Cellular Basis for Optimal Osteogenic Physical Interventions
Disuse bone loss is a critical problem in rehabilitation that has very little progress made in terms of effective countermeasures. It is a consequence of the well accepted fact that when bone tissue is isolated from functional mechanical loading, it begins to resorb at a dramatic rate. Distinct from post-menopausal osteoporosis which occurs in women with the loss of estrogen, disuse bone loss occurs with paralysis due to spinal cord injury (SCI), stroke, and is thought to be a contributing factor in age-related or senile osteoporosis. The cellular level mechanism that is responsible for disuse bone loss is poorly understood at best. For the last seven years, our laboratory has been focused on identifying a cellular level physical signal produced by bone loading resulting from typical activities of daily living with the potential to regulate bone cell metabolism. Our results to date suggest that cyclic loading on bone produces oscillatory fluid flow which is a potent signal to bone cells in terms of early cell signaling via intracellular calcium, mitogen activated protein kinase (MAPK) signaling, prostaglandin release, and upregulation of bone markers of increased osteogenesis.
We have recently discovered that interrupting continuously oscillating fluid flow with periodic rest periods can dramatically increase early signaling in bone cells. Furthermore, this ability to increase signaling seems to be very specific to the temporal parameters of the loading profile. The focus of this proposal is to identify the critical parameters of osteogenic loading both in terms of early signaling as well as downstream events such as gene regulation and mineralization. Due to the scope of the optimization problem, conducting this study with human subjects or an animal model would not be feasible. Thus, we intend to exploit the low-cost and high throughput of in vitro cell culture models. It is our intention to follow these initial studies with verification of osteogenic potential in animal experiments followed by clinical human studies. This will be achieved by taking advantage of unique physical and intellectual resources of the Palo Alto Bone and Joint Rehabilitation R&D center in the area of translational research. Experiments will also address the ability of rest-inserted loading profiles to reduce bone resorption utilizing in vitro models of osteoclast activity currently under development in our laboratory. Thus, the long-term goal of this work is to provide initial benchtop evidence to support clinical investigation of optimal rest-inserted loading profiles for combating disuse bone loss.
This project is divided into three specific aims:
- Demonstrate that increased intracellular calcium signaling due to rest-inserted loading translates into increased downstream osteogenic changes in bone cells
- Find one or more candidate optimal loading patterns
- Examine whether the resulting optimal osteogenic loading pattern also increases the formation of new bone forming cells (osteoblasts).