Context An imbalance of proangiogenic and antiangiogenic factors is thought to induce the widespread vascular dysfunction characteristic of preeclampsia (PreE). Erythropoietin (Epo), a pleiotropic cytokine, has important angiogenic and vasoactive properties; however, its contribution to maternal vascular dysfunction in PreE is unknown. Objectives Because high altitude (HA) raises the incidence of PreE, we asked whether HA increased maternal Epo and soluble Epo receptor (sEpoR) levels and whether such effects differed between PreE and normotensive controls at HA. Design, Setting, and Participants Longitudinal studies were conducted in pregnant Andean residents at HA (n = 28; 3600 m) or sea level (SL; n = 16; 300 m). Cross-sectional studies included 34 gestational age‒matched Andean PreE cases (n = 17) and controls (n = 17) in La Paz-El Alto, Bolivia (3600 to 4100 m). Results HA augmented the pregnancy-associated rise in Epo relative to SL (P = 0.002), despite similar reductions in hemoglobin (Hb) across pregnancy at each altitude (7% to 9%, P < 0.001 for both). HA PreE cases had circulating Epo levels equivalent to those of controls but greater sEpoR (P < 0.05) and reduced Hb (P = 0.06, trend). Conclusion(s) Our findings suggest that an augmented pregnancy-associated rise in Epo may be important for successful vascular adaptation to pregnancy at HA. We further speculate that the elevated sEpoR observed in PreE vs controls at HA impedes the effect of Epo to maintain endothelial function and may, in turn, be of pathological relevance for PreE at HA.

Epigenomic processes are believed to play a pivotal role for the effect of environmental exposures in early life to modify disease risk throughout the lifespan. Offspring of women with hypertensive complications of pregnancy (HTNPREG) have an increased risk of developing systemic and pulmonary vascular dysfunction in adulthood. In this preliminary report, we sought to determine whether epigenetic modifications of genes involved in the regulation of vascular function were present in HTNPREG offspring. We contrasted DNA methylation and gene expression patterns of peripheral blood mononuclear cells obtained from young male offspring of HTNPREG (n = 5) to those of normotensive controls (n = 19). In HTNPREG offspring we identified six differentially methylated regions (DMRs) including three genes (SMOC2, ARID1B and CTRHC1) relevant to vascular function. The transcriptional activity of ARID1B and CTRCH1 was inversely related to methylation status. HTNPREG offspring had higher systolic pulmonary artery pressure (sP(PA)) versus controls. Our findings demonstrate that epigenetic marks are altered in offspring of HTNPREG with a modest elevation of sP(PA) and introduce novel epigenomic targets for further study. On the basis of these findings we speculate that epigenomic mechanisms may be involved in mediating the effect of HTNPREG to raise the risk of vascular disease later in life.

Evolutionary trade-offs required for bipedalism and brain expansion influence the pregnancy rise in uterine artery (UtA) blood flow and, in turn, reproductive success. We consider the importance of UtA blood flow by reviewing its determinants and presenting data from 191 normotensive (normal, n = 125) or hypertensive (preeclampsia (PE) or gestational hypertension (GH), n = 29) Andean residents of very high (4100–4300 m) or low altitude (400 m, n = 37). Prior studies show that UtA blood flow is reduced in pregnancies with intrauterine growth restriction (IUGR) but whether the IUGR is due to resultant fetal hypoxia is unclear. We found higher UtA blood flow and Doppler indices of fetal hypoxia in normotensive women at high versus low altitude but similar fetal growth. UtA blood flow was markedly lower in early-onset PE versus normal high-altitude women, and their fetuses more hypoxic as indicated by lower fetal heart rate, Doppler indices and greater IUGR. We concluded that, despite greater fetal hypoxia, fetal growth was well defended by higher UtA blood flows in normal Andeans at high altitude but when compounded by lower UtA blood flow in early-onset PE, exaggerated fetal hypoxia caused the fetus to respond by decreasing cardiac output and redistributing blood flow to help maintain brain development at the expense of growth elsewhere. We speculate that UtA blood flow is not only an important supply line but also a trigger for stimulating the metabolic and other processes regulating feto-placental metabolism and growth. Studies using the natural laboratory of high altitude are valuable for identifying the physiological and genetic mechanisms involved in human reproductive success.

