Increased hypoxic proliferative response and gene expression in erythroid progenitor cells of Andean highlanders with chronic mountain sickness

Altitude illnesses

Millions of people visit high-altitude regions annually and more than 80 million live permanently above 2,500 m. Acute high-altitude exposure can trigger high-altitude illnesses (HAIs), including acute mountain sickness (AMS), high-altitude cerebral oedema (HACE) and high-altitude pulmonary oedema (HAPE). Chronic mountain sickness (CMS) can affect high-altitude resident populations worldwide. The prevalence of acute HAIs varies according to acclimatization status, rate of ascent and individual susceptibility. AMS, characterized by headache, nausea, dizziness and fatigue, is usually benign and self-limiting, and has been linked to hypoxia-induced cerebral blood volume increases, inflammation and related trigeminovascular system activation. Disruption of the blood-brain barrier leads to HACE, characterized by altered mental status and ataxia, and increased pulmonary capillary pressure, and related stress failure induces HAPE, characterized by dyspnoea, cough and exercise intolerance. Both conditions are progressive and life-threatening, requiring immediate medical intervention. Treatment includes supplemental oxygen and descent with appropriate pharmacological therapy. Preventive measures include slow ascent, pre-acclimatization and, in some instances, medications. CMS is characterized by excessive erythrocytosis and related clinical symptoms. In severe CMS, temporary or permanent relocation to low altitude is recommended. Future research should focus on more objective diagnostic tools to enable prompt treatment, improved identification of individual susceptibilities and effective acclimatization and prevention options.

Long noncoding RNA HIKER regulates erythropoiesis in Monge's disease via CSNK2B

Excessive erythrocytosis (EE) is a major hallmark of patients suffering from chronic mountain sickness (CMS, also known as Monge's disease) and is responsible for major morbidity and even mortality in early adulthood. We took advantage of unique populations, one living at high altitude (Peru) showing EE, with another population, at the same altitude and region, showing no evidence of EE (non-CMS). Through RNA-Seq, we identified and validated the function of a group of long noncoding RNAs (lncRNAs) that regulate erythropoiesis in Monge's disease, but not in the non-CMS population. Among these lncRNAs is hypoxia induced kinase-mediated erythropoietic regulator (HIKER)/LINC02228, which we showed plays a critical role in erythropoiesis in CMS cells. Under hypoxia, HIKER modulated CSNK2B (the regulatory subunit of casein kinase 2). A downregulation of HIKER downregulated CSNK2B, remarkably reducing erythropoiesis; furthermore, an upregulation of CSNK2B on the background of HIKER downregulation rescued erythropoiesis defects. Pharmacologic inhibition of CSNK2B drastically reduced erythroid colonies, and knockdown of CSNK2B in zebrafish led to a defect in hemoglobinization. We conclude that HIKER regulates erythropoiesis in Monge's disease and acts through at least one specific target, CSNK2B, a casein kinase.

Arginine attenuates chronic mountain sickness in rats via microRNA-144-5p

Hypobaric hypoxia is an environmental stress leading to high-altitude pulmonary hypertension. While high-altitude pulmonary hypertension has been linked to high hematocrit findings (chronic mountain sickness; CMS). The present study is designed to investigate the effect of arginine (ARG) on hypobaric hypoxia-induced CMS of rats. Hypobaric hypoxia resulted in lower body weight, decreased appetite, increased pulmonary artery pressure, and deteriorated lung tissue damage in rats. Red blood cells (RBC), hemoglobin, hematocrit, mean corpuscular volume, and mean corpuscular hemoglobin values and blood viscosity were increased in rats, which were alleviated by ARG. microRNA (miRNA) microarray analysis was used to filter differentially expressed miRNAs after ARG in rats. miR-144-5p was reduced under hypobaric hypoxia and upregulated by ARG. miR-144-5p silencing aggravated the erythrocytosis and hyperviscosity in rats, and also accentuated tissue damage and excessive accumulation of RBC. The role of miR-144-5p in rats with CMS was achieved by blocking erythropoietin (EPO)/erythropoietin receptor (EPOR). In conclusion, ARG alleviated CMS symptoms in rodents exposed to hypobaric hypoxia by decreasing EPO/EPOR via miR-144-5p.

