Learning from an animal that can regrow its head

When I hear that an animal can regrow its head, I think of a head in the chordate sense, as in "a hardened container of some kind with a brain and complex sensory organs embedded in it."

Spoiler alert: the creature in this article does not have a "head" in this sense. It's a relatively simple organism which does, admittedly, have some interesting regenerative properties. Exciting title, though.

Children already have some regenerative abilities, a lost finger tip in a child of only a few years will usually grow back if the wound is not sutured close by surgeons. Extending that to all humans might not be all that impossible.

Wikipedia has more information in the mammalian and human sections in the article on regeneration. http://en.m.wikipedia.org/wiki/Regeneration_(biology)

There's always knowledge to be gained from comparative biology. But there's knowledge and then there's applicable knowledge. I think the odds of finding anything that can be ported to humans as a therapy or enhancement on a short enough timescale to be interesting (i.e. less than 20 years from now) are pretty remote. That's true for the process of mining the biochemistry of our fellow mammals, never mind the lower animals.

The unfortunately fact of the matter is that messing with metabolism is exceedingly hard. For example: researchers have spent billions and the past two decades earnestly trying to artificially produce some of the effects of calorie restriction, a beneficial altered metabolic state that is very easily studied in numerous species. What is there to show for all of this effort? One path (rapamycin) that might, maybe, produce a drug family that can recreate just a little of the calorie restriction response - but not soon. Perhaps ten years from now. There is still no full understanding of what is actually going on in calorie restriction, just a high level sketch. Most of the money spent went on what turned out to be a dead end (sirtuins). All in all a grinding, expensive process with little to show for it.

The situation is no different when we are talking about regeneration rather than aging. There are researchers studying salamanders, lizards, zebrafish, hydra (which might or might not be ageless), MRL regenerator mice, cancer-immune naked mole rats, and so forth. There is a growth in understanding of the species-specific biochemistry involved, but in the present environment, in which the research community can't even recreate or fully understand a simple response to environmental circumstance such as calorie restriction given decades and billions of dollars, then what are the odds that they can pull something out of non-mammalian species and make it work in people? Pretty small, I'd say.

The odds of learning lots of interesting things are on the other hand pretty high. If you want to go digging via Google you'll find that a great deal has been gained in recent years in the understanding of salamander regeneration, for example, and the MRL mouse story is also fascinating.

But as to the hydra (not the same thing as the Hydractinia of the article) I penned this a while back. It's as much applicable to regeneration issues as aging issues, and for the variety of lower animals that are highly proficient regenerators.

-------------

Hydra are one of the few ageless species, or at least a good candidate for such: researchers have watched populations age for years with no signs of increased mortality rates or declining pace of reproduction. One might view these creatures as an incremental step up from bacteria or yeast: multicellular animals that can reproduce asexually via budding, and which are extremely proficient at regeneration.

One line of thought regarding the agelessness of hydra is that they simply consistently and relentlessly renew all the tissues in their body, which is accomplished by having very many stem cells that don't decline over time. Hydra might follow a strategy of eliminating the inevitable buildup of malformed proteins, aggregate waste products, and similar damage in individual cells by (a) sacrificing and then replacing damage-bearing cells, and (b) using the bacterial approach of moving as much damage as possible into one of the two daughter cells produced in any cell division. Since a hydra has no brain, any cell can be sacrificed at any time so long as it is replaced with an equivalent new cell - the whole organism can be replaced completely over any arbitrarily short period of time provided it can find the metabolic resources to do so.

There's nothing magical about making cell lineages last essentially forever. All bacteria do it, and even complex organisms like we humans are capable of it. There is, for example, the process that ensures that the first cells of a human child are biologically young and free from damage even though the parents bear decades worth of accumulated damage in their cells. It's also possible that hydra use an aggressive repair and renewal process of this nature, either when they bud or on an ongoing basis.

Aging doesn't happen because it has to, aging happens because it's almost always advantageous from an evolutionary perspective - that we age is an example of the success of the gene built upon the pain, suffering, and death of the individual who bears it. Though apparently this isn't the case for hydra, and many other types of life that are closer to what we might think of as self-replicating machines rather than populations of individual entities. One might argue that the big downside of individual entityhood is the need for brain cells that store data, and thus cannot simply be replaced at arbitrary times. Or perhaps one might argue that a necessary precondition for individual entityhood is a loss of the processes of aggressive regeneration and tissue replacement such that a thing like a brain might be able to evolve in the first place.

In any case, not everything that the aging research community works on is both interesting and potentially useful when it comes to intervening in human aging. Ongoing research into the biology of hydra is certainly interesting, but I'm dubious that we'll find anything that can inform us of a way out of our present predicament, the one in which we are aging to death. We and the hydra live in very different worlds, with very different requirements for success.

-----------

Some further hydra resources for the interested:

FoxO is a critical regulator of stem cell maintenance in immortal Hydra: http://www.uni-kiel.de/aktuell/pm/2012/2012-332-foxogen-e.sh...

Evolution of human longevity: lessons from Hydra: http://www.impactaging.com/papers/v4/n11/full/100510.html

In Swiss Lakes, Scientists Search For The Source Of Immortality: http://www.worldcrunch.com/tech-science/in-swiss-lakes-scien...

Hydra, a powerful model for aging studies: http://www.tandfonline.com/doi/full/10.1080/07924259.2014.92...