Leukocytes talking to VE-cadherin

Aberrant Activation of Notch1 Signaling in Glomerular Endothelium Induces Albuminuria

RATIONALE

Glomerular capillaries are lined with a highly specialized fenestrated endothelium and contribute to the glomerular filtration barrier. The Notch signaling pathway is involved in regulation of glomerular filtration barrier, but its role in glomerular endothelium has not been investigated due to the embryonic lethality of animal models with genetic modification of Notch pathway components in the endothelium.

OBJECTIVE

To determine the effects of aberrant activation of the Notch signaling in glomerular endothelium and the underlying molecular mechanisms.

METHODS AND RESULTS

We established the ZEG-NICD1 (notch1 intracellular domain)/Tie2-tTA/Tet-O-Cre transgenic mouse model to constitutively activate Notch1 signaling in endothelial cells of adult mice. The triple transgenic mice developed severe albuminuria with significantly decreased VE-cadherin (vascular endothelial cadherin) expression in the glomerular endothelium. In vitro studies showed that either NICD1 (Notch1 intracellular domain) lentiviral infection or treatment with Notch ligand DLL4 (delta-like ligand 4) markedly reduced VE-cadherin expression and increased monolayer permeability of human renal glomerular endothelial cells. In addition, Notch1 activation or gene knockdown of VE-cadherin reduced the glomerular endothelial glycocalyx. Further investigation demonstrated that activated Notch1 suppression of VE-cadherin was through the transcription factors SNAI1 (snail family transcriptional repressor 1) and ERG (Ets related gene), which bind to the -373 E-box and the -134/-118 ETS (E26 transformation-specific) element of the VE-cadherin promoter, respectively.

CONCLUSIONS

Our results reveal novel regulatory mechanisms whereby endothelial Notch1 signaling dictates the level of VE-cadherin through the transcription factors SNAI1 and ERG, leading to dysfunction of glomerular filtration barrier and induction of albuminuria. Graphic Abstract: A graphic abstract is available for this article.

TRAIL protects against endothelial dysfunction in vivo and inhibits angiotensin-II-induced oxidative stress in vascular endothelial cells in vitro

The vascular endothelium is critical for maintenance of cardiovascular homeostasis. Endothelial dysfunction is a key event of atherosclerosis, with oxidative stress mediated by reactive oxygen species (ROS) playing a major role. Tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is increasingly recognised to play a protective role in atherosclerosis, however the molecular mechanisms by which it exerts its beneficial effects are unclear. Here we examined if TRAIL could attenuate vascular oxidative stress and improve endothelial cell (EC) function. In coronary artery disease patients, plasma TRAIL levels were significantly reduced compared to healthy individuals, and negatively correlated with the levels of circulating 8-iso Prostaglandin F_2α, a marker of in vivo oxidative stress. In vivo, high-fat fed, atherosclerotic Trail^-/-Apoe^-/- mice exhibited a significant impairment in endothelial-dependent vasorelaxation, which correlated with increased vascular ROS and 4-hydroxynonenal compared to Apoe^-/- mice. Endothelial permeability measured by Evan's blue dye extravasation was increased in several organs of Trail^-/- mice compared to wild-type mice, which correlated with a decrease in VE-cadherin expression. In vitro in ECs, angiotensin II (AngII)-induced ROS generation involving the mitochondria, NADPH oxidase-4 (NOX-4) and eNOS, was inhibited by pre-treatment with TRAIL. Furthermore, AngII-augmented VCAM-1 expression and monocyte adhesion to ECs was inhibited by TRAIL. Finally, AngII reduced VE-cadherin expression and redistributed this protein, all of which was brought back to baseline by TRAIL pre-treatment. These findings demonstrate for the first time that TRAIL protects against several forms of endothelial dysfunction involving its ability to control EC ROS generation. Understanding the role TRAIL plays in normal physiology and disease, may lead to potential new therapies to improve endothelial function and atherosclerosis.

Indole-3-carbinol is a potent inhibitor of ischemia-reperfusion-induced inflammation

BACKGROUND

Ischemia-reperfusion (I/R) induces tissue inflammation, which is characterized by an increased leukocyte-endothelial cell interaction and leukocyte transmigration. These processes are mediated by the activation of the nuclear factor (NF)κB signaling pathway, resulting in an elevated expression of specific adhesion molecules. The phytochemical indole-3-carbinol (I3C) has been shown to exert anti-inflammatory effects by interfering with NFκB signal transduction. The aim of the present study was to investigate whether I3C is capable of counteracting the pathogenesis of I/R injury.

