Telomere Shortening

Summary

Telomeres are structures located at the ends of chromosomes that protect genetic material during cell division. They prevent chromosomes from binding with other chromosomes, fusing with themselves, and "fraying".

Based on their general function and appearance, telomeres are often compared to the plastic caps on shoelaces.

As they are also associated with disease and eventual death, telomeres have also been compared to a bomb fuse.

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Cell Division

The human body is composed of trillions of cells. Over time, cells endure "wear and tear" and eventually need to regenerate. Once a cell "wears out" it replicates itself and divides, creating a brand new cell. Many cells will divide 40-60 times during the course of a human lifetime.

The number of times a cell divides before it dies is known as the Hayflick limit, named after Leonard Hayflick, an American scientist who discovered this limitation in 1961-62.

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Telomere Shortening

In most cases, each time a cell divides it sheds a portion of its telomeres. As the cell continues to divide its telomeres get shorter and shorter. Once the telomeres are gone the chromosome has no buffer to protect its genetic material during cell division. As a result, the cell can no longer divide and dies.

The process a cell undergoes after maturity is known as cellular senescence.

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Telomeres & Aging

Telomeres may be correlated to the human aging process. Scientists speculate that as telomeres get shorter the signs of aging—gray hair, wrinkles, weaker bones, slower reaction time, etc.— become more apparent. The theory is that telomere shortening results in ageing of the entire organism, not only at the cellular level. It is important to note, however, that the aging process is complex and involves many different factors. Telomeres are one factor to consider.

The following video from NBC's Today Show explores the topic of telomeres and aging.

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Telomerase

Telomerase is an enzyme that counters telomere shortening by providing DNA to rebuild telomeres.

Normally, when a cell divides it loses part of its telomeres. As the cell continues to divide it ages and eventually dies when it reaches its Hayflick limit, i.e., its telomeres become too short and replication is no longer possible.

However, cells with telomerase don't lose telomere length as fast or at all. In fact, some cells with telomerase grow longer telomeres despite cell division. The result is cells that bypass their Hayflick limit, with some even becoming "immortal".

Cells that are known to have higher levels of telomerase are:

  • younger cells (to help them survive to maturity);
  • embryonic stem cells (which need to divide indefinitely in order to create a human being);
  • heart cells;
  • blood cells;
  • immune system cells (which need to multiply practically nonstop as they continually fend off disease); and,
  • sperm and eggs cells (which need to survive indefinitely in order to be passed to the next generation or, more broadly, to prevent extinction of the species).

From an anti-aging perspective, telomerase has generated tremendous excitement. Many have speculated that by activating this enzyme in all cells humans can retard the aging process. Some have speculated that telomerase may enable people to live 1,000 years.

The big problem facing telomerase therapies is that, while telomerase may extend the life of cells beneficial to good health and a long life, it's also the fuel that enables cancer cells to thrive.

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Telomeres & Cancer

Cancer cells don't die.

This is why cancer is so dangerous.

Cancer is a condition in which certain cells in the body avoid dying. These cells are able to continually rebuild their telomeres after each division. Fueled by telomerase, cancer cells are able to prevent telomere shortening, replicate without limitation, and (conceivably) live forever.

The accumulation of these out-of-control cells creates a tumor.

So why not treat cancer by eliminating the telomerase?

Scientists are, in fact, working on treatments that would target cells with high levels of telomerase. Just knowing that cells have telomerase activity may be a good way to detect cancer.

There are risks, however, to targeting telomerase.

Healthy cells that require telomerase for their normal processes—such as blood cells, immune system cells, and reproductive cells— may also suffer when targeting cancer cell telomerase.

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2009 Nobel Prize in Medicine

The research and discoveries relating to telomeres was recognized in 2009 with the Nobel Prize in Medicine.

Three American scientists—Elizabeth Blackburn, Carol Greider and Jack Szostak— shared the prize for, as the Nobel Assembly declared, "the discovery of how chromosomes are protected by telomeres and the enzyme telomerase."

In their press release the Nobel Assembly stated:

"This year's Nobel Prize in Physiology or Medicine is awarded to three scientists who have solved a major problem in biology: how the chromosomes can be copied in a complete way during cell divisions and how they are protected against degradation. The Nobel Laureates have shown that the solution is to be found in the ends of the chromosomes – the telomeres – and in an enzyme that forms them – telomerase."

(See the Nobel web page for this award.)

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Telomere Testing

A telomere test is a blood test that measures the length of telomeres. For more information about this test see Telomere Testing.

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