Project Summary Meniscus Meniscus initiation. therapy basic novel Previous located maintain Using a Gli1-CreER driven Hh reporter mouse line, we recently found that Gli1-labeled cells contribute to the development of the meniscus horns from 2 weeks of age. In adult and aged mice, Gli1+ cells were localized to the superficial layer of anterior and posterior meniscal horns, and gradually decreased in number during aging. In vivo, these cells co-expressed known markers of mesenchymal progenitors as well as the lubricant Prg4. In culture, meniscal Gli1+ cells possessed high progenitor activities, such as proliferation, migration, and differentiation, under the control of Hh signal. Using an in vivo mouse meniscus injury model, we showed a rapid expansion of Gli1-lineage cells at the injury site of anterior horn. Ablation of these Gli1+ cells prior to injury slowed the meniscus repair process. Strikingly, intra-articular injection of the Hh activator, Purmorphamine (Pur), following injury accelerated meniscus repair and attenuated OA progression. Based on these data, we hypothesize that the Hh/Gli1 pathway can be therapeutically targeted to treat meniscus injury tears are the most common injury to the knee, affecting both young and old populations. healing is limited, however, and loss of function leads o cartilage loss and osteoarthritis OA) Current clinical treatment is palliative, and does not restore function, and no disease modifying drug is available for the t reatment of meniscus injury. Thus, there is a critical need to better understand the biologic mechanisms and pathways regulating meniscus homeostasis and repair in order to develop therapeutics. Mesenchymal progenitors play a critical role in tissue maintenance and regeneration. studies have demonstrated the existence of mesenchymal progenitors in the meniscus, with most within the superficial layer. Hedgehog (Hh) signaling is one of a few fundamental pathways that adult stem and progenitor cells in various organs and can activate these cells post injury. t ( and prevent OA development via the mobilization of endogenous meniscus progenitors. work design Aims evaluate scaffold-mediated The objectives of this are to understand the role of this novel signaling pathway in meniscus homeostasis and repair and to a novel drug delivery system to enhance meniscus repair by locally targeting t his pathway. Our specific are to: 1) determine the function of Hh signaling in meniscus development and repair; 2) synthesize and a nanoparticle (NP)-conjugated fibrous delivery system for meniscus repair; 3) Assess Pur-NP repair in a large animal model of meniscus injury.Small (mouse) and large (minipig) animal models, and complementary experimental tools will be utilized to develop and translate this new therapy. multidisciplinary successful, this work will healing Our team has worked together to generate the exciting preliminary data supporting this proposal. provide a novel therapeutic scaffold that mobilizes meniscus progenitors to improve of tears that are otherwise considered irreparable. If

Project Narrative Meniscus tears are the most common injuries of the knee, and can lead to osteoarthritis in both young and aged populations. By taking advantage of multiple animal models, this project will investigate a novel signaling mechanism in meniscus metabolism and design an innovative drug delivery therapy to treat meniscus injury and thereby prevent osteoarthritis progression. Information garnered from these studies will be important for advancing our knowledge of joint biology and designing novel therapeutic strategies for meniscus repair.