Regeneration and Regrowth – will Humans ever Achieve it?
Limb regeneration is one of the Holy Grails of science, right up there with a cure for cancer and one for AIDS. As happens so often in the world of modern medicine, researchers are looking at the animal kingdom to provide themselves with a trail of bread crumbs that might lead to the ultimate prize.
As kids, many of us learned - and were completely fascinated by - the fact that a single starfish can regenerate new wholes from any part of its body that is severed. Relatively more complex living organisms like fish can regenerate significant portions of the brains, hearts and fins. A salamander can even regrow entire limbs.
In humans, our regenerative abilities do not even come close. At most, an individual may regrow the tip of a finger if the nail is largely intact. This is due to the presence of epithelial stem cells which may be found under the nail. Limb regeneration, however, is still in the realm of science fiction.
The exact process of regeneration is still largely not understood. What we do know is that when an injury occurs, stem cells gather at the site of the wound to form a structure known as a blastema.
In regenerative animals, one of two mechanisms may be responsible for the process. In the first, all the stem cells at the blastema are of a single type known as a multipotent or pluripotent stem cell. These are versatile stem cells that can detect the types of tissues like bone, tendon and muscle that need to be produced at the injury site and go about the task.
The second mechanism suggests that a different type of stem cells is required to create every different element of the missing structure. When required, the body sends all necessary types of stem cells to the site of the injury and they perform their respective roles.
It is the latter type that exists in the human body. However, the million dollar question is why humans are only able to regenerate minor tissue and heal wounds while the salamander – which has absolutely the same type of stem cells – can produce an entire limb.
It is quite wondrous to note that in every one of the individual research projects into regeneration, the focus is on the animal kingdom. We might consider ourselves the tip of the evolutionary tree, but the rest of the living world certainly has some admirable aces up its collective sleeve.