Expression of fibrillins and other microfibril-associated proteins in human bone and osteoblast-like cells

Fibrillin-containing microfibrils are structural components of extracellula r matrices of a diverse range of tissues, including bone. Their importance in bone biology is illustrated by the skeletal abnormalities manifest in th e congenital disorder, Marfan syndrome, which results from mutations in the fibrillin-1 gene. We investigated the expression of fibrillins and other m icrofibril-associated proteins in human bone and bone-derived osteoblasts. Analysis of RNA extracted from cancellous bone showed expression of mRNAs e ncoding fibrillin-1 and -2, MAGP-1 and -2, LTBP-2, and MP78/70 (Big-h3), In demineralized normal mature bone, fibrillin-1 was immunolocalized to fibri ls within the bone matrix and pericellularly to cells lining the endosteal surfaces of trabecular bone, some osteocytes, and cells associated with blo od vessels. LTBP-2 was also identified at the endosteal surface and within the bone matrix in a lamellar fashion. In addition, primary osteoblast-like cells cultured from human trabecular bone (obtained from patients at joint replacement surgery) were found to express abundant mRNA for fibrillins an d associated glycoproteins, Moreover, using western blot analysis, fibrilli n-1 protein was shown to be secreted into the medium and to be deposited in to the cell layer. Immunofluorescence staining of the cell layer visualized fibrillin-1 in the matrix as a three-dimensional network of fine filaments . Expression of fibrillin-1 by osteoblast-like cells was constitutive, and a number of skeletally active agents had little effect on mRNA or protein l evels. These results show that human osteoblasts from mature bone express f ibrillins and other microfibril-associated proteins, and suggest a role for these molecules in adult human bone. (Bone 27:61-67; 2000) (C) 2000 by Els evier Science Inc, All rights reserved.