Gli1+ Cells Exhibit Clonogenicity and Slow-Cycling Features at the Temporomandibular Joint (TMJ) Enthesis-Condyle Interface.

The temporomandibular joint (TMJ) relies on specialized progenitor cells for tissue maintenance and repair. We characterized TMJ-derived progenitor cells in mice and investigated the role of Evc2-mediated Hedgehog signaling. Progenitor cells from the anterior TMJ exhibited greater colony-forming capacity and an elongated morphology, while posterior cells were cuboidal, highlighting regional heterogeneity. TMJ-derived progenitors demonstrated multipotency, differentiating into osteogenic and chondrogenic lineages. Gli1-expressing, slow-cycling cells localized to the ligament attachment regions, initially accumulating there and not overlapping with specialized cells (Col1+ cells). Conditional Evc2 disruption in Gli1-expressing cells paradoxically augmented expression of Gli1 and mechanosensors (Yap, Wwtr1, Piezo1), and produced more confluent, rapidly expanding colonies. We hypothesize that these colonies are primarily composed of transit amplifying cells (TACs), which may proliferate robustly but face challenges in terminal differentiation. These results reveal critical roles for EVC2 and regional progenitor cell diversity in TMJ regenerative biology and suggest that targeting cell signaling and mechanical factors may inform novel strategies for TMJ disorder therapies.