Placental glycocalyx in normal pregnancies and pregnancies complicated with gestational diabetes mellitus and the effect of metformin treatment on the glycocalyx
Publication Date
December 11, 2024
Creator
Abstract
The placenta is a vital organ that forms the critical interface between the fetus and the mother, which is essential for normal growth and development of the fetus. The primary site of nutrition and gas exchange between the maternal and fetal circulations is the syncytiotrophoblast (ST), the outermost layer of the human placenta. The placental glycocalyx is a negatively charged layer present on the apical border of the syncytiotrophoblast (ST), basement membrane and the luminal surface of the fetal vessels. Thus, the glycocalyx could be an important component of the feto-maternal barrier. Pregnancies complicated by Gestational diabetes mellitus (GDM) are characterized by glucose intolerance that causes hyperglycaemia of any severity with onset or first recognition in pregnancy. The diabetic environment of a GDM pregnancy alters the development of the placenta and its function which have an adverse effect on the growth and development of the fetus. Management of GDM starts with lifestyle modification followed by metformin or insulin. Metformin, an antidiabetic drug, has been shown to improve endothelial glycocalyx properties in chronic hyperglycemia. Therefore, this study aimed to investigate the differential surface expression of glycocalyx in term placenta from normal, diet-controlled GDM and metformin-controlled GDM pregnancies and the effect of metformin treatment on the expression of glycocalyx in normal and diet-controlled pregnancies.
Placental chorionic villous tissue, explants and HUVECs were collected from 40 term singleton pregnancies after caesarean section. This study includes term placenta from normal pregnancies (n=17), diet-controlled GDM (n = 12) and metformin controlled GDM (N = 7). Comparison of differential surface expression of glycocalyx and syndecan-1 in chorionic villous tissue taken from freshly delivered placenta (T0) were investigated by fluorescent lectin histochemistry and immunohistochemistry, and by the systematic sampling. The effect of metformin treatment for 24 hours (T24) on differential surface expression of glycocalyx and syndecan-1 was investigated in chorionic villous trees from normal and diet-controlled GDM pregnancies. Protein expression of syndecan-1 was assessed by immunoblotting. Metformin was added on a confluent HUVEC monolayer growing on transwell inserts to investigate the effect of metformin tracer leakage across the endothelial monolayer. Statistical comparisons between two groups were performed by unpaired t-test, and among the three groups by One-Way ANOVA, and among 4 groups by Two-way ANOVA. p-value ≤ 0.05 was considered statistically significant.
The syncytiotrophoblast do not show a loss of glycocalyx in GDM pregnancies, controlled by either diet or metformin, compared to normal pregnancies. At T0, diet-controlled GDM pregnancies showed a significantly lower percentages of vascular profiles with glycocalyx on the luminal surface of placental fetal vessels compared to that of normal pregnancies. Whereas the percentages of vascular profiles with glycocalyx in metformin-controlled GDM pregnancies were similar to normal pregnancies.
To investigate the effect of metformin treatment on the placental surface expression of glycocalyx, chorionic villous trees were subjected to a 24-hour metformin treatment. 24 hours metformin treatment did not influence the expression of glycocalyx on the syncytiotrophoblast in normal and diet-controlled GDM explants. However, metformin treatment for 24 hours induced the restoration of glycocalyx in placental fetal vessels of diet-controlled GDM pregnancies. Normal explants also exhibited this significant change between untreated and treated with metformin.. Furthmore, vascular profiles within chorionic villous trees incubated without metformin from normal and diet-controlled GDM pregnancies maintained the significant difference seen at T0 between the same study groups.
Our study showed the differential surface expression of syndecan-1, a transmembrane proteoglycan, that is mostly expressed in the syncytiotrophoblast out of all the glycocalyx proteoglycans expressed in the placenta. At T0, diet-controlled GDM pregnancies showed reduced percentages of villous profiles with syndecan-1 on the syncytiotrophoblast compared to normal pregnancies. Furthermore, metformin-controlled GDM pregnancies exhibited higher percentages of villous profiles with syndecan-1 compared to diet-controlled GDM pregnancies.
We investigated the effect of metformin on the expression of syndecan-1 in normal and diet-controlled GDM pregnancies. Metformin incubation of explants for 24 hours showed a significant increase in the percentages of villous profiles with syndecan-1 in diet-controlled GDM pregnancies. This significant change was not seen in normal explants between treated and untreated. 24 hours metformin treatment did not alter the expression of syndecan-1 in normal and diet-controlled explants.
In conclusion, our study showed that metformin treatment during GDM pregnancy may restore the loss of glycocalyx in placental fetal vessels and the loss of syndecan-1 on the syncytiotrophoblast observed in diet-controlled GDM pregnancies. In ex vivo, addition of metformin to the diet-controlled GDM mimicked this restoration. Thus, metformin which readily croses the placenta may be able to improve the barrier integrity of the human placenta in pregnancies complicated by GDM, enhancing fetal health.
Item Type
ethesis
Thesis Type
PhD
Supervisors
Subjects (LC)
Associated Schools / Departments
School of Life Sciences
eprints ID
78782
UoN Repository URI
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Das, Shukla, ID 14342258 PhD Thesis corrected final.pdf
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