The molecular structure and lubricating activity of lubricin isolated from bovine and human synovial fluids

Abstract

Lubricin was isolated from bovine ankle, metacarpophalangeal and knee and human knee synovial fluids. The lubricins isolated from the bovine joint fluids had the same amino acid and carbohydrate compositions, but differences were observed in the relative molecular masses. The Mr values of bovine metacarpophalangeal and ankle lubricin determined by light-scattering measurements were about 200 000, whereas values of 132 000 and 143 000 were obtained for the bovine knee lubricin. The human knee lubricin had a similar carbohydrate composition to bovine knee lubricin except for the higher glucosamine content, and the amino acid composition differed slightly. The human sample had a lower glutamic acid content and a leucine/isoleucine ratio of 2:1 compared with 1:1 in the bovine. The Mr value of the human knee lubricin (166 000) was also lower than that of the bovine metacarpophalangeal and ankle samples. The Mr value of the bovine knee lubricin determined by sedimentation-equilibrium measurements was 171 000. The length measurements determined by electron microscopy and also the sedimentation measurements showed considerable polydispersity and indicate that the degree of extension of lubricin molecules can vary. Friction measurements showed that the human knee synovial-fluid lubricin had equivalent lubricating ability in a test system in vitro to that observed for lubricin isolated from normal bovine synovial fluids. The lubricating ability of lubricin was concentration-dependent, and each lubricin sample was able to act as a lubricant in vitro in an equivalent manner to whole synovial fluid at concentrations that are thought to occur in vivo.

PRG4 exchange between the articular cartilage surface and synovial fluid

“…Boundary lubrication is one mechanism by which the articular surface of cartilage provides low-friction properties, and is mediated in part by proteoglycan 4 (PRG4) molecules, [1][2][3][4] found both in synovial fluid (SF) and in a layer bound to the articular cartilage surface. 5 In classical descriptions of lubrication modes, boundary lubrication during surface-to-surface contact is mediated by a molecular surface layer or film attached to one or both surfaces, 6 suggesting that the PRG4 bound to the articular cartilage surface mediates boundary lubrication function in the joint.…”

Expression and mapping of lubricin in canine flexor tendon

“…[1][2][3][9][10][11][12] It has the same lubricating properties as normal synovial fluid. [9][10][11][12] Lubricin also stimulates growth of megakaryocyte colonies in vitro. 8 Loss-of-function mutations in lubricin causes camptodactyly-arthropathy-coxa varapericarditis syndrome (CACP).…”

The presence and distribution of lubricin in the caprine intervertebral disc

“…[1][2][3][4][5][6][7] Such molecules may lubricate the interfaces among bundles of collagen fibrils to facilitate the sliding of structures such as the fascicles of tendons. 7 Although earlier work suggested that glycosaminoglycans (GAGs) may be serving in this capacity, 8 more recent investigations have indicated that a lubricating glycoprotein is responsible for the tribology of the internal structures of musculoskeletal tissues.…”