Shearing of synovial fluid activates latent TGF-β

Osteoarthritis Cartilage. 2012 Nov;20(11):1374-82. doi: 10.1016/j.joca.2012.07.006. Epub 2012 Jul 31.

Abstract

Objective: TGF-β is synthesized in an inactive latent complex that is unable to bind to membrane receptors, thus unable to induce a cellular biological response until it has been activated. In addition to activation by chemical mediators, recent studies have demonstrated that mechanical forces may activate latent TGF-βvia integrin-mediated cellular contractions, or mechanical shearing of blood serum. Since TGF-β is present in synovial fluid in latent form, and since normal diarthrodial joint function produces fluid shear, this study tested the hypothesis that the native latent TGF-β1 of synovial fluid can be activated by shearing.

Design: Synovial fluid from 26 bovine joints and three adult human joints was sheared at mean shear rates up to 4000 s(-1) for up to 15 h.

Results: Unsheared synovial fluid was found to contain high levels of latent TGF-β1 (4.35 ± 2.02 ng/mL bovine, 1.84 ± 0.89 ng/mL human; mean ± radius of 95% confidence interval) and low amounts (<0.05 ng/mL) of the active peptide. Synovial fluid concentrations of active TGF-β1 increased monotonically with shear rate and shearing duration, reaching levels of 2.64 ± 1.22 ng/mL for bovine and 0.60 ± 0.39 ng/mL for human synovial fluid. Following termination of shearing, there was no statistical change in these active levels over the next 8 h for either species, demonstrating long-term stability of the activated peptide. The unsheared control group continued to exhibit negligible levels of active TGF-β1 at all times.

Conclusions: Results confirmed the hypothesis of this study and suggest that shearing of synovial fluid might contribute an additional biosynthetic effect of mechanical loading of diarthrodial joints.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Biomechanical Phenomena
  • Cattle
  • Humans
  • Middle Aged
  • Shear Strength / physiology*
  • Stifle / physiology*
  • Stress, Mechanical*
  • Synovial Fluid / chemistry
  • Synovial Fluid / metabolism*
  • Transforming Growth Factor beta / analysis
  • Transforming Growth Factor beta / metabolism*
  • Weight-Bearing / physiology

Substances

  • Transforming Growth Factor beta