The presence and distribution of lubricin in the caprine intervertebral disc

Abstract

Lubricin is a large, multifunctional glycoprotein that is known to play a role as a boundary lubricant in diarthrodial joint articulation. The hypothesis of this study was that lubricin is present in the intervertebral disc in a distribution consistent with serving to facilitate interlamellar tribology. The objectives were to: (1) determine the distribution of lubricin in the normal caprine disc; and (2) investigate the synthesis of lubricin by caprine annulus fibrosus (AF) and nucleus pulposus (NP) cells in vitro, using immunohistochemical methods. Caprine lumbar intervertebral discs from five levels and four animals were studied. Positive staining revealed the presence of the lubricin in the outer AF of nearly all samples. No staining was present in the inner AF or the NP. Within the outer AF, lubricin was prominent in the layers separating lamellae and in the extracellular matrix of the lamellae. Some of the AF cells within the lubricin-positive regions demonstrated intracellular lubricin staining, suggesting that these cells may be synthesizing the lubricin protein observed. Immunohistochemistry performed on monolayer cultures of primary AF and NP cells demonstrated intracellular lubricin staining in both cell types. Thus, lubricin is selectively present in the outer caprine intervertebral disc AF, and its distribution suggests that it may play a role in interlamellar tribology. Cells from both the annulus and nucleus were found capable of synthesizing lubricin in vitro, suggesting that these cells may be a potential source of the glycoprotein under some conditions. ß

Lubricin/proteoglycan 4 increases in both experimental and naturally occurring equine osteoarthritis

“…Lubricin has been localized to multiple fibrocartilaginous structures, including meniscus 33,34 , intervertebral disc 35,36 and the fibrocartilaginous disc of the temporomandibular joint 37–39 and a variety of other tissues. Lubricin’s biological effects extend beyond its role as a mechanical lubricant, with known roles in chondroprotection through inhibition of chondrocyte apoptosis 40 , inhibition of protein deposition and pannus formation 41 and normalization of subchondral bone remodeling 9 .…”

Measurement of local strains in intervertebral disc anulus fibrosus tissue under dynamic shear: Contributions of matrix fiber orientation and elastin content

“…The AF is a complex structure made up of unidirectional plies composed primarily of types I and II collagen arranged in layers with alternating fiber orientations. Anular plies are interconnected through a hierarchical network of smaller fibers involving interactions between aggrecan, versican, fibrilin, elastin, and lubricin (Sherratt et al 2003; Akhtar et al 2005; Shine and Spector 2008). …”

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

“…The remarkable frictional properties of the tissue are achieved, at least in part, by lubricin, a mucin-like glycoprotein present in synovial fluid (1) and localized at the surface of joint tissue (2)(3)(4). Lubricin is expressed by the proteoglycan 4 (PRG4) gene (5) and is synthesized by a number of tissues, including cartilage, meniscus, intervertebral disc, and tendon (2)(3)(4)(6)(7)(8)(9). There are numerous posttranslated products of the PRG4 gene (5,(10)(11)(12)(13)(14)(15)(16), including megakaryocytestimulating factor precursor and superficial zone protein, which have significant homology to lubricin (11,15), and as such, we will refer to them collectively as lubricin.…”