Endothelin receptor B, a candidate gene from human studies at high altitude, improves cardiac tolerance to hypoxia in genetically engineered heterozygote mice

Sex-Specific Effects of Prenatal Hypoxia on the Cardiac Endothelin System in Adult Offspring

Fetal hypoxia, a major consequence of complicated pregnancies, impairs offspring cardiac tolerance to ischemia/reperfusion (I/R) insult, however, the mechanisms remain unknown. Endothelin-1 (ET-1) signaling through the endothelin A receptors (ET_A) is associated with cardiac dysfunction. We hypothesized that prenatal hypoxia exacerbates cardiac susceptibility to I/R via increased ET-1 and ET_A levels, while ET_A inhibition ameliorates this. Pregnant Sprague-Dawley rats were exposed to normoxia (21% O₂) or hypoxia (11% O₂) on gestational days 15-21. Offspring were aged to 4 months, and hearts were aerobically perfused or subjected to ex vivo I/R, with or without pre-infusion with an ET_A antagonist (ABT-627). ET-1 levels were assessed with ELISA in aerobically perfused and post-I/R left ventricles (LV). ET_A and ET_B levels were assessed by Western blotting in non-perfused LV. As hypothesized, ABT-627 infusion tended to improve post-I/R recovery in hypoxic females (p=0.0528), however, surprisingly, ABT-627 prevented post-I/R recovery only in the hypoxic males (p<0.001). ET-1 levels were increased in post-I/R LV in both sexes regardless of the prenatal exposure (p<0.01). ET_A expression was similar among all groups, while ET_B (isoform C) levels were decreased in prenatally hypoxic females (p<0.05). In prenatally hypoxic males, ET_A signaling may be essential for tolerance to I/R, while in prenatally hypoxic females, ET_A may contribute to cardiac dysfunction. Our data illustrate that understanding the prenatal history has critical implications for treatment strategies in adult chronic diseases.

STAT3 but Not STAT5 Contributes to the Protective Effect of Electroacupuncture Against Myocardial Ischemia/Reperfusion Injury in Mice

Electroacupuncture (EA) can help reduce infarct size and injury resulting from myocardial ischemia/reperfusion (I/R); however, the underlying molecular mechanism remains unknown. We previously reported that STAT5 plays a critical role in the cardioprotective effect of remote ischemic preconditioning (RIPC). Here, we assessed the effects of electroacupuncture pretreatment (EAP) on myocardial I/R injury in the presence and/or absence of Stat5 in mice and investigated whether EAP exerts its cardioprotective effects in a STAT5-dependent manner. Adult Stat5^fl/fl and Stat5-cKO mice were exposed to EAP at Neiguan (PC6) for 7 days before the induction of I/R injury by left anterior descending (LAD) coronary artery ligation. The myocardial infarct size (IS), area at risk, and apoptotic rate of cardiomyocytes were detected. RT-qPCR and western blotting were used to measure gene and protein expression, respectively, in homogenized heart tissues. RNA-seq was used to identify candidate genes and pathways. Our results showed that EAP decreased IS and the rate of cardiomyocyte apoptosis. We further found that STAT5 was activated by EAP in Stat5^fl/fl mice but not in Stat5-cKO mice, whereas the opposite was observed for STAT3. Following EAP, the levels of the antiapoptotic proteins Bcl-xL, Bcl-2, and p-AKT were increased in the presence of Stat5, while that of interleukin 10 (IL-10) was increased in both Stat5^fl/fl and Stat5-cKO. The gene expression profile in heart tissues was different between Stat5^fl/fl and the Stat5-cKO mice with EAP. Importantly, the top 30 DEGs under EAP in the Stat5-cKO mice were enriched in the IL-6/STAT3 signaling pathway. Our results revealed for the first time that the protective effect of EAP following myocardial I/R injury was attributable to, but not dependent on, STAT5. Additionally, we found that EAP could activate STAT3 signaling in the absence of the Stat5 gene, and could also activate antiapoptotic, survival, and anti-inflammatory signaling pathways.

Evidence of the interplay of genetics and culture in Ethiopia

The rich linguistic, ethnic and cultural diversity of Ethiopia provides an unprecedented opportunity to understand the level to which cultural factors correlate with-and shape-genetic structure in human populations. Using primarily new genetic variation data covering 1,214 Ethiopians representing 68 different ethnic groups, together with information on individuals' birthplaces, linguistic/religious practices and 31 cultural practices, we disentangle the effects of geographic distance, elevation, and social factors on the genetic structure of Ethiopians today. We provide evidence of associations between social behaviours and genetic differences among present-day peoples. We show that genetic similarity is broadly associated with linguistic affiliation, but also identify pronounced genetic similarity among groups from disparate language classifications that may in part be attributable to recent intermixing. We also illustrate how groups reporting the same culture traits are more genetically similar on average and show evidence of recent intermixing, suggesting that shared cultural traits may promote admixture. In addition to providing insights into the genetic structure and history of Ethiopia, we identify the most important cultural and geographic predictors of genetic differentiation and provide a resource for designing sampling protocols for future genetic studies involving Ethiopians.

High altitude and cancer: An old controversy

Ecological studies have found that individuals that live at high altitude regions and in places where ultraviolet radiation is maximal, have lower rates of different types of cancer. However, there is evidence that in these same regions, genetic mutations that are prooncogenic, develop, as they are needed to increase human adaptability to hypoxic environments. Debate has arisen between researchers who consider high altitude environments as suitable for human longevity because of its protective effects against malignancies, and scientists that have reported an increased incidence of different type of cancers in these same regions. Evidence is presented that altitude is related to the development of genetic alterations in micro RNAs, p53 protein, lymphocyte activity, decrease in Fas Ligand and other proapoptotic molecules, as well as increase in prometastatic VGEF an HIF. Notwithstanding, higher vitamin D and ultraviolet B levels, and a better metabolic profile, taken together with lower pollution levels hves been related to lower incidence and mortality rates from malignancies in a series of epidemiological studies.

