Hypoxia Inducible Factor pathway proteins in high-altitude mammals

Long-term maternal and fetal outcomes of pulmonary hypertension in pregnancy in the southwest plateau area of China: a retrospective study

OBJECTIVE

The objective was to investigate maternal, obstetric, and neonatal outcomes of pulmonary hypertension (PH) in pregnancy based on different altitudes of residence in the southwest plateau area of China.

METHODS

Data were collected from pregnant women with PH admitted to The First People's Hospital of Yunnan Province from January 1, 2012, to December 31, 2021. All pregnant women with PH were diagnosed via echocardiography according to a pulmonary arterial systolic pressure > 30 mmHg. Patients were classified into three groups according to the altitude of residence during pregnancy. Demographic characteristics, maternal and neonatal outcomes, complications, and follow-up outcomes after discharge were reported.

RESULTS

Fifty-two pregnant women with PH were included. Among the included women, eleven (21.2%) were in the low-altitude group, twenty-six (50.0%) were in the medium-altitude group, and fifteen (28.8%) were in the high-altitude group. The overall mortality rate was 5.8%: death up to 6 weeks after delivery occurred in one patient (1.9%), and the other two patients (4.9%) died within one to four years after delivery. Preterm delivery occurred in 22 (42.3%) patients. The incidences of maternal death (11.5% vs. 0.0, p < 0.01), cesarean delivery (80.8% vs. 70.7% vs. 80.0%, p = 0.001), and live birth (84.6% vs. 72.7% vs. 80.0%, p < 0.01) were higher in the medium-altitude group than in the low- and high-altitude groups. Therapeutic abortion was performed in 15.4% of the women, with the highest rate in the high-altitude group (p < 0.01). The rates of heart failure and respiratory failure were highest in the low-altitude group (p < 0.01). No fetal death occurred, and 22 neonates (42.3%) had a low birth weight. During a median follow-up of 2.4 years, two patients died (4.9%), and seven (17.1%) still had PH.

CONCLUSION

The in-hospital mortality rate of pregnant women with PH in the plateau area is similar to that previously reported in the low-altitude region, but the long-term survival rate is lower. Therapeutic abortion is also higher in pregnant women with a high altitude of residence. These findings highlight that the risks associated with PH in pregnancy persist beyond delivery and underscore the importance of early risk assessment, rigorous multidisciplinary management, and prolonged postpartum follow-up, especially in plateau populations with limited access to specialized care.

MYLIP attenuates hypoxia tolerance by inducing K27-linked polyubiquitination and subsequent proteasomal degradation of HIF-α

Hypoxia tolerance is mainly controlled by the hypoxia signaling pathway and HIF-1α/2α serve as master regulators in this pathway. Here we identify MYLIP, an E3 ubiquitin ligase thought to specifically target lipoprotein receptors, as a downstream target of HIF-2α and a negative regulator of both HIF-1α and HIF-2α. MYLIP interacts with HIF-1α/2α and catalyzes K27-linked polyubiquitination at lysine 118/442 (HIF-1α) or lysine 117 (HIF-2α). This modification induces proteasomal degradation of HIF-1α, resulting in inhibition of hypoxia signaling. Furthermore, Mylip-deficient bluntsnout bream, zebrafish and mice are more tolerant to hypoxia. These findings reveal a role for MYLIP in regulating hypoxia signaling and identify a target for the development of fish strains with high hypoxia tolerance for the benefit of the aquaculture industry.

Under (Genetic Selection) Pressure: Human Tumors and Human Populations in Hypoxia

Arenillas and colleagues report that pheochromocytomas and paragangliomas in the setting of chronic hypoxia due to cyanotic congenital heart disease harbor, at high frequency, somatic gain-of-function mutations in the EPAS1 gene, which encodes for one of the oxygen-labile subunits of the hypoxia-inducible factor complex. Interestingly, germline loss-of-function EPAS1 alleles are under natural selection in human populations subjected to a different chronic hypoxia condition, namely, high altitude. See related article by Arenillas et al., p. 1037.

Genetic and Epigenetic Adaptation Mechanisms of Sheep Under Multi-Environmental Stress Environment

Sheep (Ovis aries), domesticated from wild Asian mouflon ~10,000 years ago, are an important livestock species adapted to various ecological environments. Recent advancements in high-throughput sequencing and global environmental databases have facilitated the exploration of genetic-environmental associations, uncovering the genetic and epigenetic mechanisms behind sheep's adaptation to multiple environments. Studies show that HIF-1α and EPAS1 enhance high-altitude adaptation via hypoxic stress regulation; UCP1 contributes to cold adaptation through non-shivering thermogenesis; SLC4A4 and GPX3 increase drought resistance by regulating renal water reabsorption; and SOCS2 likely plays a role in metabolic and stress response regulation. Additionally, sheep adapt to temperature, drought, and environmental stress through DNA methylation, transcriptional regulation (e.g., SOD1, GPX4), heat shock proteins (e.g., HSP70), and metabolic pathways (e.g., UCP1). These findings offer valuable insights for improving sheep breeding and genetic enhancement. This review summarizes the mechanisms of adaptation to high altitude, cold, heat, drought, and comprehensive climate stress.

