siRNA-induced silencing of hypoxia-inducible factor 3α (HIF3α) increases endurance capacity in rats.

Molecular mechanisms of adaptation to exercise despite a large number of studies remain unclear. One of the crucial factors in this process is hypoxia inducible factor (HIF) that regulates transcription of many target genes encoding proteins that are implicated in molecular adaptation to hypoxia. Experiments were conducted on 24 adult male Fisher rats. Real-time PCR analysis was performed for quantitative evaluation of Hif3α, Igf1, Glut-4 and Pdk-1 in m. gastrocnemius, m. soleus, in lung and heart tissues. Mitochondrial respiratory function and electron microscopy were performed. Knockdown of Hif3α using siRNA increases time of swimming to exhaustion by 1.5 times. Level of mitochondrial NAD- and FAD-dependent oxidative pathways is decreased, however efficiency of phosphorylation is increased after Hif3α siRNA treatment. Expression of HIF target genes in muscles was not changed significantly, except for increasing of Pdk-1 expression in m. soleus by 2.1 times. More prominent changes were estimated in lung and heart: Igf1 gene expression was increased by 32.5 and 37.5 times correspondingly. Glut4 gene expression in lungs was increased from undetected level till 0.3 rel. units and by 84.2 times in heart. Level of Pdk1 gene expression was increased by 249.2 in lungs and by 35.1 times in hearts, correspondingly. Some destructive changes in muscle tissue were detected in animals with siRNA-inducing silencing of Hif3α.

[The effect of uridine on the endurance of animals with different resistance to physical stress: the role of mitochondrial ATP-dependent potassium channel].

The effect of a metabolic precursor of natural activator of mitochondrial ATP-dependent potassium channel (mitochondrial K+(ATP))--uridine on animal's endurance to physical stress was studied. The endurance was determined by recording the time period during which the rat loaded with a plummet of 20% of body weight can swim until physical exhaustion at 32 degrees C. It was found that highly resistant animals swam until exhaustion for 7.40 ± 0.35 min, whereas low resistant rats hold out 2.07 ± 0.10 min only. The injection of uridine influenced the swimming time of the animals, increasing it twofold in low-resistant rats. The effect of uridine was decreased by injection of inhibitors of mitochondrial K+(ATP) channel. It was found that the injection of uridine into low resistant rats increased the rate of potassium transport in mitochondria isolated from liver of these rats, and inhibitors of the channel prevent the channel activating effect of uridine. The role of mitochondrial K+(ATP) cannel in the formation of animal's resistance to physical stress and protection of tissues from hypoxia is discussed.

HIF-3α mRNA expression changes in different tissues and their role in adaptation to intermittent hypoxia and physical exercise.

The role of HIF-3α in response to intermittent hypoxia and physical exercise was investigated in Fisher rats using reverse transcription, real-time PCR and RNA interference. Under acute hypoxia (12% O(2), 2h), the level of HIF-1α, HIF-2α, and HIF-1ß mRNA did not significantly change in the heart, lung, kidney and muscle tissues, but HIF-3α mRNA expression was strongly elevated in all tissues investigated. Five weeks of intermittent hypoxic training (IHT) led to an increase of HIF-3α mRNA in all studied tissues, but under the influence of acute hypoxia after IHT, the expression of HIF-3α mRNA did not increase in all tissues excluding skeletal muscle. Thus, IHT reduced the effect of acute hypoxia on HIF-3α mRNA expression in the heart, lung, and kidney. The expression of HIF-3α in skeletal muscle at endurance (swimming) training (ET) in combination with IHT was 6.2 times lower compared to the group with ET but without IHT and 3.3 times lower (P<0.05) compared to untrained control. After swimming training with IHT, rats demonstrated the highest level of physical endurance. RNA interference of HIF-3α significantly decreased the level of HIF-3α mRNA in both muscles investigated: by 2.6 times in m. soleus (P<0.03) and by 2.1 times in m. gastrocnemius (P<0.05) and elevated the physical endurance of rats by 50% (P<0.05) compared to control. Thus, the HIF-3α subunit is an essential member of hypoxic response. It plays a negative role in the adaptation to hypoxia, because the inhibition of HIF-3α expression leads to an increase in physical endurance.