Chronic Hypoxia Diminishes the Proliferative Response of Guinea Pig Uterine Artery Vascular Smooth Muscle Cells in Vitro

Maternal AMPK pathway activation with uterine artery blood flow and fetal growth maintenance during hypoxia

High-altitude (HA) hypoxia lowers uterine artery (UtA) blood flow during pregnancy and birth weight. Adenosine monophosphate kinase (AMPK) activation has selective, uteroplacental vasodilator effects that lessen hypoxia-associated birth weight reductions. In this study, we determined the relationship between AMPK-pathway gene expression and metabolites in the maternal circulation during HA pregnancy as well as with the maintenance of UtA blood flow and birth weight at HA. Residents at HA (2,793 m) versus low altitude (LA; 1,640 m) had smaller UtA diameters at weeks 20 and 34, lower UtA blood flow at week 20, and lower birth weight babies. At week 34, women residing at HA versus women residing at LA had decreased expression of upstream and downstream AMPK-pathway genes. Expression of the α1-AMPK catalytic subunit, PRKAA1, correlated positively with UtA diameter and blood flow at weeks 20 (HA) and 34 (LA). Downstream AMPK-pathway gene expression positively correlated with week 20 fetal biometry at both altitudes and with UtA diameter and birth weight at LA. Reduced gene expression of AMPK activators and downstream targets in women residing at HA versus women residing at LA, together with positive correlations between PRKAA1 gene expression, UtA diameter, and blood flow suggest that greater sensitivity to AMPK activation at midgestation at HA may help offset later depressant effects of hypoxia on fetal growth.NEW & NOTEWORTHY Fetal growth restriction (FGR) is increased and uterine artery (UtA) blood flow is lower at high altitudes (HA) but not all HA pregnancies have FGR. Here we show that greater UtA diameter and blood flow at week 20 are positively correlated with higher expression of the gene encoding the α1-catalytic subunit of AMP protein kinase, PRKAA1, suggesting that increased AMPK activation may help to prevent the detrimental effects of chronic hypoxia on fetal growth.

Increased uterine artery blood flow in hypoxic murine pregnancy is not sufficient to prevent fetal growth restriction†

Incomplete maternal vascular responses to pregnancy contribute to pregnancy complications including intrauterine growth restriction (IUGR) and preeclampsia. We aimed to characterize maternal vascular dysfunction in a murine model of fetal growth restriction as an approach toward identifying targetable pathways for improving pregnancy outcomes. We utilized a murine model of late-gestation hypoxia-induced IUGR that reduced E18.5 fetal weight by 34%. Contrary to our hypothesis, uterine artery blood flow as measured in vivo by Doppler ultrasound was increased in mice housed under hypobaric hypoxia (385 mmHg; 5500 m) vs normoxia (760 mmHg; 0 m). Using wire myography, uterine arteries isolated from hypoxic mice had similar vasodilator responses to the two activators A769662 and acetylcholine as those from normoxic mice, although the contribution of an increase in nitric oxide production to uterine artery vasodilation was reduced in the hypoxic vs normoxic groups. Vasoconstrictor responses to phenylephrine and potassium chloride were unaltered by hypoxia. The levels of activated adenosine monophosphate-activated protein kinase (AMPK) were reduced with hypoxia in both the uterine artery and placenta as measured by western blot and immunohistochemistry. We concluded that the rise in uterine artery blood flow may be compensatory to hypoxia but was not sufficient to prevent fetal growth restriction. Although AMPK signaling was reduced by hypoxia, AMPK was still receptive to pharmacologic activation in the uterine arteries in which it was a potent vasodilator. Thus, AMPK activation may represent a new therapy for pregnancy complications involving reduced uteroplacental perfusion.

