Impaired Lipophagy and Lipid Droplet Accumulation in Osteoblasts

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Dr. Elizabeth Rendina-Ruedy currently maintains a faculty appointment as an Assistant Professor of Medicine in the Vanderbilt Center for Bone Biology (VCBB), which is a component of the Division of Clinical Pharmacology of Vanderbilt University Medical Center (VUMC). Her 13+ years of training and research has been deeply rooted in bone biology with an emphasis in nutritional biochemistry. While the research strategy outlined in this application will take advantage of these strengths and interests, a much more molecular, transdisciplinary approach is proposed to determine the metabolic function of lipid droplets in osteo-progenitor cells. As such, Dr. Rendina-Ruedy’s mentor team, Dr. Jeff Rathmell and Dr. Cliff Rosen, epitomize the integration of the two fields, while providing impeccable support and guidance to the candidate. The applicant and her mentors have developed an individualized plan to include structured activities that will significantly enhance her research career, including: mentor-mentee contact; enhancing research skills, methodologies, and expertise; involvement in courses, workshops, and training sessions; and, the dissemination of research and knowledge. Additionally, VUMC offers an exceptional biomedical research environment, as well as supportive staff that are committed to mentoring junior scientists. The research plan expands on preliminary findings made by Dr. Rendina-Ruedy during her doctoral training, which demonstrated that bone-lining osteo- progenitor cells accumulated lipid droplets in a diet-induced obese mouse model of type 2 diabetes mellitus (T2DM). These data also corresponded to lower cancellous bone volume and a decrease in osteoblastogenesis. These data were of particular interest given that the clinical manifestation of T2DM is associated with an increase in fracture risk, independent of bone mineral density (BMD), along with a decrease in bone formation. Taken together, the hypotheses being tested in the current application are that (1) intracellular lipid droplet lipolysis via lipophagy supports bone formation by enhancing osteoblast differentiation through the generation and utilization of energy substrates; and (2) bone formation is compromised in obesity- related metabolic derangements such as T2DM, due to impaired lipophagy. These hypotheses will be addressed by integrating an innovative pulse-chase, co-localization experiment (specific aim 1A), as well as determining metabolic fuel dependency and flexibility in bone marrow stromal cells (specific aim 1B). Additionally, we will generate a novel conditional perilipin (Plin)-2 knock out, targeted in osteo-progenitor cells (Prx1-Cre) as a means to protect from diet-induced obesity compromise in bone by up-regulating lipolysis. In summary, Dr. Rendina-Ruedy’s proposed project represents a highly significant research problem in the field of bone biology that will be investigated by integrating innovative metabolic strategies. Ultimately, these data seek to provide a greater understanding of the molecular mechanisms underlying the increased fracture risk associated with obesity related metabolic perturbations, such as T2DM, and may impact future therapies.