Society: AGA

This session will cover the pathogenic and non-pathogenic constituents of the gut microbiome that induce local and systemic inflammatory response and play an important role in disease development.

Background: The intestinal epithelium is an essential interface between the microbial ecosystem and the underlying mucosa, orchestrating both immune-mediated and metabolic functions. Mitochondrial signaling and metabolism control the phenotype and function of intestinal epithelial cells (IECs) and mitochondrial perturbation is associated with chronic inflammation. We hypothesize that disruption of microbial-metabolic circuits and impaired metabolic flexibility of IECs contributes to the initiation and progression of tissue injury and chronic inflammation. Methods: To address the role of mitochondrial impairment in epithelial homeostasis, conditional deletion of Heat shock protein 60 (Hsp60) was induced in IECs of both specific-pathogen free and germ-free (GF) Hsp60^Δ/ΔIEC mice as well as in a colitis mouse model (Hsp60^Δ/ΔIEC;Il10^-/-) and in AhR-deficient mice (Hsp60^Δ/ΔIEC;AhR^-/-). Histological analysis, 16S rRNA and shallow shotgun sequencing were performed. Different molecular mechanisms were analyzed in Hsp60-deficient organoids. Results: Hsp60 deletion in IECs induces metabolic injury, defined as a disrupted mitochondrial metabolism accompanied by an irregular crypt architecture causing transient tissue injury. Mitochondrial perturbation is associated with dysbiotic changes in the microbiota including a rapid drop in species richness and changes in the bacterial community profile of Hsp60^Δ/ΔIECmice with an increased abundance of Bacteroides spp.. Tissue lesions are completely absent in the distal colon of GF mice, indicating bacterial contribution to metabolic injury. In Hsp60^Δ/ΔIEC;Il10^-/- mice, mitochondrial impairment of the epithelium accelerates inflammation, paralleled by a persistent Bacteroides spp. expansion. Clinical relevance of mitochondrial stress signaling of the epithelium and increased abundance of Bacteroides spp. are confirmed in a combined analysis of three IBD cohorts (N=560 patients). Upon colonization of GF Hsp60^Δ/ΔIECwith the synthetic minimal consortium OligoMM¹² inducing epithelial lesions, B. caecimuris expands during metabolic injury, strengthening our hypothesis. Indeed, B. caecimuris triggers tissue aberration when mono-colonizing Hsp60^Δ/ΔIECmice, confirming its deleterious role in tissue homeostasis. While lack of Aryl hydrocarbon Receptor (AhR) signaling upon metabolic injury is lethal in Hsp60^Δ/ΔIEC;AhR^-/-mice, antibiotic exposure abrogates the severity of the phenotype, highlighting that AhR ligands protect from metabolic injury. Conclusion: Bacteroides spp. were identified as key players regulating mitochondrial metabolism and host-sensing pathways critically affected cellular plasticity upon metabolic injury. Mitochondria emerge as intriguing interceptors of milieu signals in the intestine, and unresolved metabolic injury is a novel concept in the pathogenesis of intestinal inflammation.

Elisabeth Urbauer

Appearances