LEAP2 deletion in mice enhances ghrelin's actions as an orexigen and growth hormone secretagogue

Abstract

Objective The hormone liver-expressed antimicrobial peptide-2 (LEAP2) is a recently identified antagonist and an inverse agonist of the growth hormone secretagogue receptor (GHSR). GHSR's other well-known endogenous ligand, acyl-ghrelin, increases food intake, body weight, and GH secretion and is lowered in obesity but elevated upon fasting. In contrast, LEAP2 reduces acyl-ghrelin-induced food intake and GH secretion and is found elevated in obesity but lowered upon fasting. Thus, the plasma LEAP2/acyl-ghrelin molar ratio could be a key determinant modulating GHSR signaling in response to changes in body mass and feeding status. In particular, LEAP2 may serve to dampen acyl-ghrelin action in the setting of obesity, which is associated with ghrelin resistance. Here, we sought to determine the metabolic effects of genetic LEAP2 deletion. Methods We generated the first known LEAP2-KO mouse line. Food intake, GH secretion, and cellular activation (c-fos induction) in different brain regions following s.c. acyl-ghrelin administration in LEAP2-KO mice and wild-type littermates were determined. LEAP2-KO mice and wild-type littermates were submitted to a battery of tests (such as measurements of body weight, food intake, and body composition; indirect calorimetry, determination of locomotor activity, and meal patterning while housed in metabolic cages) over the course of 16 weeks of high-fat diet and/or standard chow feeding. Fat accumulation was assessed in hematoxylin & eosin-stained and oil red O-stained liver sections from these mice. Results LEAP2-KO mice were more sensitive to s.c. ghrelin. In particular, acyl-ghrelin acutely stimulated food intake at a dose of 0.5 mg/kg BW in standard chow-fed LEAP2-KO mice while a 2× higher dose was required by wild-type littermates. Also, acyl-ghrelin stimulated food intake at a dose of 1 mg/kg BW in high-fat diet-fed LEAP2-KO mice while not even a 10× higher dose was effective in wild-type littermates. Acyl-ghrelin induced a 90.9% higher plasma GH level and 77.2–119.7% higher numbers of c-fos-immunoreactive cells in the arcuate nucleus and olfactory bulb, respectively, in LEAP2-KO mice than in wild-type littermates. LEAP2 deletion raised body weight (by 15.0%), food intake (by 18.4%), lean mass (by 6.1%), hepatic fat (by 42.1%), and body length (by 1.7%) in females on long-term high-fat diet as compared to wild-type littermates. After only 4 weeks on the high-fat diet, female LEAP2-KO mice exhibited lower O 2 consumption (by 13%), heat production (by 9.5%), and locomotor activity (by 49%) than by wild-type littermates during the first part of the dark period. These genotype-dependent differences were not observed in high-fat diet-exposed males or female and male mice exposed for long term to standard chow diet. Conclusions LEAP2 deletion sensitizes lean and obese mice to the acute effects of administered acyl-ghrelin on food intake and GH secretion...

Three of a Kind: Control of the Expression of Liver-Expressed Antimicrobial Peptide 2 (LEAP2) by the Endocannabinoidome and the Gut Microbiome

“…LEAP2 is a recently discovered, a potential endogenous regulator of food intake and energy metabolism through antagonism of ghrelin action [6]. In agreement with these properties of this peptide, originally isolated from the liver as an antimicrobial agent, are the following previous findings: (1) selectively in female mice subjected to a high-fat diet, Leap2 deletion raises body weight, food intake, lean mass, and hepatic fat, and reduces O 2 consumption, heat production, and locomotor activity during the first part of the dark period [27]; (2) in both female and male lean mice, Leap2 deletion renders the animals more sensitive to the hyperphagic actions of ghrelin [27]; LEAP2 administration also reduces blood glucose levels in lean mice [6]; (3) in humans and mice, circulating LEAP2 levels display an inverse pattern compared to ghrelin, by increasing with food intake and obesity, and decreasing upon fasting and weight loss [28,29]; refeeding decreases circulating levels of ghrelin, while LEAP2 goes up to baseline levels; and (4) like other anorectic signals, LEAP2 is also produced by the small intestine [2]. Others have reported that all regions of the mouse small intestine express Leap2, with the highest expression having been found in the jejunum (whereas we detected slightly higher levels in the duodenum), with next to no detectable levels expressed in the stomach [6].…”

LEAP-2 Counteracts Ghrelin-Induced Food Intake in a Nutrient, Growth Hormone and Age Independent Manner

“…Of note, it was shown that LEAP-2 was able to inhibit some of the main in vivo biological effects of ghrelin, such as hyperphagia, hyperglycemia and GH release in mice and rats [17]. Consistent with this, mice lacking LEAP-2 displayed enhanced ghrelin-induced feeding and GH release [18]. Thus, plasma LEAP-2/acyl-ghrelin ratio seems to be determinant to modulate GHS-R1a activity [19,20].…”

“…In this context, the discovery of LEAP-2 as an endogenous non-competitive ghrelin receptor antagonist [15] raised many expectations, as well as many unanswered questions. So far, available in vivo data is quite scarce [15,17,18,21] hence our aim in providing new knowledge with particular emphasis on the assessment of acute food intake. As a whole, we provide strong evidence that central exogenous LEAP-2 administration exerts a marked anorexigenic effect in three different rodent animal models (lean, obese and aged) and also in a variety of experimental models.…”

LEAP2 reduces postprandial glucose excursions and ad libitum food intake in healthy men

“…This is further supported by a recent study indicating that LEAP2 deletion in mice enhances the actions of ghrelin. 15 Of note, it remains to be explored whether exogenous LEAP2 reduces food intake in animal models of impaired metabolic control, such as diet-induced obesity.…”

“… 6 , 7 , 14 Nevertheless, LEAP2 treatment has consistently been shown to impair ghrelin-induced food intake and hyperglycemia in rodents. 5 , 6 , 14 , 15 , 16 Notably, only two studies besides the study of Ge et al. have demonstrated effects of LEAP2 administration alone, i.e., a decrease in plasma glucose after intraperitoneal LEAP2 administration in mice 17 and reduced binge-like eating after central administration of a truncated LEAP2 form in mice.…”