Oral Presentation ESA-SRB 2023 in conjunction with ENSA

Elucidating the function of Sialic acid-binding immunoglobulin-like lectin-6 (SIGLEC6) in preeclampsia (#30)

Manju Kandel 1 2 , Lucy A Bartho 1 2 , Natalie J Hannan 1 2 , Ping Cannon 1 2 , Tuong-Vi Nguyen 1 2 , Natasha Pritchard 1 2 , Anna Nguyen 1 2 , Ciara N Murphy 1 2 , Georgia P Wong 1 2 , Stephen Tong 1 2 , Tu'uhevaha J Kaitu'u-Lino 1 2
  1. Mercy Perinatal, Heidelberg, Victoria, Australia
  2. University of Melbourne, Melbourne, VIC, Australia

SIGLEC6, a transmembrane receptor, is highly expressed in placenta in a human-specific manner. Our team (unpublished data) have identified SIGLEC6 as a novel biomarker of preeclampsia. We have shown SIGLEC6 is elevated in the maternal circulation preceding preeclampsia, among those diagnosed with preeclampsia, and is associated with increasing disease severity. The current study aimed to characterise SIGLEC6 and assess its potential role in disease pathogenesis using human (cyto)trophoblast stem cells (hTSCs), and primary Human Umbilical Vein Endothelial Cells (HUVECs). 

SIGLEC6 mRNA expression was measured in three distinct placental cell types: cytotrophoblast, syncytiotrophoblast, and extravillous trophoblast – using a first trimester hTSCs. We found that SIGLEC6 is expressed across all three cell types, with its highest expression observed in syncytiotrophoblast. Given preeclampsia is associated with placental hypoxia and inflammation, we next exposed syncytialised hTSCs to either hypoxia (1% Oxygen vs 8% Oxygen) or increasing doses of inflammatory cytokines IL-6 or TNFa.  Hypoxia increased SIGLEC6 secretion (p=0.008) and mRNA expression (p=0.008) in syncytialised hTSCs. Similarly, there was an increase in SIGLEC6 secretion (IL-6: p=0.002, and TNFa: p=0.01) and mRNA expression (IL-6: p=0.002, and TNFa: p=0.009) with inflammation.

We next assessed whether the high levels of circulating SIGLEC6 observed in the maternal circulation with preeclampsia might induce endothelial dysfunction, a clinical feature of preeclampsia.  Treatment of primary HUVECs with recombinant SIGLEC6 modestly increased VCAM1 (endothelial dysfunction marker, p=0.01), and HO-1 (cytoprotective molecule, p=0.03) mRNA expression, but had no effect on the mRNA expression of other endothelial dysfunction markers (ICAM-1 and ET-1), anti-angiogenic (sFlt-1 e15a and sFlt-1 i13), or pro-angiogenic (VEGFA, and PlGF) markers. Furthermore, increasing doses of SIGLEC6 had no effect on HUVEC proliferation. 

We demonstrate that SIGLEC6 is induced by placental hypoxia and inflammation and that high circulating levels may induce endothelial dysfunction, which is a key characteristic of preeclampsia.