(304) Maternal COVID-19 is associated with increased proliferation of placental cytotrophoblasts

Objective: Damage to the maternal-fetal interface can lead to cytotrophoblast (CTB) proliferation. Our objective was to determine how COVID-19 induced inflammation and stress affects CTB proliferation in the placental villi and membranes.

Study

Design: This study analyzed a single-nucleus RNA sequencing dataset and tissue from gestational age-matched COVID-19 (n=4) and control (n=4) placentas. We used the cell cycle scoring program in Seurat to quantify the proportion of trophoblasts in S phase (DNA replication phase) by trophoblast cell type in COVID-19 vs. control groups. Tissue immunostaining for Ki67 (proliferation marker) and KRT7 (trophoblast marker) was performed to validate trophoblast proliferation in the chorionic villi and membranes. To assess the consequences of trophoblast proliferation, the thickness of the membrane trophoblast layer was quantified by analyzing 5+ regions of interest per H&E slide using a novel cell-classification program to detect trophoblasts.

Results: Analysis of RNA sequencing data revealed an increase in the proportion of trophoblasts in S phase in COVID-19 placentas compared to control placentas for villous syncytiotrophoblasts (1.56-fold change [FC]), villous CTBs (1.51 FC), membrane CTBs (1.79 FC), and membrane extravillous trophoblasts (2.48 FC). Consistent with the transcriptomics data, we observed an increased number of Ki67-positive trophoblast nuclei in the villi (mean 13 ± 5 nuclei for COVID-19 vs. 4 ± 1 for control per high power field, p=0.0171) and membranes (mean 10 ± 2 nuclei for COVID-19 vs. 3 ± 1 for control, p=0.0006; Fig 1). Increased proliferation was associated with a thickened membrane trophoblast layer (mean 178 ± 97.5 µm for COVID-19 vs. 123 ± 72.8 µm for control, p=0.0127; Fig 2).

Conclusion: COVID-19 induced damage in the placenta is correlated with proliferation of CTBs and thickening of the membrane trophoblast layer. Alterations in trophoblast proliferation suggest a compensatory response to inflammatory stress and imply further injury to the maternal-fetal interface.