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Say the words stem cell and you’ve triggered almost as much controversy as any other two words in the English language. While some may argue that you can’t strip away the moral issues from the science of stem cell research for the study of ageing, the fact is, that’s exactly what we’re going to do. Your body naturally already uses its own stem cells to make you stronger, healthier and more resistant to the conditions that have the potential to slug away at you day after day and year after year (see Figure C.1). Your stem cells are an incredibly powerful tool – independent of what you believe we should be doing in the laboratories. And part of the reason why is that stem cells play a key role in how we recover from stress. The problem is, we lose stem cells as we age, whether by using them to repair damaged organs or because they’re destroyed by such toxins as chemotherapy or radiation or oxygen free radicals – leaving us vulnerable to stress-related conditions.

Stem cells come in two varieties:

Figure C.1 Fountain of Youth Your stem cells are the new leaders of your biological city. They want rejuvenation, not the same stuff brought on by the old guard that’s resistant to change.

Blastocysts (often mistakenly called embryonic, a charged word that has created a political and moral brouhaha): when a fertilized egg turns four days old, a cluster of specialized stem cells walls itself off to create an inner cell mass. These cells have the amazing ability to reproduce indefinitely, and, if they become embryos, they have the ability to mature, grow and differentiate themselves into every tissue that forms every piece of your bodily puzzle. But they aren’t embryos yet; they cannot go on unless they implant. At this stage, they are blastocysts, or pre-embryonic. These immortal blastocystic stem cells retain their natural and quite spectacular ability to differentiate into any and every organ. In other words, they have the luxury of deciding what to become when they grow up. Do they mature into heart cells, liver cells or brain cells? Because of their plasticity, these cells have the greatest potential to cure diseases, especially those associated with ageing, such as Parkinson’s.

Progenitor cells (also called adult stem cells): now, some of those blastocystic cells, like kids living at home when they’re thirty, stay right where they are and don’t mature into other tissues and organs. Instead, they hang back and set up shop in the bone marrow. These adult stem cells retain the ability to grow into other kinds of cells. Why is this so exciting from a medical and scientific perspective? If your own stem cells – the cells you currently have – can be used to regenerate new tissue to replace broken-down or diseased tissue and fix your own organs, then you have the opportunity to punch frailty right in the face.

One of the goals of stem cell research is to harvest some of these universal cells, grow them in laboratories and then use them to undo the damage done by such things as heart attacks, strokes, diabetes, Alzheimer’s and many other diseases associated with ageing. How do we know that this process has potential? Well, just look at the work that’s been done on the heart. Cardiology was one of the specialities most resistant to the potential power of stem cells, and the damaged heart was considered representative of the key organs that could not regenerate themselves. In research involving heart transplant, scientists studied groups of men who were transplanted with a female heart (in heart transplantation, the sex of the heart doesn’t matter, but, rather, the size). In theory, the cells of a female heart, when transplanted into a man, should have only their original double-X chromosomes, with no male Y chromosomes in them at all. But when researchers examined the hearts only a few months after transplantation, they actually found Y chromosomes in the heart – meaning that the male stem cells were migrating from the bone marrow to the heart to make periodic repairs. Similar reinvigoration of almost all of your organs continually occurs with your own full-time stem cell repairmen.

Figure C.2 Cellular Service The beauty of stem cells is that they have the ability to reproduce indefinitely – and can change into every tissue in your body.

At all stages of your life, your body responds to damage by recruiting stem cells. When you smoke, stem cells are sent to the lungs to respond to damage. Or when your skin burns from the sun, stem cells go there to make repairs. But – and this is a big but – there are two unfortunate consequences of all that repair, and it’s another example of how a valuable process has the power to backfire on you. First, the more stem cells you send in for repair (say, the more times you burn your skin from lying out by the pool unprotected), the more stem cell reproduction occurs. The more reproduction, the higher the chance that something will go wrong during cell division – meaning that your stem cells have a higher chance of differentiating into a tumour cell. Stem cells know how to replicate quickly, so, boom, you’ve got cancer. (That’s why repeated damage to an organ – via smoking, sunburn, alcohol abuse or inflammation from saturated fat or just being fat – predisposes you to cancer.) Second, if your stem cells are constantly repairing sunburn, then there won’t be enough of them available to aid in maintaining other organs.

Add to the equation the reality that as we age, our bone marrow releases fewer stem cells, meaning that we have less ability to repair damage. And that’s really why we worry about your stress level. Not because we don’t want you angry, panicky or more tense than a first-time public speaker. It’s because stress can disable your telomeres (remember the first Major Ager) and handcuff your stem cells, further weakening your ability to repair damage that happens as you age.