4. 3D placental microvasculature: a reduced vascular fraction in pre-eclampsia
For vasculature visualization, staining was performed with UEA-1 lectin39, which is a direct and less complex method compared to immunostaining17-20. Segmentation was performed with Labkit (Figures S8, S11), and network extraction and quantification with VMTK (Figure S12). Vasculature of term placenta (Figure 4A) appeared highly torturous and branched, whereas LO-PE placenta illustrated a vascular network with longer segments and decreased branching (Figure 4B). Vessel diameters varied throughout a single placental vascular network (Figures S13-S13G). Diameters in term control placenta remained steady along a 10 µm equilibrium (Figure S13G). In the LO-PE case, diameters varied highly and could become very small (Figure S13F).
Vascular fraction measured the percentage of villous volume occupied by vascular structures. Our results demonstrate a significantly lower vascular fraction for the EO-PE placenta compared to (pre-)term control placenta (Figure 4C). Moreover, the vascular fraction in EO-PE was comparable to that of a 2nd trimester placenta (Figure 4C). LO-PE and EO-PE vascular fraction did not differ significantly although LO-PE tended towards higher vascular fraction than EO-PE. Vascular content in the LO-PE placenta was significantly lower than in term control placenta, when parametric statistical tests were used (Figure 4C).
Network properties were quantitatively investigated by examining branchpoint density (see Figure S12 for details on the procedure). Our preliminary data illustrated term placenta vascular networks, to have the lowest average branchpoint density (Figure 4D). Highest tortuosity (although not significant) was observed in the IUGR placenta without PE (Figure 4E).