Chondrocyte heterogeneity: Immunohistologically defined variation of integrin expression at different sites in human fetal knees

Abstract

During development and at maturity different forms of cartilage vary in morphology and macromolecular content. This reflects heterogeneity of chondrocyte activity, in part involving differential interactions with the adjacent extracellular matrix via specialized cell surface receptors such as integrins. We undertook an immunohistological study on a series of human fetal knee joints to assess variation in the expression of integrins by chondrocytes and potential matrix ligands in articular, epiphyseal, growth plate, and meniscal cartilage. The results show that articular chondrocytes (β1+, β5αV+, α1+, α2+/-, α5+, weakly α6+, αV+) differed from epiphyseal (β1+, β5αV+, α1+/-, α2+/-, α5+, α6+, αV+) growth plate (β1+, β5αV+, α1-, α2-, α5+, α6+, αV+), and meniscal cells (β1+, β5αV+, α1+, strongly α2+, α5+, α6+, αV+ in expression of integrin subunits. There was no expression of β3, β4, β6, or β3 by chondrocytes. These results differ from previous reports on the expression of integrins by adult articular cartilage, where α2 and α6 are not seen. Variation in distribution of matrix ligands was also seen. Fibronectin, laminin and Type VI collagen were expressed in all cartilages but there was restricted expression of tenascin, ED-A and ED-B fibronectin isoforms (articular cartilage and meniscus), and vitronectin (absent from growth plate cartilage). Regulated expression of integrins by chondrocytes, associated with changes in the pericellular matrix composition, is of potential importance in control of cartilage differentiation and function in health and disease.