Dual energy x-ray absorptiometry (DXA) that is used in clinical practice to detect bone loss, may not be sufficiently sensitive to identify those individuals who are losing structural integrity of the skeleton over time. High resolution peripheral quantitative computed tomography (HR-pQCT) scanning can detect age-related compartmental skeletal deterioration that independently predicts incident fracture even after considering DXA- derived bone mineral density. This project will perform follow-up high resolution imaging in the third generation cohort of the Framingham Study (Gen3) that will be used to assess the contributions of novel molecular biomarkers of longitudinal deterioration of bone microarchitecture, as there are almost no longitudinal studies of contributors to the loss of bone microarchitecture and strength. The long term goal of this research is to identify novel molecular biomarkers of age-related changes in bone microarchitecture and strength that could be used to predict skeletal fragility by acting as a proxy for HR-pQCT, and that identify mechanistic pathways that could be targeted for drug development. The objective of this proposal is to determine the contribution of two different novel molecular biomarkers to age-related changes in bone microarchitecture and incident fractures in the Framingham Osteoporosis Study. The central hypothesis is that plasma metabolites and clonal hematopoiesis of indeterminate potential (CHIP) will be associated with declines in bone microarchitecture and strength. The hypotheses are based on recently generated preliminary data showing associations between these two novel risk factors and both BMD and fracture. Aim 1 will determine the association between plasma metabolites and a) longitudinal changes in bone microarchitecture and strength, and b) incident fracture. Approximately 700 metabolite measures have already been performed in the Gen3 cohort as well as the Offspring cohort, which will permit a replication of findings generated the Gen3 cohort by analyzing data that will be available in the Offspring. Aim 2 will determine the association of clonal hematopoiesis of indeterminate potential (CHIP) with bone density, microarchitecture and strength in the Gen3 cohort after performing deep targeted sequencing of the four most common genes implicated in CHIP (DNMT3A, TET2, ASXL1, JAK2). This proposal addresses key knowledge gaps by using state-of-the-art technologies to identify molecular determinants of longitudinal age-related declines in bone microarchitecture and strength in a large, well-characterized cohort. Results from this project will be impactful, as they will provide unique insights into the molecular mechanisms underlying age-related skeletal fragility, and may ultimately identify targets for future diagnostics and/or therapeutics. This study has the potential to transform the field in terms of defining the impact of reduced muscle mass.

Project Narrative and Relevance to Public Health Our proposed work will perform high resolution peripheral quantitative computed tomography scans in over 3,000 Framingham 3rd Generation participants to determine: 1) the role of metabolomics in age-related bone loss and fractures; and 2) to determine if clonal hematopoiesis of indeterminate potential contributes to bone density, microarchitecture and strength. Discoveries related to these aims may identify targets for therapeutic interventions to prevent skeletal deterioration and fractures, which will prevent mortality, morbidity and disability. Fracture prevention will also reduce economic costs of health care required to care for these injuries. 1