Expression of TSPO and HIF-1α genes as predictors of the organism’s resistance to hyperthermia

BACKGROUND: One of the key transcriptional regulators that determine the body’s resistance to hypoxia is the hypoxia-inducible factor HIF-1α, the study of the role of which in the body’s resistance to extreme influences can justify new directions in medical technologies for its increase. The body’s resistance to hypoxia largely determines the resistance to other critically significant influences (hyperthermia, hypothermia, hyperbaria, ionizing radiation, chemicals, etc.). However, it was not possible to find a quantitative assessment of this effect in the literature studied by us, which served as the basis for this study.

AIM: To assess the role of the level of expression of the hypoxia-inducible factor HIF-1α in various tissues of laboratory animals in increasing the resistance of animals to the effects of extreme hyperthermia.

MATERIALS AND METHODS: The study was carried out on outbred white laboratory rats obtained from the Rappolovo nursery weighing 180–220 g. For the study, preliminary laboratory animals were tested for an individual level of resistance to hyperthermia (40 animals), which made it possible to form experimental groups from highly resistant and low resistant to extreme animal influences. The definition of resistance to hyperthermia was carried out by the rate of increase in rectal temperature in animals during 20-minute air hyperthermia (40°C). 4 groups of laboratory animals were formed (2 each with high and low resistance), half of which were exposed to a pronounced adverse effect of hyperthermia. Biological material was taken from all animals (whole blood, plasma, tissues of the heart, liver, kidneys, brain), in which the expression of the HIF-1α and TSPO genes (housekeeping gene) was determined by the Real-Time-PCR method. Statistical processing of the obtained data was carried out using the ANOVA analysis of variance.

RESULTS: It has been established that the level of resistance of animals to hyperthermia is largely determined by their genetic characteristics. Even under thermocomfort conditions, the expression of the TSPO “housekeeping” gene in animals with a high level of resistance to hyperthermia differed with a high degree of reliability from low-resistant animals (in the kidneys, liver, and brain, on average, by 40–60%; in the heart, by 25%). The expression values of this gene, determined in whole blood or plasma, make it possible to differentiate groups of animals according to the level of resistance to hyperthermia. A similar relationship between animals with high and low resistance is also observed in tissues obtained immediately after thermal exposure.

CONCLUSIONS: The main organ that provides a high level of resistance to both hypoxia and hyperthermia associated with the basic (under thermal comfort conditions) expression of HIF-1α is the brain. The expression of the hypoxia-inducible factor in it is more than 300 times higher than the expression of the “housekeeping” genes. The second most important organ is the liver, in which HIF-1α expression activity is more than 15 times higher than the expression of “housekeeping” genes. Under conditions of hyperthermia, low-resistant animals show a compensatory-adaptive reaction associated with the activation of hypoxic defense mechanisms in blood cells, kidneys, and liver, in the absence of such a reaction in the tissues of the heart and brain. Animals highly resistant to hyperthermia were characterized by a significant (30 times) increase in the relative activity of HIF-1α expression mechanisms in blood cells, 2.5 times in liver cells, and a decrease in expression by 25% in the kidneys and almost 2 times in brain tissues. A high level of basal expression of the transcription factor HIF-1α under everyday (thermocomfortable) conditions may be a predictor of a high level of resistance to hyperthermia in a given animal. Probably, to increase the body’s resistance to extreme impacts, it is advisable to use medical technologies that increase the level of HIF-1α expression in everyday (thermocomfortable) conditions in key tissues — the brain, liver, and myocardium.