Date: April 1st, 2003
The tiny "caps" that keep our chromosomes from fusing together are also providing clues that could eventually lead to the achievement of one our nation's most important public health goals: extending good health well into old age.
These caps are called telomeres, and they're at the center of much of the current research into the aging process. A study recently published in science journal The Lancet links the lengths of telomeres with rate of survival among people over 60, the first study to make this connection.
What are Telomeres?
To help understand the role telomeres play within the human body, it's useful to review some basic biology. All of the tissues within the human body are made up of individual cells. These cells contain chromosomes within their nuclei. Chromosomes are the packages that hold most of our DNA - the genetic instructions that tell the cell what to do.
Telomeres are repeating DNA sequences at the ends of the chromosomes. They do not contain any genetic instructions; they simply repeat a sequence of DNA over and over. When we are young, the telomeres are very long - they may contain as many as 20,000 base pairs of DNA.
What do Telomeres do?
Telomeres are thought to serve a couple of purposes within human cells. One, the telomeres form end caps for their chromosomes. Without them, the body would have no way to know where the chromosomes ended. It would treat them as "broken" pieces of DNA and would attempt to repair them by joining them with other chromosomes. With telomeres, the body can tell where one chromosome ends and another begins.
Second, scientists theorize that telomeres may serve as genetic "clocks." As we grow and age, our cells divide. One parent cell divides into two daughter cells, making copies of the genetic information to pass on to these new cells.
Each time a cell divides and the DNA within the cell is copied, the telomeres shorten. This process continues until the telomeres reach a critical length, at which point the cell stops dividing.
The connection between telomeres and aging
It is clear based on the research up to this point that telomere shortening is related to aging. Scientists are now trying to gain more insight into the nature of that relationship. Once a cell stops dividing, it may do one of three things: die, become inactive, or transform into some sort of abnormality, such as a cancerous cell.
Scientists theorize that the loss of function for these aging cells may be a factor leading to some of the degenerative diseases that occur with old age. Studies conclusively linking all this cellular activity to the larger aging process are just beginning.
A group of researchers from the University of Utah recently advanced this topic a step further by showing for the first time an association between telomere shortening and mortality rate. Their study measured telomeres in a group of subjects who donated blood in the mid-1980s.
The researchers then compared the telomere lengths to survival data they had gathered on these subjects. According to Dr. Richard Cawthon, one of the authors of the study, they found that subjects with shorter telomeres were more than three times as likely to have died of heart disease, and more than eight times as likely to have died of infectious disease as their counterparts with longer telomeres.
Implications of the Utah study
The results of this study support the idea that telomere shortening is directly related to mortality caused by some age-related diseases. This helps point scientists in the right direction for further study.
It remains to be seen whether telomere shortening is a factor that actually causes cellular failure and thus age-related disease, or whether it is a marker - an indicator that another process is acting upon the cells, causing them to fail and shortening the telomeres at the same time.
"It looks like some more work should be done with telomeres," Dr. Cawthon said. "Either telomere shortening contributes directly to the onset of age-related diseases, or it is a marker that will lead us to the primary causes of those diseases."
Ultimately, scientists may be able to develop medications that will delay the onset of age-related disease, either by maintaining the length of our telomeres, or by addressing whatever other factor is identified as leading to these diseases. Either way, it means the potential for enjoyment of robust health well into our old age.