GOETTINGEN,Germany—Repair tissue from arthritic human joints contains migratory cartilage-producing “stem” cells that are not found in healthy cartilage that might be the key to repairing joints damaged by osteoarthritis (OA). The preliminary research, which appears in the April 3, 2009 issue of Cell Stem Cell, may pave the way for a disease modifying osteoarthritis drug.¹

“We hope ultimately to work toward utilizing these cells—which are already present in disease tissue—for the development of OA-relevant regenerative therapies,” conclude researchers who were led by Professor Nicolai Miosge from Georg August University in Goettingen, Germany.

These potentially regenerative cells may be specifically recruited to degenerating cartilage.

Damaged cartilage already has potential repair cells

In the new study, the researchers report that repair tissue from human articular cartilage during the late stages of OA contains a unique population of chondrogenic progenitor cells (CPCs).

The CPCs, which were not present in healthy cartilage, have many characteristics associated with tissue-specific stem cells, including clogenicity, multipotency, and migratory activity. The isolated CPCs have high chondrogenic potential.

In ex vivo experiments, Dr. Miosge's group showed that these cells will migrate deep into and proliferate within samples of late-stage human OA tissue.

“The physiological repair mechanisms associated with diseased cartilage are few, and all are generally overridden by matrix destruction that results in less-functional fibrocartilaginous collagen type I-rich scar-like tissue. The discovery of migratory CPCs that are able to grow from diseased cartilage tissue and that exhibit a high chondrogenic potential will open new possibilities for the future treatment of OA,” wrote lead author Sebastian Koelling, MD.

Questions remain about CPC potential in OA

More research is needed to identify how to turn on the CPCs' repair potential in damaged joint cartilage.

“We have yet to confirm that CPCs will produce an extracellular matrix that supports a more cartilage-like repair tissue with a higher physical resistance to mechanical stress than fibrocartilaginous tissue that develops during the course of OA,” the authors write.

Repairing OA with cartilage stem cells: Translating research into practice

“The findings are preliminary,” said MSKreport editorial advisor Stephen Trippel, MD, a professor of orthopaedic surgery at Indiana University School of Medicine in Indianapolis. “If further studies confirm the presence of a specific chondrogenic stem cell population, then those cells may have repair potential. However, one of the challenges of this field is that marrow-derived cells may qualify as chondrogenic stem cells and cells that have undergone chondrogenesis (ie chondrocytes), can, at least in vitro, shift their phenotype toward that of fibroblasts and back again toward that of chondrocytes,” he said. “Thus, the concept of a chondroprogenitor cell is complex.”

However, the investigators point out, “because CPCs migrate into and populate disease cartilage tissue ex vivo, CPCs may be an ideal starting point for the exploration of OA regenerative therapy options.”

References

1. Koelling S, Kruegek J, Irmer M, et al. Migratory chondrogenic progenitor cells from repair tissue during the later stages of human osteoarthritis. Cell Stem Cell. 2009; 4:324-335.