About this Research Topic
This Research Topic is part of the Physiological and Pathological Responses to Hypoxia and High Altitude series:
Physiological and Pathological Responses to Hypoxia and High Altitude
Physiological and Pathological Responses to Hypoxia and High Altitude, Volume II
Hypoxia is commonly defined as the reduced availability of oxygen in the tissues produced by different causes, which include reduction of atmospheric PO2 as in high altitudes and secondary to pathological conditions such as sleep breathing and pulmonary disorders, anemia, and cardiovascular alterations leading to inadequate transport, delivery, and exchange of oxygen between capillaries and cells. Nowadays, it has been shown that hypoxia plays a crucial role in several human pathologies, including respiratory, cardiovascular, renal, and neurological diseases in fetal, young, and adult life and is implicated in exercise and sports performance alteration. It has been proposed that the impairment in exercise performance may be associated to both convective and diffusive components of the oxygen transport. Notably, it has been estimated that there is a decrease in the maximal O2 uptake (VO2max) during exercise near 6-7% per 1,000 m increasing altitude.
Several mechanisms contribute to maintaining oxygen homeostasis. Indeed, all cells respond and adapt to hypoxia, but only a few of them may detect hypoxia and initiate a cascade of signals to produce a functional systemic response. In mammals, oxygen detection mechanisms have been studied in erythropoietin-producing cells, chromaffin cells, bulbar and cortical neurons, pulmonary neuroepithelial cells, smooth muscle cells of pulmonary arteries, and chemoreceptor cells in the carotid and aortic bodies. While the precise mechanism underpinning oxygen, sensing is not completely knowing. Several molecular entities have been proposed as oxygen sensors (i.e., Hem proteins, ion channels, NADPH oxidase, mitochondrial cytochrome oxidase, etc). Cellular adaptation to hypoxia is mediated by the oxygen-sensitive transcription factor, hypoxia-inducible factor-1, which can induce up or down-regulation of different genes to cope with the cellular effects related to a reduction in oxygen levels. Short-term responses to hypoxia included chemoreceptor-mediated reflex ventilatory and hemodynamic adaptations to manage the low oxygen while prolonged exposures to hypoxia elicit sustained physiological responses including switch from aerobic to anaerobic metabolism, vascularization, and enhancement of blood O2 carrying capacity, which are related to the human performance in high altitude. However, the underlying mechanisms of the impairment in exercise human performance during exposure to hypoxia are not entirely understood. Acute transient depressions of the chemoreflex drive and peripheral chemoreceptor denervation have been shown to be implicated in ventilation during exercise. Nevertheless, the evidence is scary and controversial. The focus of this Research Topic will be to provide an up-to-date vision on the current knowledge on oxygen sensing mechanism, physio a and pathological responses to acute or chronic hypoxia and cellular/tissue/organ adaptations to hypoxic environment.
Physiological and Pathological Responses to Hypoxia and High Altitude
Physiological and Pathological Responses to Hypoxia and High Altitude, Volume II
Hypoxia is commonly defined as the reduced availability of oxygen in the tissues produced by different causes, which include reduction of atmospheric PO2 as in high altitudes and secondary to pathological conditions such as sleep breathing and pulmonary disorders, anemia, and cardiovascular alterations leading to inadequate transport, delivery, and exchange of oxygen between capillaries and cells. Nowadays, it has been shown that hypoxia plays a crucial role in several human pathologies, including respiratory, cardiovascular, renal, and neurological diseases in fetal, young, and adult life and is implicated in exercise and sports performance alteration. It has been proposed that the impairment in exercise performance may be associated to both convective and diffusive components of the oxygen transport. Notably, it has been estimated that there is a decrease in the maximal O2 uptake (VO2max) during exercise near 6-7% per 1,000 m increasing altitude.
Several mechanisms contribute to maintaining oxygen homeostasis. Indeed, all cells respond and adapt to hypoxia, but only a few of them may detect hypoxia and initiate a cascade of signals to produce a functional systemic response. In mammals, oxygen detection mechanisms have been studied in erythropoietin-producing cells, chromaffin cells, bulbar and cortical neurons, pulmonary neuroepithelial cells, smooth muscle cells of pulmonary arteries, and chemoreceptor cells in the carotid and aortic bodies. While the precise mechanism underpinning oxygen, sensing is not completely knowing. Several molecular entities have been proposed as oxygen sensors (i.e., Hem proteins, ion channels, NADPH oxidase, mitochondrial cytochrome oxidase, etc). Cellular adaptation to hypoxia is mediated by the oxygen-sensitive transcription factor, hypoxia-inducible factor-1, which can induce up or down-regulation of different genes to cope with the cellular effects related to a reduction in oxygen levels. Short-term responses to hypoxia included chemoreceptor-mediated reflex ventilatory and hemodynamic adaptations to manage the low oxygen while prolonged exposures to hypoxia elicit sustained physiological responses including switch from aerobic to anaerobic metabolism, vascularization, and enhancement of blood O2 carrying capacity, which are related to the human performance in high altitude. However, the underlying mechanisms of the impairment in exercise human performance during exposure to hypoxia are not entirely understood. Acute transient depressions of the chemoreflex drive and peripheral chemoreceptor denervation have been shown to be implicated in ventilation during exercise. Nevertheless, the evidence is scary and controversial. The focus of this Research Topic will be to provide an up-to-date vision on the current knowledge on oxygen sensing mechanism, physio a and pathological responses to acute or chronic hypoxia and cellular/tissue/organ adaptations to hypoxic environment.
Keywords: adaptation, acclimatization, oxygen homeostasis, pathological response, hypoxia
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