SUN-098 Goldfish Insulin: Molecular Cloning, Hepatic Regulation by Spexin, and Mechanisms for Feeding Control in Fish Model

Insulin is a key hormone for metabolism and glucose homeostasis. In mammals, it also acts as a satiety factor with inhibitory effect on food intake, but its biological actions in appetite control in lower vertebrates is still unknown. Spexin (SPX), a neuropeptide with pleotropic functions, has been recently confirmed to be a novel satiety factor in fish model via functional coupling with insulin, although the details of their interactions have yet to be elucidated. In this study, using goldfish as a model, the mechanism for feeding regulation by insulin and its functional interactions with SPX at hepatic level were examined. As a first step, goldfish insulin was cloned and found to be widely expressed at tissue level, especially with high levels of expression in the liver and visceral fat. In silico modeling also showed that the 3D structure of the mature peptide of goldfish insulin was highly comparable if not identical to its human counterpart. In goldfish liver cell culture, insulin mRNA level could be up-regulated by SPX treatment via PLC/IP(3)/PKC and Ca(2+)/CaM/CaMK-II pathways, while the opposite was true by removing endogenous SPX using immunoneutralization with SPX antiserum. In whole animal experiment, IP injection with insulin was found to inhibit feeding behavior and food consumption in goldfish. Similar treatment in vivo was also effective in elevating POMC, CART, CCK and leptin mRNA levels with concurrent drop in NPY, AGRP and apelin transcript expression in the telencephalon, optic tectum and hypothalamus, the brain areas known to be involved in feeding control in fish models. Using brain cell culture prepared from these three areas, similar changes in transcript expression for the respective orexigenic and anorexigenic factors were also noted with insulin treatment in a time- and dose-dependent manner. These findings, as a whole, suggest that SPX can act in an autocrine/paracrine manner to induce insulin expression in goldfish liver and the subsequence rise of insulin in circulation presumably can inhibit food intake through differential regulation of orexigenic/anorexigenic signals expressed in brain areas involved in appetite control in fish model.