The tolerance to hypoxia is defined by a time-sensitive response of the gene regulatory network in sea urchin embryos.

Deoxygenation, the reduction of oxygen level in the oceans induced by global warming and anthropogenic disturbances, is a major threat to marine life. This change in oxygen level could be especially harmful to marine embryos that use endogenous hypoxia and redox gradients as morphogens during normal development. Here, we show that the tolerance to hypoxic conditions changes between different developmental stages of the sea urchin embryo, possibly due to the structure of the gene regulatory networks (GRNs). We demonstrate that during normal development, the bone morphogenetic protein (BMP) pathway restricts the activity of the vascular endothelial growth factor (VEGF) pathway to two lateral domains and this restriction controls proper skeletal patterning. Hypoxia applied during early development strongly perturbs the activity of Nodal and BMP pathways that affect the VEGF pathway, dorsal-ventral (DV) and skeletogenic patterning. These pathways are largely unaffected by hypoxia applied after DV-axis formation. We propose that the use of redox and hypoxia as morphogens makes the sea urchin embryo highly sensitive to environmental hypoxia during early development, but the GRN structure provides higher tolerance to hypoxia at later stages.

Hypoxia regulates the degradation of non-nuclear organelles during lens differentiation through activation of HIF1a.

Formation of the eye lens depends on the continuous differentiation of lens epithelial cells into lens fiber cells. To attain their mature structure and transparent function, nascent lens fiber cells must complete a precise cellular remodeling program hallmarked by the complete elimination of organelles to form the core lens organelle-free zone (OFZ). Lacking a blood supply, the lens resides in a hypoxic environment that results in a decreasing oxygen concentration from the lens surface to the lens core. This oxygen gradient results in a hypoxic microenvironment in the region of the lens where immature lens fiber cells initiate loss of organelles to form the core OFZ. These features of the lens suggest a potential role for low lens oxygen levels in the regulation of organelle degradation and other events critical for mature lens fiber cell formation. Hypoxia activates the master regulator of the hypoxic response, hypoxia-inducible factor 1a (HIF1a) that regulates hypoxia-responsive genes. To identify a potential role for hypoxia and HIF1a in the elimination of organelles during lens fiber cell maturation, we tested the requirement for hypoxia in the degradation of non-nuclear organelles in ex vivo cultured embryonic chick lenses by monitoring the degradation of mitochondria (MT), Golgi apparatus (GA) and endoplasmic reticulum (ER) under conditions of low (1% O2) and high (21% O2) oxygen. We also examined the requirement for HIF1a activation for elimination of these organelles under the same conditions using a specific HIF1a activator (DMOG) and a specific HIF1a inhibitor (chetomin) and examined the requirements for hypoxia and HIF1a for regulating transcription of BNIP3L that we previously showed to be required for elimination of non-nuclear lens organelles. We used ChIP-qPCR to confirm direct binding of HIF1a to the 5' untranslated region of the BNIP3L gene. Finally, we examined the effects of expressing an oxygen insensitive mutant form of HIF1a (P402A/P565A) and BNIP3L on non-nuclear organelle degradation. Our data demonstrate that hypoxia and HIF1a are required for the degradation of non-nuclear organelles during lens fiber cell formation and that they regulate this process by governing BNIP3L transcription. Our results also provide evidence that hypoxia and HIF1a are essential for achieving mature lens structure.

Hypoxia affects the ontogeny of the hypothalamus-pituitary-interrenal axis functioning in the lake whitefish (Coregonus clupeaformis).

