Mitochondrial oxidative stress and extrusion of mitochondrial DNA from endothelial cells: implications for maternal endothelial dysfunction in preeclampsia
Purpose: Preeclampsia is one of the leading causes of maternal mortality during pregnancy and a risk factor of cardiovascular disease for the mother later in life. Hypertension and endothelial dysfunction are common characteristics of the maternal syndrome in preeclampsia, and oxidative stress is considered a pathogenic mediator of these maternal features. Mitochondria are the primary cellular producers of reactive oxygen species (ROS) and overproduction of mitochondrial ROS (mtROS) is detrimental to cellular processes, often leading to cell death. Mitochondrial DNA (mtDNA) has pro-inflammatory properties when released from dying cells into the extracellular space and its concentrations are increased in women with preeclampsia. The objective of this study was to determine the effects of mtROS in mtDNA release into the extracellular space. We hypothesize that inhibition of mitochondrial transport chain results in extrusion of mtDNA from vascular endothelial cells. Also, inhibition of Complex III causes a greater release of mtDNA compared to inhibition of Complex I. Methods: Human umbilical vein endothelial cells (HUVEC) were grown to 80-90% confluency before being treated with a mitochondrial complex I inhibitor (Rotenone: 5, 10, 25 mM – 4h) and mitochondrial complex III inhibitor (Antimycin A: 10, 50, 100 mM – 4h). After treatment, the cell media supernatant was collected and stored in -80 °C until further mtDNA quantification. mtDNA was isolated using the Mag-Bind Blood & Tissue DNA HDQ 96 Kit and quantified using the TaqMan chemistry-based method of absolute qPCR. Results: HUVEC cells treated with rotenone, regardless of dose, had no effect on concentrations of extracellular mtDNA (Figure A; One-way ANOVA followed by Sidak’s post-hoc test). Concentrations of mtDNA increased in HUVECs treated with 100 mM of Antimycin A (Figure B; One-way ANOVA followed by Sidak’s post-hoc test). Lower concentrations of Antimycin A had no effect on concentrations of extracellular mtDNA (Figure B). Conclusions: Inhibition of mitochondrial respiratory chain complex III, but not inhibition of complex I, results in extrusion of mtDNA. The increase in mtDNA released from dysfunctional cells may contribute to the increased circulating mtDNA concentrations seen in pregnancies with maternal endothelial dysfunction, such as pregnancies with preeclampsia.