Measurement of mitochondrial respiration in trophoblast culture

A Novel Dual-Function Redox Modulator Relieves Oxidative Stress and Anti-Angiogenic Response in Placental Villus Explant Exposed to Hypoxia-Relevance for Preeclampsia Therapy

BACKGROUND

Preeclampsia (PE) is a severe, life-threatening complication during pregnancy (~5-7%), and no causative treatment is available. Early aberrant spiral artery remodeling is associated with placental stress and the release of oxygen radicals and other reactive oxygen species (ROS) in the placenta. This precedes the production of anti-angiogenic factors, which ultimately leads to endothelial and trophoblast damage and the key features of PE. We tested whether a novel dual-function redox modulator-AKT-1005-can effectively reduce placental oxidative stress and alleviate PE symptoms in vitro.

METHOD

Isolated human villous explants were exposed to hypoxia and assessed to determine whether improving cell-redox function with AKT-1005 diminished ROS production, mitochondrial stress, production of the transcription factor HIF1A, and downstream anti-angiogenic responses (i.e., sFLT1, sEng production). MitoTEMPO was used as a reference antioxidant.

RESULTS

In our villous explant assays, pretreatment with AKT-1005 reduced mitochondrial-derived ROS production, reduced HIF-1A, sFLT1, and sEng protein expression, while increasing VEGF in hypoxia-exposed villous trophoblast cells, with better efficiency than MitoTEMPO. In addition, AKT-1005 improved mitochondrial electron chain enzyme activity in the stressed explant culture.

CONCLUSIONS

The redox modulator AKT-1005 has the potential to intervene with oxidative stress and can be efficacious for PE therapy. Future studies are underway to assess the in vivo efficacy of HMP.

Metformin Impacts Human Syncytiotrophoblast Mitochondrial Function from Pregnancies Complicated by Obesity and Gestational Diabetes Mellitus in a Sexually Dimorphic Manner

Maternal obesity and gestational diabetes mellitus (GDM) are associated with placental dysfunction, small for gestational age (SGA) offspring, and programming of adult-onset disease. We examine how metformin, commonly used to treat type A2 GDM, affects placental metabolism as well as mitochondrial content and function. Syncytiotrophoblasts (STBs) were prepared from placentas of male and female fetuses collected at term cesarean section from lean (pre-pregnancy BMI < 25), obese (BMI > 30), and obese A2GDM women. Metformin treatment (0.001-10 mM) of STB caused no change in non-mitochondrial respiration but significant concentration-dependent (1 and 10 mM) decreases in basal, maximal, and ATP-linked respiration and spare capacity. Respiration linked to proton leak was significantly increased in STB of male A2GDM placentas at low metformin concentrations. Metformin concentrations ≥1 mM increased glycolysis in STB from placentas from lean women, but only improved glycolytic capacity in female STB. Whereas metformin had little effect on superoxide generation from male STB of any group, it gave a concentration-dependent decrease in superoxide generation from female STB of lean and obese women. Fewer mitochondria were observed in STB from obese women and male STB from lean women with increasing metformin concentration. Metformin affects STB mitochondrial function in a sexually dimorphic manner but at concentrations above those reported in maternal circulation (approximately 0.01 mM) in women treated with metformin for GDM.

Bioenergetics adaptations and redox homeostasis in pregnancy and related disorders

Pregnancy is a challenging physiological process that involves maternal adaptations to the increasing energetics demands imposed by the growing conceptus. Failure to adapt to these requirements may result in serious health complications for the mother and the baby. The mitochondria are biosynthetic and energy-producing organelles supporting the augmented energetic demands of pregnancy. Evidence suggests that placental mitochondria display a dynamic phenotype through gestation. At early stages of pregnancy placental mitochondria are mainly responsible for the generation of metabolic intermediates and reactive oxygen species (ROS), while at later stages of gestation, the placental mitochondria exhibit high rates of oxygen consumption. This review describes the metabolic fingerprint of the placental mitochondria at different stages of pregnancy and summarises key signs of mitochondrial dysfunction in pathological pregnancy conditions, including preeclampsia, gestational diabetes and intrauterine growth restriction (IUGR). So far, the effects of placental-driven metabolic changes governing the metabolic adaptations occurring in different maternal tissues in both, healthy and pathological pregnancies, remain to be uncovered. Understanding the function and molecular aspects of the adaptations occurring in placental and maternal tissue's mitochondria will unveil potential targets for further therapeutic exploration that could address pregnancy-related disorders. Targeting mitochondrial metabolism is an emerging approach for regulating mitochondrial bioenergetics. This review will also describe the potential therapeutic use of compounds with a recognised effect on mitochondria, for the management of preeclampsia.

Human placenta-derived mesenchymal stem cells induce trophoblast invasion via dynamic effects on mitochondrial function

The trophoblast is a critical cell for placental development and embryo implantation in the placenta. We previously reported that placenta‐derived mesenchymal stem cells (PD‐MSCs) increase trophoblast invasion through several signaling pathways. However, the paracrine effects of PD‐MSCs on mitochondrial function in trophoblasts are still unclear. Therefore, the objective of the study was to analyze the mitochondrial function of trophoblasts in response to cocultivation with PD‐MSCs. The results showed that PD‐MSCs regulate the balance between cell survival and death and protect damaged mitochondria in trophoblasts from oxidative stress. Moreover, PD‐MSCs upregulate factors involved in mitochondrial autophagy in trophoblast cells. Finally, PD‐MSCs improve trophoblast invasion. Taken together, the data indicate that PD‐MSCs can regulate trophoblast invasion through dynamic effects on mitochondrial energy metabolism. These results support the fundamental role of mitochondrial energy mechanism in trophoblast invasion and suggest a new therapeutic strategy for infertility.

