Macromolecular component of the subendothelium. Major component of the Descemet's membrane (basement membrane) of corneal endothelial cells. Also a component of the endothelia of blood vessels. Necessary for migration and proliferation of vascular smooth muscle cells and thus, has a potential role in the maintenance of vessel wall integrity and structure, in particular in atherogenesis. Vastatin, the C-terminal fragment comprising the NC1 domain, inhibits aortic endothelial cell proliferation and causes cell apoptosis. Homotrimers, or heterotrimers in association with alpha 2(VIII) type collagens. Four homotrimers can form a tetrahedron stabilized by central interacting C-terminal NC1 trimers (By similarity). High levels in calvarium, eye and skin of newborn mice; also in various epithelial, endothelial and mesenchymal cells. Up-regulated in astrocytes during the repair process and in mesangial cells in diabetic animals. Prolines at the third position of the tripeptide repeating unit (G-X-Y) are hydroxylated in some or all of the chains. Proteolytically cleaved by neutrophil elastase, in vitro. Proteolytic processing produces the C-terminal NC1 domain fragment, vastatin (By similarity). COL8A1(-)/COL8A2(-) mice exhibit decreased proliferation of measngial cells, reduced phosphorylation of ERK1/2 and increased p27(KIP1) expression. Diabetic COL8A1(-)/COL8A2(-) mice reveal reduced mesangial expansion and cellularity and extracellular matrix expansion.