Have you ever wondered, what is your physiological age? Is it more or less than your chronological age? Physiological age determines a person’s health condition. Are we able to determine physiological age? You would think the answer is NO. but it can be done by determining telomere’s length. “Telomere is a repetitive nucleotide sequence (having no meaningful information) at each end of chromosome to protect DNA from deterioration and or from fusion with other chromosomes.” This sequence is about 3000-15000 base pairs in length. In vertebrates this repeated sequence is TTAGGG.
Significance of Telomeres
Cells divide and increase their number, DNA duplication also occurs. Enzymes involved in this duplication process, can’t continue duplication all the way to the end so some part of DNA is lost and chromosome is shortened. This lost part is some base pairs of telomere. Somatic cells lose about 50-100 nucleotides on each cell division. In this way, telomeres, having no meaningful information, act as CAPS preventing the important information (DNA) from deterioration and preserve the critical information. Telomeres are never tied to each other which allows chromosomes to remain segregate. Without telomeres, chromosomes would fuse with each other. Telomere Shortening Telomeres shorten because of the two major factors:
- End replication problem in eukaryotes accounts for loss of 20 base pairs per cell division.
- Oxidative stress accounts for loss of 50-100 base pairs per cell division.
Oxidative stress in the body depends on lifestyle factors. Smoking, poor diet and stress can cause increase in oxidative stress. With each cell division telomeres shorten, so there are limited number of divisions that a cell can undergo, this limit is called Hayflick Limit. This is to prevent the loss of vital DNA information and to prevent production of abnormal cells. When a cell reaches this limit it undergoes apoptosis that is a programmed cell death. Telomere Lengthening to reverse telomere shortening, there is an enzyme named Telomerase that adds telomere sequence nucleotides and replenish the lost telomere nucleotides. Telomerase activity is not present in all cells. It is almost absent in somatic cells including; lung, liver, kidney cells, adult tissues, cardiac and skeletal muscles etc. In the presence of telomerase enzyme, a cell can divide to unlimited extent without ageing giving rise to tumors. That’s why it is found only in some cells in considerable concentration including germline cells and stem cells. These cells don’t show signs of ageing.
Relation between Telomere’s Shortening and Ageing
It is still controversial that whether telomere shortening is a reason of ageing or is a sign of ageing just like grey hair. Whatever it is, the thing is, it determines your physiological age because ageing cells mean an ageing body. Telomere shortening is related with poor lifestyle. People who are active and have a healthy lifestyle have the same telomere length as someone 10 years younger than them has. Depression causes increase in oxidative stress in the body so the higher the stress, the shorter the telomere is Link between Telomeres and Cancer “Cancer in general is defined as an uncontrollable rapid growth of cells.”
What causes these cells to grow uncontrollably?
These cells have active telomerase enzyme, which doesn’t let the telomere to shorten, so no Hayflick limit reaches and cell continues to divide. This is the reason why telomerase is not used as an anti-ageing medicine because it has potential to turn normal body cells into cancerous cells. Without telomerase activity cancer cells activity would stop, which is an under research treatment for cancer. However, drugs inhibiting telomerase activity, can interfere with normal functioning of cells that require telomerase. In healthy female breast there is a portion of cells named, luminal progenitors, with critically short telomere length. In these cells telomerase becomes active causing these cells to turn into cancer cells on higher activity. To tackle breast cancer, use of telomerase inhibiting drugs should be practiced. Telomere biology is very important for understanding cancer biology and scientists are working hard on it.
Reviewed by Dr. Nida Hayat Khan
Editor @ BioScience.pk