The human blood transcriptome exhibits time-of-day-dependent response to hypoxia: Lessons from the highest city in the world

Circadian clock controlled glycolipid metabolism and its relevance to disease management

The circadian clock is a critical regulator of physiological rhythms, orchestrating metabolic processes to adapt to daily environmental changes. This review focuses on the intricate relationship between circadian regulation and glycolipid metabolism, with implications for metabolic diseases. Central and peripheral clocks coordinate the rhythmic expression of key enzymes and transporters, ensuring glycolipid homeostasis. Disruptions to these rhythms can result in metabolic disorders characterized by altered glucose utilization, insulin sensitivity, and lipid storage. The molecular mechanisms underlying these processes include transcriptional-translational feedback loops involving clock factors that regulate glycolipid metabolism. Emerging therapeutic strategies, such as pharmacological and dietary interventions, highlight the translational potential of circadian biology. This review underscores the importance of circadian rhythm maintenance for glycolipid metabolism and its role in preventing metabolic disorders. Further elucidation of the molecular mechanisms linking circadian regulation to glycolipid metabolism could pave the way for precision medicine approaches tailored to individual circadian profiles.

The Impact of a High-Altitude Expedition on the Physical Performance and Nutritional Indices of Health Status of Alpinists

Objective: The aim of the study was to determine the effect a mountain expedition (>3000 m) would have on the physical performance and nutritional indices of alpinists' health status. Methods: The study included 17 men aged 30.29 ± 5.8 years participating in mountain expeditions to peaks of 5000-8000 m, lasting an average of 34 ± 6 days. The following were assessed: aerobic and anaerobic capacity, body composition and the values of selected biochemical and hematological indices of blood and urine before and after returning from the expeditions and a quantitative analysis of the alpinists' diet. Results: There was a statistically significant decrease (p ≤ 0.05) in aerobic capacity, anaerobic capacity, subjects' body mass, muscle mass and the lean body mass of the upper and lower extremities. There was a significant increase (p ≤ 0.05) in erythrocytes, hemoglobin, hematocrit, leukocytes, platelets, neutrophils, monocytes and a significant decrease (p ≤ 0.05) in total and high-density lipoprotein cholesterol, total bilirubin, albumin and total protein. A small percentage of the subjects met the requirements for iron (29.41%), folate (35.29%) and vitamin D (17.65%) supply with diet, as reflected in the blood test results. Conclusions: Despite the observed positive effect of three-week hypoxic exposure on the climbers' health, the deterioration of aerobic and anaerobic capacity was shown, which, in addition to environmental conditions and systemic inflammation, may have been influenced by adverse changes in body composition. To improve the nutritional status of the body during the expedition and upon return, alpinists should consider including the necessary supplementation of deficient components.

Integrative Proteomic and Phosphoproteomic Profiling Reveals Molecular Mechanisms of Hypoxic Adaptation in Brandt's Voles (Lasiopodomys brandtii) Brain Tissue

Rapid ascent to high altitudes by unacclimatized individuals significantly increases the risk of brain damage, given the brain's heightened sensitivity to hypoxic conditions. Investigating hypoxia-tolerant animals can provide insights into adaptive mechanisms and guide prevention and treatment of hypoxic-ischemic brain injury. In this study, we exposed Brandt's voles to simulated altitudes (100 m, 3000 m, 5000 m, and 7000 m) for 24 h and performed quantitative proteomic and phosphoproteomic analyses of brain tissue. A total of 3990 proteins and 9125 phosphorylation sites (phospho-sites) were quantified. Differentially expressed (DE) analysis revealed that while protein abundance changes were relatively modest, phosphorylation levels exhibited substantial alterations, suggesting that Brandt's voles rapidly regulate protein structure and function through phosphorylation to maintain cellular homeostasis under acute hypoxia. Clustering analysis showed that most co-expressed proteins exhibited non-monotonic responses with increasing altitude, which were enriched in pathways related to cytokine secretion regulation and glutathione metabolism, contributing to reduced inflammation and oxidative stress. In contrast, most co-expressed phospho-sites showed monotonic changes, with phospho-proteins enriched in glycolysis and vascular smooth muscle contraction regulation. Kinase activity prediction identified nine hypoxia-responsive kinases, four of which belonging to the CAMK family. Immunoblot validated that the changes in CAMK2A activity were consistent with predictions, suggesting that CAMK may play a crucial role in hypoxic response. In conclusion, this work discovered that Brandt's voles may cope with hypoxia through three key strategies: (1) vascular regulation to enhance cerebral blood flow, (2) glycolytic activation to increase energy production, and (3) activation of neuroprotective mechanisms.