Early life stages are sensitive to environmental insults and changes during critical developmental periods; this can often result in altered adult behaviour and physiology. Examining the development of the hypothalamus-pituitary-interrenal (HPI) axis and its responsiveness, or lack thereof, during development are important for understanding the short- and long-term impacts of stressors on embryonic and larval fish. We examined the ontogeny of the HPI axis in embryonic (21, 38, 63, 83 and 103 days post-fertilisation (dpf)) and larval (1, 2, 3 and 4 weeks post-hatch (wph)) lake whitefish (Coregonus clupeaformis) by quantifying changes in mRNA levels of several genes associated with HPI axis functioning and whole animal cortisol levels throughout development and in response to a severe or mild hypoxic stress. Cortisol, and crh, crhbp1, pomc and star transcripts were detected from the earliest embryonic age studied. Cortisol levels in control embryos decreased between 21 and 63 dpf, suggesting the utilisation of maternal cortisol deposits. However, by 83 dpf (70% developed) endogenous de novo synthesis had generated a 4.5-fold increase in whole embryo cortisol. Importantly, we provide novel data showing that the HPI axis can be activated even earlier. Whole body cortisol increased in eyed lake whitefish embryos (38 dpf; ~32% developed) in response to hypoxia stress. Coincident with this hypoxia-induced increase in cortisol in 38 dpf embryos were corresponding increases in crh, crhbp1, pomc and star transcript levels. Beyond 38 dpf, the HPI axis in lake whitefish embryos was hyporesponsive to hypoxia stress at all embryonic ages examined (63, 83 and 103 dpf; 54, 72 and 85% developed, respectively). Post-hatch, larvae responded to hypoxia with an increase in cortisol levels and HPI axis genes at 1 wph, but this response was lost and larvae appeared hyporesponsive at subsequent ages (2, 3 and 4 wph). Collectively our work demonstrates that during fish embryogenesis and the larval stage there are windows where the HPI axis is responsive and windows where it is truly hyporesponsive; both could be beneficial in ensuring undisrupted development particularly in the face of increasing environmental changes.

Msx1 deficiency interacts with hypoxia and induces a morphogenetic regulation during mouse lip development.

Nonsyndromic clefts of the lip and palate are common birth defects resulting from gene-gene and gene-environment interactions. Mutations in human MSX1 have been linked to orofacial clefting and we show here that Msx1 deficiency causes a growth defect of the medial nasal process (Mnp) in mouse embryos. Although this defect alone does not disrupt lip formation, Msx1-deficient embryos develop a cleft lip when the mother is transiently exposed to reduced oxygen levels or to phenytoin, a drug known to cause embryonic hypoxia. In the absence of interacting environmental factors, the Mnp growth defect caused by Msx1 deficiency is modified by a Pax9-dependent 'morphogenetic regulation', which modulates Mnp shape, rescues lip formation and involves a localized abrogation of Bmp4-mediated repression of Pax9 Analyses of GWAS data revealed a genome-wide significant association of a Gene Ontology morphogenesis term (including assigned roles for MSX1, MSX2, PAX9, BMP4 and GREM1) specifically for nonsyndromic cleft lip with cleft palate. Our data indicate that MSX1 mutations could increase the risk for cleft lip formation by interacting with an impaired morphogenetic regulation that adjusts Mnp shape, or through interactions that inhibit Mnp growth.

In utero hypoxia altered Ang II-induced contraction via PKCß in fetal cerebral arteries.

Cerebral circulation is important in fetal brain development, and angiotensin II (Ang II) plays vital roles in regulation of adult cerebral circulation. However, functions of Ang II in fetal cerebral vasculature and influences of in utero hypoxia on Ang II-mediated fetal cerebral vascular responses are largely unknown. This study investigated the effects and mechanisms of in utero hypoxia on fetal middle cerebral arteries (MCA) via Ang II. Near-term ovine fetuses were exposed to in utero hypoxia, and fetal MCA responses to Ang II were tested for vascular tension, calcium transient, and molecular analysis. Ang II caused significant dose-dependent contraction in control fetal MCA. Ang II-induced MCA constriction was decreased significantly in hypoxic fetuses. Neither losartan (AT1R antagonist, 10-5 mol/L) nor PD123,319 (AT2R antagonist, 10-5 mol/L) altered Ang II-mediated contraction in fetal MCA. Phenylephrine-mediated constriction was also significantly weaker in hypoxic fetuses. Bay K8644 caused similar contractions between the two groups. Protein expression of L-type voltage-dependent calcium channels was unchanged. There were no differences in caffeine-mediated vascular tension or calcium transients. Contraction induced by PDBu (PKC agonist) was obviously weaker in hypoxic MCA. Protein expression of PKCß was reduced in the hypoxic compared with the control, along with no differences in phosphorylation levels. The results showed that fetal MCA was functionally responsive to Ang II near term. Intrauterine hypoxia reduced the vascular agonist-mediated contraction in fetal MCA, probably via decreasing PKCß and its phosphorylation, which might play protective effects on fetal cerebral circulation against transient hypoxia.

