Telomeres are the caps at the end of each strand of DNA that protect our chromosomes. They have been allegorized commonly as the plastic tips at the end of shoelaces, which are likely to get frayed without them. Similarly, without telomeres DNA strands become damaged. They are actually disposable protective buffers blocking the ends of the chromosomes. They are consumed during cell division but are replenished by an enzyme – the telomerase reverse transcriptase.
Role of telomerase –
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The main function of telomerase is the elongation of telomeres, which enables cells to increase their replicative capacity, sometimes even indefinitely. However, low expression of telomerase, for example in some normal fibroblasts, cannot maintain telomere length.
Telomerase also shows important roles in stem cell proliferation, as well as reprogramming of induced pluripotent stem cells. An induced pluripotent stem cell is a cell taken from any tissue (usually skin or blood) from a child or adult and is genetically modified to behave like an embryonic stem cell. The mechanism of these telomerase functions is still not completely clear.
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Functions of telomeres –
Basically, telomeres function as follows:
1. They cap up chromosome ends principally protecting them from DNA degradation. Their length serves as an intrinsic biological clock that regulates the life span of the cell. In other words, they provide limits on the number of replications a cell can go through.
2. They also protect chromosomes from fusion with other chromosomal ends. Uncapped telomeres are able to initiate the DNA damage and cause end-to-end fusions, resulting in chromosomal instability, cellular senescence and apoptosis (programmed cell death). Telomere repeats are lost with each round of cell replication and most somatic cells express insufficient telomerase to compensate for the loss of telomere repeats.
Lifestyle factors impacting telomeres –
Telomere length, which can be affected by various lifestyle factors, can affect the pace of aging and onset of age-associated diseases. Telomeres are shortened as we age, but telomeres can also be shortened by stress, smoking, obesity, lack of exercise and a poor diet.
The following are the common causes responsible for the shortening of telomeres:
Aging – Telomere length negatively correlates with age. Telomere length may determine overall health, lifespan, and the rate at which an individual is aging.
Smoking – Smoking seems to have adverse effect on telomeres, shortening their length. Studies have found that the telomere attrition caused by smoking one pack of cigarettes a day for a period of 40 years is equivalent to 7.4 years of life. Oxidative stress caused by smoking is mainly responsible for telomere attrition, resulting in their shortening.
Obesity – Obesity is also associated with increased oxidative stress and DNA damage. Studies show that the excessive loss of telomeres in obese individuals may be equivalent to 8.8 years of life, an effect which seems to be worse than smoking.
Environmental pollution – Exposure to traffic and industrial pollution can adversely affect telomeres. Reduction of the length of telomeres in a person is intimately related to numbers of years and severity of exposure to environmental pollution.
Stress – The stress is associated with release of glucocorticoid hormones by the adrenal glands, which cause increased oxidative damage to DNA and accelerated telomere shortening.
Unhealthy diet – Unhealthy diet deficient in various macro and micro- nutrients can also result in shortening of telomeres as result of damage caused by oxidative stress. Dietary restriction or eating less has an extremely positive impact on health and longevity. The reduction in oxidative stress by dietary restriction is expected to preserve telomeres and other cellular components.
Lack of exercise – The duration of exercise inversely co-relates with the damage to the DNA and telomeres. Regular exercise has been found to be associated with elevated telomerase activity. Furthermore, regular exercise seems to be associated with reduced oxidative stress and may, therefore, reduce the pace of aging and age-associated diseases.
The bottom line –
Telomeres are significantly affected by age and our lifestyle. Shorter telomeres have also been implicated in genomic instability. The rate of telomere shortening is, therefore, critical to an individual’s health and pace of aging.