Associations of Short-Term Ozone Exposure With Hypoxia and Arterial Stiffness

BACKGROUND

Epidemiological studies reported associations between ozone (O3) exposure and cardiovascular diseases, yet the biological mechanisms remain underexplored. Hypoxia is a shared pathogenesis of O3-associated diseases; therefore, we hypothesized that O3 exposure may induce changes in hypoxia-related markers, leading to adverse cardiovascular effects.

OBJECTIVES

This study aimed to investigate associations of short-term O3 exposure with hypoxic biomarkers and arterial stiffness.

METHODS

We conducted a panel study involving 210 young healthy residents in 2 cities at different altitudes on the Qinghai-Tibetan Plateau in China, where O3 concentrations are high and particulate pollution is low. Participants underwent 4 repeated visits to assess ambient O3 exposure levels, hypoxic biomarkers, and arterial stiffness. We applied linear mixed-effects models to assess the associations of O3 exposure (lag1 to lag1-7 days) with hypoxic biomarkers and arterial stiffness, adjusted for confounders. Mediation analyses explored the hypoxia's role in O3-related arterial stiffness changes. We further examined effect modification by residence altitude and the robustness of results by including PM2.5 (particulate matter ≤2.5 μm in aerodynamic diameter) or NO2 in 2-pollutant models.

RESULTS

O3 exposure 1 to 7 days before visits was significantly associated with changes in multiple hypoxic biomarkers. A 10-ppb increase in O3 exposure was linked to significant decreases in oxygen saturation (SpO2) and increases in red blood cell count (RBC), hemoglobin concentration, and hematocrit, with maximum changes by -0.42%, 0.92%, 0.97%, and 1.92%, respectively. Laboratory analysis of mRNA and protein markers consistently indicated that O3 exposure activated the hypoxia-inducible factor 1 (HIF-1) signaling pathway. Additionally, a 10-ppb increase in O3 corresponded to a 1.04% to 1.33% increase in carotid-femoral pulse wave velocity (cfPWV), indicating increased arterial stiffness. RBC, hemoglobin concentration, and hematocrit increases significantly mediated the O3-cfPWV association, whereas the SpO2 reduction had an insignificant mediating effect. Associations of O3 with hypoxic biomarkers varied by altitude. The higher altitude group showed delayed associations with SpO₂ and HIF-1 expression but stronger associations with RBC indices. These associations remained robust after adjusting for copollutants.

CONCLUSIONS

O3 exposure may reduce oxygen availability, prompting compensatory increases in red blood cells and hemoglobin, which exacerbate arterial stiffening. These findings provide new insights into the mechanisms underlying O3-induced cardiovascular injury.

Acute hypoxia modulate macrophage phenotype accompanied with transcriptome re-programming and metabolic re-modeling

Introduction

Macrophages, which tend to aggregate in the hypoxic regions of tissues, have a significant impact on disease progression and outcome because of their plastic responsiveness to hypoxia, particularly in the early stages. Understanding macrophages'participation in hypoxia-related disorders requires demonstrating the impact of acute hypoxia on their survival, phenotype, and function.

Methods

Here we conducted a systematic evaluation of macrophage responses to hypoxia over 24 and 48 h including cell growth and activity, inflamatory response, macrophage polarization and transcriptional and metabolic changes.

Results

We found that acute hypoxia suppresses macrophage proliferation and phagocytosis function with a parallel change of transcriptome re-programming and metabolic re-modeling. Although macrophages accumulate transcriptome heterogeneity based on oxygen concentration and culture period, genes involved in hypoxia response, chemotaxis, and glycolytic process were commonly altered during acute hypoxia. Furthermore, the pro-inflammatory response of macrophages was activated during acute hypoxia concomitantly with an enhanced anti-inflammatory regulatory mechanism characterized by increased M2 macrophage population and anti-inflammatory metabolite itaconic acid. Aside from increased glycolysis, the key intermediates in the pentose phosphate pathway significantly increased, such as fructose 1,6-bisphosphate (fold change: 7.8), 6-phosphogluconate (fold change: 6.1), and ribose 5-phosphate (fold change: 3.9), which indicated that the pentose phosphate pathway was an important compensatory metabolic regulation that rules for the response of macrophages to acute hypoxia.