Physiological Genomics of Adaptation to High-Altitude Hypoxia

Population genomic studies of humans and other animals at high altitude have generated many hypotheses about the genes and pathways that may have contributed to hypoxia adaptation. Future advances require experimental tests of such hypotheses to identify causal mechanisms. Studies to date illustrate the challenge of moving from lists of candidate genes to the identification of phenotypic targets of selection, as it can be difficult to determine whether observed genotype-phenotype associations reflect causal effects or secondary consequences of changes in other traits that are linked via homeostatic regulation. Recent work on high-altitude models such as deer mice has revealed both plastic and evolved changes in respiratory, cardiovascular, and metabolic traits that contribute to aerobic performance capacity in hypoxia, and analyses of tissue-specific transcriptomes have identified changes in regulatory networks that mediate adaptive changes in physiological phenotype. Here we synthesize recent results and discuss lessons learned from studies of high-altitude adaptation that lie at the intersection of genomics and physiology.

Multiple mechanisms drive genomic adaptation to extreme O2 levels in Drosophila melanogaster

To detect the genomic mechanisms underlying evolutionary dynamics of adaptation in sexually reproducing organisms, we analyze multigenerational whole genome sequences of Drosophila melanogaster adapting to extreme O₂ conditions over an experiment conducted for nearly two decades. We develop methods to analyze time-series genomics data and predict adaptive mechanisms. Here, we report a remarkable level of synchronicity in both hard and soft selective sweeps in replicate populations as well as the arrival of favorable de novo mutations that constitute a few asynchronized sweeps. We additionally make direct experimental observations of rare recombination events that combine multiple alleles on to a single, better-adapted haplotype. Based on the analyses of the genes in genomic intervals, we provide a deeper insight into the mechanisms of genome adaptation that allow complex organisms to survive harsh environments.

The genomic details of adaptation to extreme environments remain challenging to characterize. Using new methods to analyze flies experimentally evolved to survive extreme O₂ conditions, the authors find a surprising level of synchronicity in selective sweeps, de novo mutations and adaptive recombination events.

Hypoxia and cancer related pathology

Hypoxic environments occur normally at high altitude, or in underground burrows and in deep sea habitats. They also occur pathologically in human ischemia and in hypoxic solid tumors. Hypoxia in various cancer types and its related molecular mechanisms are associated with a poor clinical outcome. This review will discuss how hypoxia can influence two aspects of tumorigenesis, namely the direct, cell-intrinsic oncogenic effects, as well as the indirect effects on tumor progression mediated by an altered tumor microenvironment. We will also discuss recent progress in identifying the functional roles of hypoxia-related factors (HIFs), along with their regulators and downstream target genes, in cancer stem cells and therapy. Importantly, we propose, using convergent evolution schemes to identify novel biomarkers for both hypoxia adaptation and hypoxic solid tumors as an important strategy in the future.

Targeted gene expression study using TaqMan low density array to gain insights into venous thrombo-embolism (VTE) pathogenesis at high altitude

Venous thrombo-embolism (VTE) is multi-factorial disease involving several genetic and acquired risk factors responsible for its onset. It may occur spontaneously upon climbing at High Altitude (HA). Several studies demonstrated that hypoxic conditions prevailing at HA pose an independent risk factor for VTE; however, molecular mechanism remains unknown. Present study aims to identify genes associated with HA-induced VTE pathophysiology using real time TaqMan Low-Density Array (TLDA) of known candidate genes. Gene expression of total 93 genes were studied and analyzed in patients of VTE from HA (HA-VTE) and from sea level (SL-VTE) in comparison to respective controls. Both HA-VTE and SL-VTE patients showed up-regulation of 37 genes involved in blood coagulation cascade, clot formation, platelet formation, endothelial response, angiogenesis, cell adhesion and calcium channel activity. Seven genes including ACE, EREG, C8A, DLG2, USF1, F2 and PCDHA7 were up-regulated in both HA-controls and VTE patients (both HA-VTE and SL-VTE) indicating their role during VTE event and also upon HA exposure. Ten genes; CDH18, FGA, EDNBR, GATA2, MAPK9, BCAR1, FRK, F11, PCDHA1 and ST8SIA4 were uniquely up-regulated in HA-VTE. The differentially expressed genes from the present study could be determining factors for HA-VTE susceptibility and provide insights into VTE occurrence at HA.

