SARS-CoV-2 infects cells via binding to ACE2 and TMPRSS2, which allows the virus to fuse with host cells. The
viral RNA is detected in the placenta of SARS-CoV-2-infected pregnant women and
infection is associated with adverse
pregnancy complications. Therefore, we hypothesize that
SARS-CoV-2 infection of placental cells induces pro-inflammatory
cytokine release to contribute to placental dysfunction and impaired pregnancy outcomes. First, expression of ACE2 and TMPRSS2 was measured by qPCR in human primary cultured term cytotrophoblasts (CTBs), syncytiotrophoblast (STBs), term and first trimester decidual cells (
TDCs and FTDCs, respectively), endometrial stromal cells (HESCs) as well as trophoblast cell lines HTR8, JEG3, placental microvascular endothelial cells (PMVECs) and endometrial endothelial cells (HEECs). Later, cultured HTR8, JEG3, PMVECs and HEECs were treated with 10, 100, 1000 ng/ml of recombinant (rh-)
SARS-CoV-2 S-protein ± 10 ng/ml rh-IFNγ. Pro-inflammatory
cytokines IL-1β, 6 and 8,
chemokines CCL2, CCL5, CXCL9 and CXCL10 as well as
tissue factor (F3), the primary initiator of the extrinsic coagulation cascade, were measured by qPCR as well as secreted
IL-6 and
IL-8 levels were measured by ELISA. Immunohistochemical staining for
SARS-CoV-2 spike protein was performed in placental specimens from SARS-CoV-2-positive and normal pregnancies. ACE2 levels were significantly higher in CTBs and STBs vs.
TDCs, FTDCs and HESCs, while TMPRSS2 levels were not detected in
TDCs, FTDCs and HESCs. HTR8 and JEG3 express ACE2 and TMPRSS2, while PMVECs and HEECs express only ACE2, but not TMPRSS2. rh-S-
protein increased proinflammatory
cytokines and
chemokines levels in both trophoblast and endothelial cells, whereas rh-S-
protein only elevated F3 levels in endothelial cells. rh-IFNγ ± rh-S-
protein augments expression of
cytokines and
chemokines in trophoblast and endothelial cells. Elevated F3 expression by rh-IFNγ ± S-
protein was observed only in PMVECs. In placental specimens from SARS-CoV-2-infected mothers, endothelial cells displayed higher immunoreactivity against spike
protein. These findings indicated that
SARS-CoV-2 infection in placental cells: 1) induces pro-inflammatory
cytokine and
chemokine release, which may contribute to the
cytokine storm observed in severely infected pregnant women and related placental dysfunction; and 2) elevates F3 expression that may trigger systemic or placental
thrombosis.