Bone remodeling is an elegant and tightly orchestrated process by which bone forming cells (osteoblasts) and bone removing cells (osteoclasts) work in concert to add or remove bone. In mechanically-induced bone remodeling, bone communication cells (osteocytes) are believed to sense the stimulus and then direct the remodeling response. While this theory is generally accepted, there is still much to understand about how these interactions are coordinated. Current research techniques do not allow for these signals to be fully studied. Understanding bone remodeling at the cellular level is important if the process is to be manipulated to improve bone healing after injury and to minimize the impact of bone diseases, such as osteoporosis. This project is developing a novel lab-on-a-chip system that will incorporate all three types of bone cells and will permit the cell-to-cell signals to be isolated and identified. For the first time, the difference between mechanically generated signals and biochemical signals are being clearly identified. These systems are being studied for both normal stress loading scenarios and overloading stress scenarios, for which the induced an overall response could be bone growth or bone damage, respectively. In addition to incorporating this research into undergraduate and graduate courses, planned outreach activities include the development of a learning community for inner city sixth graders who will participate in a two-year summer camp. The learning community is designed to provide a peer group for the students, with the goal of working with these like-minded students to graduate from high school and to matriculate in college.
Current experimental techniques are not appropriate for the separation of mechanically-derived cues for bone remodeling from soluble cues for this phenomenon. For example, in vitro cell models generally isolate one cell type and study its isolated response, while in vivo models require animal sacrifice and represent the remodeling environment at the time of sacrifice. To effectively study the multicellular interactions that occur in remodeling, models are needed that accurately recapitulate the environment. To that end, this research project is developing an in vitro, lab-on-a-chip bone remodeling platform that incorporates osteocytes, osteoclasts and osteoblasts and enables quantification of functional outcomes (i.e., bone formation and resorption). The experimental platform is then being utilized to address the role of soluble signals, cell-cell communication, and cell contact in mechanically-induced remodeling responses in physiological load and overload. Soluble activity is being analyzed by quantifying the effects of loading-induced osteocyte conditioned medium on bone formation and resorption. Experiments are then being repeated in co-cultures of osteoclasts and osteoblasts to incorporate soluble signals and cell contact allowing the contribution of the mechanisms to be determined. Finally, experiments are being repeated in gap-junction deficient systems to allow the contribution of cell communication to be determined.