From Experiments to Simulation: Shear-Induced Responses of Red Blood Cells to Different Oxygen Saturation Levels

Red blood cells (RBC) carry and deliver oxygen (O₂) to peripheral tissues through different microcirculatory regions where they are exposed to various levels of shear stress (SS). O₂ affinity of hemoglobin (Hb) decreases as the blood enters the microcirculation. This phenomenon determines Hb interactions with RBC membrane proteins that can further regulate the structure of cytoskeleton and affect the mechanical properties of cells. The goal of this study is to evaluate shear-induced RBC deformability and simulate RBC dynamics in blood flow under oxygenated and deoxygenated conditions. Venous blood samples from healthy donors were oxygenated with ambient air or deoxygenated with 100% nitrogen gas for 10 min and immediately applied into an ektacytometer (LORRCA). RBC deformability was measured before and after the application of continuous 5 Pa SS for 300 s by LORRCA and recorded as elongation index (EI) values. A computational model was generated for the simulation of blood flow in a real carotid artery section. EI distribution throughout the artery and its relationships with velocity, pressure, wall SS and viscosity were determined by computational tools. RBC deformability significantly increased in deoxygenation compared to oxygenated state both before and after 5 Pa SS implementation (p < 0.0001). However, EI values after continuous SS were not significant at higher SS levels (>5.15 Pa) in deoxygenated condition. Simulation results revealed that the velocity gradient dominates the generation of SS and the shear thinning effect of blood has a minor effect on it. Distribution of EI was calculated during oxygenation/deoxygenation which is 5-10 times higher around the vessel wall compared to the center of the lumen for sections of the pulsatile flow profile. The extent of RBC deformability increases as RBCs approach to the vessel wall in a real 3D artery model and this increment is higher for deoxygenated condition compared to the oxygenated state. Hypoxia significantly increases shear-induced RBC deformability. RBCs could regulate their own mechanical properties in blood flow by increasing their deformability in hypoxic conditions. Computational tools can be applied for defining hypoxia-mediated RBC deformability changes to monitor blood flow in hypoxic tissues.

The repertoire of family A-peptide GPCRs in archaic hominins

Given the importance of G-protein coupled receptors in the regulation of many physiological functions, deciphering the relationships between genotype and phenotype in past and present hominin GPCRs is of main interest to understand the evolutionary process that contributed to the present-day variability in human traits and health. Here, we carefully examined the publicly available genomic and protein sequence databases of the archaic hominins (Neanderthal and Denisova) to draw up the catalog of coding variations in GPCRs for peptide ligands, in comparison with living humans. We then searched in the literature the functional changes, phenotypes and risk of disease possibly associated with the detected variants. Our survey suggests that Neanderthal and Denisovan hominins were likely prone to lower risk of obesity, to enhanced platelet aggregation in response to thrombin, to better response to infection, to less anxiety and aggressiveness and to favorable sociability. While some archaic variants were likely advantageous in the past, they might be responsible for maladaptive disorders today in the context of modern life and/or specific regional distribution. For example, an archaic haplotype in the neuromedin receptor 2 is susceptible to confer risk of diabetic nephropathy in type 1 diabetes in present-day Europeans. Paying attention to the pharmacological properties of some of the archaic variants described in this study may be helpful to understand the variability of therapeutic efficacy between individuals or ethnic groups.

Ultrastable and Biofunctionalizable Conjugated Polymer Nanoparticles with Encapsulated Iron for Ferroptosis Assisted Chemodynamic Therapy

We report the development of novel tumor-targeted conjugated polymer nanoparticles (CPNPs) carrying iron for chemodynamic therapy (CDT). Tumor cell killing proceeds through ferroptosis, a reactive oxygen species (ROS) mechanism that is not dependent on external activation by, for example, light, as is the case in photodynamic therapy (PDT). The ferroptosis mechanism is also not heavily reliant on oxygen availability and is, therefore, promising for the treatment of hypoxic tumors. In this work, we apply this development to the case study of melanoma, a difficult to treat cancer in advanced stages due to resistance to chemotherapy. The iron-carrying CPNPs reported here are targeted to endothelin-B receptors (EDNRB) through endothelin-3 surface moieties (EDN3-CPNPs). Our results show excellent targeting to tumor cells that overexpress EDNRB, specifically for melanoma and bladder tumor cells. In these cases, efficient cell killing, over 80% at higher doses, was found. Conversely, tumor cells not targeted by the EDN3-CPNPs show little effects of CDT, with tumor cell death under 20% in most cases. The outcomes of our work demonstrate that EDN3-CPNPs enable ferroptosis-assisted CDT and present a new therapeutic avenue for tumor treatment.

Endothelin receptor B affects the perfusion of newborn intestine: possible mechanism of necrotizing enterocolitis development

BACKGROUND

Necrotizing enterocolitis (NEC) is one of the most severe gastrointestinal diseases in infancy. Hypoxia is known as one of the major risk factors for the development of NEC. Endothelin, known to regulate vasoconstriction, has two receptors (A and B). However, the role of endothelin receptor B (EDNRB) in neonatal intestinal injury remains unclear. We aimed to investigate whether EDNRB is involved in NEC pathophysiology.

METHODS

Following ethical approval (#44032), EDNRB hetero knockout mice pups (EDNRB±) and their wild-type (WT) littermates were studied. NEC was induced from postnatal day 5-9 (P5-P9) by hypoxia, gavage feeding of formula and administration of lipopolysaccharide. On P9, the ileum was harvested.

RESULTS

NEC induction in WT mice was associated with mucosal injury. However, EDNRB± NEC mice had reduced mucosal injury. Similarly, EDNRB± mice had significantly lower expression of IL-6 mRNA compared to WT NEC mice. Pimonidazole immunostaining was also significantly lower in EDNRB± compared to WT NEC, suggesting reduced tissue hypoxia.

CONCLUSIONS

Partial knockout of EDNRB results in reduced NEC severity and reduced tissue hypoxia. Intestinal perfusion and hypoxia are important elements of NEC pathogenesis. These findings are relevant to the understanding of NEC pathophysiology and to the development of novel preventive strategies for NEC.

