Placenta at single-cell resolution in early and late preeclampsia: insights and clinical implications

Preeclampsia, one of the great obstetrical syndromes, manifests through diverse maternal and fetal complications and remains a leading contributor to adverse perinatal outcomes. In this review, we describe our work on single-cell and single-nuclei RNA sequencing to elucidate the molecular mechanisms that underlie early- and late-onset preeclampsia. Analysis of 46 cell types, encompassing approximately 90,000 cells from placental tissues collected after delivery, demonstrated cellular dysregulation in early-onset preeclampsia, whereas late-onset preeclampsia showed comparatively subtle changes. These findings were observed in all cell lines, including all types of trophoblast, lymphoid, myeloid, stromal, and endothelial cells. Key findings in early-onset preeclampsia included disrupted syncytiotrophoblast and extravillous trophoblast angiogenic signaling, characterized by an up-regulation of FLT1 and down-regulation of PGF, consistent with an angiogenic imbalance. The stromal and vascular compartments exhibited stress-induced transcriptomic shifts. Both endothelial cells and pericytes showed evidence of stress, including up-regulation of heat shock proteins and markers of apoptosis. In addition, the inflammation- and stress-responsive states were more abundant in early-onset preeclampsia than in matched controls. Inflammatory pathways were markedly up-regulated in both the maternal and fetal immune cells; for example, we observed a marked increase in pro-inflammatory cytokines, including secreted phosphoprotein 1 and C-X-C motif chemokine ligand 2 and 3. Conversely, late-onset preeclampsia retained adaptive placental features with localized dysregulation of extracellular matrix remodeling and angiogenic markers, underscoring its possible maternal cardiovascular etiology. Single-cell and single-nuclei RNA sequencing investigations of placental tissues support the proposed classification of preeclampsia into a placental dysfunction type, primarily presenting early in pregnancy, and a maternal cardiovascular maladaptation type, primarily presenting later in pregnancy, each with distinct biomarkers, risk factors, and therapeutic targets. The early-onset preeclampsia findings advocate for interventions that target angiogenic pathways, such as RNA-based therapies that target specific cells of the placenta, to modulate soluble fms-like tyrosine kinase-1 levels. In contrast, late-onset preeclampsia management may benefit from maternal cardiovascular optimization, including individualized antihypertensive and metabolic treatments. These results underscore the heterogeneity of preeclampsia, emphasizing the need for individualized diagnostic and therapeutic strategies. This molecular atlas of preeclampsia advances our understanding of the complex interplay among elements of the maternal-placental-fetal array, thereby bridging clinical phenotypes and cellular mechanisms. Future research should focus on integrating these insights into longitudinal studies to develop precision medicine approaches for preeclampsia to enhance outcomes for mothers and neonates.