmáticos, tais
como fosfatidil-inositol 3 quinase (PI3K). A fosforilação do fosfoinositol 2 (PIP2) da membrana em fosfoinosiltol 3 (PIP3) pela PI3K inicia a ativação da Akt/PKB. Defeitos na fosforilação do receptor de insulina e seus
substratos têm papel importante na resistência à insulina. Estudos demonstraram que resistência à insulina está associada com pré-eclâmpsia e sua patoisiologia. O objetivo foi investigar a via de estimulação
com insulina da Akt/PKB em placenta de parturientes normais e com pré-eclampsia.
TIPO DE ESTUDO E LOCAL: Estudo do tipo transversal em um hospital universitário público de nível
terciário.
MÉTODOS: Vinte e quatro placentas (12 normais, 12 com PE) foram coletadas, estimuladas e analisadas
por Western blot para quantiicar a fosforilação da Akt/PKB.
RESULTADOS: A estimulação com insulina foi conirmada comparando os grupos estimulados (1,14 ± 0,10)
e não estimulados (0.91 ± 0.08; P < 0.001). A fosforilação de Akt/PKB não foi diferente na placenta de pacientes normais (1,26 ± 0,16) e com PE (1,01 ± 0,11; P = 0,237).
CONCLUSÕES: A estimulação in vitro da placenta humana com insulina foi bem estabelecida. Não houve
diferença na fosforilação da Akt/PKB após estimulação em placentas de pacientes normais e PE. Contudo,
não é possível descartar a participação desta via de sinalização na patoisiologia da PE, uma vez que os
substratos da Akt/PKB ainda precisam ser investigados.
PALAVRAS-CHAVE:
Pré-eclâmpsia.
Placenta.
Resistência à insulina.
Receptor de insulina.
Proteínas proto-oncogênicas c-akt.
Sao Paulo Med J. 2011; 129(6):387-91
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ORIGINAL ARTICLE | Ferreira GD, Orcy RB, Martins-Costa SH, Ramos JGL, Brum IS, Corleta HVE, Capp E
INTRODUCTION
Preeclampsia is a multi-systemic disease and is considered to be
one of the most signiicant health problems in pregnancy. It occurs
mainly in nulliparous women, particularly ater the 20th week of
gestation, and most frequently near delivery.1 It is diagnosed when
the patient presents gestational hypertension associated with proteinuria, vasoconstriction of the maternal vascular bed and, consequently, increased vascular resistance.2-4 he incidence ranges from
2-5% to more than 10% of pregnancies in developing countries,
where prenatal care is still inadequate.1 It can afect both maternal
and fetal health,5 leading to fetal growth restriction, prematurity
and, in severe cases, maternal and perinatal death.6-8 Studies have
shown that insulin resistance is associated with preeclampsia and
contributes towards its pathophysiology.9
he insulin receptor belongs to the family of tyrosine kinases
(RTKs). he binding of insulin triggers phosphorylation and activates cytoplasmic substrates such as phosphatidylinositol 3 kinase
(PI3K). Phosphorylation of membrane phosphoinositide 2 (PIP2)
to phosphoinositide 3 (PIP3) by PI3K starts Akt/PKB activation.10,11
Defects in phosphorylation of the insulin receptor and its substrates, and non-activation of PI3K-Akt/PKB has an important
role in developing insulin resistance.10,12 If not activated, the Akt/
PKB pathway will also not phosphorylate its substrates, which participate in various cell functions, such as control of metabolism,
survival, glucose uptake, proliferation, growth and angiogenesis.13
OBJECTIVE
he aims of this study were to achieve in vitro insulin stimulation
of the human placenta and to investigate the expression of the
protein Akt/PKB in the baseline state and ater stimulation, in the
placentas of normal and preeclampsia patients.
METHODS
A cross-sectional study with control group was performed. Twenty-four women participated, including 12 patients who presented
a medical diagnosis of preeclampsia and 12 normotensive pregnant women (control group). he samples were divided into four
groups: stimulated controls, non-stimulated controls, stimulated
preeclampsia patients and non-stimulated preeclampsia patients.
