Question: What's your thoughts or hypothesis on human regeneration?

Juan Carlos Lopez-Baez answered on 13 Mar 2014:

Hi @em1ly7

Very good question! Well, my thought on it is that human regeneration will be one of the key medical advances of the future!

See, I think that learning about regeneration from other animals, such as zebrafish, will help us understand and know how to be able to activate the regeneration in our bodies. Regeneration can be achieved in two ways:

1. By the activation of special cells inside our organs called stem cells.
2. If there are no stem cells in the organ, by the creation of these cells via a process called “dedifferentiation”, which is when normal cells change the expression of their genes (these are the bits of information in our DNA that tell the cell how to be) to make them be similar to those of a stem cell.

As humans, we have the capacity to regenerate some of our organs using stem cells in them, unfortunately it is only a handful of organs that have these cells. Two great examples of this regeneration are the skin and the blood system. In both, cells are continuously been lost and created, with the new cells replacing the old cells all the time (even as we speak). It is said that 2.4 million blood cells are made every second by our body to replace dying cells and that you will have a “new” skin in your body every 27 days. As these are constantly being regenerated (known as physiological regeneration), then any damage to them will be dealt with reasonably quickly. This is the reason why if you have a small wound it will cure in a few days or weeks and if you give blood, you body will quickly make more blood cells to restore the balance again.

Humans are also able to regenerate some organs after they have been damaged, which under normal conditions will not be regenerating (this is called reparative regeneration). Some examples of tissues and organ that are able to do that are the muscles, the liver and some parts of the brain. The liver is the organ with the most extraordinary capacity to regenerate, as it can make a new liver even if only 1/5th of it is left. Muscles on the other hand can regenerate when damaged, but are not as efficient as livers in doing so. Lastly, the neurons in our brains can regenerate, but they are very slow in doing that and most of the time not very efficient. The reason for all this regeneration is that each one of these organs have specialised stem cells in them that become activated when the damage happens.

In regenerative medicine they are trying to uncover how do stem cells work in the different organs and what are the signals needed to activate them. They are also looking at the process of dedifferentiation and trying to see whether it is something that can be activated in humans, in the organs that have no stem cells in them. We are still some years away from being able to have routine regenerative treatments in humans, but very big advances are being made. The goal will be that in some years we would be able to treat patients that have lost a leg or have other damaged tissues or organs by activating the regeneration process inside of them.