Abstract This Exploratory/Developmental Research Grant will establish a new preclinical model of bone accrual following preterm birth. The rationale is the presence of metabolic bone disease of prematurity that negatively affects the skeletal health of preterm babies and the accumulating evidence of increased bone fragility in former preterm babies entering later decades of life. While there are data for human subjects showing that preterm birth is associated with skeletal deficiencies, successful intervention strategies that target the skeleton are rare, partly because little is known about the underlying mechanisms. A barrier to the field is the lack of a preclinical model in which bone tissue is directly interrogated and mechanistic studies are performed. We have preliminary data of impaired postnatal bone development in a porcine model of prematurity in which we have also identified heightened acetylation of histone 3 in cortical bone osteocytes. Based on these new findings, we propose a novel scientific model system that has the high-risk, high-benefit merit to substantially advance the field. We will test the hypothesis that premature birth in the pig model is associated with diminished bone properties. Our analyses will focus on postnatal bone development through sexual maturity and the possibility of improving early postnatal bone growth. In Aim 1, we assess bone mass, structure and composition by using dual energy x-ray absorptiometry, microcomputed tomography, Raman spectroscopy and backscatter scanning electron microscopy, bone function through mechanical testing to understand whole bone and material properties and will determine if the model replicates the high levels of circulating alkaline phosphatase and low levels of circulating phosphate that are the clinical signs most commonly monitored to diagnose metabolic bone disease of prematurity. These studies will determine if the deficits we have seen up to postnatal day 19 persist through the attainment of sexual maturity at 6 months. In Aim 2, we examine proximate mechanisms (bone resorption and bone formation) and likely ultimate mechanisms (epigenetic reprograming of gene expression and gut microbiome). In Aim 3, we determine if the resulting phenotype is modifiable through use of a feeding formula based on egg yolk, leveraging an already funded study in which the primary endpoint is neuro development. In future studies, we plan to use the model to examine age-related bone loss, but believe it is logical to first evaluate the usefulness of the model to understand how preterm birth affects postnatal skeletal development through early adolescence. Thus, we propose an innovative preclinical, physiological model to study bone accrual following premature birth, its underlying mechanisms and possible treatment. Identifying deficits in bone growth, modeling, remodeling, structure, density and strength in preterm neonates would greatly facilitate the design, preclinical testing, and event...