Apigenin and rutaecarpine target cellular senescence to prevent aging-bone phenotype in human mesenchymal skeletal stem cells

Osteoporosis is a systemic aging-related disease that causes reduction and deterioration of bone mass, density, and microstructure leading to increased risk of bone fragility and fractures. Current pharmacological interventions to treat osteoporosis target reduction of bone resorption and induction of bone formation. However, the long-term use of anti-osteoporotic drugs exhibit side effects like increased risk factor of developing cardiovascular diseases. Thus, there is a need for new therapeutic approaches. In this study we identified Apigenin (Api) and Rutaecarpine (Rut), plant-derived antioxidants, employing a functional screen of a natural product library (144 compounds). Api and Rut were found to exert significant induction on osteogenesis of bone marrow mesenchymal stromal stem cells (BMSCs) in vitro. In order to determine the osteogenic effects of Api and Rut, we used an ex-vivo organotypic embryonic chick-femur culture model, on which they both significantly increased the average bone volume and cortical thickness of the chick-femur compared to control. Global gene expression profiling and protein analysis revealed the activation of a number of signaling pathways, including focal adhesion kinase (FAK), transforming growth factor b (TGFb), selenium, and oxidative stress. In addition, treatment with Api and Rut during oxidative insult with tert-butyl hydrogen peroxide, reduced the levels of the senescence-associated secretory phenotype (SASP) and senescence (P53, P16, and P21) markers. It also reduced intracellular ROS levels, measured with DCFDA, and gene expression of antioxidant defense enzymes (HMOX1 and SOD2). Furthermore, in vitro treatment with Api and Rut of primary hBMSCs from elderly subjects, characterized by low osteoblastic differentiation ability, significantly enhanced osteoblast formation when compared with primary hBMSCs from young donors. Api and Rut enhance osteoblastic differentiation and bone formation via reducing the senescence-associated phenotype with aging and thus represent a potential therapy to reduce the progression of osteoporosis.