Abstract
Ghrelin-system components [native ghrelin, In1-ghrelin, Ghrelin-O-acyltransferase enzyme (GOAT) and receptors (GHS-Rs)] are expressed in a wide variety of tissues, including the pancreas, where they exert different biological actions including regulation of neuroendocrine secretions, food intake and pancreatic function. The expression of ghrelin system is regulated by metabolic conditions (fasting/obesity) and is associated with the progression of obesity and insulin resistance. Cortistatin (CORT), a neuropeptide able to activate GHS-R, has emerged as an additional link in gut-brain interplay. Indeed, we recently reported that male CORT deficient mice (cort−/−) are insulin-resistant and present a clear dysregulation in the stomach ghrelin-system. The present work was focused at analyzing the expression pattern of ghrelin-system components at pancreas level in cort−/− mice and their control littermates (cort +/+) under low- or high-fat diet. Our data reveal that all the ghrelin-system components are expressed at the mouse pancreatic level, where, interestingly, In1-ghrelin was expressed at higher levels than native-ghrelin. Thus, GOAT mRNA levels were significantly lower in cort−/− mice compared with controls while native ghrelin, In1-ghrelin and GHS-R transcript levels remained unaltered under normal metabolic conditions. Moreover, under obese condition, a significant increase in pancreatic expression of native-ghrelin, In1-ghrelin and GHS-R was observed in obese cort+/+ but not in cort−/− mice. Interestingly, insulin expression and release was elevated in obese cort+/+, while these changes were not observed in obese cort−/− mice. Altogether, our results indicate that the ghrelin-system expression is clearly regulated in the pancreas of cort+/+ and cort −/− under normal and/or obesity conditions suggesting that this system may play relevant roles in the endocrine pancreas. Most importantly, our data demonstrate, for the first time, that endogenous CORT is essential for the obesity-induced changes in insulin expression/secretion observed in mice, suggesting that CORT is a key regulatory component of the pancreatic function.
Highlights
Ghrelin gene (GHRL) is a complex gene whose processing generates, either through alternative splicing or post-translational modifications, a wide variety of transcripts and proteins with multiple functions [1,2,3,4]
Ghrelin is a 28-amino acid multifunctional hormone predominantly produced by the stomach, and lower amounts are generated in wide variety of tissues including the pancreas, where it can act as a paracrine/ autocrine factor [5,6,7,8,9]
Expression of ghrelin, In1-ghrelin variant, Ghrelin-O-acyltransferase enzyme (GOAT) and receptors (GHS-Rs) and ghrelin O-acyltransferase (GOAT) in the pancreas of cort+/+ and cort2/2 mice were determined by qRT-PCR (Fig. 1)
Summary
Ghrelin gene (GHRL) is a complex gene whose processing generates, either through alternative splicing or post-translational modifications, a wide variety of transcripts and proteins with multiple functions [1,2,3,4]. Ghrelin is a 28-amino acid multifunctional hormone predominantly produced by the stomach, and lower amounts are generated in wide variety of tissues including the pancreas, where it can act as a paracrine/ autocrine factor [5,6,7,8,9]. In addition to pre-pro-ghrelin, other splice variants of GHRL, such as In1ghrelin or des-Glu14-Ghrelin can be generated in several tissues ([13]; [2]). In1-ghrelin variant is susceptible to be acylated since it shares the same start codon, the signal peptide and the first 12aa of ghrelin, which includes the putative acylation site at Ser and the residues found to be necessary for acylation (Gly and Phe4) [14]
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