Gap junction permeability between tenocytes within tendon fascicles is suppressed by tensile loading
- 800 Downloads
Gap junction communication is an essential component in the mechanosensitive response of tenocytes. However, little is known about direct mechanoregulation of gap junction turnover and permeability. The present study tests the hypothesis that mechanical loading alters gap junction communication between tenocyte within tendon fascicles. Viable tenocytes within rat tail tendon fasicles were labelled with calcein-AM and subjected to a fluorescent loss induced by photobleaching (FLIP) protocol. A designated target cell within a row of tenocytes was continuously photobleached at 100% laser power whilst recording the fluorescent intensity of neighbouring cells. A mathematical compartment model was developed to estimate the intercellular communication between tenocytes based upon the experimental FLIP data. This produced a permeability parameter, k, which quantifies the degree of functioning gap functions between cells as confirmed by the complete inhibition of FLIP by the inhibitor 18α-glycyrrhentic acid. The application of 1N static tensile load for 10 min had no effect on gap junction communication. However, when loading was increased to 1 h, there was a statistically significant reduction in gap junction permeability. This coincided with suppression of connexin 43 protein expression in loaded samples as determined by confocal immunofluorescence. However, there was an upregulation of connexin 43 mRNA. These findings demonstrate that tenocytes remodel their gap junctions in response to alterations in mechanical loading with a complex mechanosensitive mechanism of breakdown and remodelling. This is therefore the first study to show that tenocyte gap junctions are not only important in transmitting mechanically activated signals but that mechanical loading directly regulates gap junction permeability.
KeywordsTendon Gap junction FLIP Connexin Mechanotransduction
The present study was funded by an the UK Engineering and Physical Science Research Council (EPSRC) Platform Grant (No. EP/E046975/1).
This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.
- Banes AJ, Horesovsky G, Tsuzaki M, Boitano S, Lawrence WT, Brown T, Weinhold P, Kenamond C, Benjamin M, Ralphs JR, McNeilly C, Burt J, Miller L (1999a) The connexin 43 gap junction is a mechanosensitive gene in avian flexor tendon cells. In: Caterson B, Archer C, Benjamin M, Ralphs J (eds) The biology of the synovial joint. Harwood Academic Publishers, Netherlands, pp 279–299Google Scholar
- Garcia M, Knight MM (2010) Cyclic Loading Opens Hemichannels to Release ATP as Part of a Chondrocyte Mechanotransduction Pathway. J Orthop Res 28: 510–515Google Scholar
- Lavagnino M, Arnoczky SP, Tian T, Vaupel Z (2003) Effect of amplitude and frequency of cyclic tensile strain on the inhibition of MMP-1 mRNA expression in tendon cells: an in vitro study. Connect Tissue Res 44: 181–187Google Scholar
- McNeilly CM, Banes AJ, Benjamin M, Ralphs JR (1996) Tendon cells in vivo form a three dimensional network of cell process linked by gap junctions. J Anat 189: 593–600Google Scholar
- Screen HRC, Lee DA, Bader DL, Shelton JC (2004) An investigation into the effects of the hierarchical structure of tendon fascicles on micromechanical properties. Proc Inst Mech Eng H 218H: 109–119Google Scholar
- Wall ME, Banes AJ (2005) Early responses to mechanical load in tendon: role for calcium signaling, gap junctions and intercellular communication. J Musculoskelet Neuronal Interact 5: 70–84Google Scholar