Fetal heart rate monitoring and neonatal outcome in a population of early- and late-onset intrauterine growth restriction.

AIM: The early-onset intrauterine growth restriction (IUGR) is associated with severe placental insufficiency and Doppler abnormalities. The late-onset IUGR is associated with mild placental insufficiency and normal Doppler velocimetry. The computerized cardiotocographic (cCTG) monitoring is used to evaluate the fetal well-being in pregnancies complicated by IUGR. Our aim was to investigate the cardiotocographic characteristics of IUGR fetuses and to identify every cCTG difference between Healthy and IUGR fetuses. METHODS: Four hundred thirty pregnant women were enrolled starting from the 28th week of gestation until the time of delivery: 200 healthy and 230 IUGR fetuses. Fetal heart rate (FHR) baseline (FHR), short-term variability (STV), long-term irregularity (LTI), delta, interval index (II), approximate entropy (ApEn), high frequency (HF), low frequency (LF), movement frequency (MF), LF/(HF + MF) ratio (LF/(HF + MF)) and number of decelerations were examined. Newborn baby data were also collected. RESULTS: The parameters of short- and medium-term variability discriminate between IUGR and healthy fetuses before 36 weeks including FHR, STV, LTI and delta discriminate between each subgroup of IUGR were compared to each one of the other two (P < 0.05). CONCLUSION: cCTG is a useful tool for the evaluation of chronic hypoxemia, which causes a delay in the maturation of all components of the autonomic and central nervous system. However, cCTG requires integration with fetal ultrasound and Doppler vessels evaluation to improve the ability to predict the neonatal outcome.

Impact of uteroplacental insufficiency on ovarian follicular pool in the rat.

BACKGROUND: A low oxygen supply to the fetus causes intrauterine growth restriction and can affect gonadal development of the offspring, having a potential impact on fertility. We investigated histology and gene expression in the postnatal rat ovary after fetal hypoxia induced by uterine artery ligation. METHODS: Sprague-Dawley rats underwent uterine artery ligation at day 19 of gestation. Offspring were sacrificed at 5, 20 and 40 days post-partum. Follicles were counted and classified in hematoxylin-eosin stained sections. Gene expression of 90 genes was analyzed by TaqMan® Low Density Array. RESULTS: A significantly lower number of total and primordial follicles was detected in 20 days post-partum intrauterine growth restricted animals. Follicle density was not different at 40 days post-partum, suggesting that compensatory mechanisms occurred during the pre-pubertal window. Uterine artery ligation modified the expression of 24 genes involved in different cellular functions, among which proliferation, apoptosis and metabolism. CONCLUSION: Ovarian follicle pool was affected by fetal hypoxia in early life, but this effect did not persist in puberty. Genes involved in cellular processes were affected at all ages, potentially implying long-term genetic alterations. Further analyses are needed to elucidate later effects of fetal hypoxia on ovarian function and fertility.

Long-term exposure to high altitude hypoxia during pregnancy increases fetal heart susceptibility to ischemia/reperfusion injury and cardiac dysfunction.

