PROJECT SUMMARY/ABSTRACT Peripheral nerve dysfunction is associated with skeletal fragility in humans and in preclinical models. While proprioceptive deficits play a significant role in increased fracture risk, loss of local innervation may deplete bone of neuronal factors critical for skeletal homeostasis. This presents new challenges for maintaining bone health in patients with neuropathy and those undergoing nerve-modifying treatments. Specifically, it may affect the therapeutic efficacy of weight-bearing exercise. Mechanically loading bone through exercise is a well-established requirement for bone health. Compression of long bones results in skeletal remodeling to increase strength. In addition, bone cells secrete neurotrophic cues after loading that may facilitate nerve sprouting towards the skeleton, modifying endogenous skeletal innervation patterns. Considering this emerging role of nerves in skeletal metabolism, local neuroskeletal signaling may be required to facilitate load-induced bone formation. The central goal of this proposal is to investigate the plasticity and necessity of neuroskeletal crosstalk in the anabolic response of bone to compressive loading. To accomplish this, the proposed research is divided into two aims. In Aim 1, novel neuroskeletal niches involved in load-induced bone formation will be defined. To investigate how native neuroskeletal niches are modified during skeletal adaptation, a 5-day regimen of in vivo axial compression will be conducted on mice to induce lamellar bone formation, followed by histology and imaging of the tibia. Nerves in bone will be mapped using a novel pan-neuronal Baf53b-Ai9 reporter mouse and immunostaining for nerve subtypes. In addition, local Ngf and Wnt1 gene expression will be mapped in relation to defined neuroskeletal niches using in situ hybridization. To study the spatial localization and relative quantities of axons, mineralizing surface, and gene expression, a novel image analysis workflow (RadialQuant) will be used. In Aim 2, the necessity of these neuroskeletal niches for load-induced bone formation will be evaluated. To test this, a model of tibial denervation will be developed by evaluating neuronal loss after one-week of femoral and/or sciatic neurectomy using the imaging techniques employed in Aim 1. To test the necessity of innervation in skeletal adaptation, the hindlimb will be denervated accordingly prior to cyclic axial compression as in Aim 1. Techniques from Aim 1 will be used isolate the effect of loading and denervation on axon density, mineral apposition, and gene expression. The long-term career goal of the applicant is to run an independent research laboratory. In addition to the research plan, the training plan is designed to achieve this goal through development of new technical skills, mentorship, and critical synthesis of literature. The two-year fellowship will be conducted at the Washington University School of Medicine under the mentorship of Dr. Eri...