Curcumin alone does not enhance chondrogenesis in MSCs. A: 14 days high-density culture. Apoptosis or necrosis was observed in MSC cultures (a), MSC cultures treated with curcumin (c) or MSC cultures pre-stimulated four hours with curcumin, followed by incubation with curcumin (e). In contrast, chondrogenesis was observed in MSC cultures treated with the chondrogenic induction medium alone (b), in combination with curcumin (d) or a hour-hour pre-stimulation with curcumin, followed by a combination of curcumin and the chondrogenic induction medium (f). Magnification, 6000×; bar, 1 μm; C, chondrocytes; F, fibroblast-like cells; M, ECM; GF, chondrogenic induction medium. B: The ultrastructural findings above were confirmed by western blotting. Immunoblots of whole cell lysates were probed using antibodies that recognize CSPGs, collagen type II, β1-integrin, Shc, activated-ERK1/2 and Sox-9. Each experiment was performed in triplicate. Expression of the housekeeping gene β-actin was not affected. GF, chondrogenic induction medium.