Bile acids are steroid molecules that are synthesized from cholesterol in the liver hepatocytes. Their synthesis represents a major excretory pathway for removal of cholesterol from the body. Recent studies show that bile acids also function as powerful regulatory molecules helping to coordinately control cholesterol, lipoprotein, and glucose metabolism in the liver. Bile acids are able to regulate the expression of numerous genes and activities of proteins through 2 distinct, yet highly coordinated cellular mechanisms. They can activate specific nuclear receptors (i.e. FXR, PXR, Vitamin D) and cell signaling pathways (i.e. JNK1/2, ERK1/2, AKT, protein kinase C). Each bile acid appears to show some degree of specificity as to which nuclear receptor and cell signaling pathway that it activates, suggesting that the bile acid pool composition may be an important regulator of liver metabolism.
The specific aims of the current grant renewal application are: 1) Determine the identity of the G protein coupled receptor(s) (GPCR), which transduces conjugated bile acid signaling in primary hepatocytes via ERBB1 and the insulin receptor, to ERK1/2 and AKT pathways. Determine the molecular mechanism(s) by which the pertussis toxin sensitive GPCR signal causes activation of ERBB1 and the insulin receptor in primary hepatocytes. 2) Determine the mechanism(s) of activation of the JNK1/2 pathway by bile acids in primary rodent hepatocytes and in vivo. Determine how different bile acids activate acidic sphingomyelinase (ASM) in vitro. 3). Characterize the activation of the JNK1/2, ERK1/2 and AKT signaling pathways by different bile acids in the chronic bile fistula rat and mouse models. Determine the effects of different bile acid infusion (IV and ID) on the activation of cell signaling pathways, levels of selected lipid signaling molecules, and mRNA levels of key genes involved in cholesterol and glucose metabolism.
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