Abstract Body: Introduction: Superimposed preeclampsia (SI-PE) is a hypertensive disorder of pregnancy (HDP) defined by a sudden increase of blood pressure in pregnancy above a chronic hypertension baseline, typically with evidence of end-organ damage attributable to microvascular injury. The mechanisms of vascular dysregulation in SI-PE compared to other HDPs remain unknown; though abnormalities in endothelial and vascular smooth muscle cell function are hypothesized to play a role. We hypothesized that placental blood vessels in SI-PE have transcriptional profiles distinct from other HDPs that occur in the absence of chronic hypertension.

Methods: Single cell RNA sequencing was performed on fresh whole-thickness placentas from patients with SI-PE (n=4), preeclampsia without severe features/ gestational hypertension (n=4), preeclampsia with severe features (n=5), and healthy controls (n=4). Endothelial cells (EC) and vascular smooth muscle/decidual (VSM/D) cells were identified based on canonical marker expression. Differential expression patterns within these cell types were compared across disease states.

Results: In SI-PE compared to all other groups, 818 VSM/D and 1,155 EC transcripts were significantly differentially expressed. Gene ontology analysis compared to controls prioritized collagen fibril organization, cell adhesion, and extracellular matrix (ECM) organization as top differentiating processes in VSM/D cells, and angiogenesis and negative regulation of cell adhesion in ECs. Pseudotime analysis modeled trajectories of gene modulation in vascular cells across the spectrum from healthy controls to SI-PE. The SI-PE VSM/D cells that were most different from controls expressed modules of transcripts involved in vascular remodeling and ECM reorganization. Within these modules, members of the laminin-PTEN pathway and interleukin 6 cytokine family signal transducer (IL6ST) expression specifically differentiated SI-PE from other HDPs. In ECs, cell adhesion disruption pathways and LIFR, a component in the IL6 cytokine family receptors, differentiated SI-PE from other HDPs.

Conclusions: Differential expression of transcripts related to vascular cell function, extracellular matrix and fibrosis, cellular interactions, and cytokine response distinguished human placental vascular cells in SI-PE from other HDPs. Mechanistic studies and biomarker development may leverage the specific transcript patterns and pathways identified for SI-PE.