Abstract
Introduction: High altitude is a natural laboratory, within which the clinical study of human physiological response to hypobaric hypoxia (HH) is possible. Failure in the response results in progressive hypoxemia, inflammation, and increased tissue oxidative stress (OxS). Thus, investigating temporal changes in key transcription factors (TFs) HIF-1α, HIF-2α, NF-κB and NRF2 mRNA levels, relative to OxS and inflammatory markers, may reveal molecular targets which contrast deleterious effects of hypoxia.
Material and Methods: Biological samples and clinical data from 15 healthy participants were collected at baseline and after rapid, passive ascent to 3830m (24h and 72h). Gene expression was assessed by qPCR and ROS generation was determined by EPR spectroscopy. Oxidative damage and cytokine levels were estimated by immuno or enzymatic methods. The effect of HH exposure on the different clinical parameters and gene expression over time was evaluated by analysis of variance (ANOVA) for repeated measures of ΔCt for gene mRNA levels; comparison of two time- points was carried out by means of paired samples t-test and Bonferroni correction was applied. Data were analyzed using SPSS 23.0. All P-values were two sided, and differences were considered significant at P<0.05.
Results: Hypoxia transiently enhanced HIF-1α mRNA levels over time reaching a peak after 24h. Whereas, HIF-2α and NRF2 mRNA levels increased over time. In contrast, the NF-κB mRNA levels remained unchanged. Plasma levels of IL-1β and IL-6 also remained within normal ranges. ROS production rate and markers of OxS damage were significantly increased over time.
Discussion: The analysis of TF-gene expression suggests that HIF-1α is a lead TF during sub- acute HH exposure. The prolongation of the HH exposure led to a switch between HIF-1α and HIF-2α/NRF2, suggesting the activation of new pathways. These results provide new insights regarding the temporal regulation of TFs, inflammatory state, and ROS homeostasis involved in human hypoxic response, potentially relevant to the mediation of diseases that induce a hypoxic state.