Polygenic adaptation leads to a higher reproductive fitness of native Tibetans at high altitude

Flores S, Esquivel E, Ding Y, Peitzsch M, Robles-Guirado JÁ, Regojo Zapata RM, Pozo-Kreilinger JJ, Iglesias C, Dwight T, Muir CA, Oleaga A, Garrido-Lestache Rodríguez-Monte ME, Del Cerro MJ, Martínez-Bendayán I, Álvarez-González E, Cubiella T, Lourenço DM, A. Pereira MA, Burnichon N, Buffet A, Broberg C, Dickson PV, Fraga MF, Llorente Pendás JL, Rueda Soriano J, Buendía Fuentes F, Toledo SP, Clifton-Bligh R, Dienstmann R, Villanueva J, Capdevila J, Gimenez-Roqueplo AP, Favier J, Nuciforo P, Young WF, Bechmann N, Opotowsky AR, Vaidya A, Bancos I, Weghorn D, Robledo M, Casteràs A, Dos-Subirà L, Adameyko I, Chiara MD, Dahia PL, Toledo RA. Convergent Genetic Adaptation in Human Tumors Developed Under Systemic Hypoxia and in Populations Living at High Altitudes

SIGNIFICANCE

This study reveals a broad convergence in genetic adaptation to hypoxia between natural populations and tumors, suggesting that insights from natural populations could enhance our understanding of cancer biology and identify novel therapeutic targets. See related commentary by Lee, p. 875.

Transcriptomic analysis of iPSC-derived endothelium reveals adaptations to high altitude hypoxia in energy metabolism and inflammation

Tibetan adaptation to high-altitude hypoxia remains a classic example of Darwinian selection in humans. Amongst Tibetan populations, alleles in the EPAS1 gene - whose protein product, HIF-2α, is a central regulator of the hypoxia response - have repeatedly been shown to carry some of the strongest signals of positive selection in humans. However, selective sweep signals alone may only account for some of the phenotypes that differentiate high-altitude adapted populations from closely related lowlanders. Therefore, there is a pressing need to functionally probe adaptive alleles and their impact at both the locus-specific and genome-wide levels and across cell types to uncover the full range of beneficial traits. To this end, we established a library of induced pluripotent stem cells (iPSCs) derived from Tibetan and Han Chinese individuals, a robust model system allowing precise exploration of allelic effects on transcriptional responses, and we differentiated them into vascular endothelium. Using this system, we focus first on a hypoxia-dependent enhancer (ENH5) that contributes to the regulation of EPAS1 to investigate its locus-specific effects in endothelium. Then, to cast a wider net, we harness the same experimental system to compare the transcriptome of Tibetan and Han Chinese cells in hypoxia and find evidence that angiogenesis, energy metabolism and immune pathways differ between these two populations with different histories of long-term residence at high altitude. Coupled with evidence of polygenic adaptations targeting the same pathways, these results suggests that the observed transcriptional differences between the two populations were shaped by natural selection.

Maternal-fetal mechanisms underlying adaptation to hypoxia during early pregnancy

During the process of implantation, the embryo first attaches to the uterine epithelium and then invades the underlying stroma, resulting in the transformation of the stroma into a secretory tissue that surrounds the embryo. An intricate dialogue allows the developing embryo and the maternal tissue to be in constant communication with each other. In many mammals, including humans, embryo implantation and early pregnancy events take place in a low-oxygen environment regulated by hypoxia-inducible transcription factors. The mechanisms by which maternal and embryonic tissue compartments adapt to hypoxia are essential for the success of pregnancy outcomes. In this review we highlight recent work describing signaling pathways that operate in the hypoxic uterus to facilitate embryo implantation and promote the successful establishment of pregnancy.

