Type XVIII Collagen

Summary Type XVIII collagen possesses features of collagens and proteoglycans and is localized in various basement membrane zones. Endostatin, the carboxyl-terminal fragment of type XVIII collagen, has been found to inhibit angiogenesis and tumor growth. There are three isoforms of type XVIII collagen: short, middle, and long. The short isoform is present in vascular and epithelial basement membrane structures, and the long isoform is highly expressed in the liver. Nonsense and missense mutations of type XVIII collagen lead to the autosomal recessive disorder Knobloch syndrome-1, which is characterized by eye abnormalities. COL18A1−/− knockout mice likewise suffer from eye abnormalities and manifest broadened basement membrane structures. This suggests that type XVIII collagen not only is involved in eye development but also has an important role in maintaining basement membrane integrity. Type XVIII collagen is the prime example of a collagen that holds structural properties in the intact form and signaling potential in the degraded form.