Preeclampsia link to gestational hypoxia

Complications of pregnancy remain key drivers of morbidity and mortality, affecting the health of both the mother and her offspring in the short and long term. There is lack of detailed understanding of the pathways involved in the pathology and pathogenesis of compromised pregnancy, as well as a shortfall of effective prognostic, diagnostic and treatment options. In many complications of pregnancy, such as in preeclampsia, there is an increase in uteroplacental vascular resistance. However, the cause and effect relationship between placental dysfunction and adverse outcomes in the mother and her offspring remains uncertain. In this review, we aim to highlight the value of gestational hypoxia-induced complications of pregnancy in elucidating underlying molecular pathways and in assessing candidate therapeutic options for these complex disorders. Chronic maternal hypoxia not only mimics the placental pathology associated with obstetric syndromes like gestational hypertension at morphological, molecular and functional levels, but also recapitulates key symptoms that occur as maternal and fetal clinical manifestations of these pregnancy disorders. We propose that gestational hypoxia provides a useful model to study the inter-relationship between placental dysfunction and adverse outcomes in the mother and her offspring in a wide array of examples of complicated pregnancy, such as in preeclampsia.

Fluorinated methacrylamide chitosan hydrogel dressings enhance healing in an acute porcine wound model

Wound healing involves multiple interrelated processes required to lead to successful healing outcomes. Phagocytosis, inflammation, cell proliferation, angiogenesis, energy production, and collagen synthesis are all directly or indirectly dependent on oxygen. Along with other critical factors, such as nutrition and comorbidities, availability of oxygen is a key determinant of healing success. Previously, we have presented a novel oxygenated hydrogel material that can be made into dressings for continuous localized oxygen delivery to wounds. In this study, an acute porcine wound model was used to test the healing benefits of these oxygenated MACF (MACF + O₂) hydrogel dressings compared to controls, which included commercial Derma-Gel^TM hydrogel dressings. Wound closure and histological analyses were performed to assess re-epithelialization, collagen synthesis, angiogenesis, and keratinocyte maturation. Results from these assays revealed that wounds treated with MACF + O₂ hydrogel dressings closed faster as compared to Derma-Gel (p<0.05). Targeted metabolomics via liquid chromatography separation and mass spectrometric detection (LC-MS/MS) and a biochemical assay determined the concentration of hydroxyproline in wound samples at days 14 and 21, showing that MACF + O₂ hydrogel dressings improved wound healing via an upregulated collagen synthesis pathway as compared to Derma-Gel (p<0.05). Histological evidence showed that MACF + O₂ hydrogel dressings improve new blood vessel formation and keratinocyte maturation over all other treatments.

Chronic hypoxia alters maternal uterine and fetal hemodynamics in the full-term pregnant guinea pig

Placental hypoxia is associated with maternal hypertension, placental insufficiency, and fetal growth restriction. In the pregnant guinea pig, prenatal hypoxia during early gestation inhibits cytotrophoblast invasion of spiral arteries, increases maternal blood pressure, and induces fetal growth restriction. In this study the impact of chronic maternal hypoxia on fetal heart structure was evaluated using four-dimensional echocardiography with spatiotemporal image correlation and tomographic ultrasound, and uterine and umbilical artery resistance/pulsatility indexes and fetal heart function were evaluated using pulsed-wave Doppler ultrasound. Pregnant guinea pigs were exposed to normoxia (n = 7) or hypoxia (10.5% O₂, n = 9) at 28-30 days gestation, which was maintained until full term (65 days). At full term, fetal heart structure and outflow tracts were evaluated in the four-chamber view. Fetal heart diastolic function was assessed by E wave-to-A wave diastolic filling ratios (E/A ratios) of both ventricles and systolic function by the myocardial performance index (or Tie) of left ventricles of normoxic (n = 21) and hypoxic (n = 17) fetuses. There were no structural abnormalities in fetal hearts. However, hypoxia induced asymmetric fetal growth restriction and increased the placental/fetal weight compared with normoxic controls. Hypoxia increased Doppler resistance and pulsatility indexes in the uterine, but not umbilical, arteries, had no effect on the Tie index, and increased the E/A ratio in left, but not right, ventricles. Thus, prolonged hypoxia, starting at midgestation, increases uterine artery resistance and generates fetal growth restriction at full term. Furthermore, the enhanced cardiac diastolic filling with no changes in systolic function or umbilical artery resistance suggests that the fetal guinea pig systemic circulation undergoes a compensated, adaptive response to prolonged hypoxia exposure.