Testosterone Decreases Placental Mitochondrial Content and Cellular Bioenergetics

Placental mitochondrial dysfunction plays a central role in the pathogenesis of preeclampsia. Since preeclampsia is a hyperandrogenic state, we hypothesized that elevated maternal testosterone levels induce damage to placental mitochondria and decrease bioenergetic profiles. To test this hypothesis, pregnant Sprague–Dawley rats were injected with vehicle or testosterone propionate (0.5 mg/kg/day) from gestation day (GD) 15 to 19. On GD20, the placentas were isolated to assess mitochondrial structure, copy number, ATP/ADP ratio, and biogenesis (Pgc-1α and Nrf1). In addition, in vitro cultures of human trophoblasts (HTR-8/SVneo) were treated with dihydrotestosterone (0.3, 1.0, and 3.0 nM), and bioenergetic profiles using seahorse analyzer were assessed. Testosterone exposure in pregnant rats led to a 2-fold increase in plasma testosterone levels with an associated decrease in placental and fetal weights compared with controls. Elevated maternal testosterone levels induced structural damage to the placental mitochondria and decreased mitochondrial copy number. The ATP/ADP ratio was reduced with a parallel decrease in the mRNA and protein expression of Pgc-1α and Nrf1 in the placenta of testosterone-treated rats compared with controls. In cultured trophoblasts, dihydrotestosterone decreased the mitochondrial copy number and reduced PGC-1α, NRF1 mRNA, and protein levels without altering the expression of mitochondrial fission/fusion genes. Dihydrotestosterone exposure induced significant mitochondrial energy deficits with a dose-dependent decrease in basal respiration, ATP-linked respiration, maximal respiration, and spare respiratory capacity. In summary, our study suggests that the placental mitochondrial dysfunction induced by elevated maternal testosterone might be a potential mechanism linking preeclampsia to feto-placental growth restriction.

Placental function in maternal obesity

Maternal obesity is associated with pregnancy complications and increases the risk for the infant to develop obesity, diabetes and cardiovascular disease later in life. However, the mechanisms linking the maternal obesogenic environment to adverse short- and long-term outcomes remain poorly understood. As compared with pregnant women with normal BMI, women entering pregnancy obese have more pronounced insulin resistance, higher circulating plasma insulin, leptin, IGF-1, lipids and possibly proinflammatory cytokines and lower plasma adiponectin. Importantly, the changes in maternal levels of nutrients, growth factors and hormones in maternal obesity modulate placental function. For example, high insulin, leptin, IGF-1 and low adiponectin in obese pregnant women activate mTOR signaling in the placenta, promoting protein synthesis, mitochondrial function and nutrient transport. These changes are believed to increase fetal nutrient supply and contribute to fetal overgrowth and/or adiposity in offspring, which increases the risk to develop disease later in life. However, the majority of obese women give birth to normal weight infants and these pregnancies are also associated with activation of inflammatory signaling pathways, oxidative stress, decreased oxidative phosphorylation and lipid accumulation in the placenta. Recent bioinformatics approaches have expanded our understanding of how maternal obesity affects the placenta; however, the link between changes in placental function and adverse outcomes in obese women giving birth to normal sized infants is unclear. Interventions that specifically target placental function, such as activation of placental adiponectin receptors, may prevent the transmission of metabolic disease from obese women to the next generation.

Delta-9-tetrahydrocannabinol disrupts mitochondrial function and attenuates syncytialization in human placental BeWo cells

The psychoactive component in cannabis, delta-9-tetrahydrocannabinol, can restrict fetal growth and development. Delta-9-tetrahydrocannabinol has been shown to negatively impact cellular proliferation and target organelles like the mitochondria resulting in reduced cellular respiration. In the placenta, mitochondrial dysfunction leading to oxidative stress prevents proper placental development and function. A key element of placental development is the proliferation and fusion of cytotrophoblasts to form the syncytium that comprises the materno-fetal interface. The impact of delta-9-tetrahydrocannabinol on this process is not well understood. To elucidate the nature of the mitochondrial dysfunction and its consequences on trophoblast fusion, we treated undifferentiated and differentiated BeWo human trophoblast cells, with 20 µM delta-9-tetrahydrocannabinol for 48 hr. At this concentration, delta-9-tetrahydrocannabinol on BeWo cells reduced the expression of markers involved in syncytialization and mitochondrial dynamics, but had no effect on cell viability. Delta-9-tetrahydrocannabinol significantly attenuated the process of syncytialization and induced oxidative stress responses in BeWo cells. Importantly, delta-9-tetrahydrocannabinol also caused a reduction in the secretion of human chorionic gonadotropin and the production of human placental lactogen and insulin growth factor 2, three hormones known to be important in facilitating fetal growth. Furthermore, we also demonstrate that delta-9-tetrahydrocannabinol attenuated mitochondrial respiration, depleted adenosine triphosphate, and reduced mitochondrial membrane potential. These changes were also associated with an increase in cellular reactive oxygen species, and the expression of stress responsive chaperones, HSP60 and HSP70. These findings have important implications for understanding the role of delta-9-tetrahydrocannabinol-induced mitochondrial injury and the role this might play in compromising human pregnancies.

