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Name: Carl S.
Status: Educator
Age: 30s
Location: N/A
Country: N/A
Date: June 2002

Do rates of cellular division for the same type of cell change over the course of a human life. For example, do skin cells in the epidermis divide more quickly in a fetus than in a teen, than in a 20 year old, etc.? If so, is it possible to mark the age (pre or post natal) at which cells seem to be their most robust? And, if varying rates do exist, can they be attributed to changes in nutrition delivery or do they appear to be tied do some other factor? Would a cell culture continue to divide at a steady rate ad infinitum given perpetual optimal nutrition and environment?

Dear Carl:

Cells from older individuals generally do proliferate at a slower rate than those from younger individuals when grown in culture. The difference is not usually very dramatic, however, perhaps half the rate of cells from a newborn infant at most. This evidence would indicate that the phenomenon is not dependent upon nutrition, since these cells would be grown under identical conditions. But it is difficult to know how the growth rates of these cells would compare in the organism itself rather than in culture, since other exogenous factors could act to either accelerate or decelerate proliferation differently depending upon age of the organism. Nonetheless, aging does seem to reduce the intrinsic proliferative capacity of many cell types. Although difficult to generalize, maximum proliferative capacity would probably be observed in the cells from the youngest individuals, as you suggest.

Our current knowledge from cells in culture indicates that unless they are "transformed" or "immortalized", as occurs in cancer cells, they all have a finite life span. The only qualification to this conclusion would be that perhaps they are not growing under completely optimum conditions in these cultures, e.g. in the presence of some yet-to-be discovered super-growth factor. Along these lines, there is actually a great deal of current interest in the effect of an endogenous enzyme known as telomerase, which controls the length of the chromosomal termini, on cellular aging. In fact, it's been shown that delaying the natural shortening of these terminal sequences, known as telomeres, by activating telomerase can extend cellular life span. This phenomenon is actually thought to play a role in cellular transformation to a cancerous state, in some instances. An article by Dr. Jerry Shay, one of the experts in this field from the University of Texas, is available that reviews these concepts very nicely, if you're interested:

It does require Adobe Acrobat Reader to load, though, but it is freely available if you need it. Thank you for the excellent questions,

Jeff Buzby, Ph.D. Children's Hospital of Orange County

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