Discussion

These findings highlight that acute hypoxia suppresses macrophage viability and phagocytosis, while acute hypoxia modifies the transcriptome and metabolome in specific inflammatory responses and metabolic pathways to facilitate the adaptation of macrophage in hypoxic conditions.

Multi-omics reveals immune response and metabolic profiles during high-altitude mountaineering

The physiological perturbations induced by high-altitude exposure in mountain climbers, manifesting as immunological and metabolic deviations, have been previously reported but are not fully understood. In this study, we obtain multi-omic profiles of climbers' blood samples, including single-cell transcriptomic analysis of 375,722 immune cells, and plasma metabolomics and lipidomics. Longitudinal analysis reveals dynamic immune response profiles, during the acclimatization period, characterized by the downregulation of inflammatory responses in myeloid cell subsets and by the enhancement of immune effector processes in cytotoxic CD8+ T, γδT, and CD16+ natural killer cells. In contrast, during extreme-altitude mountaineering, the activation of inflammatory responses and impairment of immune effector function are observed, concomitant with an increased cellular response to hypoxia and oxidative stress pathways. Furthermore, glycolysis and antioxidant gene expression are upregulated during extreme-altitude mountaineering. Plasma metabolic analysis reveals significant alterations, involving enhanced glutamine and fatty acid metabolism.

Resetting of the Human Circadian Melatonin Rhythm by Ambient Hypoxia

Circadian clocks in the body drive daily cycles in physiology and behavior. A master clock in the brain maintains synchrony with the environmental day-night cycle and uses internal signals to keep clocks in other tissues aligned. Work in cell cultures uncovered cyclic changes in tissue oxygenation that may serve to reset and synchronize circadian clocks. Here we show in healthy humans, following a randomized controlled single-blind counterbalanced crossover study design, that one-time exposure to moderate ambient hypoxia (FiO2 ~15%, normobaric) for ~6.5 h during the early night advances the dim-light onset of melatonin secretion by 9 min (95% CI: 1-16 min). Exposure to moderate hypoxia may thus be strong enough to entrain circadian clocks to a 24-h cycle in the absence of other entraining cues. Together, the results provide direct evidence for an interaction between the body's hypoxia-sensing pathway and circadian clocks. The finding offers a mechanism through which behaviors that change tissue oxygenation (e.g., exercise and fasting/eating) can affect circadian timing and through which hypoxia-related diseases (e.g., obstructive sleep apnea and chronic obstructive pulmonary disease) can result in circadian misalignment and associated pathologies. Trial Registration: Registration number: DRKS00023387; German Clinical Trials Register: http://www.drks.de.

Oral antioxidant edaravone protects against cognitive deficits induced by chronic hypobaric hypoxia at high altitudes

Chronic hypobaric hypoxia at high altitudes can impair cognitive functions, especially causing deficits in learning and memory, which require therapeutic intervention. Here, we showed that mice subjected to hypobaric hypoxia (simulating an altitude of 5000 m) for one month experienced significant cognitive impairment, accompanied by increased biomarker levels of oxidative stress in the brain and blood. Oral administration of a novel formulation of edaravone, a free radical scavenger approved for the treatment of ischaemic stroke and amyotrophic lateral sclerosis, significantly alleviated oxidative stress and cognitive impairments caused by chronic hypobaric hypoxia. Furthermore, oral edaravone treatment also mitigated neuroinflammation and restored hippocampal neural stem cell exhaustion. Additionally, periostin (Postn) is vital in the cognitive deficits caused by chronic hypobaric hypoxia and may be a molecular target of edaravone. In conclusion, our results suggest that oxidative stress plays a crucial role in the cognitive deficits caused by chronic hypobaric hypoxia and that oral edaravone is a potential medicine for protecting against cognitive deficits caused by chronic hypobaric hypoxia in high-altitude areas.

Hepatic BMAL1 and HIF1α regulate a time-dependent hypoxic response and prevent hepatopulmonary-like syndrome

The transcriptional response to hypoxia is temporally regulated, yet the molecular underpinnings and physiological implications are unknown. We examined the roles of hepatic Bmal1 and Hif1α in the circadian response to hypoxia in mice. We found that the majority of the transcriptional response to hypoxia is dependent on either Bmal1 or Hif1α, through shared and distinct roles that are daytime determined. We further show that hypoxia-inducible factor (HIF)1α accumulation upon hypoxia is temporally regulated and Bmal1 dependent. Unexpectedly, mice lacking both hepatic Bmal1 and Hif1α are hypoxemic and exhibit increased mortality upon hypoxic exposure in a daytime-dependent manner. These mice display mild liver dysfunction with pulmonary vasodilation likely due to extracellular signaling regulated kinase (ERK) activation, endothelial nitric oxide synthase, and nitric oxide accumulation in lungs, suggestive of hepatopulmonary syndrome. Our findings indicate that hepatic BMAL1 and HIF1α are key time-dependent regulators of the hypoxic response and can provide molecular insights into the pathophysiology of hepatopulmonary syndrome.

