Profiling of G protein-coupled receptors in vagal afferents reveals novel gut-to-brain sensing mechanisms

Abstract

Objectives

G protein-coupled receptors (GPCRs) act as transmembrane molecular sensors of neurotransmitters, hormones, nutrients, and metabolites. Because unmyelinated vagal afferents richly innervate the gastrointestinal mucosa, gut-derived molecules may directly modulate the activity of vagal afferents through GPCRs. However, the types of GPCRs expressed in vagal afferents are largely unknown. Here, we determined the expression profile of all GPCRs expressed in vagal afferents of the mouse, with a special emphasis on those innervating the gastrointestinal tract.

Methods

Using a combination of high-throughput quantitative PCR, RNA sequencing, and in situ hybridization, we systematically quantified GPCRs expressed in vagal unmyelinated Na _v1.8-expressing afferents.

Results

GPCRs for gut hormones that were the most enriched in Na _v1.8-expressing vagal unmyelinated afferents included NTSR1, NPY2R, CCK1R, and to a lesser extent, GLP1R, but not GHSR and GIPR. Interestingly, both GLP1R and NPY2R were coexpressed with CCK1R. In contrast, NTSR1 was coexpressed with GPR65, a marker preferentially enriched in intestinal mucosal afferents. Only few microbiome-derived metabolite sensors such as GPR35 and, to a lesser extent, GPR119 and CaSR were identified in the Na _v1.8-expressing vagal afferents. GPCRs involved in lipid sensing and inflammation (e.g. CB1R, CYSLTR2, PTGER4), and neurotransmitters signaling (CHRM4, DRD2, CRHR2) were also highly enriched in Na _v1.8-expressing neurons. Finally, we identified 21 orphan GPCRs with unknown functions in vagal afferents.

Conclusion

Overall, this study provides a comprehensive description of GPCR-dependent sensing mechanisms in vagal afferents, including novel coexpression patterns, and conceivably coaction of key receptors for gut-derived molecules involved in gut-brain communication.

Highlights

• •

  Profiling of G protein coupled receptors expression in unmyelinated vagal afferents.

• •

  GLP1R, NPY2R and CCK1R are preferentially coexpressed in fibers innervating the GI muscularis.

• •

  NTS1R is the only receptor for gut hormone coexpressed with Gpr65, a marker for GI mucosal afferents.

• •

  The receptors for ghrelin and GIP are not present in the vagal afferents.

• •

  Receptors for inflammatory lipids are broadly expressed in unmyelinated vagal afferents.