BACKGROUND: High altitude hypoxia (HAH) exposure affects fetal development. However, the fetal cardiovascular responses to the HAH are not well understood. We have tested the hypothesis that long-term HAH exposure alters the hypoxia/ischemia-sensitive gene expressions, leading to an increase in fetal heart susceptibility to ischemia/reperfusion (I/R) injury and cardiac dysfunction. METHODS: Time-dated pregnant sheep were exposed to high-altitude (3820 m) or were maintained at sea level (~300 m) for 110 days. Fetal hearts were isolated from the near-term ewes and subjected to I/R in a Langendorff preparation. RESULTS: HAH decreased the fetal body and heart weights in the female but not male fetuses. HAH had no effect on the left ventricle (LV) function at baseline, but increased the LV infarct size and attenuated the post-ischemic recovery of LV function in both male and female fetuses, as compared with the normoxic groups. HAH increased the protein levels of hypoxia-inducible factor (HIF)-1α and DNA methyltransferases type 3b (DNMT3b), but attenuated protein kinase C epsilon (PKCε) levels in the fetal hearts. AHA induced a 4.3 fold increase of miR-210 in the males and a 2.9 fold increase in female hearts. In addition, HAH had no effect on mTOR protein and phosphorylation levels but increased the autophagy biomarker, LC3B-II protein levels and LC3B-II/LC3B-I ratio in the fetal hearts. CONCLUSION: The results suggest that gestational HAH exposure induces in utero programming of the hypoxia/ischemia-sensitive gene expression pattern in the developing heart and increases cardiac susceptibility to I/R injury.

Perinatal changes in cardiac geometry and function in growth-restricted fetuses at term.

OBJECTIVE: To evaluate the effect of fetal growth restriction (FGR) at term on fetal and neonatal cardiac geometry and function. METHODS: This was a prospective study of 87 pregnant women delivering at term, comprising 54 normally grown and 33 FGR pregnancies. Fetal and neonatal conventional and spectral tissue Doppler and two-dimensional speckle tracking echocardiography were performed a few days before and within hours after birth. Fetal cardiac geometry, global myocardial deformation and performance and systolic and diastolic function were compared between normal and FGR pregnancies before and after birth. RESULTS: Compared with normally grown fetuses, FGR fetuses exhibited more globular ventricular geometry and poorer myocardial deformation and cardiac function (left ventricular (LV) sphericity index (SI), 0.54 vs 0.49; right ventricular (RV) SI, 0.60 vs 0.54; LV torsion, 1.2 °/cm vs 3.0 °/cm; LV isovolumetric contraction time normalized by cardiac cycle length, 121 ms vs 104 ms; interventricular septum early diastolic myocardial peak velocity/atrial contraction myocardial diastolic peak velocity ratio, 0.60 vs 0.71; P < 0.01 for all). The poorest perinatal outcomes occurred in FGR fetuses with the most impaired cardiac functional indices. When compared with normally grown neonates, FGR neonates showed persistent alteration in cardiac parameters (LV-SI, 0.53 vs 0.50; RV-SI, 0.54 vs 0.44; LV torsion, 1.1 °/cm vs 1.4 °/cm; LV myocardial performance index (MPI'), 0.52 vs 0.42; P < 0.01 for all). Paired comparison of fetal vs neonatal cardiac indices in FGR demonstrated that birth was associated with a significant improvement in some, but not all, cardiac indices (RV-SI, 0.60 vs 0.54; RV-MPI', 0.49 vs 0.39; P < 0.001 for all). CONCLUSIONS: Compared with normal pregnancies, FGR fetuses and neonates at term exhibit altered cardiac indices indicative of myocardial impairment that reflect adaptation to placental hypoxemia and alterations in hemodynamic load around the time of birth. Elucidating potential mechanisms that contribute to the alterations in perinatal cardiac adaptation in FGR could improve management and aid the development of better therapeutic strategies to reduce the risk of adverse pregnancy outcome. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.

Oxygen and lack of oxygen in fetal and placental development, feto-placental coupling, and congenital heart defects.

