ABSTRACT
MyD88 adapter-like (Mal)-deficient mice displayed increased susceptibility to oral but not intraperitoneal infection with Salmonella Typhimurium. Bone marrow chimeras demonstrated that mice with Mal-deficient non-hematopoietic cells were more susceptible to infection, indicating a role for Mal in non-myeloid cells. We observed perturbed barrier function in Mal(-/-) mice, as indicated by reduced electrical resistance and increased mucosa blood permeability following infection. Altered expression of occludin, Zonula occludens-1, and claudin-3 in intestinal epithelia from Mal(-/-) mice suggest that Mal regulates tight junction formation, which may in part contribute to intestinal integrity. Mal interacted with several protein kinase C (PKC) isoforms in a Caco-2 model of intestinal epithelia and inhibition of Mal or PKC increased permeability and bacterial invasion via a paracellular route, while a pan-PKC inhibitor increased susceptibility to oral infection in mice. Mal signaling is therefore beneficial to the integrity of the intestinal barrier during infection.
Subject(s)
Intestinal Mucosa/metabolism , Membrane Glycoproteins/metabolism , Protein Kinase C/metabolism , Receptors, Interleukin-1/metabolism , Animals , Cell Line , Gene Expression Regulation , Humans , Intestinal Mucosa/immunology , Intestinal Mucosa/microbiology , Intestines/immunology , Intestines/microbiology , Membrane Glycoproteins/deficiency , Membrane Glycoproteins/genetics , Mice , Mice, Knockout , Permeability , Protein Binding , Protein Transport , Receptors, Interleukin-1/deficiency , Receptors, Interleukin-1/genetics , Salmonella Infections/genetics , Salmonella Infections/immunology , Salmonella Infections/metabolism , Salmonella Infections/microbiology , Salmonella typhimurium/immunology , Signal Transduction , Tight Junction Proteins/genetics , Tight Junction Proteins/metabolismABSTRACT
Macrophages activated by the Gram-negative bacterial product lipopolysaccharide switch their core metabolism from oxidative phosphorylation to glycolysis. Here we show that inhibition of glycolysis with 2-deoxyglucose suppresses lipopolysaccharide-induced interleukin-1ß but not tumour-necrosis factor-α in mouse macrophages. A comprehensive metabolic map of lipopolysaccharide-activated macrophages shows upregulation of glycolytic and downregulation of mitochondrial genes, which correlates directly with the expression profiles of altered metabolites. Lipopolysaccharide strongly increases the levels of the tricarboxylic-acid cycle intermediate succinate. Glutamine-dependent anerplerosis is the principal source of succinate, although the 'GABA (γ-aminobutyric acid) shunt' pathway also has a role. Lipopolysaccharide-induced succinate stabilizes hypoxia-inducible factor-1α, an effect that is inhibited by 2-deoxyglucose, with interleukin-1ß as an important target. Lipopolysaccharide also increases succinylation of several proteins. We therefore identify succinate as a metabolite in innate immune signalling, which enhances interleukin-1ß production during inflammation.
