Immortal worms defy aging

February 29, 2012

Planarian flatworm (credit: The University of Nottingham)

Researchers from The University of Nottingham have discovered how planarian flatworms overcome the aging process to be potentially immortal: they can rejuvenate their telomeres.

The discovery, funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and Medical Research Council (MRC), may eventually lead to alleviating aging and age-related characteristics in human cells.

Planarian worms have amazed scientists with their apparently limitless ability to regenerate. Researchers have been studying their ability to replace aged or damaged tissues and cells in a bid to understand the mechanisms underlying their longevity.

“We’ve been studying two types of planarian worms; those that reproduce sexually, like us, and those that reproduce asexually, simply dividing in two,” said Dr. Aziz Aboobaker from the University’s School of Biology.

“Both appear to regenerate indefinitely by growing new muscles, skin, guts and even entire brains over and over again.

“Usually when stem cells divide — to heal wounds, or during reproduction or for growth — they start to show signs of aging. This means that the stem cells are no longer able to divide and so become less able to replace exhausted specialized cells in the tissues of our bodies.

“Our aging skin is perhaps the most visible example of this effect. Planarian worms and their stem cells are somehow able to avoid the aging process and to keep their cells dividing.”

Each time an animal cell divides, the protective telomere “cap” gets shorter. When they get too short, the cell loses its ability to renew and divide. In an immortal animal, we would therefore expect cells to be able to maintain telomere length indefinitely so that they can continue to replicate. Aboobaker predicted that planarian worms actively maintain the ends of their chromosomes in adult stem cells, leading to theoretical immortality.

Previous work, leading to the award of the 2009 Nobel Prize for Physiology or Medicine, had shown that telomeres could be maintained by the activity of an enzyme called telomerase. In most sexually reproducing organisms, the enzyme is most active only during early development. So as we age, telomeres start to reduce in length.

This project identified a possible planarian version of the gene coding for this enzyme and turned down its activity. This resulted in reduced telomere length and proved it was the right gene. They were then able to confidently measure its activity and resulting telomere length and found that asexual worms dramatically increase the activity of this gene when they regenerate, allowing stem cells to maintain their telomeres as they divide to replace missing tissues.

“The next goals for us are to understand the mechanisms in more detail and to understand more about how you evolve an immortal animal,” said Aboobaker.

“The worms are a model system in which we can ask questions, like is it possible for a multicellular animals to be immortal and avoid the effects of aging?,” he told KurzweilAI.

“If so, how does this animal do this in comparison to animals that don’t? Of course we hope that this impacts humans, that’s why we do it. But we aren’t planning on making any drugs or medicines… other people are, I’m sure.”

Ref.: Thomas C. J. Tan et al., , Telomere maintenance and telomerase activity are differentially regulated in asexual and sexual worms, Proceedings of the National Academy of Sciences, 2012 [DOI: 10.1073/pnas.1118885109] (open access)