TRAPing Ghrelin-Activated Circuits: A Novel Tool to Identify, Target and Control Hormone-Responsive Populations in TRAP2 Mice.

Iris Stoltenborg,Marie V Le May,Erik Schéle,Suzanne L Dickson,Fiona Peris-Sampedro,Roger A H Adan

doi:10.3390/ijms23010559

Abstract

The availability of Cre-based mouse lines for visualizing and targeting populations of hormone-sensitive cells has helped identify the neural circuitry driving hormone effects. However, these mice have limitations and may not even be available. For instance, the development of the first ghrelin receptor (Ghsr)-IRES-Cre model paved the way for using the Cre-lox system to identify and selectively manipulate ghrelin-responsive populations. The insertion of the IRES-Cre cassette, however, interfered with Ghsr expression, resulting in defective GHSR signaling and a pronounced phenotype in the homozygotes. As an alternative strategy to target ghrelin-responsive cells, we hereby utilize TRAP2 (targeted recombination in active populations) mice in which it is possible to gain genetic access to ghrelin-activated populations. In TRAP2 mice crossed with a reporter strain, we visualized ghrelin-activated cells and found, as expected, much activation in the arcuate nucleus (Arc). We then stimulated this population using a chemogenetic approach and found that this was sufficient to induce an orexigenic response of similar magnitude to that induced by peripheral ghrelin injection. The stimulation of this population also impacted food choice. Thus, the TRAPing of hormone-activated neurons (here exemplified by ghrelin-activated pathways) provides a complimentary/alternative technique to visualize, access and control discrete pathways, linking hormone action to circuit function.

Highlights

The brain ghrelin signaling system comprises neuronal networks that are targeted by the stomach-derived hormone, ghrelin [1], whose primary role is to ensure that we seek out and consume food [2,3,4]
Unraveling the role of the specific populations of ghrelin-responsive neurons has often involved the site-specific injections of ghrelin or GHSR ligands, which induce an orexigenic response at most brain areas targeted, including the arcuate nucleus (Arc) and many others [16,17,18,19,20,21,22]
To demonstrate the engagement of the orexigenic systems, we further explored whether the cells activated by a DREADD agonist colocalized with agouti-related peptide (AgRP) using RNAscope

Summary

Introduction

The brain ghrelin signaling system comprises neuronal networks that are targeted by the stomach-derived hormone, ghrelin [1], whose primary role is to ensure that we seek out and consume food [2,3,4] Other ligands targeting this system include synthetic growth hormone secretagogues (GHS) [5] and liver-enriched antimicrobial peptide 2 (commonly referred to as LEAP2), an endogenous inverse agonist [6,7]. Unraveling the role of the specific populations of ghrelin-responsive neurons has often involved the site-specific injections of ghrelin or GHSR ligands, which induce an orexigenic response at most brain areas targeted, including the arcuate nucleus (Arc) and many others [16,17,18,19,20,21,22] Such approaches invariably raise questions, about the spread of the hormone from the injection site and do not provide information about the precise populations of cells activated by ghrelin

Methods

Results

Conclusion