Convergent evolution in human and domesticate adaptation to high-altitude environments

Humans and their domestic animals have lived and thrived in high-altitude environments worldwide for thousands of years. These populations have developed a number of adaptations to survive in a hypoxic environment, and several genomic studies have been conducted to identify the genes that drive these adaptations. Here, we discuss the various adaptations and genetic variants that have been identified as adaptive in human and domestic animal populations and the ways in which convergent evolution has occurred as these populations have adapted to high-altitude environments. We found that human and domesticate populations have adapted to hypoxic environments in similar ways. Specific genes and biological pathways have been involved in high-altitude adaptation for multiple populations, although the specific variants differ between populations. Additionally, we found that the gene EPAS1 is often a target of selection in hypoxic environments and has been involved in multiple adaptive introgression events. High-altitude environments exert strong selective pressures, and human and animal populations have evolved in convergent ways to cope with a chronic lack of oxygen.

This article is part of the theme issue ‘Convergent evolution in the genomics era: new insights and directions'.

Novel insight into the genetic basis of high-altitude pulmonary hypertension in Kyrgyz highlanders

The Central Asian Kyrgyz highland population provides a unique opportunity to address genetic diversity and understand the genetic mechanisms underlying high-altitude pulmonary hypertension (HAPH). Although a significant fraction of the population is unaffected, there are susceptible individuals who display HAPH in the absence of any lung, cardiac or hematologic disease. We report herein the analysis of the whole-genome sequencing of healthy individuals compared with HAPH patients and other controls (total n = 33). Genome scans reveal selection signals in various regions, encompassing multiple genes from the first whole-genome sequences focusing on HAPH. We show here evidence of three candidate genes MTMR4, TMOD3 and VCAM1 that are functionally associated with well-known molecular and pathophysiological processes and which likely lead to HAPH in this population. These processes are (a) dysfunctional BMP signaling, (b) disrupted tissue repair processes and (c) abnormal endothelial cell function. Whole-genome sequence of well-characterized patients and controls and using multiple statistical tools uncovered novel candidate genes that belong to pathways central to the pathogenesis of HAPH. These studies on high-altitude human populations are pertinent to the understanding of sea level diseases involving hypoxia as a main element of their pathophysiology.

Sonic hedgehog promotes endothelial differentiation of bone marrow mesenchymal stem cells via VEGF-D

Background

Bone marrow-derived mesenchymal stem cells (BMSCs) have been proved to be capable of differentiating into endothelial cells (ECs), however, the differentiation efficiency is rather low. Sonic hedgehog (Shh), an important factor in vascular development and postnatal angiogenesis, exerted promotional effect on new vessel formation in the ischemic animal models. Therefore, the current study aims to investigate whether Shh could induce the endothelial differentiation of BMSCs both in vitro and in vivo, as well as the mechanism of differentiation induction.

Methods

The current study over-expressed Shh in BMSCs by lentivirus transduction. Reverse-transcription quantitative polymerase chain reaction (RT-qPCR) analysis was performed to determine the angiogenic factors in both control BMSCs and Shh over-expressed BMSCs. Immunocytochemistry was also conducted to examine the EC markers. Angiogenesis was determined by in vitro tube-forming assay on Matrigel and in vivo Matrigel plug in severe combined immunodeficient (SCID) mice. Last, mRNA sequencing analysis was used to elaborate the underlying mechanisms. Loss of function study was performed by vascular endothelial growth factor D (VEGF-D) siRNA.

Results

Shh expression was increased by about 3,000-fold and 5,000-fold at 3 days-transfection and 7 days-transfection, respectively. Patched 1 (Ptch1), the receptor for Shh, had a two-fold increase after transduction. The angiogenic factors such as hepatocyte growth factor (HGF), angiopoietin-1 (Ang-1), insulin-like growth factor 1 (IGF1) and vascular endothelial growth factor A (VEGF-A) had at least a 1.5-fold increase after transduction. Expression of EC-lineage markers, CD31 and VE-cadherin, on Shh-overexpressed BMSCs were increasingly detected by immunocytostaining. Angiogenesis of BMSCs could be efficiently induced by Shh overexpression in the in vitro tube-formation assay and in vivo Matrigel plug. Additionally, mRNA sequencing analysis revealed that Shh activation upregulated the expression of several pro-angiogenic factors, like Angptl4, Egfl6, VEGF-D. Loss of function study by VEGF-D siRNA confirmed that Shh enhanced the angiogenic ability of BMSCs via VEGF-D.

Conclusions

This study demonstrated that Shh could promote endothelial differentiation of BMSCs via VEGF-D.

Mitochondrial dysfunction in iPSC-derived neurons of subjects with chronic mountain sickness

Patients with chronic mountain sickness (CMS) suffer from hypoxemia, erythrocytosis, and numerous neurologic deficits. Here we used induced pluripotent stem cell (iPSC)-derived neurons from both CMS and non-CMS subjects to study CMS neuropathology. Using transmission electron microscopy, we report that CMS neurons have a decreased mitochondrial volume density, length, and less cristae membrane surface area. Real-time PCR confirmed a decreased mitochondrial fusion gene optic atrophy 1 (OPA1) expression. Immunoblot analysis showed an accumulation of the short isoform of OPA1 (S-OPA1) in CMS neurons, which have reduced ATP levels under normoxia and increased lactate dehydrogenase (LDH) release and caspase 3 activation after hypoxia. Improving the balance between the long isoform of OPA1 and S-OPA1 in CMS neurons increased the ATP levels and attenuated LDH release under hypoxia. Our data provide initial evidence for altered mitochondrial morphology and function in CMS neurons, and reveal increased cell death under hypoxia due in part to altered mitochondrial dynamics. NEW & NOTEWORTHY Induced pluripotent stem cell-derived neurons from chronic mountain sickness (CMS) subjects have altered mitochondrial morphology and dynamics, and increased sensitivity to hypoxic stress. Modification of OPA1 can attenuate cell death after hypoxic treatment, providing evidence that altered mitochondrial dynamics play an important role in increased vulnerability under stress in CMS neurons.

