Telomeres are DNA sequences found at the end of our chromosomes, and telomeres are non-coding, meaning that they do not code for any proteins. Surprisingly, these seemingly unimportant DNA segments possess enormous significance. Telomeres have been receiving great attention from the scientific community due to their relations to aging and cancer. To understand their significance, we will first investigate the purpose of telomeres.
IMG Credit: Stanford Medicine - Stanford University
What Are Telomeres?
Whenever cells divide, DNA is replicated to ensure that the two daughter cells contain the same genetic material as the parent cell. DNA polymerase III is the enzyme responsible for synthesizing new DNA strands based on the sequences of the old DNA strands. DNA polymerase III can only add nucleotides (monomers of DNA) to the 3’ end of the new strand. This creates an interesting problem at the very end of the chromosome as one of the strands can not be fully replicated.
IMG Credit: Jack Slater Youtube
What this means is that our new DNA will be shorter than the original, and this is commonly referred to as the ‘End Replication Problem.’ To prevent important genes from eroding, our chromosomes have non-coding, repeating sequences at the end called telomeres. Telomeres shorten everytime our DNA undergoes replication, so shorter telomeres are associated with older ages. The pace of telomere shortening is also known to be influenced by lifestyle factors such as diet. Smoking, obesity, and exposure to pollution were also found to be associated with faster telomere shortening. On the other hand, eating less and exercising may help preserve telomeres and consequently reduce the pace of aging.
There is an enzyme called telomerase that can add additional sequences and lengthen telomeres, thus preventing telomere erosion to a certain extent. While telomerase can be abundantly found in cells such as sperms and eggs, the enzyme is not commonly found for other body cells as the associated gene is turned off. With less telomerase, these cells are subject to aging as a result of shortening telomeres.
Telomeres and Cancer
Telomerase is abundant and very active in cancer cells. This makes sense because without telomerase restoring telomeres, cells would not be able to divide indefinitely and uncontrollably. This is one of the reasons why the science community directs great attention towards telomeres. If there is a way to prevent the activity of telomerase enzymes in cancer cells, we would be able to eventually stop cancer cells from dividing, since cancer cells’ chromosomes would erode everytime they replicate.
However, there are still barriers to overcome. Telomeres can sometimes be maintained through other mechanisms besides telomerase, and evidence based on mouse models suggests that these dangerous and unstable mechanisms may develop after the use of telomerase-targeted therapy. Also, inhibiting telomerase does not immediately stop cancer, since cells will still divide in the absence of telomerase enzymes until their telomeres reach a critically short length. Hopefully, such barriers will be overcome soon through persistent research efforts.
Telomeres and Aging
There is another important question to address when discussing the topic of telomeres. If shortening telomeres are responsible for aging, could we slow down, prevent, or even reverse aging with the help of telomerase enzymes? Diseases such as dyskeratosis are also associated with reduced telomerase activity and rapid telomere shortening. Could we treat these diseases through increasing telomerase activity?
A major barrier to this exciting approach is the risks of cancer development. Increasing telomerase activity would require great precision in order to simultaneously prevent any cells from becoming uncontrollable. However, scientists do still view this as a promising approach towards precise disease treatment and anti-aging efforts, and more research is on the way.
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