Different patterns of collagen-proteoglycan interaction: a scanning electron microscopy and atomic force microscopy study

The extracellular matrix of unfixed, unstained rat corneal stroma, visualiz ed with high-resolution scanning electron microscopy and atomic force micro scopy after minimal preliminary treatment, appears composed of straight, pa rallel, uniform collagen fibrils regularly spaced by a three-dimensional, i rregular network of thin, delicate proteoglycan filaments. Rat tail tendon, observed under identical conditions, appears instead made of heterogeneous , closely packed fibrils interwoven with orthogonal proteoglycan filaments. pre-treatment with cupromeronic blue just thickens the filaments without a ffecting their spatial layout. Digestion with chondroitinase ABC rids the t endon matrix of all its interconnecting filaments while the corneal stroma architecture remains virtually unaffected, its fibrils always being separat ed by an evident interfibrillar spacing which is never observed in tendon. Our observations indicate that matrix proteoglycans are responsible for bot h the highly regular interfibrillar spacing which is distinctive of corneal stroma, and the strong interfibrillar binding observed in tendon. These op posite interaction patterns appear to be distinctive of different proteogly can species. The molecular details of proteoglycan interactions are still i ncompletely understood and are the subject of ongoing research.