Carolin Wohlfarth, Stefanie Schmitteckert, Janina D. Härtle, Lesley A. Houghton, Harsh Dweep, Marina Fortea, Ghazaleh Assadi, Alexander Braun, Tanja Mederer, Sarina Pöhner, Philip P. Becker, Christine Fischer, Martin Granzow, Hubert Mönnikes, Emeran A. Mayer, Gregory Sayuk, Guy Boeckxstaens, Mira M. Wouters, Magnus Simrén, Greger Lindberg, Bodil Ohlsson, Peter Thelin Schmidt, Aldona Dlugosz, Lars Agreus, Anna Andreasson, Mauro D'Amato, Barbara Burwinkel, Justo Lorenzo Bermejo, Ralph Röth, Felix Lasitschka, Maria Vicario, Marco Metzger, Javier Santos, Gudrun A. Rappold, Cristina Martinez, Beate Niesler

• Irritable bowel syndrome (IBS) is a gut-brain disorder involving alterations in intestinal sensitivity and motility. Serotonin 5-HT4 receptors are promising candidates in IBS pathophysiology since they regulate gut motor function and stool consistency, and targeted 5-HT4R selective drug intervention has been proven beneficial in subgroups of patients. We identified a single nucleotide polymorphism (SNP) (rs201253747) c.*61 T > C within the 5-HT4 receptor gene \(HTR4\) to be predominantly present in diarrhoea-IBS patients (IBS-D). It affects aIrritable bowel syndrome (IBS) is a gut-brain disorder involving alterations in intestinal sensitivity and motility. Serotonin 5-HT4 receptors are promising candidates in IBS pathophysiology since they regulate gut motor function and stool consistency, and targeted 5-HT4R selective drug intervention has been proven beneficial in subgroups of patients. We identified a single nucleotide polymorphism (SNP) (rs201253747) c.*61 T > C within the 5-HT4 receptor gene \(HTR4\) to be predominantly present in diarrhoea-IBS patients (IBS-D). It affects a binding site for the miR-16 family and miR-103/miR-107 within the isoforms \({HTR4b/i}\) and putatively impairs \(HTR4\) expression. Subsequent miRNA profiling revealed downregulation of miR-16 and miR-103 in the jejunum of IBS-D patients correlating with symptoms. \(In\) \(vitro\) assays confirmed expression regulation via three 3′UTR binding sites. The novel isoform \(HTR4b\_2\) lacking two of the three miRNA binding sites escapes miR-16/103/107 regulationin SNP carriers. We provide the first evidence that \(HTR4\) expression is fine-tuned by miRNAs, and that this regulation is impaired either by the SNP c.*61 T > C or bydiminished levels of miR-16 and miR-103 suggesting that \(HTR4\) might be involved in the development of IBS-D.…