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

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.