A clinical-pathogenetic approach on associated anomalies and chromosomal defects supports novel candidate critical regions and genes for gastroschisis

BACKGROUND

Gastroschisis has been assumed to have a low rate of syndromic and primary malformations. We aimed to systematically review and explore the frequency and type of malformations/chromosomal syndromes and to identify significant biological/genetic roles in gastroschisis.

METHODS

Population-based, gastroschisis-associated anomalies/chromosomal defects published 1950-2018 (PubMed/MEDLINE) were independently searched by two reviewers. Associated anomalies/chromosomal defects and selected clinical characteristics were subdivided and pooled by race, system/region, isolated, and associated cases (descriptive analysis and chi-square test were performed). Critical regions/genes from representative chromosomal syndromes including an enrichment analysis using Gene Ontology Consortium/Panther Classification System databases were explored. Fisher's exact test with False Discovery Rate multiple test correction was performed.

RESULTS

Sixty-eight articles and 18525 cases as a base were identified (prevalence of 17.9 and 3% for associated anomalies/chromosomal defects, respectively). There were 3596 associated anomalies, prevailing those cardiovascular (23.3%) and digestive (20.3%). Co-occurring anomalies were associated with male, female, American Indian, Caucasian, prenatally diagnosed, chromosomal defects, and mortality (P < 0.00001). Gene clusters on 21q22.11 and 21q22.3 (KRTAP), 18q21.33 (SERPINB), 18q22.1 (CDH7, CDH19), 13q12.3 (FLT1), 13q22.1 (KLF5), 13q22.3 (EDNRB), and 13q34 (COL4A1, COL4A2, F7, F10) were significantly related to biological processes: blood pressure regulation and/or vessel integrity, angiogenesis, coagulation, cell-cell and/or cell-matrix adhesion, dermis integrity, and wound healing (P < 0.05).

CONCLUSIONS

Our findings suggest that gastroschisis may result from the interaction of several chromosomal regions in an additive manner as a pool of candidate genes were identified from critical regions supporting a role for vascular disruption, thrombosis, and mesodermal deficiency in the pathogenesis of gastroschisis.

Cardiac-specific knockout and pharmacological inhibition of Endothelin receptor type B lead to cardiac resistance to extreme hypoxia

Oxygen plays a central role in cardiac energy metabolism. At high altitude where the ambient oxygen level is low, we found EDNRB is associated with human hypoxia adaptation. Our subsequent study in global heterozygous knockout mice (Ednrb^-/+) revealed that cardiac function was conserved in these mice when exposed to extreme hypoxia. The major goal of this study was (i) to determine the functional role of cardiomyocyte EdnrB in maintaining cardiac function under hypoxic stress and (ii) to validate the phenotypes we detected in Ednrb^-/+ mice using EDNRB blockers. Unlike the global knockouts, cardiac-specific heterozygote (EdnrB^flox/+) and homozygote (EdnrB^flox/flox) EdnrB knockout mice were phenotypically normal. When treated with graded low levels of oxygen (10% and 5% O₂), both EdnrB^flox/+ and EdnrB^flox/flox were hypoxia tolerant. The cardiac indexes at 10% and 5% O₂ for EdnrB^flox/+ were significantly higher and lactate levels were significantly lower when compared to the cre-negative controls (P < 0.05). Simultaneously, mice treated with BQ-788 (EDNRB-specific blocker) had a significantly higher cardiac index (P < 0.005) and significantly lower lactate levels (P < 0.0001) than in control mice. A similar result was obtained with mice treated with Bosentan (non-specific). These data indicate that a lower level or complete lack of EdnrB in the cardiomyocytes significantly improves cardiac performance under extreme hypoxia, a novel role of cardiomyocyte EdnrB in the regulation of cardiac function. Furthermore, this rescue under extreme hypoxia can also be achieved using EDNRB-specific pharmacological agents, e.g., BQ-788. This systematically confirms, both genetically and pharmacologically, the protective role of a lower EDNRB under extreme hypoxia stress.

KEY MESSAGES

Under normal condition, cardiomyocytes-specific EdnrB knockout mice, both heterozygote and homozygote, are phenotypically normal. Under hypoxic condition, a lower level or complete deletion of cardiomyocyte EdnrB conserves cardiac function by maintaining high cardiac index. Similarly, mice treated with both specific (BQ-788) and non-specific (Bosentan) EDNRB blockers are tolerant to hypoxia by maintaining better cardiac function. The oxygen perfusion under extreme hypoxia is better in the mice with lower EDNRB, as depicted by lower lactate level at 5% oxygen. Our current study systematically confirms, both genetically and pharmacologically, the protective role of a lower EDNRB under extreme hypoxia stress. Overall, it supports our hypothesis that studies on human hypoxia adaptation provide new insight to common disease pathogenesis and treatments.

