Comparative analysis of fresh chondrocytes, cultured chondrocytes and chondroprogenitors derived from human articular cartilage.

Interest in chondroprogenitors arose due to their inherent stem cell like properties, and their initial characterization was based on identification of a small percentage of CD49e positive cells in cultured chondrocytes (CC). It was further noted that when fresh chondrocytes (FC; reported to express low CD49e) were subjected to fibronectin adhesion assay, an isolate of chondroprogenitors was obtained, which was highly positive for CD49e, thus making it a distinguishing marker for this cell population. However, this notion was challenged when reports demonstrated high CD49e expression in CC as well. Therefore, our aim was to compare CD49e expression in FC, CC and chondroprogenitors. Chondrocytes and chondroprogenitors were isolated from articular cartilage of osteoarthritic joints from three patients. Assessment of classic fibronectin receptor (CD49e, CD29), positive (CD105, CD73, CD90) and negative (CD45, CD34) mesenchymal stem cell marker expression in all groups was performed, as chondroprogenitors fulfill the minimal criteria laid down by International Society for Cellular Therapy. Following this, adipogenic, osteogenic and chondrogenic differentiation was assessed by Oil red O, Alizarin Red and Alcian Blue staining respectively. Our observations indicate that FC show significantly low surface marker expression as compared to CC and chondroprogenitors, whereas no significant difference was seen in values when CC and chondroprogenitors were compared. Moreover, comparable results were exhibited when trilineage differentiation potential was compared across groups. Since CC and chondroprogenitors show similar characteristics, there is a pressing need for a specific differentiating marker to isolate a pure population of chondroprogenitors.