A unique maternal and placental galectin signature upon SARS-CoV-2 infection suggests galectin-1 as a key alarmin at the maternal-fetal interface

Abstract

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic imposed a risk of infection and disease in pregnant women and neonates. Successful pregnancy requires a fine-tuned regulation of the maternal immune system to accommodate the growing fetus and to protect the mother from infection. Galectins, a family of β-galactoside-binding proteins, modulate immune and inflammatory processes and have been recognized as critical factors in reproductive orchestration, including maternal immune adaptation in pregnancy. Pregnancy-specific glycoprotein 1 (PSG1) is a recently identified gal-1 ligand at the maternal-fetal interface, which may facilitate a successful pregnancy. Several studies suggest that galectins are involved in the immune response in SARS-CoV-2-infected patients. However, the galectins and PSG1 signature upon SARS-CoV-2 infection and vaccination during pregnancy remain unclear. In the present study, we examined the maternal circulating levels of galectins (gal-1, gal-3, gal-7, and gal-9) and PSG1 in pregnant women infected with SARS-CoV-2 before vaccination or uninfected women who were vaccinated against SARS-CoV-2 and correlated their expression with different pregnancy parameters. SARS-CoV-2 infection or vaccination during pregnancy provoked an increase in maternal gal-1 circulating levels. On the other hand, levels of PSG1 were only augmented upon SARS-CoV-2 infection. A healthy pregnancy is associated with a positive correlation between gal-1 concentrations and gal-3 or gal-9; however, no correlation was observed between these lectins during SARS-CoV-2 infection. Transcriptome analysis of the placenta showed that gal-1, gal-3, and several PSG and glycoenzymes responsible for the synthesis of gal-1-binding glycotopes (such as linkage-specific N-acetyl-glucosaminyltransferases (MGATs)) are upregulated in pregnant women infected with SARS-CoV-2. Collectively, our findings identify a dynamically regulated "galectin-specific signature" that accompanies the SARS-CoV-2 infection and vaccination in pregnancy, and they highlight a potentially significant role for gal-1 as a key pregnancy protective alarmin during virus infection.

Keywords: COVID-19; PSG1; SARS-CoV-2; galectin-1; galectin-3; galectin-7; galectin-9.

Figure 1

Galectins dynamics upon SARS-Cov-2 infection or vaccination during pregnancy. Maternal circulating levels of gal-1 (A), gal-3 (B), gal-7 (C), and gal-9 (D) in the PRINCE cohort analyzed by ELISA in healthy pregnant women (pregnant^control, n = 20), pregnant women infected by SARS-CoV-2 (pregnant^SARS-CoV-2, n = 20), pregnant women vaccinated against SARS-CoV-2 (pregnant^BNT162b2, n = 30), and non-pregnant vaccinated women (non-pregnant^BNT162b2, n = 30). Circulating levels of gal-1 (E), gal-3 (F), and gal-9 (G) in the Yale IMPACT cohort analyzed by ELISA in healthy pregnant women (pregnant^control, n = 5) or pregnant women infected by SARS-CoV-2 (pregnant^SARS-CoV-2, n = 11). *P < 0.05, **P < 0.01, and ****P < 0.0001 as analyzed by Kruskal–Wallis test or Welch’s t-test. In all figures, circulating levels of galectins and PSG1 were determined in triplicate for each serum sample.

Figure 2

SARS-CoV-2 infection or vaccination altered the maternal circulating levels. Correlations in PRINCE cohort between serum values of gal-1 and gal-3 (A), gal-1 and gal-9 (B), gal-1 and gal-7 (C), or gal-3 and gal-9 (D). Pregnant^control, healthy pregnant women (n = 20); pregnant^SARS-CoV-2, pregnant women infected by SARS-CoV-2 (n = 20); pregnant^BNT162b2, pregnant women vaccinated against SARS-CoV-2 (n = 30); non-pregnant^BNT162b2, non-pregnant vaccinated women (n = 30). The Spearman correlation coefficient (ρ) is shown. P < 0.05 was considered statistically significant (green) and P > 0.05 not significant (gray) as analyzed with the Spearman statistical test.

Figure 3

Maternal circulation of PSG1 is only upregulated upon SARS-CoV-2 infection during pregnancy. PSG1. (A, B) Maternal circulating levels of PSG1 in the PRINCE cohort (A) or the Yale IMPACT cohort (B). (C–E) Correlations between serum values of gal-1 and PSG1 in the PRINCE cohort. Pregnant^control, healthy pregnant women; pregnant^SARS-CoV-2, pregnant women infected by SARS-CoV-2; pregnant^BNT162b2, pregnant women vaccinated against SARS-CoV-2. *P < 0.05 as analyzed by Kruskal–Wallis test or the Welch’s t-test.

Figure 4

Transcriptome analysis of placenta during acute SARS-CoV-2 infection. (A) Heatmap showing the scaled expression of galectins and PSG genes from RNA sequencing data in the placenta of the Yale IMPACT cohort. Enzymes involved in the synthesis of N-glycans (B) and O-glycans (D), showing the preferred ligand for gal-1. Heatmaps for the expression of the enzymes involved in the synthesis of N-glycans (C) and O-glycans (E), involved in terminal extension (F) or glycan degradation (G). Control, healthy pregnant women; SARS-CoV-2, pregnant women infected by SARS-CoV-2. *P < 0.05, **P < 0.01, and ***P < 0.001 as analyzed with the Welch’s t-test.

Figure 5

Schematic diagram highlighting galectin and PSGs fingerprints in pregnancy upon SARS-CoV-2 infection and in women subjected to vaccination. In maternal circulation, levels of gal-1 and PSG1 increased during COVID-19 disease in pregnancy. Vaccination with BNT162b2 caused an upregulation of gal-1 circulating levels mimicking the viral infection. During SARS-CoV-2 infection, placental transcription regulation of gal-1 and gal-3 dominates the galectin signature creating a protective microenvironment. In addition, upregulation of PSGs by the trophoblast cells contributes to immune modulation during COVID-19 disease.