Lipopolysaccharide induces H1 receptor expression and enhances histamine responsiveness in human coronary artery endothelial cells
Histamine is a well-recognized modulator of vascular inflammation. We have shown that histamine, acting via H1 receptors (H1R), synergizes lipopolysaccharide (LPS)-induced production of prostaglandin I2 (PGI2), PGE2 and interleukin-6 (IL-6) by endothelial cells. The synergy between histamine and LPS was partly attributed to histamine -induced expression of Toll-like receptor 4 (TLR4). In this study, we examined whether LPS stimulates the H1R expression in human coronary artery endothelial cells (HCAEC) with resultant enhancement of histamine responsiveness. Incubation of HCAEC with LPS (10–1000 ng/ml) resulted in two-fold to fourfold increases in H1R mRNA expression in a time-dependent and concentration-dependent fashion. In contrast, LPS treatment did not affect H2R mRNA expression. The LPS-induced H1R mRNA expression peaked by 4 hr after LPS treatment and remained elevated above the basal level for 20–24 hr. Flow cytometric and Western blot analyses revealed increased expression of H1R protein in LPS-treated cells. The specific binding of [3H]pyrilamine to H1R in membrane proteins from LPS-treated HCAEC was threefold higher than the untreated cells. The LPS-induced H1R expression was mediated through TLR4 as gene silencing by TLR4-siRNA and treatment with a TLR4 antagonist inhibited the LPS effect. When HCAEC were pre-treated with LPS for 24 hr, washed and challenged with histamine, 17-, 10- and 15-fold increases in PGI2, PGE2 and IL-6 production, respectively, were noted. Histamine-induced enhancement of the synthesis of PGI2, PGE2 and IL-6 by LPS-primed HCAEC was completely blocked by an H1R antagonist. The results demonstrate that LPS, through TLR4 activation, up-regulates the expression and function of H1R and amplifies histamine-induced inflammatory responses in HCAEC.
Document Type: Research Article
Affiliations: 1: Division of Allergy, Clinical Immunology and Rheumatology, Department of Medicine, University of Kansas Medical Center, Kansas City, KS 2: Pharmacology, Toxicology and Therapeutics, University of Kansas Medical Center, Kansas City, KS 3: Flow Cytometry Core Laboratory, University of Kansas Medical Center, Kansas City, KS, USA
Publication date: April 1, 2011