Bacterial lipopolysaccharide promotes profibrotic activation of intestinal fibroblasts

Abstract

Abstract Background Fibroblasts play a critical role in intestinal wound healing. Lipopolysaccharide (LPS) is a cell wall component of commensal gut bacteria. The effects of LPS on intestinal fibroblast activation were characterized. Methods Expression of the LPS receptor, toll-like receptor (TLR) 4, was assessed in cultured primary human intestinal fibroblasts using flow cytometry and confocal microscopy. Fibroblasts were treated with LPS and/or transforming growth factor (TGF) β1. Nuclear factor κB (NFκB) pathway activation was assessed by inhibitory κBα (IκBα) degradation and NFκB promoter activity. Fibroblast contractility was measured using a fibroblast-populated collagen lattice. Smad-7, a negative regulator of TGF-β1 signalling, and connective tissue growth factor (CTGF) expression were assessed using reverse transcriptase–polymerase chain reaction and western blot. The NFκB pathway was inhibited by IκBα transfection. Results TLR-4 was present on the surface of intestinal fibroblasts. LPS treatment of fibroblasts induced IκBα degradation, enhanced NFκB promoter activity and increased collagen contraction. Pretreatment with LPS (before TGF-β1) significantly increased CTGF production relative to treatment with TGF-β1 alone. LPS reduced whereas TGF-β1 increased smad-7 expression. Transfection with an IκBα plasmid enhanced basal smad-7 expression. Conclusion Intestinal fibroblasts express TLR-4 and respond to LPS by activating NFκB and inducing collagen contraction. LPS acts in concert with TGF-β1 to induce CTGF. LPS reduces the expression of the TGF-β1 inhibitor, smad-7.