For the first time, Japanese scientists successfully regenerated functional joints in frogs – a breakthrough that may pave the way for functional joint regeneration in humans and other mammals in the future.

A team of researchers from Kyoto University hopes to apply this newly discovered "reintegration" technique in helping transplanted tissues integrates with original limbs and organs following amputation or surgery.

The researchers published their findings in the journal Regeneration.

Some animals – newts, for example – can regenerate a smaller yet fully functioning limb once the original part has been detached. Frogs are deemed to be the middle ground between these animals and mammals incapable of regenerating their limbs.

Frogs regrow "spikes" or cartilage rods that protrude from affected areas – new cartilage limbs that do not have joints and therefore are incapable of bending at will.

In order to be functional, joints need to integrate multiple tissues, namely two opposing skeletons for an interlocking system and muscles that insert into those skeletal tissues. Frogs do not have this tissue-reconnecting ability.

What then is the mechanism that the Japanese team dubbed "reintegration"?

When a frog limb is broken off at an elbow joint, the link between the remaining and regenerated tissues impacts the regenerated elbow's regrowth, such that it is closely similar to the original tissue.

"As a result, the tissue attached to the joint is more similar in size to the original limb," explained the authors led by Kiyokazu Agata in a press release.

They intend to experiment with regenerating functional joint in mice next time, activating the said mechanism.

Further understanding of this process is deemed highly consequential for humans. In the United States alone, there are almost 2 million individuals living with limb loss, with 54 percent from vascular disease such as diabetes and peripheral arterial conditions, 45 percent from trauma, and less than 2 percent from cancer.

About 185,000 amputations take place in the country every year. In 2009, for instance, the cost of amputations in hospitals reached over $8.3 billion.

The grim news is that almost half of those amputated due to vascular disease will likely die within five years, a mortality rate higher than those for breast, colon, and prostate cancers. Of diabetics whose first legs were amputated, an estimated half will require second-leg amputation within two to three years.

Photo: Chris Luczkow | Flickr

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