Our lab has a long standing interest in the mechanisms leading to the state of chronic, low-grade inflammation, which is an intrinsic component of the aging process and many aging-associated diseases. In the past we reported that the hepatic response to Interleukin 12 (IL-12), a major mediator of systemic inflammation, is augmented during aging leading to excessive production of IGFBP1, a protein that is secreted by the liver, binds to the Insulin-like Growth Factor 1 (IGF1), and neutralizes its bioactivity. Hepatic IL-12 hyperresponsiveness is caused by the intrinsic activation of an evolutionary conserved cellular stress response pathway involving neutral sphingomyelinase and its product, ceramide. Here we hypothesize that this IL-12 hyperresponsiveness impairs the insulin signaling pathway in liver. First, we will investigate how aging-associated IL-12 hyperresponsiveness affects the insulin pathway and will study the interactions between key molecules in the two cascades PI3K, Akt-1, and Foxo1 (for insulin), and ceramide, IRAK-1 and JNK (for IL-12). Studies will be done in isolated hepatocytes in vitro and in animals in vivo. Young, aged and aged calorie restricted rats will be used. The regulation of IGFBP1 mRNA transcription by the two pathways will be investigated. These molecular studies will be complemented by assays of insulin- and IGFBP1-dependent functions in vivo, which include tests of IGF1 bioactivity, muscle functions and glucose regulation. Throughout the experiments cause and effect relations will be tested by overexpression and silencing approach using adenovirus-mediated gene transfer. These studies may help to elucidate the cellular and molecular pathways responsible for muscle waste, frailty, and glucose dysregulation in the elderly. They may also reveal a novel mechanism for integration of inflammatory and metabolic signaling pathways and how aging affects these interactions. )
Understanding the mechanisms that dysregulate liver functions during aging is very important for improving the health of older Americans, because liver plays critical role in many functions, including glucose homeostasis, innate immune response, drug metabolism etc.).
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