THE ASSOCIATION OF HUMAN FIBULIN-1 WITH ELASTIC FIBERS - AN IMMUNOHISTOLOGICAL, ULTRASTRUCTURAL, AND RNA STUDY

We examined the pattern of fibulin-1 mRNA and protein expression in hu man tissues and cell lines. Fibulin-1 transcripts were found in RNA is olated from most tissues and a variety of cultured cells, including fi broblasts, smooth muscle cells, and several epithelial cell lines, but not endothelial cells, lymphomyloid cells, or a number of carcinoma a nd melanoma lines. Immunohistochemical analysis showed that fibulin-1 is an intercellular component of connective tissues, predominantly ass ociated with matrix fibers in tissues such as the cervix, dermis, inti mal and medial layers of blood vessels, heart valves, meningeal tissue of the brain, Wharton's jelly of the umbilical cord, testis, and lung . Most of the fibers that were immunoreactive with fibulin-1 antibodie s also stained with antibodies to the elastic fiber proteins elastin a nd fibrillin, as well as with Verhoeff's elastin stain. Immunoelectron microscopic analysis of elastin fibers of skin and saphenous vein rev ealed that fibulin-1 was located within the amorphous core of the fibe rs, similar to elastin, but it was not in the fibrillin-containing, el astin-associated microfibrils. Our finding that fibulin-1 is an elasti c fiber component suggests several possible new functions for fibulin- 1, e.g., that it is a structural protein that contributes to the elast ic properties of connective tissue fibers or that is involved with the process of fibrogenesis.