Assessing hypoxic damage to placental trophoblasts by measuring membrane viscosity of extracellular vesicles.

INTRODUCTION: As highly sophisticated intercellular communication vehicles in biological systems, extracellular vesicles (EVs) have been investigated as both promising liquid biopsy-based disease biomarkers and drug delivery carriers. Despite tremendous progress in understanding their biological and physiological functions, mechanical characterization of these nanoscale entities remains challenging due to the limited availability of proper techniques. Especially, whether damage to parental cells can be reflected by the mechanical properties of their EVs remains unknown. METHODS: In this study, we characterized membrane viscosities of different types of EVs collected from primary human trophoblasts (PHTs), including apoptotic bodies, microvesicles and small extracellular vesicles, using fluorescence lifetime imaging microscopy (FLIM). The biochemical origin of EV membrane viscosity was examined by analyzing their phospholipid composition, using mass spectrometry. RESULTS: We found that different EV types derived from the same cell type exhibit different membrane viscosities. The measured membrane viscosity values are well supported by the lipidomic analysis of the phospholipid compositions. We further demonstrate that the membrane viscosity of microvesicles can faithfully reveal hypoxic injury of the human trophoblasts. More specifically, the membrane of PHT microvesicles released under hypoxic condition is less viscous than its counterpart under standard culture condition, which is supported by the reduction in the phosphatidylethanolamine-to-phosphatidylcholine ratio in PHT microvesicles. DISCUSSION: Our study suggests that biophysical properties of released trophoblastic microvesicles can reflect cell health. Characterizing EV's membrane viscosity may pave the way for the development of new EV-based clinical applications.

Small extracellular vesicles from plasma of women with preeclampsia increase myogenic tone and decrease endothelium-dependent relaxation of mouse mesenteric arteries.

Preeclampsia (PE) is a common syndrome of pregnancy, characterized by new-onset hypertension and proteinuria after gestational week 20, or new onset of hypertension and significant end-organ dysfunction. In the worst cases, it can threaten the survival of both mother and baby. Extracellular vesicles (EVs) are lipid-bilayer nanoparticles released from cells. They are involved in cell-cell communication and transport of diverse cargo molecules. Small extracellular vesicles (sEVs, exosomes) are defined by their size and biogenesis within the endocytic compartment of the cell or reverse budding of the plasma membrane. The function of circulating gestational EVs, released from maternal organs or the placenta, remains to be explored. Here, we focused on sEVs that circulate in the maternal blood in the third trimester of human pregnancy and hypothesized that sEVs from pregnant women with PE play a role in regulation of vessel tone. When compared to sEVs from women with uncomplicated pregnancies, ex vivo exposure of isolated mouse mesenteric arteries to sEVs purified from the plasma of pregnant women with PE led to constriction in response to intraluminal pressure. This effect was not observed using microvesicles from the plasma of women with PE or using PE plasma that was depleted of EVs. Blood vessels exposed to sEVs from women with PE were also more resistant to methacholine-stimulated relaxation. Immunofluorescence microscopy confirmed the presence of sEVs within the vessel wall. Together, these data support the notion that circulating sEVs from pregnant women play a role in the regulation of arterial tone.

Placental small extracellular vesicles: Current questions and investigative opportunities.

The discovery of regulated trafficking of extracellular vesicles (EVs) has added a new dimension to our understanding of local and distant communication among cells and tissues. Notwithstanding the expanded landscape of EV subtypes, the majority of research in the field centers on small and large EVs that are commonly termed exosomes, microvesicles and apoptotic cell-derived vesicles. In the context of pregnancy, EV-based communication has a special role in the crosstalk among the placenta, maternal and fetal compartments, with most studies focusing on trophoblastic EVs and their effect on other placental cell types, endothelial cells, and distant tissues. Many unanswered questions in the field of EV biology center on the mechanisms of vesicle biogenesis, loading of cargo molecules, EV release and trafficking, the interaction of EVs with target cells and the endocytic pathways underlying their uptake, and the intracellular processing of EVs inside target cells. These questions are directly relevant to EV-based placental-maternal-fetal communication and have unique implications in the context of interaction between two organisms. Despite rapid progress in the field, the number of speculative, unsubstantiated assumptions about placental EVs is concerning. Here we attempt to delineate existing knowledge in the field, focusing primarily on placental small EVs (exosomes). We define central questions that require investigative attention in order to advance the field.

Concentric organization of A- and B-type lamins predicts their distinct roles in the spatial organization and stability of the nuclear lamina.

The nuclear lamina is an intermediate filament meshwork adjacent to the inner nuclear membrane (INM) that plays a critical role in maintaining nuclear shape and regulating gene expression through chromatin interactions. Studies have demonstrated that A- and B-type lamins, the filamentous proteins that make up the nuclear lamina, form independent but interacting networks. However, whether these lamin subtypes exhibit a distinct spatial organization or whether their organization has any functional consequences is unknown. Using stochastic optical reconstruction microscopy (STORM) our studies reveal that lamin B1 and lamin A/C form concentric but overlapping networks, with lamin B1 forming the outer concentric ring located adjacent to the INM. The more peripheral localization of lamin B1 is mediated by its carboxyl-terminal farnesyl group. Lamin B1 localization is also curvature- and strain-dependent, while the localization of lamin A/C is not. We also show that lamin B1's outer-facing localization stabilizes nuclear shape by restraining outward protrusions of the lamin A/C network. These two findings, that lamin B1 forms an outer concentric ring and that its localization is energy-dependent, are significant as they suggest a distinct model for the nuclear lamina-one that is able to predict its behavior and clarifies the distinct roles of individual nuclear lamin proteins and the consequences of their perturbation.