Role of endogenous lipids in the regulation of biphasic insulin secretion.

点击翻译按钮获取中文摘要

There are three sources of free fatty acids (FFA) 1) exogenously-derived FFAs, 2) endogenously-synthesized FFAs (de novo lipogenesis (DNL)) and 3) release from internal triglyceride stores. DNL occurs primarily in liver cells, however, many tissue types are able to produce limited amounts of lipid. The role of this small amount of DNL in these cell types is not completely understood. For example, insulin secreting cells of the pancreas express enzymes that lead to DNL in proportion to the amount of glucose exposure. This glucose driven DNL has been proposed to be important in generating metabolic signaling molecules important for regulating insulin exocytosis. It has also been suggested that glycerolipid (GL)/ FFA cycling from internal triglyceride stores may also play a role in the regulation of insulin release. Inhibition of this cycling suppresses FFA augmentation of glucose-stimulated insulin release. We have published results showing that the effects of manipulating four key enzymes (PC, CL, ACC and FAS) and three metabolic carriers (pyruvate carrier, citrate carrier and dicarboxylate carrier) that are involved in DNL lead to conflicting results for and against a role of DNL in regulating insulin exocytosis. We will continue to investigate the role of DNL in the regulation of glucose-stimulated insulin release using newly developed tools in the lab. We have also identified several glucose derived endogenous lipid species that may be critical for regulating biphasic insulin secretion using a metabolomics approach. A number of questions arise from these metabolomics studies for example what is the source of these glucose derived endogenous lipids (e.g. release from triglyceride (TG) stores or from DNL) and how might these lipids be involved in regulating biphasic insulin release. We will expand on these studies to further investigate the role of endogenous lipids in the regulation of biphasic insulin release. Hypothesis: Endogenous lipids generate signaling molecules that are critical to the metabolic regulation of biphasic insulin secretion. Experimental approach: We have identified several endogenous lipid species that may be critical for regulating biphasic insulin secretion using a metabolomics approach. We will use molecule cloning techniques, siRNAs and siRNA adenoviruses, metabolic assays, enzymatic assays, secretion assays, fluorescent imaging and metabolomics to measure metabolite profiles and metabolic fluxes in key endocrine models of fuel regulated secretion. The combination of these approaches will allow us to study all aspects of the metabolic regulation of biphasic insulin secretion by DNL. Novelty and significance: It is well known that exogenous lipids regulate insulin secretion but the role of endogenous is less well defined. These studies will provide invaluable insights towards understanding the unique role of lipids play in the regulation of exocytosis.