Penelope Mason answered on 7 Jan 2014:
That is actually something that lots of people are working on at the moment. Rejuvenation in humans, however, is massively complicated because we are so highly differentiated. It is possible in the lab to revert a differentiated cell (e.g. skin, heart muscle) back to pluripotency – basically where it’s still a jack of all trades and can become one of many different cell types, and this tends to reset it’s ‘clock’. However, to try to revert cells in a living organism whilst its living is not feasible and I don’t think it ever will be.
Another approach would be to find a way to replenish the stem cell stocks that we have, and allow them to do what they actually do normally – replace old worn-out cells with new ones at the right time in the right place. This at least narrows down how much we would have to interfere. It is still pretty implausible at the moment.
One way to get an idea for how difficult it would be to keep a human rejuvenated is to look at Aubrey de Grey’s strategies for engineered senescence. Aubrey’s a theoretical scientist and most of the things he proposes are currently just not possible at the moment but even if they were, you see how much we would need to intervene. For example, even if we could turn telomerase on in our cells and so stop them dying, we would have basically created a cancer cell. Thus turning telomerase on would have to be precisely calculated in particular cells at particular times, and closely controlled. We just aren’t anywhere near this at the moment.
On a brighter note, there are inherent capacities for rejuvenation in us – for example liver cells have a great capacity for regeneration, hence alcoholics may do enormous amounts of damage to their livers and still have functional capacity. Another good tissue for this is skeletal muscle – it has been shown that the muscle we lose as we get older is largely replaceable into old age, and there have been a few studies on old ladies to prove it! So basically, if you keep exercising throughout life you can retain a lot of your skeletal (and heart) muscle.
Sorry, long answer, and I’ve only scratched the surface…
David Christensen answered on 7 Jan 2014:
Penny’s given a really great answer, but I’ll just add a little bit.
Regenerative medicine is a big research field with the aim of doing just that; helping our bodies rejuvenate. At the moment the most likely way for us to be able to do this is basically by making replacements for anything that is going wrong in our bodies. We’ve had organ transplants that do this for a long time now, but in the future we will be able to make new organs for a patient rather than needing donors to give away their organs.
Or the other option would be to give a small cellular transplant which would help the body repair itself. An example where this might help soon is in repair to broken bones. If we can give stem cells to encourage the bone to repair itself properly, then this would be far better than artificial replacements like those given to older people who suffer hip fracture.
Jennifer Tullet answered on 8 Jan 2014:
You’ve already got really nice answers to this question but just to add something else…
I guess you were really asking about humans here but lots of other animals do rejuvenate very well e.g. Hydra and Brittlestars – scientists are very interested in studying these organisms to find out what it is about their cells that make them able to do this so that we might be able to apply it to ourselves one day.