Six1-Eya1 Axis Governs Myofiber Remodeling and Fibrosis in Extraocular Myopathy: Insights from Single-Cell RNA Sequencing and Mesenchymal Stem Cell Therapy in Thyroid Eye Disease.

Thyroid eye disease (TED) is an autoinflammatory condition characterized by fibrosis in orbital fat and extraocular muscles, primarily driven by TSH receptor antibodies and inflammatory cytokines. While research has predominantly focused on the involvement of fat tissue, the understanding of myopathy in TED remains limited. This study developed a TED mouse model and isolated myoblasts from both control individuals and TED patients for analysis. Single-cell RNA sequencing was used to investigate myofiber type changes in TED and their alterations following treatment with human-derived mesenchymal stem cells. Key regulatory genes involved in myofiber differentiation and fibrosis in myofibroblasts were identified, and their expression balance was validated in myoblasts derived from both normal individuals and TED patients. Our analysis revealed a disease-associated shift in myofiber types and identified Six1 and Eya1 as central regulators of myofiber differentiation and fibrosis suppression. These regulatory effects were validated in primary myoblasts isolated from both control and TED patients. Collectively, our findings uncover a novel role for the Six1/Eya1 axis in modulating muscle remodeling and fibrosis in TED and provide a foundation for the development of targeted therapies for TED-associated myopathy.