Endothelial sensing of AHR ligands regulates intestinal barrier immunity [AHR KO RNA-seq]
The blood and lymphatic vasculature is lined by functionally specialised endothelial cells (ECs). In the intestine, ECs act as an essential physical barrier, controlling nutrient transport, facilitating tissue immunosurveillance, and coordinating angiogenesis and lymphangiogenesis to ensure appropriate tissue perfusion and drainage. Conversely, endothelial maladaptation can lead to pathological angiogenesis and the perpetuation of inflammation in chronic inflammatory diseases. However, whether enteric ECs actively engage in the regulation of intestinal homeostasis and pathology through integration of environmental cues is currently unknown. Here, we show that the aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor, acts as critical node for EC-sensing of dietary and microbial metabolites.  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 ECs, identifying transcriptional networks and putative biological roles across endothelial subtypes. Analyses of AHR mediated responses at single-cell resolution identified tissue-protective transcriptional signatures and regulatory networks promoting quiescence and vasculoprotection. Endothelial AHR-deficiency in mice resulted in cellular activation, proliferation, and initiation of angiogenic pathways disrupting tissue homeostasis. In human ECs, AHR signalling promoted quiescence through cell cycle arrest and tempered endothelial inflammatory responses. Together, our data provide a comprehensive dissection of the impact of environmental sensing across the spectrum of enteric endothelia, demonstrating that endothelial AHR signalling serves to promote homeostasis and prevent aberrant inflammatory responses at the intestinal barrier. Overall design: Examination of small intestinal tissue-wide changes between endothelial-AHR deficient mice and littermate controls at steady state by RNA sequencing.