New Insights into the Genetic Basis of Monge's Disease and Adaptation to High-Altitude

Human high-altitude (HA) adaptation or mal-adaptation is explored to understand the physiology, pathophysiology, and molecular mechanisms that underlie long-term exposure to hypoxia. Here, we report the results of an analysis of the largest whole-genome-sequencing of Chronic Mountain Sickness (CMS) and nonCMS individuals, identified candidate genes and functionally validated these candidates in a genetic model system (Drosophila). We used PreCIOSS algorithm that uses Haplotype Allele Frequency score to separate haplotypes carrying the favored allele from the noncarriers and accordingly, prioritize genes associated with the CMS or nonCMS phenotype. Haplotypes in eleven candidate regions, with SNPs mostly in nonexonic regions, were significantly different between CMS and nonCMS subjects. Closer examination of individual genes in these regions revealed the involvement of previously identified candidates (e.g., SENP1) and also unreported ones SGK3, COPS5, PRDM1, and IFT122 in CMS. Remarkably, in addition to genes like SENP1, SGK3, and COPS5 which are HIF-dependent, our study reveals for the first time HIF-independent gene PRDM1, indicating an involvement of wider, nonHIF pathways in HA adaptation. Finally, we observed that down-regulating orthologs of these genes in Drosophila significantly enhanced their hypoxia tolerance. Taken together, the PreCIOSS algorithm, applied on a large number of genomes, identifies the involvement of both new and previously reported genes in selection sweeps, highlighting the involvement of multiple hypoxia response systems. Since the overwhelming majority of SNPs are in nonexonic (and possibly regulatory) regions, we speculate that adaptation to HA necessitates greater genetic flexibility allowing for transcript variability in response to graded levels of hypoxia.

The joint effect of the endothelin receptor B gene (EDNRB) polymorphism rs10507875 and nitric oxide synthase 3 gene (NOS3) polymorphism rs869109213 in Slovenian patients with type 2 diabetes mellitus and diabetic retinopathy

Increasing evidence suggests that endothelin and nitric oxide synthase genes and their products exert biological effects on the vasculature via the nitric oxide or endothelin pathway. The aim of the study was to evaluate the association of rs10507875 and rs869109213 (alone or in interaction) with diabetic retinopathy (DR) in subjects with type 2 diabetes mellitus (T2DM). We genotyped the single nucleotide polymorphism rs10507875 of the endothelin receptor B gene (EDNRB) and variable number tandem repeats rs869109213 of the nitric oxide synthase 3 gene (NOS3) in 270 Slovenian patients with DR and T2DM and 256 controls with T2DM without clinical signs of DR. The genotyping was performed using either real-time polymerase chain reaction (PCR) or standard PCR. We found a significant association between the genotypes of NOS3 rs869109213 polymorphism and the risk of DR in the co-dominant model (4a4b genotype; 1.99-fold increased risk [1.09-3.65]; 95% confidence interval [CI]; p = 0.02), co-dominant model (4a4a genotype; 4.16-fold increased risk [1.03-16.74]; 95% CI; p = 0.04), and dominant model (4a4a and 4a4b genotypes; 2.22-fold increased risk [1.26-3.92]; 95% CI; p = 0.01) compared to the 4b4b genotype. Moreover, the joint effect of the two polymorphisms on DR risk was greater than the individual effect of each polymorphism in the analyzed genetic models. Additionally, adjusted odds ratio showed an increased risk in dominant × dominant (4.15-fold [1.40-12.26]; 95% CI; p = 0.01) and recessive × dominant (2.24-fold [1.25-4.01]; 95% CI; p = 0.02) genotype combinations of the two polymorphisms. In conclusion, our results indicate that NOS3 rs869109213 polymorphism alone or in a combination with EDNRB rs10507875 polymorphism may be associated with DR in Slovenian patients with T2DM.

Integrative Genomics of Emphysema-Associated Genes Reveals Potential Disease Biomarkers

Chronic obstructive pulmonary disease is the third leading cause of death worldwide. Gene expression profiling across multiple regions of the same lung identified genes significantly related to emphysema. We sought to determine whether the lung and epithelial expression of 127 emphysema-related genes was also related to lung function in independent cohorts, and whether any of these genes could be used as biomarkers in the peripheral blood of patients with chronic obstructive pulmonary disease. To that end, we examined whether the expression levels of these genes were under genetic control in lung tissue (n = 1,111). We then determined whether the mRNA levels of these genes in lung tissue (n = 727), small airway epithelial cells (n = 238), and peripheral blood (n = 620) were significantly related to lung function measurements. The expression of 63 of the 127 genes (50%) was under genetic control in lung tissue. The lung and epithelial mRNA expression of a subset of the emphysema-associated genes, including ASRGL1, LPHN2, and EDNRB, was strongly associated with lung function. In peripheral blood, the expression of 40 genes was significantly associated with lung function. Twenty-nine of these genes (73%) were also associated with lung function in lung tissue, but with the opposite direction of effect for 24 of the 29 genes, including those involved in hypoxia and B cell-related responses. The integrative genomics approach uncovered a significant overlap of emphysema genes associations with lung function between lung and blood with opposite directions between the two. These results support the use of peripheral blood to detect disease biomarkers.

Reduced Cardiac Calcineurin Expression Mimics Long-Term Hypoxia-Induced Heart Defects in Drosophila

BACKGROUND

Hypoxia is often associated with cardiopulmonary diseases, which represent some of the leading causes of mortality worldwide. Long-term hypoxia exposures, whether from disease or environmental condition, can cause cardiomyopathy and lead to heart failure. Indeed, hypoxia-induced heart failure is a hallmark feature of chronic mountain sickness in maladapted populations living at high altitude. In a previously established Drosophila heart model for long-term hypoxia exposure, we found that hypoxia caused heart dysfunction. Calcineurin is known to be critical in cardiac hypertrophy under normoxia, but its role in the heart under hypoxia is poorly understood.

