CO-localization of integrins and matrix metalloproteinases in the extracellular matrix of chondrocyte cultures

Abstract

β1-integrins were found in the cartilage matrix, suggesting their implication in the assembly of its architectural scaffold, but the mechanism for this event is not yet clear.

Matrix metalloproteinases (MMPs) may be involved in an integrin-shedding mechanism and matrix β1- integrins may act to alter MMP activity. To begin to address this question, this study was designed to determine whether β1-integrins and MMPs are colocalized in the chondrocytes or in the extracellular matrix of cartilage.

We investigated high-density cultures of limb buds of 12-day-old mouse embryos by double immunofluorescence, immunoelectron microscopy and by coimmunoprecipitation assays in order to examine the localization of β1-integrins and matrix metalloproteinases (MMP-1, MMP-3 and MMP-9) in cartilage.

It was found, that all investigated MMPs and β1- integrins were specifically CO-localized in high-density cartilage cultures. Immunogold and immunofluorescence labelling of both β1-integrins and MMPs were observed not only at the surface of chondrocytes but mainly also in the pericellular space and distributed between collagen fibrils in the extracellular matrix (ECM) as well. Results of immunoprecipitation experiments suggest a functional association of MMPs and β1- integrins in chondrocytes as already described for other cell types.

Further investigations are needed to elucidate the functional association between β1-integrins and MMPs in chondrocytes.