Expression of Notch family members in cultured murine articular chondrocytes.

The Notch family is involved in cell differentiation during embryogenesis. Osteoarthritic chondrocytes undergo morphological and biochemical changes leading to the de-differentiation process. In the study reported here, we were interested in the involvement of the Notch pathway in murine articular chondrocyte de-differentiation. Articular chondrocytes were subjected to several cell culture passages and treated with or without a Notch inhibitor, N-[N-(3, 5-difluorophenacetyl-L-alanyl)]-S-phenylglycine t-Butyl Ester (DAPT). Chondrocyte morphology was studied using optical microscopy. Immunocytochemistry and immunoblot were performed to study the expression of collagens and Notch family members. Without DAPT treatment, chondrocyte de-differentiation resulted in fibroblast-like morphology. This was confirmed by immunocytochemical staining and immunoblot analysis, which showed an increase in collagen type I (col I) and a decrease in collagen type II (col II) expression. With DAPT treatment, de-differentiation was delayed. Immunocytochemistry and immunoblot analysis showed during the first passages inhibition of col II expression, which then was re-instituted during the last passage, suggesting chondrocyte re-differentiation. In the study reported here, we showed that inhibition of the Notch receptor not only delayed the de-differentiation process, but also chondrocyte re-differentiation, which confirms the involvement of the Notch pathway in chondrocyte de-differentiation.