Evaluation of proteoglycan content (glycosaminoglycan) of articular cartilage by Toluidine- Blue (TB) staining –magnification: X1000; A) The control group: Metachromatic staining reaction in proteoglycan component is indicative of the presence of GAG in the hyaline cartilage matrix, B) The OA group: The absence of metachromasia is due to reduction of GAG, which indicates structural changes. The arrow, arrow head and star symbols, are respectively hallmark of the formation of a self- renewed fibrouse, cartilage and bone tissues, C) The ASC group. The arrows show The metachromatic regions around the cells that are indicative of renovation of GAG, D) Chondron group. The metachromatic areas around the cells represent the production of glycosaminoglycan, E) Co-culture of chondron and ASC group. Normal hyaline cartilage with less total glycosaminoglycan content compared to the control group.