Neuron/Glial Antigen 2-Type VI Collagen Interactions During Murine Temporomandibular Joint Osteoarthritis

The degeneration of articular cartilage underscores the clinical pathology of temporomandibular joint osteoarthritis (TMJ-OA) and is promoted through dysfunctional biochemical or biophysical signaling. Transduction of these signals has a multifaceted regulation that includes important cell-matrix derived interactions. The matrix encapsulating the cells of the mandibular condylar cartilage (MCC) is rich in type VI collagen. Neuron/glia antigen 2 (NG2) is a type I transmembrane proteoglycan that binds with type VI collagen. This study defines the temporospatial dynamics of NG2-type VI collagen interactions during the progression of TMJ-OA. Membrane-bound NG2 is found to colocalize with pericellular type VI collagen in superficial layer cells in the MCC perichondrium but is present at high levels in the cytosol of chondroblastic and hypertrophic cells. When TMJ -OA is induced using a surgical instability model, localized disruptions of pericellular type VI collagen are observed on the central and medial MCC and are associated with significantly higher levels of cytosolic NG2. NG2 localized within the cytosol is found to be transported through clathrin and dynamin mediated endocytic pathways. These findings are consistent with NG2 behavior in other injury models and underscore the potential of NG2 as an entirely novel molecular mechanism of chondrocyte function contextually linked with TMJ-OA.