G Duraine

University of California, Davis, Davis, CA, United States

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Publications (3)11.18 Total impact

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    ABSTRACT: Boundary lubrication is characterized by sliding surfaces separated by a molecularly thin film that reduces friction and wear of the underlying substrate when fluid lubrication cannot be established. In this study, the wear and replenishment rates of articular cartilage were examined in the context of friction coefficient changes, protein loss, and direct imaging of the surface ultrastructure, to determine the efficiency of the boundary lubricant (BL) layer. Depletion of cartilage lubricity occurred with the concomitant loss of surface proteoglycans. Restoration of lubrication by incubation with synovial fluid was much faster than incubation with culture media and isolated superficial zone protein. The replenishment action of the BL layer in articular cartilage was rapid, with the rate of formation exceeding the rate of depletion of the BL layer to effectively protect the tissue from mechanical wear. The obtained results indicate that boundary lubrication in articular cartilage depends in part on a sacrificial layer mechanism. The present study provides insight into the natural mechanisms that minimize wear and resist tissue degeneration over the lifetime of an organism.
    Journal of biomechanics 08/2012; 45(14):2426-31. · 2.66 Impact Factor
  • G D DuRaine, S M T Chan, A H Reddi
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    ABSTRACT: Superficial Zone Protein (SZP) is expressed by the superficial zone chondrocytes and is involved in boundary lubrication of the articular cartilage surface. SZP protein expression is dependent on anatomical location and is regulated by the transforming growth factor-β (TGF-β) pathway. The hypothesis of this study was that between load-bearing, and non-load-bearing locations, of the femoral medial condyle alternative splice isoforms of SZP are different, and regulated by TGF-β1. Using reverse transcription-polymerase chain reaction (RT-PCR) we identified differentially expressed SZP alternative splicing. Using recombinant proteins of the N-terminal region produced from these isoforms, we identified differences in binding to heparin and the extracellular matrix. We identified a novel splice form of SZP (isoform E), lacking exons 2-5. Differences in alternative splicing were observed between anterior load-bearing locations of the femoral medial condyle (M1) compared to the posterior non-load-bearing location (M4). TGF-β1 increased splicing out of exons 4 and 5 encoding a heparin binding domain. The minimal induction time for changes in splicing by TGF-β1 at the M1 location was 1h, although this did change total SZP mRNA levels. Inhibition of Smad3 phosphorylation inhibited TGF-β1 induced splicing, and SZP protein expression. Recombinant proteins corresponding to isoforms upregulated by TGF-β1 had reduced binding. The SZP dimerization domain is located within exon 3. In conclusion, alternative splicing of SZP is regulated by TGF-β1 signaling and may regulate SZP interaction with heparin/heparan sulfate or other components in the extracellular matrix of articular cartilage by splicing out of the heparin binding domain.
    Osteoarthritis and Cartilage 10/2010; 19(1):103-10. · 4.26 Impact Factor
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    ABSTRACT: To determine the roles of superficial zone protein (SZP), hyaluronan (HA), and surface-active phospholipids (SAPL) in boundary lubrication of articular cartilage through systematic enzyme digestion using trypsin, hyaluronidase, and phospolipase-C (PLC) surface treatments. The friction coefficient of articular cartilage surfaces was measured with an atomic force microscope (AFM) before and after enzyme digestion. Surface roughness, adhesion, and stiffness of the articular surface were also measured to determine the mechanism of friction in the boundary lubrication regime. Histology and transmission electron microscopy were used to visualize the surface changes of treatment groups that showed significant friction changes after enzyme digestion. A significant increase in the friction coefficient of both load-bearing and non load-bearing regions of the joint was observed after proteolysis by trypsin. Treatment with trypsin, hyaluronidase, or PLC did not affect the surface roughness. However, trypsin treatment decreased the adhesion significantly. Results indicate that the protein component at the articular cartilage surface is the main boundary lubricant, with SZP being a primary candidate. The prevailing nanoscale deformation processes are likely plastic and/or viscoelastic in nature, suggesting that plowing is the dominant friction mechanism. The findings of this study indicate that SZP plays an intrinsic and critical role in boundary lubrication at the articular surface of cartilage, whereas the effects of HA and SAPL on the tribological behavior are marginal.
    Osteoarthritis and Cartilage 07/2010; 18(7):956-63. · 4.26 Impact Factor

Publication Stats

27 Citations
11.18 Total Impact Points

Institutions

  • 2010–2012
    • University of California, Davis
      • • Center for Comparative Medicine
      • • Department of Orthopaedic Surgery
      Davis, CA, United States