| Abstract |
This project aims at revealing the possible connection between
expression of Hypoxia Inducible Factors (HIF) and their pathway in
pregnancies affected with Fetal Growth Restriction (FGR) together or
not with preeclampsia.
FGR is a complex condition in the field of current Obstetrics. The
failure of a foetus to achieve its genetically determined growth potential
is associated with significantly increased perinatal morbidity and
mortality as well as being a major determinant of cardiovascular disease
and glucose intolerance in adult life. FGR is not a disease entity with a
unique pathophysiology. The term FGR is generally used for a foetus that
presents reduced velocity pattern of growth (&λτ΄΄0th centile). A variety of
factors have been involved in this situation including infectious, congenital
abnormalities, drug abuse or chemical substances, abnormalities of the
placenta, immunological and anatomical factors. In most cases, however,
incomplete placentopoiisis (placental formation) is the cause for the
insufficient supply of nutritious substances and oxygen to the fetus that
subsequently causes the deceleration of his growth. Hypoxia appears to
constitute a common pathophysiological mechanism in almost the majority
of the cases, and regardless the underlying pathology leads to the delay
of fetal growth. Preeclampsia comprises a pathologic condition that, as
many others, may cause foetus hypoxia.
Preeclampsia affects 4-6% of pregnancies and it may have serious
consequences for the maternal health as well as for the development and
well-being of the foetus. This pathological entity is characterized by an
increase of the arterial pressure beyond the 20th week of gestation as
well as by proteinuria and/or oedema. Although a variety of conditions
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(including chronic hypertension, coagulopathies, immunological and genetic
disorders, nutrition insufficiencies or abuses) appear to constitute risk
factors and have been connected with higher risk of the disease;
however, the molecular mechanisms and the precise causes that are
hidden in the underlying pathophysiology remain unclear and raise a field
of further investigation. Base on the studies of last decade, it has been
revealed that the disturbance in the balance of circulating angiogenic
factors (sFlt-1, VEGF1, PlGF) has an important role in the pathophysiology
of preeclampsia that leads to endothelium abnormalities of vessels as well
as to the symptoms of the disease. These factors are regulated by
several other factors and conditions, but hypoxia seems to be one of the
most important.
One of the more important processes at the development of
gestation is the physiologic formation of the fetal-placental unit that
begins with the infiltration of cytotrophoblasts into the endometrium and
is completed when conjunction with the spiral arteries has occurred.
During this process, structural changes are required both for the
endothelium of endometrium that receives cytotrophoblasts invasion and
for the elastic walls of spiral arteries. This process includes the passage
from a hypoxia condition into a condition of physiologic oxygenation in a
cellular level; in this process the role of Hypoxia Inducible Factors (HIF)
is critical.
HIF-1 constitutes probably the most essential response of the cell
to the hypoxia. It acts in the cell nucleus, by inducing the expression of
many genes that play role in angiogenesis, cell cycle and metabolism. HIF-
2 appears to have a similar function, while the data regarding HIF-3 are
still insufficient. As the regulation of these factors is depending on the
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oxygen concentration, a clear relationship is obvious between them and
the hypoxia conditions of as FGR and preeclampsia. The regulation of HIF
appears to relate not only with the induction/suspension of their
expression, but also post-translationally with their degradation. Factors
PHD-1, 2 and 3, as well as VHL play a role of their degradation. In some
pathological situations, this model is probably disturbed and hypoxia
maintains the regulating action of HIF in active levels.
It is obvious that all the above factors appear to possess a critical
role in the process of pathogenesis of both FGR and preeclampsia. The
adequate comprehension of the pathway of regulation of HIF may give an
impulse to development of intervention models in those particular
pathologic conditions that are related with hypoxia, common in many
pregnancies. ANXA5 is also crucial for the uteroplacental unit due to its
antithrombotic action.
During this study the action and regulation of the above mentioned
factors (HIF-1a,-2a,-3a, ARNT, PHD-1,-2,-3, VHL and ANXA5) was
investigated in term placentas from 49 FGR gestations related or not to
preeclampsia compared to 30 term placentas from normal pregnancies.
FGR and preeclampsia were diagnosed with clinical and laboratory data
and cases with particular pathological cause such as thrombophilia,
chromosomal defects, infections and others were excluded. All placentas
were examined by a pathologist. RT-PCR was the molecular technique of
choice to determine expression profiles for each gene. Western blotting
and immunohistochemistry was also performed in selected cases.
Statistical analysis was processed with the use of SPSS software.
The final results revealed marked downregulation of PHD-2, PHD-3
and ANXA5, slight upregulation of HIF-1a and HIF-2a, along with PHD-1,
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while ARNT, HIF-3a and VHL expressions didn’t produce significant
differences between FGR and normal placentas.
ANXA5 was expected to be downregulated, since placentas from
FGR and preeclamptic pregnancies showed infarcts presence.
Downregulation of PHD-2 and PHD-3, along with upregulation of HIF-1a
and HIF-2a points out the inducible effect that hypoxia seems to have in
HIF transcriptional pathway. Stabilization of HIF-a subunits by reduction
of PHD proteins is more crucial for activation of HIF than HIF
expression by itself. Moreover, with the clinical and demographic data
correlation analysis along with expression profiles, a new model is
introduced. Based on these results, it can be hypothesized that FGR
babies with less severe disease, are able to produce a signal stimulated by
the reduced placental nutrient and oxygen availability in order to
overcome it, in contrast to FGR babies with a more adverse outcome that
fail to produce this signal. This adaptation model is evident through the
different expression pattern of the genes examined.
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