Expression of the relaxin family peptide 4 receptor by enterochromaffin cells of the mouse large intestine

• Published in: Cell and tissue research 2022-07, Vol.389 (1), p.1-9
• Main Authors: Koo, Ada, Pustovit, Ruslan V., Woodward, Orla R. M., Lewis, Jo E., Gribble, Fiona M., Hossain, Mohammed Akhter, Reimann, Frank, Furness, John B.
• Format: Article
• Language: English
• Subjects: Alosetron; Animals; Biomedical and Life Sciences; Biomedicine; Calcitonin gene-related peptide; Colon; Enteric nervous system; Enterochromaffin Cells - metabolism; Enteroendocrine Cells - metabolism; Human Genetics; Immunoreactivity; Insulin; Intestine, Large; Labeling; Large intestine; Mice; Molecular Medicine; Nerve endings; Peptides; Proteomics; Receptors, G-Protein-Coupled - metabolism; Receptors, Peptide - metabolism; Reflexes; Regular; Regular Article; Relaxin; Sensory neurons; Serotonin; Serotonin S3 receptors
• ISSN: 0302-766X; 1432-0878
• DOI: 10.1007/s00441-022-03635-8

The gastrointestinal hormone, insulin-like peptide 5 (INSL5), is found in large intestinal enteroendocrine cells (EEC). One of its functions is to stimulate nerve circuits that increase propulsive activity of the colon through its receptor, the relaxin family peptide 4 receptor (RXFP4). To investigate the mechanisms that link INSL5 to stimulation of propulsion, we have determined the localisation of cells expressing Rxfp4 in the mouse colon, using a reporter mouse to locate cells expressing the gene. The fluorescent signal indicating the location of Rxfp4 expression was in EEC, the greatest overlap of Rxfp4 -dependent labelling being with cells containing 5-HT. In fact, > 90% of 5-HT cells were positive for Rxfp4 labelling. A small proportion of cells with Rxfp4 -dependent labelling was 5-HT-negative, 11–15% in the distal colon and rectum, and 35% in the proximal colon. Of these, some were identified as L-cells by immunoreactivity for oxyntomodulin. Rxfp4 -dependent fluorescence was also found in a sparse population of nerve endings, where it was colocalised with CGRP. We used the RXFP4 agonist, INSL5-A13, to activate the receptor and probe the role of the 5-HT cells in which it is expressed. INSL5-A13 administered by i.p. injection to conscious mice caused an increase in colorectal propulsion that was antagonised by the 5-HT 3 receptor blocker, alosetron, also given i.p. We conclude that stimuli that excite INSL5-containing colonic L-cells release INSL5 that, through RXFP4, excites 5-HT release from neighbouring endocrine cells, which in turn acts on 5-HT 3 receptors of enteric sensory neurons to elicit propulsive reflexes.