Activation of Aryl Hydrocarbon Receptor Mediates Indoxyl Sulfate-Induced Monocyte Chemoattractant Protein-1 Expression in Human Umbilical Vein Endothelial Cells

Abstract

Circulation Journal Official Journal of the Japanese Circulation Society http://www. j-circ.or.jp positive correlation between chronic kidney disease (CKD) and cardiovascular disease (CVD) has been demonstrated, but the causative role of uremic toxin remains unclear. 1-3 A number of retention compounds act as uremic toxins, accumulating in the blood of CKD patient, and elevated circulating uremic toxins negatively affect biological function through induction of oxidative stress. The removal of uremic solutes, therefore, has the potential to prevent CVD. However, protein-bound retention solutes are insufficiently eliminated even by hemodialysis. 4-6 Indoxyl sulfate (IS) is a protein-bound uremic toxin metabolized in the liver from indole, a tryptophan metabolite that is formed by intestinal bacteria. Together with CKD progression, IS accumulates in the blood, which leads to cellular toxicity by inducing oxidative stress. 7In particular, recent studies have suggested that IS is associated with vascular damage by inducing vasoactive substances related to atherogenesis such as chemokines, cytokines or cell adhesion molecules. 8,9 As a possible mechanism of the process, we previously demonstrated that IS mediates monocyte chemoattractant protein-1 (MCP-1) expression in human umbilical vein endothelial cells (HUVECs) by producing reactive oxygen species (ROS) through NADPH oxidase activation. 10 MCP-1 is a chemokine that is involved in early stage of atherosclerosis through the recruitment of monocytes from the blood stream to the subendothelial space. 11-13 Moreover, others have shown that IS-induced vascular damage exhibits inflammatory effects in monocytes, vascular smooth muscle cells or cardiac myocytes.

The Kidney and Uremic Toxin Removal: Glomerulus or Tubule?

“…At present, kynurenine, kynurenic acid, indoleacetic acid, and indoxyl sulfate-all indolic products of tryptophan metabolism-have been shown to bind to the AhR or induce the expression of AhR response genes, such as CYP1A1. 38,[93][94][95][96][97] Moreover, as shown in Table 3, all four metabolites activate the AhR at concentrations either similar to the highest C max determined in dialysis patients (eg, indole acetic acid) or at levels decisively lower than the C max , for instance indoxyl sulfate. To date, the clinical implications of AhR activation in the setting of CKD development and progression remain unclear, however, it has been postulated that uremic solutes might evoke dioxinlike toxicity, 38 leading to suppression of immune responses, induction of carcinogenesis and accelerating tumor growth, and promoting atherosclerosis.…”

Aryl Hydrocarbon Receptor Mediates Indoxyl Sulfate-Induced Cellular Senescence in Human Umbilical Vein Endothelial Cells

“…We therefore examined the effects of AhR blockade on cellular senescence. Pretreatment with ANF (10 μmol/L) or CH223191 (10 μmol/L) 39) , AhR inhibitors, for one hour rescued the IS-induced cellular senescence in the HUVECs (Fig. 3A).…”

“…It has been reported that the mechanism by which IS induces oxidative stress involves the transport of IS into the cell via organic anion transporters (OAT1, OAT3), where it then activates nicotinamide adenine dinucleotide phosphate (NADPH) oxidase in endothelial, renal tubular and glomerular mesangial cells [34][35][36][37][38] . Although it is unknown how IS activates NADPH oxidase, we recently found that aryl hydrocarbon receptor (AhR), which is expressed in human umbilical vein endothelial cells (HUVECs), is involved in the upregulation of NADPH oxidase-4 induced by IS 39) . AhR is a ligand-activated nuclear receptor/transcription factor belonging to the basic helix-loophelix/per-AhR nuclear translocator (ARNT)-Sim fam-mined using a Nampt colorimetric assay kit (CycLex) according to the manufacturer's instructions.…”

“…We recently reported that the mechanism by which IS increases oxidative stress in HUVECs is AhR-dependent 39) . We therefore examined the effects of AhR blockade on cellular senescence.…”

“…Furthermore, the enhancement of AhR by polychlorinated biphenyls (PCBs) has been demonstrated to cause endothelial inflammation in association with an increased expression of monocyte chemotactic protein-1 (MCP-1) and vascular cell adhesion protein-1 (VCAM-1) 43) . We previously found that IS activates AhR as its ligand, which in turn, induces the MCP-1 expression via the actions of mitogen-activated protein kinase (MAPK)/nuclear factor-kB (NF-kB) in HUVECs 39,44) . These reports indicate that AhR is involved in the pathogenesis of endothelial dysfunction and inflammation; however, it remains unclear whether AhR activation causes cellular senescence in endothelial cells.…”