Sulforaphane improves syncytiotrophoblast mitochondrial function after in vitro hypoxic and superoxide injury

INTRODUCTION

Placental mitochondrial dysfunction contributes to the oxidative stress that underlies preeclampsia. Here, we assessed whether sulforaphane (SFN) could improve syncytiotrophoblast mitochondrial function after in vitro hypoxic and superoxide injury.

METHODS

Placental cytotrophoblasts were isolated from healthy term placentae (n = 12) and incubated for 48 h in 8% O₂ ± 1 μM SFN before acute (4hrs) or chronic (24hrs) hypoxic (1% O₂), or superoxide (xanthine/xanthine oxidase) injury. Cytotrophoblasts were also isolated from preeclamptic placentae (n = 5) and cultured in 8% O₂ ± 1 μM SFN. Mitochondrial respiration was measured using the Seahorse MitoStress XF assay. Cells were stained with mitotracker red to assess mitochondrial membrane health and mitochondrial gene expression assessed using RT-qPCR.

RESULTS

SFN prevented significant reductions in syncytiotrophoblast mitochondrial maximal respiration, spare respiratory capacity, basal respiration and ATP production following acute hypoxia. Chronic hypoxia only reduced maximal and spare respiratory capacity. SFN prevented these negative changes and increased respiration overall. Alternatively, acute superoxide injury significantly increased mitochondrial maximal respiration and spare respiratory capacity. SFN treatment further increased basal respiration following superoxide injury and prevented significant decreases in ATP production and coupling efficiency. In preeclamptic placentae, SFN significantly increased mitochondrial maximal respiration, spare respiratory capacity, basal respiration and ATP production, and decreased proton leak. SFN up-regulated mRNA expression of mitochondrial complexes and corrected an up-regulation in fission gene expression observed after hypoxic-superoxide injury. Finally, preliminary results suggest SFN prevented hypoxia-induced impairment of mitochondrial membrane structure.

DISCUSSION

SFN mitigated hypoxia and superoxide induced changes to syncytiotrophoblast mitochondrial function in vitro, and improved mitochondrial respiration in trophoblast cells from preeclamptic placentae.

Mechanistic Target of Rapamycin Complex 1 Promotes the Expression of Genes Encoding Electron Transport Chain Proteins and Stimulates Oxidative Phosphorylation in Primary Human Trophoblast Cells by Regulating Mitochondrial Biogenesis

Trophoblast oxidative phosphorylation provides energy for active transport and protein synthesis, which are critical placental functions influencing fetal growth and long-term health. The molecular mechanisms regulating trophoblast mitochondrial oxidative phosphorylation are largely unknown. We hypothesized that mechanistic Target of Rapamycin Complex 1 (mTORC1) is a positive regulator of key genes encoding Electron Transport Chain (ETC) proteins and stimulates oxidative phosphorylation in trophoblast and that ETC protein expression is down-regulated in placentas of infants with intrauterine growth restriction (IUGR). We silenced raptor (mTORC1 inhibition), rictor (mTORC2 inhibition) or DEPTOR (mTORC1/2 activation) in cultured term primary human trophoblast (PHT) cells. mTORC1 inhibition caused a coordinated down-regulation of 18 genes encoding ETC proteins representing all ETC complexes. Inhibition of mTORC1, but not mTORC2, decreased protein expression of ETC complexes I–IV, mitochondrial basal, ATP coupled and maximal respiration, reserve capacity and proton leak, whereas activation of mTORC1 had the opposite effects. Moreover, placental protein expression of ETC complexes was decreased and positively correlated to mTOR signaling activity in IUGR. By controlling trophoblast ATP production, mTORC1 links nutrient and O₂ availability and growth factor signaling to placental function and fetal growth. Reduced placental mTOR activity may impair mitochondrial respiration and contribute to placental insufficiency in IUGR pregnancies.

AP39, a Modulator of Mitochondrial Bioenergetics, Reduces Antiangiogenic Response and Oxidative Stress in Hypoxia-Exposed Trophoblasts: Relevance for Preeclampsia Pathogenesis

Although the cause of preeclampsia, a pregnancy complication with significant maternal and neonatal morbidity, has not been fully characterized, placental ischemia attributable to impaired spiral artery remodeling and abnormal secretion of antiangiogenic factors are thought to be important in the pathogenesis of the disease. Placental ischemia could impair trophoblast mitochondrial function and energy production, leading to the release of reactive oxygen species (ROS). ROS have been shown to stabilize hypoxia-inducible factor (HIF)-1α, which, in turn, may induce transcription of antiangiogenic factors, soluble fms-like tyrosine kinase 1 (sFLT1), and soluble endoglin in trophoblasts. Herein, we tested whether the angiogenic imbalance and oxidative stress in the preeclamptic placenta may be prevented by improving mitochondrial function. First, to evaluate the cause-effect relationship between mitochondrial function and sFLT1 production, a human trophoblast primary cell culture model was established in which hypoxia induced mitochondrial ROS production and concurrent sFLT1 increase. Second, treatment with AP39, a novel mitochondria-targeted hydrogen sulfide donor, prevented ROS production, reduced HIF-1α protein levels, and diminished sFLT1 production. Finally, AP39, a modulator of mitochondrial bioenergetics enhanced cytochrome c oxidase activity, reversed oxidative stress and antiangiogenic response in hypoxic trophoblasts. These results suggest that placental hypoxia induces ROS production, HIF-1α stabilization, and sFLT1 up-regulation; these pathophysiological alterations can be attenuated by mitochondrial-targeted antioxidants.

