Human derived tendon cells contribute to myotube formation in vitro

Skeletal muscle possesses remarkable adaptability to mechanical loading and regenerative potential following muscle injury primarily due to satellite cell activity. Although the roles of several types of interstitial cells in skeletal muscle have been documented, the signaling interplay between the skeletal muscle and the adjacent tendon tissue has not been elucidated. Here, we tested whether human tendon derived cells (tenocytes) could induce human myogenic cells (myoblasts) proliferation and differentiation in vitro using co-culture experiments that allowed us to investigate the effect of tenocytes secretion upon myogenic progression. This was done in vitro by introducing insert wells with either myoblasts, tenocytes, or no cells (control) into a myoblast containing well (co-culture). Immunofluorescence analysis revealed a higher fusion index (≥5 nuclei within one Desmin ⁺ myotube) and a higher myotube diameter in co-cultures with tenocytes compared to myoblasts condition. Correspondingly, MHC-IIX gene expression was up-regulated when co-cultured with tenocytes. However, the proliferation of myoblasts (either Ki67 or BrdU + cells) was not enhanced under the presence of tenocytes. These findings show that tenocytes influence myotube formation upon human primary cells in vitro and contribute to understanding the role of tendon derived cells in skeletal muscle during development and regeneration.