Cross Talk of Mechanical and Hormonal Signals to Increase Bone Mass

Massachusetts General Hospital, Boston MA

Investigators

Abstract

Project Summary Intermittent parathyroid hormone (PTH) injections are a potent anabolic treatment for osteoporosis but the bone anabolic effect of PTH is greatly diminished in absence of mechanical loading, such as in patients with low physical activity. Finding an alternative approach to mimic mechanical signals would be beneficial. The mechanisms underlying the synergistic effect of mechanical loading and hormonal signaling are unknown. Understanding how these signals work together is crucial to develop ‘next generation’ therapies that optimally stimulate bone formation. In this career development proposal, an innovative approach is taken to investigate how the signals downstream of mechano-transduction and PTH signaling are integrated within bone cells. Focal Adhesion Kinase (FAK) is a tyrosine kinase that controls osteocyte mechanotransduction. Intermittent cAMP signaling plays a key role in bone anabolism downstream of PTH. Preliminary data, show that FAK inhibition, via PDE8A inhibition, synergizes with PTH to increase cAMP signaling in cultured osteocytes. Therefore, the rationale of this proposal is to identify the details of the FAK/PDE8A interaction and show that a similar pathway operates in vivo. The proposed research is significant because it will advance understanding of molecular cell biology downstream of mechanical and hormonal signaling in bone cells and will provide new targets for therapies to treat osteoporosis. Aim 1 will confirm the phosphorylation and regulation of PDE8A by FAK and identify molecular details of this interaction. Based on the results of a phospho-proteomic analysis, it is predicted that FAK phosphorylates tyrosine residue Y315 in the PAS region of PDE8A, inhibiting its enzymatic function. Aim 2 will investigate the effects of FAK/PDE8A axis inhibition in bone mass and bone formation parameters using a hindlimb unloading mouse model. It is predicted that FAK inhibition will rescue the diminished PTH effect caused by hindlimb unloading. RNA sequencing in RNA from long bones of the treated mice, will identify additional secreted factors that mediate bone anabolism. The long-term goal of this work is to elucidate the mechanisms by which mechanical and hormonal signaling act synergistically to increase bone anabolism and identify molecules that can be targeted as an alternative to physical activity with the goal to treat osteoporosis. This study will take place in the Mass General Hospital Endocrine Unit, a renowned training environment for skeletal biology research under the supervision of co-mentors Drs. Marc Wein and Henry Kronenberg. In addition, several collaborators, with additional expertise will contribute further to the research and training goals of this project. The candidate will acquire the necessary skills (technical, conceptual, intellectual, grant and manuscript writing, leadership, mentorship, and public speaking) to establish an independent NIH-funded academic research career in skeletal biology research with the goal of identifying new therapeutic avenues for bone disorders.