Immune consequences of exercise in hypoxia: A narrative review

Immune outcomes are key mediators of many health benefits of exercise and are determined by exercise type, dose (frequency/duration, intensity), and individual characteristics. Similarly, reduced availability of ambient oxygen (hypoxia) modulates immune functions depending on the hypoxic dose and the individual capacity to respond to hypoxia. How combined exercise and hypoxia (e.g., high-altitude training) sculpts immune responses is not well understood, although such combinations are becoming increasingly popular. Therefore, in this paper, we summarize the impact on immune responses of exercise and of hypoxia, both independently and together, with a focus on specialized cells in the innate and adaptive immune system. We review the regulation of the immune system by tissue oxygen levels and the overlapping and distinct immune responses related to exercise and hypoxia, then we discuss how they may be modulated by nutritional strategies. Mitochondrial, antioxidant, and anti-inflammatory mechanisms underlie many of the adaptations that can lead to improved cellular metabolism, resilience, and overall immune functions by regulating the survival, differentiation, activation, and migration of immune cells. This review shows that exercise and hypoxia can impair or complement/synergize with each other while regulating immune system functions. Appropriate acclimatization, training, and nutritional strategies can be used to avoid risks and tap into the synergistic potentials of the poorly studied immune consequences of exercising in a hypoxic state.

Exome sequencing in extreme altitude mountaineers identifies pathogenic variants in RTEL1 and COL6A1 previously associated with respiratory failure

Adaptation of humans to challenging environmental conditions, such as extreme temperature, malnutrition, or hypoxia, is an interesting phenomenon for both basic and applied research. Identification of the genetic factors contributing to human adaptation to these conditions enhances our understanding of the underlying molecular and physiological mechanisms. In our study, we analyzed the exomes of 22 high altitude mountaineers to uncover genetic variants contributing to hypoxic adaptation. To our surprise, we identified two putative loss-of-function variants, rs1385101139 in RTEL1 and rs1002726737 in COL6A1 in two extremely high altitude (personal record of more than 8500 m) professional climbers. Both variants can be interpreted as pathogenic according to medical geneticists' guidelines, and are linked to inherited conditions involving respiratory failure (late-onset pulmonary fibrosis and severe Ullrich muscular dystrophy for rs1385101139 and rs1002726737, respectively). Our results suggest that a loss of gene function may act as an important factor of human adaptation, which is corroborated by previous reports in other human subjects.

Circadian Clock and Hypoxia

The timing of life on Earth is remarkable: between individuals of the same species, a highly similar temporal pattern is observed, with shared periods of activity and inactivity each day. At the individual level, this means that over the course of a single day, a person alternates between two states. They are either upright, active, and communicative or they lie down in a state of (un)consciousness called sleep where even the characteristic of neuronal signals in the brain shows distinctive properties. The circadian clock governs both of these time stamps-activity and (apparent) inactivity-making them come and go consistently at the same approximate time each day. This behavior thus represents the meeting of two pervasive systems: the circadian clock and metabolism. In this article, we will describe what is known about how the circadian clock anticipates daily changes in oxygen usage, how circadian clock regulation may relate to normal physiology, and to hypoxia and ischemia that can result from pathologies such as myocardial infarction and stroke.

Hypoxia and Activation of Neutrophil Degranulation-Related Genes in the Peripheral Blood of COVID-19 Patients