Low oxygen concentration (hypoxia) is part of normal embryonic development, yet the situation is complex. Oxygen (O2 ) is a janus gas with low levels signaling through hypoxia-inducible transcription factor (HIF) that are required for development of fetal and placental vasculature and fetal red blood cells. This results in coupling of fetus and mother around midgestation as a functional feto-placental unit (FPU) for O2 transport, which is required for continued growth and development of the fetus. Defects in these processes may leave the developing fetus vulnerable to O2 deprivation or other stressors during this critical midgestational transition when common septal and conotruncal heart defects (CHDs) are likely to arise. Recent human epidemiological and case-control studies support an association between placental dysfunction, manifest as early onset pre-eclampsia (PE) and increased serum bio-markers, and CHD. Animal studies support this association, in particular those using gene inactivation in the mouse. Sophisticated methods for gene inactivation, cell fate mapping, and a quantitative bio-reporter of O2 concentration support the premise that hypoxic stress at critical stages of development leads to CHD. The secondary heart field contributing to the cardiac outlet is a key target, with activation of the un-folded protein response and abrogation of FGF signaling or precocious activation of a cardiomyocyte transcriptional program for differentiation, suggested as mechanisms. These studies provide a strong foundation for further study of feto-placental coupling and hypoxic stress in the genesis of human CHD.

Fetal hypoxemia causes abnormal myocardial development in a preterm ex utero fetal ovine model.

In utero hypoxia is a major cause of neonatal morbidity and mortality and predisposes to adult cardiovascular disease. No therapies exist to correct fetal hypoxia. In a new ex utero fetal support system, we tested the hypothesis that hypoxemic support of the fetus impairs myocardial development, whereas normoxic support allows normal myocardial development. Preterm fetal lambs were connected via umbilical vessels to a low-resistance oxygenator and placed in a sterile-fluid environment. Control normoxic fetuses received normal fetal oxygenation, and hypoxemic fetuses received subphysiologic oxygenation. Fetuses with normal in utero development served as normal controls. Hypoxemic fetuses exhibited decreased maximum cardiac output in both ventricles, diastolic function, myocyte and myocyte nuclear size, and increased myocardial capillary density versus control normoxic fetuses. There were no differences between control normoxic fetuses in the fetal support system and normal in utero controls. Chronic fetal hypoxemia resulted in significant abnormalities in myocyte architecture and myocardial capillary density as well as systolic and diastolic cardiac function, whereas control fetuses showed no differences. This ex utero fetal support system has potential to become a significant research tool and novel therapy to correct fetal hypoxia.

The effects of embryonic hypoxic programming on cardiovascular function and autonomic regulation in the American alligator (Alligator mississippiensis) at rest and during swimming.

Reptilian embryos naturally experience fluctuating oxygen levels in ovo, and developmental hypoxia has been established to have long-term impacts on cardiovascular function in vertebrates. In the present study, we investigated the impact of developmental 21% (normoxia) and 10% O2 (hypoxia) on juvenile (4-year-old) American alligator cardiovascular function in animals at rest and during swimming. In both experimental groups, combined right aortic and right subclavian blood flow approximately doubled during swimming. Carotid blood flow increased during swimming in the hypoxia-programmed animals only, and both carotid and left aortic blood flow reached higher values in swimming hypoxic-programmed animals compared to the normoxic group. However, pulmonary blood flow, which increased two to threefold during swimming (in both groups), was higher in normoxic-programmed animals at both rest and swimming. The differences between programming groups were preserved after cholinergic blockade (atropine), but reduced by adrenergic receptor antagonists (propranolol and phentolamine). Propranolol and phentolamine also blunted the incremental increases in blood flows during swimming, which was especially clear in the hypoxia-programmed animals. Alteration in adrenergic control and relative cardiac size (which was increased in hypoxic-programmed alligators) may account for the differences between the experimental groups.

Reduced fetal movements and cerebroplacental ratio: evidence for worsening fetal hypoxemia.

