Jay G D, Torres J R, Warman M L, Laderer M C, Breuer K S
Division of Engineering and Department of Emergency Medicine, Brown University, Providence, RI 02912, USA.
Proc Natl Acad Sci U S A. 2007 Apr 10;104(15):6194-9. doi: 10.1073/pnas.0608558104. Epub 2007 Apr 2.
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-particle-tracking microrheology. The time-dependent ensemble-averaged mean-squared displacements of all of the particles were measured over a range of physiologically relevant frequencies. The mean-squared 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 (alpha approximately 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.
滑液是一种半稀释的透明质酸盐（HA）聚合物溶液，其流变学取决于HA与蛋白质的相互作用，而润滑素是一种在滑液和软骨表面发现的HA结合蛋白，在负载下有助于边界润滑。润滑素基因缺陷的个体出现早熟性关节衰竭。润滑素在滑液流变学中的作用尚不清楚。我们使用多粒子追踪微流变技术研究滑液中润滑素与HA之间的分子相互作用。通过多粒子追踪微流变分别追踪嵌入正常和缺乏润滑素的滑液样本中的颗粒（平均直径200nm）。在一系列生理相关频率范围内测量所有颗粒随时间变化的系综平均均方位移。对于简单的HA溶液和来自基因缺乏润滑素个体的滑液，均方位移与时间滞后的相关性斜率为1，而正常滑液的斜率小于1（α约为0.6）。这些数据与相同样本的宏观流变学研究相关。我们发现，在生理剪切速率下，缺乏润滑素患者的滑液不存在亚扩散和弹性行为。我们得出结论，润滑素赋予滑液消散哺乳动物运动诱导的应变能的能力，这是一种不同于边界润滑的软骨保护特性。
