Roles of Type V Collagen in the Structure and Biomechanics of TMJ Condylar Cartilage

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PROJECT SUMMARY Temporomandibular joint (TMJ) disorder is characterized by the irreversible breakdown of the mandibular condylar cartilage extracellular matrix (ECM). The condylar cartilage ECM has a specialized bilayer layout of a fibrocartilage layer covering a secondary hyaline cartilage layer. The development of effective TMJ regeneration strategies is challenged by our incomplete understanding of how certain molecules in the ECM are linked to the structure and biomechanical functions of this unique fibrous-hyaline hybrid tissue. This project will study the roles of collagen V, the regulator of collagen I fibrillogenesis, in the development of condylar cartilage ECM in vivo. The overall objective is to determine the roles of collagen V in regulating the establishment of TMJ condylar cartilage ECM during post-natal development. Our central hypothesis is that collagen V is crucial for proper biomechanical function of the TMJ condylar cartilage, because it regulates the collagen fibril structure of both the fibrous and hyaline layers. To test the central hypothesis, in Aim 1, we will determine the impact of collagen V loss on the formation and maturation of condylar cartilage. This will be achieved by studying the structural and biomechanical phenotype of condylar cartilage ECM in global collagen V-knockdown mice, and in our newly established, cartilage-specific collagen V inducible knockout (cKO) mice under normal TMJ loading. Next, since the influence of collagen V on the fibrous layer is well known, in Aim 2, we will determine the role of collagen V in regulating the formation of the hyaline cartilage layer. First, we will test if collagen V impacts the hyaline layer by altering the load transfer between the fibrous and hyaline layers. This will be achieved by studying if the phenotype of the hyaline layer in cKO mice is mitigated under reduced TMJ loading in vivo. Second, we will test if collagen V regulates the chondrogenesis of progenitor cells in the fibrous layer, as well as the resulted biosynthesis and assembly of hyaline cartilage neo-matrix in the absence of mechanical loading. A number of innovative approaches will be utilized. Using cKO mice, we will delineate collagen V activities at each stage of TMJ growth, and minimize confounding effects related to off-target changes of other TMJ tissues. Applying atomic force microscopy (AFM)-nanomechanical tests, we will quantify the mechanical changes of murine condylar cartilage as a result of collagen V deficiency. Applying laser capture microdissection with microfluidic qPCR, we will delineate gene expression profiles of cells in the fibrous versus hyaline layers. Successful completion of this study will elucidate new molecular activities that govern the formation of the condylar cartilage ECM, which is necessary for developing tissue engineering and disease intervention strategies to target this highly specialized, fibrous-hyaline hybrid tissue.