Preserved peak exercise capacity in Andean highlanders with excessive erythrocytosis both before and after isovolumic hemodilution

In chronic mountain sickness (CMS), increased blood oxygen (O₂)-carrying capacity due to excessive erythrocytosis (EE, [Hb] ≥ 21 g/dL) could be offset, especially during exercise by both impaired cardiac output (Q̇t) and O₂ diffusion limitation in lungs and muscle. We hypothesized that EE results in reduced peak V̇o₂ despite increased blood O₂-carrying capacity, and that isovolumic hemodilution (IVHD) improves exercise capacity. In 14 male residents of Cerro de Pasco, Peru (4,340 m), six with and eight without EE, we measured peak cycle-exercise capacity, V̇o₂, Q̇t, arterial blood gas parameters, and (resting) blood volume. This was repeated for participants with EE after IVHD, reducing hematocrit by 20% (from 67% to 53%). From these data, we quantified the major O₂ transport pathway components (ventilation, pulmonary alveolar-capillary diffusion, Q̇t, and blood-muscle mitochondria diffusion). Participants with EE had similar peak V̇o₂, systemic O₂ delivery, and O₂ extraction as non-EE controls, however, with lower Q̇t and higher arterial [O₂]. After IVHD, peak V̇o₂ was preserved (but not enhanced), with lower O₂ delivery (despite higher Q̇t) balanced by greater O₂ extraction. The considerable variance in exercise capacity across the 14 individuals was explained essentially completely by differences in both pulmonary and muscle O₂ diffusional conductances and not by any differences in ventilation, [Hb], nor Q̇t. In conclusion, EE does not result in lower peak V̇o₂ in Andean males, and IVHD maintains, but does not enhance, exercise capacity.NEW & NOTEWORTHY Male Andean highlanders with and without excessive erythrocytosis (EE) have similar peak V̇o₂ at 4,340 m, with higher arterial [O₂] in EE and lower cardiac output (Q̇t), thus maintaining similar O₂ delivery. Peak V̇o₂ in participants with EE was unaffected by isovolumic hemodilution (hematocrit reduced from 67% to 53%), with lower O₂ delivery balanced by slightly increased Q̇t and greater O₂ extraction. Differences in lung and muscle diffusing capacity, and not hematocrit variation, accounted for essentially all interindividual variance in peak V̇o₂.

Identification of Suitable Reference Genes for Lowlanders Exposed to High Altitude and Ladakhi Highlanders

Sharma, Vandana, Rajeev Varshney, and Niroj Kumar Sethy. Identification of suitable reference genes for lowlanders exposed to high altitude and Ladakhi highlanders. High Alt Med Biol. 23:319-329, 2022. Background: Identifying a stable and reliable reference gene (RG) is a prerequisite for the unbiased and unambiguous analysis of gene expression data. It has become evident that conventionally used housekeeping genes such as beta-actin (ACTB), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and peptidylprolyl Isomerase A (PPIA) exhibit varied expression patterns under hypoxia. Hence, the identification of stable RGs for humans exposed to hypobaric hypoxia can enhance the accuracy of gene expression studies by limiting the negligent use of random housekeeping genes. Methods: Using TaqMan™ array-based quantitative real-time quantitative polymerase chain reaction, we evaluated the expression of 32 commonly used human RGs among lowlanders at Delhi (altitude 216 m, SL), lowlanders at Leh (altitude 3,524 m) after 1 day (HA-D1) and 7 days (HA-D7), as well as indigenous Ladakhi highlanders at the same altitude. The expression stability of the RGs was evaluated using geNorm, NormFinder, BestKeeper, Delta CT method, and RefFinder algorithms. Results: Our studies identify TATA-box binding protein (TBP), proteasome 26S subunit, ATPase 4 (PSMC4), and tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein zeta (YWHAZ) as the most stable human RGs for normalizing human gene expression under hypobaric hypoxia. In addition, we report the combination of TBP and cyclin-dependent kinase inhibitor 1B (CDKN1B) as the most stable RG for studying lowlander gene expression during high-altitude exposure. In contrast, RPL30 and 18S exhibited maximum variation across study groups and were identified as the least stable RGs.

