Chondrogenic differentiation capacity of human mesenchymal progenitor cells derived from subchondral cortico-spongious bone.

Microfracture is frequently used to repair articular cartilage defects and allows mesenchymal progenitors to migrate from subchondral bone into the defect and form cartilaginous repair tissue. The aim of our study was to analyze the cell surface antigen pattern and the differentiation capacity of cells derived from human subchondral bone. Human progenitor cells were derived from subchondral cortico-spongious bone and grown in the presence of human serum. Stem cell-related cell surface antigens were analyzed by flowcytometry. Cortico-spongious progenitor (CSP) cells showed presence of CD73, CD90, CD105, and STRO-1. Multilineage differentiation potential of CSP cells was documented by histological staining and by gene expression analysis of osteogenic, adipogenic, and chondrogenic marker genes. CSP cells formed a mineralized matrix as demonstrated by von Kossa staining and showed induction of osteocalcin, independent of osteogenic stimulation. During adipogenic differentiation, the adipogenic marker genes fatty acid binding protein 4 and peroxisome proliferative activated receptor gamma were induced. Immunohistochemical staining of cartilage-specific type II collagen and induction of the chondrocytic marker genes cartilage oligomeric matrix protein, aggrecan, and types II and IX collagen confirmed TGF beta 3-mediated chondrogenic lineage development. CSP cells from subchondral bone, as known from microfracture, are multipotent stem cell-like mesenchymal progenitors with a high chondrogenic differentiation potential.