David A. Reed - US grants

ABSTRACT Chondrocyte-pericellular matrix derived signaling maintains tissue integrity in the temporomandibular joint Temporomandibular disorders affect 3-7% of the population. TMJ condylar cartilage integrity is central to TMJ health and many TMDs are associated with its degeneration. The pathophysiology of degenerative joint disease (DJD) in the TMJ is ill-defined and contemporary molecular targets for clinical intervention have yet to be determined. Chondrocyte-pericellular matrix derived signaling is a known regulator of cartilage homeostasis and it represents a promising potential therapeutic target for DJD. The major component of the pericellular matrix in the TMJ is type VI collagen. Nerve/glial antigen 2 (NG2) is a known receptor of type VI collagen, but NG2-type VI collagen interactions have not been studied in detail in mandibular condylar cartilage. In other cell types, the NG2-pericellular matrix interactions are a critical regulator of cell proliferation, differentiation, migration, and viability. Our preliminary data illustrate that a) NG2 colocalizes with type VI collagen in healthy articular chondrocytes in the TMJ, b) that this colocalization is disrupted during degeneration, c) that degenerative changes are associated with high levels of internalized NG2, d) and that internalized NG2 is closely associated with a marker for oxidative stress, OMI/HtrA2. We hypothesize that cartilage degeneration in TMJ DJD is mediated, in part, by proteolytic cleavage of the NG2 ectodomain, activation, and internalization to regulate oxidative stress through OMI/Htra2 pathway. We will test this hypothesis with two specific aims. In aim 1, we will implicate ectodomain proteolysis in NG2 activation and internalization by linking cartilage degeneration with NG2 internalization and measured protease levels in wild-type and protease knockout mice and cells. In aim 2, we will define the functionality of NG2 as a mediator of oxidative stress by linking cartilage degeneration with markers of oxidative stress, ER stress, and autophagy in wild-type and NG2 knockout mice and cells. Together, these aims define and evaluate an entirely novel molecular mechanism of chondrocyte function that is contextually linked to mechanical and metabolic oxidative stresses known to cause TMDs. Long term, we seek to use these data to solve clinical problems associated with defining precise methods of TMD classification, prevention, and treatment.

ABSTRACT Cell-matrix regulation of fibrochondrocytes in TMJ OA Disorders of the temporomandibular joint (TMJ) affect between 3-7% of the population and osteoarthritis (OA) is the most common pathology associated with TMJ dysfunction. TMJ OA is a disease of cartilage degeneration and chondrocyte apoptosis. One of the key factors leading to chondrocyte apoptosis is the suppression of the cytoprotective process of autophagy. Autophagy is one of the earliest cellular responses to TMJ OA and has been shown to be a viable therapeutic target for attenuating the progression of cartilage degeneration. A major gap in knowledge is how mechanical and inflammatory stress leads to the eventual suppression of autophagy, apoptosis, and cartilage degeneration. To address this gap, my lab has developed expertise in a preclinical, surgical induction mouse model of TMJ OA that closely corresponds to the human condition and identified a three-step pathogenesis model linking mechanical damage to ECM changes and chondrocyte apoptosis that includes 1) the depletion of Collagen VI (Col VI) following surgically-induced TMJ OA 2) the proteolysis of a Col VI chondrocyte receptor, Neuron/Glial antigen 2 (NG2) and 3) the reduction of autophagy. The overall goal of our study is to test the hypothesis that injury-induced Col VI degeneration activates an NG2-dependent pathway that accelerates TMJ cartilage degeneration by suppressing autophagy. Based on the preliminary data included in this application, we have designed a research plan to mechanistically define how NG2 binding with Col VI is necessary for the maintenance of autophagy and how NG2 monoclonal antibody therapy can attenuate the progression TMJ cartilage degradation by protecting autophagy. The proposed work is innovative because it focuses on a novel molecular mechanism of chondrocyte function that contextually links matrix dysfunction with loss of a cytoprotective cellular mechanism implicated in the progression of TMJ OA. The significance of this research lies in the potential application to the clinical problems of TMJ OA and represents a leap forward in our knowledge of TMJ OA pathophysiology. We anticipate that the outcomes of our study will inform new therapeutic approaches that attenuate the progression of TMJ OA and restore TMJ health in patients that would otherwise require alloplastic total joint replacement.