Regulation of energy metabolism during early mammalian development: TEAD4 controls mitochondrial transcription

Early mammalian development is crucially dependent on the establishment of oxidative energy metabolism within the trophectoderm (TE) lineage. Unlike the inner cell mass, TE cells enhance ATP production via mitochondrial oxidative phosphorylation (OXPHOS) and this metabolic preference is essential for blastocyst maturation. However, molecular mechanisms that regulate establishment of oxidative energy metabolism in TE cells are incompletely understood. Here, we show that conserved transcription factor TEAD4, which is essential for pre-implantation mammalian development, regulates this process by promoting mitochondrial transcription. In developing mouse TE and TE-derived trophoblast stem cells (TSCs), TEAD4 localizes to mitochondria, binds to mitochondrial DNA (mtDNA) and facilitates its transcription by recruiting mitochondrial RNA polymerase (POLRMT). Loss of TEAD4 impairs recruitment of POLRMT, resulting in reduced expression of mtDNA-encoded electron transport chain components, thereby inhibiting oxidative energy metabolism. Our studies identify a novel TEAD4-dependent molecular mechanism that regulates energy metabolism in the TE lineage to ensure mammalian development.

Platelets in preeclamptic pregnancies fail to exhibit the decrease in mitochondrial oxygen consumption rate seen in normal pregnancies

Cellular oxygen consumption and lactate production rates have been measured in both placental and myometrial cells to study obstetrics-related disease states such as preeclampsia. Platelet metabolic alterations indicate systemic bioenergetic changes that can be useful as disease biomarkers. We tested the hypothesis that platelet mitochondria display functional alterations in preeclampsia. Platelets were harvested from women in the third trimester of either a healthy, non-preeclamptic or preeclamptic pregnancy, and from healthy, non-pregnant women. Using Seahorse respirometry, we analyzed platelets for oxygen consumption (OCR) and extracellular acidification (ECAR) rates, indicators of mitochondrial electron transport and glucose metabolism, respectively. There was a 37% decrease in the maximal respiratory capacity measured in platelets from healthy, non-preeclamptic compared with preeclamptic pregnancy (P<0.01); this relationship held true for other measurements of OCR, including basal respiration; ATP-linked respiration; respiratory control ratio (RCR); and spare respiratory capacity. RCR, a measure of mitochondrial efficiency, was significantly lower in healthy pregnant compared with non-pregnant women. In contrast with increased OCR, basal ECAR was significantly reduced in platelets from preeclamptic pregnancies compared with either normal pregnancies (−25%; P<0.05) or non-pregnant women (−22%; P<0.01). Secondary analysis of OCR revealed reduced basal and maximal platelet respiration in normal pregnancy prior to 34 weeks’ estimated gestational age (EGA) compared with the non-pregnant state; these differences disappeared after 34 weeks. Taken together, findings suggest that in preeclampsia, there exists either a loss or early (before the third trimester) reversal of a normal biologic mechanism of platelet mitochondrial respiratory reduction associated with normal pregnancy.

Soluble Fms-Like Tyrosine Kinase-1 Alters Cellular Metabolism and Mitochondrial Bioenergetics in Preeclampsia

Preeclampsia is a maternal hypertensive disorder that affects up to 1 out of 12 pregnancies worldwide. It is characterized by proteinuria, endothelial dysfunction, and elevated levels of the soluble form of the vascular endothelial growth factor receptor-1 (VEGFR-1, known as sFlt-1). sFlt-1 effects are mediated in part by decreasing VEGF signaling. The direct effects of sFlt-1 on cellular metabolism and bioenergetics in preeclampsia, have not been established. The goal of this study was to evaluate whether sFlt-1 causes mitochondrial dysfunction leading to disruption of normal functioning in endothelial and placental cells in preeclampsia. Endothelial cells (ECs) and first-trimester trophoblast (HTR-8/SVneo) were treated with serum from preeclamptic women rich in sFlt-1 or with the recombinant protein. sFlt-1, dose-dependently inhibited ECs respiration and acidification rates indicating a metabolic phenotype switch enhancing glycolytic flux. HTR-8/SVneo displayed a strong basal glycolytic metabolism, remaining less sensitive to sFlt-1-induced mitochondrial impairment. Moreover, results obtained in ECs exposed to serum from preeclamptic subjects demonstrated that increased sFlt-1 leads to metabolic perturbations accountable for mitochondrial dysfunction observed in preeclampsia. sFlt-1 exacerbated mitochondrial reactive oxygen species (ROS) formation and mitochondrial membrane potential dissipation in ECs and trophoblasts exposed to serum from preeclamptic women. Forcing oxidative metabolism by culturing cells in galactose media, further sensitized cells to sFlt-1. This approach let us establish that sFlt-1 targets mitochondrial function in ECs. Effects of sFlt-1 on HTR-8/SVneo cells metabolism were amplified in galactose, demonstrating that sFlt-1 only target cells that rely mainly on oxidative metabolism. Together, our results establish the early metabolic perturbations induced by sFlt-1 and the resulting endothelial and mitochondrial dysfunction in preeclampsia.

