The role of soluble FMS-like tyrosine-kinase-1, vascular endothelial growth factor and placental growth factor in HIV associated pre-eclamptic pregnancies : a South African perspective.
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Date
2013
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Abstract
Introduction and aims.
South Africa is the epicenter of the HIV/AIDS pandemic. Hypertensive disorders of pregnancy
(15.7%) are the second cause of maternal deaths of which pre-eclampsia represents 83%. Normal
pregnancy requires a balance between pro- and anti-angiogenic factors to necessitate effective
vasculogenesis, angiogenesis and placental development, however, pre-eclampsia is characterised
by an excess anti-angiogenic state. The hypoxic placenta releases excess anti-angiogenic factors
into the maternal circulation causing endothelial dysfunction. However, there is no data to verify
if HIV infection affects pre-eclampsia, or if the angiogenic imbalance is affected. Contradictory
data exists on the association between HIV infection and pre-eclampsia. In an attempt to assess
the role of HIV infection in pre-eclampsia, this study examined the immunolocalisation of sFlt-1,
sEng, PlGF and VEGF in placentae of HIV negative and positive normotensive and pre-eclamptic
pregnancies at term using immunohistochemistry (IHC) and immunoelectron microscopy (IEM).
Additionally, we estimated the placental expression of sFlt-1, sEng, PlGF and VEGF to verify if
the HIV negative differed from the HIV positive cohorts. We further evaluated the maternal
serum to determine if variations existed in the circulating levels of these factors in HIV negative
and positive normotensive and pre-eclamptic pregnancies.
Methods.
Following institutional ethical approval and informed consent, placental biopsies and maternal
serum were collected post-delivery. For IHC and IEM, 130 and 25 placentae were evaluated,
respectively. Following conventional immunohistochemical processing, 5μm sections were
immunostained & immunoexpression of the various antibodies were evaluated with the Zeiss
Axioscope A1 interfaced with an AxioVision Image analysis software package (version 4.8.3) in
combination with the auto-measurement module (Carl Zeiss, Germany). Post-conventional
immunoelectron processing, ultra-thin sections were immunolabelled. Sections were post-fixed,
contrast enhanced with uranyl acetate and Reynolds lead citrate and viewed on a Jeol 1011
Transmission Electron Microscope. Additionally, the placental expressions of these factors were
assessed using RT-PCR. In an attempt to confirm if maternal circulating levels of these factors
differed, we quantitatively evaluated these factors in serum from HIV negative normotensives,
HIV negative pre-eclamptics, HIV positive normotensives, and HIV positive pre-eclamptics using
ELISA techniques.
Results and Discussion.
The expression of sFlt-1, sEng, PlGF and VEGF was confirmed using immunohistochemistry,
RT-PCR and ELISAs. Irrespective of the HIV status, sFlt-1 and sEng was elevated with the
concomitant reduction in PlGF in pre-eclamptic compared to normotensive pregnancies. The
levels of VEGF were however undetectable across all study groups. It is plausible that this lack of
effect of HIV status on the factors under study may be attributed to the treatment regimen as
HAART is known to restore the immune response of HIV positive preeclamptic women.
However, a concise anti-retroviral treatment history in our study was unavailable.
Additionally, this study is novel in that it ultrastructurally immunolocalises sFlt-1, sEng, PlGF and
VEGF within the placenta. This immunoelectron localisation data corresponds to our
immunohistochemical data. Our study further demonstrates strong immunoreactivity of both
placental sFlt-1 and sEng in pre-eclampsia with concurrent elevations in the maternal circulation.
A qualitative increase in the occurrence of syncytial knots in the pre-eclamptics compared to the
normotensive pregnancies was noted. These observations support the detachment of antixxx
angiogenic rich microparticles from syncytial knots in the pre-eclamptics compared to the
normotensive pregnancies was noted. These observations support the detachment of antiangiogenic rich microparticles from syncytial knots and their subsequent deportation and elevation
in the maternal circulation. Moreover, their consequent antagonistic effects on VEGF, PlGF and
TGF-β, disrupts the vascular endothelial maintenance.
The strong immunoreactivity of sFlt-1, sEng, PlGF and VEGF was observed in villous endothelial
cells. Moreover, a strong sFlt-1 and sEng but a weak PlGF and VEGF immunoreactivity was
noted in syncytio- and cytotrophoblasts. This immunoexpression within trophoblasts is suggestive
of their autocrine mode of action on normal trophoblast functions including invasion,
differentiation and production. It is plausible that the angiogenic imbalance observed in our study,
will impact on placental function, by modifying trophoblast activity thereby contributing to
abnormal placentation.
Conclusion.
Our study supports the hypothesis that pre-eclampsia is characterized by an imbalance between
pro- and anti-angiogenic factors. Whether the pregnancy is complicated by immune
insufficiencies or not, does not affect the role of the anti-angiogenic factors in pre-eclampsia
development. Nevertheless, the neutralising effect of HIV infection on the immune system may
be insufficient in the development of pre-eclampsia. To our knowledge, the quantification of
serum pro-/anti-angiogenic factors in HIV-associated pre-eclampsia is novel. In conclusion, our
data reinforces the hypothesis that increased concentrations of sFlt-1 and sEng are involved in the
pathogenesis of pre-eclampsia and indicates their possible use as discriminatory factors between
diseases.
Description
Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2013.
Keywords
Preeclampsia--South Africa--Molecular aspects., Placenta--Tumours--South Africa., Vascular endothelial growth factors--South Africa., Protein-tyrosine kinase., Theses--Optics and imaging.