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• Role of intermittent hypoxic expression of Hypoxia Inducible Factors and NFKB in endurance exercise
  Atif A Baig
  Published on: 17 November 2014

• Published on: 17 November 2014

  Role of intermittent hypoxic expression of Hypoxia Inducible Factors and NFKB in endurance exercise

  • Atif A Baig, Medical Researcher
  • Other Contributors:
    • Sulaiman I, Faruk R, Aliya S, Zahri MK, Uday YH Abdullah, Manaf A, Zubaidi AL

  We have read the respective article and we agreed with all great findings. Nevertheless, we wish to emphasize the need to address the role of some molecular and physiological markers that may elaborate and possibly support the findings of the study. Intermittent hypoxia exposure can enhance the generation of red blood cells, which may consequentially increase hemoglobin concentration and hematocrit depending on the model...

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  We have read the respective article and we agreed with all great findings. Nevertheless, we wish to emphasize the need to address the role of some molecular and physiological markers that may elaborate and possibly support the findings of the study. Intermittent hypoxia exposure can enhance the generation of red blood cells, which may consequentially increase hemoglobin concentration and hematocrit depending on the model of IHE exposure and its effect on serum hypoxia inducible factors (HIF-1 alpha, HIF-2alpha and HIF-3 alpha), erythropointin (EPO) levels and some signaling pathways (such as those mediated by the nuclear factor-kappa light chain B: NF-kB for stress and inflammation examinations) [1]. Hypoxia-inducible factors (HIF-1 alpha, HIF-2alpha and HIF-3alpha) are transcriptional regulatory factors that orchestrate cellular responses to hypoxia and regulates oxygen homeostasis[2]. However hypoxic induction of HIF-1alpha and HIF-2alpha leads to the transcriptional activation of HIF- 3alpha expression as a target gene, which in turn is involved in the reverse negative regulation of other HIFs activities [3]. Less intramuscular hypoxic shifts of metabolic parameters (lactate and pyruvate concentration, lactate/pyruvate and NAD/NADH ratios) after IHT [4] are accompanied by marked decrease of HIF-3alpha expression and increase in the resistance to physical exercise (with up to 70% increase endurance and 25% oxygen pressure in muscle). This indicates the importance of establishing the changes in HIFs system included in this study. Successive normobaric hypoxia-reoxygenation cycles in intermittent hypoxia exposure is associated with generation of cytosolic reactive oxygen species (ROS) which aid in transduction of cellular signals by stabilizing the HIF alpha subunits and promoting its translocation to nucleus and subsequent dimeruization with its alpha subunit to form complexes that binds to hypoxia response element (HRE) to express certain genes (e.g EPO, VEGF, NOS/HO-1 etc) that mediate cellular oxygen adaptation mechanism that will in the long run reflect on exercise performance and endurance[5]. Erythropoiesis is a classic physiologic response to hypoxia that is mediated by the HIFs through inducing cell-type specific gene expression changes that result in increased erythropoietin (EPO) production in kidney, liver and facilitates erythroid progenitor maturation and proliferation. HIF-2 is the main transcription factor that regulates EPO synthesis in the kidney and liver and plays a critical role in the regulation of intestinal iron uptake [6]. Although the heart rate during graded swim test was found to be the same before and after IHE, cardiac responses to hypoxia are quite dependent on carotid body function, which is deeply affected by its oxygen sensing capability. Tissue specificity of HIF-1 homolog (HIF-2alpha) may play an important role in the stable heart rate observed because irrespective of the wide expression of HIF-1 in many cells, including the carotid body glomus cells, hypoxia elicits different responses in different cell types [7]. Additionally, endurance training and intermittent hypoxia are effective preventive strategies against stress induced cardiac and mitochondrial dysfunction. There is need to support the findings of normal heart rate with further studies on signaling pathways, consequent metabolic and redox remodeling associated with a cardioprotective phenotype. This could be achieved by analyzing the myocardial heat shock proteins, cyclooxygenase-2 activity, endoplasmic reticulum stress proteins, nitric oxide production, myocardial antioxidant capacity, sarcolemmal and mitochondrial adenosine triphosphate (ATP)-sensitive potassium channels [8]. In order to obtain a viable result, the inclusion and exclusion criteria must address previous exposure ti intermittent hypobaric hypoxia as it has been reported to decreases myocardial infarction size, reduces the number of ventricular arrhythmias, and improves the recovery of cardiac contractile function against acute ischemia-reperfusion (I/R) injury [9]. The crucial role of mitochondria in cellular energetics, metabolism and intracellular signaling processes regulating cell death and survival [10] has made it important to assess the role of mitochondria in the 4.8% and 1.6% performance declines observed in middle-distance (MD) and long-distance (LD) subjects as reported by the study.

  References: [1]. Zhang, C. Y., Zhang, J. X., L?, X. T., & Li, B. Y. (2009). Effects of intermittent hypoxic exposure on the parameter of erythrocyte and serum hypoxia inducible factor-1 alpha and erythropoietin levels. Xi bao yu fen zi mian yi xue za zhi= Chinese journal of cellular and molecular immunology, 25(10), 932. [2]. Semenza, G. (2009). Regulation of oxygen homeostasis by hypoxia- inducible factor 1. Physiology, 24:97-106. [3]. Hara, S., Hamada, J., Kobayashi, C., Kondo, Y., Imura, N. (2001). Expression and characterization of hypoxia-inducible factor (HIF)-3? in human kidney: suppression of HIF-mediated gene expression by HIF-3?. Biochemical and Biophysical Research Communications, 287:808-813. [4]. Semenza, G.L. (2001). HIF-1 O2 and the 3 PHDs: how animal cells signal hypoxia to the nucleus. Cell 107, 1-3. [5]. Mankovskaya, I., Drevitskaya, T., Dosenko, V., Gavenauskas, B., Moiseenko E. (2006). Expression of transcriptional factor HIF subunits in rat tissues under acute and intermittent hypoxia. Hypoxia Medical Journal, 35:1-2. [6]. Haase, V. H. (2013). Regulation of erythropoiesis by hypoxia- inducible factors. Blood reviews, 27(1), 41-53. [7]. Lahiri, S., Di Giulio, C., & Roy, A. (2002). Lessons from chronic intermittent and sustained hypoxia at high altitudes. Respiratory physiology & neurobiology, 130(3), 223-233. [8]. Kavazis, A.N. (2009). Exercise preconditioning of themyocardium. Sports Med, 11:923-35 [9]. Ostadal, B. and Kolar, F. (2007). Cardiac adaptation to chronic high- altitude hypoxia: beneficial and adverse effects. Respir Physiol Neurobiol. 2(3):224-36. [10]. Ascensao A, Magalhaes J, Soares JM, et al. Moderate endurance training prevents doxorubicin-induced in vivo mitochondriopathy and reduces the development of cardiac apoptosis. Am J Physiol Heart Circ Physiol 2005;2:H722-31.

  Conflict of Interest:

  None declared

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  Conflict of Interest:
  None declared.

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