Maternal vascular responses to hypoxia in a rat model of intrauterine growth restriction

Intrauterine growth restriction (IUGR) is a common pregnancy complication and is a leading cause of fetal morbidity and mortality. Placental hypoxia contributes to adverse fetal consequences, such as IUGR. Exposing pregnant rats to hypoxia can lead to IUGR; however, assessment of maternal vascular function in a rat model of hypoxia, and the mechanisms that may contribute to adverse pregnancy outcomes, has not been extensively studied. We hypothesized that exposing pregnant rats to hypoxia will affect maternal systemic vascular function and increase the uterine artery resistance index (RI), which will be associated with IUGR. To test this hypothesis, pregnant rats were kept in normoxia (21% O₂) or hypoxia (11% O₂) from gestational day (GD) 6 to 20 Maternal blood pressure, uteroplacental resistance index (RI) (ultrasound biomicroscopy), and vascular function (wire myography) were assessed in uterine and mesenteric arteries. Fetal weight was significantly reduced (P < 0.001), while maternal blood pressure was increased (P < 0.05) in rats exposed to hypoxia. Maternal vascular function was also affected after exposure to hypoxia, including impaired endothelium-dependent vasodilation responses to methacholine in isolated uterine arteries (pEC₅₀ normoxia: 6.55 ± 0.23 vs. hypoxia: 5.02 ± 0.35, P < 0.01) and a reduced uterine artery RI in vivo (normoxia: 0.63 ± 0.04 vs. hypoxia: 0.53 ± 0.01, P < 0.05); associated with an increase in umbilical vein RI (normoxia: 0.35 ± 0.02 vs. hypoxia: 0.45 ± 0.04, P < 0.05). These data demonstrate maternal and fetal alterations in vascular function due to prenatal exposure to hypoxia. Further, although there was a compensatory reduction in uterine artery RI in the hypoxia groups, this was not sufficient to prevent IUGR.

Maternal uterine vascular remodeling during pregnancy

Remodeling of the maternal uterine vasculature during pregnancy is a unique cardiovascular process that occurs in the adult and results in significant structural and functional changes in large and small arteries and veins, and in the creation of the placenta--a new fetomaternal vascular organ. This expansive, hypertrophic process results in increases in both lumen circumference and length, and is effected through a combination of tissue and cellular hypertrophy, endothelial and vascular smooth muscle hyperplasia, and matrix remodeling. This review summarizes what is currently known about the time course and extent of the remodeling process, and how local vs. systemic factors influence its genesis. The main focus is on upstream maternal vessels rather than spiral artery changes, although the latter are considered from the overall hemodynamic perspective. We also consider some of the underlying mechanisms and provide a hypothetical scenario that integrates our current knowledge. Abrogation of this adaptive vascular process is associated with several human gestational pathologies such as preeclampsia and intrauterine growth restriction (IUGR), which not only raise the risk of infant mortality and morbidity but are also a significant source of maternal mortality and susceptibility to cardiovascular and other diseases for both mother and neonate later in life.

Higher estrogen levels during pregnancy in Andean than European residents of high altitude suggest differences in aromatase activity

CONTEXT

Uteroplacental hypoxia has been reported to lower estrogen levels in preeclampsia as the result of reduced aromatase activity.

OBJECTIVE

We asked whether the chronic hypoxia of residence at high altitude in the absence of preeclampsia lowered estrogen, whether such effects differed in Andean vs European high-altitude residents, and whether such effects were related to uterine artery diameter or blood flow.

