How humans regenerate ribs decoded

Unlike salamanders, mammals can't regenerate lost limbs, but they can repair large sections of their ribs - and now scientists have discovered what gives rib cells their healing power.
A team directed by University of California, San Francisco Stem Cell researcher Francesca Mariani took a closer look at rib regeneration in both humans and mice.
Using CT imaging, the first author of the paper, Marissa K Srour, Mariani and their colleague Janice Lee, monitored the healing of a human rib that had been partially removed by a surgeon.
The eight centimetres of missing bone and one centimetre of missing cartilage did partially repair after six months.

To better understand this repair process, they surgically removed sections of rib cartilage - ranging from three to five millimetres - from a related mammal, mice.
When they removed both rib cartilage and its surrounding sheath of tissue - called the "perichondrium," the missing sections failed to repair even after nine months.

However, when they removed rib cartilage but left its perichondrium, the missing sections entirely repaired within one to two months.
They also found that a perichondrium retains the ability to produce cartilage even when disconnected from the rib and displaced into nearby muscle tissue - further suggesting that the perichondrium contains progenitor or stem cells.

"We believe that the development of this model in the mouse is important for making progress in the field of skeletal repair, where an acute clinical need is present for ameliorating skeletal injury, chronic osteoarthritis and the severe problems associated with reconstructive surgery," said Mariani.
"At the early stages in our understanding, the mouse provides us with an exceptional ability to make progress, and we are excited about the potential for using cells derived from the rib perichondrium or using rib perichondrium - like cells for regenerative therapy," Miriani said.
The study was published in the Journal of Bone and Mineral Research.