High-Altitude Erythrocytosis: Mechanisms of Adaptive and Maladaptive Responses

Erythrocytosis, or increased production of red blood cells, is one of the most well-documented physiological traits that varies within and among in high-altitude populations. Although a modest increase in blood O₂-carrying capacity may be beneficial for life in highland environments, erythrocytosis can also become excessive and lead to maladaptive syndromes such as chronic mountain sickness (CMS).

Stroke-Related Mortality at Different Altitudes: A 17-Year Nationwide Population-Based Analysis From Ecuador

Introduction: Worldwide, more than 5.7% of the population reside above 1,500 m of elevation. It has been hypothesized that acute short-term hypoxia exposure could increase the risk of developing a stroke. Studies assessing the effect of altitude on stroke have provided conflicting results, some analyses suggest that long-term chronic exposure could be associated with reduced mortality and lower stroke incidence rates.

Methods: An ecological analysis of all stroke hospital admissions, mortality rates, and disability-adjusted life years in Ecuador was performed from 2001 to 2017. The cases and population at risk were categorized in low (<1,500 m), moderate (1,500–2,500 m), high (2,500–3,500 m), and very high altitude (3,500–5,500 m) according to the place of residence. The derived crude and direct standardized age-sex adjusted mortality and hospital admission rates were calculated.

Results: A total of 38,201 deaths and 75,893 stroke-related hospital admissions were reported. High altitude populations (HAP) had lower stroke mortality in men [OR: 0.91 (0.88–0.95)] and women [OR: 0.83 (0.79–0.86)]. In addition, HAP had a significant lower risk of getting admitted to the hospital when compared with the low altitude group in men [OR: 0.55 (CI 95% 0.54–0.56)] and women [OR: 0.65 (CI 95% 0.64–0.66)].

Conclusion: This is the first epidemiological study that aims to elucidate the association between stroke and altitude using four different elevation ranges. Our findings suggest that living at higher elevations offers a reduction or the risk of dying due to stroke as well as a reduction in the probability of being admitted to the hospital. Nevertheless, this protective factor has a stronger effect between 2,000 and 3,500 m.

Protective role of estrogen against excessive erythrocytosis in Monge's disease

Monge's disease (chronic mountain sickness (CMS)) is a maladaptive condition caused by chronic (years) exposure to high-altitude hypoxia. One of the defining features of CMS is excessive erythrocytosis with extremely high hematocrit levels. In the Andean population, CMS prevalence is vastly different between males and females, being rare in females. Furthermore, there is a sharp increase in CMS incidence in females after menopause. In this study, we assessed the role of sex hormones (testosterone, progesterone, and estrogen) in CMS and non-CMS cells using a well-characterized in vitro erythroid platform. While we found that there was a mild (nonsignificant) increase in RBC production with testosterone, we observed that estrogen, in physiologic concentrations, reduced sharply CD235a+ cells (glycophorin A; a marker of RBC), from 56% in the untreated CMS cells to 10% in the treated CMS cells, in a stage-specific and dose-responsive manner. At the molecular level, we determined that estrogen has a direct effect on GATA1, remarkably decreasing the messenger RNA (mRNA) and protein levels of GATA1 (p < 0.01) and its target genes (Alas2, BclxL, and Epor, p < 0.001). These changes result in a significant increase in apoptosis of erythroid cells. We also demonstrate that estrogen regulates erythropoiesis in CMS patients through estrogen beta signaling and that its inhibition can diminish the effects of estrogen by significantly increasing HIF1, VEGF, and GATA1 mRNA levels. Taken altogether, our results indicate that estrogen has a major impact on the regulation of erythropoiesis, particularly under chronic hypoxic conditions, and has the potential to treat blood diseases, such as high altitude severe erythrocytosis.

