Preeclampsia‐derived small extracellular vesicles disrupt blood–brain barrier integrity and activate glial cells <i>in vitro</i>

Structural and functional integrity of the blood-brain barrier (BBB) is crucial for maintaining brain homeostasis. Preeclampsia, characterized by new-onset hypertension and endothelial dysfunction in pregnancy, often involves BBB disruption and neurological complications. Small extracellular vesicles (sEVs) have emerged as potential drivers of BBB disruption during preeclampsia; however, their impact on maternal brain health, particularly at the cellular level, remains understudied. Here, the effect of preeclampsia-derived sEVs on BBB integrity and cellular responses of brain endothelial cells, microglia and astrocytes was investigated. Circulating sEVs were isolated from plasma of healthy women and women with late-onset preeclampsia and studied in human-based mono-, bi- or tri-culture models using transwell and microfluidic (BBB-on-a-chip) systems. In these models, EV-associated signals were detected within brain endothelial cells consistent with intracellular uptake and trafficking. EV-derived cargo was detected in cells on the abluminal side of the endothelial layer, suggesting possible transfer across the barrier, although the underlying mechanism remains unclear. Exposure to preeclampsia-derived sEVs (PE-sEVs) was also associated with changes in brain endothelial cell protein composition and subcellular localization, accompanied by functional alterations of BBB properties, including increased permeability. Finally, astrocytes and microglia responded to PE-sEV exposure, as evidenced by increased IBA1 and GFAP expression, IL-6 release, and enhanced astrocyte migration. These findings suggest that circulating sEVs, including those of placental origin, may be involved in maternal brain alterations in preeclampsia potentially through effects on BBB integrity and glial activation. This may indicate the possible relevance of circulating sEVs as biomarkers and in the pathophysiology of the disease. KEY POINTS: Preeclampsia is a pregnancy-related condition involving high blood pressure and endothelial dysfunction, and is often associated with disruption of the blood-brain barrier (BBB) and neurological complications. Circulating small extracellular vesicles (sEVs) normally increase during pregnancy but are further elevated in preeclampsia, and may carry inflammatory cargo to the maternal brain. Using in vitro models, including an organ-on-a-chip, composed of human brain endothelial cells, microglia and astrocytes, this study examined how sEVs from healthy and preeclamptic pregnancies affect BBB properties, and glial activation. Results support the notion that preeclampsia-derived sEVs increase BBB permeability, traverse the endothelial layer, and induce glial responses including microglial activation and astrocyte reactivity by increased IL-6 release and cellular motility. The observed alterations may link placental dysfunction to maternal cerebrovascular injury, highlighting sEVs as potential modulators of brain damage in preeclampsia and as promising diagnostic or therapeutic targets.