Abstract
Introduction
Primary cilia are organelles found singularly on almost every cell in the body, including tenocytes. Tendon is a hierarchical, composite structure, and previous work from our group has suggested that the cell populations in the inter-fascicular matrix (IFM) may be different from those within the fascicle matrix (FM). This study investigated how stress deprivation influenced the primary cilia of both cell types, and the mechanics of the IFM and the FM.
Materials and Methods
Rat tail tendons were dissected and then either tested immediately (fresh), or maintained in media for 1 week, either stress deprived or at 4% static strain. Fascicles and IFM were then either, fixed and imaged to determine cilia length (n = 80–160 cilia per group from across 3 rats), or mechanically tested to determine the static and viscoelastic properties of both the fascicles and the IFM (n = 6–8 per group).
Results
Cilia length in the IFM and FM of fresh samples were not significantly different. After 1 week of stress deprivation, the cilia had significantly increased in length in both the IFM and FM, however the increase in length in the IFM was significantly greater than that in the FM. Cilia in tissue maintained at 4% static strain were significantly shorter than those in stress deprived tissue, however they remained longer than those in fresh tissue.
The tensile strength of the fascicles was not affected by stress deprivation or static strain conditions. However, the viscoelastic properties of the stress deprived fascicles were significantly reduced. By contrast, the tensile strength of the IFM was significantly reduced in the stress deprived samples, indicative of greater degradation in this region.
Discussion
This is the first time differences in the cilia have been observed between tendon regions. Their different response to stress deprivation provides further evidence that these populations of cells respond differently to changes in mechanical stimulation.
Cilia length increased more in the region where there was more mechanical degradation, suggesting that cilia are responding to their local mechanical environment.