Sexual dimorphism in activation of placental autophagy in obese women with evidence for fetal programming from a placenta-specific mouse model

The incidence of maternal obesity and its co-morbidities (diabetes, cardiovascular disease) continues to increase at an alarming rate, with major public health implications. In utero exposure to maternal obesity has been associated with development of cardiovascular and metabolic diseases in the offspring as a result of developmental programming. The placenta regulates maternal-fetal metabolism and shows significant changes in its function with maternal obesity. Autophagy is a cell-survival process, which is responsible for the degradation of damaged organelles and misfolded proteins. Here we show an activation of autophagosomal formation and autophagosome-lysosome fusion in placentas of males but not females from overweight (OW) and obese (OB) women vs. normal weight (NW) women. However, total autophagic activity in these placentas appeared to be decreased as it showed an increase in SQSTM1/p62 and a decrease in lysosomal biogenesis. A mouse model with a targeted deletion of the essential autophagy gene Atg7 in placental tissue showed significant placental abnormalities comparable to those seen in human placenta with maternal obesity. These included a decrease in expression of mitochondrial genes and antioxidants, and decreased lysosomal biogenesis. Strikingly, the knockout mice were developmentally programmed as they showed an increased sensitivity to high-fat diet-induced obesity, hyperglycemia, hyperinsulinemia, increased adiposity, and cardiac remodeling. In summary, our results indicate a sexual dimorphism in placental autophagy in response to maternal obesity. We also show that autophagy plays an important role in placental function and that inhibition of placental autophagy programs the offspring to obesity, and to metabolic and cardiovascular diseases.

Gestational differences in murine placenta: Glycolytic metabolism and pregnancy parameters

The placenta is a complex and essential organ composed largely of fetal-derived cells, including several different trophoblast subtypes that work in unison to support nutrient transport to the fetus during pregnancy. Abnormal placental development can lead to pregnancy-associated disorders that often involve metabolic dysfunction. The scope of dysregulated metabolism during placental development may not be fully representative of the in vivo state in defined culture systems, such as cell lines or isolated primary cells. Thus, assessing metabolic function in intact placental tissue would provide a better assessment of placental metabolism. In this study, we describe a methodology for assaying glycolytic function in structurally-intact mouse placental tissue, ex vivo, without culturing or tissue dissociation, that more closely resembles the in vivo state. Additionally, we present data highlighting sex-dependent differences of two mouse strains (C57BL/6 and ICR) in the pre-hypertrophic (E14.5) and hypertrophic (E18.5) placenta. These data establish a foundation for investigation of metabolism throughout gestation and provides a comprehensive assessment of glycolytic function during placental development.

Down-regulation of PDK4 is Critical for the Switch of Carbohydrate Catabolism during Syncytialization of Human Placental Trophoblasts

Pyruvate dehydrogenase kinase (PDK) is known as a gatekeeper directing the carbon flux into glycolysis via inhibition of the pyruvate dehydrogenase complex. During syncytialization of placental trophoblasts, both ATP production and oxygen consumption are increased to meet enhanced energetic demands by syntiotrophoblasts. We hypothesized that down-regulation of PDK expression may play a central role in the switch from glycolysis to oxidative phosphorylation (OXPHOS) during syncytialization. By using primary human trophoblasts, we demonstrated that PDK4 was the dominating PDK isoform in human cytotrophoblasts, and its abundance was substantially decreased upon syncytialization, which was accompanied by decreases in lactate production and increases in ATP production. Knock-down of PDK4 expression reduced lactate production and increased ATP production, while over-expression of PDK4 increased lactate production and decreased ATP production, indicating that down-regulation of PDK4 is key to the shift from glycolysis to OXPHOS during syncytialization. Moreover, human chorionic gonadotropin (hCG)/cAMP/PKA pathway was demonstrated to be involved in the down-regulation of PDK4 expression upon syncytialization. Taken together, our findings disclosed that down-regulation of PDK4 is critical for the metabolic shift from glycolysis to OXPHOS during syncytialization, which may be a prerequisite for the proper implementation of syncytiotrophoblast functions.

Tropomyosin Receptor Kinase B Agonist, 7,8-Dihydroxyflavone, Improves Mitochondrial Respiration in Placentas From Obese Women

Maternal obesity negatively impacts the placenta, being associated with increased inflammation, decreased mitochondrial respiration, decreased expression of brain-derived neurotrophic factor (BDNF), and its receptor, tropomyosin receptor kinase B (TRKB). TRKB induction by 7,8-dihydroxyflavone (7,8-DHF) improves energy expenditure in an obesity animal model. We hypothesized that TRKB activation would improve mitochondrial respiration in trophoblasts from placentas of obese women. Placentas were collected from lean (pre-pregnancy BMI < 25) and obese (pre-pregnancy BMI > 30) women at term following cesarean section delivery without labor. Cytotrophoblasts were isolated and plated, permitting syncytialization. At 72 hours, syncytiotrophoblasts (STs) were treated for 1 hour with 7,8-DHF (10 nM-10 M), TRKB antagonists (ANA-12 (10 nM-1 M), Cyclotraxin B (1 nM-1M)), or vehicle. Mitochondrial respiration was measured using the XF24 Extracellular Flux Analyzer. TRKB, MAPK, and PGC1α were measured using Western blotting. Maternal obesity was associated with decreased mitochondrial respiration in STs; however, 7,8-DHF increased basal, ATP-coupled, maximal, spare capacity, and nonmitochondrial respiration. A 10 μM dose of 7,8-DHF reduced spare capacity in STs from lean women, with no effect on other respiration parameters. 7,8-DHF had no effect on TRKB phosphorylation; however, there was a concentration-dependent decrease of p38 MAPK phosphorylation and increase of PGC1α in STs from obese, but not in lean women. TRKB antagonism attenuated ATP-coupled respiration, maximal respiration, and spare capacity in STs from lean and obese women. 7,8-DHF improves mitochondrial respiration in STs from obese women, suggesting that the obese phenotype in the placenta can be rescued by TRKB activation.

