Plasma Proteomics of Ladakhi Natives Reveal Functional Regulation Between Renin–Angiotensin System and eNOS–cGMP Pathway

Human adaptation to high altitude: a review of convergence between genomic and proteomic signatures

Both genomics- and proteomics-based investigations have identified several essential genes, proteins, and pathways that may facilitate human adaptive genotype/phenotype in a population-specific manner. This comprehensive review provides an up-to-date list of genes and proteins identified for human adaptive responses to high altitudes. Genomics studies for indigenous high-altitude populations like Tibetans, Andeans, Ethiopians, and Sherpas have identified 169 genes under positive natural selection. Similarly, global proteomics studies have identified 258 proteins (± 1.2-fold or more) for Tibetan, Sherpa, and Ladakhi highlanders. The primary biological processes identified for genetic signatures include hypoxia-inducible factor (HIF)-mediated oxygen sensing, angiogenesis, and erythropoiesis. In contrast, major biological processes identified for proteomics signatures include 14–3-3 mediated sirtuin signaling, integrin-linked kinase (ILK), phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT), and integrin signaling. Comparing genetic and protein signatures, we identified 7 common genes/proteins (HBB/hemoglobin subunit beta, TF/serotransferrin, ANGPTL4/angiopoietin-related protein 4, CDC42/cell division control protein 42 homolog, GC/vitamin D-binding protein, IGFBP1/insulin-like growth factor-binding protein 1, and IGFBP2/insulin-like growth factor-binding protein 2) involved in crucial molecular functions like IGF-1 signaling, LXR/RXR activation, ferroptosis signaling, iron homeostasis signaling and regulation of cell cycle. Our combined multi-omics analysis identifies common molecular targets and pathways for human adaptation to high altitude. These observations further corroborate convergent positive selection of hypoxia-responsive molecular pathways in humans and advocate using multi-omics techniques for deciphering human adaptive responses to high altitude.

Proteomic and clinical biomarkers for acute mountain sickness in a longitudinal cohort

Ascending to high-altitude by non-high-altitude natives is a well-suited model for studying acclimatization to extreme environments. Acute mountain sickness (AMS) is frequently experienced by visitors. The diagnosis of AMS mainly depends on a self-questionnaire, revealing the need for reliable biomarkers for AMS. Here, we profiled 22 AMS symptom phenotypes, 65 clinical indexes, and plasma proteomic profiles of AMS via a combination of proximity extension assay and multiple reaction monitoring of a longitudinal cohort of 53 individuals. We quantified 1069 proteins and validated 102 proteins. Via differential analysis, machine learning, and functional association analyses. We found and validated that RET played an important role in the pathogenesis of AMS. With high-accuracies (AUCs > 0.9) of XGBoost-based models, we prioritized ADAM15, PHGDH, and TRAF2 as protective, predictive, and diagnostic biomarkers, respectively. Our findings shed light on the precision medicine for AMS and the understanding of acclimatization to high-altitude environments.

Estrogen receptor (ESR1 and ESR2)-mediated activation of eNOS-NO-cGMP pathway facilitates high altitude acclimatization

Higher levels of circulatory nitric oxide (NO) and NO metabolites reportedly facilitate high altitude acclimatization. But the underlying factors and molecular pathways promoting NO production at high altitude has been poorly characterized. Studying healthy lowlanders at sea level (C, lowlander) and high altitude (3500 m, after day 1, 4 and 7 of ascent), we report higher protein levels of eNOS and eNOS^Ser1177, higher plasma levels of BH₄, NOx (nitrate and nitrites), cGMP and lower levels of endogenous eNOS inhibitor ADMA during healthy high altitude acclimatization. Our qRT-PCR-based gene expression studies identified higher levels of eNOS/NOS3 mRNA along with several other eNOS pathway genes like CALM1, SLC7A1 and DNM2. In addition, we observed higher mRNA levels of estrogen (E2) receptors ERα/ESR1 and ERβ/ESR2 at high altitude that transcriptionally activates NOS3. We also observed higher mRNA level of membrane receptor ERBB2 that phosphorylates eNOS at Ser1177 and thus augments NO availability. Evaluating E2 biosynthesis at high altitude, we report higher plasma levels of CYP11A1, CYP19A1, E2, lower levels of testosterone (T) and T/E2 ratio as compared to sea level. Correlation studies revealed moderate positive correlation between E2 and NOx (R = 0.68, p = 0.02) after day 4 and cGMP (R = 0.69, p = 0.02) after day 7 at high altitude. These findings suggest a causative role of E2 and its receptors ESR1 and ESR2 in augmenting eNOS activity and NO availability during healthy high altitude ascent. These results will aid in better understanding of NO production during hypobaric hypoxia and help in designing better high altitude acclimatization protocols.