Spatial, chemical, and mechanical signals all contribute to lineage allocation of pluripotent mesenchymal stem cells (MSCs). When the fate of MSCs tips in favor of adipogenesis and away from osteogenesis in conditions such as unloading, aging, or estrogen deficiency, bone quality is diminished and risk of fracture increases. Dynamic skeletal loading inhibits adipogenesis in vitro and in vivo by enhancing ?-catenin activity in MSCs. MSC potential is preserved by a signaling cascade, which is initiated at focal adhesions (FAs) setting off a cascade of ?mTORC2 to ?Akt to 'GSK3? and ??-catenin. How mTORC2 is activated by force at the FA is unknown. Our preliminary data suggests mTORC2 requires Src for activation. Src kinases participate in mechanically regulated signaling events notably in activating RhoA necessary for new FA formation. Our data indicates that mTORC2 is required for RhoA activation, suggesting that the requirement of Src in RhoA activation may be indirect via the activation of mTORC2. The focus of this proposal will be to examine the role of Src kinases in strain-dependent mTORC2 activation and the contribution of those signaling events to cytoskeletal adaptation. These questions will be examined through the following specific aims: 1) determine how mechanical activation of Src-family kinases causes mTORC2 activation;2) define the role of mTORC2 in force-dependent RhoA activation;3) determine if mechanical activation of Src is enhanced by cytoskeletal adaptation. Pharmacological inhibition/knockdown studies will be performed using primary marrow-derived MSC to examine Src kinases and other signaling molecules associated with mechanical regulation of cytoskeletal remodeling. These studies have implications for understanding the mechanism by which mechanical loading regulates cytoskeletal assembly and reinforcement, a process essential for proper regulation of mechanosensation and cytoskeletal adaptation. The research training outlined in this proposal, combined with an outstanding mentoring committee and the ample resources of UNC provide the perfect environment to foster the necessary scientific growth to launch a productive, independent academic research career.

Public Health Relevance

Osteoporosis and obesity are two of the most debilitating conditions in the United States. While osteoporosis severely affects the elderly, often resulting i fractures, obesity is a major health concern among children and adolescents. Estimates indicate that 25% of American children are overweight, while 11% are obese;an enormous concern in that obese children are predisposed to type2 diabetes and have an increased lifetime risk of cardiovascular disease and cancer. A sedentary lifestyle perpetuates both of these conditions. In contrast, exercise helps mesenchymal stem cells develop into bone rather than fat. The studies proposed here will examine how mechanical forces, similar to those during walking or exercise, regulate the fate of mesenchymal stems cells to develop into bone cells or fat cells. These studies will be essential to the design of effective exercise interventions to promote bone health and prevent excess fat formation.

National Institute of Health (NIH)
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Postdoctoral Individual National Research Service Award (F32)
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Special Emphasis Panel (ZRG1-F10B-S (20))
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Sharrock, William J
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University of North Carolina Chapel Hill
Internal Medicine/Medicine
Schools of Medicine
Chapel Hill
United States
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Thompson, William R; Guilluy, Christophe; Xie, Zhihui et al. (2013) Mechanically activated Fyn utilizes mTORC2 to regulate RhoA and adipogenesis in mesenchymal stem cells. Stem Cells 31:2528-37