Millions of Americans and people worldwide suffer bone diseases due to injuries, bone defects, and spinal defects, and therefore are in great need of effective treatments to regenerate bone and promote bone growth. Among treatments being explored in modern medicine, administration of growth factors that prompt our own body to regrow bone represents an attractive direction due to its non-invasiveness and utilization of our own cells, including bone- forming stem cells. Such treatment with bone growth factors has been approved by the FDA and is successfully used in clinics, however a recognized drawback of this treatment is that the administration of extremely high doses of very pure growth factor inevitably causes severe side effects in some patients. Our team believes current high doses are not necessary, with better tactics to present growth factors to cells, e.g. 5 growth factors bound together as a well-defined cluster versus 1000 individual growth factor molecules swimming around the cells. With this research, we hope to develop more effective ways to present growth factors than the current approach of injecting high dosage. Our approach is inspired by the way nature itself ?administers? these growth factors, which is always in combination with other proteins that provide the necessary context and help fine-tune cellular responses. This proposal builds on our discovery that COMP, a protein originally isolated from cartilage, can bind to multiple bone growth factors all at once. We plan to study how the COMP binds to growth factors, how many growth factors each COMP can carry (1 to 10), and which of the situations work best towards bone regeneration. We believe our results shall demonstrate that this multi-valent binding provides a new platform to present the growth factors to stem cells, to which cells respond with dramatically enhanced activities including robust bone formation and growth. The results from this investigation shall greatly enhance our current understanding of how bone growth factors regulate bone formation at the cellular level, and bring us a giant step closer to non-invasive and stem cell based therapy for bone regeneration.
The research goal is to determine how the multivalent presentation of growth factors regulates responses of osteogenic stem cells. Our preliminary investigations indicate that cartilage oligomeric matrix protein (COMP) can bind growth factors such as bone morphogenetic protein (BMP), in a multivalent fashion, 1-10 BMPs per COMP. The central hypothesis of this R01 research is that one of the multivalent presentations of BMP by COMP greatly enhances BMP?s osteogenic activity, by impacting the BMP based cellular signaling processes. The research plan is designed to demonstrate the enhancement and unveil the mechanism and molecular players involved in the signaling cascades in vitro, then validate the concept in vivo. First, single-, di- to multi-valent binding sites will be engineered using nanotechnology to produce designed valence to present growth factor. Then, cellular responses to presentation will be systematically studied to reveal the mechanism; including clustering of BMP-receptors due to the multivalent-templates; recruiting of intracellular signal transduction proteins including Smad, p38, and Rho/ROCK based actin remodeling; and the resulting changes in gene expression. Next, the conditions (e.g., ratio and formulation) of COMP presentation of BMPs will be determined to ascertain the multivalency to promote cellular signaling cascades towards bone growth. Finally, the optimal formulation leading to the multivalent BMP presentations will be demonstrated in vivo using two clinically relevant rat models: spinal fusion, and critical sized femoral defects. The team is well poised to carry out the proposed interdisciplinary Aims described above; the PI has a solid record of research in cartilage matrix biochemistry, COMP and BMP growth factor biology. The PI and co-PIs have ongoing collaborations with the surgeon to perform the pre-clinical animal models, high-resolution bio-imaging and nanotechnology to perform proposed multivalent binding investigations. This R01 research represents the first comprehensive investigation of the impacts of growth factor presentation on osteogenesis, from in vitro protein binding, protein-cell interactions, cellular signaling processes, to in vivo validation. The impact of these studies will advance our understanding of growth factor activity and identify a means to regulate growth factor based osteogenic activities, with a translational focus to improve clinical delivery of growth factors with much reduced side effects. The conclusions from this investigation provide a new paradigm to regulate osteogenesis, and stem cell differentiation in general, i.e. by the molecular level engineering of growth factor presentation.
| Tran, Victoria; Karsai, Arpad; Fong, Michael C et al. (2018) Label-Free and Direct Visualization of Multivalent Binding of Bone Morphogenetic Protein-2 with Cartilage Oligomeric Matrix Protein. J Phys Chem B : |