Information such as age, use of hormonal medication, family history of diabetes mellitus, gynecological and obstetric history, fasting glucose, blood pressure, proteinuria, glucose tolerance test of
the mother and gestational age was gathered before the birth.
his study was submitted to and approved by the Research Ethics
Committee of the Research and Postgraduate Program Group of
Hospital de Clínicas de Porto Alegre (GPPG 08-124).
Sample preparation
Approximately 30 g of placenta were obtained immediately ater
cesarean sections. he samples were washed with phosphate388
Sao Paulo Med J. 2011; 129(6):387-91
bufered saline (PBS) (4 °C) to remove excess blood and were
taken to the laboratory for preparation and stimulation with
insulin.
he preparation of the placenta was performed in accordance with Klein et al.,14 with modiications. he tissue was
weighed in the laboratory, separated from blood vessels and cut
in slices. One gram of tissue was incubated in 5 ml of bovine
serum albumin (BSA) bufer: 32 mM of HEPES, 195 mM of
NaCl, 7.2 mM of KCl, 1.8 mM of KH2PO4, 8.3 mM of glucose
and 1% albumin in distilled H2O. Briely, the placental tissue
was digested with collagenase type I (Gibco, Invitrogen Corporation) and incubated at 37 °C under orbital stirring (100 rpm)
for 45 minutes. Ater this, a 250 mm ilter was used to separate out and remove large particles and remaining ibrin. For
cell separation, the sample was divided into two 50 ml tubes
and centrifuged at 2000 x g for 10 minutes at 30 °C. Ater the
supernatant had been discarded, a small portion of the sample
was viewed under a microscope to observe the viability of the
cells for stimulation. he cells were then homogenized with 0.5
ml of PBS. hese samples were transferred to two 1.5 ml tubes,
which were incubated with 0.5 ml of a stimulation bufer containing 50 mM of Tris-HCl (pH 7.4), 0.01% BSA, 1 mM of ATP,
2 mM of MgCl2, 1 mM of EDTA, 5 mM of sodium pyrophosphate, 1 mM of sodium orthovanadate and 50 mM of sodium
luoride, with and without insulin [10-7 M] for eight minutes at
37 °C.9 For analysis, placental pieces were pooled and homogenized. Protein concentrations were measured using Bradford’s
method.15
he samples were analyzed using Western blot.16,17 Samples
of 60 µg of protein (per lane) were loaded onto 10% acrylamide
gel. he proteins were transferred to nitrocellulose membranes
by means of a semidry system. Rabbit polyclonal antibodies
(Santa Cruz, California, United States) were used: total anti-Akt
(sc-8312) and phosphor-Akt (Ser473) (sc-7985).
Statistical analysis
Statistical analysis was performed by means of the Statistical
Package for the Social Sciences (SPSS) 15.0 sotware. he data
were tested using Student’s t test for paired samples and independent samples, for parametric variables, and were shown as
means ± standard deviations (SD). he signiicance level was
taken to be P < 0.05.
RESULTS
he patients with preeclampsia fulilled the diagnostic criteria, presenting proteinuria over 300 mg/dl and hypertension. In
the normotensive group, there were no patients with proteinuria over 300 mg/dl. he normotensive and preeclampsia groups
did not difer signiicantly in age (26.8 ± 4.1 versus 27.8 ± 8.2;
P = 0.714), body mass index (BMI) (28.4 ± 3.5 versus 31.3 ± 4.1;
Insulin stimulation of Akt/PKB phosphorylation in the placenta of preeclampsia patients | ORIGINAL ARTICLE
P = 0.08) or number of pregnancies (2.5 ± 2.1 versus 1.8 ± 1.1;
P = 0.303) (Table 1). he mean gestational age was approximately
four weeks shorter in the preeclampsia group (35.6 ± 0.5 versus
39.1 ± 0.4; P < 0.001), while the fasting glucose levels (mg/dl)
were signiicantly higher in the preeclampsia group (91.58 ± 2.83
versus 76.00 ± 2.39; P < 0.001). Diastolic and systolic blood
pressures were signiicantly higher in the preeclampsia patients
(P < 0.001) (Table 1).
