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

Abstract

ß1-int eg rin s we re found in th e ca rtil age matri x, suggesting their implication in the assembly of its architectural sca ffold , but the mechanism fo r this event is not yet clear. Matrix metalloproteinases (MMPs) may be involved in an int egrin -shedding mechanism and matri x 131- integrins may ac t to alter MMP activity. To begin to address this qu esti o n, this stud y was desig ned to determin e wheth er ß1-in teg rin s and MMPs arc colocali zed in th e chondrocy tes or in the ex trace llul ar matrix of cartil age. We investigated high-densit y cultures of limb buds of 12-day -old mo use embryos by double immunoflu o re ce nce, immun oe lectron mi c rosco py and by coimmunoprccipitation assays in order to examine the loca li za ti o n o f ß1-int egrin s and matri x me ta ll oproteinases (MMP-1, MMP-3 and MMP-9) in cartilage. It was found , that all investigated MMPs and 13 1- integrins we re specifically co-loca li zed in high-density cartil age cultures. Immunogold and immunofluorescence labelling of both ß1-integrins and MMPs were observed not only at the surface of chondrocytes but mainl y also in th e pe rice llul ar space a nd distributed be tw ee n coll agen fibrils in th e ex trace llular matrix (ECM) as we ll. Res ults o f immun oprecipitati o n ex pe riments suggest a fun cti onal assoc iati on of MMPs and 13 Lintegrins in chondrocytes as already described fo r other cell types. Further investigations are needed to elu cidate the fun ctional association between Bl-integrins and MMPs in chondrocytes.