Neuropeptide AF Induces Piecemeal Degranulation in Murine Mucosal Mast Cells: A New Mediator in Neuro‐Immune Communication in the Intestinal Lamina Propria?

Abstract

Neuropeptides AF (NPAF), FF (NPFF) and SF (NPSF) are RFamide neuropeptides known to be widely expressed in the mammalian central nervous system, where they fulfill a wide range of functions with pain modulation being the most prominent one. Recent evidence indicates that RFamides act as mediators in mast cell–sensory nerve communications related to allergic disease. Previous work by our group has shown that the expression levels of some members of the Mas‐related gene receptor (Mrgpr) family in both enteric neurons and mucosal mast cells change during intestinal inflammation. The Mrgpr subtypes C11 and A4 can be activated by NPAF, while A1 and C11 are triggered by NPFF. The aim of the present study was to investigate whether RFamides of the NPFF group are expressed in the gastrointestinal tract and to identify possible targets and receptors that might be involved in RFamide‐associated mast cell modulation. To this end, the expression and distribution patterns of NPFF/AF receptors and the NPFF precursor protein were determined in bone marrow‐derived mucosal mast cells (BMMCs) by immunocytochemistry and (RT‐) PCR. BMMCs were found to express MrgprA4 and A1, and functional analysis of the effects of NPAF by means of a β‐hexosaminidase assay, mMCP‐1 ELISA, electron microscopy and live cell calcium imaging revealed a piecemeal degranulation induced by NPAF. However, knock‐out of MrgprA4 and A1 did not reduce the effect of NPAF, indicating that the BMMC response to NPAF was receptor independent. ProNPFF was expressed in neurons and BMMCs, suggesting that both cell types are potential sources of NPAF in situ. Our results show that the RFamide NPAF can be considered as a novel modulator of BMMC activity in the neuro‐immune communication in the gastrointestinal tract, although the exact signaling pathway remains to be elucidated. Anat Rec, 00:000–000, 2018. © 2018 Wiley Periodicals, Inc. Anat Rec, 301:1103–1114, 2018. © 2018 Wiley Periodicals, Inc.

Mas‐related G protein‐coupled receptor C11 (Mrgprc11) induces visceral hypersensitivity in the mouse colon: A novel target in gut nociception?

“…For example, Mrgprc11 is activated by neuropeptide AF (NPAF) and neuropeptide FF (NPFF), two FMRF‐amide peptides with a role in pain signaling . It was recently found that their common precursor gene is expressed by myenteric neurons and mucosal‐type mast cells, acting as a possible source for these ligands . Moreover, a growing body of evidence links Mrgprc11 to protease‐mediated signaling.…”

“…37,38 It was recently found that their common precursor gene is expressed by myenteric neurons and mucosal-type mast cells, acting as a possible source for these ligands. 39 Moreover, a growing body of evidence links Mrgprc11 to protease-mediated signaling. Established protease-activated receptor 2 (PAR-2) agonists, such as the PAR-2 tethered-ligand peptide SLIGRL and certain cysteine proteases, also act as Mrgprc11 agonists, thereby inducing effects that were previously considered to be solely PAR2-mediated.…”

Neuro‐immune interactions and the role of Mas‐related G protein‐coupled receptors in the gastrointestinal tract

“…We showed that Mrgprb10 was expressed de novo in mucosal MCs of Schistosoma mansoni ‐infected ileum (Avula et al, 2013) and that in vitro mucosal‐type bone marrow‐derived mast cells (BMDMCs) were found to express Mrgpra1 and Mrgpra4 mRNA, but these findings have not been confirmed in vivo (Abdellah et al, 2018). Plum et al (2020) demonstrated MRGPRX2 expression in human gut MCs.…”

“…Furthermore, MrgprC11 is known to be activated by two FMRF‐amide peptides, neuropeptide AF (NPAF) and neuropeptide FF (NPFF), which have been reported to act as mediators in MC‐sensory nerve communications (Lee et al, 2008; Lee et al, 2011; Tatemoto et al, 2006). We were able to identify, by means of RT‐PCR, possible RF‐amide sources in intrinsic and extrinsic components of the ENS, that is, in DRGs and in enteric neurons and intestinal MCs (Abdellah et al, 2018). Furthermore, immunofluorescent staining with a FMRFamide antibody clearly revealed the presence of FMRFamide in nerve fibers in both the myenteric and submucous plexuses as well as in neuroendocrine cells with typical neuropods.…”

“…Interestingly, intracolonic administration of NPAF in healthy mice induces afferent nerve sensitization and visceral hypersensitivity in an Mrgpr‐dependent manner (Castro et al, 2019). NPAF and NPFF are associated with pain signaling and inflammation, and thus might act, in association with MrgprC11, as a possible neuro‐immune axis on gut afferents (Abdellah et al, 2018; Han et al, 2002; Yang et al, 2008). In addition to being activated by these RFamide peptides, Mrgprc11 has also been linked to protease‐mediated signaling.…”