Table 1. Clinical characteristics of women with preeclampsia and
control subjects
Sample stimulation
Sample stimulation was assessed by comparing the expression of
phosphor-Akt (Ser473) in samples stimulated with insulin (+) and
not stimulated (-), both in the control group and in the preeclampsia group. he values were normalized according to total anti-Akt
protein expression (60 kDa) (Figure 1).
In the control group (n = 12), the expression of phosphorAkt (Ser473) was 1.26 ± 0.16 for samples stimulated with insulin (+) and 0.93 ± 0.12 for samples not stimulated (-), with a signiicant diference of P < 0.001. In the PE group (n = 12), the
expression was 1.01 ± 0.01 for samples stimulated with insulin
and 0.89 ± 0.11 for samples not stimulated, with a signiicant difference of P = 0.001, thus conirming that the samples had been
stimulated (Figure 2).
PE = preeclampsia; BMI = body mass index. *Student’s t test.
Age (years)
BMI (kg/m²)
Gestational age (weeks)
Systolic blood pressure (mmHg)
Diastolic blood pressure (mmHg)
Number of pregnancies
Fasting glucose (mg/dl)
Normal
26.8 ± 4.1
28.4 ± 3.5
39.1 ± 0.4
118.5 ± 10
70.6 ± 6.4
2.5 ± 2.1
76.0 ± 2.3
PE
27.8 ± 8.2
31.3 ± 4.1
35.6 ± 0.5
154.8 ± 10
97.5 ± 5.9
1.8 ± 1.1
91.5 ± 2.8
P
0.714
0.080
< 0.001*
< 0.001*
< 0.001*
0.303
< 0.001*
Figure 1. Representative Western blot analysis on placenta samples
from patients with preeclampsia (PE) and normal controls (C): sample
stimulated with insulin (+); sample not stimulated with insulin (-).
Protein expression in the preeclampsia group and control
group
To compare the expression of Akt/PKB between the preeclampsia and control group, the analyses were performed in two states:
baseline state (no stimulation with insulin) and stimulated state.
In the baseline state, the expression of phosphor-Akt (Ser473)
was 0.93 ± 0.13 in the control group (n = 12) and 0.89 ± 0.11 in
the preeclampsia group (n = 12) (P = 0.82) (Figure 3A). Among
the samples stimulated with insulin, the expression in the control group (n = 12) was 1.26 ± 0.16 and in the preeclampsia group
(n = 12), it was 1.01 ± 0.11 (P = 0.23) (Figure 3B). here was no
statistically signiicant diference between the preeclampsia group
and the control group, either in the baseline state or in the stimulated state.
DISCUSSION
Preeclampsia occurs frequently during pregnancy, and it is a multisystem disease of unknown etiology.3,18 Insulin resistance and obesity have been deined as risk factors for the development of this
disease.9,19,20
In the present study, age and BMI did not difer between the
control and preeclampsia groups. Age seems to be a risk factor for
preeclampsia, since women older than 40 years and younger than 20
years are at higher risk of preeclampsia. Being pregnant for the irst
time, among young women, may also be a factor that increases the
risk of preeclampsia among these patients.21 In the control group, six
Figure 2. Expression of phosphor-Akt (Ser473) in stimulated and nonstimulated samples. In the control group (A), 0.93 ± 0.12 for the nonstimulated samples (-) and 1.26 ± 0.16 for the stimulated samples (+)
(P < 0.001). In the preeclampsia group (B), 0.89 ± 0.11 for the non-stimulated
samples (-) and 1.01 ± 0.11 for the stimulated samples (+) (P = 0.001).
Figure 3. Expression of phosphorylation of Akt/PKB compared
between the non-stimulated control group and preeclampsia group (A)
(P = 0.828), and between the stimulated control group and preeclampsia
group (B) (P = 0.237).