OBJECTIVE: To investigate the fetal cerebroplacental ratio (CPR) in women presenting with reduced fetal movements (RFM). METHODS: This was a retrospective cohort study of data collected over an 8-year period at a fetal medicine unit at a tertiary referral center. The cohort comprised 4500 singleton pregnancies presenting with RFM at or after 36 weeks' gestation and 1527 control pregnancies at a similar gestational age without RFM. Fetal biometry and Doppler parameters were recorded and converted into centiles and multiples of the median (MoM). CPR was defined as the ratio between the fetal middle cerebral artery (MCA) pulsatility index (PI) and the umbilical artery (UA) PI. Subgroup analysis for fetal size and for single vs multiple episodes of RFM was performed. RESULTS: Compared with controls, pregnancies with RFM had lower MCA-PI MoM (median, 0.95 vs 0.97; P < 0.001) and CPR MoM (median, 0.97 vs 0.99; P = 0.018). Compared with women presenting with single episodes of RFM, pregnancies with multiple episodes (≥ 2 episodes) had lower CPR MoM (median, 0.94 vs 0.98; P = 0.003). On subgroup analysis for fetal size, compared with controls, appropriate-for-gestational-age fetuses in the RFM group had lower MCA-PI MoM (median, 0.96 vs 0.97; P = 0.003) and higher rate of CPR below the 5th centile (5.3% vs 3.6%; P = 0.015). Logistic regression analysis demonstrated an association of risk of recurrent RFM with maternal age (OR, 0.96; 95% CI, 0.93-0.99), non-Caucasian ethnicity (OR, 0.72; 95% CI, 0.53-0.97), estimated fetal weight centile (OR, 1.01; 95% CI, 1.00-1.02) and CPR MoM (OR, 0.24; 95% CI, 0.12-0.47). CONCLUSION: Pregnancies complicated by multiple episodes of RFM show significantly lower CPR MoM and MCA-PI MoM compared with those with single episodes and controls. This is likely to be due to worsening fetal hypoxemia in women presenting with recurrent RFM. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

The highs and lows of programmed cardiovascular disease by developmental hypoxia: studies in the chicken embryo.

It is now established that adverse conditions during pregnancy can trigger a fetal origin of cardiovascular dysfunction and/or increase the risk of heart disease in later life. Suboptimal environmental conditions during early life that may promote the development of cardiovascular dysfunction in the offspring include alterations in fetal oxygenation and nutrition as well as fetal exposure to stress hormones, such as glucocorticoids. There has been growing interest in identifying the partial contributions of each of these stressors to programming of cardiovascular dysfunction. However, in humans and in many animal models this is difficult, as the challenges cannot be disentangled. By using the chicken embryo as an animal model, science has been able to circumvent a number of problems. In contrast to mammals, in the chicken embryo the effects on the developing cardiovascular system of changes in oxygenation, nutrition or stress hormones can be isolated and determined directly, independent of changes in the maternal or placental physiology. In this review, we summarise studies that have exploited the chicken embryo model to determine the effects on prenatal growth, cardiovascular development and pituitary-adrenal function of isolated chronic developmental hypoxia.

Early Gestational Hypoxia and Adverse Developmental Outcomes.

Hypoxia is a normal and essential part of embryonic development. However, this state may leave the embryo vulnerable to damage when oxygen supply is disturbed. Embryofetal response to hypoxia is dependent on duration and depth of hypoxia, as well as developmental stage. Early postimplantation rat embryos were resilient to hypoxia, with many surviving up to 1.5 hr of uterine clamping, while most mid-gestation embryos were dead after 1 hour of clamping. Survivors were small and many had a range of defects, principally terminal transverse limb reduction defects. Similar patterns of malformations occurred when embryonic hypoxia was induced by maternal hypoxia, interruption of uteroplacental flow, or perfusion and embryonic bradycardia. There is good evidence that high altitude pregnancies are associated with smaller babies and increased risk of some malformations, but these results are complicated by increased risk of pre-eclampsia. Early onset pre-eclampsia itself is associated with small for dates and increased risk of atrio-ventricular septal defects. Limb defects have clearly been associated with chorionic villus sampling, cocaine, and misoprostol use. Similar defects are also observed with increased frequency among fetuses who are homozygous for thalassemia. Drugs that block the potassium current, whether as the prime site of action or as a side effect, are highly teratogenic in experimental animals. They induce embryonic bradycardia, hypoxia, hemorrhage, and blisters, leading to transverse limb defects as well as craniofacial and cardiovascular defects. While evidence linking these drugs to birth defects in humans is not compelling, the reason may methodological rather than biological. Birth Defects Research 109:1358-1376, 2017.© 2017 Wiley Periodicals, Inc.

