Effect of human myoblasts on tenogenic progression in 2D and 3D culture models

Tendon injuries and disorders associated with mechanical tendon overuse are common musculoskeletal problems. Even though tendons play a central role in human movement, the intrinsic healing process of tendon is very slow. So far, it is known that tendon cell activity is supported by several interstitial cells within the tendon. However, the interplay between the tendon and the adjacent muscle for tendon regeneration and development processes has not been fully investigated. Here, we tested whether factors released from muscle derived myogenic cells (myoblasts) enhance tenogenic progressions of human tendon derived cells (tendon fibroblasts) using two-dimensional (2D) culture model and a three-dimensional (3D)-engineered tendon construct culture model, which mimics tendon regeneration and development. The conditioned media from myoblasts and unconditioned media as control were applied to tendon fibroblasts. In 2D, immunofluorescence analysis revealed increased collagen type I expressing area and increased migration potential when conditioned media from myoblasts were applied. In the 3D-engineered human tendon construct model, wet weight, diameter, and cross-sectional area of the tendon constructs were increased in response to the application of conditioned media from myoblasts, whereas the collagen density was lower and mechanical function was reduced both at the functional level (maximum stiffness) and the material level (maximum stress and modulus). These results indicate that myoblast-derived factors extend collagen expressing area and enhance migration of tendon fibroblasts, while factors involved in the robustness of extra-cellular matrix deposition of tissue-engineered tendon constructs are lacking. Our findings suggest that adjacent muscle affects the signaling interplay in tendons.