DESIGN, SETTING, AND PARTICIPANTS

Studies at weeks 20 and 36 of pregnancy were conducted in 108 healthy Bolivian low- (400 m, n = 53) or high-altitude (3600 m, n = 55) residents of European (n = 28 low and 26 high altitude) or Andean (n = 25 low and 29 high altitude) ancestry. All groups were similar in age, nonpregnant body mass index, and pregnancy weight gain.

RESULTS

High-altitude residence increased circulating progesterone, cortisol, estrone, 17β-estradiol, and estriol levels (all P < .01). High-altitude Andeans vs Europeans at week 36 had higher progesterone, estrone, 17β-estradiol, and estriol levels as well as product to substrate ratios for the reactions catalyzed by aromatase, whereas week 36 cortisol levels were greater in the European than Andean women (all P < .05). Lower cortisol, higher estriol (both P < .01), and trends for higher progesterone and 17β-estradiol levels were associated with greater uterine artery diameters and blood flow at high altitude.

CONCLUSIONS

Chronic hypoxia does not lower but rather raises estrogen levels in multigenerational Andeans vs shorter-term Europeans, possibly as the result of greater aromatase activity. Because hypoxia alone does not lower estrogen, other attributes of the disease may be responsible for the lower estrogen levels seen previously in preeclamptic women.

Humans at high altitude: hypoxia and fetal growth

High-altitude studies offer insight into the evolutionary processes and physiological mechanisms affecting the early phases of the human lifespan. Chronic hypoxia slows fetal growth and reduces the pregnancy-associated rise in uterine artery (UA) blood flow. Multigenerational vs. shorter-term high-altitude residents are protected from the altitude-associated reductions in UA flow and fetal growth. Presently unknown is whether this fetal-growth protection is due to the greater delivery or metabolism of oxygen, glucose or other substrates or to other considerations such as mechanical factors protecting fragile fetal villi, the creation of a reserve protecting against ischemia/reperfusion injury, or improved placental O(2) transfer as the result of narrowing the A-V O(2) difference and raising uterine P(v)O₂. Placental growth and development appear to be normal or modified at high altitude in ways likely to benefit diffusion. Much remains to be learned concerning the effects of chronic hypoxia on embryonic development. Further research is required for identifying the fetoplacental and maternal mechanisms responsible for transforming the maternal vasculature and regulating UA blood flow and fetal growth. Genomic as well as epigenetic studies are opening new avenues of investigation that can yield insights into the basic pathways and evolutionary processes involved.

Chronic hypoxia increases pressure-dependent myogenic tone of the uterine artery in pregnant sheep: role of ERK/PKC pathway

Chronic hypoxia during pregnancy has profound effects on uterine artery (UA) contractility and attenuates uterine blood flow. The present study tested the hypothesis that chronic hypoxia inhibits the pregnancy-induced reduction in pressure-dependent myogenic tone of resistance-sized UAs. UAs were isolated from nonpregnant ewes (NPUAs) and near-term pregnant ewes (PUAs) that had been maintained at sea level (approximately 300 m) or at high altitude (3,801 m) for 110 days. In normoxic animals, the pressure-dependent myogenic response was significantly attenuated in PUAs compared with NPUAs. Hypoxia significantly increased myogenic tone in PUAs and abolished its difference between PUAs and NPUAs. Consistently, there was a significant increase in PKC-mediated baseline Ca(2+) sensitivity of PUAs in hypoxic animals. Hypoxia significantly increased phorbol 12,13-dibutyrate (PDBu)-induced contractions in PUAs but not in NPUAs. Whereas the inhibition of ERK1/2 by PD-98059 potentiated PDBu-mediated contractions of PUAs in normoxic animals, it failed to do so in hypoxic animals. Hypoxia decreased ERK1/2 expression in PUAs. PDBu induced membrane translocation of PKC-alpha and PKC-epsilon. Whereas there were no significant differences in PKC-alpha translocation among all groups, the translocation of PKC-epsilon was significantly enhanced in NPUAs compared with PUAs in normoxic animals, and hypoxia significantly increased PKC-epsilon translocation in PUAs. In the presence of PD-98059, there were no significant differences in PDBu-induced PKC-epsilon translocation among all groups. Treatment of PUAs isolated from normoxic animals with 10.5% O(2) for 48 h ex vivo significantly increased PDBu-induced contractions and eliminated its difference between PUAs and NPUAs. The results suggest that hypoxia upregulates pressure-dependent myogenic tone through its direct effect in suppressing ERK1/2 activity and increasing the PKC signal pathway, leading to an increase in the Ca(2+) sensitivity of the myogenic mechanism in the UA during pregnancy.