Hypoxia: From Placental Development to Fetal Programming.

Hypoxia may influence normal and different pathological processes. Low oxygenation activates a variety of responses, many of them regulated by hypoxia-inducible factor 1 complex, which is mostly involved in cellular control of O2 consumption and delivery, inhibition of growth and development, and promotion of anaerobic metabolism. Hypoxia plays a significant physiological role in fetal development; it is involved in different embryonic processes, for example, placentation, angiogenesis, and hematopoiesis. More recently, fetal hypoxia has been associated directly or indirectly with fetal programming of heart, brain, and kidney function and metabolism in adulthood. In this review, the role of hypoxia in fetal development, placentation, and fetal programming is summarized. Hypoxia is a basic mechanism involved in different pregnancy disorders and fetal health developmental complications. Although there are scientific data showing that hypoxia mediates changes in the growth trajectory of the fetus, modulates gene expression by epigenetic mechanisms, and determines the health status later in adulthood, more mechanistic studies are needed. Furthermore, if we consider that intrauterine hypoxia is not a rare event, and can be a consequence of unavoidable exposures to air pollution, nutritional deficiencies, obesity, and other very common conditions (drug addiction and stress), the health of future generations may be damaged and the incidence of some diseases will markedly increase as a consequence of disturbed fetal programming. Birth Defects Research 109:1377-1385, 2017.© 2017 Wiley Periodicals, Inc.

Cardiovascular susceptibility to in vivo ischemic myocardial injury in male and female rat offspring exposed to prenatal hypoxia.

Intrauterine growth restriction (IUGR) following prenatal hypoxia exposure leads to a higher risk of developing cardiovascular disease (CVD) in later life. Our aim was to evaluate cardiac susceptibility and its pathophysiological mechanisms following acute myocardial infarction (MI) in adult rat offspring exposed to prenatal hypoxia. Male and female rat offspring, which experienced normoxia (21% O2) or hypoxia (11% O2) in utero underwent sham or MI surgery at 12 weeks of age. Echocardiographic data revealed that both sexes had systolic dysfunction following MI surgery, independent of prenatal hypoxia. Male offspring exposed to prenatal hypoxia, however, had left ventricular dilatation, global dysfunction, and signs of diastolic dysfunction following MI surgery as evident by increased left ventricular internal diameter (LVID) during diastole (MI effect, P<0.01), Tei index (MI effect, P<0.001), and E/E' ratio (prenatal hypoxia or MI effect, P<0.01). In contrast, diastolic dysfunction in female offspring was not as evident. Cardiac superoxide levels increased only in prenatal hypoxia exposed male offspring. Cardiac sarcoendoplasmic reticulum Ca2+-ATPase2a (SERCA2a) levels, a marker of cardiac injury and dysfunction, decreased in both male and female MI groups independent of prenatal hypoxia. Prenatal hypoxia increased cardiac ryanodine receptor 2 (RYR2) protein levels, while MI reduced RYR2 in only male offspring. In conclusion, male offspring exposed to prenatal hypoxia had an increased susceptibility to ischemic myocardial injury involving cardiac phenotypes similar to heart failure involving diastolic dysfunction in adult life compared with both offspring from healthy pregnancies and their female counterparts.

Hypoxia exacerbates the cardiotoxic effect of the polycyclic aromatic hydrocarbon, phenanthrene in Danio rerio.

