["The Journal of Physiology, EarlyView. ", "\nAbstract figure legend This study assessed the impact of plasma‐derived small extracellular vesicles (sEVs) from healthy pregnant women and those diagnosed with late‐onset preeclampsia (PE) on the blood–brain barrier (BBB) integrity and glial cell response. PE patients had higher sEV concentrations than healthy controls. Circulating PE‐derived sEVs, including those of placental origin, led to structural and functional BBB breakdown in in vitro models. Furthermore, the detection of EV signals as well as the presence of EV cargo in cells beyond the BEC barrier are consistent with the translocation of sEVs across the barrier. PE‐sEVs interacted with microglia and astrocytes, triggering neuroinflammatory‐like responses, such as increased IBA1 and GFAP expression, IL‐6 release and enhanced astrocyte migration. This interaction resulted in the transfer of placenta‐specific elements, including micro‐RNAs. In the in vitro BBB models, PE‐sEVs were associated with increased endothelial permeability and decreased electrical resistance, together with reduced expression of occludin and claudin‐5. These findings suggest a possible contribution of sEVs to BBB dysfunction and glial activation in PE.\n\n\n\n\n\n\n\n\n\nAbstract\nStructural 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.\n\n\n\n\n\n\n\n\n\nKey points\n\nPreeclampsia 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.\nCirculating small extracellular vesicles (sEVs) normally increase during pregnancy but are further elevated in preeclampsia, and may carry inflammatory cargo to the maternal brain.\nUsing 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.\nResults 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.\nThe 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.\n\n\n"]