METHODS AND RESULTS

In the present study, we explore the function of calcineurin, a gene candidate we found downregulated in the Drosophila heart after lifetime and multigenerational hypoxia exposure. We examined the roles of 2 homologs of Calcineurin A, CanA14F, and Pp2B in the Drosophila cardiac response to long-term hypoxia. We found that knockdown of these calcineurin catalytic subunits caused cardiac restriction under normoxia that are further aggravated under hypoxia. Conversely, cardiac overexpression of Pp2B under hypoxia was lethal, suggesting that a hypertrophic signal in the presence of insufficient oxygen supply is deleterious.

CONCLUSIONS

Our results suggest a key role for calcineurin in cardiac remodeling during long-term hypoxia with implications for diseases of chronic hypoxia, and it likely contributes to mechanisms underlying these disease states.

High-altitude adaptation in humans: from genomics to integrative physiology

About 1.2 to 33% of high-altitude populations suffer from Monge's disease or chronic mountain sickness (CMS). Number of factors such as age, sex, and population of origin (older, male, Andean) contribute to the percentage reported from a variety of samples. It is estimated that there are around 83 million people who live at altitudes > 2500 m worldwide and are at risk for CMS. In this review, we focus on a human "experiment in nature" in various high-altitude locations in the world-namely, Andean, Tibetan, and Ethiopian populations that have lived under chronic hypoxia conditions for thousands of years. We discuss the adaptive as well as mal-adaptive changes at the genomic and physiological levels. Although different genes seem to be involved in adaptation in the three populations, we can observe convergence at genetic and signaling, as well as physiological levels. What is important is that we and others have shown that lessons learned from the genes mined at high altitude can be helpful in better understanding and treating diseases that occur at sea level. We discuss two such examples: EDNRB and SENP1 and their role in cardiac tolerance and in the polycythemic response, respectively.

Gene Expression Networks in the Murine Pulmonary Myocardium Provide Insight into the Pathobiology of Atrial Fibrillation

The pulmonary myocardium is a muscular coat surrounding the pulmonary and caval veins. Although its definitive physiological function is unknown, it may have a pathological role as the source of ectopic beats initiating atrial fibrillation. How the pulmonary myocardium gains pacemaker function is not clearly defined, although recent evidence indicates that changed transcriptional gene expression networks are at fault. The gene expression profile of this distinct cell type in situ was examined to investigate underlying molecular events that might contribute to atrial fibrillation. Via systems genetics, a whole-lung transcriptome data set from the BXD recombinant inbred mouse resource was analyzed, uncovering a pulmonary cardiomyocyte gene network of 24 transcripts, coordinately regulated by chromosome 1 and 2 loci. Promoter enrichment analysis and interrogation of publicly available ChIP-seq data suggested that transcription of this gene network may be regulated by the concerted activity of NKX2-5, serum response factor, myocyte enhancer factor 2, and also, at a post-transcriptional level, by RNA binding protein motif 20. Gene ontology terms indicate that this gene network overlaps with molecular markers of the stressed heart. Therefore, we propose that perturbed regulation of this gene network might lead to altered calcium handling, myocyte growth, and contractile force contributing to the aberrant electrophysiological properties observed in atrial fibrillation. We reveal novel molecular interactions and pathways representing possible therapeutic targets for atrial fibrillation. In addition, we highlight the utility of recombinant inbred mouse resources in detecting and characterizing gene expression networks of relatively small populations of cells that have a pathological significance.

GBT1118, a potent allosteric modifier of hemoglobin O2 affinity, increases tolerance to severe hypoxia in mice

Adaptation to hypoxia requires compensatory mechanisms that affect O₂ transport and utilization. Decreased hemoglobin (Hb) O₂ affinity is considered part of the physiological adaptive process to chronic hypoxia. However, this study explores the hypothesis that increased Hb O₂ affinity can complement acute physiological responses to hypoxia by increasing O₂ uptake and delivery compared with normal Hb O₂ affinity during acute severe hypoxia. To test this hypothesis, Hb O₂ affinity in mice was increased by oral administration of 2-hydroxy-6-{[(2S)-1-(pyridine-3-carbonyl)piperidin-2yl] methoxy}benzaldehyde (GBT1118; 70 or 140 mg/kg). Systemic and microcirculatory hemodynamics and oxygenation parameters were studied during hypoxia in awake-instrumented mice. GBT1118 increased Hb O₂ affinity and decreased the Po₂ at which 50% of Hb is saturated with O₂ (P₅₀) from 43 ± 1.1 to 18.3 ± 0.9 mmHg (70 mg/kg) and 7.7 ± 0.2 mmHg (140 mg/kg). In a dose-dependent fashion, GBT1118 increased arterial O₂ saturation by 16% (70 mg/kg) and 40% (140 mg/kg) relative to the control group during 5% O₂ hypoxia. In addition, a GBT1118-induced increase in Hb O₂ affinity reduced hypoxia-induced hypotension compared with the control group. Moreover, microvascular blood flow was higher during hypoxia in GBT1118-treated groups than the control group. The increased O₂ saturation and improved blood flow in GBT1118-treated groups preserved higher interstitial tissue Po₂ than in the control group during 5% O₂ hypoxia. In conclusion, increased Hb O₂ affinity enhanced physiological tolerance to hypoxia, as evidenced by improved hemodynamics and tissue oxygenation. Therefore, pharmacologically induced increases in Hb O₂ affinity become a potential therapeutic approach to improve tissue oxygenation in pulmonary diseases characterized by severe hypoxemia.NEW & NOTEWORTHY This study establishes that pharmacological modification of hemoglobin O₂ affinity can be a promising and novel therapeutic strategy for the treatment of hypoxic hypoxia and paves the way for the clinical development of molecules that prevent hypoxemia.

