Aldosterone augments LOX-1-mediated low-density lipoprotein uptake in human umbilical artery endothelial cells

Expanded Hemodialysis Therapy Ameliorates Uremia-Induced Systemic Microinflammation and Endothelial Dysfunction by Modulating VEGF, TNF-α and AP-1 Signaling

Abstract

Systemic chronic microinflammation and altered cytokine signaling, with adjunct cardiovascular disease (CVD), endothelial maladaptation and dysfunction is common in dialysis patients suffering from end-stage renal disease and associated with increased morbidity and mortality. New hemodialysis filters might offer improvements. We here studied the impact of novel improved molecular cut-off hemodialysis filters on systemic microinflammation, uremia and endothelial dysfunction. Human endothelial cells (ECs) were incubated with uremic serum obtained from patients treated with two different hemodialysis regimens in the Permeability Enhancement to Reduce Chronic Inflammation (PERCI-II) crossover clinical trial, comparing High-Flux (HF) and Medium Cut-Off (MCO) membranes, and then assessed for their vascular endothelial growth factor (VEGF) production and angiogenesis. Compared to HF membranes, dialysis with MCO membranes lead to a reduction in proinflammatory mediators and reduced endothelial VEGF production and angiogenesis. Cytokine multiplex screening identified tumor necrosis factor (TNF) superfamily members as promising targets. The influence of TNF-α and its soluble receptors (sTNF-R1 and sTNF-R2) on endothelial VEGF promoter activation, protein release, and the involved signaling pathways was analyzed, revealing that this detrimental signaling was indeed induced by TNF-α and mediated by AP-1/c-FOS signaling. In conclusion, uremic toxins, in particular TNF-signaling, promote endothelial maladaptation, VEGF expression and aberrant angiogenesis, which can be positively modulated by dialysis with novel MCO membranes.

Translational Perspective and Graphical Abstract

Systemic microinflammation, altered cytokine signaling, cardiovascular disease, and endothelial maladaptation/dysfunction are common clinical complications in dialysis patients suffering from end-stage renal disease. We studied the impact of novel improved medium-cut-off hemodialysis filters on uremia and endothelial dysfunction. We can show that uremic toxins, especially TNF-signaling, promote endothelial maladaptation, VEGF expression and aberrant angiogenesis, which can be positively modulated by dialysis with novel improved medium-cut-off membranes.

Scavenger Receptors as Biomarkers and Therapeutic Targets in Cardiovascular Disease

The process of atherosclerosis leads to the formation of plaques in the arterial wall, resulting in a decreased blood supply to tissues and organs and its sequelae: morbidity and mortality. A class of membrane-bound proteins termed scavenger receptors (SRs) are closely linked to the initiation and progression of atherosclerosis. Increasing interest in understanding SR structure and function has led to the idea that these proteins could provide new routes for cardiovascular disease diagnosis, management, and treatment. In this review, we consider the main classes of SRs that are implicated in arterial disease. We consider how our understanding of SR-mediated recognition of diverse ligands, including modified lipid particles, lipids, and carbohydrates, has enabled us to better target SR-linked functionality in disease. We also link clinical studies on vascular disease to our current understanding of SR biology and highlight potential areas that are relevant to cardiovascular disease management and therapy.

Contribution of lectin-like oxidized low-density lipoprotein receptor-1 and LOX-1 modulating compounds to vascular diseases

The lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) is the major receptor for binding and uptake of oxidized low-density lipoprotein (oxLDL) in endothelial cells. LOX-1 is also expressed in macrophages, smooth muscle cells and platelets. Following internalization of oxLDL, LOX-1 initiates a vicious cycle from activation of pro-inflammatory signaling pathways, thus promoting an increased reactive oxygen species formation and secretion of pro-inflammatory cytokines. LOX-1 plays a pivotal role in the development of endothelial dysfunction, foam cell and advanced lesions formation as well as in myocardial ischemia. Furthermore, it is known that LOX-1 plays a pivotal role in mitochondrial DNA damage, vascular cell apoptosis, and autophagy. A large number of studies provide evidence of a LOX-1's role in endothelial dysfunction, hypertension, diabetes, and obesity. In addition, novel insights into LOX-1 ligands and the activated signaling pathways have been gained. Recent studies have shown an interaction of LOX-1 with microRNA's, thus providing novel tools to regulate LOX-1 function. Because LOX-1 is increased in atherosclerotic plaques and contributes to endothelial dysfunction, several compounds were tested in vivo and in vitro to modulate the LOX-1 expression in therapeutic approaches.

