Endothelial sensing of AHR ligands regulates intestinal homeostasis

Abstract

Endothelial cells line the blood and lymphatic vasculature, and act as an essential physical barrier, control nutrient transport, facilitate tissue immunosurveillance and coordinate angiogenesis and lymphangiogenesis1,2. In the intestine, dietary and microbial cues are particularly important in the regulation of organ homeostasis. However, whether enteric endothelial cells actively sense and integrate such signals is currently unknown. Here we show that the aryl hydrocarbon receptor (AHR) acts as a critical node for endothelial cell sensing of dietary metabolites in adult mice and human primary endothelial cells. We first established a comprehensive single-cell endothelial atlas of the mouse small intestine, uncovering the cellular complexity and functional heterogeneity of blood and lymphatic endothelial cells. Analyses of AHR-mediated responses at single-cell resolution identified tissue-protective transcriptional signatures and regulatory networks promoting cellular quiescence and vascular normalcy at steady state. Endothelial AHR deficiency in adult mice resulted in dysregulated inflammatory responses and the initiation of proliferative pathways. Furthermore, endothelial sensing of dietary AHR ligands was required for optimal protection against enteric infection. In human endothelial cells, AHR signalling promoted quiescence and restrained activation by inflammatory mediators. Together, our data provide a comprehensive dissection of the effect of environmental sensing across the spectrum of enteric endothelia, demonstrating that endothelial AHR signalling integrates dietary cues to maintain tissue homeostasis by promoting endothelial cell quiescence and vascular normalcy.

Mechanisms and functions of intestinal vascular specialization

“…Recent single-cell RNAseq data of intestinal endothelial cells show high homeostatic expression of Plvap , especially in capillaries ( Kalucka et al, 2020 ; Tan et al, 2023 ; Wiggins et al, 2023 ), consistent with its induction in response to VEGFA ( Strickland et al, 2005 ) and its role as a functional component of fenestrae diaphragms, which are readily observed in gut capillaries ( Bernier-Latmani et al, 2022b ; Casley-Smith, 1971 ; Casley-Smith et al, 1975 ; Milici and Bankston, 1981 ; Palay and Karlin, 1959 ; Stan et al, 2012 ). These diaphragms promote vessel barrier function as mice with germline and endothelial Plvap ablation and patients with PLVAP mutations display leaky intestinal vessels and edema ( Elkadri et al, 2015 ; Stan et al, 2012 ).…”

“…These vessels are more dilated, sparse, and less branched than vessels in the villus/crypt zone (unpublished data). Recent single-cell RNA sequencing (RNAseq) data reveals that these vessels express genes for fat ( Cd36 , Fabp5 ) and water and glycerol ( Aqp1 , Aqp7 ) transport similar to those observed in muscle- and white adipose tissue–specific endothelial cells ( Fan et al, 2021 ; Kalucka et al, 2020 ; Wiggins et al, 2023 ), suggesting they perform nutrient transport to support intestinal smooth muscle metabolism.…”

“…1 E ; Bernier-Latmani et al, 2015 ; Hong et al, 2020 ; Zhang et al, 2018 ). Intestinal lymphatic endothelial cells isolated in recent single-cell RNAseq studies express common lymphatic markers such as Prox1 , Lyve1 , and Pdpn ( Kalucka et al, 2020 ; Wiggins et al, 2023 ) and subdivide into four distinct clusters. Their functional relevance remains to be determined; however, a cluster with enrichment of interferon signaling ( Wiggins et al, 2023 ) may be similar to the recently described Ptx3 + skin capillary lymphatic endothelial subset associated with immune cell recruitment ( Petkova et al, 2023 ).…”

Bioluminescence imaging of Cyp1a1-luciferase reporter mice demonstrates prolonged activation of the aryl hydrocarbon receptor in the lung

“…The provision of a bespoke Cyp1a1 ‘knock-in’ reporter mouse line that accurately portrays the dynamics of AHR signalling longitudinally in vivo, will be of considerable value in evaluating the impacts and duration of repeated challenge in individual animals. Although in these studies we have used concentrations of AHR ligands that were defined by others 72 , 80 – 82 , our observation that Cyp1a1 luminescence was induced in animals maintained on control diets but switched to a non-SPF facility, suggests that this model can detect endogenously-generated and physiologically relevant AHR activity. That said, it is also important to recognise that ex vivo Cyp1a1 mRNA analysis and Cyp1a1 -luciferase-based luminescence offer slightly different read-outs of AHR activity.…”

Aryl hydrocarbon receptor restricts axon regeneration of DRG neurons in response to injury

“…In a Huntington’s disease model, Ahr deletion led to protection against neurotoxicity and oxidative stress 80 . Recent studies also reported the role of endothelial AhR signaling in integrating dietary cues to maintain tissue homeostasis 81 and exerting protective function in the gut-lung axis 82 . AhR is also important for timely termination of the regenerative response of intestinal epithelia by restricting chromatin accessibility of regeneration-associated Yap/Tead target genes in colonic stem cells 83 .…”