

Learning from an animal that can regrow its head - pulkitpulkit
http://www.bbc.com/future/story/20141009-the-animal-that-regrows-its-head

======
titanomachy
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.

------
Rizz
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)](http://en.m.wikipedia.org/wiki/Regeneration_\(biology\))

------
exratione
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...](http://www.uni-
kiel.de/aktuell/pm/2012/2012-332-foxogen-e.shtml)

Evolution of human longevity: lessons from Hydra:
[http://www.impactaging.com/papers/v4/n11/full/100510.html](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...](http://www.worldcrunch.com/tech-science/in-swiss-lakes-scientists-
search-for-the-source-of-immortality/immortality-hydrae-biology-stem-cells-
longevity/c4s16797/)

Hydra, a powerful model for aging studies:
[http://www.tandfonline.com/doi/full/10.1080/07924259.2014.92...](http://www.tandfonline.com/doi/full/10.1080/07924259.2014.927805)

