It turns out cartilage in human joints can repair itself similarly to salamanders and zebrafish's ability to regenerate limbs. The new development was discovered by researchers at Duke Health.

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"We believe that an understanding of this 'salamander-like' regenerative capacity in humans, and the critically missing components of this regulatory circuit, could provide the foundation for new approaches to repair joint tissues and possibly whole human limbs," said in a statement senior author Virginia Byers Kraus, M.D., Ph.D., a professor in the departments of Medicine, Pathology and Orthopedic Surgery at Duke.

To make their discovery, Kraus and colleagues, including lead author Ming-Feng Hsueh, Ph.D., had to find a way to determine the age of proteins. They did so using internal molecular clocks integral to amino acids.

Through spectrometry, they were able to identify when key proteins in human cartilage, including collagens, were young, middle-aged or old.

They found that the age of cartilage grew older as you moved up the body. Therefore the cartilage in ankles is young, it is middle-aged in the knee and old in the hips.

They deduced from this that cartilage age correlated with how limb repair occurs in certain animals. Animals more readily regenerate at the furthest tips, including the ends of legs or tails.

microRNA

The researchers also found that molecules called microRNA are responsible for regulating this process in animals. And since these microRNAs are also found in humans, it means humans also possess the capacity for joint tissue repair.

"We were excited to learn that the regulators of regeneration in the salamander limb appear to also be the controllers of joint tissue repair in the human limb," Hsueh said. "We call it our 'inner salamander' capacity."

The researchers now believe that microRNAs could be turned into medicines for treating arthritis.

"We believe we could boost these regulators to fully regenerate degenerated cartilage of an arthritic joint. If we can figure out what regulators we are missing compared with salamanders, we might even be able to add the missing components back and develop a way someday to regenerate part or all of an injured human limb," Kraus said. "We believe this is a fundamental mechanism of repair that could be applied to many tissues, not just cartilage."

The study is published the journal Science Advances.