ABSTRACT
OBJECTIVE: Obesity is characterized by systemic and low-grade tissue inflammation. In the intestine, alteration of the intestinal barrier and accumulation of inflammatory cells in the epithelium are important contributors of gut inflammation. Recent studies demonstrated the role of the aryl hydrocarbon receptor (AhR) in the maintenance of immune cells at mucosal barrier sites. A wide range of ligands of external and local origin can activate this receptor. We studied the causal relationship between AhR activation and gut inflammation in obesity. METHODS: Jejunum samples from subjects with normal weight and severe obesity were phenotyped according to T lymphocyte infiltration in the epithelium from lamina propria and assayed for the mRNA level of AhR target genes. The effect of an AhR agonist was studied in mice and Caco-2/TC7 cells. AhR target gene expression, permeability to small molecules and ions, and location of cell-cell junction proteins were recorded under conditions of altered intestinal permeability. RESULTS: We showed that a low AhR tone correlated with a high inflammatory score in the intestinal epithelium in severe human obesity. Moreover, AhR activation protected junctional complexes in the intestinal epithelium in mice challenged by an oral lipid load. AhR ligands prevented chemically induced damage to barrier integrity and cytokine expression in Caco-2/TC7 cells. The PKC and p38MAPK signaling pathways were involved in this AhR action. CONCLUSIONS: The results of these series of human, mouse, and cell culture experiments demonstrate the protective effect of AhR activation in the intestine targeting particularly tight junctions and cytokine expression. We propose that AhR constitutes a valuable target to protect intestinal functions in metabolic diseases, which can be achieved in the future via food or drug ligands.
Subject(s)
Basic Helix-Loop-Helix Transcription Factors/metabolism , Intestinal Mucosa/metabolism , Obesity/metabolism , Receptors, Aryl Hydrocarbon/metabolism , Adiposity/genetics , Adult , Aged , Aged, 80 and over , Animals , Basic Helix-Loop-Helix Transcription Factors/genetics , Biomarkers , Cell Line , Comorbidity , Cytokines/metabolism , Epithelial Cells/metabolism , Female , Humans , Intestinal Mucosa/immunology , Intestinal Mucosa/pathology , Jejunum/metabolism , Lipid Metabolism , MAP Kinase Signaling System , Male , Mice , Middle Aged , Models, Biological , Obesity/etiology , Obesity/pathology , Permeability , Receptors, Aryl Hydrocarbon/genetics , Signal Transduction , T-Lymphocyte Subsets/immunology , T-Lymphocyte Subsets/metabolism , Tight Junctions/drug effects , Tight Junctions/metabolismABSTRACT
The mechanisms leading to the low-grade inflammation observed during obesity are not fully understood. Seeking the initiating events, we tested the hypothesis that the intestine could be damaged by repeated lipid supply and therefore participate in inflammation. In mice, 1-5 palm oil gavages increased intestinal permeability via decreased expression and mislocalization of junctional proteins at the cell-cell contacts; altered the intestinal bacterial species by decreasing the abundance of Akkermansia muciniphila, segmented filamentous bacteria, and Clostridium leptum; and increased inflammatory cytokine expression. This was further studied in human intestinal epithelial Caco-2/TC7 cells using the two main components of palm oil, i.e., palmitic and oleic acid. Saturated palmitic acid impaired paracellular permeability and junctional protein localization, and induced inflammatory cytokine expression in the cells, but unsaturated oleic acid did not. Inhibiting de novo ceramide synthesis prevented part of these effects. Altogether, our data show that short exposure to palm oil or palmitic acid induces intestinal dysfunctions targeting barrier integrity and inflammation. Excessive palm oil consumption could be an early player in the gut alterations observed in metabolic diseases.
Subject(s)
Gastrointestinal Microbiome/drug effects , Intestinal Mucosa/drug effects , Metabolic Syndrome/pathology , Palm Oil/adverse effects , Palmitic Acid/adverse effects , Administration, Oral , Animals , Caco-2 Cells , Cytokines/immunology , Cytokines/metabolism , Disease Models, Animal , Endoplasmic Reticulum Stress/drug effects , Endoplasmic Reticulum Stress/immunology , Feces/microbiology , Gastrointestinal Microbiome/immunology , Humans , Inflammation Mediators/immunology , Inflammation Mediators/metabolism , Intestinal Mucosa/metabolism , Intestinal Mucosa/pathology , Male , Metabolic Syndrome/immunology , Mice , Palm Oil/administration & dosage , Palm Oil/chemistry , Palmitic Acid/administration & dosage , Permeability , Tight Junctions/drug effectsABSTRACT
Scavenger receptor Class B type 1 (SR-B1) is a lipid transporter and sensor. In intestinal epithelial cells, SR-B1-dependent lipid sensing is associated with SR-B1 recruitment in raft-like/ detergent-resistant membrane domains and interaction of its C-terminal transmembrane domain with plasma membrane cholesterol. To clarify the initiating events occurring during lipid sensing by SR-B1, we analyzed cholesterol trafficking and raft-like domain composition in intestinal epithelial cells expressing wild-type SR-B1 or the mutated form SR-B1-Q445A, defective in membrane cholesterol binding and signal initiation. These features of SR-B1 were found to influence both apical cholesterol efflux and intracellular cholesterol trafficking from plasma membrane to lipid droplets, and the lipid composition of raft-like domains. Lipidomic analysis revealed likely participation of d18:0/16:0 sphingomyelin and 16:0/0:0 lysophosphatidylethanolamine in lipid sensing by SR-B1. Proteomic analysis identified proteins, whose abundance changed in raft-like domains during lipid sensing, and these included molecules linked to lipid raft dynamics and signal transduction. These findings provide new insights into the role of SR-B1 in cellular cholesterol homeostasis and suggest molecular links between SR-B1-dependent lipid sensing and cell cholesterol and lipid droplet dynamics.