Perinatal exposures exert a profound influence on physiological function, including developmental processes vital for efficient pulmonary gas transfer throughout the lifespan. We extend the concept of developmental programming to chronic mountain sickness (CMS), a debilitating syndrome marked by polycythemia, ventilatory impairment, and pulmonary hypertension that affects ∼10% of male high-altitude residents. We hypothesized that adverse perinatal oxygenation caused abnormalities of ventilatory and/or pulmonary vascular function that increased susceptibility to CMS in adulthood. Subjects were 67 male high-altitude (3,600-4,100 m) residents aged 18-25 yr with excessive erythrocytosis (EE, Hb concentration ≥18.3 g/dl), a preclinical form of CMS, and 66 controls identified from a community-based survey (n = 981). EE subjects not only had higher Hb concentrations and erythrocyte counts, but also lower alveolar ventilation, impaired pulmonary diffusion capacity, higher systolic pulmonary artery pressure, lower pulmonary artery acceleration time, and more frequent right ventricular hypertrophy, than controls. Compared with controls, EE subjects were more often born to mothers experiencing hypertensive complications of pregnancy and hypoxia during the perinatal period, with each increasing the risk of developing EE (odds ratio = 5.25, P = 0.05 and odds ratio = 6.44, P = 0.04, respectively) after other factors known to influence EE status were taken into account. Adverse perinatal oxygenation is associated with increased susceptibility to EE accompanied by modest abnormalities of the pulmonary circulation that are independent of increased blood viscosity. The association between perinatal hypoxia and EE may be due to disrupted alveolarization and microvascular development, leading to impaired gas exchange and/or pulmonary hypertension.

Andeans and Tibetans have less altitude reduction in birth weight than do shorter-resident groups, but only Tibetans are protected from pulmonary hypertension and chronic mountain sickness (CMS). We hypothesized that differences in neonatal oxygenation were involved, with arterial O-2 saturation (SaO(2)) being highest in Tibetans, intermediate in Andeans, and lowest in Han or Europeans, and that improved oxygenation in Andeans relative to Europeans was accompanied by a greater postnatal decline in systolic pulmonary arterial pressures (P-pasys). We studied 41 healthy (36 Andeans, 5 Europeans) and 9 sick infants at 3,600 m in Bolivia. The SaO(2) in healthy babies was highest at 6-24 hours of postnatal age and then declined, whereas sick babies showed the opposite pattern. Compared to that of 30 Tibetan or Han infants studied previously at 3,600 m, SaO(2) was higher in Tibetans than in Han or Andeans during wakefulness and active or quiet sleep. Tibetans, as well as Andeans, had higher values than Han while feeding. The SaO(2)'s of healthy Andeans and Europeans were similar and, like those of Tibetans, remained at 85% or above, whereas Han values dipped below 70%. Andean and European P-pasys values were above sea-level norms and higher in sick than in healthy babies, but right heart pressure decreased across 4-6 months in all groups. We concluded that Tibetans had better neonatal oxygenation than Andeans at 3,600 m but that, counter to our hypothesis, neither was SaO(2) higher nor P-pa lower in Andean than in European infants. Further, longitudinal studies in these 4 groups are warranted to determine whether neonatal oxygenation influences susceptibility to high-altitude pulmonary hypertension and CMS later in life.

Low birth weight and intrauterine growth restriction (IUGR) increase the risk of mortality and morbidity during the perinatal period as well as in adulthood. Environmental and genetic factors contribute to IUGR, but the influence of maternal genetic variation on birth weight is largely unknown. We implemented a gene-by-environment study wherein we utilized the growth restrictive effects of high altitude. Multigenerational high-altitude residents (Andeans) are protected from altitude-associated IUGR compared with recent migrants (Europeans). Using a combined cohort of low- and high-altitude European and Andean women, we tested 63 single nucleotide polymorphisms (SNPs) from 16 natural selection-nominated candidate gene regions for associations with infant birth weight. We identified significant SNP associations with birth weight near coding regions for two genes involved in oxygen sensing and vascular control, PRKAA1 and EDNRA, respectively. Next, we identified a significant association for the PRKAA1 SNP with an intermediate phenotype, uterine artery diameter, which has been shown to be related to Andean protection from altitude-associated reductions in fetal growth. To explore potential functional relationships for the effect of maternal SNP genotype on birth weight, we evaluated the relationship between maternal PRKAA1 SNP genotype and gene expression patterns in general and, in particular, of key pathways involved in metabolic homeostasis that have been proposed to play a role in the pathophysiology of IUGR. Our observations suggest that maternal genetic variation within genes that regulate oxygen sensing, metabolic homeostasis, and vascular control influence fetal growth and birth weight outcomes and hence Andean adaptation to high altitude.

