Neural Crest-Derived Cells Migrate from Nerve to Participate in Achilles tendon Remodeling

Abstract

During tendon injuries, nerve ingrowth is one of the earliest events of tendon repair and remodeling. Since peripheral neurons and associated cells are mostly derived from neural crest (NC) cells, we sought to investigate the role of NC-derived cells in tendon regeneration. Thus, we used Sox10-Cre/ROSA26-Flox-Red Fluorescent Protein (RFP) transgenic mice to trace these cells during tendon regeneration. After 4 weeks of Achilles tendon rupture, the injured tendon tissues were harvested for immunohistological analyses, cell isolation, and phenotype identification. In addition, the tenocytes were co-cultured with RFP labeled cells to examine cellular functions. Following the injury, a significant number of RFP-labeled cells penetrated into the wound site and reached a peak (∼30% of cells) after 2 weeks, and then stabilized at a level of ∼20%. Interestingly, 36.9% RFP labeled cells in the injured area expressed Tuj1, suggesting that most of the cells are peripheral neurons. Some RFP⁺/Tuj1⁺ cells were also found adjacent to newly formed blood vessels in the tendon. Importantly, the existing Neuropeptide Y (NPY) and Neuropeptide Y receptor (NPYr) in the ingrowth nerve and blood vessels showed the direct correlation with each other. In addition, there were also RFP⁺ cells (∼30%) negative for neuron markers but positive for fibroblast markers i.e., FAP (34.7%) and Vimentin (Vmt) (27.2%), and ∼10% positive for Sox10. Indeed, many RFP⁺ cells isolated from the ruptured Achilles tendon showed long spindle shapes and expressed fibroblast phenotypic markers FSP1 and FAP. Particularly, part of the Sox10⁺RFP-labeled cells exhibited osteogenic and adipogenic differentiation ability. It is concluded that after Achilles tendon injury, nerves sprout into the wound site. The NC-derived Vmt+/FAP+ mesenchymal cells and peripheral nerves participate in tendon regeneration. This article is protected by copyright. All rights reserved.