Sialylation status in placentas from pregnancies with SARS-CoV-2 infection

Recent investigations suggest the potential negative impact of SARS-CoV-2 infection on pregnant women and pregnancy outcome. In addition, some studies have described pathological changes in the placental tissue of SARS-CoV-2-positive mothers, which are related or not to the infection severity and/or infection trimester. Among the various molecules involved in the normal structure and functionality of the placenta, sialic acids (Sias) seem to play an important role. Hence, we aimed to investigate possible changes in the distribution and content of Sias with different glycosidic linkages, namely α2,3 and α2,6 Galactose- or N-acetyl-Galactosamine-linked Sias and polymeric Sia (PolySia), in placentas from pregnant women infected by SARS-CoV-2 during the three different pregnancy trimesters.

α2,3 and α2,6 Galactose-linked Sias were evaluated by lectin histochemistry (Maackia amurensis agglutinin (MAA) and Sambucus nigra agglutinin (SNA), respectively), while immunohistochemistry was used for PolySia detection.

Data showed lower levels of α2,3 Galactose-linked Sias in the trophoblast and underlying basement membrane/basal plasma membrane in placentas from women infected during the second and third infection trimester compared with uninfected cases and those infected during first trimester. On the other hand, higher levels of PolySia were detected in the trophoblast during the second and third infection trimester.

Our findings suggest that changes in the sialylation status of trophoblast and its basement membrane/basal plasma membrane, together with other concomitant factors, could be at the basis of the most common placental histopathological alterations and gestational complications found especially in pregnancies with SARS-CoV-2 infection during the second and third trimester.