A team of scientists led by researchers at the University of Chicago determined the rate at which telomeres shorten in cells from different types of human tissues. Although they found that this rate can vary, they concluded that the decrease in telomeres in blood cells can be a fairly accurate indicator for many other tissues as well.
Telomeres are regions of DNA at the ends of chromosomes that do not code for any trait. Telomeres are needed to protect the bulk of the DNA from damage during cell division. Before the cell divides, a special DNA enzyme, polymerase, moves along the DNA strand and synthesizes a copy. But the polymerase is not able to start working from the very tip of the chromosome, so it starts doubling it by moving slightly away from the edge. As a result, the chromosome shrinks slightly after each division. To ensure that the coding regions are not affected by this reduction, telomeres are located at the ends of the chromosomes. But gradually, after new and new cycles of division, telomeres will shrink more and more – this is the aging of the cell.
Telomere shortening is associated with aging and age-related diseases, but when studying these processes, telomeres are usually measured in cells that are easy to obtain from the patient, most commonly blood cells. Until now it has remained unclear to what extent telomeres in blood cells can reflect the pattern in other body tissues.
To investigate this question, the authors of the work used the Genotype-Tissue Expression (GTEx) project, which collects tissue samples from a large number of people. In total, they analyzed more than 6,000 samples of 23 different tissues from about a thousand people. They found that of these 23 tissues, 15 showed a clear positive correlation with telomere length in whole blood cells, confirming the use of blood cells as an indicator of telomere length in hard-to-reach tissues such as brain and kidney tissue.
Along the way, the scientists tested several previous theories about telomere length in various individual cases. Some have been confirmed, such as longer telomeres in people of African descent. Others were not, such as the assumption of longer telomeres in women. The report of shorter telomeres in smokers was only partially confirmed; this is indeed observed, but only in certain tissue types. These results will help to understand the extent to which telomere length is genetically determined, and how it can be affected by lifestyle, environmental exposure, or epigenetic changes over the course of a person’s life.