Research into the Aging Process
Model Organisms Have Been Useful to Learning About Aging
Aug 27, 2008
Is it Possible to Study Aging?
For a long time, aging was considered an impossible subject to study. It appears to involve the breakdown of multiple systems over time, in a messy and unpredictable way. However, aging is not identical in every organism; different types of animals have different life spans. Mice live about 3 years, elephants about 70 years, and the giant tortise almost 200 years. Therefore, aging has at least some genetic component, and scientists became interested in what allows some animals to live longer than others.
Population Studies
At the present time, it is not possible to predict how a specific, identified individual will age or how long an individual will live. To do so would require biomarkers of aging, or measures of biological parameters that change with age in a known and reproducible way. There are no known biomarkers of aging at this time. Therefore it is not possible to conduct experiments with individual organisms.
Instead, aging studies use populations of organisms, preferable organisms that can be studied in very large numbers, are very homogeneous (individuals are very similar to each other), and that have a short life span so that the experiments can be completed in a reasonable amount of time.
Organisms used to study aging are called model organisms, since they are used to model the process. The most popular model organisms presently used include the nematode C. elegans, fruit flies, and yeast. C. elegans is a very simple, transparent worm, about 1 mm long, with a maximum life span of only about a month. Individuals are virtually identical to each other, and hundreds can be cultured on Petri dishes where they eat bacteria. Fruit flies live slightly longer, and are more complex structurally than nematodes, but they are also excellent for life span studies. Yeast are a single-celled organism, and laboratories have devised ways to use both dividing yeast and stationary phase (non-dividing) yeast to study aging. All of these model organisms, though very different from human beings, share some similar biochemistry and many of the same genes with humans, meaning that what is learned from these organisms can be informative about human aging.
Aging Experiments
To study aging with populations requires having synchronized populations in which all members of the population are the same age. With nematodes or fruit flies, this can be done by letting adults lay eggs for a defined amount of time, removing the adults, and then studying the animals that hatch from the eggs. Those animals will be the same age, within a few hours.
The population is then allowed to age under controlled conditions of temperature, food source, and density. Under defined conditions, separate populations of the same organism will have similar mean (average) and maximum lifespans. The shape of the curve generated by plotting the number of organisms left alive at a given time will also have a characteristic shape which provides information about the aging rate and process. This means that if two populations are kept side by side, but one is treated with a drug, or contains a genetic mutation, it can be determined whether the drug or mutation has an effect on life span. In this way, several compounds and genes that increase lifespan in model organisms have been identified.
The aging process has proven to be amenable to scientific research. Through the use of populations of model organisms, scientists have been able to describe the life span and aging rate of those organisms, and to test hypotheses about processes that might influence aging. This has become an exciting and active area of biological research.