Lectin-like oxidized low-density lipoprotein receptor 1 pathways

BACKGROUND

The role of lectin-like oxidized low-density lipoprotein receptor (LOX)-1 has been implicated in the pathogenesis of different diseases, including atherosclerosis, hypertension, obesity, diabetes mellitus and metabolic syndrome. To date, several studies aimed at partially investigating the mechanistic role of LOX-1 in these various pathologies. Still, so far, the precise signal transduction pathways involving LOX-1 have not yet been elucidated.

MATERIALS AND METHODS

The most recent data published by the authors as well as others concerning different pathways involving LOX-1 are collected to formulate the presented updated review.

RESULTS

One of the most prominent pathways highlighted in the present review is the relationship of LOX-1 to NADPH oxidase that acts as a major source of harmful free radicals causing oxidative stress in blood vessels. Other pathways involve lipid and glucose metabolism-mediated signal transduction.

DISCUSSION

The modulatory role of LOX-1 on nitric oxide and renin/angiotensin systems as well as on fibrosis, apoptosis and inflammatory pathways is discussed.

CONCLUSION

The current review revisits LOX-1 and its related pathways, implicating LOX-1 as a target for ameliorating various pathological conditions.

LOX-1 transcription

The importance of the lectin-like oxidized LDL receptor (LOX-1) gene in cardiovascular and other diseases is slowly being revealed. LOX-1 gene expression appears to be a "canary in a coal mine" for atherogenesis, being strongly up-regulated early on in a number of cell types when they are activated, and predicting the sites of future disease. From this early time point the LOX-1 protein often participates in the disease process itself. While gene/protein expression can be regulated on a multiplicity of levels, the most basic and important mode of regulation is usually transcriptional. There are very few studies on the transcriptional regulation of the human LOX-1 promoter; fewer still on definitive mapping of the transcription factors involved. It is known that a wide variety of stimuli up-regulate LOX-1, usually/probably on the transcriptional level. Angiotensin II (Ang II) is one important regulator of renin-angiotensin system and stimulator LOX-1. Ang II is known to up-regulate LOX-1 transcription through an NF-kB motif located at nt -2158. Oxidized low density lipoprotein (ox-LDL) is another important cardiovascular regulator, particularly of atherosclerotic disease, and a strong stimulator of LOX-1. Ox-LDL is known to up-regulate LOX-1 transcription through an Oct-1 motif located at nt -1556. The subsequent enhanced LOX-1 receptor numbers and their binding by ox-LDL ligand triggers a positive feedback loop, increasing further LOX-1 expression, with a presently unknown regulatory governor. The Oct-1 gene also has its own Oct-1-driven positive feedback loop, which likely also contributes to LOX-1 up-regulation. There is also data which suggests the involvement of the transcription factor AP-1 during stimulation with Phorbol 12-myristate acetate. While the importance of NF-κB as a transcriptional regulator of cardiovascular-relevant genes is well known, the importance of Oct-1 is not. Data suggests that Oct-1-mediated up-regulation of transcription is an early event in the stimulation of LOX-1 by ox-LDL. Yet Oct-1 also down-regulates cardiovascular-relevant genes by suppressing NF-κB transactivation. Thus, Oct-1 is presently somewhat of an enigma, up-regulating and down-regulating genes seemingly at random without an overall theme (with the exception of cell cycle). Yet the up-regulation of LOX-1 by ox-LDL is a very important event in atherogenesis (both early and late) and Oct-1 is, therefore, an important transcriptional gatekeeper of this important atherogenic trigger.

Transcriptome analysis of aldosterone-regulated genes in human vascular endothelial cell lines stably expressing mineralocorticoid receptor

A series of studies have demonstrated that endothelial cell is one of the target tissues of aldosterone. Here, we have conducted a transcriptome analysis of aldosterone-inducible genes in human endothelial cell lines stably expressing human mineralocorticoid receptor (MR) by retroviral system (MR-EAhy). We found that aldosterone in physiologic concentrations robustly induced MR-dependent transcriptional response in MR-EAhy. By DNA microarray analysis, we validated 12 aldosterone-up-regulated genes among which at least seven were concomitantly associated with increased protein expression. We also found five aldosterone-down-regulated genes. Among 11 aldosterone-up-regulated genes tested, mRNA expressions of three (ESM1, SNF1LK, ANGPTL4) were significantly up-regulated in aortic tissue from aldosterone-induced hypertensive rats compared to those from control rats, suggesting their potential pathophysiologic significance in vivo. In conclusion, using MR stably expressed human endothelial cell lines, we identified a variety of aldosterone-inducible genes, suggesting their possible roles in the development and/or the protection for aldosterone-induced vascular injury.