ROLE OF INSULIN AND IGF-1 ON BROWN ADIPOCYTES

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Brown adipose tissue (BAT) is specialized for non-shivering thermogenesis in neonates. Regulation of BAT activity is critical to maintain energy homeostasis. Both insulin and insulin-like growth factor-1 (IGF-1) have been postulated to play important roles in regulation of cellular proliferation, survival, and metabolism in a variety of cellular contexts. However, the actions of these factors in BAT have not been fully elucidated. Our laboratory has successfully established brown pre-adipocyte cell lines from newborn mice and developed protocols to differentiate these cells in vitro. This model provides an excellent system to study the role of insulin and IGF-1 on regulation of metabolism and cell survival and delineate the signaling pathways involved. The studies proposed here will initially compare the similarities and differences between insulin and IGF-1 signaling pathways for glucose metabolism and protection from apoptosis. Once characterized, I will expand the scope of experimental system to different cells lines derived from mice in which the genes for distinct insulin receptor substrate (IRS) proteins are disrupted. These studies will provide understandings on the extent to which the various IRS proteins play unique versus redundant role. Furthermore, TNF-alpha has been shown to mediate obesity-linked insulin resistance. In the proposed studies, cross-talk between TNF-alpha and insulin/IGF-1 signaling pathways will be examined. Accomplishment of the proposed studies will further our understanding on hormonal controls of metabolism and survival of brown adipocytes.