The Effects Of Mechanical Loading On Mouse Achilles Tenon Stem Cell (tscs)

The major function of tendons which are constantly subjected to mechanical loading in vivo is to transmit muscle forces to bone. While appropriate mechanical loading, such as exercise, is beneficial for maintaining tendon homeostasis, chronic, repetitive mechanical loading may lead to the development of tendinopathy, which is the leading cause of chronic disabilities. However, the precise cellular and molecular mechanisms of its development remain elusive. The role of Achilles TSCs in the development of tendinopathy is not known. Objective 1. To define the effect of mechanical loading on mouse Achilles TSCs proliferation and differentiation by Mechanical stretching.2. To define the effect of mechanical loading on PGE2 secretion by Mechanical stretching 3.To define the effect of mechanical loading on TSC by Mouse treadmill running.Methods 1. Achilles TSCs were cultured in microgrooved silicone dishes and subjected to cyclic uniaxial mechanical stretching using a custom-made loading system. Achilles TSCs without stretching were used for controls. Cell numbers after stretching were determined by counting with a hemocytometer. In separate experiments, their Achilles tendons were harvested for PGE2 measurement using a commercially available enzyme immunoassay kit; Using chemical staining for lipids and calcium (Ca2+), respectively. One-way ANOVA followed by Fisher's PLSD for multiple comparisons was used for statistical analysis.2.Mouse treadmill running Ten 2.5-month-old C57BL/6J female mouse were used in a treadmill running study. Five mouse were used for treadmill running, while the remaining five mouse served as controls, which were allowed to move freely in their cages. Treadmill running protocol for mouse included one week training for treadmill running, followed by running at 13 meter/min until the mouse were exhausted. Immediately after the end of treadmill running, the mouse were sacrificed, and their Achilles tendons were harvested for PGE2 measurement using a commercially available enzyme immunoassay kit.Results We found that Achilles TSCs number markedly increased after both 4% and 8% stretching relative to unstretched control, but 8% stretching promoted proliferation more strongly than did 4% stretching (75% vs.60% over control). In addition, Stretching induced both adipogenesis and osteogenesis, as evidenced by accumulation of lipid droplets and Ca2+, respectively. The Stretching effect on Achilles TSCs adipogenesis and osteogenesis appeared to be Stretching -dose dependent.After mouse underwent a bout of rigorous treadmill running, PGE2 levels in their Achilles tendons were significantly increased compared to those in control mouse.Conclusion Cyclic mechanical stretching increased Achilles TSCs proliferation in a stretching magnitude-dependent manner. Moreover, low stretching at 4% appears to promote tenocyte differentiation. Large stretching at 8%, however, induced at least some Achilles TSCs to differentiate into adipogenic and Osteogenic lineages. This study showed for the first time that after a bout of repetitive mechanical loading via treadmill running, mouse tendons produce higher levels of PGE2 than do tendons of cage control mouse. It means that excessive mechanical loading can make mouse inflammative.