High glucose concentrations alter hypoxia-induced control of vascular smooth muscle cell growth via a HIF-1alpha-dependent pathway

Induction of diabetes can produce arterial wall hypoxia preceding the formation of vascular lesions. We therefore determined whether a dynamic interplay exists between hyperglycemia and the major regulator of hypoxia, hypoxia-inducible factor 1-alpha (HIF-1alpha) in controlling hypoxia-induced vascular smooth muscle cell growth in vitro. Bovine aortic smooth muscle cells (BASMC) were exposed to conditions of normal glucose (5.5 mM) and hyperglycemia (25 mM glucose) under normoxic (5% CO(2), 95% air) and hypoxic (2% O(2), 5% CO(2), 93% N(2)) conditions for 5 days prior to determining cell proliferation and apoptosis using FACS analysis, immunoblot QRT-PCR and caspase-3 enzymatic activity. Chronic hypoxia stimulated apoptosis and inhibited proliferation in the presence of normal glucose while hyperglycemia significantly attenuated the hypoxic-induced growth response. HIF-1alpha expression was also inhibited by hyperglycemia with a concomitant decrease in hypoxia response element (HRE) promoter transactivation. Subsequent siRNA knockdown of HIF-1alpha inhibited the hypoxia-induced changes in growth in the presence of normal glucose while concomitantly attenuating the effects of hyperglycemia on the hypoxic-induced response. These results suggest that hypoxia-induced changes in vascular cell growth are altered by hyperglycemia via inhibition of HIF-1alpha expression and activity.

Chronic Hypoxia Diminishes the Proliferative Response of Guinea Pig Uterine Artery Vascular Smooth Muscle Cells in Vitro

The pregnancy-related size enlargement of the guinea pig uterine artery is partially accomplished by hyperplasia in all layers of the vessel wall. We sought to determine the separate and combined effects of chronic hypoxia and pregnancy on the proliferative capacity of uterine artery vascular smooth muscle cells (UA VSMCs). We established primary UA VSMC cultures from a total of 13 guinea pigs using an enzymatic digestion technique. Animals were bred and kept in normoxia or hypoxia (P(B) = 463 mmHg, simulated elevation = 3962 m) for 45 days, a duration equivalent to midpregnancy in the guinea pig 63-day gestation. Nonpregnant matched controls were included. The proliferative response of UA VSMCs to 1, 3, 5 or 7 days of serum stimulation in vitro was compared. Exposure to hypoxia reduced UA VSMC proliferative response to serum stimulation relative to that seen in cells harvested from normoxic females. The inhibitory effect was present both in cells harvested from nonpregnant and pregnant animals and resulted in a lower UA VSMC proliferative response in the cells harvested from hypoxic compared with normoxic pregnant animals. Our data were consistent with our hypothesis that chronic maternal hypoxia compromises the capacity for growth and remodeling of the uterine artery during pregnancy, perhaps by interfering with the ability of vascular smooth muscle cells to de-differentiate to a proliferative phenotype. Noteworthy was that such effects of chronic hypoxia were retained in cultured cells.