Melatonin Improves Mitochondrial Respiration in Syncytiotrophoblasts From Placentas of Obese Women

Maternal obesity is associated with increased oxidative stress but decreased placental mitochondrial respiration and expression of mitochondrial electron transport chain (ETC) complexes I to V. Melatonin acts as an antioxidant and prevents oxidative stress-induced changes in cytotrophoblasts. Placentas were collected at term by cesarean delivery from obese (first trimester body mass index [BMI] ≥30, n = 10) or lean (BMI < 25, n = 6) women. Cytotrophoblasts were isolated and allowed to syncytialize for 72 hours with or without melatonin (0.1-100 µM) for the last 24 hours. Mitochondrial respiratory parameters were measured in a Seahorse XF24. Expression of ETC complexes I to V and antioxidant enzymes was measured by Western blot. Maternal clinical characteristics of patients were similar except for BMI. No significant improvement in mitochondrial respiration occurred with addition of melatonin to trophoblasts of lean women. However, in trophoblasts from obese women, melatonin (10 and 100 µmol/L) significantly increased maximal respiration ( P = .01 and P = .009, respectively) and spare capacity ( P = .02 and P = .003, respectively) compared to the untreated control. No differences were detected in the expression of ETC complexes and superoxide dismutase 1 or 2 in trophoblasts treated with melatonin. The expression of glutathione peroxidase, which was significantly greater in trophoblast of obese compared to lean women ( P < .05), was decreased back to the level seen in trophoblast of lean women with addition of melatonin ( P = .02). Improved spare respiratory capacity, the cellular reserve, could impart a protective effect to the placenta and fetus in an adverse intrauterine environment or in response to additional stressors.

[The effect of sulodexide on placental mitochondria function in rats with experimental preeclampsia]

Substitution of drinking water for 1.8% NaCl in pregnant rats caused a pronounced increase in arterial pressure by 24,3% and urinary protein by 117% to day 21 of pregnancy. State 4 respiration of isolated placental mitochondria in the group of negative control was 3- and 1.5-fold higher with malate/glutamate and succinate as substrates than in placental mitochondria isolated from uncomplicated pregnant animals. This led to a decrease of the respiratory control ratio. These results suggest that development of experimental preeclampsia is accompanied by mitochondrial dysfunction through uncoupling of oxidative phosphorylation. Daily administration of sulodexide to females with experimental preeclampsia (EP) per os at a dose of 30 LE during the whole period of gestation decreased manifestations of the disease as evidenced by a slight increase in blood pressure (by 8,6%) and less pronounces increase in urinary protein (by 58,9%). Sulodexide decreased development of mitochondrial dysfunction in EP rats as shown a decrease of non-stimulated ADP respiration with malate/glutamate and succinate (4.5- and 2.5-fold, respectively) as compared with the negative control group and the corresponding increase in the respiratory control ratio (2.5- and 1.5-fold, respectively). Thus, sulodexide reduces uncoupling of oxidative phosphorylation and enhances the functional activity of mitochondria in EP animals, possibly due to its antioxidant and endotelioprotective effects.

Mitochondrial function and glucose metabolism in the placenta with gestational diabetes mellitus: role of miR-143

A predisposing factor for development of the hyperglycaemic state of gestational diabetes mellitus (GDM) is obesity. We previously showed that increasing maternal obesity is associated with significant reductions in placental mitochondrial respiration. MicroRNA (miR)-143 has been previously shown to regulate the metabolic switch from oxidative phosphorylation to aerobic glycolysis in cancer tissues. We hypothesized that mitochondrial respiration is reduced and aerobic glycolysis is up-regulated via changes in miR-143 expression in the placenta of women with GDM. Placental tissue was collected at term from women with A1GDM (controlled by diet), A2GDM (controlled by medication) and body mass index (BMI)-matched controls (CTRL). miR-143 expression was measured by RT-PCR. Expression of mitochondrial complexes, transcription factors peroxisome proliferator-activated receptor-γ co-activator 1α (PGC1α) and peroxisome proliferator-activated receptor γ (PPARγ), components of mammalian target of rapamycin (mTOR) signalling, glucose transporter GLUT1 and glycolytic enzymes [hexokinase-2 (HK-2), phosphofructokinase (PFK) and lactate dehydrogenase (LDH)] were measured by Western blot. Trophoblast respiration was measured by XF24 Analyser. Expression of miR-143, mitochondrial complexes, and PPARγ and PGC1α, which act downstream of miR-143, were significantly decreased in A2GDM placentae compared with A1GDM and CTRL (P<0.01). Placental hPL (human placental lactogen) levels, expression of glycolytic enzymes, GLUT1 and mTOR signalling were also significantly increased by more than 2-fold in A2GDM compared with A1GDM and CTRL (P<0.05). There was a 50% reduction in mitochondrial respiration in trophoblast cells isolated from A2GDM placentae. Overexpression of miR-143 was able to increase mitochondrial respiration, increase protein expression of mitochondrial complexes and decrease expression of glycolytic enzymes by 40% compared with A2GDM. Down-regulation of miR-143 mediates the metabolic switch from oxidative phosphorylation to aerobic glycolysis in placenta of women with A2GDM.

