Telomere Length and Telomerase Activity as Biomarkers in the Diagnostics and Prognostics of Pathological Conditions.

Telomere biology still remains a topic of interest in life sciences. Analysis of several thousand clinical samples from healthy individuals performed in recent years has shown that the telomere length (TL) in peripheral blood leukocytes correlates with the TL in cells of internal organ and reflects their condition. TL decreases under the influence of damaging factors and can serve as an indicator of health status. The telomere shortening leads to the cell proliferation arrest and is considered as a marker of replicative aging of proliferating cells. A decrease in the TL in peripheral blood leukocytes is viewed as an indicator of organism aging. Recent studies have allowed to formulate the concept on the role of the CST-polymerase α/primase in the C-strand fill in after completion of 3'G overhang synthesis by telomerase during telomere replication. The discovery of the telomeric RNA (TERRA) and its role in the regulation of telomerase activity (TA) and alternative lengthening of telomeres, as well as the possibility of TERRA translation, has provided evidence of the complex epigenetic regulation of the TL maintenance. Analysis of the published data indicates that telomeres are dynamic structures, whose length undergoes significant changes under the influence of damaging factors. TL is determined not only by the chronological age, but also by the exposure to the exogenous and endogenous deleterious factors during the lifetime. A decrease in the TL due to inherited mutations in the genes coding for proteins involved in the telomere structure formation and telomere replication (primarily, proteins of the shelterin and CST complexes and telomerase) has been found in a number of hereditary diseases - telomeropathies. The assessment of TL and TA is of great importance for the diagnostics of telomeropathies and can be useful in the diagnostics of cancer. Analysis of TL can be used for monitoring the health status (e.g., in the case of exposure to ionizing radiation and space flight factors), as well as predicting individual's sensitivity to the action of various damaging agents. The application of modern advancement in genetic technologies in the analysis of TL and TA makes it available for the use in clinical and epidemiological studies, diagnostics of telomeropathies, and monitoring of astronauts' health.