EPAS1 Variations and Hematological Adaptations to High-Altitude Hypoxia in Indigenous Goats in Yunnan Province, China

The EPAS1 gene plays a central role in hypoxia adaptation in high-altitude animals. Using over 400 blood samples from goats across elevations in Yunnan (500-3500 m), this study examined hematological traits, genetic polymorphisms, and protein structure. Red blood cell (RBC) and hemoglobin (HGB) levels increased significantly with altitude (p < 0.05), reflecting improved oxygen transport. A non-synonymous SNP (g.86650 A>T, p.Gln556Leu) exhibited adaptive selection, with the T allele frequency rising at higher altitudes (p < 0.05). At 2500 m, TT genotype goats showed significantly higher RBC and HGB levels than AA genotypes (p < 0.05). Protein modeling revealed structural instability caused by the polymorphism, highlighting its role in enhancing hypoxia adaptation. These findings provide a foundation for improving high-altitude livestock genetics.

HIF2α: the interface between oxygen-sensing systems in physiology and pathology

More than 100 years after the original descriptions of altitude adaptation, it is now clear that many of these responses are mediated by a specific isoform of the transcription factor hypoxia-inducible factor (HIF-2α). Here, we review this work, including connectivity with the oxygen chemosensitive response itself, and with paraganglioma, a tumour often affecting chemosensitive tissues.

Whole-genome relaxed selection and molecular constraints in Triplophysa under adapted Qinghai-Tibetan Plateau

High-altitude environments are inhospitable, but Triplophysa, the largest taxon among the three major fish groups in the Qinghai-Tibetan Plateau (QTP), is an exception. However, the evolutionary profiling of the common ancestor and its contribution to the adaptation of existing QTP native species is unclear.We researched the comparative genomics of Triplophysa species and found that the genome-wide genes of Triplophysa and its ancestry have the characteristics of rapid evolution.Moreover, the rapid evolution of the ancestral genes was caused by relaxed selection. Natural selection analysis showed that more ancestral relaxed selection genes were under strongly purifying selection and showed higher expression in QTP endemic Triplophysa species.The change in natural selection might be associated with the adaptation to QTP. It should be noted that SPT5 homolog, DSIF elongation factor subunit (supt5h) experienced relaxed selection in common ancestral populations of Triplophysa but under purifying selection in extant species, which might be related to hypoxia adaptation of QTP. In summary, the extant species in different environments were used to infer the evolutionary profile of the common ancestor and to identify candidate genes based on changes in natural selection. Our work might provide new clues for understanding adaptation to extreme environments.

Elucidating loss-of-function mechanisms of monoallelic EPAS1 mutations underlying congenital hypoplastic anaemia in a paediatric anaemia cohort

HIF-2α, encoded by EPAS1, plays a dominant role in regulating erythropoietin (EPO) production, maintaining the dynamic balance of erythropoiesis. Gain-of-function mutations in EPAS1 cause erythrocytosis. However, anaemia caused by EPAS1 loss-of-function mutations has been confined to only one case report, and the underlying mechanism remains unclear. Herein, the reanalysis of high-throughput sequencing data from 311 patients with anaemia identified three monoallelic EPAS1 variants from three unrelated families in a paediatric anaemia cohort. The probands showed highly consistent clinical phenotypes with normocytic and normochromic anaemia, reticulocytopenia and relative deficiency of serum EPO, characterised as congenital hypoplastic anaemia. In vitro studies suggested that defects in steady-state protein abundance, nuclear localisation and binding with co-activator in EPAS1 variants lead to impaired EPO transcriptional activation. Therefore, loss-of-function mutations in EPAS1 can cause erythroid hypoplasia in an EPO-dependent manner. This study identified a new causative gene for congenital hypoplastic anaemia and clarified the molecular aetiology of loss-of-function EPAS1 mutations.