Higher oxygen content and transport characterize high-altitude ethnic Tibetan women with the highest lifetime reproductive success

We chose the "natural laboratory" provided by high-altitude native ethnic Tibetan women who had completed childbearing to examine the hypothesis that multiple oxygen delivery traits were associated with lifetime reproductive success and had genomic associations. Four hundred seventeen (417) women aged 46 to 86 y residing at ≥3,500 m in Upper Mustang, Nepal, provided information on reproductive histories, sociocultural factors, physiological measurements, and DNA samples for this observational cohort study. Simultaneously assessing multiple traits identified combinations associated with lifetime reproductive success measured as the number of livebirths. Women with the most livebirths had distinctive hematological and cardiovascular traits. A hemoglobin concentration near the sample mode and a high percent of oxygen saturation of hemoglobin raised arterial oxygen concentration without risking elevated blood viscosity. We propose ongoing stabilizing selection on hemoglobin concentration because extreme values predicted fewer livebirths and directional selection favoring higher oxygen saturation because higher values had more predicted livebirths. EPAS1, an oxygen homeostasis locus with strong signals of positive natural selection and a high frequency of variants occurring only among populations indigenous to the Tibetan Plateau, associated with hemoglobin concentration. High blood flow into the lungs, wide left ventricles, and low hypoxic heart rate responses aided effective convective oxygen transport to tissues. Women with physiologies closer to unstressed, low altitude values had the highest lifetime reproductive success. This example of ethnic Tibetan women residing at high altitudes in Nepal links reproductive fitness with trait combinations increasing oxygen delivery under severe hypoxic stress and demonstrates ongoing natural selection.

Differential gene expression and gut microbiota composition in low-altitude and high-altitude goats

Previous studies have presented evidence suggesting that altitude exerts detrimental effects on reproductive processes, yet the underlying mechanism remains elusive. Our study employed two distinct goat breeds inhabiting low and high altitudes, and conducted a comparative analysis of mRNA profiles in testis tissues and the composition of gut microbiota. The results revealed a reduced testis size in high-altitude goats. RNA-seq analysis identified the presence of 214 differentially expressed genes (DEGs) in the testis. These DEGs resulted in a weakened immunosuppressive effect, ultimately impairing spermatogenesis in high-altitude goats. Additionally, 16S rDNA amplicon sequencing recognized statistically significant variations in the abundance of the genera Treponema, unidentified_Oscillospiraceae, Desulfovibrio, Butyricicoccus, Dorea, Parabacteroides between the two groups. The collective evidence demonstrated the gut and testis played a synergistic role in causing decreased fertility at high altitudes. Our research provides a theoretical basis for future investigations into the reproductive fitness of male goats.

DATA in BRIEF of: Adaptative mechanisms indicated by placental protein expression changes in high-altitude Tibetan women during vaginal delivery

Over a period of 30,000 to 40,000 years, high-altitude Tibetans have physiologically and genetically adapted to conditions such as hypoxia, low temperature, and high-intensity ultraviolet radiation. Based on the unique physiological and morphological characteristics of the Tibetan people, they have outstanding hypoxia adaptation skills and can continue to thrive in plateau hypoxia. The placenta of high-altitude Tibetans is protected from oxidative stress during delivery; however, little is known about changes in placental protein expression during vaginal delivery. In this study, we aimed to reveal these adaptive mechanisms by studying changes in placental protein expression during vaginal delivery in high-altitude Tibetans, low-altitude Tibetans, and low-altitude Han populations. Studying the changing mechanisms of maternal responses to hypoxia at high altitudes can reveal the molecular mechanisms of maternal and fetal adaptation to hypoxia at high altitudes and provide theories for preventing and treating maternal hypoxia and intrauterine growth and development restriction caused by other diseases.

Sex-biased regulatory changes in the placenta of native highlanders contribute to adaptive fetal development

Compared with lowlander migrants, native Tibetans have a higher reproductive success at high altitude though the underlying mechanism remains unclear. Here, we compared the transcriptome and histology of full-term placentas between native Tibetans and Han migrants. We found that the placental trophoblast shows the largest expression divergence between Tibetans and Han, and Tibetans show decreased immune response and endoplasmic reticulum stress. Remarkably, we detected a sex-biased expression divergence, where the male-infant placentas show a greater between-population difference than the female-infant placentas. The umbilical cord plays a key role in the sex-biased expression divergence, which is associated with the higher birth weight of the male newborns of Tibetans. We also identified adaptive histological changes in the male-infant placentas of Tibetans, including larger umbilical artery wall and umbilical artery intima and media, and fewer syncytial knots. These findings provide valuable insights into the sex-biased adaptation of human populations, with significant implications for medical and genetic studies of human reproduction.

Human genetics: An extreme fitness landscape

A new study aims to identify how genetic and physiological adaptations to altitude affect pregnancy, childbirth and neonatal health in one of the most extreme environments on Earth, the Tibetan Plateau.