Preservation of the chondrocyte's pericellular matrix improves cell-induced cartilage formation

The extracellular matrix surrounding chondrocytes within a chondron is likely to affect the metabolic activity of these cells. In this study we investigated this by analyzing protein synthesis by intact chondrons obtained from different types of cartilage and compared this with chondrocytes. Chondrons and chondrocytes from goats from different cartilage sources (articular cartilage, nucleus pulposus, and annulus fibrosus) were cultured for 0, 7, 18, and 25 days in alginate beads. Real-time polymerase chain reaction analyses indicated that the gene expression of Col2a1 was consistently higher by the chondrons compared with the chondrocytes and the Col1a1 gene expression was consistently lower. Western blotting revealed that Type II collagen extracted from the chondrons was cross-linked. No Type I collagen could be extracted. The amount of proteoglycans was higher for the chondrons from articular cartilage and nucleus pulposus compared with the chondrocytes, but no differences were found between chondrons and chondrocytes from annulus fibrosus. The expression of both Mmp2 and Mmp9 was higher by the chondrocytes from articular cartilage and nucleus pulposus compared with the chondrons, whereas no differences were found with the annulus fibrosus cells. Gene expression of Mmp13 increased strongly by the chondrocytes (>50-fold), but not by the chondrons. Taken together, our data suggest that preserving the pericellular matrix has a positive effect on cell-induced cartilage production.