Regulation of PHD2 by HIF-1α in Erythroid Cells: Insights into Erythropoiesis Under Hypoxia

The hypoxia-inducible factor (HIF) pathway has been demonstrated to play a pivotal role in the process of high-altitude adaptation. PHD2, a key regulator of the HIF pathway, has been found to be associated with erythropoiesis. However, the relationship between changes in Phd2 abundance and erythroid differentiation under hypoxic conditions remains to be elucidated. A hemin-induced K562 erythroid differentiation model was used to explore the effects of PHD2 knockdown under hypoxia. Erythroid differentiation was assessed by flow cytometry and immunofluorescence. HIF-1α's regulation of PHD2 was examined using luciferase assays and ChIP-seq. CRISPR/Cas9 was applied to knock out EGLN1 and HIF1A, and a fluorescent reporter system was developed to track PHD2 expression. PHD2 knockdown enhanced erythroid differentiation, evident by increased CD71 and CD235a expression. Reporter assays and ChIP-seq identified an HIF-1α binding site in the EGLN1 5' UTR, confirming HIF-1α as a regulator of PHD2 expression. The fluorescent reporter system provided real-time monitoring of endogenous PHD2 expression, showing that HIF-1α significantly modulates PHD2 levels under hypoxic conditions. PHD2 influences erythropoiesis under hypoxia, with HIF-1α regulating its expression. This feedback loop between HIF-1α and PHD2 sheds light on mechanisms driving erythroid differentiation under low-oxygen conditions.

Four new genome sequences of the Pallas's cat (Otocolobus manul): an insight into the patterns of within-species variability

Manul (Otocolobus manul) is the only representative of the genus Otocolobus, which makes up the Leopard Cat lineage along with the genus Prionailurus. Their habitat is characterized by harsh environmental conditions. Although their populations are probably more stable than previously thought, it is still the case that their population size is declining. Conservation programs exist to protect manuls, but those based on captive breeding are often unsuccessful due to their increased susceptibility to diseases. The manul is therefore a suitable model species for evolutionary and diversity studies as well as for studying mechanisms of adaptation to harsh environment and mechanisms of susceptibility to diseases. Recently, the genome of the O. manul based on nanopore long-range sequencing has been published. Aiming to better understand inter- and intraspecific variation of the species, we obtained information on genome sequences of four other manuls, based on whole genome resequencing via the Illumina platform. On average, we detected a total of 3,636,571 polymorphic variants. Information on different types of structural variants and on the extent of SNP homozygosity, not available from the reference genome, was retrieved. The average whole-genome heterozygosity was almost identical to that found in the O. manul reference genome. In this context, we performed a more detailed analysis of the candidate gene EPAS1 potentially related to adaptation to the hypoxic environment. This analysis revealed both inter- and intraspecific variation, confirmed the presence of a previously described non-synonymous substitution in exon 15 unique to manuls and identified three additional unique non-synonymous substitutions located in so far not analyzed EPAS1 exonic sequences. The analysis of lncRNA located in the intron 7 of EPAS1 revealed interspecific variability and monomorphic nature of the sequence among analyzed manuls. The data obtained will allow more detailed analyses of the manul genome, focusing on genes and pathways involved in their adaptation to the environment and in susceptibility to diseases. This information can be helpful for optimizing conservation programs for this understudied species.

The evolutionary history of wild and domestic brown rats (Rattus norvegicus)

The brown rat (Rattus norvegicus) occupies nearly every terrestrial habitat with a human presence and is one of our most important model organisms. Despite this prevalence, gaps remain in understanding the evolution of brown rat commensalism, their global dispersal, and mechanisms underlying contemporary adaptations to diverse environments. In this Review, we explore recent advances in the evolutionary history of brown rats and discuss key challenges, including finding and accurately dating historical specimens, disentangling histories of multiple domestication events, and synthesizing functional variation in wild rat populations with the development of laboratory strains. Advances in zooarchaeology and population genomics will usher in a new golden age of research on the evolutionary biology of brown rats, with positive feedbacks on their use as biomedical models.

Comparative DNA methylation reveals epigenetic adaptation to high altitude in snub-nosed monkeys

DNA methylation plays a crucial role in environmental adaptations. Here, using whole-genome bisulfite sequencing, we generated comprehensive genome-wide DNA methylation profiles for the high-altitude Yunnan snub-nosed monkey ( Rhinopithecus bieti) and the closely related golden snub-nosed monkey ( R. roxellana). Our findings indicated a slight increase in overall DNA methylation levels in golden snub-nosed monkeys compared to Yunnan snub-nosed monkeys, suggesting a higher prevalence of hypermethylated genomic regions in the former. Comparative genomic methylation analysis demonstrated that genes associated with differentially methylated regions were involved in membrane fusion, vesicular formation and trafficking, hemoglobin function, cell cycle regulation, and neuronal differentiation. These results suggest that the high-altitude-related epigenetic modifications are extensive, involving a complete adaptation process from the inhibition of single Ca 2+ channel proteins to multiple proteins collaboratively enhancing vesicular function or inhibiting cell differentiation and proliferation. Functional assays demonstrated that overexpression or down-regulation of candidate genes, such as SNX10, TIMELESS, and CACYBP, influenced cell viability under stress conditions. Overall, this research suggests that comparing DNA methylation across closely related species can identify novel candidate genomic regions and genes associated with local adaptations, thereby deepening our understanding of the mechanisms underlying environmental adaptations.