Excessive Erythrocytosis and Chronic Mountain Sickness in Dwellers of the Highest City in the World

Background

While millions of people are living permanently at high altitude (>2,500 m) worldwide, the mechanisms underlying their tolerance to chronic hypoxia and those responsible for the occurrence of chronic mountain sickness (CMS) remain to be elucidated. Excessive erythrocytosis (EE) is thought to be the main mechanism responsible for CMS symptoms and is included in the definition of CMS, but the precise interplay between EE and symptoms of CMS requires further investigations.

Methods

The present study benefits from an exceptional dataset coming from 1,594 dwellers of La Rinconada, the highest city in the world (5,100-5,300 m). Based on individual clinical characteristics, subjects were categorized according to the presence of EE and CMS diagnosis, based on current guidelines.

Results

In this population of relatively young [32 (23; 39) years] highlanders residing in La Rinconada for only a few years [3 (2; 5) years], the internal prevalence of EE (44%) was high, whereas the internal prevalence of CMS (14%) was similar compared to previous reports in highlander populations living at lower altitude (∼4,000 m) in the Andes. Individuals with EE reported less symptoms compared to individuals with lower hematocrit values. Multivariable analysis revealed that age and sex are the main factors associated with EE, whereas age, hematocrit and number of years living at La Rinconada are factors associated with CMS symptoms.

Conclusion

In this specific population of La Rinconada, high hematocrit values were observed but were associated with limited symptoms. These results raise important questions regarding the definition of EE and CMS and their underlying mechanisms in high-altitude populations.

The 2018 Global Research Expedition on Altitude Related Chronic Health (Global REACH) to Cerro de Pasco, Peru: an Experimental Overview

NEW FINDINGS

What is the central question of this study? Herein, a methodological overview of our research team's (Global REACH) latest high altitude research expedition to Peru is provided. What is the main finding and its importance? The experimental objectives, expedition organization, measurements and key cohort data are discussed. The select data presented in this manuscript demonstrate the haematological differences between lowlanders and Andeans with and without excessive erythrocytosis. The data also demonstrate that exercise capacity was similar between study groups at high altitude. The forthcoming findings from our research expedition will contribute to our understanding of lowlander and indigenous highlander high altitude adaptation.

ABSTRACT

In 2016, the international research team Global Research Expedition on Altitude Related Chronic Health (Global REACH) was established and executed a high altitude research expedition to Nepal. The team consists of ∼45 students, principal investigators and physicians with the common objective of conducting experiments focused on high altitude adaptation in lowlanders and in highlanders with lifelong exposure to high altitude. In 2018, Global REACH travelled to Peru, where we performed a series of experiments in the Andean highlanders. The experimental objectives, organization and characteristics, and key cohort data from Global REACH's latest research expedition are outlined herein. Fifteen major studies are described that aimed to elucidate the physiological differences in high altitude acclimatization between lowlanders (n = 30) and Andean-born highlanders with (n = 22) and without (n = 45) excessive erythrocytosis. After baseline testing in Kelowna, BC, Canada (344 m), Global REACH travelled to Lima, Peru (∼80 m) and then ascended by automobile to Cerro de Pasco, Peru (∼4300 m), where experiments were conducted over 25 days. The core studies focused on elucidating the mechanism(s) governing cerebral and peripheral vascular function, cardiopulmonary regulation, exercise performance and autonomic control. Despite encountering serious logistical challenges, each of the proposed studies was completed at both sea level and high altitude, amounting to ∼780 study sessions and >3000 h of experimental testing. Participant demographics and data relating to acid-base balance and exercise capacity are presented. The collective findings will contribute to our understanding of how lowlanders and Andean highlanders have adapted under high altitude stress.