The Deepwater Horizon oil spill of 2010 released a mixture of polycyclic aromatic hydrocarbons (PAHs) into the Gulf of Mexico presenting a complex exposure regime for native species. Concurrently, the Gulf has experienced an increase in hypoxic events due to agricultural runoff from the Mississippi River outflow. This combination presents a unique physiological challenge to native species and a challenge for researchers. The purpose of this study was to determine how the cardiotoxic PAH, phenanthrene interacts with hypoxia to affect the cardiovascular system of larval zebrafish (Danio rerio). We exposed zebrafish larvae to 0, 1, 100, and 1000 µg/L of phenanthrene in combination with normoxia and hypoxia. At late hatching, video of hearts and vessels were used to measure heart rate (ƒH), stroke volume (SV), cardiac output (Q), red blood cell velocity, and caudal vessel diameter. We found that the highest concentration of phenanthrene caused a 58, 80, and 84% decrease in ƒH, Q, and arterial red blood cell velocity in normoxia and an 88, 98, and 99% decrease in hypoxia, respectively. Co-exposed larvae also experienced higher rates of edema and lordosis in addition to a 33% increase in mortality rate with co-exposure to hypoxia at the 1000 µg/L concentration of phenanthrene. At 12 dpf, baseline swimming behavior was similar between treatments indicating partial recovery from embryonic exposure. This study shows that phenanthrene decreases cardiac parameters, most significantly heart rate and that this effect is exacerbated by simultaneous exposure to hypoxia.

Embryonic hypoxia programmes postprandial cardiovascular function in adult common snapping turtles (Chelydra serpentina).

Reduced oxygen availability (hypoxia) is a potent stressor during embryonic development, altering the trajectory of trait maturation and organismal phenotype. We previously documented that chronic embryonic hypoxia has a lasting impact on the metabolic response to feeding in juvenile snapping turtles (Chelydra serpentina). Turtles exposed to hypoxia as embryos [10% O2 (H10)] exhibited an earlier and increased peak postprandial oxygen consumption rate, compared with control turtles [21% O2 (N21)]. In the current study, we measured central blood flow patterns to determine whether the elevated postprandial metabolic response in H10 turtles is linked to lasting impacts on convective transport. Five years after hatching, turtles were instrumented to quantify systemic ([Formula: see text]) and pulmonary ([Formula: see text]) blood flows and heart rate (fH) before and after a ∼5% body mass meal. In adult N21 and H10 turtles, fH was increased significantly by feeding. Although total stroke volume (VS,tot) remained at fasted values, this tachycardia contributed to an elevation in total cardiac output ([Formula: see text]). However, there was a postprandial reduction in a net left-right (L-R) shunt in N21 snapping turtles only. Relative to N21 turtles, H10 animals exhibited higher [Formula: see text] due to increased blood flow through the right systemic outflow vessels of the heart. This effect of hypoxic embryonic development, reducing a net L-R cardiac shunt, may support the increased postprandial metabolic rate we previously reported in H10 turtles, and is further demonstration of adult reptile cardiovascular physiology being programmed by embryonic hypoxia.

Effect of Hypoxemia on Fetal Ventricular Deformation in a Chronically Instrumented Sheep Model.

We hypothesized that in near-term sheep fetuses, hypoxemia changes myocardial function as reflected in altered ventricular deformation on speckle-tracking echocardiography. Fetuses in 21 pregnant sheep were instrumented. After 4 d of recovery, fetal cardiac function was assessed by echocardiography at baseline, after 30 and 120 min of induced fetal hypoxemia and after its reversal. Left (LV) and right (RV) ventricular cardiac output and myocardial strain were measured. Baseline mean (standard deviation [SD]) LV and RV global longitudinal strains were -18.7% (3.8) and -14.3% (5.3). Baseline RV global longitudinal and circumferential deformations were less compared with those of the left ventricle (p = 0.016 and p < 0.005). LV, but not RV, global longitudinal strain was decreased (p = 0.003) compared with baseline with hypoxemia. Circumferential and radial strains did not exhibit significant changes. In the near-term sheep fetus, LV global longitudinal and circumferential strains are more negative than RV strains. Acute hypoxemia leads to LV rather than RV dysfunction as reflected by decreased deformation.