Evidence-Based Revised View of the Pathophysiology of Preeclampsia

Preeclampsia is a life-threatening vascular disorder of pregnancy due to a failing stressed placenta. Millions of women risk death to give birth each year and globally each year, almost 300,000 lose their life in this process and over 500,000 babies die as a consequence of preeclampsia. Despite decades of research, we lack pharmacological agents to treat it. Maternal endothelial oxidative stress is a central phenomenon responsible for the preeclampsia phenotype of high maternal blood pressure and proteinuria. In 1997, it was proposed that preeclampsia arises due to the loss of VEGF activity, possibly due to elevation in anti-angiogenic factor, soluble Flt-1 (sFlt-1). Researchers showed that high sFlt-1 and soluble endoglin (sEng) elicit the severe preeclampsia phenotype in pregnant rodents. We demonstrated that heme oxygenase-1 (HO-1)/carbon monoxide (CO) pathway prevents placental stress and suppresses sFlt-1 and sEng release. Likewise, hydrogen sulphide (H₂S)/cystathionine-γ-lyase (Cth) systems limit sFlt-1 and sEng and protect against the preeclampsia phenotype in mice. Importantly, H₂S restores placental vasculature, and in doing so improves lagging fetal growth. These molecules act as the inhibitor systems in pregnancy and when they fail, preeclampsia is triggered. In this review, we discuss what are the hypotheses and models for the pathophysiology of preeclampsia on the basis of Bradford Hill causation criteria for disease causation and how further in vivo experimentation is needed to establish 'proof of principle'. Hypotheses that fail to meet the Bradford Hill causation criteria include abnormal spiral artery remodelling and inflammation and should be considered associated or consequential to the disorder. In contrast, the protection against cellular stress hypothesis that states that the protective pathways mitigate cellular stress by limiting elevation of anti-angiogenic factors or oxidative stress and the subsequent clinical signs of preeclampsia appear to fulfil most of Bradford Hill causation criteria. Identifying the candidates on the roadmap to this pathway is essential in developing diagnostics and therapeutics to target the pathogenesis of preeclampsia.

Sexual dimorphism in miR-210 expression and mitochondrial dysfunction in the placenta with maternal obesity

BACKGROUND

Maternal obesity is a major problem in obstetrics, and the placenta is involved in obesity-related complications via its roles at the maternal-fetal interface. We have recently shown a causative role for micro(mi)RNA-210, a so called 'hypoxamir' regulated by HIF-1α, in mitochondrial dysfunction in placentas from women with preeclampsia. We also reported mitochondrial dysfunction in placentas with maternal obesity. Here we hypothesized that expression of miR-210 is dysregulated in the placentas with obesity.

METHODS

Placentas from uncomplicated pregnancies were collected at term from healthy weight or control (CTRL, pre-pregnancy body mass index (BMI)<25), overweight (OW, BMI=25-24.9) and obese (OB, BMI>30) women following C-section with no labor. Expression of miRNA-210 and its target genes was measured by reverse transcription-PCR and Western Blot, respectively. Mitochondrial respiration was assessed by Seahorse Analyzer in syncytiotrophoblast (ST) 72 h after cytotrophoblast isolation.

RESULTS

Expression of miR-210 was significantly increased in placentas of OB and OW women with female but not male fetuses compared with CTRL placentas of females. However, expression of HIF-1α in these placentas remained unchanged. Levels of tumor-necrosis factor-alpha (TNFα) were increased in OW and OB placentas of females but not males, and in silico analysis suggested that activation of miR-210 expression in these placentas might be activated by NFκB1 (p50) signaling. Indeed, chromatin Immunoprecipitation assay showed that NFkB1 binds to placental miR-210 promoter in a fetal sex-dependent manner. Female but not male STs treated with TNFα showed overexpression of miR-210, reduction of mitochondrial target genes and decreased mitochondrial respiration. Pre-treatment of these STs with small interfering RNA to NFkB1 or antagomiR-210 prevented the TNFα-mediated inhibition of mitochondrial respiration.

CONCLUSIONS

Our data suggest that the inflammatory intrauterine environment associated with maternal obesity induces an NFκB1-mediated increase in miR-210 in a fetal sex-dependent manner, leading to inhibition of mitochondrial respiration and placental dysfunction in the placentas of female fetuses.

Endothelial dysfunction and preeclampsia: role of oxidative stress

Preeclampsia (PE) is an often fatal pathology characterized by hypertension and proteinuria at the 20th week of gestation that affects 5-10% of the pregnancies. The problem is particularly important in developing countries in where the incidence of hypertensive disorders of pregnancy is higher and maternal mortality rates are 20 times higher than those reported in developed countries. Risk factors for the development of PE include obesity, insulin resistance and hyperlipidemia that stimulate inflammatory cytokine release and oxidative stress leading to endothelial dysfunction (ED). However, how all these clinical manifestations concur to develop PE is still not very well understood. The related poor trophoblast invasion and uteroplacental artery remodeling described in PE, increases reactive oxygen species (ROS), hypoxia and ED. Here we aim to review current literature from research showing the interplay between oxidative stress, ED and PE to the outcomes of current clinical trials aiming to prevent PE with antioxidant supplementation.

