Chronic Intestinal Pseudo-Obstruction (CIPO): interplay between enteric nervous system, serotonin and mucosa-associated microbiota

Introduction: Chronic intestinal pseudo-obstruction (CIPO) is a rare disease characterized by symptoms and radiological signs suggestive of intestinal obstruction, in the absence of lumen-occluding lesions. It results from an extremely severe impairment of propulsive motility. Serotonin (5-HT, a local mediator and neurotransmitter) release is linked to intestinal peristaltic and secretory reflexes. The intestinal microbiota and the enteric nervous system (ENS) interact and this results in effects on the synthesis of 5-HT, its release and the subsequent serotonin receptors’ activation. The interplay between ENS/5-HT and dysbiosis in CIPO remains largely unclear. The project aim was to assess correlations between gut microbiota and intestinal serotonin-related genes expression in CIPO pediatric patients. For this purpose, mucosa-associated microbiota (MAM) has been characterized, and changes in gastrointestinal (GI) serotonin pathway have been evaluated. Material and Methods: We collected biopsies of the colon, the ileum and the duodenum from 7 pediatric CIPO patients and 7 age-/sex-matched healthy controls at Cesare Arrigo Childrens’ Hospital (Alessandria, Italy). After DNA extraction, the MAM was assessed by next generation sequencing (NGS) of the V3-V4 region of the bacterial RNA 16s, on an Illumina Miseq platform. The expression of genes implicated in serotoninergic pathway (TPH1, SLC6A4, 5-HTR3 and 5-HTR4) was established by qPCR, after total RNA extraction from the same tissue samples. Correlation analyses were performed to highlight relationships between MAM and the expression of genes linked to the production (TPH1), transport (SLC6A4) and reception (5-HTR3, 5-HTR4) of 5-HT in CIPO patients. Results: Our results revealed a colonic MAM different in its composition and biodiversity with respect to controls. Network analysis evidenced, in CIPO patients, a microbial ecosystem with fewer species, less connected, and with a greater number of non-synergistic relationships compared to controls. qPCR analysis results revealed alterations, a general a decrease, in the expression of serotonin-related genes for CIPO patients when compared to controls. Correlation analysis between the expression of serotonin-related genes and the colon-associated gut microbiota showed some significant but weak correlations, probably due to the low number of samples analyzed. Discussion and conclusion: Results showed, for the first time in CIPO patients, a specific colon-associated MAM, an altered expression of genes related to intestinal serotonin pathway and significant, but weak, interconnections between the microbiota and serotonin-related genes expression, indicating that alterations in this pathway seem to be related to the altered MAM. A possible malfunctioning in the 5-HT pathway, maybe linked to or triggered by an altered microbiota, could be a mechanism underlying the intestinal motility disorder in CIPO patients. Our results could also represent the first step to design a new therapy targeting the microbiota or targeting the serotonin pathways, improving treatment outcomes and quality of life for CIPO patients.