Homeostasis of the intervertebral disc requires regulation of STAT3 signaling by the adhesion G-protein coupled receptor ADGRG6

Degenerative changes of the intervertebral disc (IVD) are a leading cause of disability affecting humans worldwide. While this is primarily attributed to trauma and aging, genetic variation is associated with disc degeneration in humans. However, the precise mechanisms driving the initiation and progression of disease remain elusive due to a paucity of genetic animal models. Here, we discuss a novel genetic mouse model of endplate-oriented disc degeneration. We show that the adhesion G-protein coupled receptor G6 (ADGRG6) mediates several anabolic and catabolic factors, fibrotic collagen genes, pro-inflammatory pathways, and mechanical properties of the IVD, prior to the onset of overt histopathology of these tissues. Furthermore, we found increased IL-6/STAT3 activation in the IVD and demonstrate that treatment with a chemical inhibitor of STAT3 activation ameliorates disc degeneration in these mutant mice. These findings establish ADGRG6 as a critical regulator of homeostasis of adult disc homeostasis and implicate ADGRG6 and STAT3 as promising therapeutic targets for degenerative joint diseases. Author summary Degenerative changes of the intervertebral disc (IVD) are a leading cause of disability affecting humans worldwide. While this is primarily attributed to trauma and aging, genetic variation is associated with disc degeneration in humans. However, the precise mechanisms driving the initiation and progression of disease remain elusive due to a paucity of genetic animal models. Here, we discuss a novel genetic mouse model of endplate-oriented disc degeneration. We show that the adhesion G-protein coupled receptor G6 (ADGRG6) mediates fibrotic collagen expression, causing increased mechanical stiffness of the IVD prior to the onset of histopathology in adult mice. Furthermore, we found increased IL-6/STAT3 activation in the IVD and demonstrate that treatment with a chemical inhibitor of STAT3 activation ameliorates disc degeneration in these mutant mice. Our results demonstrate that ADGRG6 regulation of STAT3 signaling is important for IVD homeostasis, indicating potential therapeutic targets for degenerative joint disorders.