[PDF] [Full Text] [Abstract] , October 15, 2014; 28 (20): 2189-2204. Genes Dev. Abigail W. Bigham and Frank S. Lee Human high-altitude adaptation: forward genetics meets the HIF pathway [PDF] [Full Text] [Abstract] , March 5, 2015; 370 (1663): . Phil. Trans. R. Soc. B Vargas and Lorna G. Moore Vaughn A. Browne, Colleen G. Julian, Lillian Toledo-Jaldin, Darleen Cioffi-Ragan, Enrique Uterine artery blood flow, fetal hypoxia and fetal growth

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.

Chronic mountain sickness (CMS) is considered to be a loss of ventilatory acclimatization to high altitude (>2500 m) resulting in marked arterial hypoxemia and polycythemia. This case-control study explores the possibility that sleep-disordered breathing (SOB) and associated oxidative stress contribute to the etiology of CMS. Nocturnal respiratory and Sa(O2), patterns were measured using standard polysomnography techniques and compared between male high-altitude residents (aged 18-25) with preclinical CMS (excessive erythrocytosis (EE), n = 20) and controls (n = 19). Measures of oxidative stress and antioxidant status included isoprostanes (8-ISO-PGF2(alpha)), superoxide dismutase and ascorbic acid. EE cases had a greater apnea-hypopnea index, a higher frequency of apneas (central and obstructive) and hypopneas during REM sleep, and lower nocturnal Sa(O2) compared to controls. 8-iso-PGF2(alpha) was greater in EE than controls, negatively associated with nocturnal Sa(O2), and positively associated with hemoglobin concentration. Mild sleep-disordered breathing and oxidative stress are evident in preclinical CMS, suggesting that the resolution of nocturnal hypoxemia or antioxidant treatment may prevent disease progression. (C) 2013 Elsevier B.V. All rights reserved.

The Office of Research on Women’s Health (ORWH) initiated its signature research and career development programs in women’s health based on a paradigm that views interdisciplinary approaches as essential to moving forward the science associated with women’s health and to increasing understanding of the contributions of sex and gender factors to human health and disease. From the beginning it was hoped that supporting interdisciplinary research efforts and building a cadre of interdisciplinary women’s health researchers would help to reduce the fragmented approach to women’s health issues and encourage more comprehensive, integrated approaches to women’s health and new ways of evaluating those who conduct such research. ORWH supports innovative ways to encourage collaborative, interdisciplinary research that is team based to improve women’s health through two major initiatives, the …

Chronic exposure to hypoxia raises the risk of pregnancy disorders characterized by maternal vascular dysfunction and diminished fetal growth. In an effort to identify novel pathways for these hypoxia-related effects, we assessed gene expression profiles of peripheral blood mononuclear cells (PBMCs) obtained from 43 female, high-altitude or sea-level residents in the nonpregnant state or during pregnancy (20 or 36 wk). Hypoxia-related fetal growth restriction becomes apparent between 25 and 29 wk of gestation and continues until delivery. Our sampling strategy was designed to capture changes occurring before (20 wk) and during (36 wk) the time frame of slowed fetal growth. PBMC gene expression profiles were generated using human gene expression microarrays and compared between altitudes. Biological pathways were identified using pathway analysis. Modest transcriptional differences were observed between altitudes in the nonpregnant state. Of the genes that were differentially expressed at high altitude vs. sea level during pregnancy (20 wk: 59 probes mapped to 41 genes; 36 wk: 985 probes mapped to 700 genes), several are of pathological relevance for fetal growth restriction. In particular, transcriptional changes were consistent with the negative regulation of peroxisome proliferator-activated receptor (PPAR) at high altitude; such effects were accompanied by reduced birth weight (P <0.05) and head circumference (P <0.01) at high altitude vs. sea level. Our findings indicate that chronic exposure to hypoxia during pregnancy alters maternal gene expression patterns in general and, in particular, expression of key genes involved in metabolic homeostasis that have been proposed to play a role in the pathophysiology of fetal growth restriction.Julian, C. G., Yang, I. V., Browne, V. A., Vargas, E., Rodriguez, C., Pedersen, B. S., Moore, L. G., Schwartz, D. A. Inhibition of peroxisome proliferator-activated receptor : a potential link between chronic maternal hypoxia and impaired fetal growth.

