N-Terminal Liver-Expressed Antimicrobial Peptide 2 (LEAP2) Region Exhibits Inverse Agonist Activity toward the Ghrelin Receptor

Abstract

The ghrelin receptor or growth hormone secretagogue receptor (GHSR) is a G-protein-coupled receptor that controls growth hormone and insulin secretion, food intake, and reward-seeking behaviors. Liver-expressed antimicrobial peptide 2 (LEAP2) was recently described as an endogenous antagonist of GHSR. Here, we present a study aimed at delineating the structural determinants required for LEAP2 activity toward GHSR. We demonstrate that the entire sequence of LEAP2 is not necessary for its actions. Indeed, the N-terminal part alone confers receptor binding and activity to LEAP2. We found that both LEAP2 and its N-terminal part behave as inverse agonists of GHSR and as competitive antagonists of ghrelin-induced inositol phosphate production and calcium mobilization. Accordingly, the N-terminal region of LEAP2 is able to inhibit ghrelin-induced food intake in mice. These data demonstrate an unexpected pharmacological activity for LEAP2 that is likely to have an important role in the control of ghrelin response under normal and pathological conditions.

Growth hormone secretagogue receptor signalling affects high‐fat intake independently of plasma levels of ghrelin andLEAP2, in a 4‐day binge eating model

“…The same dose of systemically‐injected LEAP2 1‐12 , which is even shorter than LEAP2 1‐14 , blocks the orexigenic effects of systemically‐injected ghrelin to the same extent as full‐length LEAP2, indicating that the experimental conditions were accurate with respect to unmasking the effects of circulating LEAP2 1‐14. Thus, acute increments of plasma LEAP2, and the resulting blockade of endogenous ghrelin action, do not affect HF intake in our experimental conditions. The i.c.v.‐injected ghrelin tended to increase HF intake on experimental day 1, and such an increment masked HF intake escalation over the successive days.…”

“…The current results also suggest that centrally‐injected hormones act on brain areas involved in HF intake that were not targeted by systemically‐injected hormones. Of note, LEAP2 1‐14 displays full bioactivity; however, it may not fully resemble all of the physiological features of LEAP2, such as plasma clearance or brain accessibility. Thus, the ability of circulating LEAP2 to act on brain areas regulating HF intake should be tested using an intact version of the hormone.…”

“…LEAP2 1‐14 was dissolved in PBS. For s.c. injections, mice were injected with 600 pmol g ‐1 BW of LEAP2 1‐14 because this dose of s.c.‐injected LEAP2 fully blocks the orexigenic effects of 60 pmol g ‐1 BW of ghrelin . For i.c.v.…”

“…In vitro, GHSR shows an unusually high constitutive activity that signals with approximatey 50% of its maximum activity, in the absence of ghrelin . Constitutive GHSR activity is reduced by LEAP2, indicating that this ligand also acts as an inverse agonist of the receptor . A role for constitutive GHSR activity in humans is supported by a naturally occurring mutation of GHSR that abolishes constitutive activity without altering ghrelin‐evoked activity and leads to familial short stature .…”

“…Growth hormone secretagogue receptor activity potently regulates food intake. Ghrelin administration rapidly stimulates feeding in satiated humans and rodents, and LEAP2 administration abolishes ghrelin‐induced food intake in mice . The fact that plasma ghrelin in humans and rodents rises before meals and decreases post‐prandially suggests that endogenous ghrelin is linked to food intake regulation .…”