Severe COVID-19 is characterized by systematic hyper-inflammation and subsequent damage to various organs. Therefore, it is critical to trace this cascade of hyper-inflammation. Blood transcriptome has been routinely utilized in the interrogation of host immune response in COVID-19 and other infectious conditions. In this study, consensus gene dysregulation in the blood was obtained from 13 independent transcriptome studies on COVID-19. Among the up-regulated genes, the most prominent functional categories were neutrophil degranulation and cell cycle, which is clearly different from the classical activation of interferon signaling pathway in seasonal flu. As for the potential upstream causal factors of the atypical gene dysregulation, systemic hypoxia was further examined because it is much more widely reported in COVID-19 than that in seasonal flu. It was found that both physiological and pathological hypoxia can induce activation of neutrophil degranulation-related genes in the blood. Furthermore, COVID-19 patients with different requirement for oxygen intervention showed distinctive levels of gene expression related to neutrophil degranulation in the whole blood, which was validated in isolated neutrophils. Thus, activation of neutrophil degranulation-related genes in the blood of COVID-19 could be partially attributed to hypoxia. Interestingly, similar pattern was also observed in H1N1 infection (the cause of Spanish flu) and several other severe respiratory viral infections. As for the molecular mechanism, both HIF-dependent and HIF-independent pathways have been examined. Since the activation of neutrophil degranulation-related genes is highly correlated with disease severity in COVID-19, early detection of hypoxia and active intervention may prevent further activation of neutrophil degranulation-related genes and other harmful downstream hyper-inflammation. This common mechanism is applicable to current and future pandemic as well as the severe form of common respiratory infection.

Disrupted circadian rhythms in the plateau pika

The plateau pika (Ochotona curzoniae) is the most populous mammal on the 'third pole', the Qinghai-Tibet Plateau, and is presumed to have inhabited the region before the plateau rose up from sea level. Herein we discuss the disrupted circadian rhythm in the plateau pika and the gene polymorphism behind this phenotype, placing these findings in the broader context of circadian rhythms under extreme conditions.

Dexamethasone prophylaxis protects from acute high-altitude illness by modifying the peripheral blood mononuclear cell inflammatory transcriptome

Acute high-altitude (HA) exposure can induce several pathologies. Dexamethasone (DEX) can be taken prophylactically to prevent HA disease, but the mechanism by which it acts in this setting is unclear. We studied the transcriptome of peripheral blood mononuclear cells (PBMCs) from 16 subjects at low altitude (LA, 225 m) and then 3 days after acute travel to HA (3500 m) during the India-Leh-Dexamethasone-Expedition-2020 (INDEX2020). Half of the participants received oral DEX prophylaxis 4 mg twice daily in an unblinded manner, starting 1 day prior to travel to HA, and 12 h prior to the first PBMC collection. PBMC transcriptome data were obtained from 16 subjects, half of whom received DEX. The principal component analysis demonstrated a clear separation of the groups by altitude and treatment. HA exposure resulted in a large number of gene expression changes, particularly in pathways of inflammation or the regulation of cell division, translation, or transcription. DEX prophylaxis resulted in changes in fewer genes, particularly in immune pathways. The gene sets modulated by HA and DEX were distinct. Deconvolution analysis to assess PBMC subpopulations suggested changes in B-cell, T-cell, dendritic cell, and myeloid cell numbers with HA and DEX exposures. Acute HA travel and DEX prophylaxis induce significant changes in the PBMC transcriptome. The observed benefit of DEX prophylaxis against HA disease may be mediated by suppression of inflammatory pathways and changing leukocyte population distributions.

Clinical and biochemical indices of people with high-altitude experience linked to acute mountain sickness

BACKGROUND

Acute mountain sickness (AMS) is a major health issue for people travelling to high altitudes. This study was designed to comprehensively evaluate the changes in clinical characteristics and biochemical indices of high-altitude travelers and determine whether these changes were associated with AMS.

METHODS

A total of 14 clinical indices and 52 biochemical indices were determined in 22 subjects before and during acute high-altitude exposure. Six hours after passive ascent to 3648 m (Lhasa, China), the Lake Louise Scoring (LLS) system 2018 was used to assess AMS, which was defined as headache with a total LLS ≥3.

RESULTS

Before travelling to high altitudes, uric acid (UA), platelet distribution width (PDW), mitral peak E velocity (MVE), and ejection fraction (EF) were significantly higher in AMS-resistant individuals than in AMS-susceptible ones (all p < 0.05). A good predictive value of UA (0.817, 95% CI: 0.607-1.000) and PDW (0.844, 95% CI: 0.646-1.000) for AMS-susceptible subjects was found. With high-altitude experience, 14 subjects were diagnosed as having AMS. Compared with non-AMS, the changes in UA and number of neutrophils in AMS presented a significant difference (all p < 0.05). The high-altitude-induced changes in UA, area under the curve, specificity, and sensitivity for identifying AMS were 0.883 (95% CI: 0.738-1.000), 83.30%, and 90.00%, respectively.

CONCLUSION

Human presents a compensatory physiological and biochemical response to high-altitude travel at early phase. The UA concentration before travel and its trend with high-altitude experience exhibited good performance for identifying AMS.