Perlecan is a large and complex protein composed of multiple modules which have growth-regulatory and cell adhesion among its properties. These studies are designed to characterize the heparan sulfate proteoglycan (HSPG) perlecan in the synovium at the molecular, biochemical and immunochemical levels and determine the gene expression and regulation of perlecan in normal synovial cells and synovial cells derived from rheumatoid arthritis (RA) and osteoarthritis (OA). The tissue-specific nature of synovial cell produced perlecan along with any differences in the gene expression and biochemical characteristics (i.e. size and side chain composition) of perlecan in synovium will be of fundamental importance to understanding the function of the synovium. A unique feature of this research proposal is that the synovium has been a tissue overlooked in regard to this proteoglycan primarily due to the normal and expected distribution of perlecan as part of the basement membrane. Without our recent cloning of the first human perlecan cDNA (and subsequent entire 14.5 kb cDNA), studies of perlecan mRNA using specific human perlecan probes were not possible. In preliminary studies, we have identified that synovial cells express perlecan and that there is significantly less perlecan mRNA expressed in RA synovial cells in comparison to non-arthritic and OA derived synovial cells. Although the complex character of the perlecan core protein has been partly elucidated where specific domains could be involved in important biological functions such as binding growth factors and prolonging their half-life, the precise role perlecan occupies in the synovium is presently unknown. Proinflammatory cytokines, IL-1 and TNF-alpha as well as TGF-beta and FGF will be examined in this proposal for their effects on perlecan gene transcription and biosynthesis. The existence of alternatively spliced perlecan transcripts in synovial cells will be investigated and the effects of these cytokines on their expression determined. Since perlecan is one of the major components of the classic basement membrane and had not been identified in the synovium until these studies, its further characterization in the synovium will provide new and important information. Recent studies show there are shared structural features between synovium and basement membranes, therefore, it would seem likely that many of the functions would also be in common. The presence and character of perlecan in the synovium would be of basis importance to re- defining the structure and function of this specialized tissue. The realized goals of this proposal will substantially add to our understanding of the synovium in normal joint homeostasis and in arthritis-related pathology.