ObjectivesHigh‐altitude hypoxia, or decreased oxygen levels caused by low barometric pressure, challenges the ability of humans to live and reproduce. Despite these challenges, human populations have lived on the Andean Altiplano and the Tibetan Plateau for millennia and exhibit unique circulatory, respiratory, and hematological adaptations to life at high altitude. We and others have identified natural selection candidate genes and gene regions for these adaptations using dense genome scan data. One gene previously known to be important in cellular oxygen sensing, egl nine homolog 1 (EGLN1), shows evidence of positive selection in both Tibetans and Andeans. Interestingly, the pattern of variation for this gene differs between the two populations. Continued research among Tibetan populations has identified statistical associations between hemoglobin concentration and single nucleotide polymorphism (SNP) genotype at EGLN1 and a second gene, endothelial PAS domain protein 1 (EPAS1).MethodsTo measure for the effects of EGLN1 and EPAS1 altitude genotypes on hemoglobin concentration among Andean highlanders, we performed a multiple linear regression analysis of 10 candidate SNPs in or near these two genes.ResultsOur analysis did not identify significant associations between EPAS1 or EGLN1 SNP genotypes and hemoglobin concentration in Andeans.ConclusionsThese results contribute to our understanding of the unique set of adaptations developed in different highland groups to the hypoxia of high altitude. Overall, the results provide key insights into the patterns of geneticadaptation to high altitude in Andean and Tibetan populations. Am. J. Hum. Biol. 25:190–197, 2013. © 2013 Wiley Periodicals, Inc.

One causal model of preeclampsia (PE) postulates that placental hypoxia alters the production of angiogenic growth effectors (AGEs), causing an imbalance leading to maternal endothelial cell dysfunction. We tested this model using the natural experiment of high-altitude (HA) residence. We hypothesized that in HA pregnancies 1) circulating soluble fms-like tyrosine kinase 1 (sFlt-1) is increased and placental growth factor (PlGF) decreased, and 2) AGE concentrations correlate with measures of hypoxia. A cross-sectional study of healthy pregnancies at low altitude (LA) (400 m) versus HA (3600 m) compared normal (n = 80 at HA, n = 90 at LA) and PE pregnancies (n = 20 PE at HA, n = 19 PE at LA). Blood was collected using standard serum separation and, in parallel, by a method designed to inhibit platelet activation. AGEs were measured by enzyme-linked immunosorbent assays. AGEs did not differ between altitudes in normal or PE pregnancies. AGE concentrations were unrelated to measures of maternal or fetal hypoxia. PlGF was lower and sFlt-1 higher in PE, but overlapped considerably with the range observed in normal samples. PlGF correlated with placental mass in both normal and PE pregnancies. The contribution of peripheral cells to the values measured for AGEs was similar at LA and HA, but was greater in PE than in normotensive women. Hypoxia, across a wide physiological range in pregnancy, does not alter levels of circulating AGEs in otherwise normal pregnancies. Peripheral cell release of AGEs with the hemostasis characteristic of standard blood collection is highly variable and contributes to a doubling of the amount of sFlt-1 measured in PE as compared to normal pregnancies.

We present a cohort of ca. 25,000 birth records from Bolivia of men and women who are currently adults. We used this cohort to test the hypothesis that high altitude reduces birth weight and that highland ancestry confers graduated protection against this effect. Birth records were obtained from obstetric clinics and hospitals in La Paz (3,600 m) and Santa Cruz (420 m). Only singleton, healthy term (>37 wk) pregnancies of nonsmoking mothers were included. Andean, Mestizo, or European ancestry was determined by validated analysis of parental surnames. High altitude reduced body weight (3,396 ± 3 vs. 3,090 ± 6 g) and length (50.8 ± 0 vs. 48.7 ± 0 cm) at birth (P < 0.001). Highland ancestry partially protected against the effects of high altitude on birth weight (Andean = 3,148 ± 15 g; Mestizo = 3,081 ± 6 g; and European = 2,957 ± 32 g; trend P < 0.001) but not on birth length. The effects of high-altitude pregnancy on birth size were similar for male and female babies. High altitude reduces birth weight and highland native ancestry confers graduated protection. Given previous studies linking reduced birth weight with increased risk of cardiovascular disease, further study is warranted to test whether adults from high-altitude pregnancy are at increased risk of developing cardiovascular disease.

