Intermittent parathyroid hormone (PTH) (1-34) is currently the only anabolic agent approved for the treatment of osteoporosis, and is actively under clinical investigation to treat localized osseous defects in the oral cavity and other skeletal sites. Studies have attributed PTH anabolic actions to mechanisms that extend beyond direct PTH signaling in osteoblastic cells. An evolving theory is that hematopoietic cells residing in the bone marrow environment mediate PTH anabolism. Of interest, PTH signaling regulates the expression of genes which support both hematopoietic stem cells (HSCs) and megakaryocytes. Both HSCs and megakaryocytes are strong candidate regulators of PTH anabolic actions. Proteoglycan-4 (prg4) is a novel PTH responsive gene that was identified in the project laboratory. Prg4 protein product actions have been implicated in articular joint protection, HSC expansion, and megakaryopoiesis. Loss-of-function mutations in prg4 result in the osteopenic and arthritic condition of camptodactyly-arthropathy-coxa vera-pericarditis syndrome. The role of prg4 as a mediator of bone remodeling and PTH anabolism is unknown with preliminary data from the project laboratory supporting its role in anabolic actions of PTH. Two specific aims will optimize strong in vitro and in vivo strategies built upon the use of prg4 deficient mice to investigate the overall hypothesis that proteoglycan-4 mediates PTH actions in skeletal anabolism and hematopoiesis. The first specific aim will elucidate the intrinsic role of proteoglycan4 in osteoblastogenesis and the second aim will determine the role of proteoglycan-4 in anabolic actions of PTH. Primary bone marrow stromal cell cultures will be utilized for in vitro osteoblastogenesis studies. An in vivo intermittent PTH study will be carried out to analyze the impact of proteoglycan-4 in hematopoiesis (HSC expansion and megakaryopoiesis), bone remodeling, and PTH skeletal actions. An ex vivo PTH cell expansion model will be used to further elucidate the role of proteoglycan-4 in hematopoietic and stromal cell proliferation, differentiation, and apoptosis. These studies will identify the role of proteoglycan-4 in bone remodeling and PTH actions. In addition to improving our understanding of actions of PTH in bone, the proposed F30 fellowship research training plan will provide a strong basic-translational science research training experience for Mr. Chad Novince, a 6th year joint DDS/PhD candidate. Mr. Novince is an aspiring dental scientist whose research interests are focused in the investigation of hematopoietic cells as potential mediators of PTH anabolic actions. The F30 fellowship will support Mr. Novince's research studies investigating the role of proteoglycan-4 in PTH skeletal actions, as well as enhancing his career development. PUBLIC HEALTH RELEVANCE: Parathyroid hormone (PTH) is currently the only bone forming therapeutic agent approved to treat osteoporosis (condition of decreased bone mass). The proposed research will delineate the role of a novel protein called proteoglycan-4 as a mediator of the bone forming capacity of PTH. A more thorough understanding of PTH bone forming actions will optimize its clinical potential, supporting its use for localized bone defects which afflict the oral-facial region (arising from periodontal/gum disease, fractures, cancer) and other skeletal sites.