Redefine Aging: Stem Cells and Telomeres for Increased Longevity

Scott: Dr. Park, first, one thing you talk about is that we have two methods of defining age in our body. One is chronological from the date we were born, and the other is the age of our body. Can you talk about how they differ?

Ed Park, MD, MPH: Well, chronologically we measure in years, but that's pretty much useless. It's a source of incredible anxiety for people. What's a little more reliable is the telomere age. Some people say age is a number. Well, that's not really true but telomeres, you can objectively measure how much fuse or wick you have on the ends of your chromosomes, and as we get older, they shorten. 

The reason I say the number, the age, doesn't matter is because you have people who live 900 years in the Bible, if you believe in that. You have kids who live 13 years and die of old age. Likewise with cars, you don't drive your car off the lot and expect it to last 2.4 million miles, but there's a gentleman who's driven his Volvo for 2.4 million miles. It doesn't matter as long as you do the maintenance and the repair. I'm looking at a time when we can be 100, 200, 300. No problem, as long as you do the maintenance and repair.

Scott: You mentioned telomeres. Talk about those a little bit; what they are and then their role in our aging.

Ed Park, MD, MPH: It's not just us. Plants, animals, fungi, anything that's more complicated than a single-celled bacterium needs caps at the ends of their chromosomes. So there are two strands running and the ends have to be capped, otherwise they'll fall apart like shoelaces. When you are fertilized as an egg, the whole thing is reset to the endowment of 15,000 in humans. So every time a cell divides, they shorten by about 50 to 100.

Luckily, there are special cells called stem cells which function like queen bees, and they're able to actively lengthen them throughout your life. The telomeres will erode with time, but that's okay because you don't want all the drone bees, the honey bees, the worker bees, to live. You just want the queens to take care of themselves. It's actually a really good analogy, because queen bees will live years whereas her little clones, her drones, will only live months. So throughout our bodies we're just trying to save the stem cells.

Telomeres are actively lengthened by an enzyme called telomerase, which every single plant and animal has only in their stem cells, and it's able to prevent that shortening in all of the routine, run-of-the-mill cells.

Scott: Explain the stem cells that we have in our body right now, the ones you're talking about. When we think of stem cells, we think they're the taboo with the embryonic and injectable kind. So talk about the ones you're talking about.

Ed Park, MD, MPH: Well, that whole thing about stem cells was kind of a distraction. It injected a lot of heat into a debate and not much light.

At the basic level, a stem cell has two characteristics. One, it can immortalize itself like we talked about. In 2009, the Nobel prize was awarded for telomerase. It's an enzyme that lengthens the ends. It gives you more DNA. Right? It keeps the wick growing so the wick doesn't burn out.

But the other characteristic of a stem cell is that it divides asymmetrically, meaning it doesn't make two daughters; it makes one other mother, and a daughter. Right? It makes a perfect copy of itself, and the other one is a less-perfect daughter. It can run off copies, copies, copies. That's what a stem cell is. 

But it's on a continuum. Stem cells can have various degrees of stem-ness. A fertilized egg can and does become all cell types. Every time you differentiate to different layers like endodermic . . . these are technical things, but every time you go farther down the line in differentiation, you lose the potential to become all kinds of cells and you lose some of that immortality also.