Aging results in a breakdown of homeostasis. A full understanding of aging probably will require a complete elucidation of homeostatic mechanisms at the molecular level. Perhaps it would be easier to understand a related question, how do animals avoid aging. Unfortunately, aging of the soma is a near universal phenotype of multicellular animals. Fortunately there are exceptions, for example, individuals of asexual planaria species, either age slowly or perhaps not at all, that is they possess negligible senescence. They are the most complex animal that appears to have this capability. It has been hypothesized that their whole body regenerative capacity is responsible. Pluripotent adult stem cells called neoblasts, the only planarian cell type capable of cell division, are responsible for their unusual regenerative capability. We hypothesize that incomplete regenerative processes in multicellular animals may be seen as utlimately responsible for aging. By understanding how planaria use these stem cells to rejuvenate themselves, we will understand better how aging works in organisms such as ourselves with more limited stem cell function.
The generation of iPS cells from human somatic cells, and the directed differentiation of them into each distinct cell type in the human body, is just the prelude towards rejuvenation of aged tissues. In essence, the reprogrammed pluripotent stem cells are very similar to neoblasts, except they lack critical imprinted information on how to integrate into the host tissue correctly. A feasible solution is to preprogam iPS cells to inhibit any negative side effects, and to integrate using the the correct spatial-temporal information. Such synthetic circuitry is achievable with circuits such as those created by the our iGEM teams.
Turritopsis dohrnii, discovered in 1883, is the only animal capable of reverting itself by transdifferentiation from a mature adult to a younger rejuvenated form. Turritopsis dohrnii is biologically immortal and its limitless ability to continually bypass death by rejuvenation brings promise that a similar process in humans is scientifically possible.
Hydra have a long history in biological research because of their unique ability to avoid cellular aging by replacing old or damaged cells. Similar to the planaria, hydra can regenerate body segments