Search and functional analysis for novel bioactive peptides associated with regulation of energy balance and feeding behavior

点击翻译按钮获取中文摘要

Obesity is one of the most serious problems worldwide, because it is associated with lifestyle-related disease such as hypertension, cardiovascular disease and type 2 diabetes. The aims of this study are to identify endogenous ligands for orphan GPCRs associated with regulation of energy balance and feeding behavior, and to clarify the biochemical and pathophysiological significance of the ligands.We established stable mammalian cell lines expressing human BRS-3 or other orphan GPCRs to monitor changes in the intracellular second messenger that were induced by rat tissue extracts. Changes in the intracellular calcium concentration and cyclic AMP were measured using the FLIPR System (Molecular Device) and AlphaScreen (Packard), respectively. Several [Ca^<2+>]I-increasing activities for BRS-3 were found in rat brain and intestinal extracts. These were further purified by successive chromatography to prove known peptides, having cross-reactivity to BRS-3. The highest [Ca^<2+>]I-increasing activity for one other orphan receptor was found in rat brain extract. This was finally purified as a single peptide, and partial amino acid sequence indicated that this was a novel peptide. This peptide inhibited food intake in rats when injected intracerebroventricularly.Ghrelin, a novel peptide purified from stomach as an endogenous ligand for the growth hormone secretagogue receptor in our laboratory, is an acylated peptide that stimulates food intake and the secretion of growth hormone. A single intravenous injection of somatostatin reduced the systemic plasma concentration of ghrelin in rats, and continuous infusion of somatostatin into the gastric artery of the vascularly perfused rat stomach suppressed ghrelin secretion. These findings indicate that ghrelin secretion from the stomach is regulated by gastric somatostatin.