Zonal interdependence in the temporomandibular joint cartilage

The temporomandibular joint (TMJ) cartilage is biomechanical sensitive. Cells in TMJ cartilage are zonally arranged, earlier differentiated in the super zone and late differentiated in the deep zone. The purpose was to detect the zonal interdependence in TMJ cartilage under dental biomechanical stimulations. Here, we obtained the Sox9^CreER ; Rosa26^tdTomato and Col10^CreER ; Rosa26^tdTomato mice to label super zone Sox9-expressing (Sox9⁺ ) or deep zone Col10-expressing (Col10⁺ ) cells by tdTomato (TdT), and Sox9^CreER ; Rosa26^DTA and Col10^CreER ; Rosa26^DTA mice to ablate Sox9⁺ or Col10⁺ cells selectively. These mice were subjected to unilateral anterior crossbite (UAC) or bilateral anterior elevation (BAE) dental stimulation, which promoted terminal differentiation or proliferation of TMJ chondrocytes, respectively. In both UAC and BAE models, the Sox9-TdT⁺ cells performed as proliferation and mature differentiation, showing as expressing Ki67 and Col-X, respectively; while the Col10-TdT⁺ cells performed as terminal differentiation, showing as expressing osteocalcin (OCN). In both Sox9⁺ - and Col10⁺ -cells ablation groups, there were reductions in cell number, cartilage thickness and matrix amount, subchondral bone loss, and condylar deformation. The UAC-promoted terminal differentiation was enhanced, and the BAE-promoted cellular proliferation was ruined. Impressively, when Col10⁺ cells were ablated, the UAC-promoted DAP3 expression, an anoikis marker, was further increased, while the BAE-suppressed DAP3 expression was instead greatly increased. These findings demonstrated that the cartilage zones function interdependently. The super zone harbors the cells that undergo differentiation to deep zone cells, the deep zone contains load-bearing matrix which is structural essential for the cells located inside or superficial.