JMJD3-driven epigenetic reprogramming of p16INK4a-positive cells promotes tendon regeneration.

Tendon healing is a complex biological process that involves inflammation, cellular reprogramming, and extracellular matrix (ECM) remodeling. The cyclin-dependent kinase inhibitor p16INK4a is a well-characterized tumor suppressor associated with cell-cycle regulation under conditions of cellular stress and senescence. Although genetic ablation of p16INK4a+ cells has shown beneficial effects in age-associated tendinopathies, the cellular identity and functional contribution of p16INK4a+ cells during tendon regeneration remain poorly understood. In this study, we demonstrate that an injury-induced accumulation of p16INK4a+ cells in a murine Achilles tendon injury model promotes tendon structural and functional recovery. Using a murine tendon puncture model combined with single-cell RNA sequencing and in situ immunostaining, we identify these p16INK4a+ cells as predominantly mesenchymal cells characterized by elevated ECM gene expression. Mechanistically, p16INK4a+ cells exhibit increased activity of the histone demethylase JMJD3 (KDM6B), accompanied by reduced H3K27me3 levels and enhanced expression of ECM-related genes, including Col1a1 and Col3a1, thus supporting organized collagen deposition and tissue remodeling. Genetic deletion or pharmacological inhibition of JMJD3 resulted in increased H3K27me3 levels, disrupted collagen organization, and reduced biomechanical strength. Conversely, pharmacological reduction of H3K27me3 was associated with enhanced ECM gene expression and accelerated tendon repair. Together, these findings identify a JMJD3-associated epigenetic program in p16INK4a+ cells that contributes to ECM remodeling during tendon healing, highlighting the beneficial and context-dependent role of p16INK4a+ cells in musculoskeletal tissue repair.