Consistent localization of SARS-CoV-2 spike glycoprotein and ACE2 over TMPRSS2 predominance in placental villi of 15 COVID-19 positive maternal-fetal dyads

Abstract

Introduction: While the COVID-19 pandemic continues to have a significant global health impact, rates of maternal to infant vertical transmission remain low (<5%). Parenchymal changes of placentas from COVID-19 infected mothers have been reported by several groups, but the localization and relative abundance of SARS-CoV-2 viral proteins and cellular entry machinery has not been fully characterized within larger placental tissue cohorts.

Methods: An extended placental tissue cohort including samples from 15 COVID-19 positive maternal-fetal dyads (with n = 5 cases with evidence of fetal transmission) in comparison with 10 contemporary COVID-19 negative controls. Using comparative immunofluorescence, we examined the localization and relative tissue abundance of SARS-CoV2 spike glycoprotein (CoV2 SP) along with the co-localization of two SARS-CoV2 viral entry proteins angiotensin-converting enzyme 2 (ACE2) and transmembrane serine protease 2 (TMPRSS2).

Results/conclusions: CoV2 SP was present within the villous placenta in COVID-19 positive pregnancies with and without evidence of fetal transmission. We further identified the predominance of ACE2 expression in comparison with TMPRSS2. Importantly, both CoV2 SP and ACE2 expression consistently localized primarily within the outer syncytiotrophoblast layer placental villi, a key physiologic interface between mother and fetus. Overall this study provides an important basis for the ongoing evaluation of SARS-CoV-2 physiology in pregnancy and highlights the importance of the placenta as a key source of primary human tissue for ongoing diagnostic and therapeutic research efforts to reduce the global burden of COVID-19.

Keywords: ACE2; COVID-19; Placenta; SARS-CoV-2; TMPRSS2; Vertical transmission.

Fig. 1

Gross subchorionic and intervillous fibrosis in placental tissues from pregnancies affected by COVID-19. Representative gross images of full thickness term placental biopsies. COVID: Placental tissues from pregnant women who were SARS-CoV-2 positive upon admission screening (full cohort, n = 15). Control: Placental tissues from pregnant women who were SARS-CoV-2 negative upon admission screening (full cohort, n = 10). D: Decidua, V: Villous tissue, C: Chorionic plate.

Fig. 2

Consistent SARS-CoV-2 spike glycoprotein expression in placental tissues with and without evidence of fetal transmission. A. Representative 200× brightfield images of AEC immunohistochemistry for SARS-CoV-2. B. Representative images (200×) of SARS-CoV-2 immunofluorescence. C. Graphical analysis of comparative fluorescence quantitation. COVID and Control: tissue cohorts as described in Fig. 1. Fluorescence Ratio: ratio of corrected total cell fluorescence of target antigen/secondary only control. COVID FT^Pos: COVID-19 affected pregnancies with evidence of fetal transmission, COVID FT^Neg: COVID-19 affected pregnancies without evidence of fetal transmission. ***p < 0.001. Scale bars: 50 μm.

Fig. 3

ACE2 over TMPRSS2 predominance in villous placental compartment. A. Representative images (200×) of ACE2 and TMPRSS2 co-immunofluorescence. B. Graphical analysis of comparative fluorescence quantitation. COVID and Control: tissue cohorts as described in Fig. 1. Fluorescence Ratio: ratio of corrected total cell fluorescence of target antigen/secondary only control. ***p < 0.001, *p < 0.05. Scale bars: 50 μm.