BACKGROUND: Preeclampsia (PE) is more common at high than low altitude and contributes to the altitude-related decline in birth weight. Since inflammatory markers are implicated in PE, we asked if such markers differed in PE vs. normotensive pregnant (NORM) women residing at high altitude (3600-4100 m), and were related to uterine artery blood flow (UA BF) or fetal growth. METHODS: Subjects were 33 Andean pregnant residents of Bolivia, comprising six with early-onset PE (≤ 34 wk), 12 with late-onset PE (> 34 wk), and 15 gestational-age matched NORM. Maternal pro- and anti-inflammatory cytokines were measured using a multiplex bead-based assay and UA BF by Doppler ultrasound. RESULTS: PE compared to NORM women had higher levels of the pro-inflammatory cytokines IL-6 and IL-8 as well as higher levels of the anti-inflammatory cytokine IL-1ra, but only IL-6 levels were higher when gestational age was controlled. Women with early- vs. late-onset PE had higher TNFα levels, and higher IL-6 was negatively correlated with birth weight in all women at ≤ 34 wk. We suggest that pro-inflammatory factors influence both the timing and severity of PE at high altitude.

Most individuals throughout the Americas are admixed descendants of Native American, European, and African ancestors. Complex historical factors have resulted in varying proportions of ancestral contributions between individuals within and among ethnic groups. We developed a panel of 446 ancestry informative markers (AIMs) optimized to estimate ancestral proportions in individuals and populations throughout Latin America. We used genome-wide data from 953 individuals from diverse African, European, and Native American populations to select AIMs optimized for each of the three main continental populations that form the basis of modern Latin American populations. We selected markers on the basis of locus-specific branch length to be informative, well distributed throughout the genome, capable of being genotyped on widely available commercial platforms, and applicable throughout the Americas by minimizing within-continent heterogeneity. We then validated the panel in samples from four admixed populations by comparing ancestry estimates based on the AIMs panel to estimates based on genome-wide association study (GWAS) data. The panel provided balanced discriminatory power among the three ancestral populations and accurate estimates of individual ancestry proportions (R-2 > 0.9 for ancestral components with significant between-subject variance). Finally, we genotyped samples from 18 populations from Latin America using the AIMs panel and estimated variability in ancestry within and between these populations. This panel and its reference genotype information will be useful resources to explore population history of admixture in Latin America and to correct for the potential effects of population stratification in admixed samples in the region.

Oxidative stress has been implicated in the uteroplacental ischemia characteristic of preeclampsia and small-for-gestational-age (SGA) birth, both of which are more common at high (>2500 m) vs low altitude. Since Andeans are protected relative to Europeans from the altitude-associated rise in SGA, we asked whether alterations in maternal antioxidant status or oxidative stress contributed to their protection. Enzymatic antioxidant (erythrocyte catalase and superoxide dismutase [SOD]) activity and a plasma marker of lipid peroxidation (8-iso-PGF2 alpha) were measured during pregnancy and in the non-pregnant state in Andean or European residents of low (400 m) or high altitude (3600-4100 m). Pregnancy and altitude increased catalase and/or SOD activity to a greater extent in Andeans than Europeans. 8-iso-PGF2 alpha levels were independent of altitude and pregnancy. SOD was lower in mothers of SGA infants at weeks 20 and 36. Our findings are consistent with the possibility that elevated enzymatic antioxidant activity contributes to Andean protection against altitude-associated SGA.

Pro-versus anti-inflammatory cytokine balance is important for successful pregnancy. Chronic hypoxia alters cytokine levels and increases the frequency of fetal growth restriction (FGR). Multigenerational Andean (AND) versus shorter duration European (EUR) high-altitude (HA) residents are protected from altitude-associated FGR. To address whether ancestry group differences in cytokine levels were involved, we conducted serial studies in 56 low-altitude ([LA]; 400 m; n = 29 AND and n = 27 EUR) and 42 HA residents (3600-4100 m; n = 19 ANDs and n = 23 EURs). Pregnancy raised pro- (interleukin 1β [IL-1β]) and anti- (IL-10) inflammatory cytokines and HA lowered IL-6 and tumor necrosis factor-α (TNF-α) near term. There were no ancestry group differences in cytokine levels at any time, but HA reduced IL-1β in ANDs only near term. Higher IL-1β levels correlated with uterine artery (UA) blood flow at 20 weeks in ANDs at HA, suggesting that IL-1β may play a role in AND protection from altitude-associated reductions in fetal growth.