Reactive oxygen species mediate ET-1-induced activation of ERK1/2 signaling in cultured feline esophageal smooth muscle cells

Endothelin-1 induces pulmonary but not aortic smooth muscle cell migration by activating ERK1/2 MAP kinase

Endothelin 1 (ET-1) is an endogenous peptide that promotes vasoconstriction, endothelial and smooth muscle cell (SMC) proliferation, and fibrosis. ET-1 receptor antagonists are an important treatment strategy for pulmonary arterial hypertension, but less effective in systemic vascular disease. This observation suggests a special role for ET-1 in the pulmonary circulation. We hypothesized that ET-1 contributes to the pathogenesis of pulmonary arterial hypertension, in part, by promoting pulmonary vascular SMC migration. ET-1 treatment promoted migration in 3 distinct types of cultured pulmonary SMC. Pulmonary SMC migration was blocked by an ETA receptor selective agonist and a combined ETA-ETB antagonist, but not by a selective ETB antagonist. In contrast to the effect on pulmonary SMCs, ET-1 had no effect on migration of aortic SMCs. Flow cytometry showed that the ETA receptor was expressed at comparable levels on pulmonary and aortic SMCs, excluding receptor density as an explanation for the divergent effect. ET-1-induced pulmonary SMC migration was blocked by the structurally distinct MEK inhibitors PD98059 and U0126, consistent with a role for ERK1/2 MAP kinase. By Western blot in cultured cells and immunohistochemistry in ex vivo vessels, ET-1 stimulated phosphorylation of ERK1/2 as efficaciously as platelet-derived growth factor in pulmonary, but not aortic, SMCs. In conclusion, ET-1 induces SMC migration, with the ETA receptor tightly coupled to ERK1/2 phosphorylation only in the pulmonary circulation. This finding may help explain the striking difference in the efficacy of endothelin receptor blockers for pulmonary hypertension as compared to that for systemic cardiovascular disease.

Potentiation of epithelial innate host responses by intercellular communication

The epithelium efficiently attracts immune cells upon infection despite the low number of pathogenic microbes and moderate levels of secreted chemokines per cell. Here we examined whether horizontal intercellular communication between cells may contribute to a coordinated response of the epithelium. Listeria monocytogenes infection, transfection, and microinjection of individual cells within a polarized intestinal epithelial cell layer were performed and activation was determined at the single cell level by fluorescence microscopy and flow cytometry. Surprisingly, chemokine production after L. monocytogenes infection was primarily observed in non-infected epithelial cells despite invasion-dependent cell activation. Whereas horizontal communication was independent of gap junction formation, cytokine secretion, ion fluxes, or nitric oxide synthesis, NADPH oxidase (Nox) 4-dependent oxygen radical formation was required and sufficient to induce indirect epithelial cell activation. This is the first report to describe epithelial cell-cell communication in response to innate immune activation. Epithelial communication facilitates a coordinated infectious host defence at the very early stage of microbial infection.

All body surfaces are covered by a single layer of epithelial cells. Epithelial cells form a physical barrier to separate the underlying sterile tissue from the environment. In addition, epithelial cells actively sense bacterial and viral infection. The recognition of pathogenic microorganisms results in cell stimulation and the secretion of soluble mediators that attract professional immune cells to the site of infection. This first line host defence works very efficiently despite the often low number of pathogens and the limited amount of mediators secreted per epithelial cell. We therefore investigated whether infection of one individual epithelial cell would result in activation of other, non-infected cells within a confluent epithelial monolayer resulting in a more substantial host response. Indeed, using the model of the gut pathogen Listeria monocytogenes and monitoring infection and epithelial activation at a single cell level, we can clearly show that the epithelial response is mainly mediated by non-infected cells. Also, we identify oxygen radicals as potential mediators to facilitate horizontal epithelial communication upon immune stimulation. Our results thus provide a novel concept of a coordinated epithelial host response upon microbial infection facilitated by horizontal epithelial communication.

Hypercholesterolaemia induces early renal lesions characterized by upregulation of MMP-9 and iNOS and ETAR: alleviated by a dual endothelin receptor antagonist CPU0213 and simvastatin

Objectives

We aimed to investigate hypercholesterolaemia-induced early renal lesions which result in abnormal expression of endothelin A receptor (ETAR), induced nitric oxide synthase (iNOS) and matrix metalloproteinase 9 (MMP-9). We hypothesized that this is due to an upregulated endothelin (ET) pathway consequent to hypercholesterolaemia and that CPU0213, a dual ET antagonist, could mitigate these changes.

Methods

Rats were randomly divided into four groups: (1), control; (2), high-fat diet for 60 days (HFD); HFD rats medicated in the last 15 days with either (3) CPU0213 (30 mg/kg daily, s.c.) or (4) simvastatin (4 mg/kg daily, p.o.).

Key findings

Body weight, serum triglycerides, total cholesterol and low-density-lipoprotein cholesterol were significantly increased, whereas high-density lipoprotein cholesterol decreased in the HFD group, relative to normal. Meanwhile, these changes were associated with upregulation of mRNA and protein of ETAR, iNOS and MMP-9 in the kidney. The lipid-lowering effect of simvastatin was predominant, lessening abnormal expression of these molecules in the kidney dramatically. Interestingly, CPU0213 significantly normalized expression of mRNA and protein of ETAR, iNOS and MMP-9, comparable with simvastatin, leaving no changes in hyperlipidaemia.

Conclusions

CPU0213 relieves renal lesions by blunting hypercholesterolaemia caused by the upregulated ET system, iNOS and MMP-9 in the kidney. This indicates that CPU0213 is promising in treating patients with end stage renal disease.

Oxidative-dependent integration of signal transduction with intercellular gap junctional communication in the control of gene expression

Research on oxidative stress focused primarily on determining how reactive oxygen species (ROS) damage cells by indiscriminate reactions with their macromolecular machinery, particularly lipids, proteins, and DNA. However, many chronic diseases are not always a consequence of tissue necrosis, DNA, or protein damage, but rather to altered gene expression. Gene expression is highly regulated by the coordination of cell signaling systems that maintain tissue homeostasis. Therefore, much research has shifted to the understanding of how ROS reversibly control gene expression through cell signaling mechanisms. However, most research has focused on redox regulation of signal transduction within a cell, but we introduce a more comprehensive-systems biology approach to understanding oxidative signaling that includes gap junctional intercellular communication, which plays a role in coordinating gene expression between cells of a tissue needed to maintain tissue homeostasis. We propose a hypothesis that gap junctions are critical in modulating the levels of second messengers, such as low molecular weight reactive oxygen, needed in the transduction of an external signal to the nucleus in the expression of genes. Thus, any comprehensive-systems biology approach to understanding oxidative signaling must also include gap junctions, in which aberrant gap junctions have been clearly implicated in many human diseases.