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S U M M A R Y Osteoarthritis is a chronic, debilitating joint disease characterized by progressive destruction of articular cartilage. Recently, a number of studies have identified a chondroprogenitor cell population within articular cartilage with significant potential for repair/regeneration. As yet, there are few robust biomarkers of these cells. In this study, we show that monoclonal antibodies recognizing novel chondroitin sulfate sulfation motif epitopes in glycosaminoglycans on proteoglycans can be used to identify metabolically distinct subpopulations of cells specifically within the superficial zone of the tissue and that flow cytometric analysis can recognize these cell subpopulations. Fluorochrome colocalization analysis suggests that the chondroitin sulfate sulphation motifs are associated with a range of cell and extracellular matrix proteoglycans within the stem cell niche that include perlecan and aggrecan but not versican. The unique distributions of these sulphation motifs within the microenvironment of superficial zone chondrocytes, seems to designate early stages of stem/progenitor cell differentiation and is consistent with these molecules playing a functional role in regulating aspects of chondrogenesis. The isolation and further characterization of these cells will lead to an improved understanding of the role novel chondroitin sulfate sulfation plays in articular cartilage development and may contribute significantly to the field of articular cartilage repair. (J Histochem Cytochem 56:125-138, 2008)

The early concepts concerning hematopoietic and epithelial stem cells that were derived from kinetic studies have been greatly enhanced by new information about a range of other properties of somatic and embryonic stem cells. Firstly, the stem and amplifying pattern characteristically established by epithelial lineages has been found to represent an intrinsic pattern that is generated by somatic epithelial stem cells without the need for additional environmental information. Secondly, it is now apparent that somatic epithelial stem cells are plastic and can be directed into a range of new pathways of differentiation by heterotypic interactions. The mechanisms of this plasticity need to be reconciled with the normally stable commitment of these cells to production only of progeny entering a tightly restricted range of phenotypic pathways. The present review discusses the intrinsic properties of epithelial stem cells and how they may be acted upon by connective tissues to generate a wide range of phenotypically different epithelial structures.

KS in the mouse is predominantly undersulfated and generates an immunostaining pattern that differs from that observed in corneas of other mammalian species thus far investigated. The mouse cornea resembles other mammalian corneas in the presence of filamentous arrays of small, collagen-associated stromal PGs visualized by cationic dye staining. However, large dye-positive structures with a CS/DS component are also present and appear to be unique to the cornea of this species.