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PhilO

Aging and Stem Cells

2 posts in this topic

I had an idea about aging that I wanted to pass by Dr. RJM for his thoughts.

I've read recently that there's a relatively recent theory that stem cells may be critical to the formation and maintenance of cancerous tumors. If I understand the theory correctly, it's basically the idea that the stem cells themselves are cancerous, and are actually responsible for the tumor growth. The theory has been tested in at least one instance by showing that implanting a small number of stem cells from cancerous tumors into another animal, is sufficient to cause cancer, whereas it takes many more cells from a whole tumor to induce cancer.

So, the thought occured to me that perhaps this may apply to aging generally - that it's the aging and degradation of the stem cells that lead to aging of the whole organism. From a practical standpoint, if that were true, it would seem to be much easier to "fix" aged stem cells and put them back into the body, than to try to figure out a way to "fix" every aged cell in the body.

I'd like to know what Dr. RJM thinks of this hypothesis.

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Dear PhilO,

First, my apologies for the long delay in answering your question.

I have scanned the cancer literature only superficially (it is impossible to read all of the biological and medical literature, even within a specialized area: in 2004, The Journal of Biological Chemistry alone exceeded 56 000 pages, and reading an 8-page article carefully can take several hours). Here, I will focus on aging, leaving any detailed discussion of cancer for a separate thread, possibly on the Biology & Medicine section of The Forum. Having said that, I think your summary of the relationship between stem cells and cancer is a reasonable preamble, setting the context for your hypothesis about aging.

Concerning aging, I think stem cell research has a lot of potential, but not in the way you suggest. Specifically, there is only limited evidence that aging of stem cells leads to aging of the whole organism. The cells which are most obviously damaged or likely to be lost in old animals are those which do not divide and are not replaced. Generally, highly differentiated cells such as neurons fall into this category. The trick with stem cells would be to induce differentiation to replace damaged cells, without triggering uncontrolled proliferation, i.e. some cell division but not too much. If that could be achieved and if, further, (i) the damaged cells could be induced to die at a controlled rate to make room for their replacements, and (ii) the resulting molecular debris could be cleared from the tissue rather than being stored as undegradable 'junk' in neighbouring cells, then we could circumvent the need to prevent or repair damage in the existing cells.

It is theoretically possible that either the cell replacement or damage prevention / repair strategies could ultimately yield the knowledge we need to slow, stop or reverse the aging process. The emphasis of my own work has been on the prevention or repair of damage, but both approaches have amazing potential and both still require what I would describe as "landmark discoveries" for that potential to be realized.

Cordially,

RJM

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