Telomeres and aging

Dr Yousef Elshrek

• Inside the nucleus of a cell, genes are arranged along twisted,

double-stranded molecules of DNA called chromosomes.

• At the ends of the chromosomes are stretches of DNA called

telomeres.

• Telomeres are a region of repetitive nucleotide sequences at

each end of a chromatid, which protects the end of the

chromosome from deterioration or from fusion with

neighboring chromosomes.

• Its name is derived from the Greek nouns telos (τέλος) 'end'

and merοs (μέρος, root: μερ-) 'part.'

• For vertebrates, the sequence of nucleotides in telomeres is

TTAGGG.

The sequence of nucleotides in telomeres

• During chromosome replication, the enzymes that duplicate DNA cannot continue their duplication all the way to the end of a chromosome, so in each duplication the end of the chromosome is shortened (this is because the synthesis of Okazaki fragments requires RNA primers attaching ahead on the lagging strand).

• The telomeres are disposable buffers at the ends of chromosomes which are truncated during cell division; their presence protects the genes before them on the chromosome from being truncated instead (They also stop chromosomes from fusing to each other.

• Telomeres function by preventing chromosomes from losing base pair sequences at their ends

• The telomere can reach a length of 15,000 base pairs.

• However, each time a cell divides, some of the

telomere is lost (usually 50-250 base pairs per

division).

• When the telomere becomes too short, the

chromosome reaches a "critical length" and can no

longer replicate.

• This means that a cell becomes "old" and dies by a

process called apoptosis.

• Each time a cell divides, the telomeres get shorter.

• When they get too short, the cell can no longer divide; it becomes inactive or "senescent" or it dies.

• This shortening process is associated with aging, cancer, type of food and a higher risk of death.

How do the cells have any DNA left?

Because of telomeres

Telomeres and aging • Cellular aging, or senescence, is the process by which a

cell becomes old and dies.

• It is due to the shortening of chromosomal telomeres to the point that the chromosome reaches a critical length.

• Cellular aging is analogous to a wind up clock.

• If the clock stays wound, a cell becomes immortal and constantly produces new cells.

• If the clock winds down, the cell stops producing new cells and dies.

• Body cells are constantly aging.

• Being able to make the body's cells live forever certainly creates some exciting possibilities.

• Telomerase research could therefore yield important discoveries related to the aging process.

• Why are telomeres important? • The length of the telomeres is connected to the aging

of the cell, and also the aging of the whole body.

• The older we get, the shorter our telomeres, and once they get too short, the DNA begins to become damaged and deteriorates.

• The cells also stop dividing.

• Recently, scientists can speed up or slow down this process.

• Most of the data coming out now can be thought of as the first baby steps, which are fascinating, but we should remember that they very far from being "proved".

Does drinking soda effect on telomeres length?

• The soda study appeared online in the American Journal of Public Health this month, led by Dr. Cindy Leung.

• The research looked at what people were eating in a sample of a nation-wide ongoing study in the United States called the National Health and Nutrition Examination Surveys (NHANES).

• They looked at a random sample of these people and found out what they were drinking in the way of sugar-sweetened beverages, fruit juice, and diet soda on one day 14 years ago.

• Since blood samples where also taken at that time, the researchers were able to check the genetic material in their white blood cells.

• Specifically, they measured the length of the telomeres, which are like end-caps to the chromosomes that seem to be protective of the DNA.

• What did this study show? There were some interesting results. First of all, it was consistent with other work that has shown an association between being overweight or obese and shorter telomeres, as well as other factors such as smoking, exercise, race, and socioeconomic conditions.

• With regard to the beverages, the most striking result was that people who drank sugar-sweetened soda had, on average, shorter telomeres, and it really didn't take a lot of soda for this connection to emerge.

• On average, people drank about 12 oz of soda per day, and this was enough for a significant difference in telomere length, the equivalent of about 2.9 years of aging.

• The more the soda consumed, the shorter the telomeres.

• People who drank diet soda or sugar-sweetened

beverages that weren't carbonated did not show a

difference in telomere length, but the

participants were not drinking nearly as much per

day - just a third to a half a cup on average.

• There has been a huge increase in non-carbonated

sugar-sweetened beverages over the last 15 years

or so, but at the time they weren't as popular, so

there is less data about them.

• Fruit juice consumption initially looked as it if it

might be good for telomere length, but once the

researchers factored in other data that could

explain the difference, the correlation went away.

• On the one hand, drinking sugar-sweetened

soda is associated with obesity, metabolic

syndrome, cardiovascular disease, and

wanting to eat more (thereby consuming

excess calories).

• Shortened telomeres are also associated

with some of those things, so it could just be

part of the package, and we really don't

know yet what causes what.

• a key question is: How is sugar-sweetened

soda linked to these things?

• Is it because it causes blood sugar to go up

rapidly?

• If that is so, than other high glycemic foods

should also be implicated - sugar isn't even as

glycemic as starch, such as in potatoes, cereal,

etc., although it's much easier to quickly get a

big hit of sugar when it's in liquid form.

• Could it the fructose witch doesn’t raise blood

sugar , but has problems of its own?

• Is it something else in the soda?

• It's important that to understand what's

happening in the cells to cause this effect.

• Another obvious possibility is that people who drink soda make other poor food choices.

• It should consider to take Healthy Eating Index into account, which is derived from various components of the diets that include fruits, vegetables, etc.

• It believes that the beverages has possible effects of diet.

• There are other aspects of diet which are associated with changes in telomere length.

• Basically, eating a nutrient-rich diet, containing lots of vitamins, minerals, and phytonutrients seems to be the way to go.

• Vegetables and fruits in particular are associated with less DNA damage.

• One study showed that more omega 6 fats in the diet was associated with shorter telomeres, whereas more omega 3 fats were associated with longer telomeres.

• This is consistent with the fact that inflammation is associated with shorter telomeres, and it shouldn't be surprising that preliminary studies have shown that foods that have high levels of anti-inflammatory agents such as the omega3 fats in fatty cold-water fish, the curcumin in turmeric and the polyphenols in olive oil are associated with less DNA damage in general, and longer telomeres in particular.

• Other lifestyle factors which may be

associated with telomere length include

exercise (longer), stress (shorter), smoking

(shorter) and meditation (longer).

Sources: • Leung, C. et al Soda and Cell Aging: Associations Between Sugar-

Sweetened Beverage Consumption and Leukocyte Telomere

Length in Healthy Adults From the National Health and Nutrition

Examination Surveys. American Journal of Public Health.

Published online ahead of print Oct 16, 2014. • Ligi, P. Diet, nutrition and telomere length. Journal of Nutritional

Biochemistry 22:10 895–901. October 2011.