Expression of β1 integrins during periosteal chondrogenesis

Abstract Objective The interactions between integrins and extracellular matrix proteins are known to modulate cell behavior, and may be involved in regulating cartilage formation and repair. The purpose of this study was to determine the patterns and localization of expression of the β1 integrins during cartilage formation by periosteum, which is used to repair articular cartilage. Design Periosteal explants from 2-month-old rabbit medial proximal tibiae were cultured in agarose suspension for 0 to 6 weeks, with 10ng/ml transforming growth factor-β1 added for the first 2 days of culture. Integrin expressions were measured by reverse transcriptase-polymerase chain reaction (RT-PCR) and localized by immunohistochemistry. Results Normal periosteum expressed the α1, α3, α5, β1 subunits at low levels, and the proteins for all but the α3 subunits were identified by immunohistochemistry in the periosteum. Significant two- to five-fold up-regulation of the mRNA expression of the α1, α3, α5 and β1 integrin subunits during the early proliferative stage of chondrogenesis was observed. The initial change was a five-fold increase in α5 expression on day 2 and a two-fold increase in α3 expression. On day 5, α1 expression was up-regulated (four-fold). β1 expression was broadly up-regulated (three to four-fold) from day 5 to 14. In the early stage of chondrocyte differentiation, after day 14, α1 expression was down-regulated, while there was upregulation of α3 (three-fold), α5 (three-fold) and β1 (four-fold) expressions. Thereafter, α1 expression was down-regulated, while α3, α5 and β1 expressions were up-regulated again during matrix synthesis. Immunohistochemistry confirmed this late decrease in α1 levels and increase in α3, α5 and β1 levels in chondrocytes. Conclusions These observations indicate that the β1 integrins play an important role in the process of chondrogenesis in periosteum.