Type V Collagen Exhibits Distinct Regulatory Activities in TMJ Articular Disc versus Condylar Cartilage During Postnatal Growth and Remodeling.

Understanding matrix molecular activities that regulate the postnatal growth and remodeling of temporomandibular joint (TMJ) condylar cartilage and articular disc will enable the development of effective regenerative strategies targeting TMJ disorder. This study elucidated the distinct roles of type V collagen (collagen V) in regulating these two units. Studying the TMJ of young adult Col5a1^+/- mice, we found loss of collagen V resulted in substantial changes in the proliferation, clustering, and density of progenitors in condylar cartilage, but did not have a major impact on disc cells that are more fibroblast-like. Although loss of collagen V led to thickened collagen fibrils with increased heterogeneity in the disc, there were no significant changes in local micromodulus except for a reduction at the posterior end of the inferior side. Following the induction of aberrant occlusal loading by the unilateral anterior crossbite (UAC) procedure, both wild-type (WT) and Col5a1^+/- condylar cartilage exhibited salient remodeling, and Col5a1^+/- condyle developed more pronounced degeneration and hypertrophy at the posterior end than the WT. In contrast, neither UAC nor collagen V deficiency induced marked changes in the morphology or mechanical properties of the disc. Together, our findings highlight the distinct roles of collagen V in regulating these two units during postnatal growth and remodeling, emphasizing its more crucial role in condylar cartilage due to its impact on the highly mechanosensitive progenitors. Results thus provide the foundation for using collagen V to improve the regeneration of TMJ and the care of patients with TMJ disorder. STATEMENT OF SIGNIFICANCE: Successful regeneration of temporomandibular joint (TMJ) condylar cartilage and articular disc remains a significant challenge due to the limited understanding of matrix molecular activities that regulate the formation and remodeling of these tissues. This study demonstrates that collagen V plays distinct and critical roles in these processes. In condylar cartilage, collagen V is essential for regulating progenitor cell fate and maintaining matrix integrity. In the disc, collagen V also regulates fibril structure and local micromechanics, but has a limited impact on cell phenotype or its remodeling response. Our findings establish collagen V as a key component in maintaining the integrity of these two units, with a more crucial role in condylar cartilage due to its impact on progenitor cell activities.