ALPHA-1-VIII COLLAGEN IS EXPRESSED IN THE RAT GLOMERULUS AND IN RESIDENT GLOMERULAR CELLS

Current knowledge regarding the molecular composition of extracellular matrices in the glomerulus does not explain how these components inte ract to form stable three-dimensional structures. The recent recogniti on that short-chain collagens such as type VIII collagen function as m olecular bridges in some nonrenal tissues has raised the possibility t hat such molecules may serve a similar function in the glomerulus. We have recently shown that cultured rat mesangial cells synthesize and s ecrete several short-chain collagenous proteins, one of which has prop erties similar to alpha1-VIII collagen. In the present study we have i solated a rat mesangial cell alpha1-VIII collagen cDNA clone, the sequ ence of which is 81% homologous to mouse alpha1-VIII collagen. We used this cDNA to determine that alpha1-VIII collagen mRNA is expressed in rat renal cortex and in cultured glomerular mesangial, epithelial, an d endothelial cells. Additionally, we demonstrated that alpha1-VIII co llagen is secreted by cultured mesangial cells as an 80-kDa translatio n product. By immunocytochemistry, alpha1-VIII collagen localized to t he media of large intrarenal arteries and to the capillary loops and t he mesangium of normal rat kidney. These results indicate that type VI II collagen is a normal constituent of the rat glomerulus as well as l arge intrarenal arteries. We speculate that type VIII collagen may fun ction in part to determine the three-dimensional organization of the s ubendothelial and mesangial matrices.