Cellular Basis of Aging

Theoretically speaking aging starts the day one is born. This is true chronologically. After birth initially there is the growth and development phase then the stable phase of adulthood and finally gradual deterioration in bodily function begins to set in. Practically speaking, most studies of the aging process have concentrated on the decline of bodily function.

The "hidden agenda" behind the study of aging is mankind’s quest for immortality. The rationale being that if we know why the body is ageing and what makes it age the process could be slowed or stopped to enable us to lead a longer and healthier life.

Although bodily function declines with age, the aging process must be distinguished from diseases which occur in old age. Very often the differentiation between age related decline and mild disease is very subtle and hard to distinguish. For example, memory and the ability to form new memory declines almost universally with age. In most people this is of no consequence and this process has been given various names by scientists such as "age associated memory impairment" or "benign senescence of old age." However, in some people this progresses to dementia or Alzheimer's disease. In the very early, mild stages of these diseases, it is impossible to predict if the memory disorder will progress.

Diane E. Meier has written in the chapter entitled "The Cell Biology of Aging" in the book Geriatric Medicine about verifiable observations of aging. These are shown in the table.

She points out that different mammalian species have different life spans which are relatively fixed within species. This suggests a genetic basis for the lifespan. Secondly, she points out that within species longevity may also have a genetic basis. For example, members of certain families live longer than member of other families. She goes on to list other verifiable observations such as the relationship between the period required to bear and tear the young and lifespan, the relationship between adversity and lifespan. She also talks about the decline of human organs with age, the death of cells due to age, and the decline of cellular function with age. She gives specific examples such as progeria in which the aging process is accelerated. Finally she talks about the limited dividing potential of human cells in culture which may also have a genetic control.

Based on these observations she has summarized the various theories of aging as proposed by numerous authors into two broad categories: one, the wear and tear theory and the second, genetic program theory.

The wear and tear theories are based on the deterioration of cells with continued function much as a machine gets worn out with continued use. One other theory which has become extremely popular recently is the oxidative damage theory due to free radicals generated by the body. Free radicals are electrically charged particles which are generated by the body during metabolism. Somehow the body has not developed an adequate mechanism to neutralize these particles. Damage caused by these particles has been called the oxidative damage and is the basis for the increasing popularity of people taking anti-oxidants such as Vitamin-B-complex and Vitamin-E daily. The rationale being that these compounds neutralize the pre-radicals and prevent oxidative damage. She also talks about the mechanisms of cellular damages such as lipofscin accumulation within cells, macromolecular cross linkage leading to abnormal mechanical properties, mutations in cells due to random errors during the phase of cell division leading to form abnormal protein.

The other set of theories grouped under the genetic program theories are linked to the genetic control of the body. This is the area of enormous research around the world. The Human Genome project by the National Institutes of Health, U.S.A. hopes to determine the entire genetic code of humans in the very near future. This giant project involving scientists from around the world will revolutionize our understanding why the body ages and why many diseases occur. At this stage the implications of this project are hard to imagine and appear like a page in science fiction.
CELL BIOLOGY OF AGING: VERIFIABLE OBSERVATIONS:

Verifiable life spans among mammals.
Longevity as a hereditary function
Number offspring per year inversely related to species life span.
Caloric deprivation prematuration increases life span.
Linear decline in organ physiologic functioning with age.
Cells and organs die as a part of normal growth and development, as well as aging.
Cellular function declines with age.
Disease models of premature aging: Progeria, Werner's syndrome, diabetes, mellitus, Down's syndrome.
Finite dividing potential of human cells in culture.