The role of TLR2 and 4-mediated inflammatory pathways in endothelial cells exposed to high glucose

• Published in: PloS one 2014-10, Vol.9 (10), p.e108844
• Main Authors: Mudaliar, Harshini, Pollock, Carol, Ma, Jin, Wu, Huiling, Chadban, Steven, Panchapakesan, Usha
• Format: Article
• Language: English
• Subjects: Activation; Adhesion; Animals; Biology and Life Sciences; Cell adhesion; Cell adhesion molecules; Cell Line; Chemokines; Complications; Cytokines; Diabetes mellitus; Diabetes Mellitus, Experimental - genetics; Diabetes Mellitus, Experimental - immunology; Diabetes Mellitus, Experimental - pathology; Diabetics; Endothelial cells; Endothelial Cells - immunology; Endothelial Cells - pathology; Endothelium; Exposure; Gene Deletion; Glucose; Glucose - immunology; Health aspects; High mobility group proteins; HMGB1 protein; Humans; Hyperglycemia; Immune system; Inflammation; Inflammation - genetics; Inflammation - immunology; Inflammation - pathology; Inhibition; Intercellular adhesion molecule 1; Intercellular Adhesion Molecule-1 - immunology; Interleukin; Interleukin 8; Medicine and Health Sciences; Mice; Mice, Inbred BALB C; Microvasculature; Monocyte chemoattractant protein; Monocyte chemoattractant protein 1; NF-κB protein; Pathways; Proteins; Receptors; Signal Transduction; Signaling; Streptozocin; Synthesis; TLR2 protein; TLR4 protein; Toll-Like Receptor 2 - genetics; Toll-Like Receptor 2 - immunology; Toll-Like Receptor 4 - genetics; Toll-Like Receptor 4 - immunology; Toll-like receptors; Vascular cell adhesion molecule 1
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0108844

Postprandial hyperglycemia induces inflammation and endothelial dysfunction resulting in vascular complications in patients with diabetes. Toll-like receptors (TLRs) are central to the regulation of inflammatory responses through activation of nuclear factor-kappa B (NF-ĸB). This study examined the role of TLR2 and 4 in regulating inflammation and endothelial dysfunction when exposed to fluctuating glucose concentrations. HMEC-1 cells (a human microvascular endothelial cell line) were exposed to control (5 mM), 30 mM (high), fluctuating (5/30 mM) and 11.2 mM glucose (approximate glycaemic criteria for the diagnosis of diabetes mellitus) for 72 h. Cells were assessed for TLR2, 4, high mobility group box -1 (HMGB1), NF-ĸB, monocyte chemoattractant protein-1 (MCP-1), interleukin-8 (IL-8), intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). Fluctuating glucose concentrations maximally upregulated TLR4 but not TLR2 expression with increased NF-ĸB activation, IL-8 and ICAM-1 expression. HMGB1 was increased in the supernatants of cells exposed to 30 mM and 11.2 mM glucose compared to control. The addition of recombinant HMGB1 induced NF-ĸB activation and synthesis of proinflammatory cytokines and chemokines, which were prevented by TLR2 or 4 signalling inhibition. An additive effect when both TLR2 and 4 signalling pathways were inhibited was observed. However, only inhibition of TLR4 signalling suppressed the synthesis of MCP-1, IL-8 and ICAM-1. In vivo, streptozotocin-induced diabetic mice exhibited an increase in glomerular ICAM-1 which was not evident in TLR2(-/-) or TLR4(-/-) diabetic mice. Collectively, our results suggest that targeting the signalling pathway of TLR2 and 4 may be of therapeutic benefit in attenuating vascular inflammation in diabetic microangiopathy.