Unlike salamanders, mammals can’t regenerate lost limbs, but they can repair large sections of their ribs.

In a new study in the Journal of Bone and Mineral Research, a team directed by USC Stem Cell researcher Francesca Mariani, PhD, takes a closer look at rib regeneration in both humans and mice.

The first author of the paper, USC medical student Marissa K. Srour, was a USC undergraduate when she started the project, which earned a 2011 USC Discovery Scholar Prize, recognizing exceptional new scholarship.

Using CT imaging, Srour, Mariani and their colleague Janice Lee, MD, DDS, from the University of California, San Francisco, monitored the healing of a human rib that had been partially removed by a surgeon. The missing bone and cartilage partially repaired after six months.

To better understand this repair process, they removed sections of rib cartilage 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,” said Mariani, assistant professor of Cell and Neurobiology and principal investigator in the Eli and Edythe Broad Center for Regenerative Medicine and Stem Cell Research at Keck Medicine of USC.

Additional co-authors include: Jennifer L. Fogel, PhD, Kent T. Yamaguchi, MD, Aaron P. Montgomery, Audrey K. Izuhara, Aaron L. Misakian, Stephanie Lam and Daniel L. Lakeland, PhD, from USC; and Mark M. Urata, MD, DDS, from Children’s Hospital Los Angeles.

Funding for this project came from an Oral and Maxillofacial Surgery Foundation Research Award; the Baxter Medical Scholar Research Fellowship; USC undergraduate fellowships; the Provost, Dean Joan M. Schaeffer, and Rose Hills fellowships; a California Institute of Regenerative Medicine (CIRM) training fellowship; CIRM BRIDGES fellowships through California State University, Fullerton, and Pasadena City College; and the James H. Zumberge Research and Innovation Fund.

The laboratory  also received support for this study and future work from a new $450,000 National Institutes of Health (NIH) Exploratory/Developmental Research Grant Award (R21AR064462) from the NIH’s National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS). The lab will also continue its pioneering research through a second new grant from the Merck Investigator Studies Program as well as through a USC Regenerative Medicine Initiative Award with colleagues Gage Crump, PhD, and Jay Lieberman, MD.

As Mariani explained, “These grants will allow us to accelerate the discovery of new regenerative therapies for the patients who need them the most.”

— By Cristy Lytal