Human cells unable to express decoron produced disorganised extracellular matrix lacking "shape modules" (interfibrillar proteoglycan bridges)

The shapes of extracellular matrices are determined by positioning collagen fibrils in the right places, oriented and maintained viv-à-vis each other. The fibrils are linked orthogonally by dermatan/chondroitin sulfates or keratan sulfate (in small proteoglycans) attached every ∼65 nm via their protein moieties to collagen fibrils at specific binding sites. These regular repeating structures are the “shape modules.” The characteristic arrays of orthogonal interfibrillar bridges were missing and the extracellular matrix was totally disorganized in matrices produced by fibroblasts taken postmortem from skin of an electively aborted fetus which did not express decoron in culture, thus supporting the shape module hypothesis. Biglycon, dermatan sulfate, heparan sulfate, collagen, and hyaluronan were produced by these cells but did not contribute to a normal extracellular matrix. A similar electron histochemical and biochemical survey of extracellular matrices produced by seven normal and eight osteogenesis imperfecta cell lines from donors of different ages and both sexes showed no comparable disruptions of their matrices. This investigation appears to be the first to demonstrate systematically proteoglycan:collagen interactions in matrices produced by cultured human cells.