Biochemistry and functional significance of collagen cross-linking.

The biophysical characteristics of vascular tissues are dependent largely on the properties of fibrillar collagens. Considering the predominant structural component, collagen type I, the present review describes the mechanisms of formation and maturation of lysyl oxidase-mediated cross-linking, leading to an understanding of how intracellular collagen-modifying enzymes affect the patterns of cross-links produced. An important distinction is made between the enzyme-mediated cross-linking, essential for optimum tissue function, and the non-enzymatic aging processes that generally lead to structural changes deleterious to function. Finally, the extracellular matrix of vascular tissue is a multicomponent system and the role of other major constituents, such as elastin and glycosaminoglycans, in modifying tissue properties should be considered. Some details of newer methods being developed to quantify these constituents will be presented.