A Cre-Driver Rat Model for Anatomical and Functional Analysis of Glucagon(Gcg)-Expressing Cells in the Brain and Periphery

Abstract

ABSTRACTObjectiveThe glucagon gene (Gcg) encodes preproglucagon, which is cleaved to form glucagon-like peptide 1 (GLP1) and other mature signaling molecules implicated in metabolic functions. To date there are no transgenic rat models available for precise manipulation of GLP1-expressing cells in the brain and periphery.MethodsTo visualize and manipulateGcg-expressing cells in rats, CRISPR/Cas9 was used to expressiCreunder control of theGcgpromoter. Gcg-Cre rats were bred with tdTomato reporter rats to tagGcg-expressing cells. Cre-dependent AAVs and RNAscopein situhybridization were used to evaluate the specificity ofiCreexpression by GLP1 neurons in the caudal nucleus of the solitary tract (cNTS) and intermediate reticular nucleus (IRt), and by intestinal and pancreatic secretory cells. Food intake was assessed in heterozygous (Het) Gcg-Cre rats after chemogenetic stimulation of cNTS GLP1 neurons expressing an excitatory DREADD.ResultsWhile genotype has minimal effect on body weight or composition in chow-fed Gcg-Cre rats, homozygous (Homo) rats have lower plasma glucose levels. In neonatal and adult Gcg-Cre/tdTom rats, reporter-labeled cells are present in the cNTS and IRt, and in additional brain regions (e.g., basolateral amygdala, piriform cortex) that lack detectableGcgmRNA in adults but display transient developmental or persistently lowGcgexpression. Compared to wildtype (WT) rats, hindbrainGcgmRNA and GLP1 protein in brain and plasma are markedly reduced in Homo Gcg-Cre rats. Chemogenetic stimulation of cNTS GLP1 neurons reduced overnight chow intake in males but not females, the effect in males was blocked by antagonism of central GLP1 receptors, and hypophagia was enhanced when combined with a subthreshold dose of cholecystokinin-8 to stimulate gastrointestinal vagal afferents.ConclusionsGcg-Cre rats are a novel and valuable experimental tool for analyzing the development, anatomy, and function ofGcg-expressing cells in the brain and periphery. In addition, Homo Gcg-Cre rats are a unique model for assessing the role ofGcg-encoded proteins in glucose homeostasis and energy metabolism.HighlightsA transgenic Gcg-Cre rat model expressesiCreunder control of theGcgpromoteriCreis expressed by GLP1-positive cells in the hindbrain, pancreas, and intestineAdditional brain regions display transient and/or very low levels ofGcgexpression+/+ Gcg-Cre rats display a marked knockdown ofGcgmRNA and GLP1 proteinChemogenetic activation ofGcgneurons suppresses food intake in +/- Gcg-Cre rats