13 July 2011

Newts re-grow eye lens 18 times over

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The Japanese newt can regenerate its eye lens 18 times over a period of 16 years and retain its structural and functional properties, a new study has found.
Cynops pyrrhogaster

A Japanese newt, Cynops pyrrhogaster. The newt is one of a few vertebrates with spectacular regenerative capabilities. New research has proven that age and repeated injury do not affect this ability. Credit: P. Tsonis, Kenta Nakamura

LONDON: The Japanese newt can regenerate its eye lens 18 times over a period of 16 years and retain its structural and functional properties, a new study has found.

Published in the current issue of Nature Communications, it’s hoped that the findings will increase our understanding of tissue regeneration, particularly in regards to repeated injury and ageing, with future applications in the treatment of burns.

“This is the first time such a study was undertaken for such a long time and with so many repetitions of regeneration,” said co-author Panagiotis Tsonis, director of the Centre for Tissue Regeneration and Engineering at Dayton University, Ohio. “The idea was conceived by the first author, Goro Eguchi, and the inspiration was simple: to answer a fundamental question in regenerative biology.”

Re-growing legs and tails

For 250 years, scientists have known that newts have remarkable regenerative abilities, able to re-grow entire limbs after amputation and restoring their spinal function after paralysing damage.

This ability makes them ideal subjects for studies of tissue regeneration as scientists hope to unravel the secret behind the newt’s marvellous capability for repairing damage to its body as if it never happened.

Although widely studied, the extent to which adult newts retain their regenerative capability with progressing time and age has remained unanswered.

Regenerating an eye lens 18 times

In their study, Tsonis and his team, together with collaborators at the National Institute for Basic Biology in Okazaki, Japan and the Sanford Children’s Health Research Centre in California, have shown that the Japanese newt maintains its ability to regenerate its lens up to 18 times over a period of 16 years.

Plus the tissue of the 17th and 18th regenerated lenses showed structural and functional properties identical to a virginal lens of a younger animal that has never experienced lens regeneration.

In 1994, the scientists collected adult male newts Cynops pyrrhogaster of an estimated age of 14 years in Okazaki, Japan, and succeeded in keeping the animals alive for over 16 years in laboratory conditions.

“The species we used is doing well in a laboratory set and it was believed that with good care they can live long,” said Tsonis. The newts lived to be approximately 30 years of age, exceeding their average lifespan in the wild by five years.

New versus old lens

The lens of each animal was repeatedly removed in a process called lensectomy, during which the researchers made a small cut into the newt’s cornea and extracted the lens while leaving the rest of the eye unharmed.

In all 18 consecutive experiments, the animals were able to generate a new lens within five months, showing that older newts experiencing repeated lensectomies could recover equally rapidly as after their first procedure.

The scientists further examined the regenerated lenses under the microscope and found that the size and transparency of the lens and the structure of its fibres were identical to those of control animals that have not undergone lensectomy.

DNA tests of the lens tissues further confirmed that there were no substantial genetic differences between the two groups.

Findings could help burn victims

The effect repeated damage and aging have on regenerative properties of cells is still poorly understood. This research therefore provides pioneering answers in the field of tissue regeneration.

“Facing the problem of diminished healing capacity in elderly human being, scientists assumed that successful regeneration in the tailed amphibian might be restricted to younger animals as well,” said Kerstin Reimers-Fadhlaoui from Hannover Medical School in Germany, an expert in the field of tissue regeneration who was not involved in the study.

The aspiration is to ultimately translate the findings into mammals and provide new therapies for patients with degenerative diseases, debilitating injuries, or burn victims. However, it is a long way from newts to humans.

“Subsequent research with varying experimental settings and model organisms carefully compared to the model of newt lens regeneration are needed to answer the question if the biological mechanisms underlying the observed repeated regeneration are common or highly specialised,” said Reimers-Fadhlaoui.

But there is still hope, she added. “The mode of cellular stem cell renewal assumed by the authors of the study has been observed by other researchers, for example in mammalian skin regeneration.”

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