The GHSR1a antagonist LEAP2 regulates islet hormone release in a sex-specific manner

Abstract

LEAP2, a liver-derived antagonist for the ghrelin receptor, GHSR1a, counteracts effects of ghrelin on appetite and energy balance. Less is known about its impact on blood glucose-regulating hormones from pancreatic islets. Here we investigate whether acyl-ghrelin (AG) and LEAP2 regulate islet hormone release in a cell type- and sex-specific manner. Hormone content from secretion experiments with isolated islets from male and female mice was measured by radioimmunoassay and mRNA expression by qPCR. LEAP2 enhanced insulin secretion in islets from males (p<0.01) but not females (p<0.2), whilst AG-stimulated somatostatin release was significantly reversed by LEAP2 in males (p<0.001) but not females (p<0.2). Glucagon release was not significantly affected by AG and LEAP2. Ghsr1a, Ghrelin, Leap2, Mrap2, Mboat4 and Sstr3 islet mRNA expression did not differ between sexes. In control male islets maintained without 17-beta oestradiol (E2), AG exerted an insulinostatic effect (p<0.05), with a trend towards reversal by LEAP2 (p=0.06). Both were abolished by 72h E2 pre-treatment (10 nmol/l, p<0.2). AG-stimulated somatostatin release was inhibited by LEAP2 from control (p<0.001) but not E2-treated islets (p<0.2). LEAP2 and AG did not modulate insulin secretion from MIN6 beta cells and Mrap2 was downregulated (P<0.05) and Ghsr1a upregulated (P<0.0001) in islets from Sst^-/- mice. Our findings show that AG and LEAP2 regulate insulin and somatostatin release in an opposing and sex-dependent manner, which in males can be modulated by E2. We suggest that regulation of SST release is a key starting point for understanding the role of GHSR1a in islet function and glucose metabolism.