PROJECT SUMMARY / ABSTRACT The goals of this proposal are to: 1) obtain experimental skills and career training necessary to develop an independent research program investigating mechanisms of bone development and disease, and 2) characterize a novel target of bone remodeling called G protein-gated inwardly-rectifying K+ channel 3 (Girk3), a key regulator of potassium flux and physiological processes. Our data demonstrate that Girk3-/- mice develop high bone mass after skeletal maturity and have low interleukin-1 beta (IL-1β) and other circulating cytokines. The overall objective of this proposal is to test the hypothesis that Girk3 deletion enhances bone density in adult skeletons by altering the secretion of IL-1β and other monocyte-derived cytokines that modify bone resorption. During the mentored K99 phase, the specific aims are to identify how deletion of Girk3 in monocytes affects bone mass (Aim 1) and to determine how Girk3 regulates cytokine production by blood and bone marrow monocytes (Aim 2). Methods used to evaluate the role of Girk3 in bone remodeling will include dynamic and static histomorphometry, osteoblast and osteoclast differentiation assays, cytometry by time-of-flight (CyTOF), single cell RNA-sequencing (scRNA-seq), and bioinformatics. Completion of this aim will facilitate my transition into the independent R00 phase when the specific aim (Aim 3) will be to determine if Girk3 deletion can prevent bone loss in a murine model of osteoporosis via inhibition of IL-1β. The K99 phase will be conducted at Mayo Clinic and will focus on obtaining mentored training in professional development through meetings with a curated mentorship team, regular attendance and presentations at research seminars and national research conferences, participating in workshops on grantsmanship and responsible conduct in research, and seeking out networking opportunities, as well as conducting the experiments in Aims 1 and 2 and publishing the results. The R00 phase will be conducted in my independent laboratory and will focus on completion and publication of Aim 3 and developing an R01 application based on the results. The proposed plan synergizes new skills in osteoclast and ion channel biology, unbiased spectometry, single cell RNA sequencing and bioinformatics, and bone histomorphometry with prior expertise in endocrinology and osteoblast biology to create my own unique research trajectory. The career development plan and research strategy outlined in this application will produce a robust foundation for an independent research career in musculoskeletal biology.