195 Preservation of the Chondrocytes Pericellular Matrix Improves Cell-Induced Cartilage Formation (original) (raw)

2009, Osteoarthritis and Cartilage

Purpose: Chondrocytes are often used for cartilage tissue engineering. However, in native cartilage, the chondrocytes are surrounded by a pericellular matrix, together forming the chondron. Since cells are influenced by their surroundings, we hypothesized that retaining the pericellular microenvironment would influence the synthetic capacity of the chondrocytes. Therefore the aim of this study was to investigate whether the pericellular matrix has an effect on cell-induced cartilage formation. Methods: Chondrocytes and chondrons isolated from nucleus pulposus (NP), annulus fibrosus (AF), and articular cartilage (AC) from goats, were cultured for 25 days in alginate beads. After 7, 18 and 25 days of culture, the amount of proteoglycans present in the alginate beads was measured and collagen was extracted from the beads. Immunoblotting for type II collagen was performed on the collagen extracted from the alginate beads. Protein expression of matrix metalloproteinase 2 (Mmp2) and Mmp9 was analyzed by zymography and gene expression levels of Mmp13 were measured by real-time PCR. Results: Chondrons and chondrocytes were successfully isolated from AC, AF, and NP. The amount of proteoglycans found in the alginate beads was significantly higher in the chondrons from AC and NP compared to the chondrocytes, but no differences were found between chondrons and chondrocytes from AF. The type II collagen that was extracted from the alginate beads containing the chondrons from all the cartilage sources was cross-linked, whereas the type II collagen produced by the chondrocytes consisted only of non-crosslinked alpha1 (II) chains. Both Mmp2 and Mmp9 expression were higher by the chondrocytes from AC and NP compared to the chondrons, no differences were found with the AF cells. At day 0 the gene expression levels of MMP13 were low in both chondrocytes and chondrons. However, after 18 and 25 days of culture, there was a significant increased expression by the chondrocytes and not by the chondrons. Conclusions: This study shows that maintaining the native chondrocytes pericellular matrix affects both anabolic and catabolic activities. The cross-links present in the type II collagen produced by the chondrons isolated from all the different tissues suggests that the pericellular matrix has an effect on the expression or the activity of enzymes involved in collagen cross-linking. The type II collagen produced by the chondrons does more resemble the collagen found in the native tissues. It is also likely that the altered cell-ECM interactions caused by removal of the pericellular matrix plays a role in the increased expression of the matrix metalloproteinases. Taken together, our data suggest that the extracellular matrix surrounding the chondrocytes is essential for maintaining its proper composition and that preserving the thin matrix layer surrounding the chondrocytes improves cell-induced hyaline cartilage formation.