Current Ideas About the Regulation of the Activity of Thyroid Hormones and the Mechanism of Their Action at the Cellular Level (Review)

Thyroid hormones (THs) are involved in a number of physiological processes occurring in a living organism. They participate in the regulation of the nervous, respiratory, cardiovascular, muscular, and osteoarticular systems, as well as in the processes of thermogenesis, sleep and wakefulness, and reproductive function, and modulate a number of neurotransmitter systems in the brain. Studying the mechanism of TH action in the body is necessary both to understand the reactions these hormones are involved in and to develop ways to regulate their activity. Based on the results of the analysis of Russian and foreign studies for 2011–2023, in line with the current ideas about the regulation of activity and cellular-level mechanism of action of THs, the review points out the specific features and principles of cellular regulation of THs, describes the processes of TH activation under the action of deiodinase enzymes, and characterizes the biological effect of TH regulation. In addition, the mechanisms of genomic and non-genomic action of THs are presented. It has been shown that the genomic (“classical”) action of THs through modulation of the transcription of specific genes affects the growth, development, differentiation and maintenance of the normal functioning of target tissues. Non-genomic mechanisms of TH action are mediated by the plasma membrane or cytoplasmic receptors and regulate the processes of growth, development and metabolism in the body. At the same time, the non-genomic action of THs can both be realized independently of the genomic action and complement, enhance or inhibit the effects of TH binding to transcriptionally active nuclear receptors during the implementation of TH genomic action. According to the results of the study, TH action at the genomic and non-genomic levels is realized in a complex manner, and it is the interaction between the genomic and nongenomic influence of THs that determines the effectiveness of thyroid regulation of cellular processes.