93 Characterizing the key mediators of SARS-CoV-2 infection in the human placenta: is vertical transmission possible?

Abstract

Previous coronavirus outbreaks (SARS and MERS) were linked to severe pregnancy outcomes including miscarriage and stillbirth. With exception of anecdotal reports, vertical transmission of SARS-CoV2 remains unproven. Emerging evidence has implicated the angiotensin converting enzyme 2 (ACE2) in SARS-CoV-2 viral entry and its pro-inflammatory effects with respiratory syndromes. The serine protease TMPRSS2 is required for spike protein priming and subsequent viral replication. Little is understood regarding the expression of ACE2 and TMPRSS2 in human placentas. We examined these proteins in term human placentas and maternal blood. Unlabored, term cesarean placentas were collected from uncomplicated pregnancies (n=10). Gene expression and western blot analyses for ACE2 and TMPRSS2 was conducted using intervillous biopsies. Placenta proteins were compared to commercially available human lung samples, a human cytotrophoblasts (BeWo cells) and recombinant proteins. Previously banked maternal plasma samples from uncomplicated pregnancies across gestation were analyzed by ELISA (n =12 donors). Placental ACE2 expression was significantly greater than TMPRSS2 (Figure1.A). Both were present at predicted sizes corresponding to recombinant proteins and in greater amount than lung samples. Qualitatively, the abundance of ACE2 in placenta samples corresponds with 1ng of recombinant protein vs. 0.1ng for TMPRSS2 (Figure1.B). BeWo cells appear to have a greater amount of TMPRSS2 vs. ACE2. In maternal plasma, ACE2 was highly variable and undetectable most samples (Figure 2). Despite the few reports of vertical transmission, our results indicate human placentas have endogenous ACE2 and TMPRSS2 and possibly at greater levels than the lung. ELISA results suggest that maternal blood is not a major contributor of placental ACE2 in most pregnancies. Since the proteins necessary for SARS-CoV-2 infection are present, other element(s) may influence or are required for vertical transmission. Future studies planned to address placental innate immune responses against this variant of coronavirus.View Large Image Figure ViewerDownload Hi-res image Download (PPT)