Alterations in CD44 isoforms and HAS expression in human articular chondrocytes during the de- and re-differentiation processes

Abstract

Abstract. The purpose of this study was to investigate the expression of different CD44 and hyaluronan synthase isoforms in cartilage, their alterations during the chondrocyte dedifferentiation process in monolayer culture and during the redifferentiation process on 3D scaffolds. Chondrocytes isolated from human articular cartilage were cultured as a monolayer for up to 36 days and were seeded on two different 3D scaffolds (HYAFF ® 11 and Bio-Gide ® ). Expression levels of CD44s, CD44-lt, CD44-st, HAS1, HAS2, HAS3 and UDPGD were determined by real-time RT-PCR at different time points. At the protein level CD44 and CD90 were analyzed by flow cytometry. HAS2 was found to be the predominantly expressed hyaluronan synthase in chondrocytes and was not subjected to any regulation during the dedifferentiation process. CD44s, CD44-lt, CD44-st and UDPGD, however, were upregulated immediately after cell isolation. In addition, a high cell density was found to significantly increase CD44-st and CD44-lt expression. Redifferentiation on 3D scaffolds reversed the increase of the CD44 expression. Our data point out that CD44 expression does not correlate with matrix assembly in chondrocytes and that CD44 has a regulatory function in chondrocytes, not necessarily on differentiation, but probably on proliferation.

Chondrogenic capacity and alterations in hyaluronan synthesis of cultured human osteoarthritic chondrocytes

“…Although there are several reports that have shown the expression pattern or functions of HAS isoforms in cell lines, synovial cells or chondrocytes [3,6,19–22], there seems no consensus as to how isoform usage affects the synthesis or function of HA in human joints. The present study demonstrates that all three HAS isoforms are expressed in nearly equal copy numbers by the cells of intact OA cartilage and primary chondrocyte cultures with a slight preponderance of HAS1 in the native cartilage.…”

The influence of scaffold architecture on chondrocyte distribution and behavior in matrix-associated chondrocyte transplantation grafts

“…A recent study showed upregulation of certain CD44 isoforms during dedifferentiation of chondrocytes in 2D culture [51], suggesting even better binding properties in their dedifferentiated stage. Chondrocytes seeded onto the hyaluronan web for graft generation are also dedifferentiated because they are kept in 2D conditions before 3D cultivation.…”

Pronounced Biomaterial Dependency in Cartilage Regeneration Using Nonexpanded Compared with Expanded Chondrocytes

“…The positive effects of high-molecular-weight HA may be mediated by creating a favorable environment for regeneration by reducing degradative enzymes, rather than by having a direct stimulatory effect on cartilage matrix synthesis. Lack of a similar effect on expanded chondrocytes may be explained by the altered expression of CD44 by expansion [49]. It may also be possible that the high amount of sulfated GAGs measured by the dimethylmethylene blue assay, which is generally thought to represent aggrecan production by chondrocytes, may at least partly be explained by the production of other proteoglycans.…”