Article: Reesink, HL; Bonnevie, ED; Liu, S; Shurer, CR; Hollander, MJ; Bonassar, LJ; Nixon, AJ; (2016) “Galectin-3 Binds to Lubricin and Reinforces the Lubricating Boundary Layer of Articular Cartilage”, Scientific Reports, 6
Abstract: Lubricin is a mucinous, synovial fluid glycoprotein that enables near frictionless joint motion via adsorption to the surface of articular cartilage and its lubricating properties in solution. Extensive O-linked glycosylation within lubricin’s mucin-rich domain is critical for its boundary lubricating function; however, it is unknown exactly how glycosylation facilitates cartilage lubrication. Here, we find that the lubricin glycome is enriched with terminal beta-galactosides, known binding partners for a family of multivalent lectins called galectins. Of the galectin family members present in synovial fluid, we find that galectin-3 is a specific, high-affinity binding partner for lubricin.
Considering the known ability of galectin-3 to crosslink glycoproteins, we hypothesized that galectins could augment lubrication via biomechanical stabilization of the lubricin boundary layer. We find that competitive inhibition of galectin binding results in lubricin loss from the cartilage surface, and addition of multimeric galectin-3 enhances cartilage lubrication. We also find that galectin-3 has low affinity for the surface layer of osteoarthritic cartilage and has reduced affinity for sialylated O-glycans, a glycophenotype associated with inflammatory conditions. Together, our results suggest that galectin-3 reinforces the lubricin boundary layer; which, in turn, enhances cartilage lubrication and may delay the onset and progression of arthritis.
Funding Acknowledgement: Harry M. Zweig Memorial Fund for Equine Research; NIH from the National Center for Research Resources [T32ODO11000]; Grayson-Jockey Club Storm Cat Career Development Award; NSF GRFP [11-582]; NYSTEM [CO29155]; National Institutes of Health (NIH) [P41GM10349010, S10OD018516]
Funding Text: The authors thank John O’Donnell, Holger Sondermann and Cynthia Kinsland for their excellent technical assistance and use of FPLC equipment for the purification of equine lubricin and recombinant galectins. The authors acknowledge C. Bertozzi for providing recombinant human galectin-1 and galectin-3 constructs. Funding for this research was provided by the Harry M. Zweig Memorial Fund for Equine Research (A.J.N., H.L.R.), NIH grant number T32ODO11000 from the National Center for Research Resources (H.L.R.), the Grayson-Jockey Club Storm Cat Career Development Award (H.L.R.), and the NSF GRFP 11-582 (EDB). Imaging data was acquired in the Cornell BRC-Imaging Facility using the shared, NYSTEM (CO29155)- and NIH (S10OD018516)-funded Zeiss LSM880 confocal/multiphoton microscope. Glycan analysis was supported in part by the National Institutes of Health (NIH)-funded Research Resource for Biomedical Glycomics (NIH grant no P41GM10349010) to Parastoo Azadi at the Complex Carbohydra!