Histamine induces Toll‐like receptor 2 and 4 expression in endothelial cells and enhances sensitivity to Gram‐positive and Gram‐negative bacterial cell wall components

Abstract

SUMMARYHistamine is a major inflammatory molecule released from the mast cell, and is known to activate endothelial cells. However, its ability to modulate endothelial responses to bacterial products has not been evaluated. In this study we determined the ability of histamine to modulate inflammatory responses of endothelial cells to Gram-negative and Gram-positive bacterial cell wall components and assessed the role of Toll-like receptors (TLR) 2 and 4 in the co-operation between histamine and bacterial pathogens. Human umbilical vein endothelial cells (HUVEC) were incubated with lipopolysaccharide (LPS), lipoteichoic acid (LTA), or peptidoglycan (PGN) in the presence or absence of histamine, and the expression and release of interleukin-6 (IL-6), and NF-jB translocation were determined. The effect of histamine on the expression of mRNA and proteins for TLR2 and TLR4 was also evaluated. Incubation of HUVEC with LPS, LTA and PGN resulted in marked enhancement of IL-6 mRNA expression and IL-6 secretion. Histamine alone markedly enhanced IL-6 mRNA expression in HUVEC, but it did not stimulate proportional IL-6 release. When HUVEC were incubated with LPS, LTA, or PGN in the presence of histamine marked amplification of both IL-6 production and mRNA expression was noted. HUVEC constitutively expressed TLR2 and TLR4 mRNA and proteins, and these were further enhanced by histamine. The expression of mRNAs encoding MD-2 and MyD88, the accessory molecules associated with TLR signalling, were unchanged by histamine treatment. These results demonstrate that histamine up-regulates the expression of TLR2 and TLR4 and amplifies endothelial cell inflammatory responses to Gram-negative and Gram-positive bacterial components.

Histamine Directly and Synergistically with Lipopolysaccharide Stimulates Cyclooxygenase-2 Expression and Prostaglandin I2 and E2 Production in Human Coronary Artery Endothelial Cells

“…In previous studies, 10 M concentration of histamine was found to be sufficient to induce near-maximum stimulation of inflammatory responses in endothelial cells (9,16). Therefore, HCAEC were incubated with 10 M histamine for 1, 2, 4, and 8 h to evaluate the kinetic profile of COX-1 and COX-2 mRNA expression.…”

“…HCAEC were grown in EGM-2 MV containing 1 g/ml hydrocortisone acetate, 50 ng/ml gentamicin, 50 g/ml amphotericin B, and the recommended concentrations of human epidermal growth factor, vascular endothelial growth factor, human fibroblast growth factor-B, recombinant insulin-like growth factor-1, ascorbic acid, and 5% FBS, as described previously (9,16). At confluence, the cells were detached from the culture flasks using trypsin-EDTA, washed twice, and resuspended in fresh EGM-2 MV.…”

“…Recently, we have shown that histamine stimulates TLR2 and TLR4 expression in endothelial cells and enhances inflammatory responses to Gram-positive and Gram-negative bacterial cell wall components (16). Thus, histamine is not only able to induce inflammatory responses directly, but also has the potential to amplify infection-associated activation of endothelial functions (16).…”

“…Recently, we have shown that histamine stimulates TLR2 and TLR4 expression in endothelial cells and enhances inflammatory responses to Gram-positive and Gram-negative bacterial cell wall components (16). Thus, histamine is not only able to induce inflammatory responses directly, but also has the potential to amplify infection-associated activation of endothelial functions (16). The objectives of this study were to determine the role of histamine in the regulation of COX-2 gene expression in vitro and in vivo and to evaluate its regulatory function on the production of PGE 2 , PGI 2 , and TXA 2 in naive and LPS-stimulated human coronary artery endothelial cells (HCAEC).…”

Receptors involved in cell activation by antiphospholipid antibodies

“…Human umbilical vein EC (HUVEC) express high levels of TLR4 and low amounts of TLR1, TLR2, and TLR6 [47,48]. Increased expression of TLR2 by EC in response to inflammatory mediators such as TNF, LPS, IL-1β, IFNγ and histamine in vivo and in vitro [49][50][51][52], however, provides a mechanism allowing EC to respond to TLR2 ligands under inflammatory conditions. TLR2 and TLR4 are both expressed on platelets [53] and on monocytes [54].…”