Mechanical Loading Modulated Heterotopic Ossification In Tendon Through The MTORC1 Signaling Pathway

Tendinopathy is one of the most common sports injury disease, including Achilles tendinitis, supraspinatus tendinitis, jumping knee, tennis elbow, with the ratio of 48%. In normal labor population, morbidity accounted for more than 40%. For the unknown etiology and limited treatment, about 30% of the patients with tendinopathy get worse. Tendon disease seriously affects the sporty people’s quality of life and the career of a player. In people’s normal physiological conditions, the movement process of tendon injury and tendon repair maintained a certain balance. When this balance is broken, it will result in pathological, and tendon micro damage is aggravating, eventually become tendinopathy. Clinical studies have found that in the tendinopathy patients, tendon tissue contains heterotopic ossification, and heterotopic ossification is one of the important pathological manifestations of tendinopathy. Heterotopic ossification may be caused by overuse of the tendon and tendon micro-damage accumulation due to ossification of the tendon but the mechanism is not very clear. Tendon cells are the main functional cells of the tendon tissue, it has the function of extracellular matrix synthesis and secretion, involved in the repair of tendon damage. Tendon cells as dialysis cells, does not have the ability to update itself, and the repair function is weak, without differentiation potential. Heterotopic ossification in the tendon needs a bone progenitor cells to differentiate into bone tissue, but resource is still unclear. Study of tendon stem cells differentiate into osteoblasts regulated micro-injury effects is important with scientific and clinical value.Physical therapy especially eccentric training with mechanical loading as its main functional element has promising result on tendinopathy. However, excessive mechanical loading is also an important factor of tendon heterotopic ossification. The dual effects that mechanical loading may have in the pathogenesis and rehabilitation of tendinopathy have not yet been clarified.mTOR (mammalian target of rapamycin) is a conservative threonine protein kinase, with TOR molecule has protein kinase function. mTOR has two types of complexes:mTORCl and mTORC2. MTORC1 is mainly involved in the regulation of cell growth and energy metabolism, participated in the translation of proteins, nucleic acid synthesis, lipogenesis, Glycolysis and Autophagy and other important physiological processes. MTORC1 can be inhibited by its selective inhibitor rapamycin. mTORC2 is involved in fat formation, glucose metabolism and controlling of the actin cytoskeleton, apoptosis and other life activities, its catalytic substrate for Akt and PKC-a. MTORC2 cannot be inhibited by rapamycin. Several studies have shown that mechanical stress can increase the phosphorylation of mTORCl downstream protein p70S6k, which means mTORCl signaling pathways can be activated. MTORC1 specific inhibitor rapamycin or mTORCl knockout can stimulated or inhibited osteogenic differentiation, but the mechanism is not clear.Based on the previous reports, we propose the following hypothesis: mechanical loading modulated heterotopic ossification in tendinopathy through the mTORCl signaling pathways. In the present study, an Achilles tenotomy rat model and a tendon cells stretch model were employed to investigate the role mechanical loading may play in regulating HO of the tendon through the mTORC1 signaling pathway in calcific tendinopathy. Our study was divided into three parts.1.The effects of different elongation mechanical loading on osteogenic differentiation and heterotopic ossification.2.The effects of different elongation mechanical loading on the mTORCl signaling pathway of tendon stem cells and tendon tissue.3.The effects of inhibition of mTORCl signaling pathway on mechanical loading induced osteogenic differentiation and heterotopic ossification.