Conclusions
The present results underline the suitability of CD166 as a biomarker to identify and, in particular, localize and/or enrich resident MPC with a high chondrogenic potential in human articular cartilage. The percentage of MPC in both OA and normal cartilage is substantially higher than previously reported, suggesting a yet unexplored reserve capacity for regeneration.
Methods
Specimens of human osteoarthritic (OA; n = 11) and normal (n = 3) cartilage were used for either cell isolation or immunohistochemistry. Due to low numbers, isolated cells were expanded for 2 weeks and then analyzed by flow cytometry (FACS) or immunofluorescence in chamber slides for the expression of CD105 and CD166. Following immunomagnetic separation of CD166+/- OA cells, multi-lineage differentiation assays were performed. Also, the zonal distribution of CD166+ cells within the matrix of OA and normal cartilage was analyzed by immunohistochemistry.
Results
FACS analysis showed that 16.7 ± 2.1% (mean ± SEM) of OA and 15.3 ± 2.3 of normal chondrocytes (n.s.) were CD105+/CD166+ and thus carried the established MPC marker combination. Similarly, 13.2% ± 0.9% and 11.7 ± 2.1 of CD105+/CD166+cells, respectively, were identified by immunofluorescence in adherent OA and normal chondrocytes. The CD166+ enriched OA cells showed a stronger induction of the chondrogenic phenotype in differentiation assays than the CD166+ depleted cell population, underlining the chondrogenic potential of the MPC. Strikingly, CD166+ cells in OA and normal articular cartilage sections (22.1 ± 1.7% and 23.6% ± 1.4%, respectively; n.s.) were almost exclusively located in the superficial and middle zone. Conclusions: The present results underline the suitability of CD166 as a biomarker to identify and, in particular, localize and/or enrich resident MPC with a high chondrogenic potential in human articular cartilage. The percentage of MPC in both OA and normal cartilage is substantially higher than previously reported, suggesting a yet unexplored reserve capacity for regeneration.