MATERIALS AND METHODS

We investigated the inhibitory effect of I3C on endothelial surface protein expression during hypoxia and reoxygenation by flow cytometry. Moreover, the subcellular localization of NFκB was analyzed by immunofluorescence and Western blot. Adhesion protein levels on leukocytes after tumor necrosis factor-α stimulation were determined using flow cytometry. Finally, leukocyte-endothelial cell interaction and leukocyte transmigration during I/R was investigated in dorsal skinfold chambers of BALB/c mice by means of repetitive intravital fluorescence microscopy and immunohistochemistry.

RESULTS

I3C suppressed the expression of E-selectin and intercellular adhesion molecule-1 on human dermal microvascular endothelial cells by reducing the transcriptional activity of NFκB. Furthermore, surface protein levels of macrophage-1 antigen as well as activated lymphocyte function-associated antigen-1 were markedly reduced on I3C-treated leukocytes. In vivo, I3C treatment decreased the numbers of adherent and transmigrated leukocytes. This was associated with a reduced macromolecular leakage when compared with vehicle-treated controls.

CONCLUSIONS

These novel results indicate that I3C reduces the expression of endothelial and leukocytic adhesion proteins, resulting in attenuated leukocyte-endothelial cell interactions during I/R. Accordingly, dietary supplements containing I3C may be beneficial for the treatment of I/R-induced inflammation.

TNF-α regulates the proteolytic degradation of ST6Gal-1 and endothelial cell-cell junctions through upregulating expression of BACE1

Endothelial dysfunction and monocyte adhesion to vascular endothelial cells are two critical steps in atherosclerosis development, and emerging evidence suggests that protein sialylation is involved in these processes. However, the mechanism underlying this phenomenon remains incompletely elucidated. In this study, we demonstrated that treatment with the proinflammatory cytokine TNF-α disrupted vascular endothelial cell-cell tight junctions and promoted monocyte endothelial cell adhesion. Western blotting and Sambucus nigra lectin (SNA) blotting analyses revealed that TNF-α treatment decreased α-2, 6-sialic acid transferase 1 (ST6Gal-I) levels and downregulated VE-Cadherin α-2, 6 sialylation. Further analysis demonstrated that TNF-α treatment upregulated β-site amyloid precursor protein enzyme 1 (BACE1) expression, thus resulting in sequential ST6Gal-I proteolytic degradation. Furthermore, our results revealed that PKC signaling cascades were involved in TNF-α-induced BACE1 upregulation. Together, these results indicated that the proinflammatory cytokine TNF-α impairs endothelial tight junctions and promotes monocyte-endothelial cell adhesion by upregulating BACE1 expression through activating PKC signaling and sequentially cleaving ST6Gal-I. Thus, inhibition of BACE1 expression may be a new approach for treating atherosclerosis.

Oxidative and pro-inflammatory impact of regular and denicotinized cigarettes on blood brain barrier endothelial cells: is smoking reduced or nicotine-free products really safe?

Background

Both active and passive tobacco smoke (TS) potentially impair the vascular endothelial function in a causative and dose-dependent manner, largely related to the content of reactive oxygen species (ROS), nicotine, and pro-inflammatory activity. Together these factors can compromise the restrictive properties of the blood–brain barrier (BBB) and trigger the pathogenesis/progression of several neurological disorders including silent cerebral infarction, stroke, multiple sclerosis and Alzheimer’s disease. Based on these premises, we analyzed and assessed the toxic impact of smoke extract from a range of tobacco products (with varying levels of nicotine) on brain microvascular endothelial cell line (hCMEC/D3), a well characterized human BBB model.

Results

Initial profiling of TS showed a significant release of reactive oxygen (ROS) and reactive nitrogen species (RNS) in full flavor, nicotine-free (NF, “reduced-exposure” brand) and ultralow nicotine products. This release correlated with increased oxidative cell damage. In parallel, membrane expression of endothelial tight junction proteins ZO-1 and occludin were significantly down-regulated suggesting the impairment of barrier function. Expression of VE-cadherin and claudin-5 were also increased by the ultralow or nicotine free tobacco smoke extract. TS extract from these cigarettes also induced an inflammatory response in BBB ECs as demonstrated by increased IL-6 and MMP-2 levels and up-regulation of vascular adhesion molecules, such as VCAM-1 and PECAM-1.

Conclusions

In summary, our results indicate that NF and ultralow nicotine cigarettes are potentially more harmful to the BBB endothelium than regular tobacco products. In addition, this study demonstrates that the TS-induced toxicity at BBB ECs is strongly correlated to the TAR and NO levels in the cigarettes rather than the nicotine content.