Expression of the hypoxia-inducible factor as a predictor of the resistance of the organism of laboratory animals to hypoxia

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.

AIM: To evaluate the quantitative contribution of the level of expression of the hypoxia-inducible factor HIF-1α in various tissues of laboratory animals to the increase in the resistance of animals to the effects of hypoxic hypoxia.

MATERIALS AND METHODS: The study was carried out on outbred white laboratory rats obtained from the Rappolovo nursery weighing 180–220 g. To conduct the study, animals were previously tested for an individual level of resistance to hypoxia, which made it possible to form experimental groups from highly resistant and low resistant animals. 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. Total RNA was isolated from the test material by affinity sorption,synthesis of the first strand of cDNA, amplification, followed by determination of the expression level of the HIF-1α gene in rats was carried out according to the instructions and the manufacturer’s protocol by PCR with detection of the accumulation of reaction products in real time (Real-Time PCR) using a CFX-96 detecting amplifier (Bio-Rad, USA) and specific primers and probes for the HIF-1α gene in rats (DNK-Sintez, Russia). 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 hypoxia is largely determined by their genetic characteristics. Even under normoxic conditions, the expression of the TSPO housekeeping gene in animals with a high level of resistance to hypoxia differed with a high degree of reliability from low-resistance animals (in the kidneys, liver, and brain, on average, by 40–60%; in the heart, by 25%). The values of the expression of this gene, determined in whole blood or plasma, make it possible to differentiate groups of animals according to the level of resistance to hypoxia. A similar ratio between animals with high and low resistance is also observed in tissues obtained immediately after hypoxic exposure. An analysis of the reaction of the genomic regulation system to extreme exposure showed that it increased the expression of the TSPO gene by 1.6–2 times equally in all tissues, regardless of the level of animal resistance. For the HIF-1α gene, similar patterns were found, but the severity of their manifestations is more and significant.

CONCLUSIONS: The main organ that provides a high level of resistance to hypoxia associated with the basic (under normoxic 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 moderate hypoxia, a compensatory-adaptive reaction is noted, associated with the activation of hypoxic defense mechanisms in blood and liver cells, and in low-resistant animals, also in the brain tissue. In the myocardium, such a compensatory-adaptive reaction is activated only in the group of highly resistant animals. A high level of basal expression of the HIF-1α transcription factor under daily (normoxic) conditions may be a predictor of a high level of resistance to hypoxia in a given animal.