Impaired mitochondrial function in human placenta with increased maternal adiposity

The placenta plays a key role in regulation of fetal growth and development and in mediating in utero developmental programming. Obesity, which is associated with chronic inflammation and mitochondrial dysfunction in many tissues, exerts a programming effect in pregnancy. We determined the effect of increasing maternal adiposity and of fetal sex on placental ATP generation, mitochondrial biogenesis, expression of electron transport chain subunits, and mitochondrial function in isolated trophoblasts. Placental tissue was collected from women with prepregnancy BMI ranging from 18.5 to 45 following C-section at term with no labor. Increasing maternal adiposity was associated with excessive production of reactive oxygen species and a significant reduction in placental ATP levels in placentae with male and female fetuses. To explore the potential mechanism of placental mitochondrial dysfunction, levels of transcription factors regulating the expression of genes involved in electron transport and mitochondrial biogenesis were measured. Our in vitro studies showed significant reduction in mitochondrial respiration in cultured primary trophoblasts with increasing maternal obesity along with an abnormal metabolic flexibility of these cells. This reduction in placental mitochondrial respiration in pregnancies complicated by maternal obesity could compromise placental function and potentially underlie the increased susceptibility of these pregnancies to fetal demise in late gestation and to developmental programming.

Hypoxia-induced changes in the bioactivity of cytotrophoblast-derived exosomes

Migration of extravillous trophoblasts (EVT) into decidua and myometrium is a critical process in the conversion of maternal spiral arterioles and establishing placenta perfusion. EVT migration is affected by cell-to-cell communication and oxygen tension. While the release of exosomes from placental cells has been identified as a significant pathway in materno-fetal communication, the role of placental-derived exosomes in placentation has yet to be established. The aim of this study was to establish the effect of oxygen tension on the release and bioactivity of cytotrophoblast (CT)-derived exosomes on EVT invasion and proliferation. CT were isolated from first trimester fetal tissue (n = 12) using a trypsin-deoxyribonuclease-dispase/Percoll method. CT were cultured under 8%, 3% or 1% O2 for 48 h. Exosomes from CT-conditioned media were isolated by differential and buoyant density centrifugation. The effect of oxygen tension on exosome release (µg exosomal protein/10(6)cells/48 h) and bioactivity were established. HTR-8/SVneo (EVT) were used as target cells to establish the effect (bioactivity) of exosomes on invasion and proliferation as assessed by real-time, live-cell imaging (Incucyte™). The release and bioactivity of CT-derived exosomes were inversely correlated with oxygen tension (p<0.001). Under low oxygen tensions (i.e. 1% O2), CT-derived exosomes promoted EVT invasion and proliferation. Proteomic analysis of exosomes identified oxygen-dependent changes in protein content. We propose that in response to changes in oxygen tension, CTs modify the bioactivity of exosomes, thereby, regulating EVT phenotype. Exosomal induction of EVT migration may represent a normal process of placentation and/or an adaptive response to placental hypoxia.

Methods for assessing mitochondrial function in diabetes

A growing body of research is investigating the potential contribution of mitochondrial function to the etiology of type 2 diabetes. Numerous in vitro, in situ, and in vivo methodologies are available to examine various aspects of mitochondrial function, each requiring an understanding of their principles, advantages, and limitations. This review provides investigators with a critical overview of the strengths, limitations and critical experimental parameters to consider when selecting and conducting studies on mitochondrial function. In vitro (isolated mitochondria) and in situ (permeabilized cells/tissue) approaches provide direct access to the mitochondria, allowing for study of mitochondrial bioenergetics and redox function under defined substrate conditions. Several experimental parameters must be tightly controlled, including assay media, temperature, oxygen concentration, and in the case of permeabilized skeletal muscle, the contractile state of the fibers. Recently developed technology now offers the opportunity to measure oxygen consumption in intact cultured cells. Magnetic resonance spectroscopy provides the most direct way of assessing mitochondrial function in vivo with interpretations based on specific modeling approaches. The continuing rapid evolution of these technologies offers new and exciting opportunities for deciphering the potential role of mitochondrial function in the etiology and treatment of diabetes.

Oxygen delivery and fetal-placental growth: beyond a question of supply and demand?

Towards the end of the first trimester, blood flow and oxygenation rise within the placenta, supporting an increased capacity for mitochondrial oxidative metabolism in both the placenta and developing fetus. In this regard, the placenta acts uniquely as both a conduit of oxygen to the fetal circulation and a significant consumer of oxygen in order to support its own energy demands for the processes of nutrient transport and protein synthesis for hormone production and growth. When the supply of oxygen becomes restricted, for example during chronic exposure to hypobaric hypoxia at high altitude, placental and fetal tissues respond in order to optimise the allocation of oxygen between competing demands. In this case, the placenta appears to remodel its metabolism to decrease oxygen consumption, probably by increasing ATP production via glycolysis. This process can maintain oxygen supply to the fetus but is still associated with growth restriction. Oxidative stress, a feature of pre-eclampsia, might elicit similar metabolic changes in the absence of hypoxia. This review considers what is known about the metabolic response of the placenta and fetal tissues to hypoxia and oxidative stress, and suggests possible mechanisms that might underlie such metabolic remodelling using lessons from other tissues and organ systems. Aspects of the hypoxia response that remain to be addressed are highlighted and future studies suggested. Much remains unknown about the coordinated metabolic response of the fetal-placental unit to chronic hypoxia and oxidative stress, but it would appear to be more than a simple question of supply and demand.