Background & Aims
Abdominal pain, diarrhea and/or constipation are common symptoms in patients with disorders of gut-brain interaction. While studies have focused on overgrowth of bacteria in the small intestine (SI) as one potential cause, our group has shown that alterations in SI microbial composition, and not overgrowth, are strongly associated with specific patient symptoms (1). Due to technical challenges and a lack of models, mechanisms of pain signaling from the SI and the physiologic effects of the human SI microbiome are not well-understood. The aim of this study was to develop and utilize new models to measure the effects of the human SI microbiome on visceral hypersensitivity.
Methods
We established a dedicated model to study the physiologic effects of the human SI microbiome in germ-free (GF) mice and developed a novel ex vivo spinal cord-SI preparation from mice that genetically express optical reporters of activity to study the transmission of luminal signals in pain pathways from the SI. We colonized GF mice with SI aspirates collected from patients with and without abdominal pain (AP or healthy control, HC), assessed visceral sensitivity by measuring visceromotor responses (VMRs) to graded distension, and used ex vivo/in vitro calcium imaging to record activation of enteroendocrine (EE) and enterochromaffin (EC) cells and sensory neurons in dorsal root ganglia (DRG).
Results
AP mice had higher VMRs at pressures of 30, 45 and 60 mmHg compared to HC mice, indicating that the pain phenotype was transferred to recipient GF mice via the SI microbiome. In our ex vivo spinal cord-SI preparation, acute luminal exposure to AP SI aspirate induced Ca2+ responses in DRG sensory neurons that were often more robust than mechanical activation. Luminal signals can activate neuronal terminals of DRG sensory neurons directly or indirectly via neuro-epithelial communication by first activating EC cells that release transmitters to drive neuronal activity. Therefore, we used Ca2+ imaging in in vitro models to determine if EC cells and/or DRG sensory neurons are directly activated by microbial products in the SI aspirate from AP patients. AP SI aspirate caused activation in QGP-1 cells (a model for EC cells), primary EE and EC cells, and primary DRG sensory neurons that was greater than HC.
Conclusions
Abdominal pain may be driven by SI microbial products that engage pain pathways by activating DRG sensory neurons directly and indirectly via EC cells. To develop mechanism-based therapeutic interventions, ongoing and future work will (1) identify specific microbes and metabolites in patient SI aspirates, (2) define the effects of chronic exposure to pain-producing microbes and/or metabolites, and (3) determine the molecular mechanisms of activation and sensitization of neuro-epithelial pain pathways.
References
1. Saffouri GB, Shields-Cutler RR, Chen J, Yang Y, Lekatz HR, Hale VL, et al. Small intestinal microbial dysbiosis underlies symptoms associated with functional gastrointestinal disorders. Nat Commun. 2019;10(1):2012.
Presenting Author
Kristen Smith-Edwards
Poster Authors
Kristen Smith-Edwards
Lead Author
Topics
- Mechanisms: Biological-Systems (Physiology/Anatomy)