Spexin as a Satiety Factor in Mouse via Regulatory Actions Within the Hypothalamus

Spexin (SPX) is a pleiotropic peptide with highly conserved protein sequence from fish to mammals and its biological actions are mediated by GalR2/GalR3 receptors expressed in target tissues. Recently, SPX was found to be a novel satiety factor in fish models but whether the peptide has a similar function in mammals is still unknown. Using the mouse as a model for mammalian species, the functional role of SPX in feeding control and the mechanisms involved were investigated. After food intake, serum SPX could be up-regulated in mice with parallel elevations of transcript expression and tissue content of SPX in the glandular stomach but not in other tissues examined. As revealed by immunostaining, food intake also intensified SPX signals in different cell types within the gastric mucosa of glandular stomach. Furthermore, IP injection of SPX was effective in reducing food consumption with parallel drops in transcript expression of NPY, AgRP, NPY type 5 receptor (NPY5R) and ghrelin receptor (GHSR) in the hypothalamus, and these inhibitory effects could be blocked by GalR3 but not GalR2 antagonism. In agreement with the central actions of SPX, similar inhibition on food intake and hypothalamic expression of NPY, AgRP, NPY5R and GHSR could be observed with ICV injection of SPX. In the same study, parallel rises of transcript expression of leptin receptor (LepR) and melanocortin 4 receptor (MC4R) were also observed in the hypothalamus. These findings, taken together, suggest that the role of SPX as a satiety factor is well-conserved in the mouse. Probably, food consumption can induce SPX production in glandular stomach and contribute to the postprandial rise of SPX in circulation. Through GalR3 activation, this SPX signal can act within the hypothalamus to trigger feedback inhibition on food intake by differential modulation of the feeding regulators (NPY & AgRP) and their receptors (NPY5R, GHSR, LepR & MC4R) involved in the feeding circuitry of the brain.