Sao Paulo Med J. 2011; 129(6):387-91
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ORIGINAL ARTICLE | Ferreira GD, Orcy RB, Martins-Costa SH, Ramos JGL, Brum IS, Corleta HVE, Capp E
patients were overweight (BMI from 25 kg/m2 to 29.9 kg/m2) and
four patients were obese (BMI ≥ 30.0 kg/m2), while in the preeclampsia group, ive patients were overweight and six were obese.
Obesity is a major risk factor for preeclampsia, given that an increase
in BMI of 7 kg/m2 doubles the risk of disease.22
Soonthornpun et al. demonstrated that even with no signiicant
diference in BMI, women with preeclampsia had higher serum triglycerides and lower HDL levels than seen in the control group.23 Villa
et al. investigated the fatty acid proile in women with preeclampsia
and controls, and found that even without a diference in BMI, the
preeclampsia group showed higher levels of oleic acid, linoleic acid
and arachidonic acid, and increased insulin resistance.19
Preterm delivery (deined as gestational age < 37 weeks) is a
common complication in preeclampsia patients (15-67%).3 As
expected, in this study, the mean gestational age at delivery was
lower in the preeclampsia group. However, this did not seem to
inluence our results.
Preeclampsia is one of the most important diseases during
pregnancy, but its molecular mechanisms are not fully understood yet.24 Since the role of the placenta in the pathogenesis of
preeclampsia is undisputed, and Akt/PBK action in insulin resistance is evident,25-28 we analyzed the expression of Akt/PKB at
the baseline and with insulin stimulation, in placental tissue from
preeclampsia and normal pregnancies. Ater insulin binding,
the receptor is autophosphorylated, and it phosphorylates cytoplasmic substrates such as insulin receptor substrate 1 and PI3
kinase (PI3K). Ater phosphorylation, PI3K triggers phosphorylation of Akt/PKB at serine (ser473) and threonine (thr308)
sites.29 Phosphorylated Akt/PKB translocates to the cytoplasm or
to the nucleus, where it activates substrates with diferent actions
on metabolism, growth and cell survival.13 Scioscia et al. showed
that there was a decrease in tyrosine phosphorylation of IRS1, in
insulin-stimulated preparations of human placenta from preeclampsia patients, compared with normal placenta, thus demonstrating that there is a lower level of insulin signaling in women
with preeclampsia.9
In our study, sample stimulation was conirmed when the
expression of phospho-Akt/PKB (p-Ser 473) was compared
between insulin-stimulated and non-stimulated placenta cells. his
signaling transduction pathway is an important milestone in the
molecular mechanisms for insulin resistance syndrome in patients
with preeclampsia.9 Data from Scoscia suggested that there was signiicantly higher serine phosphorylation of IRS1 and IRS2 in insulin-treated samples from preeclampsia patients. On the other hand,
the insulin signal transduction signal was impaired in the controls,9
as also described in other insulin resistant states (diabetes type 2).
Kunjara et al. demonstrated that accumulation of inositol phosphoglycan (P-IPG), a putative second insulin messenger, exerted several insulin-mimetic actions in placental tissue from preeclampsia
patients and might be associated with insulin resistance.30
390
Sao Paulo Med J. 2011; 129(6):387-91
Orcy et al. previously studied the Akt/PKB expression pathway in
the baseline state in the placenta, skeletal muscle and adipose tissue of
preeclampsia patients. However, their indings did not show any signiicant diference in protein between the groups of patients.6 Similarly, our results also showed that there were no signiicant diferences
in baseline protein expression of Akt/PKB between the placentas of
preeclampsia patients and controls. Likewise, there was no diference
in stimulated Akt/PKB phosphorylation.
CONCLUSIONS
In vitro stimulation of the human placenta using insulin has been
well established. he expression of Akt/PKB in preeclampsia patients
and controls, both at the baseline and in insulin-stimulated placenta
samples, was similar. his suggests that there is similar activity of
this pathway in these groups of women. Nevertheless, it cannot be
ruled out that the Akt/PKB signaling pathway may have a role in the
pathophysiology of preeclampsia, since the phosphorylation of Akt/
PKB substrates still needs to be investigated.
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E-mail: edcapp@ufrgs.br
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