The role of lubricin in the mechanical behavior of synovial fluid

Abstract

Synovial fluid is a semidilute hyaluronate (HA) polymer solution, the rheology of which depends on HA-protein interactions, and lubricin is a HA-binding protein found in synovial fluid and at cartilage surfaces, where it contributes to boundary lubrication under load. Individuals with genetic deficiency of lubricin develop precocious joint failure. The role of lubricin in synovial fluid rheology is not known. We used a multiple-particle-tracking microrheology technique to study the molecular interactions between lubricin and HA in synovial fluid. Particles (200 nm mean diameter) embedded in normal and lubricin-deficient synovial fluid samples were tracked separately by using multiple-particletracking microrheology. The time-dependent ensemble-averaged mean-squared displacements of all of the particles were measured over a range of physiologically relevant frequencies. The meansquared displacement correlation with time lag had slopes with values of unity for simple HA solutions and for synovial fluid from an individual who genetically lacked lubricin, in contrast to slopes with values less than unity (␣ Ϸ 0.6) for normal synovial fluid. These data correlated with bulk rheology studies of the same samples. We found that the subdiffusive and elastic behavior of synovial fluid, at physiological shear rates, was absent in fluid from a patient who lacks lubricin. We conclude that lubricin provides synovial fluid with an ability to dissipate strain energy induced by mammalian locomotion, which is a chondroprotective feature that is distinct from boundary lubrication.diffusion ͉ hyaluronic acid ͉ microheology ͉ PRG4 ͉ Einstein-Stokes relation

Alteration of articular cartilage frictional properties by transforming growth factor β, interleukin‐1β, and oncostatin M

“…Lubricin has been shown to play several important roles in the maintenance of joint metabolism, including boundary lubrication of cartilage (17,18) and chondroprotection, by contributing to the elastic absorption and energy dissipation of synovial fluid (19) and inhibiting synovial cell overgrowth (20). Lubricin has been observed to lubricate a range of bearings, from latex-glass to cartilage-cartilage, in the boundary mode regime (18,(21)(22)(23), although the mechanism of lubrication is not fully understood.…”

Distribution of Lubricin in the Ruptured Human Rotator Cuff and Biceps Tendon: A Pilot Study

“…It is synthesized by synovial cells [1,24] and plays an important role in joint lubrication [15,31]. Subsequent reports indicate another protein, superficial zone protein synthesized by superficial zone chondrocytes [26], is homologous to megakaryocyte stimulating factor [7] and lubricin [14] and that these proteins are products of the megakaryocyte stimulating factor gene [14].…”

Advances in Bio-inspired Tribology for Engineering Applications

“…Investigations into lubricin are also being made by Alexandra et al [23] to synthesize and characterize a libricin mimic which will be able to behave similar to lubricin in synovial fluids and be able to reduce friction and adhesion on articular cartilage surface. Recently, many such research concerning role of lubricin and boundary layer lubrication have been analyzed with respect to the lubrication and wear mechanisms observed in synovial joints and articular joints in general [24][25][26][27][28][29][30][31]. These researches are aimed to help better understand the technology behind one of nature's most effective lubrication mechanism.…”