Novel function of histamine signaling in hyperlipidemia-induced atherosclerosis: Histamine H1 receptors protect and H2 receptors accelerate atherosclerosis

Abstract

Histamine is not only essential for acute inflammatory reactions, but it also participates in a chronic inflammatory disorder. We generated apolipoprotein E (apoE) and histamine receptors (HHRs), including the major H1 and H2 receptors (HH1R, HH2R) double knockout mice (DKO) to clarify the role of HHRs in hyperlipidemia-induced atherosclerosis, in which apoE-KO and DKO mice were fed a high cholesterol diet. We found that pronounced hyperlipidemia-induced atherosclerotic progression occurred in HH1R/apoE-DKO mice, but in HH2R/apoE-DKO mice less atherosclerosis, despite pro-atherogenic serum cholesterol levels compared with apoE-KO mice. Furthermore, the increased expressions of scavenger receptors (SRs), such as SR-A, CD36 and lectin-like oxidized low-density lipoprotein receptor 1 (LOX-1), nuclear factor-kappa B (NFκB), monocyte chemoattractant protein (MCP-1), matrix metalloproteinases (MMPs) or liver X receptor (LXR)-related inflammatory signaling factors, were consistent with the pro-atherogenic phenotype of HH2R/apoE-DKO mice. We hypothesize that histamine/HH1R and HH2R signaling has conflicting innate functions, inflammatory/atherogenic and anti-inflammatory/anti-atherogenic actions, and that there are innate links between histamine signaling and hyperlipidemia-induced atherosclerosis, independently of serum cholesterol metabolism. Specific histamine signaling blockers, in particular, HH2R blockers, are a possible novel therapeutic target for hyperlipidemia-induced atherosclerosis.