In Greek mythology, Achilles was the son of the mortal Peleus and Thetis, the goddess of the sea.
In order to make his son invulnerable, Thetis carried it upside down and immersed it in the Styx River when he was just born. However, Achilles' heel pinched by his mother was accidentally exposed outside the Styx River, leaving the only fatal weakness in his body. In the Trojan War, Achilles was shot in the ankle by Paris and died.
In the human body, there is also such a soft spot- Achilles tendon. As its name suggests, the Achilles tendon is one of the most powerful and fragile tendons in the body. The Achilles tendon could endure a load close to 8 times the body weight during exercise, making it extremely sensitive to injury. Furthermore, due to the unique nature of tendons, failing to consult a doctor soon after an injury can lead to chronic tendon disease, which is characterized by pain, swelling, and movement problems. Heterotopic ossification of tendon is a special type of chronic tendon disease, that is, the bone grows in the place (tendon) where the it shouldn’t, further destroying the morphological structure and function of the tendon tissue. Famous athletes such as Xiang Liu and Kobe Bryant had to retire early from sports due to a lack of a radical solution for Achilles tendon injuries.
Figure 1 Achilles tendon - the powerful and fragile Achilles heel of the human body (picture from the Internet)
Using single-cell sequencing technology, the Ouyang Hongwei team of Zhejiang University revealed tissue microenvironment changes during tendon heterotopic ossification alters gene expression and cell fate determination of tendon stem progenitor cells, and demonstrated that this process can be blocked by small molecule inhibitor BIBF1120, providing a novel treatment for heterotopic tendon ossification.
The authors firstly found that the tendon specific transcription factor MKX decreased significantly in heterotopic ossified human tendon, and knockout of Mkx lead to spontaneous ossification of mouse tendon, suggesting that MKX plays a critical role in heterotopic ossification of tendon.
Fig. 2 Heterotopic ossification of tendon caused by decreased MKX expression or Mkx knockout
Further studies revealed that Mkx knockout mouse tendon cells expressed high levels of angiogenesis related genes, resulting in vascular invasion and tendon extracellular matrix microenvironment remodeling, and abnormal activation of osteogenic and chondrogenic differentiation related genes in tendon stem progenitor cells. These data indicated that inhibition of angiogenesis may improve the tendon tissue microenvironment and prevent HO progression.
Figure 3 Single cell sequencing reveals tendon cell subpopulations and altered gene expression pattern
Therefore, the author focused on finding drugs that can inhibit angiogenesis process. Finally, they found that local injection of BIBF1120 significantly inhibited the neovascularization of tendon after injury, and significantly alleviated the tendon heterotopic ossification.
Figure 4 Small molecule inhibitor BIFB1120 significantly improved the microenvironment of tendon injury and inhibited heterotopic ossification
This work was published in Bone research entitled "Single cell analysis reveals investment of angiogenesis concerns progress of heterotopic ossification in Mkx-/- mice". The first author of the paper is Junxin Lin, a postdoctoral researcher of the Zhejiang University-University of Edinburgh Institute. The corresponding authors are professor Hongwei Ouyang and Wanlu Liu. The research was supported by the National Key R&D Program of China (2017YFA0104900), the National Natural Science Foundation of China (31830029, 81501937, 81522029) and the Fundamental Research Funds for the Central Universities (K20200099).
Link：https://www.nature.com/articles/s41413-021-00175-9
