Project Summary Osteoarthritis (OA) is the most common form of degenerative joint disease affecting millions of people worldwide and lead to a tremendous financial burden. Currently there are no disease modifying therapies available for OA, due to limited understanding of the genetic factors and pathways underling OA progression. Therefore, a comprehensive understanding of signaling pathways driving the pathogenesis of OA will motivate innovation for early diagnosis and disease modifying therapeutics. This proposal will further the molecular characterization of a genetic mutant mouse of the Adhesion G protein-coupled receptor G6 (Adgrg6) gene. ADGRG6 is enriched in articular cartilage in human and mouse, and we have demonstrated its involvement in human OA. Loss of Adgrg6 in the articular cartilage in mouse leads to OA-like joint pathology, and dysregulation of both cAMP and STAT3 signaling pathway. Interestingly, cAMP signaling is previously indicated to drive chondroprotective mechanisms, and STAT3 activation is associated with OA development in human. Based on these novel findings, we hypothesize that homeostasis of articular cartilage requires precise regulation of both cAMP and STAT3 signaling. This hypothesis will be tested under three specific aims: 1. We will specifically activate cAMP signaling in articular cartilage using a novel Gs-coupled DREADD mouse, and determine the transcriptional network regulated by cAMP signaling. We will determine the cellular effectors of cAMP signaling during OA development in Adgrg6 mutant mice and in post-traumatic mouse model of OA. 2. We will determine the downstream effectors of STAT3-mediated signaling during OA progression using the post-traumatic mouse model of OA by analysis of STAT3 dependent gene regulation. 3. We will determine the efficacy of targeting STAT3 and cAMP signaling pathways for treatment of OA-like joint pathology using the post-traumatic mouse model of OA. We will utilize innovative pharmaceutical approaches for localized, slow-release delivery of disease modifying therapies targeting these pathways. Taken together, this proposed study will utilize mouse genetics, combined with modern genomics and pharmaceutic approaches to define the role of cAMP and STAT3 signaling in articular cartilage homeostasis and OA pathogenesis, which may accelerate our diagnosis and treatment of human OA.