Physiological Changes to the Cardiovascular System at High Altitude and Its Effects on Cardiovascular Disease

Riley, Callum James, and Matthew Gavin. Physiological changes to the cardiovascular system at high altitude and its effects on cardiovascular disease. High Alt Med Biol. 18:102-113, 2017.-The physiological changes to the cardiovascular system in response to the high altitude environment are well understood. More recently, we have begun to understand how these changes may affect and cause detriment to cardiovascular disease. In addition to this, the increasing availability of altitude simulation has dramatically improved our understanding of the physiology of high altitude. This has allowed further study on the effect of altitude in those with cardiovascular disease in a safe and controlled environment as well as in healthy individuals. Using a thorough PubMed search, this review aims to integrate recent advances in cardiovascular physiology at altitude with previous understanding, as well as its potential implications on cardiovascular disease. Altogether, it was found that the changes at altitude to cardiovascular physiology are profound enough to have a noteworthy effect on many forms of cardiovascular disease. While often asymptomatic, there is some risk in high altitude exposure for individuals with certain cardiovascular diseases. Although controlled research in patients with cardiovascular disease was largely lacking, meaning firm conclusions cannot be drawn, these risks should be a consideration to both the individual and their physician.

Hirschsprung's disease: clinical dysmorphology, genes, micro-RNAs, and future perspectives

On the occasion of the 100th anniversary of Dr. Harald Hirschsprung's death, there is a worldwide significant research effort toward identifying and understanding the role of genes and biochemical pathways involved in the pathogenesis as well as the use of new therapies for the disease harboring his name (Hirschsprung disease, HSCR). HSCR (aganglionic megacolon) is a frequent diagnostic and clinical challenge in perinatology and pediatric surgery, and a major cause of neonatal intestinal obstruction. HSCR is characterized by the absence of ganglia of the enteric nervous system, mostly in the distal gastrointestinal tract. This review focuses on current understanding of genes and pathways associated with HSCR and summarizes recent knowledge related to micro RNAs (miRNAs) and HSCR pathogenesis. While commonly sporadic, Mendelian patterns of inheritance have been described in syndromic cases with HSCR. Although only half of the patients with HSCR have mutations in specific genes related to early embryonic development, recent pathway-based analysis suggests that gene modules with common functions may be associated with HSCR in different populations. This comprehensive profile of functional gene modules may serve as a useful resource for future developmental, biochemical, and genetic studies providing insights into the complex nature of HSCR.

Pulmonary vascular and ventricular dysfunction in the susceptible patient (2015 Grover Conference series)

Pulmonary blood vessel structure and tone are maintained by a complex interplay between endogenous vasoactive factors and oxygen-sensing intermediaries. Under physiological conditions, these signaling networks function as an adaptive interface between the pulmonary circulation and environmental or acquired perturbations to preserve oxygenation and maintain systemic delivery of oxygen-rich hemoglobin. Chronic exposure to hypoxia, however, triggers a range of pathogenetic mechanisms that include hypoxia-inducible factor 1α (HIF-1α)-dependent upregulation of the vasoconstrictor peptide endothelin 1 in pulmonary endothelial cells. In pulmonary arterial smooth muscle cells, chronic hypoxia induces HIF-1α-mediated upregulation of canonical transient receptor potential proteins, as well as increased Rho kinase-Ca2+ signaling and pulmonary arteriole synthesis of the profibrotic hormone aldosterone. Collectively, these mechanisms contribute to a contractile or hypertrophic pulmonary vascular phenotype. Genetically inherited disorders in hemoglobin structure are also an important etiology of abnormal pulmonary vasoreactivity. In sickle cell anemia, for example, consumption of the vasodilator and antimitogenic molecule nitric oxide by cell-free hemoglobin is an important mechanism underpinning pulmonary hypertension. Contemporary genomic and transcriptomic analytic methods have also allowed for the discovery of novel risk factors relevant to sickle cell disease, including GALNT13 gene variants. In this report, we review cutting-edge observations characterizing these and other pathobiological mechanisms that contribute to pulmonary vascular and right ventricular vulnerability.

Senp1 drives hypoxia-induced polycythemia via GATA1 and Bcl-xL in subjects with Monge's disease

Azad and collaborators propose that Senp1 drives excessive erythropoiesis in high-altitude Andean dwellers suffering from chronic mountain sickness.

In this study, because excessive polycythemia is a predominant trait in some high-altitude dwellers (chronic mountain sickness [CMS] or Monge’s disease) but not others living at the same altitude in the Andes, we took advantage of this human experiment of nature and used a combination of induced pluripotent stem cell technology, genomics, and molecular biology in this unique population to understand the molecular basis for hypoxia-induced excessive polycythemia. As compared with sea-level controls and non-CMS subjects who responded to hypoxia by increasing their RBCs modestly or not at all, respectively, CMS cells increased theirs remarkably (up to 60-fold). Although there was a switch from fetal to adult HgbA0 in all populations and a concomitant shift in oxygen binding, we found that CMS cells matured faster and had a higher efficiency and proliferative potential than non-CMS cells. We also established that SENP1 plays a critical role in the differential erythropoietic response of CMS and non-CMS subjects: we can convert the CMS phenotype into that of non-CMS and vice versa by altering SENP1 levels. We also demonstrated that GATA1 is an essential downstream target of SENP1 and that the differential expression and response of GATA1 and Bcl-xL are a key mechanism underlying CMS pathology.