The galactosaminoglycan-containing decorin and its impact on diseases.

Decorin, a member of the small leucine-rich proteoglycans, is involved in many physiological and pathological processes. Decorin functions not only as structural molecule in organizing the extracellular matrix but also as signaling molecule controlling cell growth, morphogenesis and immunity. Mutations in decorin or alterations in the post-translational modifications of the glycosaminoglycan (GAG) chain lead to connective tissue disorders such as the congenital stromal corneal dystrophy and the Ehlers-Danlos syndrome. The summarized data reveal that decorin has a large impact on biological processes also because of the complex structure of the GAG chain. The complexity of decorin also covers the binding and sequestering of growth factors and their signaling. This shows that the decorin protein and the dermatan sulfate chain of decorin have both a structural function and a signaling function. Since defects in the biosynthesis of either the protein core or the GAG chain lead to structural alterations in the extracellular matrix and changes in the protein expression profile of the cells embedded in the matrix, this review focuses on the insights of structural function of decorin and includes data about dermatan sulfate.